|
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?Audio Amp notes.
The uBitx has always
had challenges with the audio amp. It has insufficient gain for the
condenser mic that is provided. Solutions include:
a. Use a mic with an
amplifier built in.
b. Add an additional
amplification stage such as the SSM2167.
c. Increase the mic
circuit gain.
Mic amplifier
circuit with suggested modifications. Also showing the load of the
following stage.
SEE ATTACHED FILE
Analysis:
Given that the
receive transistor Q70 is connected directly to the output of the
microphone amplifier, the output of the mic amp must be less than
0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive
required to achieve 550mV out of the mic amp is 200mV. Most have
claimed that the mic amp has a gain of around 20 due to the collector
resistance of 1k divided by the emitter resistance of 47 ohms. This
simple analysis is incorrect because it neglects the load impedance
of the mixer circuit. Spice analysis and actual observation shows the
actual gain to be about 2x or 3x.
A big problem with
this mic amplifier is that it is incorrectly biased. With the
originally specified bias resistor R61 set at 2.2k, the transistor
runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k,
the circuit can easily output the 550 mV (1.1V P-P) originally
suggested.
In my own uBitx, I
have chosen to use the SSM2167 as a preamp in order to enjoy some
voice compression. However, the simplest solution is to decrease R63
to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since
that circuit should fully drive the mixer with a mic output of only
40 mV. But before doing anything else, increase R61 to 10K.
|
Thanks for the analysis. There are two other significanr issues with the current mic amplifier. 1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive. 2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive. These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier. - f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?Audio Amp notes.
The uBitx has always
had challenges with the audio amp. It has insufficient gain for the
condenser mic that is provided. Solutions include:
a. Use a mic with an
amplifier built in.
b. Add an additional
amplification stage such as the SSM2167.
c. Increase the mic
circuit gain.
Mic amplifier
circuit with suggested modifications. Also showing the load of the
following stage.
SEE ATTACHED FILE
Analysis:
Given that the
receive transistor Q70 is connected directly to the output of the
microphone amplifier, the output of the mic amp must be less than
0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive
required to achieve 550mV out of the mic amp is 200mV. Most have
claimed that the mic amp has a gain of around 20 due to the collector
resistance of 1k divided by the emitter resistance of 47 ohms. This
simple analysis is incorrect because it neglects the load impedance
of the mixer circuit. Spice analysis and actual observation shows the
actual gain to be about 2x or 3x.
A big problem with
this mic amplifier is that it is incorrectly biased. With the
originally specified bias resistor R61 set at 2.2k, the transistor
runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k,
the circuit can easily output the 550 mV (1.1V P-P) originally
suggested.
In my own uBitx, I
have chosen to use the SSM2167 as a preamp in order to enjoy some
voice compression. However, the simplest solution is to decrease R63
to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since
that circuit should fully drive the mixer with a mic output of only
40 mV. But before doing anything else, increase R61 to 10K.
|
Thanks!
I never expected such a quick response from the designer himself!
My takeaway is that driving the modulator with 550mV is too much. 150mV is more appropriate?
Dan Damon
On Sat, Jul 15, 2023 at 7:19?PM Ashhar Farhan < farhanbox@...> wrote: Thanks for the analysis. There are two other significanr issues with the current mic amplifier. 1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive. 2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive. These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier. - f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?Audio Amp notes.
The uBitx has always
had challenges with the audio amp. It has insufficient gain for the
condenser mic that is provided. Solutions include:
a. Use a mic with an
amplifier built in.
b. Add an additional
amplification stage such as the SSM2167.
c. Increase the mic
circuit gain.
Mic amplifier
circuit with suggested modifications. Also showing the load of the
following stage.
SEE ATTACHED FILE
Analysis:
Given that the
receive transistor Q70 is connected directly to the output of the
microphone amplifier, the output of the mic amp must be less than
0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive
required to achieve 550mV out of the mic amp is 200mV. Most have
claimed that the mic amp has a gain of around 20 due to the collector
resistance of 1k divided by the emitter resistance of 47 ohms. This
simple analysis is incorrect because it neglects the load impedance
of the mixer circuit. Spice analysis and actual observation shows the
actual gain to be about 2x or 3x.
