Fuzz sounding horrible through effects loop

[Transistor-Transistor]

So I built a fuzz and tested it with a solid state amp, it sounded amazing. I forgot to test it with a tube amp until I had already soldered it together and put it in a box.
After I finished it I finally tested it with the tube amp and it sounded like complete garbage through the effects loop. Do I need to add a buffer to the end or just make the output boost stage higher impedance or something else entirely? If you give me an hour I can make a schematic if you need it.

[Zveeen]

Do you run the pedal through the FX loop in your amp?
What circuit is it based on?
Did you put it in front of your SS amp when testing?

Cheers

[Transistor-Transistor]

1. I ran it through the fx loop.
2. It's based on an old tweako schematic I found in the archives with a LPB1 style clean boost after it to make up for the soft clipping volume loss.
3. And yes

[Zveeen]

Why did you run it through the FX loop in your amp?
Have you tried how it sounds when you put the Fuzz before your amp?
First suspect is really the impedance going into the fuzz, maybe even the volume going into the fuzz.
Can you describe how it sounded?

[Transistor-Transistor]

Well my whole rig is through the FX loop and I like making sure that the pedals I work on sound good through it. I did try it before the amp and it sounded a little better but still not great. It sounds very thin, and it takes away a lot of distortion. Thats why I'm blaming the impedance.

[Zveeen]

You can try modding it like EQD with their Eruptor Fuzz. It has a Buffer followed by an "guitar pickup simulator" consisting of an inductor/Transformer, resistor and capacitor.
Maybe even put a 100k or so potemtiometer in front of the buffer configured like the Relax/Push knob of the Mastotron from Zvex, considering you have a whole preamp section before your Fuzz circuit.
Either way I am curious what you come up with, to resolve this issue.

Cheers

[R.G.]

FX loops are funny. They are in general not guitar-signal level on tube amps, and many solid state amps. They're frequently line(ish) level, about 1Vpeak. This is about 10x the peak signal from single coil pickups. They are frequently optimized for either 600ohm send/receive, or 10K receive impedances, and what this does to pedals is up to debate. Might be signal level as well as impedances. All depends on the specific amp and pedal.

[Zveeen]

Ok, seems our assumption was right.
Thank you R.G.