R/E/P > Klaus Heyne's Mic Lab

regulated power for tube mics-- impact on sound?

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David Bock:
when you're dealing with the most common single stage single ended tube mic amp, everything you do or change is audible. This includes capsule, tube, xfmr, AND PSU's.
In short, topology and implementation matter.
There are a few different  B+ reg techniques, and they do sound different from each other.
There are also very expensive vintage mics that get used by pro's everyday that have NO B+ reg.
Remember that your decisions about what psu type to use will have to take into account it's effect on sound, as well as all the usual specs (hum, noise, heater/B+ ramp up, impeadance vs. frequency, shorts capability, cost, size, power draw, field generation). Looking at the specs side only might provide functionality, but not necessarily an ideal sonic signature (please don't get the idea that there's no such thing as a sonic signature- every piece of gear has one by definition).

soapfoot:
David B.,

Would you be willing to share how you power your 47-style mics, or is that proprietary information?

I'd love to get more thoughts also on the way these things affect the subtle (or not-so-subtle) changes in the sound of the microphone.

ttown:
In my limited experience with tube mic PSUs, I have to say that the PSU has a rather remarkable effect on the final sound.

I have taken the same mic (e.g., Neumann KM54/56/64 and Schoeps m221a/b) and powered them from different PSUs and the most audible effect is on the noise floor.

Although uncertain, I would guess that the issue is more to do with the quality of the op-amps in the PSUs vs. the actual voltage applied to the mic, on the H+ and/or on the anode side.

We tend to think of tube mic PSUs as simply supplying voltage, but they also have op-amp circuitry of varrying quality - which can have a rather profound effect on the final sound of the tube mic!

zebra50:
Quote:
We tend to think of tube mic PSUs as simply supplying voltage, but they also have op-amp circuitry of varrying quality


Hi!

Can you give us an example of this?

Thanks!

ttown:
Here's a good read on op-amps and PSUs:
http://tangentsoft.net/audio/opamp-ps.html

The take-home message is that poor regulation of DC power typically results in higher (audible) noise levels.  

I can offer an anecdotal example.  Up until a month ago I had a fully functional aftermarket PSU for my SM69 tube mic (I fried the PSU late one night during a session by plugging it into a step-up transformer by mistake - but that's another story!).  That PSU had a higher noise level with the same mic than two other AC701 PSUs that I have, being especially notably noisier than a PSU from Peter Drefahl, so I wondered why?

I took apart the now fried SM69 tube PSU only to discover crumby Russian-made op-amps/DC voltage regulators that were likely the source of the higher noise floor!

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