Made some Dogear tweaks today...

[Normster]

...based on his recommendations to the Bassman layout.

1. Checked the Treble pot, 258K - wOOt!
2. Double checked the OD Level - crap, I DID have a 1MA in there. Replaced with 100kB.
3. Yanked out the 25uF Cks on V1, replaced with 5uF/1uF.
4. Replaced the 3.3k Rk on V2a with a 2.7k.
5. Repaired a bad solder joint on the .001uF Bass pot cap.

The tone is just a bit brighter at the same settings, but the real kicker is the harmonics! With the PAB on, Gain at 2:00, and Master at 9:00, this thing will sustain for days. Turn just a little sideways and the next octave starts to sing. Amazing difference!

Sorry it took so long for me to get back into this amp, Scott, but you still da man!!!

[dogears]

So was I right about that high side thing??? Shhh....

...based on his recommendations to the Bassman layout.

1. Checked the Treble pot, 258K - wOOt!
2. Double checked the OD Level - crap, I DID have a 1MA in there. Replaced with 100kB.
3. Yanked out the 25uF Cks on V1, replaced with 5uF/1uF.
4. Replaced the 3.3k Rk on V2a with a 2.7k.
5. Repaired a bad solder joint on the .001uF Bass pot cap.

The tone is just a bit brighter at the same settings, but the real kicker is the harmonics! With the PAB on, Gain at 2:00, and Master at 9:00, this thing will sustain for days. Turn just a little sideways and the next octave starts to sing. Amazing difference!

Sorry it took so long for me to get back into this amp, Scott, but you still da man!!!

[Normster]

So was I right about that high side thing??? Shhh....

So far, you haven't been wrong yet. hehe

Actually, the thing that was most out of whack was the OD Level pot. I can't believe I forgot to swap that out when I changed to non-HRM. (As you may recall, I was originally going to build this as a '97 and changed direction about halfway through.) I didn't even think about it until you mentioned it on my layout. I wouldn't go so far as to say that it sounded like "muddy crap" but it did kill the harmonics. With the 100kB pot the amp is finally ALIVE.

Of course, it could also be the spiffy new knobs I put on it.

[Bob-I]

The tone is in the knobs.

I've never had that harmonic bloom like you mentioned even with the dogears tweaks but I'm very happy with what I have.

[Darkbluemurder]

As far as the Treble pot I agree that a high reading 250kA is good. Mine reads 270k. I had a PP in there for a low midboost but I took it out to simplify things. The 270k was in the gain position before and was swapped with a low reading 250kA pot (actually 200k). The difference between 270k and 200k is audible. 200k is a tad brighter and more harmonically rich.

With 1MA as level pot it must be darker since at say 2 or 3 the signal has to pass approx. 750k-800k resistance which could impose a noticeable high frequency roll-off. With a 100kA the same setting would only have a 75k-80k series resistance which would probably not provide any noticeable hi-freq roll-off. I can imagine that only at very high level pot settings (i.e. near full-up) 1 MA and 100kA could sound similar as far as series resistance is concerned. However, the grid load into the next stage is hugely different so that will definitely make a difference, too.

[Tdale]

What if I can't find a 250+ treble pot? Is there any way of getting a higher value some way, using components?

Tommy

[Normster]

What if I can't find a 250+ treble pot? Is there any way of getting a higher value some way, using components?

Tommy

Just hang a resistor from either the input or ground. For example, if your pot reads 238k, add a 20k and you're in the ball park.

[ayan]

What if I can't find a 250+ treble pot? Is there any way of getting a higher value some way, using components?

Tommy

Just hang a resistor from either the input or ground. For example, if your pot reads 238k, add a 20k and you're in the ball park.

Careful: if you hang a resistor from the input lug of a treble pot, you will be cheating yourself out of treble and gain (since the output is derived from the wiper, which will in this case never benefit from added isolation from the bass cap if the extra resistor is between the input lug and the treble cap instead). You can hang it from the output, but it does not go to ground, it goes to one of the poles of the PAB relay, provided you're doing a true ODS inplementation.

Cheers,

Gil

[dogears]

Gil,

Why would it matter which side you connect too? The pot is a voltage divider so it wouldn't it only matter if you run your pot to one extreme or another? You are correct in that you can never get as much treble by hanging it in front, but if you normally run your treble pot between 10 and 12, you should be able to run between 10:30 and 12:30 to get the same effect. No? Fwiw, I hung it to the PAB in my Glaswerks. But in my Fuchs, it is next to impossible to do it on the PAB side. Much easier on the input side.

Thanks for the help Gil!

What if I can't find a 250+ treble pot? Is there any way of getting a higher value some way, using components?

Tommy

Just hang a resistor from either the input or ground. For example, if your pot reads 238k, add a 20k and you're in the ball park.

Careful: if you hang a resistor from the input lug of a treble pot, you will be cheating yourself out of treble and gain (since the output is derived from the wiper, which will in this case never benefit from added isolation from the bass cap if the extra resistor is between the input lug and the treble cap instead). You can hang it from the output, but it does not go to ground, it goes to one of the poles of the PAB relay, provided you're doing a true ODS inplementation.

Cheers,

Gil

[ayan]

Gil,

Why would it matter which side you connect too? The pot is a voltage divider so it wouldn't it only matter if you run your pot to one extreme or another? You are correct in that you can never get as much treble by hanging it in front, but if you normally run your treble pot between 10 and 12, you should be able to run between 10:30 and 12:30 to get the same effect. No? Fwiw, I hung it to the PAB in my Glaswerks. But in my Fuchs, it is next to impossible to do it on the PAB side. Much easier on the input side.

