Re: Pat's Mic (Fetzer Valve Mic)
Le 05/05/2022 ¨¤ 19:27, TheCanDo via
groups.io a ¨¦crit?:
Could
the JFET and/or the transistor be replaced by using a Quad JFET
Opa?? An example would be the?OPA1644 (quad).
In terms of functionalities, it would certainly work.
However, the subject here is getting the circuit to sound like a
vacuum tube. An opamp could not do that.
? Not sure if there are?triple
Op Amps but could that be something too?
No. only singles, duals and quads.
However a combination of a dual with a single? or three singles
could be functional.
A quad would probably exceed the available current.
I like minimizing
parts when I can.
(Almost) Everybody does.
But minimalism is not a proper design endeavour. It takes what it
takes to make the thing work.
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Re: Pat's Mic (Fetzer Valve Mic)
May I suggest you decrease significantly C8. In combination with
R15, its -3dB cut-off is at 0.015 Hz.
! Would think 100nF is largely enough there. It may not be the
answer to your problem, though, just speculating.
Le 06/05/2022 ¨¤ 05:11, Homero Leal a
¨¦crit?:
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Hi all,
?
Here's a
quick update on the test build with the latest?PCB.
?
I'm
experiencing a weird low frequency noise below 1khz. It's?not
too high, but can be perceived. At first I thought?it was only
room noise, but the?noise remains if I replace the capsule
with a small ceramic capacitor. So, it's
definitely?something?on the circuit.
?
I have been
doing some tests trying to isolate the problem.??At first, I thought
it was caused by the current regulator, but it seems to be
caused by the JFET, or a combination of JFET and VR.?
?
If I remove
the JFET and leave only both OPAs, the noise is gone (VR in
place).
?
Also, if I
replace the VR for a single 2k resistor, the noise is gone.?
HL
?
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Re: Pat's Mic (Fetzer Valve Mic)
Hi all,
?
Here's a quick update on the test build with the latest?PCB.
?
I'm experiencing a weird low frequency noise below 1khz. It's?not too high, but can be perceived. At first I thought?it was only room noise, but the?noise remains if I replace the capsule with a small ceramic capacitor. So, it's definitely?something?on the circuit.
?
I have been doing some tests trying to isolate the problem.??At first, I thought it was caused by the current regulator, but it seems to be caused by the JFET, or a combination of JFET and VR.?
?
If I remove the JFET and leave only both OPAs, the noise is gone (VR in place).
?
Also, if I replace the VR for a single 2k resistor, the noise is gone.?
HL
?
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Re: Pat's Mic (Fetzer Valve Mic)
Hello Homero,
I hope all is well.? Has there been any further developments on this circuit, and have you had a chance to run any tests???
I am rather new with some of these concepts.? Could the JFET and/or the transistor be replaced by using a Quad JFET Opa?? An example would be the?OPA1644 (quad).? Not sure if there are?triple Op Amps but could that be something too?? I like minimizing parts when I can.
On Friday, April 29, 2022, 06:25:18 AM PDT, goldenhours_71 <davidstalling@...> wrote:
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Here is the actual software:
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For ease of use and implementation, wouldn¡¯t free software be a convenient solution? ?
I realize physical interface is more satisfying and this is a DIY group, but I thought I¡¯d mention this:
the plug in is free (the mic, very much -not- free), but using your own mic into the plug in..
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Re: Pat's Mic (Fetzer Valve Mic)
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Re: Pat's Mic (Fetzer Valve Mic)
Scott Wurcer used to be a member here and he did a thorough study of using a charge amp in a mic. As I recall it was very impressive, and probably about 6 or 7 years ago. The designs might still be in the files etc if you look for Scott¡¯s work. It was also written up in Linear Audio here? and here?
There is also good information here?
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I know I haven't really posted before but I am so sorry to hear that P@T?passed.... I didn't know until now.? I really appreciated his insights.? He's been a good teacher and I will miss his wisdom. Homero, thank you for doing this.? I think it's an amazing way to honor your friend.? I would love to build this mic when you finalize the design.? I have been looking at a design similar to this one with the idea of having a Charge Amp with an Opa.? Henry at Audioimprov gave me some really great leads for some schematics from this site but I'm not sure where my notes are.? The main difference seemed to be that the JFET was BEFORE the Opa.? Thanks everyone for all of you passion and heart you put into our hobby.? :)
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Re: Pat's Mic (Fetzer Valve Mic)
I know I haven't really posted before but I am so sorry to hear that P@T?passed.... I didn't know until now.? I really appreciated his insights.? He's been a good teacher and I will miss his wisdom. Homero, thank you for doing this.? I think it's an amazing way to honor your friend.? I would love to build this mic when you finalize the design.? I have been looking at a design similar to this one with the idea of having a Charge Amp with an Opa.? Henry at Audioimprov gave me some really great leads for some schematics from this site but I'm not sure where my notes are.? The main difference seemed to be that the JFET was BEFORE the Opa.? Thanks everyone for all of you passion and heart you put into our hobby.? :)
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Re: Pat's Mic (Fetzer Valve Mic)
Thank you Jules, Phil and Scott!
