Fetzers cascaded - this is pretty cool

[blackieNYC]

[edit -there IS a 1u coupling cap after the 2nd FET. Will "edit"drawing. Thanks]
two at andard J201 fetzers with D and S resistors selected according to ROG's Fetzer.  If you've built one, you know the Fetzer is not intended as a transparent boost.  The lows I've kept clean while the highs have a wide range of color.
the volume pot between the two acts as a "drive".  I used J201s for the gain, around 16dB each but - there is substantial loss due to passive filters, tone controls, clipping diodes, etc.  My final output is not high gain, and that's really not what I was shooting for. A recovery stage could be added, but for me, if it can get to unity gain and a pinch beyond, that's enough for this thing.
The audio passes thru the first Fetzer stage, with the slight colorization they contribute. (I once measured a circuit based on the ROG instructions as having 5% THD).
The lows (as full range audio initially) skip the 2nd circuit and proceed directly to a low pass filter and then to the tone control - a high/low blend pot.
The audio also continues to a 2nd Fetzer stage.  This has the standard Fetzer 33K/220p ultrasonic LP filter, which is probably redundant and can be left out.  Then there is what should be a drastic high pass filter, rolling off at 9KHz.  (It doesn't sound that way and must be interacting with other impedances.
The highs thru this 2nd stage get Fetzered twice, the lows once.  Depending on the drive pot, the highs get a little sparkle, or a lot of sparkle.  The high pass filter was tweaked up to the current 9KHz mark by ear - I got rid of a slight fattiness when the drive was turned up high and clipping the 2nd stage.  Now only highs, and not a lot of mids, are "sparkled" or clipped.
You can get some additional distortion with diode clippers.  These are schottkys because the signal amplitude isn't much here.  This clipping stage is optional, but also can sound quite good. The pot to dial in distortion is a must if you add clippers.  It will of course reduce the highs in level as you clip, but this is easily made up for with the Drive or the Tone.
It so happened that with the highs coming straight off the drain, the tone control receives a similar amount of bass and treble for a useful range of the pot.  You might have to add some series resistance to one or the other.  I find the tone range to be useful at all settings.  the extreme settings are not too dark or too bright to serve some purpose I guess.
Though a single fetzer stage is a FET equivalent of  a Fender input stage, this is not an attempt to reproduce a certain amp's front end. Selectively overdriven. This thing can be very very subtle.  With a wide range of subtlety.  (Now there's a ridiculous oxymoronic sentence, but...  really.) The lows are clean and the highs can be slightly sparklier than neutral, ranging up thru obviously distorted highs.  Like the tone, I think I've got a lot of useful range in the Drive control.  Maxed out completely is not my favorite sound this thing can make, but I don't find it worth tweaking further.
Single notes have a pleasant little bite and clarity, and those jangley chords are magnificent!  
On my breadboard, on it's way to a box.  Can't find anything more to tweak really.  Might be done.  
Must get recording and schematic software one of these days.

[GibsonGM]

They are fun to play with, aren't they??  You can get some awesome tones this way! 

Check out the Catalinbread "RAH"....mosfets, but same idea.  BIG sound...poor man's tube preamp....

[duck_arse]

the bass signal will be out of phase with the treble, at the tone pot.

looks like you've made a "fetz-rite".

[midwayfair]

the bass signal will be out of phase with the treble, at the tone pot.

looks like you've made a "fetz-rite".

That would actually be really cool!

[Mark Hammer]

1) A bunch of ZVex designs are simply cascaded SHOs.  That's not to demean them at all.  Rather it underscoress that your thinking is not out of whack.

2) How much of what you get is a result of the Fetzer supply voltage?  For example, if stage 1 used 9v and stage 2 used 18v (for more headroom), would you get the same coloration, or is what you hear a product of running up against headroom limitations?  Again, not a criticism, but something to play around with.

(I'm saying all of this without being able to see any pics/drawings you might have posted)

[GGBB]

No coupling cap after the 2nd stage? How does that affect the diode clipping? Very interesting!

[blackieNYC]

the bass signal will be out of phase with the treble, at the tone pot.
looks like you've made a "fetz-rite".
Yes indeed.  I think it's giving me a pleasant scoop. Meaning to sweep it and see what the scoop turns out to actually be. A lot of impedances interfering with filters- that's why ingave up on the big muff filter values and went by ear for the highs. The scoop doesn't seem huge, but I find I'm generally fond of a scoop, so I really must measure it with my tone centered.  [Edit: there is no measured scoop with the drive up full, and a little -1.5dB down when the drive is at 12:00 -  just the drive pot bypass cap tipping up the high end a little bit.  I may listen again without that thing]

Headroom and +18:  the low headroom on the 2nd FET I'm convinced it is helping me.  I might not go to the trouble of adding 18, but I might be missing out on something there. I'm just digging it as is!  The attenuator between stages is accomplishing what a higher supply voltage would do, doncha think?  I'm starting to like it with the drive up all the way too- that "wide range of subtlety".  (That description isstill is making me laugh)
[edit: oh, yes - the voltage won't help the FET headroom.  thanks Mid]
There is a cap on the output of the 2nd FET.  Noted now in drawing - thanks. Will fix. 1uf

[wavley]

I have a fetzer valve at the front end of a splitter that is always on for me because it sounds good.  So its Guitar-->Doomidrive-->old Masco Tube mixer modded to be a preamp (also this is where my lap steel plugs in)-->Fetzer Valve/splitter-->one output to my tuner, the other to a Moog MF boost and the rest of my rig.

