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Author Topic: regulated power for tube mics-- impact on sound?  (Read 11214 times)

soapfoot

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regulated power for tube mics-- impact on sound?
« on: January 18, 2011, 11:54:13 am »

Is regulated power as a positive or not in tube microphone power supplies?

How much does the load resistance presented by the microphone vary during normal operation?  Is it small enough to be negligible?

Is there any benefit (or downside) to a regulated supply?
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brad williams

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Re: regulated power for tube mics-- impact on sound?
« Reply #1 on: January 18, 2011, 12:04:38 pm »

Can you be more specific?

Regulated AC supply into the tube mic PSU, or regulated DC PSU?

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

soapfoot

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Re: regulated power for tube mics-- impact on sound?
« Reply #2 on: January 18, 2011, 12:09:26 pm »

Sorry, regulated DC PSU.
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brad williams

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Re: regulated power for tube mics-- impact on sound?
« Reply #3 on: January 18, 2011, 01:22:57 pm »

Ah, gotcha.

The dominant consumption in terms of current is usually the heater. Since this doesn't change much with signal, I'd imagine that it's largely insignificant. -That doesn't preclude regular checks though.

For my own microphone, I'm building a slightly 'improved' power supply in that it will have -among other things- a relay in the HT line BEFORE the C/R/C/R/C ladder, energised by a current sensing circuit in the HEATER feed.

That way, if the mic is unplugged, the PSU voltage won't rocket upwards. -Since that's incorporated, it may as well be regulated and adjustable, since that adds very little to the difficulty, with modern designs.

I'm also contemplating a constant CURRENT drive for the heater, which is much kinder on startup.

Of course in this design, the heater is being fed along a separate conductor. -If you think about how the heater is fed in a U47 circuit, significant variations in AC voltage can alter the way that everything is balanced, so that particular design is likely to be 'differently-sensitive' compared to a design with the heater fed separately.

A regulated HEATER voltage with unregulated HT is a third combination to consider.

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

soapfoot

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Re: regulated power for tube mics-- impact on sound?
« Reply #4 on: January 18, 2011, 01:54:03 pm »

I have a lot to learn about power supply design.  I know the basic building blocks, but I need to learn more about regulation and how to work toward a target voltage.
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brad williams

David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #5 on: January 18, 2011, 02:49:52 pm »

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

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Re: regulated power for tube mics-- impact on sound?
« Reply #6 on: January 18, 2011, 02:58:10 pm »

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.
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brad williams

ttown

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Re: regulated power for tube mics-- impact on sound?
« Reply #7 on: January 18, 2011, 10:59:47 pm »

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!
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zebra50

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Re: regulated power for tube mics-- impact on sound?
« Reply #8 on: January 19, 2011, 03:44:53 am »

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!
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Stewart Tavener
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ttown

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Re: regulated power for tube mics-- impact on sound?
« Reply #9 on: January 19, 2011, 12:10:16 pm »

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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David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #10 on: January 19, 2011, 12:43:21 pm »

Quote:

Here's a good read on op-amps and PSUs:

I think it's safe to say that since we're discussing B+ and heaters we're talking about tube mics,  the overwhelming majority of which do not contain op amps. So too for the power supplies, the majority of which do not use op amps or voltage referenced comparators to provide B+ or heaters. The most common heater circuits use three terminal regs or a single xistor, common for B+ to have single pass xistor, zeners, or even none regulation. This op amp reg B+ is mainly an aftermarket phenomena which does not yet affect the majority of tube mics, thankfully. Just to keep it modern, the recent Neumann mics are use switching psu's, which is a whole other discussion.

soapfoot

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Re: regulated power for tube mics-- impact on sound?
« Reply #11 on: January 19, 2011, 01:38:38 pm »

In a circuit where the bias is tapped off the heater and applied as a positive voltage to the cathode do you think a heater supply with a linear regulator like a 7806 would be too noisy?
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brad williams

David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #12 on: January 19, 2011, 02:07:10 pm »

I can guarantee it.
BTW, about that whole opamp psu link that was provided: bear in mind that high voltage, high impedance tube stages are completely different things than low impedance  opamps.

soapfoot

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Re: regulated power for tube mics-- impact on sound?
« Reply #13 on: January 19, 2011, 02:11:53 pm »

in such a circuit, would one be better off with no regulation at all.. a bunch of Pi filters and maybe a choke?

