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Basic DIY microphone amp, tube or SS
Basic DIY microphone amp, tube or SS
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Old 4th October 2019, 03:40 AM   #11
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by sgrossklass View Post
Tube mic preamps are not a trivial exercise ...

It may be easier to build sort of a line-level effects device.
Indeed. Be very clear about why you want a tube pre-amp.

Everything Russel Hamm said in 1973 remains true, if not more so (as clipping your ADC is the worst sort of ugly short of feeding an illegal sequence into your DAC).

Mintz, in his rebuttal, became perhaps the first person to try and emulate a simple valve circuit with a complex transistor one. (See the wikipedia entry on soft clipping)

I've just built a little progressive clipper, which, so far, seems to do what it should (softening a fizzy solid state guitar amp clipping stage). (No FFTs yet!). It is based on the late Fred Nachbaur's dogzilla, but with different diode chains to get initially asymmetric clipping (final clipping is symmetric to avoid DC drift).

Hamm 1973 21(4) JAES "Tubes vs Transistors - Is There An Audible Difference?" (pdf here)

Last edited by thoglette; 4th October 2019 at 03:44 AM.
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Old 4th October 2019, 06:57 AM   #12
andyjevans is offline andyjevans  United Kingdom
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Update - I have bought a used Rode TN-2A which works fine in terms of volume with my Edirol FA-101 using the Firewire output. So I have a working setup at last. The sound is super clean, as you would expect from this combination. I have yet to learn how to treat the mic input in Garageband with reverb, equalisation etc. and this may help make the sound less dry and clean. But I'm now wondering what else I can do to "personalise" the sound a bit. I don't want to use a tube microphone - don't see the point - but I'm curious about a transformer mic. I could build one of those, and I like what I've heard of Oktava plus a U87 clone would be nice. And then I'm so used to tube technology that building a tube input stage wouldn't be difficult. Initially it could feed the line in on my Mac. I have yet to try the Edirol into the line in - must see what the difference in sound is.

I'll start looking at simple tube circuits that can be used. For instance a phono stage without the equalisation should work, no? I'm sure there are plenty of other designs I could use. Any suggestions?
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Old 5th October 2019, 03:15 AM   #13
thoglette is offline thoglette  Australia
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Originally Posted by andyjevans View Post
I'll start looking at simple tube circuits that can be used. For instance a phono stage without the equalisation should work, no?
It would work, and if built competently it won't sound any different to your existing set up. That is, hyper clean.

I.E. it won't do what you want it to do, which is to impart some "flavour".

Any audible difference will come from what you (currently) consider to be a flawed design or implementation: devices biased in incorrect ways (e.g. cold clipper for early onset of 2nd harmonic ) or being overdriven (classic transformer/tape head "sound")
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Old 5th October 2019, 07:09 AM   #14
andyjevans is offline andyjevans  United Kingdom
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Originally Posted by thoglette View Post
It would work, and if built competently it won't sound any different to your existing set up. That is, hyper clean.
I.E. it won't do what you want it to do, which is to impart some "flavour".
That's not exactly how I see it, though I agree that if the basics are covered like frequency response and noise performance you might get substantially the same results. In my audio setup I build with directly heated triodes for a reason - I get more "inner transparency" within the sound of the voices and instruments and the timbre is closer to the original acoustic instruments which I am familiar with from being a pro musician. For instance with microphones there's more "inner transparency" in a Neumann U87 than in the TLM series. What I'm seeking to avoid is graininess (a hard sound) and "thickness" described variously as "dull", "veiled" etc. I achieve this with DHTs and very simple circuits with a minimum of components (though elaborate power supplies) and no global feedback.

I don't know how the above applies to very small signals - I sold my LPs years ago and haven't built a phono stage for at least 15 years, probably more. In theory I like the sound of ribbons and transformers, though I'm not convinced in the case of microphones, though I have heard some good sound samples. This is completely new territory for me - microphones.

It could be the case, also, that I want some sort of "flavour" which is a different thing from the transparency I seek in my audio setup. Something that would flatter my voice, which could be all kinds of added equalisation, reverb etc. Early days yet. I need to talk to a studio engineer about recording vocals - that should be educational and would save time over simple trial and error.
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Old 5th October 2019, 08:51 AM   #15
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by andyjevans View Post
That's not exactly how I see it, though I agree that if the basics are covered like frequency response and noise performance you might get substantially the same results. In my audio setup I build with directly heated triodes for a reason - I get more "inner transparency" within the sound of the voices and instruments and the timbre is closer to the original acoustic instruments which I am familiar with from being a pro musician.
You've correctly corrected me: a well built DHT system should have much better low level performance than anything else on the planet (for the doubters, the 45 triode is still the most linear device ever made and the poor supply rail noise rejection of a DHT SET amp means that the power supply has to be good - ergo: none of the sagging and 120hz intermodulation of AB designs).

Quote:
Originally Posted by andyjevans View Post
It could be the case, also, that I want some sort of "flavour" which is a different thing from the transparency I seek in my audio setup. ..... Early days yet. I need to talk to a studio engineer about recording vocals - that should be educational and would save time over simple trial and error.
Plus several. Nothing to add!

Last edited by thoglette; 5th October 2019 at 08:52 AM. Reason: spelling and grammar
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