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Old 28th September 2010, 06:45 PM   #11
banat is offline banat  Serbia
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It is strange but work OK.Actualy first half of ecc 83 is GG(grouded grid) based input stage,so cathode of that first stage have double function:first function is to DC suply condenser capsule(FET) and in same time same stage cathode is modulated with AF from same MIC capsule(FET),actualy this is hibryd cascode stage,upper stage is triode and lower stage is MIC(FET).

Second stage(half of ecc83) is actualy voltage gain stage.It cood be rewired in many way:For lower SE(unbalanced) impendance output(and voltage)cood be rewired to be Cathode follower, so that depends from what you want(and where) to conect Mic preamp output.

BTW I developed and succesfully use this MIC preamp design long time ago,newer have the problem,work very stable and sonic performance mostly depend from Condeser FET Capsule quality.Best Regard

Last edited by banat; 28th September 2010 at 06:52 PM.
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Old 28th September 2010, 07:09 PM   #12
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Originally Posted by banat View Post
It is strange but work OK.Actualy first half of ecc 83 is GG(grouded grid) based input stage,so cathode of that first stage have double function:first function is to DC suply condenser capsule(FET) and in same time same stage cathode is modulated with AF from same MIC capsule(FET),actualy this is hibryd cascode stage,upper stage is triode and lower stage is MIC(FET).

Second stage(half of ecc83) is actualy voltage gain stage.It cood be rewired in many way:For lower SE(unbalanced) impendance output(and voltage)cood be rewired to be Cathode follower, so that depends from what you want(and where) to conect Mic preamp output.

BTW I developed and succesfully use this MIC preamp design long time ago,newer have the problem,work very stable and sonic performance mostly depend from Condeser FET Capsule quality.Best Regard
OK I understand. The "capsule" has a FET stage in it. So the first stage will have a lot of gain based on a cascode with a 100K load resistor. It's a lot of extra circuit and stages compared to a simple tube mic circuit like the Auracle mic (which is the same circuit used by Neumann, AKG, etc.). Why 2 gain stages in a tube mic? (unless you want to drive a line input directly)

Where do you get this capsule and what's it's cost, performance, etc. ? What's the selection available? The only advantage I see is you don't have to deal with the giga-ohm impedance of the capsule in your circuit, but at what cost? There are plenty of excellent standard condenser capsules readily available at low cost.

What did you plug your mic into for an amplifier?

If you want to drive a standard mic pre you'll want ~ 200ohm output impedance. At that point you might as well parallel the sections of the ECC83 and use a 12:1 step-down transformer. Or use a 6072 with a 10:1 stepdown. Or a 5840 with a 7:1 etc... There is little to be gained by removing the output transformer if you end up with 100K ohms output impedance.

So it still looks a little strange to me and I wonder what's the advantage over the circuit everyone else uses? It certainly has some drawbacks...

Cheers,
Michael
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Old 28th September 2010, 07:36 PM   #13
imagios is offline imagios  Czech Republic
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One more thing on the tube... I assume that if I change the delivered one with the mentioned Telefunken 12AU7 that the socket will fit and I dont need to revire any cables, or are there diferences within the tubes?
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Old 28th September 2010, 07:36 PM   #14
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Originally Posted by imagios View Post
Can any one tell me what to expect from this kit?
DIY Vacuum Tube Condenser Microphone Kit
.

I looked at that page and I am more interested in the FET microphone kit.
Does anyone know if it is sold in Europe or in Asia, since shipping from US to EU is prohibitively expensive ?
Maybe these kits are sold under different names by different companies, much like the Chinese mics are.
They might also be sold on Ebay.
Any info you might have will be appreciated.
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Old 28th September 2010, 07:39 PM   #15
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I have no experience with those mic capsules with built in FETs, but I think they are to be powered by a few volts, and loaded with a low impedance. So using a tube's cathode that way is pretty smart I think since it does both give it a few volts to work from, and amplifies the signal (and presents a low impedance). The rest of the circuit I agree isn't optimum, but I'm sure it works ok if farely short cables are use to a high Z input.
Nothing wrong in having lots of gain at the mic, better S/N ratio.

