freestompboxes.org

guitarpkr76 wrote:

mmolteratx wrote:Well, update on PCB status. They came in today, but I accidentally ordered a previous revision that doesn't work. Will reorder in the next few days.

That stinks, man. I don't mind paying a little extra when you get the new ones to help offset the cost of the bad boards.

Nah, don't worry about it. It just needs a trace cut and a jumper. I'll just use them as Tubescreamer boards when friends ask me for one for cheap. I also redid the board a bit to make it even cleaner in the mean time, so it gives me the chance to order a batch of the new and improved ones.

Awesomeness of symmetry!

Beautiful layout

Looks great.

any news on the revised pcb?
I would be really happy to get a couple or 3 pcs if available.
Many thanks

Paolo

Reordered, but I didn't go for the speedier service this time. Could be as long as a month from last Wednesday, though hopefully they'll be here sooner.

Thanks!
Paolo

im up for two boards if i still can get on the list

I bread boarded this circuit this weekend using the MC33172N op amp as well as the original. I love the vocal-like mid range of this circuit but I can't deal with the fizzy decay. If you have it set on the verge of breakup it seems the fizz is too much. I will try clipping diodes or LEDs in the first stage, might help but may change the sound too much. We'll see.

Try something with a higher forward voltage like blue LEDs rather than the usual diodes which makes it that bit closer to a Tubescreamer.

You might also try lifting a leg on the 3mm LED just to determine where the fizz is coming from. It's still part of the circuit even at the minimum "accent" setting. The accent control should still function as a second gain control without it.

I tried blue and red leds in both the first and second stages in all sorts of configurations and they helped a bit but the fizzy decay was never totally gone. I don't get it because other pedals with leds in the feedback loop don't seem to have this problem. I need to isolate what stage is causing the problem. I would really like to improve this circuit without changing the voicing because I really like how it sounds. I have never heard another pedal with this mid voicing. The leds did effect the tone a little bit but not much.

It can't be that I'm using 2n3904's for buffers???

No definitely not, you could use pretty much anything

Ripdivot wrote:I tried blue and red leds in both the first and second stages in all sorts of configurations and they helped a bit but the fizzy decay was never totally gone. I don't get it because other pedals with leds in the feedback loop don't seem to have this problem. I need to isolate what stage is causing the problem. I would really like to improve this circuit without changing the voicing because I really like how it sounds. I have never heard another pedal with this mid voicing. The leds did effect the tone a little bit but not much.

If you pull out the 3mm LED and turn the accent control all the way down, you should be able to isolate the op-amp clipping in the first stage. If that's where the fizz is coming from, maybe increasing the 82pf cap a bit would help tone it down without changing the qualities you like. If you find the fizz is coming from the LED, you might try a 5mm LED with a higher vf to limit it's contribution.

I tried a bunch of different leds but still has the fizz. Near as I can tell the fizz is in both stages. I changed (R6?) the 1k8 resistor to 1k2 to get rid of some of the bottom end. I also removed the red led and swapped out the 82pf cap for a 150pf. I like this configuration best but there is still some fizz. It's the nature of the beast but I can live with it. I found it isn't as big of deal with a band as it is playing it by myself. To me this pedal has a lot in common with some fuzz pedals.

I built a Zen clone and had the same problem with fizz.... which is why I don't use that pedal.

I also tried swapping diodes and other components but could get rid of it. Could it have something to do with a bad pot?

It's a stumper for sure....

TT

I dont know much about fx pedal design rules, but in amp world fizz happens when you overloading first gain stage with to much low freq's. Lower cap value for first coupling cap usually doing the job

What I'm calling "fizz" is maybe slightly misunderstood but seems to be a common problem. I could even hear it a bit in Pete Thorn's demo of the Dumbloid. When the note decays there is a static or fizziness when it transitions from dirty to clean. It's fine when it's totally dirty and also when it's totally clean but the transition is where you here it. I think it's just how the op amp transitions, after all this is op amp distortion. It's definitely happening in the first stage because I bypasses the second stage to try and isolate it. Hard to tell if the second stage is making it worse but I assume it is because that stage contributes to the gain.

By the way, I built a zen a few years ago and it doesn't exhibit this static in the decay at all. I like the voicing of the dumbloid a lot better though.

I'm just a little girl but looking at Eisy's schematic - 1uF/C2 is the cap I would change to something smaller

Or maybe small resistor/bypass capacitor network after C2 would help to shift some freq's?

I dont know, just guessing - I know shit about these things