A big problem with
this mic amplifier is that it is incorrectly biased. With the
originally specified bias resistor R61 set at 2.2k, the transistor
runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k,
the circuit can easily output the 550 mV (1.1V P-P) originally
suggested.
In my own uBitx, I
have chosen to use the SSM2167 as a preamp in order to enjoy some
voice compression. However, the simplest solution is to decrease R63
to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since
that circuit should fully drive the mixer with a mic output of only
40 mV. But before doing anything else, increase R61 to 10K.
|
Yes, that would be appropriate. - f
Thanks!
I never expected such a quick response from the designer himself!
My takeaway is that driving the modulator with 550mV is too much. 150mV is more appropriate?
Dan Damon
On Sat, Jul 15, 2023 at 7:19?PM Ashhar Farhan < farhanbox@...> wrote: Thanks for the analysis. There are two other significanr issues with the current mic amplifier. 1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive. 2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive. These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier. - f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?Audio Amp notes.
The uBitx has always
had challenges with the audio amp. It has insufficient gain for the
condenser mic that is provided. Solutions include:
a. Use a mic with an
amplifier built in.
b. Add an additional
amplification stage such as the SSM2167.
c. Increase the mic
circuit gain.
Mic amplifier
circuit with suggested modifications. Also showing the load of the
following stage.
SEE ATTACHED FILE
Analysis:
Given that the
receive transistor Q70 is connected directly to the output of the
microphone amplifier, the output of the mic amp must be less than
0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive
required to achieve 550mV out of the mic amp is 200mV. Most have
claimed that the mic amp has a gain of around 20 due to the collector
resistance of 1k divided by the emitter resistance of 47 ohms. This
simple analysis is incorrect because it neglects the load impedance
of the mixer circuit. Spice analysis and actual observation shows the
actual gain to be about 2x or 3x.
A big problem with
this mic amplifier is that it is incorrectly biased. With the
originally specified bias resistor R61 set at 2.2k, the transistor
runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k,
the circuit can easily output the 550 mV (1.1V P-P) originally
suggested.
In my own uBitx, I
have chosen to use the SSM2167 as a preamp in order to enjoy some
voice compression. However, the simplest solution is to decrease R63
to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since
that circuit should fully drive the mixer with a mic output of only
40 mV. But before doing anything else, increase R61 to 10K.
|
Dan,
Which ubitx do you have? just curious. Also would you have any more info on the preamp you are using?
It always nice to hear from Ashhar the designer in regards to these fine rigs.one reads on the main website for his creations and he encourages the modding and such of his designs. PRETTY COOL. Alot of companies dont do this.
I recently bought a ubitx v6.2 and havent tried it out too much on SSB. Been on CW mainly. I notice the Microphone has been changed. And i like it. seems to fit the hand better, and is light and not bulky. Only contacts i made with it on SSB was a contest and they gave me a good signal report. forgot to ask about the audio.HI HI. but was thinking about adding? either a preamp or mod the input to the modulator circuit by changing the gain of the microphone stage too. like the info you and Ashhar was validating.
maybe an led circuit to indicate an over drive condition to prevent distortion on the Audio.Make it where it starts lighting up when the higher voltage starts hitting the microphone amp?
wanting to buy a couple more ubitxs for my collection and then end of year or first of year, buy the SBITX.Ive seen one in action,since one of my friends in another state bought one completed. after he checked and double checked the connections and such since postal employees arent nice, he fired his right up. he is using a steady 12vdc battery bank from a solar generator. which is actually lithium batteries in a case with current and volt meters and inverter to run AC stuff too. Sbitx seems to like it .
73
David
ac9xh
|
Hi David,
I think Dan mentioned he was using the SSM2167.
I have used the same device on my uBITX V6 and it seems to work reasonably well for both TX and RX paths.
On the modules I used, the resistors for setting the noise gate threshold and compression ratio were fitted incorrectly, although I used digital potentiometers in the end so that I can adjust the settings from firmware. 
See threads below.
?
73, Dave
|
Dave ,
nice pic.
guess i needed to clarify? that i was after any schematics or companies who sell these cheaper than the rest.HI HI.
Looks like a small neat little board.Is the parts being fitted incorrectly a common problem with this board?Glad to hear a fellow ubitx v6 user applying this board to their circuitry.
?alot of very small amps are prone to clipping and such, but with babysitting, they can be manipulated quite well. You and Dans usage of the amp board is a good idea..
