FETs

  • Thread starter Thread starter PhilGood
  • Start date Start date
PhilGood

PhilGood

Juice box hero
I have a small question needing a concise answer.

I like upgrading my mics, and often swap out components on the cheaper ones to see what improvements I can get. I have done all the capacitor upgrades from Gus on my MXL 2003's and recently discovered that I like the sound of the capsule from an M-Audio Nova in the 2003 rather than the stock capsule. The stock capsule is a great capsule (Same one as in the V77) and works incredibly well in other tube mics I have built. The M-Audio capsule sounds much fuller and has less harshness in the high end when paired with the 2003's electronics. It actually doesn't sound so good with the Nova's electronics, but seems like a perfect combo in the 2003.

So...I have been wondering if there may be an improvement by upgrading the FET's, if there is such a thing.

Will it change the sound at all?

Any suggestions?
 
Bump.

Would love to hear from Gus, Marik, Flatpicker, Harvey, or anyone who can offer advise about FET's.

Are there improvements to be made, or are the stock FET's to be just left alone.

IMO I have got my 2003's to sound as close to a U87 as I can imagine.
 
...Phil...on a sidenote, we know that the 2003 capsule was manufactured by 797Audio for MXL, but do you know who supplied the capsules for the M-Audio mics you refer to?...I know that Groove Tubes was involved with M-Audio...might that particular capsule be similar to/same as one used in the Groove Tube production models?...the current M-Audio Sputnik seems to be getting rave reviews for it's sound (also more full-bodied, and less harsh than many of the other Chinese LDCs)...

...also, have you tried swapping out the 797Audio capsule in your V77 with the M-Audio capsule?...the V77 is already quite good, but would that Nova capsule be an improvement in your estimation?...just curious... ;)
 
Don't know, Dennis, but it's worth a try! I tend to think it's a "proper match" kind of thing. The 797 capsule is the 2nd best sounding capsule I've used in the Royer tube mics. 1st place is the capsule from the Superlux brand. The 797 is the best one for the Ela M that I built.

I'm going to be swapping around some capsules again and maybe I'll give that a shot.

Don't want to do to much fiddling with capsules though. I've damaged a couple already - purely by accident.
 
PhilGood said:
Don't know, Dennis, but it's worth a try! I tend to think it's a "proper match" kind of thing. The 797 capsule is the 2nd best sounding capsule I've used in the Royer tube mics. 1st place is the capsule from the Superlux brand.

...now I gotta convince you to upgrade my Royer modded 2001 to a Peluso capsule...does it ever end???......... :confused:
 
I know that one of the changes that Michael Joly highlights in his Oktava PE mod is replacing the stock F.E.T.s with much nicer ones.
 
kidvybes said:
...now I gotta convince you to upgrade my Royer modded 2001 to a Peluso capsule...does it ever end???......... :confused:

If you want, I'd be happy to install it for you.
 
kojdogg said:
I know that one of the changes that Michael Joly highlights in his Oktava PE mod is replacing the stock F.E.T.s with much nicer ones.

Maybe I'll shoot him an email and see what he thinks.
 
PhilGood said:
I have a small question needing a concise answer.

...I have been wondering if there may be an improvement by upgrading the FET's, if there is such a thing.

Concise answer - Depending on the original FET used and your willingness to individually select and bias a replacement there may be benefits to changing it to another device.

Less consise answer - There are several parameters of a FET that affect the performance of the capsule and overal sound of the mic. Gate input capacitance, transient response (which is related to input capacitance), noise spectrum / absolute noise figure and biasing requirements are probably the most important.

Ideally, the gate input capacitance should present a minimum load on the capsule to preserve all the transient detail and HF extension the capsule is capable of. And it would be advantageous if the self-noise a particular device has both a low absolute measurment and also a spectral distribution such that the noise declines rather than rises with frequency. And finally biasing requirements are going to influence maximum signal headroom.

A note on biasing - even if a magic FET could be found with ideal input capacitance and noise spectrum it will still have to be biased individually to achieve lowest distortion and maximum headroom due to variations in the manufacturing process. (Just a fact of life with FETs). I've seen recommendations for simply setting a static DC bias for FETs but far lower distortion can be obtained by biasing using a real-time 2nd harmonic dstortion analysis technique.

Back to the concise answer - probably not worth changing the FET in a China-built mic unless you want to study FET data sheets, do harmonic distortion analysis biasing and audition several different FET types and manufacturers.

Oh - the popular "Dorsey Mod" that uses the 2SK170 FET was intended as a simple "plug and play" FET swap. The particular version of that FET recomended is a fairly low noise device and will bias aproximately correctly (signal operating point ok, distortion not nulled though) using a fixed (non-trimable) bias network suggested but it has a relatively poor input capacitance spec and thus transient response compared to other devices.
 
Last edited:
MichaelJoly said:
Back to the concise answer - probably not worth changing the FET in a China-built mic unless you want to study FET data sheets, do harmonic distortion analysis biasing and audition several different FET types and manufacturers.

I think this is the answer I was looking for.

Thanks Michael!
 
Back
Top