Do you see any benefit to fast recovery epitaxial diodes in the bridge rectifier?
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brad williams

David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #14 on: January 19, 2011, 02:21:54 pm »

BTW I appreciate Brad using his whole real name, but who is "ttown"?
Quote:

in such a circuit, would one be better off with no regulation at all.. a bunch of Pi filters and maybe a choke?
them's gonna be some big chokes.
Quote:

Do you see any benefit to fast recovery epitaxial diodes in the bridge rectifier?
a basic fast recovery helps but you don't need to go hexfred.

soapfoot

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Re: regulated power for tube mics-- impact on sound?
« Reply #15 on: January 19, 2011, 02:35:52 pm »

so no choke then?  Just RC pi filters?
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brad williams

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Re: regulated power for tube mics-- impact on sound?
« Reply #16 on: January 19, 2011, 02:37:58 pm »

dbock wrote on Wed, 19 January 2011 14:21

BTW I appreciate Brad using his whole real name, but who is "ttown"?


Profile says "Terence Town".

The power supply as described sounds like a bad example... I don't know of ANY commercial tube mic power supplies which use op-amps for regulation.

If someone fits one as aftermarket, then that's THEIR mistake... just bad engineering.

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #17 on: January 19, 2011, 06:28:34 pm »

I thought people were supposed to use their real names on this forum. Having to look them up under profiles is a loophole that shouldn't be accepted.
The use of Real Names in the age of "power through internet anonymity" is one of the great features of this forum, and I would urge all posters to participate fully.  

piedpiper

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Re: regulated power for tube mics-- impact on sound?
« Reply #18 on: January 19, 2011, 06:36:36 pm »

a little ironic considering the marked similarity between your own user name and lack of signature in your posts and that of "ttown".

...and thanks for all the great info.

respectfully,
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Tim Britton

row, row, row your boat...

Dominick

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Re: regulated power for tube mics-- impact on sound?
« Reply #19 on: January 19, 2011, 06:51:53 pm »

Moderators could require you to register with your real full name on the new forums.
That would be a step in the right direction
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Dominick Costanzo

David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #20 on: January 19, 2011, 07:31:45 pm »

Quote:

a little ironic considering the marked similarity between your own user name and lack of signature in your posts and that of "ttown".
I definitely take liberty assuming I'm a little more well known here than ttown. will change asap.

Jim Williams

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Re: regulated power for tube mics-- impact on sound?
« Reply #21 on: January 19, 2011, 08:16:05 pm »

Check with some of the design work on precision regulators done by Walter Jung of Analog Devices. He has published many papers on the subject of precision regulation for audio circuits.
Yes, they use precision opamps for the references. They are not a bad choice, but maybe one of the better ones.
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Jim Williams
Audio Upgrades

piedpiper

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Re: regulated power for tube mics-- impact on sound?
« Reply #22 on: January 19, 2011, 11:18:37 pm »

I hear you, David, and know who you are, of course, but I'm guessing that assuming everyone would might be an oversight. It's just that the similarity struck me as  funny and I couldn't resist mentioning it. Thanks for your gracious response.
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Tim Britton

row, row, row your boat...

ttown

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Re: regulated power for tube mics-- impact on sound?
« Reply #23 on: January 20, 2011, 02:12:17 am »

Sorry for the oversight guys, no need to read into things, I just forgot to sign the post.  

Also, not making any inferences about which PSUs use op-amps and which don't.  I was asked to give an example of how a PSU can influence audio output from a mic, and this is what I found when I opened a Russian-made PSU for an AC701 tube mic.  I stand by what I said regarding the comparison with the Drefahl PSU.  It was notably quieter than the Russian op-amp-based PSU.

