Voltage rating for 2SK30A Jfet in Korg OVD-1

[jaycobie]

I've been wanting to try my Korg OVD-1 overdrive with a higher voltage than the standard 9-volts.
I've gone through the parts and I know the 4558DV, the diodes and capacitors can go to atleast 16v.

I am however not electrically literate enough to tell if the 2SK30A Jfet in the first buffer stage will handle overvoltage, and was hoping someone here could tell me if I have nothing to worry about when running the pedal at about 12-15v?

Thanks!

[duck_arse]

from the toshiba datasheet:

Low noise: NF = 0.5dB (typ.) (V DS = 15 V, V GS = 0, R G = 100 kΩ, f = 120 Hz)

as they have test figures at 15V drain to source, you .....

have nothing to worry about when running the pedal at about 12-15v?

[PRR]

In this position, there's no strong reason to use 2SK30A. The 2SK30A's good noise figure is moot in a guitar input with 10k in series. The 2SK30A is now hard to buy. Any general purpose JFET will work well here.

Any general purpose JFET is rated 30V or more.

[anotherjim]

Isn't this a commercial pedal with the 2SK30 buffer in by design?
The position of clamping diodes D6,D7 is .... interesting.

[antonis]

The position of clamping diodes D6,D7 is .... interesting.

It indeed is, Jim..
(taking into account that diodes are also active on by-pass mode..)

[jaycobie]

I was perhaps off topic by asking for advice about a commercially made pedal, but didn't want to risk screwing up what is now a very valuable pedal to me.

It works beautifully at 15v. All the glorious harmonics that the Korg OVD-1 already had, just cleaner and louder.

I will say that, since it's a buffered bypass pedal, 15v causes it to bypass above unity gain. I don't mind, but FYI for anyone else out there about to experiment.

I'd personally say that it's worth the current $250-300ish market value, given that you're all-in on tube screamers.

[duck_arse]

.... just cleaner and louder.

the best kinds.

I will say that, since it's a buffered bypass pedal, 15v causes it to bypass above unity gain.

interesting observation. the buffer circuit used can't reach unity, at any supply voltage, we are told by the theory.

[antonis]

the buffer circuit used can't reach unity, at any supply voltage, we are told by the theory.

Which theοry is much more well disposed towards buffers than real world items confort themselves..

@jaycobie: By using higher power supply voltage permits you to also use higher Source resistor (for the same Drain current) resulting into higher voltage gain (considering V_GS & g_m constant) but you can NEVER reach unity..
(only in the purely theoretical case of using an IDEAL current source instead of Source resistor toghether with an INFINITE resistive value load..)

[jaycobie]

Right, ok. Didn't mean to ruffle any theoretical feathers by using inaccurate language.
What I meant was: The bypassed tone through the pedal is louder to my ears when using a higher supply voltage.

[antonis]

That simply can't happen..
(unless of course, clean signal amplitude is higher than 4.5V peak)

[anotherjim]

Is it possible that the particular JFET isn't biasing properly with 9v supply? They may have been using up parts that failed the specs for phasers or whatever but they thought would be fine as buffers.

[antonis]

Everything is possible Jim but, IMHO, in such a case, buffer should distort..

[duck_arse]

you could test your perceptions by putting the bypassed korg into a true true-bypass switcher/looper thing, with nothing but a dpdt switch, and then listen to the buffer as compared to a piece of wire.