"WHAMMY" Pass DIY headphone amp guide

[NIXIE62]

I said a long time ago, Chinese rotary switch with SMD resistors is death for that Alps. Both sonically and in terms of channel balance. 🤣
I put in a 100k pot because I had a few pieces at home. That's what I use for tube devices. For Whammy it is better to take a 20k or 50k pot.

 

[mistahMax]

As a sanity check if you still have the old pot it would be worth measuring it out of circuit.

Turn it to minimum just as if it were in the amp and then turn it up a little by about the same amount of rotation you would be using when the the worst imbalance occurs. Now measure the resistance on each gang as follows.

From middle leg to one of the end legs. Note the result down.

From middle leg to other end leg. Note the result down.

From end to end. Note the result down.

Do the same for the other gang. So that is six readings. When you measure make sure your fingers are not touching the probes or pins at that will alter the result. Lets see what the imbalance is.



Make 100% sure these parts are correct in value (I think we did this but check). Differences in some of the resistor values (actual incorrect values, not tolerance) could interact with the pot and give an apparent gain difference. Unlikely but check.



Don't use a log pot 🙂 They are often terrible for channel balance. Use a linear pot and fake the log law with the addition of a single resistor if you wish which goes from wiper to ground.

@Mooly , Do you have a recommendation on a particular linear pot? I believe linear pot provides larger range at the lower volumes and I would like to try this.

I also believe that the original Alps made in Japan should not have these issues.

-Max

 

[Mooly]

Nothing to specific I'm afraid because I haven't bought any in a long time. I have found these OMEG pots to be surprisingly good though and inexpensive:

https://www.omeg.co.uk/potentiometers/unswitched/eco/eco-2-gang/

And of course ALPS.

Did I post this earlier, can't remember:

https://sound-au.com/pots.htm

Look at the headers for 'Potentiometer Tapers' and 'Changing the Law of a Pot'