... but let's not loose the woods for the trees here.  The point is that a PSU can influence a mic's audio quality.  I am no expert and have limited experience as I stated in my post above.

Thanks,
Terrence Town
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ssltech

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Re: regulated power for tube mics-- impact on sound?
« Reply #24 on: January 20, 2011, 08:07:28 am »

Jim Williams wrote

 Check with some of the design work on precision regulators done by Walter Jung of Analog Devices. He has published many papers on the subject of precision regulation for audio circuits.
Yes, they use precision opamps for the references. They are not a bad choice, but maybe one of the better ones.


A noisy, poorly designed supply shouldn't paint ALL of them with the same brush, but a good tube mic B+ PSU shouldn't require the convoluted hoop-leaping that an op-amp circuit would entail.

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #25 on: January 20, 2011, 01:50:02 pm »

Quote:

... but let's not loose the woods for the trees here. The point is that a PSU can influence a mic's audio quality. I am no expert and have limited experience as I stated in my post above.

Ahh, but that's the point, you  listened. One of the traps for audio design is believing in something's superiority before listening. I could write a whole paper on this but don't have time today.
Quote:

a good tube mic B+ PSU shouldn't require the convoluted hoop-leaping that an op-amp circuit would entail.

Definitely not required but has been (EAR, Blue,*) and can be done. Usually the op amp will be acting as a comparator against a voltage reference. If done well, there IS lower noise overall and a different response characteristic to the mic, which, is a matter of taste, not right and wrong (yes there is right and wrong in the world no apologies to Nietzsche).
*fwiw Korby, Bradley, and Hampton supplies are regulated but I don't recall if they use op amps.

R-AP.SCI

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Re: regulated power for tube mics-- impact on sound?
« Reply #26 on: January 21, 2011, 03:51:18 am »

Good day to all,

    I am currently experimenting with varying power supply topologies and have begun to employ the methodology stated by Mr.Williams employing the Jung precision regulators. In the heater section that is....(and tubed in the HV!!!...FUN). Thus far it most definitely has outperformed all traditional LM317 and like type 3pin chip regulators across the board...(in terms of noise etc) and I enjoy the sonic outcome. I will post definitive measurements when a final design has been achieved. I personally enjoy regulation of tube mic power supplies (not to say that other types aren't to be lauded, as some classic, beautiful sounding and legendary tube mics do not employ regulation).

    I also have liked the fairchild 1N4934 fast recovery diodes in rectification applications. Try those too!...(i'm a bit of sucker for overbuilding and experimentation)

    It is of course an entire circuit consideration and as far as I'm concerned one that can and does have sonic affects.

  I rather enjoy this thread as it (indirectly) addresses a many times overlooked section in the industry (sometimes, in my opinion, expressed in the vein of "does it work?"..."yes."..."does it screw anything up?"..."no."..."GREAT, DONE!")...or in the sense of it meeting a perfunctory electrical standard...and no further. If there isn't already, one of us should start a thread dedicated to the design considerations and implementation of power supplies in total...(not just "modding" or "regulation" etc).

 I have attached photos of the Bradley and Drefahl power supplies (the Bradley photo is from his site, it is a dual supply and appears to have a vertically oriented 3pin regulator chip heat sunk on the left hand side of the unit. The Drefahl I own and it is regulated - both HV and heater- by traditional 3pin chips, no opamp style regulation in either...in my opinion both are good supplies...(I have used the Bradley).

