First vacuum tube project. JFET preamp microphone

Thread Starter

MrMezy

Joined Mar 16, 2024
1
Hi 2 years ago I acquired a High Quality Microphone module and a 2N4416 JFET for a microphone circuit Designed by Diy Perks on youtube. Since It has been so long since I have shelved the project (Almost 2 years). I have regained interest in the project after finding a store near me with an old stock of vacuum tubes Starting a newfound interest in building a quality amp. The Idea to build a tube amp microphone to plug into my home computer sounds really appealing to me. I am unsure about a lot of things though like where to find the output transformer, would the transformer be expensive, Would I need more then one tube for amplification or could I rely on my 2N4416 JFET, Do I need to "Overdrive" my final tube to receive the supposed audio quality benefits of using a vacuum tube, and will I actually be able to capture any of the harmonic distortions associated with tubes.

My local antique store has a vacuum tube radio In for parts condition I think I could bargain for $10. Is there a chance its contained transformer would be capable of impedance matching to my microphone output or would it only be useful to drive a speaker similar to the one inside the radio?
 

MrChips

Joined Oct 2, 2009
30,946
Welcome to AAC!

It depends on what you want to do with the microphone. Most microphones will plug in directly to the PC mic input or to an audio mixer. Active microphones usually have a FET preamp that provides sufficient signal output to drive just about any amplifier.
 

LowQCab

Joined Nov 6, 2012
4,209
The supposed magic "Tone" from Tubes is a running joke that just won't die.

If You want a truly excellent sound from your Microphone,
get a used LapTop-Computer and install Breakaway-Audio-Enhancer, from Claeson Edwards.

It's a 7-Band Compressor/EQ originally designed specifically for use by FM-Broadcast-Radio-Stations.
If I remember correctly, it costs around ~$35.00 for a Lifetime-Home-Licence.
( It's been a while, the price may be higher now )

It's the best Audio processor that I've ever experienced since around ~1975, Hardware or Software.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
18,986
The supposed magic "Tone" from Tubes is a running joke that just won't die.

If You want a truly excellent sound from your Microphone,
get a used LapTop-Computer and install Breakaway-Audio-Enhancer, from Claeson Edwards.

It's a 7-Band Compressor/EQ originally designed specifically for use by FM-Broadcast-Radio-Stations.
If I remember correctly, it costs around ~$35.00 for a Lifetime-Home-Licence.
( It's been a while, the price may be higher now )

It's the best Audio processor that I've ever experienced since around ~1975, Hardware or Software.
.
.
.
As for the "tube sound", it is indeed very difficult to produce that particular distortion as was produces by a 1962 technology tube amp that has been abused for ten years and suffered running the poor 6L6GC tubes a bit beyond their ratings all of those years. And when that level of electronic sophistication is coupled with a quad of speakers that eight years earlier were damaged by feedback bursts, the "sound " can no longer be recalled, but only imagined.
The biggest challenge with using the tubes and parts from that old radio is that they will be the wrong parts Wrong resistance values and incorrect capacitance values, and certainly the wrong tube types. The correct resistors and capacitors are available NEW, UNUSED, in perfect condition, for purchase, from a number of suppliers.
And a much moore detailed description of the high quality microphone part will undoubtedly be understood by many here, who may have experience with that exact item.
 

Audioguru again

Joined Oct 21, 2019
6,758
I made a vacuum tubes Heathkit amplifier 62 years ago. It produced plenty of "tooobs'' distortion (distortion is the opposite of "audio quality") but much less than AM radios of that time. I had its distortion measured at a nearby shop and saw the distortion increase until the worn out tubes were replaced each year.

"Overdrive" produces severe distortion. Is that what you want?

Vacuum tubes wear out, transistors do not wear out. Why use antique tubes?
 

MisterBill2

Joined Jan 23, 2018
18,986
I made a vacuum tubes Heathkit amplifier 62 years ago. It produced plenty of "tooobs'' distortion (distortion is the opposite of "audio quality") but much less than AM radios of that time. I had its distortion measured at a nearby shop and saw the distortion increase until the worn out tubes were replaced each year.

