Different brands of potentiometers...sounds different???

[sebastian]

Hallo!

I tried to compare some potentiometers used in old marshall (a superbass from '78) and 80's (a 4010 JCM800) with a classic modern Alpha taiwan (24mm,solder lugs,for 8mm mounting hole). I try this because the sound came out from an old Marshall amp is ALWAYS different than a handwired amp built with the same transformer,same brands of resistors ande same tubes.I compare old and newer Marshall pots with modern Alpha and these sound to my ears much linear and "with scooped mids" than the sound of old and 80's marshall pots (more midrange,more low mids,more brilliant highs,that made the amp sounds like a "real marshall" !!!!) .
I also tried some days ago,some others Alpha pot,24mm but with 3/8 mounting hole,and these have another different sound!!
The difference that I hear between all these types of potentiometers are REAL and not subtle,but very audible (expecially if I compare an old marshall pot with a modern Tyco electronics from RS components) .Anyone has hear some differences ???

Regards

Sebastiano

[drz400]

Hallo!

I t.Anyone has hear some differences ???

Regards

Sebastiano

I have thought the same thing in the past but did spectrum and frequency tests on a Audio Precision test station and we found no difference. What I did find is that Marshall was not consistant in their choice of Audio vs Linear and that the pots can easily have a 20% variance in value and in taper. Once I matched the pot values within 2% and matched the resistance of getting the same numbers the was no difference picked up by spectrum or frequency sweeps. I did manage to make a plexi 50 which I A/B'd to a firends bone dry stock original and neither owner could tell a difference (great players too) I used Heyboer Iron and Large diameter Alpha shaft pots (CE)

[jjman]

I changed the Vib channel volume pot on my DR to a push-pull of the same value. Now the 2 channels have different volumes when set on the same number (below ~5.) Previously they were close. Different taper.

[sebastian]

I changed the Vib channel volume pot on my DR to a push-pull of the same value. Now the 2 channels have different volumes when set on the same number (below ~5.) Previously they were close. Different taper.

Yes this is right,but the difference that I hear is not a difference in volume(tweaking the volume level a bit postitive and a bit neegative) but a consistent difference in sound spectrum

[Richie]

Check some of the wah pedal mod guys forums, and see what they think about pots and the effect it has on the wah pedal. I know this is a bit different, but is also still along the same lines.

[jjman]

I changed the Vib channel volume pot on my DR to a push-pull of the same value. Now the 2 channels have different volumes when set on the same number (below ~5.) Previously they were close. Different taper.

Yes this is right,but the difference that I hear is not a difference in volume(tweaking the volume level a bit postitive and a bit neegative) but a consistent difference in sound spectrum

Yes but a different set of tapers could result in a change in "tone." For example, if the Treble pot is tapered a little "faster" and/or the Mid a little "slower" (at the same "settings") it may sound like the sound spectrum changed becoming brighter, while the overall perceived "volume" did not change.

However, it would be interesting if pots had their own frequency response. I'm thinking they should be pretty flat in the limited audio spectrum of a guitar amp ?

[Lonely Raven]

I'm no expert, but that's my thoughts exactly. I test each and every pot I install, both for total resistance and whatever resistance at 12 O'clock. Even in the same batch they vary (sometimes wildly). If I want to repeat knob settings from one amp to another, I make sure they measure the same, especially at 12 Oclock which is where I typically start my knob dialing and go up or down from there.

This is independant of apparent volume of course.

[drz400]

One thing to make sure is that you compare apples to apples.
You could also try and parrallel stacked pots.

Carbon Deposited as a carbon composition ink on an insulating (usually a phenolic resin) body Most common material, especially for cheap to average quality pots. Has a reasonable life, and noise level is quite acceptable in most cases. (DC should not be allowed to flow through any pot used for audio control) 0.1 to 0.5W

Cermet Ceramic/metal composite, using a metallic resistance element on a ceramic substrate High quality trimpots, and some conventional panel mount types (not very common). Low noise, and high stability. Relatively limited life (200 operations typical for trimpots) 0.25 to 2W
(or more)

Conductive Plastic Special impregnated plastic material with well controlled resistance characteristics High quality (audiophile and professional) pots, both rotary and linear (slide). Excellent life, low noise and very good mechanical feel 0.25 to 0.5W

Wire wound Insulating former, with resistance wire wound around it, and bound with adhesive to prevent movement High power and almost indefinite life. Resistance is "granular", with discrete small steps rather than a completely smooth transition from one resistance winding to the next. Low noise, usually a rough mechanical feel.