Hiss/Noise only in the FX Loop (Friedman Runt)?

Fenderish

I have measured the loop level and it's very very low, that's why the gain to get back to the line level is so high whiche is the cause of hiss/hum.

It's about ten times lower than a classic marshall/metropoulos/tube-town loop. I can't really figure why Dave chose to set it that low. I'm trying to figure how to set it to a higher level but i have a hard time following the traces on this black PCB. If someone know how to modify the loop circuit to put it between a -10dbV and a +4dBu, i'd be grateful...
(it uses 2 LND150)

Modulus_Amps

ICBM said:

I really don't understand why it seems to be such a difficult concept for many amp designers, but the evidence is that it is.

Probably because it was not in Radiotrons designer handbook, or something you could easily copy from vintage amps.

I think we take our easy access to information these days for granted, I built my first valve amp in 2003 with no internet help, that was a challenge.

@Fenderish said:

It's about ten times lower than a classic marshall/metropoulos/tube-town loop. I can't really figure why Dave chose to set it that low. I'm trying to figure how to set it to a higher level but i have a hard time following the traces on this black PCB. If someone know how to modify the loop circuit to put it between a -10dbV and a +4dBu, i'd be grateful...
(it uses 2 LND150)

I thought it was based on the Metro loop? Presumably there is a voltage divider that needs adjusted

I imagine it is set low so that it has zero chance of causing issue with pedals in the loop? there will be a reason I suspect

Fenderish

Oh I'm pretty sure that's the reason, absolutely no pun intended. It's just that there aren't many pedal that have problems with "classic" loops nowadays so I'm not sure it was necessary to lower it so much, but maybe dave himself has vintage pedals that can't cope with some classic loop levels so that it justified that level !

Anyway, the VR8 trim acts like a send level and is set fairly low, it's just needed to find the two resistors who set the return level to replace one or both with a trim and voila  

MarcTT69

Her is a correction for the FX loop Hiss on some version of Runt 50 and Runt 20 : 

https://www.facebook.com/share/p/cmHKSxPbV3jfx4qc/?mibextid=WC7FNe

On Runt20 the resistor is R53
On Runt50 the resistor is R62