On Mon, Apr 11, 2022 at 01:40 PM, Mic Scharf wrote:
On Sat, Apr 9, 2022 at 07:31 PM, Arjay 1949 wrote:
I did think about that Jerry, but decided that as the existing project PCB already has 2 x dual amps - each with one amp configured as a non inverting buffer and the other as an inverter - it might just be possible to reconfigure, using the majority of the existing components on the PCB?.....
How would it be with 3 opamps? regarding not concentrating on the existing PCB
I think you could try something like this..... You could use a dual OPA1642 and a single OPA1641. By not regulating the op-amp supply, - and carefully selecting the feed resistors for the regulated voltage multiplier supply -? it should be possible to keep the total current drain to around 6 or 7mA, which is not so close to the phantom power current limit.? I'm guessing this is the type of thing Jerry had in mind in post #3 of this thread?... 
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On Sat, Apr 9, 2022 at 07:31 PM, Arjay 1949 wrote:
I did think about that Jerry, but decided that as the existing project PCB already has 2 x dual amps - each with one amp configured as a non inverting buffer and the other as an inverter - it might just be possible to reconfigure, using the majority of the existing components on the PCB?.....
How would it be with 3 opamps? regarding not concentrating on the existing PCB
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On Mon, Apr 11, 2022 at 11:34 AM, Mic Scharf wrote:
Is C8 and C9 still necessary?? C13,C14?
Probably not.? In fact it would probably be better to simply regulate the Voltage Multiplier? DC supply, and not the op-amp supply That might help minimise current drain -? which is going to be pushing the limit in this configuration - but I'm not sure how easy that would be to do on the existing VM PDBs? ....
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Is C8 and C9 still necessary?? C13,C14?
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of what would be involved, using the existing dual PCB.
Notice the output is now single single sided (but still balanced !)?
Because you are now deriving the power for both dual op-amps from one phantom power source you are approaching the limit of available current (10mA ) .
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Re: Idea for variable pattern microphone
Quiescent current of each section is rated at 2.3mA maximum, for
a total of 9.2mA, which is still within specs. Does not leave much
for operating currents, but it shouldn't be an issue. Typically,
current draw will be about 8mA.
Le 10/04/2022 ¨¤ 20:33, Jules Ryckebusch
a ¨¦crit?:
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Each channel draws the same quiescent current. ?So one of these is
like 2 opa1642 ?Which Is too much for Phantom Power. ?
Best Regards,
Jules Ryckebusch?
?
OPA1644 is the quad version of the 1641 (single) and 1642
(dual)
The advantage of having only two power pins for 4 opamps is
often negated by the more difficult layout.
Le 10/04/2022 ¨¤ 20:05, Mic Scharf
a ¨¦crit?:
With an OPA 1644?
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Re: Idea for variable pattern microphone
On Sun, Apr 10, 2022 at 07:33 PM, Jules Ryckebusch wrote:
Each channel draws the same quiescent current. ?So one of these is like 2 opa1642 ?Which Is too much for Phantom Power. ?
Best Regards,
?
Jules Ryckebusch?
?
?You might just keep it in spec (max 10mA) if you don't regulate the op-amp supply, and? just regulate the voltage mulitplier (VM) supply. I found that using 27k feed resistors to the VM circuitry allowed around 1mA for the hex inverter and c.500uA for the zener itself. It's cutting it bit fine, but you might get away with it! :)?
?
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Re: Hex inverter issue. Alice OPA
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Re: Idea for variable pattern microphone
Remember, you have another op-amp / mixer available at the mic input, so you could feed the front buffer straight to pin 2 of the XLR. Make the 4th op-amp a non-inverting buffer if you want to get rid of a few resistors. Both pins of the cable are actively driven.
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Re: Idea for variable pattern microphone
Each channel draws the same quiescent current. ?So one of these is like 2 opa1642 ?Which Is too much for Phantom Power. ? Best Regards,
Jules Ryckebusch?
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On Apr 10, 2022, at 13:28, Jerry Lee Marcel <jerryleemarcel@...> wrote:
?
OPA1644 is the quad version of the 1641 (single) and 1642 (dual)
The advantage of having only two power pins for 4 opamps is often
negated by the more difficult layout.
Le 10/04/2022 ¨¤ 20:05, Mic Scharf a
¨¦crit?:
With an OPA 1644?
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Re: Idea for variable pattern microphone
OPA1644 is the quad version of the 1641 (single) and 1642 (dual)
The advantage of having only two power pins for 4 opamps is often
negated by the more difficult layout.
Le 10/04/2022 ¨¤ 20:05, Mic Scharf a
¨¦crit?:
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Re: Idea for variable pattern microphone
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Re: Hex inverter issue. Alice OPA
What are you using for Capules? ?SimpleP48 is for Electret ones that have a built in FET. ? Best Regards,
Jules Ryckebusch?
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On Apr 10, 2022, at 12:56, LonDek <londekpolska@...> wrote:
? Jerry, I have measured 32mV.