I was fishing for a pic, like you posted, and info on the best outlet to obtain them.like you stated ,it works for the ubitx, but i have several bitx40s that this will work on too.
Im always searching for small stuff like this to either stock for another QRP project
Anyway,Dave,
thanks for the picture. looks like it would be very easy to mount to the radio.
73
David
ac9xh
|
Dave,
read your posts you linked to. great info!!!!
May i ask where you purchased these boards from?Or ,what Company do you recommend buying these from?
73
David
ac9xh
|
Dave,
answered my own question. found several outlets selling these critters. I dont do ebay anymore,so i buy direct .
found some ranging from $4 to $6.working voltage for them stated 3v-5v.
73
David
ac9xh
|
Hi David,
The boards I used were from eBay (?4~?5 in the UK) and all had the two resistors fitted incorrectly. Like all components from these sites, the devices may be clones, but they do seem to work as per the datasheet. You can buy the chips slightly cheaper, but using the modules saves the hassle of the SMD’s.
The modules are more or less as per the application schematic.?
On the TX side, for an electret microphone insert you will need to add the DC biasing and probably a potentiometer on the input and output to adjust the levels. I used digital pots in place of R1, R2 and also for the output level adjustment.
On the RX side, I used an amplified version of the AVG CAP (SSM2167 Pin-6) signal to drive the S-Meter input on the Raduino (CONTROLS1 Pin-8, Arduino Pin-11 [A7]) using the KD8CEC firmware.
73, Dave
|
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
toggle quoted message
Show quoted text
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
?
|
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
toggle quoted message
Show quoted text
Could this be fixed with a 9T:2T transformer between C63 and the
mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify
which parts from the emitter of Q6 should be removed? (Just C62
and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other
significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the
modulator needs a 50 ohms drive.
2. The gain is not less but too much. The
electrer mic produces about 50mV of audio, the modulatoe
needs less than 150mv drive. A gain of two or three is more
than sufficient. The apparent loss is due to the mismatch
between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter
follower with a 47 ohms resistor in series with the output
of the emitter follower and removing the emitter bypass of
the original mic amplifier.
- f
I've been working on the uBitx audio
circuit for a while now and I think I've
discovered a problem that I've never seen anyone
mention before. If anyone has experience with this
circuit, please review and let me know if I've
missed anything. Here are my notes:
?
?Audio
Amp notes.
?
The
uBitx has always had challenges with the audio
amp. It has insufficient gain for the
condenser mic that is provided. Solutions
include:
?
a.
Use a mic with an amplifier built in.
b.
Add an additional amplification stage such as
the SSM2167.
c.
Increase the mic circuit gain.
?
Mic
amplifier circuit with suggested
modifications. Also showing the load of the
following stage.
?
SEE
ATTACHED FILE
?
Analysis:
Given
that the receive transistor Q70 is connected
directly to the output of the microphone
amplifier, the output of the mic amp must be
less than 0.6v. We’ll say 550 mV to give us a
bit of safety margin.
The
input drive required to achieve 550mV out of
the mic amp is 200mV. Most have claimed that
the mic amp has a gain of around 20 due to the
collector resistance of 1k divided by the
emitter resistance of 47 ohms. This simple
analysis is incorrect because it neglects the
load impedance of the mixer circuit. Spice
analysis and actual observation shows the
actual gain to be about 2x or 3x.
A
big problem with this mic amplifier is that it
is incorrectly biased. With the originally
specified bias resistor R61 set at 2.2k, the
transistor runs out of emitter current at
about 160mV of output voltage. In addition to
limiting output, this causes distortion of the
audio waveform. By increasing R61 to 10k, the
circuit can easily output the 550 mV (1.1V
P-P) originally suggested.
In
my own uBitx, I have chosen to use the SSM2167
as a preamp in order to enjoy some voice
compression. However, the simplest solution is
to decrease R63 to 10 to 22 ohms. I’d advise
not to go lower than 10 ohms, since that
circuit should fully drive the mixer with a
mic output of only 40 mV. But before doing
anything else, increase R61 to 10K.
|
Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?
Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?
Thanks, Andy
toggle quoted message
Show quoted text
On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
|
toggle quoted message
Show quoted text
Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?
Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?
