OD trimmer question

[grtamp]

When you set the OD input trim , the amp is ON in overdrive mode? I must put a signal input or without signal?
Thanks

[martin manning]

I believe the nominal setting for a network with a 220k resistor and a 100k trimmer is to put the the trimmer's wiper at ~25k DC resistance to ground. Assuming the OD relay is wired in the usual way, where the energized state is OD "on", you can measure this directly with the amp powered up in standby mode and OD switched "on". Or, assuming a 220k resistor in front of the trimmer, 25k OD "on" will measure 23k with the amp switched off, due to the 220k being paralleled with the trimmer. No signal needed. Having said all that, you should really set it by ear.

[grtamp]

Hi Martin , thanks for your explanation , I set my trim to 45Kohm from wiper to ground for take a equal level volume between clean and od channel , I tryed 25K to ground , but I get less volume!
45K is too much?

[martin manning]

Hi, you have three controls that will all affect the volume on the OD:

This trimmer, which sets the input signal level for the first stage; the "Level" or "Drive" control on the front panel, which does the same thing for the second stage; and finally the "Ratio" or (OD) "Volume" control on the front panel, which sets the output level. The Ratio/OD Volume is what is used to balance the clean and OD volume levels in use.

My take on the function of this trimmer is that it determines the minimum level of distortion that you get with the OD switched on. If you want more, the front-panel Level/Drive control is dialed up.

[grtamp]

Thanks Martin for your support!

[Structo]

Yes this was a later revelation about adjusting the trimmer with the amp on and switched into overdrive.
At least I didn't understand it until we were discussing #183.

It's funny but it still ends up to be around 9:30-10:00 on the trimmer.

If you set it too high, you lose note definition and the articulate way the amp is supposed to sound like.

Sure are fun amps to play though, when everything is dialed in.