Vintage Fender Verb amps & their volume pots

[wizard333]

Various 1M pots still result in breakup early on the pot with a 3 stage Fender reverb circuit. Those things hit the PI surprisingly hard when turned up, harder than some 3 stage high gain channels.

250k and 680 would work, or any other combination. You're just changing where on that throw of the pot clean stops and breakup begins, and adding more breakup at the high range of the pot. I've come to really like that 100k/470k combo, so you might try 250k and 333k or whatever. The other advantage in any channel of having that constant series resistance between your treble pot output and your channel volume is the tone stays more constant over the throw of the volume pot, and doesn't get as 'thin' when the pot is turned down.

[JoeM]

OK, thanks. I'll try it with both the 333k and 680k.

[Gaz]

You could also just put a voltage divider after the volume control for the same result. The benefit would be that you could just use an ordinary 1M pot, and you would not have to alter the bright cap value to match the frequency response.

One benefit I see to both these methods is that you could alternately wire the bright switch across the series resistor instead of the pot itself. That way, the bright switch would work even if the volume pot is all the way up. I think the Rivera-designed Concert Fenders did just that.

[Chuck H]

I've often been plagued by pot settings not matching up with "my" particular sense of aesthetics. I find the slower log pots eminently useful. For standard sized pots (23/24mm), Bourns makes a 10% taper called a "guitar pot" available through Mouser. At a setting of five this pot would value the same as an equivalent 30% taper pot at about three. It works! And it's worth doing. The BF/SF circuit does clip the power tubes ahead of the preamp. So altering the "perceived" volume at a given pot setting results in the same maximum volume possible. No one gets hurt. For smaller pots (13mm and 16MM) I don't have a solution. But I don't think altering the actual range of the amps original circuitry is a good option.

JM2C

[wizard333]

To each their own. It works great and sounds good, so to me, its a great option.

[JoeM]

I'm not having a problem with my older Fenders, its my DRRI with the 30% taper pot that really is touchy at the low end. wizard333s idea seems like a great solution. I never play my Fenders into the range where they're breaking up anyway.

[Jazz P Bass]

It truly is assine of Fender that they do what they do.
Above 2.5 -3 & you get breakup.
Just got off of a '93 Super Amp. (pro series)
Same thing.
WTF.

[Gaz]

I've often been plagued by pot settings not matching up with "my" particular sense of aesthetics. I find the slower log pots eminently useful. For standard sized pots (23/24mm), Bourns makes a 10% taper called a "guitar pot" available through Mouser. At a setting of five this pot would value the same as an equivalent 30% taper pot at about three. It works! And it's worth doing. The BF/SF circuit does clip the power tubes ahead of the preamp. So altering the "perceived" volume at a given pot setting results in the same maximum volume possible. No one gets hurt. For smaller pots (13mm and 16MM) I don't have a solution. But I don't think altering the actual range of the amps original circuitry is a good option.

JM2C

Do you have a link to the pots? Are you talking about the Bourns PDA24 series with the long solder tabs? I have some here and they measure 15%. I have some others that I think are the PDB series and those 10%.

The mod suggested is great, but it is really about perception of the user. I like the idea of a 10% taper since you can still have the dirt if you want it. I actually think if you are doing a Fender build from scratch and wanna keep the gain on tap, a pre-PI master volume is good alternative to clean up the amp a bit.

[Chuck H]

They are the PDB I was looking at. Perhaps more helpful is that Bourns call this taper "A2". And it's a 10%. I need to do a little more research before this recommendation though. Because Bourns does have other "musical system" pots that aren't "low torque". I much prefer a higher rotational torque for amplifiers. And I did find these by Bourns for a build once. I'll link when I have something.

[Chuck H]

Well, looking on line I see the PDA24 that you mentioned. They are indicated as a 10% taper. But if you measure 15% then 15% it is. I think these are what I used.

[Gaz]

Well, looking on line I see the PDA24 that you mentioned. They are indicated as a 10% taper. But if you measure 15% then 15% it is. I think these are what I used.

The torque thing is exactly why I was asking. I got my pots from Apex Jr. Some were PDA's and some PDB's, however the PDB's do have a high torque unlike the ones sold on Mouser and AES/CE. They are both fine pots, but the torque is a little different on both models, which bugs me. I wish I could get either the PDA's or B's in all the values I need from one damned place...

[loudthud]

I'm looking for a family of pots to use on a project. Actually, it may morf into a series of projects with several amps all needing slightly different pot values and tapers. Looking at offereings from Mouser I'm not seeing the 24mm Alpha pots, but instead offerings from the company BI technologies a part of TT electronics in Fullerton California (Hey, Fullerton's got to count for something). Link: BI Technologies Main Page . They look like Alpha parts. Anybody tried them? What bugs me about the 16mm Alpha pots is the extra small M7 bushing.

[JoeM]

I finally did the mod to my DRRI. I used a 250k pot with a 680k resistor. Other than having to deal with removing the old pot and brackets used on the PCB, the mod is simple and aided by the fact there's a wire jumper on the board that can be replaced with the series resistor. (Vibrato channel) Now, the amp's volume comes up smoothly from 1 to 4, 4 and above the volume increases faster, full volume about 7, 8 or so. So much easier to dial in the volume now, especially when I'm just at home playing.