so I built this from the Fetzer ... opinions plz ?

[Derringer]

Hi, I'm pretty new to this and I've recently become fascinated by the Fetzer idea and started experimenting.
This is the first time I have tried to just make something up that hasn't been entirely scripted.
It's breadboarded and I dig how it sounds through my P1-Ex.

I'd just like to know form those of you with more experience if you see any places that I did something obviously strange or if you see spots that you might improve on.

The only thing more that I'd like to get out of it is more grind and less fizz when I turn up the gain. But otherwise, with the controls tweaked right, and a P-90 equipped axe, I'm digging it.

Opinions please.

Thanks.

noob-builder Bill

[petemoore]

  Take a look at amp sims and notice many similarities and differences.
  Less fizz could be a two pole LP filter at the end [see Supreaux, ROG] or maybe a pot and cap to ground for variable treble shunt.
  More grind, inclined to suggest a third stage, two Jfets work good as shown [you can try reducing the source resistor, three of course still uses the first to boost mostly, but then the two after that would see enough signal to distort more heavily.
  Hybrid stuff is cool.
  With successive gain stages multiplying [within their ability @9v] the amplitude of everything [maybe having troulbes with certain frequencies more than others], some frequency taming may be needed, treble can easily start becoming harsh, bass can become loose and 'overburdensome'.
  Some simple [cap to ground] LP filtering 'in the middle of the circuit.

[frankclarke]

Looks good. Higer gain/transconductance JFETs would might be good if you are using wimpy JFETs. J201's are gainy. A SHO-style MOSFET stage in front of (or replacing) Q1 would give you more gain too.

[Derringer]

Yes, these are J201's and I have them biased for ~4.5 v


Thanks for the info folks!


Bill

[Dragonfly]

Looks kinda familiar ! 

I experimented with the same thing a few years back....




Take a look at the ROG Peppermill for a simple, great sounding light OD...

http://www.runoffgroove.com/peppermill.html

[dschwartz]

hey it looks nice!! some easy tweaks you can make:

- less fizz/treble: Put a cap in parallel to the second stage´s trimpot..try different values between 3nf and 100pf..

- More bass out: make the output cap (22nF) larger , like 100nf or even bigger.

- tighter/less muddy bass: make the first stage´s output cap smaller (like 3.3n or 4.7n) and/or make the source cap a lot smaller (like 680n)

- more stability: put a 1M resistor to ground at the input of stage 2.

- better gain control: put a small value cap (like 100pF to 470pF) from the first output cap to the input of the second fet (lugs 1, 2 of the pot.. i think). This will give more spark at low gains.

- voltage filtering: add a big filtering cap to the 9v line..100uf at least..maybe a 100 ohm resistor in series too.

- better output level: That 2n2 cap is working as a variable low pass filter.. at full volume, it does nothing..so..take that out. and put a resistor in series before the 6n8 cap..try a trimpot to set the value where you like best..

- less hiss/ radio recieving: put 220pf caps between gate and source of each fet..

well..i hope it helps..post the results!!

[petemoore]

- more stability: put a 1M resistor to ground at the input of stage 2.
  That node will see 500k or less through the gainpot wiper to ground.

[snap]

More stability when the wiper fails, but the flying Dragons 1k3 is much more interesting.

[raulgrell]

You could try using a BJT for the first stage, maybe for more gain, add one between the stages... I like the sound of a JFET output thought, so keep that.

With that in mind, try putting an LED in the source of the output stage...

Post back results!

[dschwartz]

- more stability: put a 1M resistor to ground at the input of stage 2.
  That node will see 500k or less through the gainpot wiper to ground.

well i´m not perfect ok?? haha

i should added a gate stopper resistor before the 1M resistor i mentioned..a 33k or 68k ..that tames the highs a litle bit..

[petemoore]

  Daft..I used to miss those all the time, now I look for that kind of thing and jump on it !
  Wouldn't hurt, just not necessary.
  this is all good stuff though !
  - less fizz/treble: Put a cap in parallel to the second stage´s trimpot..try different values between 3nf and 100pf..

- More bass out: make the output cap (22nF) larger , like 100nf or even bigger.

- tighter/less muddy bass: make the first stage´s output cap smaller (like 3.3n or 4.7n) and/or make the source cap a lot smaller (like 680n)

- better gain control: put a small value cap (like 100pF to 470pF) from the first output cap to the input of the second fet (lugs 1, 2 of the pot.. i think). This will give more spark at low gains.

- voltage filtering: add a big filtering cap to the 9v line..100uf at least..maybe a 100 ohm resistor in series too.

- better output level: That 2n2 cap is working as a variable low pass filter.. at full volume, it does nothing..so..take that out. and put a resistor in series before the 6n8 cap..try a trimpot to set the value where you like best..

- less hiss/ radio recieving: put 220pf caps between gate and source of each fet..
 

[Derringer]

wow!

thanks guys


first chance I get I'm hitting these tweaks up

[Derringer]

OK .... FINALLY got back to this recently.

I tried a few things and found that I liked a bare-bones design best. It sounds fantastic through my P1-Ex ... makes it sound like a much bigger amp! Thick, meaty, raunchy etc etc etc. This is where it will mostly be used.

However, I tried it out as a boost engine on my big amp during band practice and wasn't all that surprised that it still sounded pretty darn good. I think if I were to build something like this again, specifically as a booster for my band, I'd try smaller bypass caps on at least one of the stages to give the higher frequencies more emphasis.

If I ever get a chance to record it, I will ... but take my word ... I'm very pleased with it on my P1-Ex ... infact, this box sounds best of everything I've built so far (fuzzes) when used with my P1-Ex.

Here's the design I went with. ... hehe ... you'll see just how simplified it is ... but damn ... simple = really good in this case. Just having the two gains, pre-and post, allows for a rather usable range of distortion characteristics.


and here's the box


I'm happy with how the paint came out too. I just tried something new ... three spray-colors, and just randomly went to town until I started to see how I wanted the colors to blend. Screwed up a couple corners while sanding ... but learned form that for next time.

Thanks for the help!

[Renegadrian]

Looks good!!! 

[arawn]

loioks great!!!