Just waiting?to receive latest?PCB revision. Will try to upload some recording tests over the next few days.
If somebody wants to do some more "formal" tests on this design, please send me an email and let me know . I don't have the best conditions/equipment to do it?@home.
El mi¨¦, 13 abr 2022 a la(s) 20:08, Scott Helmke ( scott@...) escribi¨®:
Homero,
That's a really cool project and a nice tribute to Pat.?
Would love to hear a comparison to a regular mic.
Thanks,
-Scott
On 4/12/22 20:22, Homero Leal wrote:
HI folks!
As some of you may know, one of the dreams of our friend Patrick
Davis (aka. P@T,
Enjoybiking) was the idea of designing a mic that could have the
"tube" sound, but that could also be very cheap to build.
We discussed the topic many times, and the idea of having a solid
state tube emulation was a really fascinating option that was
always on the table.
Some time ago I found a paper from Dimitri Danyuk called "Triode
Emulator", and in this paper he proposes very a simple way to
"emulate" triode behavior using a JFET with very specific values
for drain and source resistors.
Later, I found this page:
Which provides a way to calculate (look at the end of the page)
the required drain and source resistor values using some JFET
parameters like:
And also the input voltage of the circuit (VCC).
So, I decided to try a design using the Dimitri Danyuk approach,
with the values calculated from the Fetzer Valve page.
You could find the schematic here:
/g/MicBuilders/files/Homero%20Leal%27s%20Files/Pat%27s%20Mic/Pat%27s%20Mic.png
Circuit design uses a Charge Amplifier input stage, a JFET middle
stage (providing the "valve" tone"), and finally a impedance
balanced output stage with a Sallen Key HPF at about 19.XHz.
Also, a custom voltage regulator is used, using a BC549C NPN and a
zener, very similar to the one used on some very known chinese
mics. This VR provides about 9.4V for VCC.
I used two drain resistors and two source resistors, so it could
be easier to approach the right values calculated by the Fetzer
Valve page, by using the combination of two resistors.
As the JFET stage may have an amplification level on the signal, I
also used two capacitors for the charge amplifier, this way you
could reduce output level by placing an additional capacitor (some
math required).
I know the design may have some room for improvement, but I can
confirm I have working mic with this design, and it seems to my
untrained ear, that it has a very sleek and warm sound, very
similar to the sound of the valve mics.
For the build, I used a cheap Zramo donor mic from Amazon, which
that very nice 26mm electret capsule we have talked about before.
I decided to name this schematic? "Pat's Mic"...
in memory of our friend and former member of this group, P@T?(Patrick
Davis, R.I.P.)
This post is for your review and consideration, and please if you
have any ideas for improvement, don't hesitate to let me know.
Thank you, and kind regards!
HL
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
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Re: Pat's Mic (Fetzer Valve Mic)
Why do you need RD1 and RD2, wouldn't be one RD enough? Same for RS.Resistor?values for RD and RS need to be very specific, depending on IDSS, VP JFET values, and input voltage. Two resistors are used to make it easy to match the required values. Look at the ?page a the bottom, for the calculator.
Would we need a HexInverter or something else for the polarisation Voltage?
Yes, if you want to use a LDC capsule.
With the OPA and the Fet and T1 could there be a problem with the current from the Phantompower?
Yes, if the JFET IDSS value is to high. OPA1642 uses about 3.6mA. So, it is recommended to use a JFET with a low IDSS. The one I used has a 2.1mA IDSS value.
Regards!
HL
El jue, 14 abr 2022 a la(s) 02:16, Mic Scharf ( micscharf@...) escribi¨®: Why do you need RD1 and RD2, wouldn't be one RD enough? Same for RS.
Would we need a HexInverter or something else for the polarisation Voltage?
With the OPA and the Fet and T1 could there be a problem with the current from the Phantompower?
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Re: Pat's Mic (Fetzer Valve Mic)
Any recording tests you could share?
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Re: Bipolar condenser for P48 basic with EM272?
Unless there is a need for a high pass filter, using a larger
coupling cap won't hurt.
Yes.
Something that's
often forgotten is the series reactance of a cap is a noise
source, just like a series resistance.
Only resistances are a source of brownian noise. Reactances are
not.
So if your coupling
cap is 3dB down at 50Hz working into , say, 1K ohm, it has a noise
contribution at 50HZ same as a 1K resistor.
This is where it takes some discussion.
I take it as a 3.2uF capacitor, that has a reactance of 1Kohm at
50Hz. Its brownian noise contribution is zero.
But the noise current of the active device (FET, BJT, vacuum
tube...) developped across the capacitor will contribute to noise
as much as a 1k resistor at 50Hz, as much as a 10k resistor at
5Hz, as much as a 100R resistor at 500Hz.
