5E3 Volume linear pots?

[cminor9]

One thing about the 5E3 circuit that drives me nuts is that the volume pot doesn't do anything below about 8 o'clock. As you turn it up, nothing happens, then all of the sudden, after about 8 o'clock. you get volume. I know that you'd normally use audio tapers for volume, but I also understand that the 5E3's volume controls work a little differently than most amps. I figure the pot is providing so much resistance at 8 o'clock and below that the voltage is just being shunted to ground (or through the other channel's volume pot if it's turned up.) Wouldn't a linear ramp-up on the volume pots cure this somewhat?

Found almost what I was looking for here: http://music-electronics-forum.com/s...ead.php?t=1049 but not specifically. Anyone have any thoughts on this? Believe it or not, there are times that I'd appreciate *less* volume than the 5E3 gives me at it's lowest setting.

Or is my build just jacked up? My understanding is that this is just a characteristic of the circuit itself, but feel free to correct a wrong assumption on my part.

Or should I just play my 5E3 later in the evening after 9 o'clock?

*ducks*

[Bruce / Mission Amps]

...

Or is my build just jacked up? My understanding is that this is just a characteristic of the circuit itself, but feel free to correct a wrong assumption on my part. ...
*ducks*

I don't think I ever heard this complaint before so my vote is: you've made the wrong assumption and it is jacked up.

[cminor9]

Thanks for the quick reply!

I don't think I ever heard this complaint before so my vote is: you've made the wrong assumption and it is jacked up.

Seriously?

Truthfully, I could live with it as-is, but 1) the volume weirdness bothers me so my curiosity won't let me leave it alone, and 2) in trying to "fix" it I might learn something.

So, I wonder what could be causing this? Not getting any other symptoms of problems like hum, squeal, oscillations, etc. Bad pots? Bad grounds? I am at a loss, because the amp sounds great so I don't think there are any parasitic oscillations or anything like that unless my ears (and those of my bandmates) are jacked up too.

[Bruce / Mission Amps]

"Seriously?" No.
OK I might have been a little hard sounding there for the little bit of fun... actually it sounds like the same complaint everyone has about the goofy way Fender wired those pots and even when using a heavily tapered audio pot, it still is very sensitive.
Does the volume just suddenly go from nothing at "off" to about 1/3 volume with another 1/8 turn of the pot and at between 9:00 and 10:00 it sounds like it is just about full clean output?
If so that is what happens with the classic tweed volume controls and modern made "audio" taper pots that are available.

I've switched over to the newest CTS pots that MOJO sells and they seem slightly better as far as taper.

[tubeswell]

You might have better results with a 2M Linear pot that has been tapered with a 1M resistor from the wiper to the ground.

Or you could see if a 1M linear pot with a 500k tapering resistor would be enough to hold the signal up.

In my humble experience quite a few modern audio taper pots are crap (as Bruce as inferred).

FWIW I did a spreadsheet with plots a year or so back when I was trying to assess the values of different combination of pot tapers for a mod I was doing at the time. The tapers that I measured from 'audio taper' pots on some of the plots have a noticeable 'two-line curve', whereas I have concluded that the eminently more reliable method of getting a good log taper is using a linear pot with the tapering resistor from wiper to ground (or wiper to input for antilog taper). If I could load up an excel spreadsheet, you could see what I am talking about

[teemuk]

The tapers that I measured from 'audio taper' pots on some of the plots have a noticeable 'two-line curve'...

Yes. That's due the common practice of making cheap log pots using resitive strips that have a "dual-resistivity coating". See link: http://www.jaycar.com.au/images_uploaded/potprimr.pdf

[cminor9]

Thanks, guys!

Bruce, you freaked me out, glad you were kidding My amp works pretty close to what you described. I thought I read that somewhere, that this is how these work but I wanted someone here to confirm that. I trust people here more than some random page from a google search. I thought it horribly shoddy that a product would get shipped out the door with the controls working like that, so its interesting to see you state that this is a result of modern pots with the old circuit. That makes a lot more sense than "that's just how it is", and is more reassuring than thinking my amp has a problem. Good info.

tubeswell, I might try that. That makes sense, I never thought of that. In very nontechnical terms, that would essentially force the signal through the pot instead of letting it go to ground when the pot is turned down low, thus giving me back the lower range of the pot, right?

Speaking of cheap pots, I have CTS pots in this amp. Although people speak highly of them, I am not impressed. I am no engineer, but there is something that bugs me about plastic shafts. Seems *really* cheap to me. Pots have been frustrating me as of late, actually -- trying to order online it's either CTS (or cheaper) or $15 pots from Allesandro (not ready to spend nearly $50 for three pots). I found some sealed noname pots on Antique Electronic Supply that I put into a guitar with good results, but there weren't any 1M pots there. I think I might try the ones from MOJO, like Bruce talked about, for my next project or when these plastic shafts get buggered.

[Paul P]

I believe the "Potentiometers by Alessandro for Amps, Alessandro's military
spec, carbon potentiometers" at Antique Electronic Supply are wrongly
described. These are PEC (Precision Electronic Components) pots made in
Canada, MIL spec. Here's the datasheet :

http://www.precisionelectronics.com/...tyle%20RV4.pdf

You can buy these from Digi-key for 9.00 $US each for linear and 11.44 $US
each for log tapers :

http://dkc3.digikey.com/PDF/T082/P1843.pdf

I have these in my amp and they seem pretty good, the best I was able to
find.

Paul P

[tubeswell]

Thanks, guys!

tubeswell, I might try that. That makes sense, I never thought of that. In very nontechnical terms, that would essentially force the signal through the pot instead of letting it go to ground when the pot is turned down low, thus giving me back the lower range of the pot, right?

Yep the resistor in parallel lowers the range of the pot.

[cminor9]

Man, digikey was one of the first places I looked, but sometimes I have trouble finding stuff there (too many search options). Thanks for leading me right to it. I knew I could find good pots with having to pay the Allessandro surcharge. I think I'll get some next time I have too hit up digikey for some parts. Thanks, Paul P!