Definitive clean master bright question

[Luthierwnc]

Hi All,

I'm working on another D -- an HRM -- and have been wrestling with how to put a bright cap on the clean master without draining highs to ground in OD mode. The easy answer electronically is to just add another relay but that is real estate intensive. Other posts include putting the bright cap across the the N/C throws but not grounding the OD entrance in clean mode. A version of that has an extra coupling cap and bleed resistor to simulate the master load. Another possibility is putting a lot more resistance on the bottom of the master pot.

Where is the state of technology on one-relay overdrive switches right now? Thanks, Skip

PS PM is fine. It won't be re-shared or used commercially, sh

[dogears]

I wouldn't bother.

But, if you must, just lift the clean master with a 20M resistor when in OD. Hang a 1.1M resistor to ground on the OD network to simulate the master's load.

I'd leave it stock and instead do a bright switch on clean only switch.

[Luthierwnc]

Here's where I've gotten so far. Panel bright is: relay controlled on one throw, off in center and continuous on the other throw.

[Tonegeek]

I have done it this way before with no ill effects:

[Luthierwnc]

Thanks Tonegeek. That seems to do it all. I'm sure I'll fiddle with the cap value. 47 puffs seems like a lot. sh

[Tonegeek]

Thanks Tonegeek. That seems to do it all. I'm sure I'll fiddle with the cap value. 47 puffs seems like a lot. sh

Agreed. I don't recommend that value, just the supporting circuit. Personally, I have not had much luck using bright caps anywhere past the initial volume pot. Even at that I use a small value in series with some resistance and it is still more of an effect than compensation for turning down the pot. The problem with bright caps is they don't seem to evenly track the value of the pot. It would be great if you could find a cap or C/R combination that exactly compensated for the loss of high when you turn down the pot, but I don't think it exists, at least my ears havent had the pleasure. Maybe I need to build my amps to be a bit muddy at gig volume and then tweak with the bright caps. I usually tweak using the parallel C/R method which sounds more natural to me. I know lots of people use caps across the masters so I suppose I can't write it off just yet.

[Luthierwnc]

I can't make it work on paper or in my head but it almost seems like you could use a dual-gang pot. The bleed factor is mostly a problem when the clean master is turned-down. As the resistance in decreased between lugs 1 and 2 of the clean master, the resistance between the cap and lugs 2 and 3 is increased. Maybe you change the carbon element in the cap pot, run a resistor across the cap pot to change the linearity or do a little artistic scraping on the element itself. Someone cleverer than me will need to run with it from here.

[Tonegeek]

I can't make it work on paper or in my head but it almost seems like you could use a dual-gang pot. The bleed factor is mostly a problem when the clean master is turned-down. As the resistance in decreased between lugs 1 and 2 of the clean master, the resistance between the cap and lugs 2 and 3 is increased. Maybe you change the carbon element in the cap pot, run a resistor across the cap pot to change the linearity or do a little artistic scraping on the element itself. Someone cleverer than me will need to run with it from here.

Looks like you got a good start on it to me. There is probably math for doing this, but you could also do it by trial and error using 2 linear pots and a spectrum analyzer or just your ears. You hook the pots up like your schematic and then for every 100k on the volume pot, you set the bright pot to where it sounds good and record the resistance reading. Then you figure out how to taper the bright pot value so it tracks the measurements you made. then swap that carbon trace with one in a dual gang pot. I still think there would be some issues because your ear is not linear and I am guessing that if you turned up the volume somewhere else on the amp it would change the response, but still it would have to be better than the more conventional bright cap. I also have to wonder if the knee where response rolls off is going to change now that there is another changing resistance. Thinking about that just hurts my head!

[dogears]

I used a 270k/760k network in my Glaswerks proto on the HRM side. I put a 47pf across the 760k to simulate the bleed. The master in that amp is lifted by 22M when the OD is on since the amp has non HRM too.

The OD has a dedicated master in both modes.