Effects Loop Problem

[passfan]

Finished up a Hiwatt CS-30 and I am having issues with the send on the effects loop. It is putting out 4 volts which is overloading my outboard gear. I've thought about raising the feedback resistor to drop the gain hence the send output but I am wondering if there is something easier.

[Structo]

Maybe you need to put a trimmer there as a voltage divider for the Send, to drop that signal down.

[passfan]

Maybe you need to put a trimmer there as a voltage divider for the Send, to drop that signal down.

And shunt the excess to ground ? How will losing 3 volts effect the gain of the rest of the amp ?

[d95err]

There is a voltage divider at FX return (100k/56k). Removing that would be a first step to reduce the gain lost by trimming the send level down. Use something like a 33k - 68k series resistor first, followed by a 100k - 220k resistor to ground instead. You can also add a cathode bypass cap to the return stage for another 4dB or so of gain.

That should probably be enough to compensate for trimming the send level down (depending on what type of outboard gear you're using).

[passfan]

There is a voltage divider at FX return (100k/56k). Removing that would be a first step to reduce the gain lost by trimming the send level down. Use something like a 33k - 68k series resistor first, followed by a 100k - 220k resistor to ground instead. You can also add a cathode bypass cap to the return stage for another 4dB or so of gain.

That should probably be enough to compensate for trimming the send level down (depending on what type of outboard gear you're using).

Good point. So I can/will be shunting the excess to ground right , before the send ?

[jjman]

Yes. You can use a pot or 2 resistors. May as well use a pot so you can fine tune the send strength at max gain/tone settings. Bring the send pot down until the signal is weak enough for your setup. You can then replace the pot with 2 resistors if desired. The scheme doesn't show it but presumably the send connects directly to the return when nothing is plugged into the loop. In that case the send normal sees 156k to ground. So a 156k pot would be parity but that doesn't exist. 250k should work.

You mention model 30 but the scheme says model 20 BTW.

[passfan]

Yes. You can use a pot or 2 resistors. May as well use a pot so you can fine tune the send strength at max gain/tone settings. Bring the send pot down until the signal is weak enough for your setup. You can then replace the pot with 2 resistors if desired. The scheme doesn't show it but presumably the send connects directly to the return when nothing is plugged into the loop. In that case the send normal sees 156k to ground. So a 156k pot would be parity but that doesn't exist. 250k should work.

You mention model 30 but the scheme says model 20 BTW.

Yes the difference between the 20 and the 30 is a quad instead of a pair on the output. A lot of the circuit I verified from actual photos found on the web. Thanks for the info.