Randall RG100ES overdrive problem

[tonepumpamps]

Hello everyone,
I'm having a little trouble with a Randall RG100 I have in the shop. The amp has a pull pot on the treble control that is a sustain/boost function.
the amp works great and overdrives well normally until you pull out the sustain/boost knob. It adds drive and sustain but drops the volume way down.
I checked the clipping diodes that are engaged when the knob is pulled and they check good. (I even replaced them after messing with it awhile just in case there was something funky going on with them).
It looks simple enough pull the switch engage symetrical clipping.
What am I missing?
Any help would be appreciated.
thanks.

[km6xz]

According the the diagram, the two clipping diodes will limit level at the top of the Master vol control to 0.6 volts either positive or negative. The drive signal that the clipper can act o n when activated has two series 4 volt zeners so it is not going to clip until the signal is 4 volts. So I would expect a big difference. What does the signal measure measure with and without the sustain switch in the "on" position. You could add a series resistor with the sustain switch to allow a higher level signal before being clipped. But the job of the clipper is to act as a simple hard limiter.

[JHow]

I have one of these and that is the way it seems to work for me. When I engage the diode clipping, I turn up the volume. I have never measured it like km6xz is saying, however.

[ExDementia]

I just registered to reply to this thread.

On the RG100es, pulling the sustainer on cuts the volume significantly. This is by design, its meant for lower volume practice or recording. In the late 80s with the RG100es XP, they changed it so there is no drop in volume. Here's a link to a download of the manual from Randall. They also have the wiring schematics available.

Nothings wrong with your amp, its just the way it was made.

http://www2.randallamplifiers.com/Ab...t-Manuals.html

[J M Fahey]

Thanks

*If* you have the schematic or wiring diagram, please post it here, I was always curious as to how they managed it.
The schematics that float everywhere are of the old version.
Thanks again.

[tonepumpamps]

Thanks for all the replies.
I'm attaching the schematic I found for the amp for everyone to peruse.

Thanks again!!

[vidmachine]

I have the XP version and the volume still drops a bit when the Sustain Boost is on. My Rocker Switch failed and I Replaced it with a mini toggle. The symptom was volume fluctuations for no reason.