Jules, It does work, but 90% of signal is white noise alone. There are no 50Hz components visible to me in EQ, so that tells me everything should be grounded properly. Also in sound test you can hear me tapping and blowing air into mic. I've tried 2 different capsules, no difference. These 2 capsules work well with simple P48 circuit.
If you connect a 1G resistor in series with the multimeter, it
forms a voltage divider by 1/1000, so every mV you me??? asure is
an acual volt at the circuit's output. You should measure 80mV.
Le 10/04/2022 ¨¤ 13:50, LonDek a ¨¦crit?:
I've connected 1 gigaohm resistor in series with
multimeter, and then measured milivolts. Everything is still
invalid, voltages are same as without 1gohm resistor.
Actually, once the capacitor is charged, there is no more
current drawn, except the fraction of femtoAmpere due to
residual resistance of the insulating materials, which is
way higher than gigaohms.
In normal circumstances, no current should go through the
1G resistors, except during the transient charging phase.
Le 09/04/2022 ¨¤ 22:05, Jules Ryckebusch a ¨¦crit?:
That would
actually cause what you are seeing. Big?question: Does
it work when providing bias voltage to the capsule?
Remember?those are literally?a 50-100pF capacitor?that
we are charging up to provide?a static bias too. They
draw minimal current and most is to the 1Gig resistor
to ground that develops the signal.?
Jules
Hello
The internal resistance of my meter appears to
be 955kOhm so about 1MOhm.
Best regards
Wiktor Molak
--
Best
Regards,
Jules
Ryckebusch
214 399
0931
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Re: Hex inverter issue. Alice OPA
Jerry, I have measured 32mV.
Jules, It does work, but 90% of signal is white noise alone. There are no 50Hz components visible to me in EQ, so that tells me everything should be grounded properly. Also in sound test you can hear me tapping and blowing air into mic. I've tried 2 different capsules, no difference. These 2 capsules work well with simple P48 circuit.
If you connect a 1G resistor in series with the multimeter, it
forms a voltage divider by 1/1000, so every mV you me??? asure is
an acual volt at the circuit's output. You should measure 80mV.
Le 10/04/2022 ¨¤ 13:50, LonDek a ¨¦crit?:
I've connected 1 gigaohm resistor in series with
multimeter, and then measured milivolts. Everything is still
invalid, voltages are same as without 1gohm resistor.
Actually, once the capacitor is charged, there is no more
current drawn, except the fraction of femtoAmpere due to
residual resistance of the insulating materials, which is
way higher than gigaohms.
In normal circumstances, no current should go through the
1G resistors, except during the transient charging phase.
Le 09/04/2022 ¨¤ 22:05, Jules Ryckebusch a ¨¦crit?:
That would
actually cause what you are seeing. Big?question: Does
it work when providing bias voltage to the capsule?
Remember?those are literally?a 50-100pF capacitor?that
we are charging up to provide?a static bias too. They
draw minimal current and most is to the 1Gig resistor
to ground that develops the signal.?
Jules
Hello
The internal resistance of my meter appears to
be 955kOhm so about 1MOhm.
Best regards
Wiktor Molak
--
Best
Regards,
Jules
Ryckebusch
214 399
0931
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Sure post more details!
I think a new PCB wouldn't be a problem, just need the correct schematic.
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Re: Idea for variable pattern microphone
That would do it. Got a lead on one that is 20-20K and inexpensive? I just used my last batch of good ones on a 12 channel mic splitter. They were pico brand and $67 each.
Best Regards,
Jules Ryckebusch
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Re: Idea for variable pattern microphone
I'll look at it further. This was my first attempt. :-)
That's pretty damn clever!
I'm quite fond of my fully balanced outputs though, but I know we're pretty much limited to two x OPA1642s (providing 4 op-amps) with phantom power.
Is there a way of making the mixing OpAmp fully differential and blending the rear into the + / - or both via a pot to achieve the same? Thus leaving one OpAmp for inverting the signal to provide fully balanced?
-- Best Regards,
Jules Ryckebusch
214 399 0931
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Re: Idea for variable pattern microphone
That's pretty damn clever!
I'm quite fond of my fully balanced outputs though, but I know we're pretty much limited to two x OPA1642s (providing 4 op-amps) with phantom power.
Is there a way of making the mixing OpAmp fully differential and blending the rear into the + / - or both via a pot to achieve the same? Thus leaving one OpAmp for inverting the signal to provide fully balanced?
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Idea for variable pattern microphone
You guys all have me thinking here. As I was falling asleep?last night I thought of this. See attached. In essence we take the both diaphragms?and go to a High Z buffer. Then the rear goes to a unity gain inverter. We take the in phase and out of phase and feed the ends of a potentiometer. Then the wiper varies between in phase at one end, out of phase at the other and zero in the middle. That feeds a summing amp with the front diaphragm. The only weird thing is we have the front?inverted due to the summing mixer?being inverting. I am sending it to Pin 3 with pin 2 impedance matched.?
Just an idea here. One of the challenges is that phantom power is our limit here. But there are really good low power op amps?that are bipolar input which?works for the inverter and summing mixer.
Thoughts?
-- Best Regards,
Jules Ryckebusch
214 399 0931
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Mic Scharf