Uni-Mods

[Jonaz]

I thought there's got to be a way to de-clutter the preamp stage and those bootstrapped phase splitters in the Uni-Vibe.

Since the purpose of the bootstrapping is to raise the input impedance and given that FET's inherently take advantage of this property, couldn't the phase splitters in the Uni-Vibe be greatly simplified? The values of the Drain and Source resistors may have to be experimented with but theoretically, this approach should work without having to resort to using a buffer prior to each phase splitter, right?

[Jonaz]

Here are two more designs that might benefit from using the above arrangement. Anyone care to weigh in?

[slacker]

I think it should work, I suppose the important question is will it sound the same?

[R.G.]

I think it should work, I suppose the important question is will it sound the same?

100% correct. There's no real trick to modifying the univibe. Jonaz, you go through a few of the many mods that have been proposed or thought of over the years.

However, whether they sound the same, and to whom they sound the same or different is quite another matter.

When I first released the Neovibe, back in the 1990s, I was roundly castigated on the usenet (since the WWW hadn't been invented yet, usenet was all there was) for changing the RC filtering on the power supply to a three terminal regulator. The critics said it could not sound the same because something not even in the audio path was different.

So - can you do the mods? Sure - those and many others. Will you like the result? Don't know, try it and see. Let us know how it turns out.

[Jonaz]

Thanks guys!

Ah...half wave rectified goodness with loads of ripple to go around. Can't change that, you'd have
removed the...noise genie

I'll probably be tarred and feathered for revealing this but a few years back I modded a fellas original
Uni-vibe with a copy of GEO's "mods and updates". Hey, that's what the owner wanted.

I'll post my findings if I can get anything useful out of this mod.

[Gus]

Nothing wrong trying it out might sound very good you just need to try.

Benefit is not the term I would use different is.

Read about the transconductance different between JFEts and BJTs

If I was to manufacturer a product like the ones posted about, I would use BJTs with bootstrapping or darlingtons or opamps because the circuit would not need selecting JFETs to work in the circuit.  There are ways to work with JFETs to design a repeatable circuit using a selected JFET part number without matching but it is more parts.

[Jonaz]

Nothing wrong trying it out might sound very good you just need to try.

Benefit is not the term I would use different is.

Read about the transconductance different between JFEts and BJTs

If I was to manufacturer a product like the ones posted about, I would use BJTs with bootstrapping or darlingtons or opamps because the circuit would not need selecting JFETs to work in the circuit.  There are ways to work with JFETs to design a repeatable circuit using a selected JFET part number without matching but it is more parts.

Thanks Gus!

I would use the term benefit because implementing FET phase splitters without the bootstrap sections would reduce parts count drastically given that there's four stages of phase shift. As far as the sound goes, well I'm sure it would alter the sonic character somehow.

How would transconductance characteristics of BJT VS. FET come into play when using a phase splitter that has no gain?