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MAX9814 mic preamp and DC bias capacitor

[email protected] All Messages By This Member #40653 I am wiring up the Adafruit AGC Electret Microphone Amplifier - MAX9814 for use with the uBITX and wonder if I need to put a capacitor at the audio output. I found a web site that says "Connect the OUT pin to a 1uF-100uF capacitor (really any value will do). If the capacitor is polarized, connect the OUT pin to the positive side". Any info appreciated! Jeff AD6RH
Michael Hagen All Messages By This Member #40656 开云体育 The mic input on uBit has a pull up bias resistor, so connect you cap + side going into uBitX.? The low frequency response of you mic circuit will be affected by smaller capacitors because of the low value pullup.? Try 10uf?? Look at uBit schematic at HF Signals. See what they got in there?? This keeps the DC off the output of you Mic Amp circuit. 73's Mike, WA6ISP On 1/29/2018 9:59 AM, jlco001 via Groups.Io wrote: I am wiring up the Adafruit AGC Electret Microphone Amplifier - MAX9814 for use with the uBITX and wonder if I need to put a capacitor at the audio output. I found a web site that says "Connect the OUT pin to a 1uF-100uF capacitor (really any value will do). If the capacitor is polarized, connect the OUT pin to the positive side". Any info appreciated! Jeff AD6RH -- Mike Hagen, WA6ISP 10917 Bryant Street Yucaipa, Ca. 92399 (909) 918-0058 PayPal ID "MotDog@..." Mike@...
M Garza #40657 Hi Jeff, That is what I did.? I used a 1uf non polarized cap.? It works fine.? It also prevents the board level bias current from going back into the max9814 board. I need to wire in a mic gain control, though.? I have it set to the lowest gain and it picks up a mosquito passing by... Marco - KG5PRT? toggle quoted message Show quoted text On Jan 29, 2018 11:59 AM, "jlco001 via Groups.Io" <jlco001=[email protected]> wrote: I am wiring up the Adafruit AGC Electret Microphone Amplifier - MAX9814 for use with the uBITX and wonder if I need to put a capacitor at the audio output. I found a web site that says "Connect the OUT pin to a 1uF-100uF capacitor (really any value will do). If the capacitor is polarized, connect the OUT pin to the positive side". Any info appreciated! Jeff AD6RH
Dave Bottom #40667 uBITX Mic Audio I think that the rig only needs slightly more gain in the existing Mic PreAmp.? I believe adjusting values to add gain is really all that is needed.? Don't need 40 dB extra gain. Attached PDF is the Mic Pre-amp used 50 years ago in the SBE SB-33 SF-1 solid state rig that first used bilateral amplifiers.? ?It had plenty of gain and for a Dynamic Mic with significantly lower output than any of the typical Electret-Condenser Mics.? Also note that the Mic PreAmp was powered only when the rig was in TX and a simple diode was used to shut off the Mic PreAmp in RX with the same TX voltage.? I used this rig in the '60s and I don;t recall any Pop when going from RX>TX / TX>RX. The "Signal Splitter" was used to isolate the TX and RX Audio. Dave WI6R toggle quoted message Show quoted text On Mon, Jan 29, 2018 at 10:14 AM, M Garza <mgarza896@...> wrote: Hi Jeff, That is what I did.? I used a 1uf non polarized cap.? It works fine.? It also prevents the board level bias current from going back into the max9814 board. I need to wire in a mic gain control, though.? I have it set to the lowest gain and it picks up a mosquito passing by... Marco - KG5PRT? On Jan 29, 2018 11:59 AM, "jlco001 via Groups.Io" <jlco001=[email protected]> wrote: I am wiring up the Adafruit AGC Electret Microphone Amplifier - MAX9814 for use with the uBITX and wonder if I need to put a capacitor at the audio output. I found a web site that says "Connect the OUT pin to a 1uF-100uF capacitor (really any value will do). If the capacitor is polarized, connect the OUT pin to the positive side". Any info appreciated! Jeff AD6RH -- 73 Dave WI6R Mic preamp.pdf Mic preamp.pdf
ekelley All Messages By This Member #40675 开云体育 I miss my old SBE 33, wish I had kept it. Ed On 1/29/2018 1:00 PM, Dave Bottom wrote: toggle quoted message Show quoted text uBITX Mic Audio I think that the rig only needs slightly more gain in the existing Mic PreAmp.? I believe adjusting values to add gain is really all that is needed.? Don't need 40 dB extra gain. Attached PDF is the Mic Pre-amp used 50 years ago in the SBE SB-33 SF-1 solid state rig that first used bilateral amplifiers.? ?It had plenty of gain and for a Dynamic Mic with significantly lower output than any of the typical Electret-Condenser Mics.? Also note that the Mic PreAmp was powered only when the rig was in TX and a simple diode was used to shut off the Mic PreAmp in RX with the same TX voltage.? I used this rig in the '60s and I don;t recall any Pop when going from RX>TX / TX>RX. The "Signal Splitter" was used to isolate the TX and RX Audio. Dave WI6R On Mon, Jan 29, 2018 at 10:14 AM, M Garza <mgarza896@...> wrote: Hi Jeff, That is what I did.? I used a 1uf non polarized cap.? It works fine.? It also prevents the board level bias current from going back into the max9814 board. I need to wire in a mic gain control, though.? I have it set to the lowest gain and it picks up a mosquito passing by... Marco - KG5PRT? On Jan 29, 2018 11:59 AM, "jlco001 via Groups.Io" <jlco001=[email protected]> wrote: I am wiring up the Adafruit AGC Electret Microphone Amplifier - MAX9814 for use with the uBITX and wonder if I need to put a capacitor at the audio output. I found a web site that says "Connect the OUT pin to a 1uF-100uF capacitor (really any value will do). If the capacitor is polarized, connect the OUT pin to the positive side". Any info appreciated! Jeff AD6RH -- 73 Dave WI6R
[email protected] All Messages By This Member #40701 Partial success. I got the mic to transmit, but audio from the mic comes thru when the the radio on receive. I tried a 10uF polarized capacitor in both directions (uBITX side negative, and then positive) and got the same results. I'm powering the preamp from a battery. I might try getting a double-pole double-throw switch to turn on power only when in transmit. The old HT speaker mic housing I used only has a single-pole switch. BTW - I set it at 40db and it is HOT! Thanks for the help! Jeff? ??
