Sabbra Caddabra noisy until I run a buffer before it

[chork]

I've run into dirt pedals that don't like buffers before them, but a Sabbra Caddabra clone I built on perfboard (https://effectslayouts.blogspot.com/2015/03/catalinbread-sabbra-cadabra.html) is very noisy without a buffer in front. I turn on my EUNA clone and the noise floor drops super low and it sounds great. I've tried a few half assed things like a series resistor and pulldown resistor at input to no avail.

Ideas much appreciated!

Edit: schematic and images 3 posts down..sorry!

 

[Big Monk]

In general, a good troubleshooting post needs pictures and a schematic.

 

[micmac]

Hi chork,

I had a noisy Sabbra Cadabra until I changed my JFETs to ones with a higher VP. I had some with a VP of ~1.5V for Q2-Q4 in the pedal. I replaced them with some with VP of ~2,1V and that solved the problem. Maybe you have them in sockets and a few more lying around to try this. I think VP for Q6 should be low on the other hand because it's a buffer if I remember correctly. Maybe somebody else can confirm.

 

[jcpst]

Thread 'Important: Supplying Pictures when an Issue arises with a PCB Build !!!'
https://forum.pedalpcb.com/threads/...s-when-an-issue-arises-with-a-pcb-build.7081/

 

[chork]

Apologies! Here is the schematic https://docs.pedalpcb.com/project/Sabbath.pdf and here are some pictures. Comparing the schematic to the perfboard layout the 1M pulldown resistor does seem to be missing. The fact that the buffer completely eliminates the noise makes me think this is just an impedance problem, but I am still super new to this.

 

[FormulaFourteen]

If it helps, I owned an original Sabbra and it was horrifically noisy. So if you've managed to kill the noise in any configuration you've managed better than Catalinbread did with mine!

 

[comradehoser]

Adding a pulldown resistor should be very very easy to install and uninstall if you're curious to test. It's just one leg of a1m T'd into the input line before it hits the circuit, other leg to ground.

 

[lowpitch]

I don't think a pull down will help much here. It's a basic treble booster into a multi gain stage JFET preamp. It's always going to be noisy. Trying different BJTs and JFETs might help.

 

[andrewsrea]

I owned a Sabbra Cadabra and its cousin, the Gallello, - both were noisy due to the built-in treble booster.

 

[chork]

I tried a few things even going as far as throwing a jfet buffer in front to try to mimic whatever the EUNA was doing to help, but nothing made a noticeable difference. I ended up ripping it all out and keeping the stock configuration after everyone's comments. I will just be happy tat the EUNA somehow makes it quiet.

Thanks!