Scott, sure... I am saying that you can cheat yourself out of treble by putting a resistor between the treble pot and cap, so yes, if you never run your treble high enough you can always redial the control higher up to regain the treble you will lose by adding the resistor at the input of the pot. But if we have to caveat things that way, I can't help but wonder why would you need to add a resistor at all in the first place? Let's put it this way: all other things being equal and all controls kept unchanged (but we can start from any setting you choose), add a resistor to the top of the treble pot and lose treble; add it at the bottom of the treble pot and you will gain midrange. That's the way the tone stacks work...

Gil

[dogears]

Gil,

Changing the treble pot has a modest effect on the knee frequency of the treb cap. I modeled it. Unless you have a bunch of pots to choose from when you build, you may wind up with a low one. In the case of the Fuchs amps, the pots are card mounted. Makes swapping them very difficult as they are dpdt.

In any event, all things equal, you can't get the same frequency response graph with a 230k and a 260k treble pot, even by turning the controls.

Scott, sure... I am saying that you can cheat yourself out of treble by putting a resistor between the treble pot and cap, so yes, if you never run your treble high enough you can always redial the control higher up to regain the treble you will lose by adding the resistor at the input of the pot. But if we have to caveat things that way, I can't help but wonder why would you need to add a resistor at all in the first place? Let's put it this way: all other things being equal and all controls kept unchanged (but we can start from any setting you choose), add a resistor to the top of the treble pot and lose treble; add it at the bottom of the treble pot and you will gain midrange. That's the way the tone stacks work...

Gil

[ayan]

Gil,
Changing the treble pot has a modest effect on the knee frequency of the treb cap. I modeled it. Unless you have a bunch of pots to choose from when you build, you may wind up with a low one. In the case of the Fuchs amps, the pots are card mounted. Makes swapping them very difficult as they are dpdt.

In any event, all things equal, you can't get the same frequency response graph with a 230k and a 260k treble pot, even by turning the controls.

Scott,

We have both agreed that changing the pot, or putting a resistor either before or after it, will change the frequency response of the tone stack. I'm curious as to how you modeled this? The closest model I think is available out there is Duncan Amps' TSC, which can help visualize everything we've been saying using a Fender tone stack (close enough) -- it still doesn't have the Dumble tone stack.

Not to beat this one to death, but, the change in frequency knee between using a 230K and a 250K pot is very minor compared to the treble loss (at max settings) resulting from the addition of a 20K resistor at the input of the treble pot. I think if you model that as well, you will be able to see it too.

Cheers,

Gil

[Tdale]

What tone stack should I use? I see different ones, but which one is best? The hybrid-A?

Tommy

[dogears]

Hi Gil,

Is the Vox model closer??

I don't think the loss of full treble pot is a big deal, for me. I never ever come close to getting up there in my settings.

Best bet is to use a cherry picked treble pot. I agree on that.....

So, the big question is, have you measured other Dumble treble pots? Just curious....

Gil,
Changing the treble pot has a modest effect on the knee frequency of the treb cap. I modeled it. Unless you have a bunch of pots to choose from when you build, you may wind up with a low one. In the case of the Fuchs amps, the pots are card mounted. Makes swapping them very difficult as they are dpdt.

In any event, all things equal, you can't get the same frequency response graph with a 230k and a 260k treble pot, even by turning the controls.

Scott,

We have both agreed that changing the pot, or putting a resistor either before or after it, will change the frequency response of the tone stack. I'm curious as to how you modeled this? The closest model I think is available out there is Duncan Amps' TSC, which can help visualize everything we've been saying using a Fender tone stack (close enough) -- it still doesn't have the Dumble tone stack.

Not to beat this one to death, but, the change in frequency knee between using a 230K and a 250K pot is very minor compared to the treble loss (at max settings) resulting from the addition of a 20K resistor at the input of the treble pot. I think if you model that as well, you will be able to see it too.

Cheers,

Gil

[ayan]

What tone stack should I use? I see different ones, but which one is best? The hybrid-A?

Tommy

Tommy, I think the only valid answer is to try them all and see which one you like the best. Here are the possibilities:

1. Old, 70s TS -- Treble: 330pF cap, 250KA pot; Bass: .1uF cap, 250KA pot with 1K tail to ground; Middle: 100KB pot, .047uF cap; slope = 100K. Don't know of anyone who uses this at this point, maybe the "non SLX" Fuchs? Not sure; I don't care for it.

2. Early 80s TS -- Treble: 330pF cap, 250KA pot; Bass: .1uF cap, 250KA pot with 1K tail to ground; Middle: 100KB pot, .047uF cap; slope = 150K. I like this guy, except I prefer a linear pot for the treble. I think this TS is suited for people who don't use a "super phat" treble pickup sound and that prefer to have the option of having a "clear" positions 2 and 4 w/Strat, and use a guitar with humbuckers on the neck pickup.

3. Skyliner TS: Treble: 330pF equivalent cap in normal (non MID Boost) mode, 250KB pot; Bass: .1uF cap, 500KA pot with .001uF cap across end lugs, and 10K tail to ground; Middle: 250KA pot, .01uF cap. This TS will give you a a lot more lower mids than the ones above, and -- as per my experience -- it will never give you a "thinner" sound suitable for the neck pickup in a Gibson or a Strat on positions 2 and 4. I tried to like this TS a few times, but always ripped it out.

Of course, then there are all kinds of variations, like running the Skyliner pot values but with the earlier 80s caps, or having a few choices of middle cap like Gary Johnson puts in his amps, etc. In the end, there is some overlaps between the sounds that can be had, but to me it boils down to the fact that I like for my tone knobs to be set halfway up and tweak from there. The early 80s with the substitute cap gives me that, but it may sound too middy and thin for some people that want a super phat Tele sound on the bridge pickup for example.

cheers,

Gil