Bright caps on EXP volume pot

[rooster]

In Dave Hunter's book, KF does an interview. In it he talks briefly about attaching flying leads to any part of a circuit - i.e., perhaps, the bright caps on the volume pot. He states that this will add an antena to the circuit, which in turn will alter the circuit. I think his point was to keep it simple here. The author also touched on the subject of added gain stages at the same time, and I think KF's response was meant to sort of blanket both subjects.

OK, that said, have any of you altered the bright caps layout on the Express? I have. What I hear is that the caps should be attached to the 'outside' lead of the volume pot, with the center tap on the switch going to the wiper of the pot. In fact, I attach the caps as close to the volume pot lug as possible.

What this did - oddly enough - was stop an antenna effect from the original layout.

Comments?

[mumford]

I'm not sure I follow you-- you mean attach the body of the cap close to the pot and trail the lead to the switch rather than the other way around?

[rooster]

Yes, that's the idea. Stock, the cap is sitting in the middle of the wiper and hot side of the pot - the antenna would be any leadwire going to the cap. Attaching the caps to the outside lug, they are at the end of the road, so to speak.

From what I can hear, and I tried it all 3 ways, stock, and then to the wiper, and then to the outside lug, the antenna effect is pretty much removed from the circuit running to the outside volume pot lug.

A simple test, to see if there is anything to this antenna thing, would be to just attach the cap to the volume pot lugs, like the bright cap on a Fender Deluxe Reverb. for example. If you can hear a difference, than you might want to try something new.

[rooster]

Alright, more. As I look at the photos of Francesca, I see that the bright caps are put in the circuit one way, and as I look at the photos of Kelly - if that is Kelly - I see that it is done another way. ??

So I am now thinking that KF changed his circuit design along the way. Which makes a lot of sense to me because one way is definitely quieter than the other. Which also means that Ron's builder guide is showing the layout of Francesca - the circuit that KF moved away from.

Hmm. Glen, do you want to weigh in here? I would like to know how your bright switch is wired if you can share. In the end, as simple as this circuit is, the bright switch is very important. In fact, if everybody here is running with the Francesca example instead of the Kelly version, I suspect the bright switch is not something too many here are using. In my first build I did iti the Francesca way and I couldn't use it. Now I can.

[geetarpicker]

Yep I just checked and my original (and my two clones) are both of the "revised" version apparently. The center terminal of the switch ties to the center lug of the pot, and the two caps are tied on one end and go to the terminal on the pot that is the farthest away.

I always run the bright switch in the full 500pf position, which on mine is in the down position.

[guitarsnguns04]

I do find my bright switch induces an antena effect...Im going to have to try this out.Thanks for posting this.

[guitarsnguns04]

I assume v1a grid still connects to the center lug of the pot with the switch center terminal?

[rooster]

Glen - Wow, that's crazy, but now I can see where you could do that with the amp wired this way. Before when you were saying that you were running with the 500pf cap - and I had just finished my first EXP build, wired the 'wrong' way - I couldn't understand how you could be getting the tone you were getting. OK, but I get this now. With my amp wired the way it was I was getting all kinds of 'shot' noise with the 500pf cap engaged. In fact, I was really struggling with the 100pf cap. Thank you for sharing your EXPerience once again, Glen. You make this site happen.

Too, if you remember, when I was blaming the V1 tube for causing some high pitched howling when I turned all the controls all the way up? I now suspect it was this bright switch wiring all along. Even disengaged, wired like Francesca, I think there are issues.

It would be interesting to see how many people building these amps are using the Francesca bright switch layout vs. the Kelly. I have to think that Ron is using the Francesca layout since he posted the info? I wonder how many others. ???? And what about Ceriatone for that matter? Aren't they building off the Francesca amp circuit?

guitarsnguns04: Yes. When you make the changes let me know? Thanks.

[57goldtop]

It would be interesting to see how many people building these amps are using the Francesca bright switch layout vs. the Kelly. I have to think that Ron is using the Francesca layout since he posted the info? I wonder how many others. ???? And what about Ceriatone for that matter? Aren't they building off the Francesca amp circuit?

guitarsnguns04: Yes. When you make the changes let me know? Thanks.

I just had a look at my build and checked out the Ceriatone layout, the bright switch wiring is the same as in Fransesca with the two ends of the caps wired to the center terminal of the vol pot. This is how I wired mine following the Fransesca pics.

I made the changes quickly and there's definitely a difference. btw.. full bright is down on my build.

[funkmeblue]

I'm a little confused, any drawings or a better break down on where to connect what, I'm a little slow

[sliberty]

I am unclear on why this difference in wiring would make a difference in noise or tone. Please elaborate.

By the way - I wired per kelly, so I guess I will be leaving it alone anyway. But I want to understand the nuance here.

[rooster]

Find the 'Kelly' circuit in the 'TW Files' header. Look at the pot layout, things should be clear. Then look at the pics of Francesca - or go to Ron's Build Guide - there you will see the Francesca bright switch layout.

The two are not the same, which means KF changed his layout somewhere along the way. If you don't see how they are different, then you need to look at it more closely. One version has the caps attached to the center lug of the volume pot, the other to the outside lug - big difference if you actually use the bright switch.

[sliberty]

I can see what the layout differences are, but they are not significant from a signal flow point of view. Both put the engaged cap across the volume pot on the same lugs (center and right side with left side grounded).

What IS different is the layout only, and since it doesn't consititute a signal flow difference (as near as I can tell), I am not clear on why it would result in a tonal difference. Its the subtle lead dress issue that I am asking about.

[rooster]

OK, my brain power and verbage will not solve this riddle. If you tried both versions you wouldn't be asking the question. So try both versions and then you can answer the question yourself.

FWIW, I always defer to Glen for the ultimate knowledge source here. He has signed in on the Kelly version. If this isn't enough to motivate you, Brother, cool.

[strato17]

OK I kinda understand now...(correct me if wrong).

Francesca - The two caps are tied on one end. This then connects with a flying lead to the middle terminal on the pot. The center terminal of the switch connects with the right terminal of the pot.

Kelly - The caps are still tied on one end, which is connected to the right terminal on the pot. The center terminal on the switch is connected to the center terminal on the pot.

On the Francesca system, I have two wires.... one that attaches from the pot to the caps, and one from the switch to the pot.

Does the kelly system still have a wire from the caps to the pot, or are the cap's own leads used to connect to the pots directly?

Or is the only difference between the two is the change in where things are connected?