Thanks, Andy
On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
|
Thanks Doc - I hadn't seen that lecturer yet. Based on the first couple of minutes, I'll subscribe and watch.
? ?I'm not an EE and don't have a career's worth of tribal knowledge to fall back on. At 61 I don't feel much more anchored in this than when I was 14 and trying to apply my crystal radio knowledge to a multi-band SSB receiver project from an ARRL handbook. LOL
I can work through the math for a single transistor amplifier and adjust gain. (Primarily thanks to Farhan's feedback amp vid, and Charlie Morris' ZL2ZTM tutorials.)? I don't have any idea what happens to that amp when I glue on another BJT. (Is it added like a stage with a cap separating them, or like the way Q12 is added to Q11?) I've already fallen flat with the "Audio isn't RF so no, not gonna get through this by winding a toroid!" Glitch. Ha!
? ?I also wasn't clear on exactly which of the feedback parts Farhan suggested should be removed from the existing amp. I understand that R63, C62, and R64, all on the emitter of Q6 are 'feedback', and I think I understand that the paralleled C62 and R64 are probably the AC feedback parts.? Should both be removed, or one, or?
? ?Anyway...thanks again.? 73, Andy
toggle quoted message
Show quoted text
On Mon, Jan 22, 2024 at 05:34 PM, Gordon Gibby wrote:
Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?
Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?
Thanks, Andy
On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
?
?
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Doc, in the linked vid at 11:10, it makes sense that the output impedance is about 5 Ohms. Then, after a jump edit, he multiplies it by 10 and uses 50 Ohms to solve for the output cap. Where did the 10 come from? It was an easy to follow vid until that Deus ex machina moment.?
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On Mon, Jan 22, 2024 at 05:34 PM, Gordon Gibby wrote:
Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?
Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?
Thanks, Andy
On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
?
?
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|
|
Sorry Doc - no, didn't help.? There are a number of different ways to couple and bias an emitter follower and I don't know how to translate Farhan's instructions to add "...an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier."
I've asked some specific questions but not received useful answers.
I do have a couple of different amp boards and can insert one of those into the hand mic case, but hoped to figure out Farhan's comment as it seemed to lead to a simpler and more elegant solution.
I'll continue to stay off voice and stick with data until I'm back on land and have my proto and testing tools.
73, Andy
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Show quoted text
On Mon, Jan 22, 2024 at 05:34 PM, Gordon Gibby wrote:
Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?
Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?
Thanks, Andy
On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
?
?
|
Andy, that’s fine, but if you’ll hit the books for a bit, you can learn this stuff easily. It’s taught in thousands of places and there are many examples in Ashhar’s schematics. In my early days I sat and read from the ARRL handbook to learn this kind of stuff because the Internet did not exist. ?You can easily learn what you need and until you have conquered that hill, the rest of us giving you spoonfeed instructions won’t really be that long-term useful. ?Get yourself back on dryland, get your gear, read a bit and this will be Childs play
73
Gordon
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On Jan 31, 2024, at 20:03, AndyH <awhecker@...> wrote:
?Sorry Doc - no, didn't help.? There are a number of different ways to couple and bias an emitter follower and I don't know how to translate Farhan's instructions to add "...an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier." I've asked some specific questions but not received useful answers. I do have a couple of different amp boards and can insert one of those into the hand mic case, but hoped to figure out Farhan's comment as it seemed to lead to a simpler and more elegant solution. I'll continue to stay off voice and stick with data until I'm back on land and have my proto and testing tools. 73, Andy On Mon, Jan 22, 2024 at 05:34 PM, Gordon Gibby wrote:
Probably, Raj.? Ultimately I'm trying to understand how to implement Farhan's mod.?
Since I don't yet know how to create the emitter follower he described, I'll go back to applying fiberglass to the bottom of my boat.?
Thanks, Andy
On Mon, Jan 22, 2024 at 12:22 AM, Raj vu2zap wrote:
Andy,
You are talking about a hard to get audio transformer!
Raj
On 22/01/2024 8:21 AM, AndyH wrote:
Could this be fixed with a 9T:2T transformer between C63 and the mixer pad, and rebiasing Q6 for a gain of 2-3?
And/or, could someone flesh out the emitter follower and specify which parts from the emitter of Q6 should be removed? (Just C62 and R64?)
? ?Thanks!
