what should I expect from different mic circuits?

[stefanzap]

For building my little mics, I've been using the famed Schoeps-Dorsey-Helmke circuit. :wink:

I'm happy with it, but of course - always curious.

So, my question -

How does the Shoeps-Dorsey-Helmke circuit hold up against other circuits?
What should I expect from other circuits?
What do the different circuits do, well, differently?

I get the tube thing. That's easy enough, but in terms of solid state stuff, how does the circuit affect the sound? I mean, technically, shouldn't it NOT affect the sound?

Given the same capsule, what does a transformer based circuit do the sound?
etc.

Looking forward to the information

 

[Gus]

you get the tube thing?

just build a bunch of stuff thats the best way.

 

[stefanzap]

Yeah, I get the Tube thing. It's nice warm sound. Makes you feel all fuzzy.
:wink:

Seriously, I have enough experience with tube amps to know the difference, and certainly, Tube mics, Ribbon mics, Condenser mics and different size diaphragms, that's all fairly obvious tonally and theoretically.

I'm hoping I can get some specifics about what, given the same capsules, different solid state circuits would do to the sound.

All you experienced purveyors of EE knowledge - Please, elucidate these mysteries.

I don't want to re-fry the wheel, unnecessarily.

 

[Gus]

Microphones everything counts IMO. I have built a number of tube and solid state circuits in microphones and I am still learning new things.

 

[Svart]

wow that is quite a wide subject.

I suggest reading http://www.groupdiy.com/index.php?topic=256 the microphone meta.

And Gus is right, everything seems to count, even the material of the screens counts.

 

[stefanzap]

Yeah, I know it's a wide subject.
And I have gone through the mic meta, and am asking this as not a pro, but not a complete newbie either.

I have also done quite a bit of experimenting with body shapes, grilles, foam, etc.
These things are of interest and yes - of absolute importance in the sound, but my question is strictly about the circuit.

I've done experimenting with different fets, resistors, caps, etc. but all based around this beautifully simple schoeps circuit. I'm not talking about replacing film caps with other caps. I'm talking about completely different circuits.

Let's put it this way: all other things being the same (body, capsule, grille, etc), what do different circuits do to the sound?
(and no cheating like saying - well, the circuit size wouldn't allow for...)

Specifics?
Okay, I"ll throw some out that it would seem would be affected somehow: self noise, dynamics, transient response times, FQ response...

Can anyone tell me how these things are affected by different circuits?
Are there better circuits out there? If so, how are they better?

There would (I would think) be differences or we wouldn't have a need for so many different, and more complex circuits, correct?

Gus, what have you learned from the different solid state circuits?

 

[gyraf]

Parameters that can easily be quantified should be relatively easy to find published (or calculate on your own).

If you don't know Klaus Heyne's mic forum over at PSW already, here's a link:
http://recforums.prosoundweb.com/index.php/f/33/1517/

What you may in-fact be looking for, is description of perceived sonic characteristics. And those are far from easyly converted to plain, common language. And often not quantifyable at all.

As Gus says:

just build a bunch of stuff thats the best way

Jakob E.

 

[burdij]

I am testing two fet condenser mikes right now. One uses the (apparently widely copied) Schoepps circuit. The other uses a circuit almost identical to the U87 (preamp side anyway). The two use the same capsule type (a U87 copy, 34mm) and identical power inverters to polarize the capsules. There is a difference in the screen designs. The one with the U87 type circuit has a cylindrical screen, the one with the Schoepps, a "chisel" shape. Both have plenty of space inside the screen around the capsule.

What I have noticed so far is that the mike with the U87 style fet followed by transformer circuit sounds "bigger", "closer" with some "guts". The Schoepps style mike sounds more in the background, more nasal, more "clinical" with less bass, clearly more "distant". This result surprises me and supports the observation that the circuit topology (and, I am sure, the near capsule environment) plays as much of a role in the sound as the capsule itself.