Raj vu2zap Member Profile All Messages By This Member #40742 Just decrease the value of R63 for more gain! toggle quoted message Show quoted text At 30/01/2018, you wrote: uBITX Mic Audio I think that the rig only needs slightly more gain in the existing Mic PreAmp.? I believe adjusting values to add gain is really all that is needed.? Don't need 40 dB extra gain.
M Garza #40766 Could I change R64 to a 220 ohm resistor?? I think 1k is too high.? I am using the max9814 on 40 dB and it is way too much. Thanks, Marco - KG5PRT? toggle quoted message Show quoted text On Jan 30, 2018 2:47 AM, "Raj vu2zap" <rajendrakumargg@...> wrote: Just decrease the value of R63 for more gain! At 30/01/2018, you wrote: >uBITX Mic Audio > >I think that the rig only needs slightly more gain in the existing Mic PreAmp.?? I believe adjusting values to add gain is really all that is needed.?? Don't need 40 dB extra gain.
Michael Hagen All Messages By This Member #40771 开云体育 I put a 1K to a 2K pot to ground.? Take the output to your capacitor from the wiper. You can adjust all the way to ground (nothing out). 73's Mike, WA6ISP On 1/30/2018 8:33 AM, M Garza wrote: Could I change R64 to a 220 ohm resistor?? I think 1k is too high.? I am using the max9814 on 40 dB and it is way too much. Thanks, Marco - KG5PRT? On Jan 30, 2018 2:47 AM, "Raj vu2zap" <rajendrakumargg@...> wrote: Just decrease the value of R63 for more gain! At 30/01/2018, you wrote: >uBITX Mic Audio > >I think that the rig only needs slightly more gain in the existing Mic PreAmp.?? I believe adjusting values to add gain is really all that is needed.?? Don't need 40 dB extra gain. -- Mike Hagen, WA6ISP 10917 Bryant Street Yucaipa, Ca. 92399 (909) 918-0058 PayPal ID "MotDog@..." Mike@...
M Garza #40773 So, mic gain control for the win. Thanks Mike! Marco - KG5PRT? toggle quoted message Show quoted text On Jan 30, 2018 11:04 AM, "Michael Hagen" <motdog@...> wrote: I put a 1K to a 2K pot to ground.? Take the output to your capacitor from the wiper. You can adjust all the way to ground (nothing out). 73's Mike, WA6ISP On 1/30/2018 8:33 AM, M Garza wrote: Could I change R64 to a 220 ohm resistor?? I think 1k is too high.? I am using the max9814 on 40 dB and it is way too much. Thanks, Marco - KG5PRT? On Jan 30, 2018 2:47 AM, "Raj vu2zap" <rajendrakumargg@...> wrote: Just decrease the value of R63 for more gain! At 30/01/2018, you wrote: >uBITX Mic Audio > >I think that the rig only needs slightly more gain in the existing Mic PreAmp.?? I believe adjusting values to add gain is really all that is needed.?? Don't need 40 dB extra gain. -- Mike Hagen, WA6ISP 10917 Bryant Street Yucaipa, Ca. 92399 (909) 918-0058 PayPal ID "MotDog@..." Mike@...
[email protected] All Messages By This Member #40891 I used another mic housing with a DPDT switch and wired it so voltage is supplied only when PTT is engaged. I am using a CR2032 3v button cell. Seems to work fine, but I have not compared the stock vs. preamp mic with anyone on the air yet. Definitely has more avg power on the watt meter. I can hear some peaks come thru the speaker when transmitting. I may try installing a pot to dial back the gain. Jeff AD6RH
Arvo W0VRA All Messages By This Member #40893 I'm working on something similar.? It looks like Q6 is part of the ?B's mic pre.? When TX goes high, Q6 turns on and passes the signal into the mixer and so on.? RX also goes low and turns off Q70.? So if you wanna skip the ?B's mic pre you have to turn off that signal during RX.? This is because TX and RX share all that mixing and filtering and modulating stuff that I don't quite understand yet. If someone who knows what they are talking about can confirm this, I'll give myself another high five.

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