    I don't think that "whats required" should be the ceiling. We as designers of tube microphones owe it to the giants of history to honor their progress and ingenuity.
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R-AP.SCI

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Re: regulated power for tube mics-- impact on sound?
« Reply #27 on: January 21, 2011, 03:52:27 am »

...sorry, here is the Drefahl.
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Gustav

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Re: regulated power for tube mics-- impact on sound?
« Reply #28 on: January 21, 2011, 06:49:21 am »

3 pin regulators have opamps inside.  They have a pass device and an error amp and a voltage reference and maybe some other things like over temp and over current protection

http://en.wikipedia.org/wiki/File:LDO.png
http://en.wikipedia.org/wiki/Voltage_regulator

Gustav
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johnR

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Re: regulated power for tube mics-- impact on sound?
« Reply #29 on: January 21, 2011, 06:58:25 am »

Use of standard voltage regulator ICs doesn't necessarily result in noisy power supplies. They are quite efficient noise generators, as are zener diodes, so adequate filtering is required to attenuate the noise.
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R-AP.SCI

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Re: regulated power for tube mics-- impact on sound?
« Reply #30 on: January 21, 2011, 02:05:10 pm »

Salutations.....

    I simply meant to comment upon the differences between the 2 differing topologies/methodologies (not to imply that 3pin ic's don't have opamps in them)....as I have found the discrete style of Mr.Jung's favorable within the conditions and applications i have employed them, in comparison to the more "traditional" 3pin ic.

    And of course I never meant to imply that the use of said 3pin ic's necessitate a noisy supply, simply that i have found otherwise to have less noise in comparison (again in this type of application, and depending upon the implementation the opposite could occur)....as for example the Drefahl supply is quite low in noise.

    Absolutely, appropriate filtering of any ac-dc conversion-regulation circuit is paramount to well performing power supplies, regardless of regulation topology and should span an entire circuit consideration as well...(this is also something i feel has been sometimes executed to a lowest common denominator)

...my apologies for not being more specific and possibly adding confusion.

    What about a bi-polar discrete shunt...maybe Bruno Putzeys could chime in...I believe he might use this methodology in his Grimm audio tube power supply.
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David Bock

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Re: regulated power for tube mics-- impact on sound?
« Reply #31 on: January 21, 2011, 03:03:47 pm »

yes the three term regs have op amps another can of worms.
@r-ap.sci the EAR & blue supplies I mentioned are shunts. You also went on about discreet vs. ic for heater but failed to mention setup. For example, a 3 terminal device can be used effectively as a current source for a heater which is quieter than using it as a v reg.

R-AP.SCI

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Re: regulated power for tube mics-- impact on sound?
« Reply #32 on: January 21, 2011, 05:26:48 pm »

Very true Mr.Bock...I was just speaking from my experiences with my experiments and what I know of some popular supplies.. and thanks for the info on the Blue and EAR supplies as I did not know what they were and wasn't about to get some and open them up! Do you have a favored topology regarding regulation (if any) for your offerings? Or are they designed and implimented on a case by case basis? I do not mean to pry or overstep any line of proprietary stuff of yours...its just that being a designer of your regard it would be great to hear what you think is best for your offerings and why...perhaps giving us some food for thought!
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ttown

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Re: regulated power for tube mics-- impact on sound?
« Reply #33 on: January 23, 2011, 02:59:43 pm »

David Bock wrote on Thu, 20 January 2011 12:50

Quote:

... but let's not loose the woods for the trees here. The point is that a PSU can influence a mic's audio quality. I am no expert and have limited experience as I stated in my post above.

Ahh, but that's the point, you  listened. One of the traps for audio design is believing in something's superiority before listening. I could write a whole paper on this but don't have time today.


Well, I do try!

... but more on 'listening', I happened to go to the West LA music demo day and a very cool guy from your shop was demo'ing each of your current line-up, David.  Here's a plug for you - I was floored by the sound of your 251.  

Mind you, I was just talking through each of the mics (while my speaking voice won't shatter glass, my singing voice likely would!), and he had a Mackie 1604 there that I was listening to through monitor cans... but the Bock 251 really stood out as linear and balanced.  I even liked it better than your flagship model with the elliptical capsules.

In keeping with the subject of this thread, I noticed that all of your mics except the 195 use dedicated PSUs.  How much of your sound comes from this design  decision - is it possible to get the same sound from a P48 mic?

-Terrence Town
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