Feeler: Super quiet tube mic psu

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e.oelberg

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Joined
Aug 14, 2004
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791
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Berlin
I try to talk mister Funk into designing a tube (mic) psu 5.6-.6.5 V  & 100-160 V . His other audio Psu designs are incredible quiet and I don't see designs
much different than  done in the 60ies for tube use. I know my limits, I also dont like building PSU. I'd be in for 5 myself. Maybe there are others who might be interested, I know that Andreas Grosser tried to talk him also into building one. If we could come up with a number of people interested he might be convinced to pick up work.

here are some links, check the specs
http://funk-tonstudiotechnik.de/PWS-04a-FFT.pdf
http://funk-tonstudiotechnik.de/NETZTEILE.htm


nicholas
 
It's not that difficult to build a modern power supply that doesn't add any noise to a tube microphone. Any time you have heater and cathode connected it gets a little critical, but in the end other noise sources will be dominant IMHO. Recently built a new power supply for a Neumann CMV-3 (directly heated RE084) and while this vintage beauty is not the lowest noise tube microphone on the planet I was able to use a LM317 with some decoupling for the 4V. In general I prefer regulated voltages to prevent changes in line voltage to affect performance and sound from day to day.

Martin
 
I built a supply using a 317 and one like Max proposed it for the MK7 project. But I had also the experience of swapping a lm317 based PSU for a Funk in a
mic pre (48V) in it is a difference, did you check the specs? ... but maybe you are right and the other noise sources will anyway dominate.

nicholas
 
There is a link somewhere at this site for a old microphone article on building your own microphone.  Look close at the supply schematics.

Next it is not hard to design a low noise supply, how much money do you want to spend and how big a box?  It also depends on the tube circuit in the microphone some circuits are more supply noise sensitive.

 
Hi Gus !

I built 4 PSU for tube mics and they work and they are reasonable silent. Far away from the specs of funk psu's though as you seem to agree
the other noise sources (tube, maybe capsule) seem in the way for betters snr. To clarify, the mic's are all great, but as I record often very
silent music, I wouldn't mind better SNR


thank you, Nicholas
 
e.oelberg said:
To clarify, the mic's are all great, but as I record often very
silent music, I wouldn't mind better SNR

Perhaps you should clarify what kind of noise you are getting. Post FFT plot of your noise floor maybe. My guess is your tubes are bad and that there's nothing wrong with your PSU's.

Did you cherry pick your tubes? Because you absolutely must. The usual pentodes-as-triodes that we see in tube mics are not really designed for the task and in a way work outside their specifications. Maybe less than quarter of these types of tubes have the very low noise and microphonics required for mic amp usage. You are left with the task of manually picking the most suitable ones.

[edit]

Another area of critical importance is how you have set up your mic grounds. Easy to make mistakes there. You mentioned you have built a PSU using the passive ioaudio/Max design. That to me hints you have problems anywhere BUT the PSU.
 
I'll have a look  what I could trim with ground, I did star grounding. The tubes are cherry picked of 6 6072 a five star 6072 in a elam e251 circuit 200m to ground instead of 68m. I guess I'm just a little picky, the mic sounds fantastic btw
 
http://www.conditionedresponse.com/DIY/microphones/Debenham.pdf

I would use a full wave on the B+ but look close at the design of the heater supply and bias.  Note the passive heater supply and the two other heater supplies.  Does anyone know the year it was published?

It seems people overlook the circuit design of this PDF, I don't recall any posts about the circuits.  Dale has built the capsule IIRC.

 
Hi,

A current source for the heater, and a super reg for the High voltage supply makes a dead quiet supply, check de Vacuumstate site, and the Duncan power calculation tool is also very handy for the high voltage.

DJN
 
Ok I took the advices and bought two more tubes in search of a really silent one. One of this tube, a GE JG-6072a is scary quiet. It's the 8th 6072 tube I try, I checked also ecc801s in the circuit, also not bad. The Mic ( is now my most quiet mic in the drawer. Next thing to improve with the mic is the Bass respone.

nicholas
 

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