Bright Caps on Volume Pot

[greg]

I have built a single ended EL84 based 6 watter that is very similar to a Matchless Spitfire in all of the major component areas. It sounds great cranked, but it sounds particularly thin at low volumes.

I haven't messed with bright cap substitutions much, and I am wondering if the 180pf bright cap's affect is diminished enough when the amp is cranked that it has no real affect at that point. I really only play this amp either cranked at gigs or at bedroom levels (either on 3 or on 10), so if the bright cap is doing nothing when cranked, I should be able to remove it (or find a value better suited to songle coils) that makes it sound "rounder" at low volume without affecting the cranked tone which it currently possesses - right??

Thanks,
Greg

[Enzo]

Bright caps across volume controls are essentially shorted out by the control when it is at the top of its travel, so yes it becomes irrelevant when the amp is cranked.

So yes, try removing it or using different values. Not to say other forces are not at work here.

[greg]

Yeah, I am sure there is much more at work here than just the bright cap, but it seems like the best starting place.

Thanks for the reply.
Greg

[Ray Ivers]

Greg,

Is this a non-master amp? Used with an attenuator?

I've found larger-than-usual 'bright' caps useful across the gain controls of high-gain preamps, to change the frequency response of the overdrive circuit at various gain settings - and also very small-value ones to add 'chime' (high-treble boost) in a clean preamp channel. IMO they can sometimes make single-coils too edgy-sounding at low pot settings, but YMMV.

I've also used 'dull' caps connected between the pot wiper and ground. These reduce treble when the amp is cranked to reduce single-coil 'splatter', but allow full-range response at low gain settings - might be worth a quick try-out in your amp.

Ray

[greg]

It is a non-master circuit used without an attenuator - it is just loud enough with a Celestion Blue to use live. Of course, I have to carry two amps and 2 1x12s to a gig, but it still seems much less stressful onstage than fighting with getting the sound I want out of pedals + 1 amp (with clicking ODs and Delay off and on). Now I need to pony up for one of those Tone Bone head switchers to lighten the load.

The dull cap seems like a cool idea. That one would have to be switchable.

I've got some work to do - thanks for the replies.

[Enzo]

A dull cap - I like that. Never had a name for it before.