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Hi! Just uploaded two THD Graphs, one for a Pat's Mic build and the other one for an OPA Alice build. I tried to use the same Input levels on both tests. Here are the graphs: Pat's Mic Build :

*1. Is the charge amp being accomplished through the Op Amps? * Yes, the first OPA (1C1A) is in a charge amp configuration. *2. Is it possible to use a Jfet with a built in diode for the

It is quite possible, but, as I wrote earlier, it wouldn't result in the "tube sound" the dicrete JFET is supposed to bring.

Homero - Thank you for the updates!??1. Is the charge amp being accomplished through the Op Amps??? 2. Is it possible to use a Jfet with a built in diode for the triode section?? Maybe something

Thank you Jerry Lee and Henry, @Jerry Lee Marcel <jerryleemarcel@...> I reduced the value of C8 to 1uf. Also there was an error on the C15 value, it should be 1000p instead of 0.1uf. @William

An additional RC filter would work, or simply adding a resistor between the BC549 and C14, and increasing C14 to push the RC time constant below audibility. The op-amps have good power supply noise

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. No. only singles, duals and

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,

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

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

Here is the actual software: https://austrian.audio/polardesigner/

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

Here is a great implementation of Wurcer's chargeamp by forum member Zapnspark: /g/MicBuilders/files/Zapnspark/Occam-3b.pdf

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

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

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

Will try to share some tests next Friday or Saturday. Regards! HL

*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

Any recording tests you could share?

Yes. Only resistances are a source of brownian noise. Reactances are not. This is where it takes some discussion. I take it as a 3.2uF capacitor, that has a reactance of 1Kohm at 50Hz. Its