Deluxe AB763 tone circuit question

[mikepukmel]

Hi All,
When I built this amp, I put pots in the empty tremolo holes for midrange, replacing the 6.8K 'mid balance' resistors in the stock circuit. Some of you guys mentioned that "this amp is plenty bright as it is" but I didn't understand that point until I got the pots installed: The pots only cut and make the too bright amp even brighter.

So, going to yank the pots and figure out what else to put in there, which leads to the question: 6.8k is the stock value. The pots I put in are 10k. If I put a larger value than 6.8k, say 12k, what values could I increase to get more mid out of the circuit without causing some other problem?

I did download Duncan's tone stack simulator, and I see the green lines change shape, but I don't know what Im looking at.

Oddly, to me anyway, above a certain point, the mid pot (if that's what's in there instead of a resistor) acts more like a volume control than a tone control.

Thanks,
MP
Happy New Year to all of you who celebrate such things

[Leo_Gnardo]

Don't yank your mid control just yet. You can insert a 6K8 resistor between ground & the "bottom" tab on your mid pot, then mid "all the way down" is stock, and anything up from there is boost. I have some customers who want mid controls on (Fender & similar) amps that have none, but they have no need for cut, only boost, & this is the solution. Then what value mid pot? Although 10K is Fender's choice in their classic black & silverface amps that have mid, you can use 25K or even 50K for lots of mid boost. Mind you, with mids cranked way up, your treble & bass controls won't do much any more, iow the mid becomes an all pass or auxiliary volume control. Nonetheless, hundreds of happy crustomers here have had their mids done thataway.

Happy New Calendar. What number's on it is just to satisfy those who adhere to some sort of more or less global convention, right? Probably a good idea to do that, if only to organize bill & tax payments so the house/car/etc. won't get repossessed, or get you kicked out of your rental.

[mikepukmel]

Cool, way better than removing the pots, thanks Leo, will do. I only have 10k pots now, can try out and order 25k's if its not enough.

Thanks and happy new year to you as well, Leo. I think we're about to enter 2019, but a quick google shows the Chinese lunar calendar, we're about to see the year of the Pig! So, we got that goin' fer us now.

[Randall]

YES! I needed to know this, thank you. Makes so much sense.

[Dave H]

When I built this amp, I put pots in the empty tremolo holes for midrange, replacing the 6.8K 'mid balance' resistors in the stock circuit. Some of you guys mentioned that "this amp is plenty bright as it is" but I didn't understand that point until I got the pots installed: The pots only cut and make the too bright amp even brighter.

Does it have a 'bright' cap across the vol pot?

Changing the bass and mid caps in the tonestack to 22n reduces the depth of the mid notch and boosts the lower mids..

[mikepukmel]

Don't yank your mid control just yet. You can insert a 6K8 resistor between ground & the "bottom" tab on your mid pot, then mid "all the way down" is stock, and anything up from there is boost. I have some customers who want mid controls on (Fender & similar) amps that have none, but they have no need for cut, only boost, & this is the solution. Then what value mid pot? Although 10K is Fender's choice in their classic black & silverface amps that have mid, you can use 25K or even 50K for lots of mid boost. Mind you, with mids cranked way up, your treble & bass controls won't do much any more, iow the mid becomes an all pass or auxiliary volume control. Nonetheless, hundreds of happy crustomers here have had their mids done thataway.

Happy New Calendar. What number's on it is just to satisfy those who adhere to some sort of more or less global convention, right? Probably a good idea to do that, if only to organize bill & tax payments so the house/car/etc. won't get repossessed, or get you kicked out of your rental.

Did that, resistors at the bottom of the (non OEM) mid pot. Really helps a lot, thanks! The range of the mid pots are now very useful. Like them this way.


Also, on another friends suggestion, I changed the slope resistor on this channel, and it also took some bright off. But, maybe reduce that a bit . All in all, amp sounds much different, and with the new mod to the mid pots, much more usable.

[mikepukmel]

Does it have a 'bright' cap across the vol pot?

Changing the bass and mid caps in the tonestack to 22n reduces the depth of the mid notch and boosts the lower mids..

Dave, yes, the vibrato channel has a cap across the vol pot, its the stock value 47pf. The normal channel does not. In this schematic (Im using) the bass cap is 0.1 and the mid cap is 0.047. So, I should raise the mid, and reduce the bass to get the effects you're talking about? Def going to try that this weekend!

[mikepukmel]

Akk, gotta start keeping better notes. Its not like software, can just jump back one version with the press of a button.

Anxious to see how these mods interact with the overdrive mod. That made the normal channel more screechy.

[Dave H]

In this schematic (Im using) the bass cap is 0.1 and the mid cap is 0.047. So, I should raise the mid, and reduce the bass to get the effects you're talking about?

No, try lowering both caps to 22n (0.022u)

[mikepukmel]

Will do, thanks Dave.

[mikepukmel]

Don't yank your mid control just yet. You can insert a 6K8 resistor between ground & the "bottom" tab on your mid pot, then mid "all the way down" is stock, and anything up from there is boost. I have some customers who want mid controls on (Fender & similar) amps that have none, but they have no need for cut, only boost, & this is the solution. Then what value mid pot? Although 10K is Fender's choice in their classic black & silverface amps that have mid, you can use 25K or even 50K for lots of mid boost. Mind you, with mids cranked way up, your treble & bass controls won't do much any more, iow the mid becomes an all pass or auxiliary volume control. Nonetheless, hundreds of happy crustomers here have had their mids done thataway.

Happy New Calendar. What number's on it is just to satisfy those who adhere to some sort of more or less global convention, right? Probably a good idea to do that, if only to organize bill & tax payments so the house/car/etc. won't get repossessed, or get you kicked out of your rental.

Hi Leo, hope all is well with you and family! So, regarding the mid pot mod, (if I can get some of the junk off my workbench today):

connect the wiper lug to the input from the amp side. Connect other lug as shown below. View is from the bottom of the pot.

Please excuse my terrible ms paint drawing.

[mikepukmel]

About 3 1/2 seconds after posting the first sketch I realized the mistake.