I run mine at 15v, just because it was an easy voltage to get (rectified and filtered tap off a spyder XFMR), I really only gave it more juice more for the splitter part and because I could.  The whole thing plays really well with the doomidrive, tube mixer, fetzer set up, no one thing is doing too much distorting and it really sounds mean when I dig into it.

[midwayfair]

Headroom and +18:  the low headroom on the 2nd FET I'm convinced it is helping me.  I might not go to the trouble of adding 18, but I might be missing out on something there. I'm just digging it as is!  The attenuator between stages is accomplishing what a higher supply voltage would do, doncha think? 

More voltage = more gain, not more headroom. Headroom is device-specific with FETs. The Fetzer valve and Supreaux Deux articles talk about this.

[Ice-9]

I think you could possibly benefit from a biasing resistor to ground from the first Jfet's gate, although it should pretty much self bias without it would be better with a resistor in place.

[Kipper4]

What does it sound like?

[blackieNYC]

It brightens pleasantly, with harmonic content added in the high end that you wouldn't really call overdrive or distortion upon hearing it. A wider range version of that one setting you've got one on particular overdrive pedal, you know, with the drive all the way down, volume up to make up the gain, where it's not quite clean but not quite dirty. The Tone and the Drive work together nicely.  I play it thru a tube amp that is fairly bright I suppose, and this can add a sparkle to it that I don't find harsh.  I don't know what to compare it too.  Highs slightly distorted, lows almost completely clean, and I don't think that would be easy to point out in hearing it.  I'm sorry - i will put a demo together, but it won't be soon...   Give it a try.  You can breadboard one up and skip the fetzer calculations (just initially) and use J201s with a 12-20k drain resistor and a 1.2-1.6k source resistor and get the idea. Skip the clippers for now also.  The key is the low value cap that sends only highs thru the 2nd stage. Try anything. Everything under 1nf I found to be too much and brought out an undesirable honky crunch with the Drive up. Try a 680pf, try a 220pf.  Jangly chords.
I think everyone should have a single fetzer around anyway.

[Kipper4]

Thanks Blackie
I'll bread it over the weekend if i get the chance.
I guess the drain voltages are around 4.5v.
I'll probably bias it by ear and to taste anyway.

[amz-fx]

Cascading fets can make nice tones. I used 4 jfet gain stages in the Fet Muff years ago, and really liked the sound (especially with bass guitar).

Here is a short sound sample with it cranked:

http://www.muzique.com/fetmuff.htm

For some more fun, try this:  http://www.diystompboxes.com/distmaker/DistMaker.swf

regards, Jack

[Mark Hammer]

Yahtzee!!!  

(In retrospect, I guess I should have said Boggle!)

[midwayfair]

For some more fun, try this:  http://www.diystompboxes.com/distmaker/DistMaker.swf

This is hilarious.

[blackieNYC]

My project, and the DistMaker, are on hold pending the arrival of a new breadboard.  Mine dates back to when resistor leads were made of 14 gauge wire.  It also appears a Tesla coil was built on the breadboard.  Perhaps by Tesla himself.
I'm trying some 5457 FET's in place of the input J201 for a bit more headroom at the expense of gain. Not that big a difference between this change and attenuating the input with a trimmer.

[blackieNYC]

This one is better.  The schematic in the first post is good, but I would modify it with a comment recommending this one.
Highly!  I've got a full range of overdrive, which gets cleaner than even my Azabache.
The great thing about this OD is that the lows stay cleaner than the highs.  Splitting off an almost-standard BMP filter, the lows go thru a 5457 Fetzer, which has more headroom than the J201 Fetzer, which the highs go through.  The input stage is a 5457, which is unlikely to clip the input signal, but has the possibility of clipping the following stages.  There is an unmarked voltage divider at the Treble end of the Tone control - this was a pot adjusted so the middle of the tone control would be flat.  I used a 1M tone control and ended up with 300K series resistance, 700K to ground.  Start with a pot.  This can be flat from 80Hz up. The tone control is useful throughout its range.  Must make demo.
Don't skip the Fetzer calculations for the drain and source resistors - at runoff groove.com
I love the sound of the highs distorting more than the lows, at least in this mild application.  I think any listener would be hard pressed to identify that that is what's going on here.  At a heavier overdrive, yes, but here it's very smooth.  Dirt and clarity at the same time.
And very little dirt under 12:00 on the input drive pot.  Maybe too little for some.  Clipping diodes in the Big Muff output gain makeup stage work well, but you might want a 2nd tone control to roll off highs after those clippers.

I had a thought - for my breadboard, i plan on having some Fetzers, buffers, and boosters ready - with leads that connect to my breadboard if I wish.  Just to have them around when needed - not to go in the enclosure, just to stay with the breadboard.

[duck_arse]

nice work, blackie.

[blackieNYC]

The above schematic, the "this one is better" drawing- forget clipping diodes on the output buffer.  Put a pair on the High output only, with a 50k pot, which can dial the diodes completely out for the jangly fetzer highs, or add a nice fuzz on the highs.