Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hey. Been busy lately, but built a custom pedal for a friend, channel switching for his engl fireball 100 and a valvewizard smalltime delay.

He loves how it sounds, but when put in the fx loop (parallell, full wet) the volume gets lowered alot.

I know that line level loops can cause this, but accirding to the manual the send/returns are -20 to +/-0 with -10 nominal. So it shouldnt drop that much? Manual http://www.englamps.de/uploads/tx_ddfproducts/E635-OM.pdf (http://www.englamps.de/uploads/tx_ddfproducts/E635-OM.pdf).

The pedal does not distort, no input clipping and looks like unity gain more or less? But, as i read the schematic, the output is inverted, and being a parallell fx loop, maybe this is the issue? Or is it an impedance/cable length issue? But doesnt really hear tone degradation.

Schematic http://www.valvewizard.co.uk/smalltime.html (http://www.valvewizard.co.uk/smalltime.html).

Naturally i could just increase the opamp gain on the output. But i feel i want to understand the issue and use the least amount of band aid instead of proper design. If the issue is the inverted signal,i will add a volume pot and an another inverting opamp. Oh, and the buffer tubes should be fine, the amp is brand new.

The owners manual is coy about Fx levels and impedances, but if the problem is cancellation then the "Dry-Fx Balance" control should give highish levels of Dry at one end and highish levels of Fx at the other, falling to a minimum at some mid setting.

An obvious first test is bridge Fx Send and Return with a known good lead and confirm that you have good output in the fully Wet setting.

Since the amp seems to have a Dry/Wet mix already you could try making the delay wet-only by lifting the 10k between the output of the first op-amp and the input of the second, i.e. its own dry path.

HTH

Thanx Roly, i have instructed him to test the amp with just a Cable in send/return. will see what the outcome is. :)