Tube microphone with ef80 tube and oep transformer.

gyraf · Nov 13, 2018

You probably shouldn't use these long, screened cables between PCB and tube.

It is very important that capsule gets to tube grid as directly as possible, running shielded cables at Gigaohm impedances is not a good thing at all.

And remember full Faraday shielding before evaluating anything..

Jakob E.

peterbach · Nov 13, 2018

Thank you sir I will do that

RuudNL · Nov 15, 2018

abbey road d enfer said:
I seriously doubt the LF performance of the OEP transformer driven by such a high impedance.

I fully agree with you. I once tried an OEP (6.45:1) transformer in the same circuit, but the results were not very good.
Low frequencies were lacking.

peterbach · Nov 15, 2018

RuudNL said:
I fully agree with you. I once tried an OEP (6.45:1) transformer in the same circuit, but the results were not very good.
Low frequencies were lacking.

I have no signal at all

Circuit is not working

RuudNL · Nov 16, 2018

It that case, it is time to find the problem!
Did you measure the voltages?
If we know the values of the anode and cathode voltages, that would give an indication of what is wrong.
(You did connect the filament voltage, did you?

)

peterbach · Nov 16, 2018

RuudNL said:
It that case, it is time to find the problem!
Did you measure the voltages?
If we know the values of the anode and cathode voltages, that would give an indication of what is wrong.
(You did connect the filament voltage, did you? )

All voltages are ok
But I getting only noise
Tube noise so the transformer is ok and the capsule capacitance measurements is 78 pico for each side
I will got crazy soon

RuudNL · Nov 16, 2018

Check if the hum increases when you come with your finger near the grid connection of the tube.
If that is the case: check the polarisation voltage of the capsule!

peterbach · Nov 16, 2018

RuudNL said:
Check if the hum increases when you come with your finger near the grid connection of the tube.
If that is the case: check the polarisation voltage of the capsule!

Yes the hum is increases when I come with my finger near the grid and the capsule also but the measurement of the polarisation voltage is 58v and I think it's perfect

peterbach · Nov 16, 2018

I will start the circuit from the beginning but with end to end soldering method and I will see the result and if it will not working I will use this attached design

abbey road d enfer · Nov 16, 2018

peterbach said:
I will start the circuit from the beginning but with end to end soldering method and I will see the result and if it will not working I will use this attached design

It's a strange circuit, with the second triode limiting headroom and overall positive feedback. Where does it come from? Seems to be designed to correct strange capsule behaviour.

BTW, you haven't succeeded in making the first circuit work, so you give up you want to start another; do you think it's the way to learn how to grok things?

peterbach · Nov 16, 2018

abbey road d enfer said:
It's a strange circuit, with the second triode limiting headroom and overall positive feedback. Where does it come from? Seems to be designed to correct strange capsule behaviour.

BTW, you haven't succeeded in making the first circuit work, so you give up you want to start another; do you think it's the way to learn how to grok things?

You are right sir
I will find the problem of the circuit

peterbach · Nov 16, 2018

The attached circuit come from
Thiele m4 microphone
West German microphone company

peterbach · Nov 16, 2018

Inside

abbey road d enfer · Nov 16, 2018

peterbach said:
The attached circuit come from
Thiele m4 microphone
West German microphone company

My understanding is that Thiele had capsules that were not on par with Neumann, so they had to compensate in the electronics.

peterbach · Nov 16, 2018

I see that the polarisation voltage is unusual in this circuit 70v and it's cathode follower transformer less circuit

peterbach · Nov 16, 2018

I will start the Oliver archut circuit again to find the problem

RuudNL · Nov 17, 2018

A very strange design indeed! With a bit of (bad) luck, the circuit will act as an oscillator (multivibrator)!
I don't think this is a good design to start with, without much experience in microphone design.
The chances that this will work correctly the first time, are minimal, IMHO.

Tube microphone with ef80 tube and oep transformer.

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