That kit sure looks like a good deal to me. Nice mic chassis and a capsule that is likely no worse than what we'll find in mics up to xxx money. Not the circuit I'd use tho, but that's just me.
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Old 28th September 2010, 07:47 PM   #16
banat is offline banat  Serbia
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Originally Posted by Michael Koster View Post
OK I understand. The "capsule" has a FET stage in it. So the first stage will have a lot of gain based on a cascode with a 100K load resistor. It's a lot of extra circuit and stages compared to a simple tube mic circuit like the Auracle mic (which is the same circuit used by Neumann, AKG, etc.). Why 2 gain stages in a tube mic? (unless you want to drive a line input directly)

Where do you get this capsule and what's it's cost, performance, etc. ? What's the selection available? The only advantage I see is you don't have to deal with the giga-ohm impedance of the capsule in your circuit, but at what cost? There are plenty of excellent standard condenser capsules readily available at low cost.

What did you plug your mic into for an amplifier?

If you want to drive a standard mic pre you'll want ~ 200ohm output impedance. At that point you might as well parallel the sections of the ECC83 and use a 12:1 step-down transformer. Or use a 6072 with a 10:1 stepdown. Or a 5840 with a 7:1 etc... There is little to be gained by removing the output transformer if you end up with 100K ohms output impedance.

So it still looks a little strange to me and I wonder what's the advantage over the circuit everyone else uses? It certainly has some drawbacks...

Cheers,
Michael
Think even Auracle Mic condenser capsule have FET built in,but suply for that FET capsule goes via resistor network/divider from B+ voltage, and Mic(FET) output is than conected traditionaly to the tube grid, personaly never like the sound and stability of condenser(FET) MIC from that way of conection to the tube grid.

From old radio/tape recorder You can have cheap Condeser(FET)capsule for first circuit probe,but on the market is so many excelent other`s FET built in condenser capsule,more expencive too.(Auracle)

I developed this Tube Mic preamp circuit under next condition/circumstances:

When I emiting(Pirates) on AM band(1600-1800khz) with DIY high power Tube Modulator/ Transmitter ordinary dynamic Mic allways goes `crayze `due huge surounding electromagnetic fields, but this type of Mic conected this` my way`(cascode) always work extreme stable, with extreme audio sensitivity and modulation quality.But for some proffesional studio/recording use this design is good too.Special without stepdown transformer on the preamp output(OTL)

Best regard

Last edited by banat; 28th September 2010 at 08:08 PM.
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Old 28th September 2010, 09:32 PM   #17
ChrisA is offline ChrisA  United States
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Originally Posted by imagios View Post
...
I have no equipment to make my own PCBs thats why I use the kits....
Not really a comment on this microphone. But I just had to say that decades ago when tubes were the only way to build electronics no one used PCBs. The classic and I think still best way to build with tubes is "point to point" or with turret boards.

Not being able to make a PCB is in fact one good reason to build with tubes.

How will this sound when you are done? Well you really are not building a microphone. All the parts that determine the sound are contained in that condenser capsule.

You were planning to build tow for stereo recording, people typically don't record a vocalist in stereo. They pan the track to stereo in the mix later, same for most instruments. Stereo might be used to record an ensomble
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Old 28th September 2010, 11:31 PM   #18
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Originally Posted by banat View Post
Think even Auracle Mic condenser capsule have FET built in,but suply for that FET capsule goes via resistor network/divider from B+ voltage, and Mic(FET) output is than conected traditionaly to the tube grid,
No, the Aurycle mic doesn't use a FET capsule, it's a straight condenser capsule polarized by 60VDC through a 1G ohm resistor.

" personaly never like the sound and stability of condenser(FET) MIC from that way of conection to the tube grid."

?? Virtually all recordings are made with mics using this circuit

"From old radio/tape recorder You can have cheap Condeser(FET)capsule for first circuit probe,but on the market is so many excelent other`s FET built in condenser capsule,more expencive too.(Auracle)"

No, I don't think so. I think you're guessing. Please point me to one.

"When I emiting(Pirates) on AM band(1600-1800khz) with DIY high power Tube Modulator/ Transmitter ordinary dynamic Mic allways goes `crayze `due huge surounding electromagnetic fields, but this type of Mic conected this` my way`(cascode) always work extreme stable, with extreme audio sensitivity and modulation quality.But for some proffesional studio/recording use this design is good too.Special without stepdown transformer on the preamp output(OTL)"

Cool. If I ever build a high power pirate AM station I'll remember that. My current interest is in high fidelity microphones for use in a recording studio. i have doubts about general high quality capsule availability.

What about the output impedance of your circuit? How does it drive a 1600 ohm load of a balanced mic pre? How does it even drive a 10K line input? It must be for a high impedance input of some kind.. Radio transmitter?