? ? ?73, Andy, KG5RKP/MM
On Sat, Jul 15, 2023 at 09:18 PM, Ashhar Farhan wrote:
Thanks for the analysis. There are two other significanr issues with the current mic amplifier.
1. The output impedance is 1000 ohms, the modulator needs a 50 ohms drive.
2. The gain is not less but too much. The electrer mic produces about 50mV of audio, the modulatoe needs less than 150mv drive. A gain of two or three is more than sufficient. The apparent loss is due to the mismatch between the 1000 ohm output and the needed 50 ohms drive.
These can be solved by adding an emitter follower with a 47 ohms resistor in series with the output of the emitter follower and removing the emitter bypass of the original mic amplifier.
- f
I've been working on the uBitx audio circuit for a while now and I think I've discovered a problem that I've never seen anyone mention before. If anyone has experience with this circuit, please review and let me know if I've missed anything. Here are my notes:
?
?Audio Amp notes.
?
The uBitx has always had challenges with the audio amp. It has insufficient gain for the condenser mic that is provided. Solutions include:
?
a. Use a mic with an amplifier built in.
b. Add an additional amplification stage such as the SSM2167.
c. Increase the mic circuit gain.
?
Mic amplifier circuit with suggested modifications. Also showing the load of the following stage.
?
SEE ATTACHED FILE
?
Analysis:
Given that the receive transistor Q70 is connected directly to the output of the microphone amplifier, the output of the mic amp must be less than 0.6v. We’ll say 550 mV to give us a bit of safety margin.
The input drive required to achieve 550mV out of the mic amp is 200mV. Most have claimed that the mic amp has a gain of around 20 due to the collector resistance of 1k divided by the emitter resistance of 47 ohms. This simple analysis is incorrect because it neglects the load impedance of the mixer circuit. Spice analysis and actual observation shows the actual gain to be about 2x or 3x.
A big problem with this mic amplifier is that it is incorrectly biased. With the originally specified bias resistor R61 set at 2.2k, the transistor runs out of emitter current at about 160mV of output voltage. In addition to limiting output, this causes distortion of the audio waveform. By increasing R61 to 10k, the circuit can easily output the 550 mV (1.1V P-P) originally suggested.
In my own uBitx, I have chosen to use the SSM2167 as a preamp in order to enjoy some voice compression. However, the simplest solution is to decrease R63 to 10 to 22 ohms. I’d advise not to go lower than 10 ohms, since that circuit should fully drive the mixer with a mic output of only 40 mV. But before doing anything else, increase R61 to 10K.
?
?
|
Andy,
If your problem is microphone audio quality on transmit from uBitx V6 (and other versions), there has been a lot of forum discussion about using different microphones, or improving the microphone supplied with the radio.
I think some radios were supplied with Baofeng microphones, which had low quality electret mic elements. Audio was sometimes improved by finding a better quality compatible mic element.??
My uBitxV6 came with a different microphone. The internal circuit board is labeled "hamshack.in". The transmit audio was reported as very poor. I confirmed this by hooking the mic to my computer mic input through a simple circuit which provided dc bias to the electret mic, I recorded the audio as I spoke, then played it back. (The computer didn't supply proper bias.) In any case, the audio was muffled and nearly unintelligible.
I had a couple of used electret mic elements (quality and specs. unknown) in my junk box. I installed them, one at a time, and tested with similar results. But I noticed that, if tested outside of the microphone housing, all three mic elements had reasonably good audio. Apparently, there were echoes inside the hollow case. The fix was to add some soft foam padding inside the case (filling the lower case, with a thinner layer behind the holes on the case front, to cover the mic element, circuit board, and space in the upper case). I saw another forum thread where someone stuffed the case with cotton. The improvement was remarkable... and did not require any modification to the radio.
Also note that transmit audio can also be poor, if the BFO calibration is not right.
Simple bias circuit (for testing mic element with computer):? Use a 9 volt battery. Connect negative lead to ground side of mic element. Connect positive lead through a 10K resistor to the positive side of the mic element. Also connect a 10 ufd capacitor (+ side) to the positive side of the mic element. (These exact resistor and capacitor values are not required. Use the closest that you have). Bias circuit is complete. Connect to computer: Negative side of mic (and battery)? to ground of mic plug; Negative side of capacitor to mic input terminal of mic plug.
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Raj vu2zap