Even at 500Hz, it
contributes as much noise as a 100 ohm resistor.
That's partly correct. the contribution of real resistor is brownian
noise + In.Z
The contribution of a reactance is only In.Z. In addition it is
phase-shifted by 90¡ã, so it combines quadratically, not
algebraically. If it is small (<1/10th), it is negligible.
In a mic, there is
a tradeoff between noise and the need to high pass filter thumps
and plosives.
Yes.
The noise
audibility is reduced by the Fletcher-Munson effect, but it's
still there on spectral plots of many mics.
Not only the physiological hearing but mainly the spectral
distribution will make it less perceptible. White noise has less
energy at LF than HF.
I use larger caps
than most engineers, because I think I can hear that LF noise.
I won't debate over teh internet what anybody hears or not. ?
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Re: Bipolar condenser for P48 basic with EM272?
Unless there is a need for a high pass filter, using a larger coupling cap won't hurt. Something that's often forgotten is the series reactance of a cap is a noise source, just like a series resistance. So if your coupling cap is 3dB down at 50Hz working into , say, 1K ohm, it has a noise contribution at 50HZ same as a 1K resistor. Even at 500Hz, it contributes as much noise as a 100 ohm resistor. In a mic, there is a tradeoff between noise and the need to high pass filter thumps and plosives.
The noise audibility is reduced by the Fletcher-Munson effect, but it's still there on spectral plots of many mics. I use larger caps than most engineers, because I think I can hear that LF noise.
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Re: Bipolar condenser for P48 basic with EM272?
Understood. That last explanation about Bipolar was really refreshing from the old days, thanks!
Why people don't use? 10uf? 63V, or even 10uf 100V?
Is it only for the space it takes physically inside the XLR connector or there is something related that can affect the frequency response??
Cheers
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Re: Bipolar condenser for P48 basic with EM272?
An aluminum electrolytic capacitor consists of two Al foil electrodes separated by a conductive electrolyte. Al forms an oxide coating on the surface on contact with air or water, and the oxide coating is the dielectric of the capacitor. So an Al electrolytic consists of two caps in series, one at the anode and one at the cathode. The anode is formed with the thicker oxide, is high voltage and lesser capacitance. The cathode is low voltage, a volt or two, and very high capacitance. The over all result is two caps in series, of which the anode primarily determines the voltage and capacity. It turns out the cathode contributes most of the tiny distortion to any signal passing through.
This is where it gets interesting. Bipolar electrolytics are NOT made as two polar caps in series. Bipolar caps have two anodes and no cathodes. Bipolar caps exhibit much less distortion than polar caps in audio coupling circuits. So to answer the OP question, bipolar caps are fine. They are actually preferred if they can be had in the desired voltage and capacity. They exhibit more than an order of magnitude less distortion. They are physically larger, because the two anodes in series have to be larger to reach the same capacity, but otherwise they are better, even in circuits where the polarity applied never changes.
Let me add that capacitor distortion is likely to be the least contributor to the sound of a mic, but still . . .
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Re: Bipolar condenser for P48 basic with EM272?
We are probably worrying about nothing TBH. Jules @ Sound Sleuth designs excellent circuits, if he says it's good, it'll likely be good.
I can only see a problem if you're intending on capturing low frequencies (e.g. 30Hz) and feeding it into a mixer with low input impedance on its mic channel (e.g. <1000 ohms). If your mixer / sound card mic input is decent it'll have >1500 Ohm on its input and so you won't see a problem.
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Re: Bipolar condenser for P48 basic with EM272?
The other issue is size of the capacitor. ?I¡¯m the 3.3uF 63V guy. ?They work great and physically allow you to build the SimpleP48 into the XLR connector. ?I use this with my ZoomF6. ? Best Regards,
Jules Ryckebusch?
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On Apr 21, 2022, at 07:51, a45porhora@... wrote:
?Thanks for the explanation Michael, the point about tolerance is really good. My plan is to connect that Mic's via XLR to a new Zoom F3, but better for a capacitor rated for at least 50V like this one: https://www.mouser.es/ProductDetail/Nichicon/UKW1H4R7MDD1TA?qs=WJSLByB5Mu28FaeGBvn6BQ%3D%3D About low frecuencies: Reading this: ?he says?
?The capacitor can be 1uF to 4.7uF without noticeable change in sound. I am using 3.3uF
What do you think about this? Cheers
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Re: Bipolar condenser for P48 basic with EM272?
Thanks for the explanation Michael, the point about tolerance is really good. My plan is to connect that Mic's via XLR to a new Zoom F3, but better for a capacitor rated for at least 50V like this one: https://www.mouser.es/ProductDetail/Nichicon/UKW1H4R7MDD1TA?qs=WJSLByB5Mu28FaeGBvn6BQ%3D%3D About low frecuencies: Reading this: ?he says?
?The capacitor can be 1uF to 4.7uF without noticeable change in sound. I am using 3.3uF
What do you think about this? Cheers
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Sey