First Build: Fetzer Valve & question

[PeterJ]

Hi all - I just built my first active effect, the Fetzer Valve, after a lot of lurking and learning. I had built an a/b box and done some repairs to FX, but this is my first from-scratch circuit.

it worked the first time and sounds great - quiet, too! Wiring the perf was easy, off-board wiring is going to take a lot more practice...

I built the high-input version of the original Fetzer, using an MPF102 (I also have a J201 that I haven;t tried yet). I also added a 100uf cap and an IN4001 on the 9v line. Here's the layout I used (adapted from the original):

My question: I get unity gain at about 1 o'clock, then just enough boost for a lead if I max the volume pot. Is this normal, or should I be getting more boost? My signal is louder when cranked all the way, but that means it's pretty much has one useful setting.

Here are my Q readings (with the effect on):
D: 4.58V
S: 2.65V
G: 72.4mV

Do these seem normal? The original ROG write-up said that Gate should be zero and Source should be half what I'm reading (but that was with the low-input layout). Any input is welcome.

Thanks to ROG for the design and everyone here for the ideas and community!
Peter

[petemoore]

  That 1m at the input needs to be on the other side of the 33k to the 33k/Gate node, that should pull the gate down.

[PeterJ]

Thanks for the reply, Pete. Interesting - that's diferent from the instructions that ROG and others have said about how to hook this up for the "high input":
"Move the 1M resistor to the left-hand side of the 68k, i.e. directly between IN and GROUND. THEN change the 68k to 33k, so that the 33k goes from junction of IN and 1M to the gate of Q1."

To do what you suggest, I could move the 1M to that junction point just before the 33K goes into the gate, right?

[MartyMart]

You have it wired correctly, MPF102 is much lower gain, try your J201 and rebias with the
trim pot .... you'll have more volume
Pinout should be the same BTW

MM.

[sta63bmx]

I cannot remember if I used an MPF102 of a J201, but I think I used an MPF102.  With the mid boost ON I get a decent volume boost for leads, but without it I don't get much gain over normal, a couple dB and that's it, sounds like yours.  It's bizarre that it kind of has a Fendery quality when it's a tiny handful of parts.

[markm]

The updated Fetzer is much better IMO.
Maybe give that a try. 

[PeterJ]

Thanks for the help, guys - I wanted to try the original as a first build, I may try the new version later. I swapped in the J201 and will test it at band practice tonite.

[PeterJ]

Hey! It sounded great with the band - basically my tone, just more of it, a tiny bit of color (in a cool way).

BUT -- I am getting a bit of a pop through my amp when I click it on or off. Will a pulldown resistor help, since there is no input cap in this design?
Thanks, all.

Peter

[petemoore]

  Sorry, I didn't know the design...I looked at the Fetzer Schematic @ ROG.
  Jfets don't create really large gains, if it's boosting and the bias looks good...that's it...Stick a J201 in or...start working up 'the' second stage...
  Going from what I see on the layout there is no pulldown resistor on the output cap, Putting one there is where I'd start with the De-Pop efforts.
  The input...has a 1meg that 'looks' like a pulldown, except there Is no input cap.

[PeterJ]

I'll give that a shot, Pete -- thanks! I'll try a 1M or a 2M2 from output to ground and see if that works.
Peter

[PeterJ]

Update: I did more searching here and read what ZVex said about using superbirght LEDs with 10M resistors to avoid this kind of switch popping. I replaced the LED witha  superbright one I had, put in the 10K and voila! Thanks for all the input, guys. This was a fun first project The box sounds great, so thanks again to the fine folks at ROG!

[petemoore]

  Sharp Graphics Peter !
 

[PeterJ]

Thanks, Pete! I think I spent as much time on the label as I did on the circuit...