MOSFET

[analag]

  What would an all MOSFET pre sound like.

 

[JohnRoberts]

The answer used to be noisy.... but I trust they have quieter mosfets these days.

JR

 

[clintrubber]

What would an all MOSFET pre sound like.

[OT]If you'd be asking pedal-maker Zvex he'd say 'sounds like a mighty good idea'.  8) :
He's selling one-FET boxes to unknowing people for good money.

FWIW, schematic here:
http://analogguru.an.ohost.de/193/schematics/Zvex_SHO.gif

[/OT]

 

[Piedwagtail]

Can we get R4/C2 and R10/C3 replaced with interstage transformers?

Robert

 

[Ptownkid]

He calls that pedal the "super hard on" oooookayyyyyy

 

[clintrubber]

He calls that pedal the "super hard on" oooookayyyyyy

Yeah, it's all very funny. Maybe part of the appeal for people (read: men) to buy it.
But I haven't heard, seen nor felt it, might be a good usable amplification-stage.
(ignoring the shameless pricing)

Bye,

  Peter

 

[Samuel Groner]

The answer used to be noisy...

Although the designer's elaborations are sparse I presume the use of an input transformer, which can be made of sufficiently high turns ratio to make voltage noise considerations much less of an issue (and current noise ain't a problem). On the other hand, I'd not see any reason for C1/R1 then (wait--a DI input?).

Samuel

 

[Svart]

This is just a take on a "booster" pedal.  There are lots of schemos for using FETs in a fairly linear region for impedance conversion and/or gain.  As with most of the Zvex stuff I've seen, he just adds tweakable parts to regular circuits for effect.  A lot of folks use these to split instrument signals to drive multiple inputs on equipment such as having a DI feed and a feed that goes to an amp.

R1/R2 have to bias the gate at(or near) VCC/2 for the gate region to be linear for audio modulation.

 

[mshilarious]

That's funny; I sketched out a high-voltage MOSFET amp earlier this year but I haven't had a chance to build it.  I used a JFET front-end though.  I think you would want to check the bias condition at M1.  Have you built this?

Oh, I also used an output transformer, just because.  Basically I wanted a tube amp without the tubes and their accompanied very expensive power transformer.  The output transformer does not have to be as expensive . . .

 

[Samuel Groner]

R1/R2 have to bias the gate at (or near) VCC/2 for the gate region to be linear for audio modulation.

I think you would want to check the bias condition at M1.

LND150 is depletion mode (i.e. JFET-like).

Samuel

 

[mshilarious]

R1/R2 have to bias the gate at (or near) VCC/2 for the gate region to be linear for audio modulation.

I think you would want to check the bias condition at M1.

LND150 is depletion mode (i.e. JFET-like).

Samuel

Oh, OK.  I didn't check the datasheet, I just saw the enhancement-mode symbol!  :-[

 

[mikep]

Wow that is harsh! I agree about the price, but I have used these in the studio and they are superb. Really, it gets results, that's why they sell. Who cares what is inside or what it is called

He calls that pedal the "super hard on" oooookayyyyyy

Yeah, it's all very funny. Maybe part of the appeal for people (read: men) to buy it.
But I haven't heard, seen nor felt it, might be a good usable amplification-stage.
(ignoring the shameless pricing)

Bye,

  Peter

 

[Svart]

R1/R2 have to bias the gate at (or near) VCC/2 for the gate region to be linear for audio modulation.

Quote
I think you would want to check the bias condition at M1.

LND150 is depletion mode (i.e. JFET-like).

Samuel

Sorry I was talking about the Zvex circuit, that's what I thought you were talking about.  :-[

 

[clintrubber]

Wow that is harsh! I agree about the price, but I have used these in the studio and they are superb. Really, it gets results, that's why they sell. Who cares what is inside or what it is called

Hi,

Yep, true, if it does the job (...  ) then that's worth the money, despite what's in it.
But that's the weird/bad/good/understandable thing with DIY, once you find out about
a low BOM it's hard to keep looking at it in the first way, you'll likely recognize that.

I wasn't meaning to bash him (Zvex), and certainly not him specifically. While I don't read that in my previous words,
apologies if it came across as harsh, wasn't meant that way. 

Bye,

  Peter

 

[clintrubber]

Sorry I was talking about the Zvex circuit, that's what I thought you were talking about.   :-[

Sorry guys, posting about the SHO wasn't meant to derail this thread.

OK, back to topic.

 

[Winston OBoogie]

What would an all MOSFET pre sound like.

Hi Rowan,
I've built a couple of pre amps using MOSFETS.  I think they sound good.  Mind you, these particular circuits of mine were usually just a single MOSFET (IRF610) loaded with a current source or maybe a differential version of the same with a pair of IRF610's.  I blatantly pilfered the idea from Nelson Pass!!  For gains between 6dB and 18dB the circuits were good ones I thought.  Standing current was typically 30 - 40mA and Vcc was 65 - 80V.  Made a very nice output stage.  One in particular I used as output for a compound J-Fet/BJT input stage mic amp. 

I like your idea of using high voltage rails for squalid state    I've done quite a bit of experimentation along similar lines. 

W.

 

[Svart]

Nice to see you around again WOB.

 

[analag]

Hi Rowan,
I've built a couple of pre amps using MOSFETS.  I think they sound good.  Mind you, these particular circuits of mine were usually just a single MOSFET (IRF610) loaded with a current source or maybe a differential version of the same with a pair of IRF610's.  I blatantly pilfered the idea from Nelson Pass!!  For gains between 6dB and 18dB the circuits were good ones I thought.  Standing current was typically 30 - 40mA and Vcc was 65 - 80V.  Made a very nice output stage.  One in particular I used as output for a compound J-Fet/BJT input stage mic amp. 

I like your idea of using high voltage rails for squalid state    I've done quite a bit of experimentation along similar lines.

I think LND150/DN2540 are some interesting devices that I'm going to try a few experiments with.

 

[tv]

Smart little circuit... valves2ss

OTOH, you are coupling interstage thru a cap.

For kicks, try to revamp this circuit:
http://radio.feld.cvut.cz/~vlk/dynamics/monteight.pdf

You will note some (quite distant) similarities to your circuit and to ... fuzzface.
For use with the LND part, IMO just use diff. ratio @R3/R4 ?? And I don't know why are they using R5. OTOH this circuit may have less swing than yours..

Seeing that LND part has Vgsoff max only -3V, I think it would be possible to juggle the biasing so that source of the second fet sits slightly higher in voltage then the bjt in original schematic. FWIW, people have built fuzzfaces with jfets and mosfets(enhan.) before...

Btw. SS Pultec?

 

[analag]

Maximum swing of that circuit is +/-50V