"Overdrive" produces severe distortion. Is that what you want?

Vacuum tubes wear out, transistors do not wear out. Why use antique tubes?
"Antique" tubes are cool, is the main reason for using them. Also, sometimes a retro project is a lot more fun, partly because the parts are big enough to handle easily. Presently I am in a project of designing a re-build of an AC/DC "All American Five tube receiver into an LF band communications receiver. Replacing the 35W4 tube with a solid state diode will allow me to add three 12 volt tubes to the heater string. One RF stage, one BFO/Productdetector section, and one that may become either a squelch stage or an additional audio gain stage, not sure which just yet. IIt will be built "1930"s style" on a pine board, with a Masonite front panel because a Bakelite panel would cost a fortune if I could locate one. And it would not be as rugged.
Doing that with ICs and surface mount devices would produce a pocket sized radio with no charm at all.
 

Audioguru again

Joined Oct 21, 2019
6,758
Cool look? Most people listen to a radio without even seeing its historical parts, shape and age.
But an old AM radio has very limited technology causing it to sound awful with poor performance.

Many years ago, my friends, family and I were pleased with the good sounds from my first hifi FM receiver.
 

MisterBill2

Joined Jan 23, 2018
18,986
The radio receiver I mentioned is for HAM radio operation where music is not even legal. AND, being a "communications receiver, the response will not include serious bass nor much above 3500Hz. Also, it is not likely that SSB with HAM equipment will ever be mistaken for lousy HI-FI, And it will not be intended to sound as good as equipment costing a hundred times as much, either. The challenge I have run into is how to add a five watt transmitter for voice operation in such a narrow bandwidth without making it a whole lot more complex, and much less fun to build.
 

LadySpark

Joined Feb 7, 2024
188
Hi 2 years ago I acquired a High Quality Microphone module and a 2N4416 JFET for a microphone circuit Designed by Diy Perks on youtube. Since It has been so long since I have shelved the project (Almost 2 years). I have regained interest in the project after finding a store near me with an old stock of vacuum tubes Starting a newfound interest in building a quality amp. The Idea to build a tube amp microphone to plug into my home computer sounds really appealing to me. I am unsure about a lot of things though like where to find the output transformer, would the transformer be expensive, Would I need more then one tube for amplification or could I rely on my 2N4416 JFET, Do I need to "Overdrive" my final tube to receive the supposed audio quality benefits of using a vacuum tube, and will I actually be able to capture any of the harmonic distortions associated with tubes.

My local antique store has a vacuum tube radio In for parts condition I think I could bargain for $10. Is there a chance its contained transformer would be capable of impedance matching to my microphone output or would it only be useful to drive a speaker similar to the one inside the radio?
Overdive distortion is a guitar thing and not a microphone amp thing.
When you build for a mic preamp or condenser mic, you build for clean and quality and the tube sound you are aiming for is harmonic richness with a low noise floor. This can happen anywhere besides the first gain stage. Also, you don't need an output transformer. Just a good tube circuit to put in after your THAT IC mic pre. I would suggest a simple line stage kit you can experiment with using one channel as a line stage, or both channels as a full preamp. https://glass-ware.stores.turbify.net/aikido12vac.html

Also, you don't have to spend a lot of money on signal transformers. That is a gimmick market that you need to find sources for them that are reasonably priced. I find input step up transformers inexpensive when they are not marketed for tube amps. Also, a lot of the transformer outputs in pro audio are using parafeed designs so that they can go cheap on the transformer and there is a lot of nice non-gapped transformers that can be used however, Their impedance convention does not interface well with modern electronics. Because most moved away from the 600 ohm i/o convention decades ago. That is why you don't need one. Edcor is a cheap place to get transformers and if you really wanted to use a transformer output to your computer, I would get a 10K:10K and parafeed it. As 2K to 10K is the modern impedance range convention for audio line level. Most of the pro audio sector is in denial of this btw, and try to use the capacitor coupling tolerance as their guide (they call it the 10 times rule) but of course it only works for them if their devices has one that is capacitor coupled. Which is typically 50%-70% of their devices.
 
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