Good quality mics use output transformers to get a low impedance output. From a condenser capsule, gain is not needed at the mic. A lot of condenser mics also use follower outputs with no gain at all (and low impedance). There's enough gain in the mic preamp.

Really, you should look into the schematics of some classic mics linked to on the Prodigy Pro page I referenced. A good base of information won't hurt.

Cheers,

michael

Last edited by Michael Koster; 28th September 2010 at 11:42 PM.
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Old 29th September 2010, 01:21 AM   #19
banat is offline banat  Serbia
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Originally Posted by Michael Koster View Post
No, the Aurycle mic doesn't use a FET capsule, it's a straight condenser capsule polarized by 60VDC through a 1G ohm resistor.

" personaly never like the sound and stability of condenser(FET) MIC from that way of conection to the tube grid."

?? Virtually all recordings are made with mics using this circuit

"From old radio/tape recorder You can have cheap Condeser(FET)capsule for first circuit probe,but on the market is so many excelent other`s FET built in condenser capsule,more expencive too.(Auracle)"

No, I don't think so. I think you're guessing. Please point me to one.

"When I emiting(Pirates) on AM band(1600-1800khz) with DIY high power Tube Modulator/ Transmitter ordinary dynamic Mic allways goes `crayze `due huge surounding electromagnetic fields, but this type of Mic conected this` my way`(cascode) always work extreme stable, with extreme audio sensitivity and modulation quality.But for some proffesional studio/recording use this design is good too.Special without stepdown transformer on the preamp output(OTL)"

Cool. If I ever build a high power pirate AM station I'll remember that. My current interest is in high fidelity microphones for use in a recording studio. i have doubts about general high quality capsule availability.

What about the output impedance of your circuit? How does it drive a 1600 ohm load of a balanced mic pre? How does it even drive a 10K line input? It must be for a high impedance input of some kind.. Radio transmitter?

Good quality mics use output transformers to get a low impedance output. From a condenser capsule, gain is not needed at the mic. A lot of condenser mics also use follower outputs with no gain at all (and low impedance). There's enough gain in the mic preamp.

Really, you should look into the schematics of some classic mics linked to on the Prodigy Pro page I referenced. A good base of information won't hurt.

Cheers,

michael

Aurycle Mic model A620,A630 and A218p does have built in FET,I never use that Models but some Philips,JVC and Panasonic FET capsule Mic

``Virtually all recordings are made with mics using this circuit``-

-So what? is that the only reason to not try another alternative better design Way.

Inside ewery old radio/tape recorder usualy exist Condeneser FET capsule-cheap one,in diameter 6-8mm,it is good for first time circuit probe but for some other Audio apllication is good too.Thats is what I mean actually but not for using in serious Studio Recordings

For low impedance balanced output(1600 ohm) and best Sonic results I sugest everybody to use pure Tube low impedance output(OTL).You know for sure about Sonic limitation/degradation of OPT in tube amps it is same here with stepdown transformer on the Mic Tube preamp output but much worse. To drive 10k line input is not the problem for atached schematic

Prodigy pro page for some Mic information-I don`t care

BTW I have lot of fun emiting on the AM band using that My Mic preamp(Pirates for Ever)

Best regard

Last edited by banat; 29th September 2010 at 01:39 AM.
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Old 29th September 2010, 01:39 AM   #20
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Quote:
Originally Posted by banat View Post
Aurycle model A620,A630 and A218p does have built in FET,I never use that Models but some Philips,JVC and Panasonic FET capsule Mic

``Virtually all recordings are made with mics using this circuit``-

-So what? is that the only reason to not try another alternative better design Way.

Inside ewery old radio/tape recorder usualy exist Condeneser FET capsule-cheap one,in diameter 6-8mm,it is good for first time circuit probe but for some other Audio apllication is good too.Thats is what I mean actually but not for using in serious Studio Recordings

For low impedance balanced output(1600 ohm) and best Sonic results I sugest everybody to use pure Tube low impedance output(OTL).You know for sure about Sonic limitation/degradation of OPT in tube amps it is same here with stepdown transformer on the Mic Tube preamp output but much worse. To drive 10k line input is not the problem for atached schematic

Prodigy pro page for some Mic information-I don`t care

BTW I have lot of fun emiting on the AM band using that My Mic preamp(Pirates for Ever)

Best regard
Rock on, my friend!

Michael
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