Oddly enough, both of these mikes sound better than my TLM103. I am starting to think I got a lemon, there. The measured response of the TLM starts to roll off dramatically below 100 Hz. It is 4-6db lower than the published response at 50Hz. Above 15KHz, it drops like a stone. This was a disappointment as I bought the mike new (and believed the hype, I guess).

I have not had a chance to run frequency response and distortion measurements on these yet. I believe that I will find the transformer version will have the usual issues with magnetics induced increases in second and even harmonics. I want to believe that the transformer-less version will be cleaner with lower harmonic content, but judging by the sound, I think I will find that the odd harmonic content is going to be the dominant harmonic form. Postulating now, this may be due to the asymmetrical gain characteristics of the fet "psuedo-source follower", the source having a gain slightly less than one and the drain having a gain slightly greater than one. I am building up a "test bed" mike that will allow me to introduce an active inverter with a gain of exactly one to use to drive the output emitter followers so that the gain relationship will be balanced to test if this is a source of additional distortion.

 

[Svart]

both of these mikes sound better than my TLM103

I've not met many people that actually like the tlm103 regardless of what the press says about it..

I'm working on a mic design myself, clean and pure are my goals for now as well is low parts count in the audio chain.

Colored mics are extremely easy to design it seems.

 

[Marik]

[quote author="burdij"]
The Schoepps style mike sounds more in the background, more nasal, more "clinical" with less bass, clearly more "distant". [/quote]

Thanks!--I encountered the same results and a few times posted here with exactly the same words. Nobody seems to listen to me, though :razz: .

However, it is a very good circuit and has its uses in some applications. Also, it can be improved.

As for the original question, neither--self noise, dynamics, transient response times, FQ response... etc. will tell you about actual sound.
The mics are pretty much like girls--you never know until you try it.

 

[Emperor-TK]

[quote author="Marik"]
The mics are pretty much like girls--you never know until you try it.[/quote]

So are you saying that we can't guess how hot the output is based solely on appearances...? :wink:

Ok... back to topic....

 

[Marik]

[quote author="Emperor-TK"][quote author="Marik"]
The mics are pretty much like girls--you never know until you try it.[/quote]

So are you saying that we can't guess how hot the output is based solely on appearances...? :wink:
[/quote]

Well... of course you can guess (I heard, some actually prefer that way), but IMHO, it is a much better idea to make sure :grin:.

 

[stefanzap]

burdij,

Great reply. That's useful stuff.

The characteristics seem in line with Schoeps mics in general - very accurate, but perhaps a bit sterile.
Would you say that is the sign of a transparent circuit or a circuit that's perhaps pulling some stuff?

Burdij - do you think the transformer is accounting for the 'bigger, closer guts' feel?


Marik, you mentioned improvements that can be made to it... any specifics? I have seen some variations from scheme to scheme, and have tried a few things myself. I'm all ears (no pun intended) on any thoughts you have.

I'm humbled by you guys and your knowledge - so it's disconcerting when I can't get a straight answer about the electronic side.

Gus, you've made some beatiful mics - do you have a favorite solid state circuit?

 

[Gus]

I think I saw the schoeps type circuit used with the PZM radio shack microphone mod. Back when stuff was ASII on the net.

 

[skipwave]

[quote author="stefanzap"]
What should I expect from other circuits?[/quote]

Expectations influence results, so try not to expect anything. Otherwise, you will end up like me; just building what you expect to be best and never truly experimenting, thus residing in a state of perpetual self-doubt. :?

[quote author="stefanzap"]What do the different circuits do, well, differently?[/quote]

Now that could open up some nice discussion.

The next mic circuit I want to build is the KM84. The simplicity is attractive, but the results are probably highly dependant on the quality of the transformer (as with any transformer balanced circuit).

 

[Kev]

[quote author="Gus"]I think I saw the schoeps type circuit used with the PZM radio shack microphone mod. Back when stuff was ASII on the net.[/quote]

ascii ??

if anyone thinks they have that document
I'd like to see it again as it could be a good addition to the PZM mod I have at the Factory

 

[stefanzap]

Isn't that epanorama page...?

http://www.epanorama.net/circuits/microphone_powering.html

Great stuff