? on the effect of Bright cap on second channel

[hasserl]

On a four input amp, such as a tweed Fender or early Marshall, does the bright cap on the one channel roll off highs on the other?

I ask this because on the latest amp I built using the classic two channel four input I put a bright cap across both volume pots, thinking that the 270k mixing resistors would prevent the bright cap of one channel from bleeding off the highs from the other. But now I question if that is true. The amp seems to lack high end and I'm wondering if the approach of using a bright cap on both channels is making things worse.

It would be good to get some Theory and Design input before I start experimenting with various bright cap values.

TIA

[black_labb]

On a four input amp, such as a tweed Fender or early Marshall, does the bright cap on the one channel roll off highs on the other?

I ask this because on the latest amp I built using the classic two channel four input I put a bright cap across both volume pots, thinking that the 270k mixing resistors would prevent the bright cap of one channel from bleeding off the highs from the other. But now I question if that is true. The amp seems to lack high end and I'm wondering if the approach of using a bright cap on both channels is making things worse.

It would be good to get some Theory and Design input before I start experimenting with various bright cap values.

TIA

it may have a bit of an effect, in that the highs will go through the 270k resistor, but not very many being 270k. you could probably compensate for this by increasing the value of the pot controling things. you could also up them to 470k resistors.

someone else may ell me im wrong, and id believe them before i believe me.

[Enzo]

I think you are over analysing. Perhaps the new amp just is not as bright as we'd like to start with. But in the name of science, if you think the "other" channel cap is draining off the highgs, disconnect it and see. Play through one channel, and unhook the cap from the other. If the amp brightens up, then you were right. If it still lacks brightness, I was right. Plenty of ways to brighten up an amp.

[hasserl]

Thanks Enzo, maybe I am over analyzing. I tend to just mull things over while I'm working on or doing other things, and this is one of the things that was drawing my thoughts.

I guess I'll just put it back up on the bench and start experimenting.

[Enzo]

A long time ago I worked with a crew of experienced field techs in the coin-op amusement trade, and like any group, we'd talk shop all the time. Inevitably someone would propose that such and such was the case, and someone else would say oh baloney, adn then over a couple beers mighty reasonings for why each answer was correct were proposed.

I soon enough would hear enough and say, "Enough, why don't we just FIND OUT?" Grab a voltmeter and see if the voltage dropped or whatever when something happened. I did this often. They could argue about anything. "The restaurant is open until 10." "No the place is open until 11." I'd come in and say, "Well why don't we just CALL them?"

One day I was across the shop, and they are debating something, and I heard one guy say, "Well, why don't you pull an Enzo, and find out?" Ah, my work is done here on this earth.

ANyway, I am a big believer in taking a few minutes to find out what can take an hour to discuss without definitive results.

[hasserl]

OK, I did some experimentint today, and I can answer my own question above, NO the bright cap on one channel does not roll off the highs from the other channel, the 270k channel mixing resistors effectively isolate the channels to prevent this.

I then went on to play around with some different caps and settled on some larger values for bright caps that seem to be effective at brightening the amp up enough for me. I'll play with it like this for awhile before deciding if I need to do any more.