Hello all, please excuse me for jumping on topics here - and I'm sure this topic has been discussed somewhere in this long thread. I built this WHAMMY amp a few years ago, and from the beginning it seems to have channel balance issue - the left channel is louder than right. How do I go about troubleshooting this?
I've been using this WHAMMY amp as a preamp to my Parasound amplifier and boy, it sounds awesome! So I would like to fix this channel balance issue - it would be great if someone can point me in the right direction. Thanks! -Max
I've been using this WHAMMY amp as a preamp to my Parasound amplifier and boy, it sounds awesome! So I would like to fix this channel balance issue - it would be great if someone can point me in the right direction. Thanks! -Max
There are only two likely causes of this. The first is an imbalance in the dual gang pot and that is really the most likely. The second is an incorrect component value.
If you link the wipers of the pot (short the middle pins one to the other) you force a mono condition that feeds identical signals to each channel. Do that and see if the imbalance remains (or not). If there is no imbalance either the pot is not great for tracking between channels or possibly R39 or R40 are an incorrect value.
If there is still an imbalance then check R2 and R3 and R5 and R7 for being correct. Also check R12 and R8 and R1 and R4. Just look for them being the correct value, don't remove them to test them, they won't be faulty (99.99 % not faulty 😉)
If you link the wipers of the pot (short the middle pins one to the other) you force a mono condition that feeds identical signals to each channel. Do that and see if the imbalance remains (or not). If there is no imbalance either the pot is not great for tracking between channels or possibly R39 or R40 are an incorrect value.
If there is still an imbalance then check R2 and R3 and R5 and R7 for being correct. Also check R12 and R8 and R1 and R4. Just look for them being the correct value, don't remove them to test them, they won't be faulty (99.99 % not faulty 😉)
Although I agree with the above possibilities, I am wondering if there ever is a situation where one or more of the opto-couplers are working properly. They are a bit of a new idea to me and I would like to know if they play into any possible volume problems.
Hi @Mooly and others, thanks for the suggestions, I have not shorted the pins on the pot but I measured the resistance and for sure, there is some imbalance between L and R - for example, I'm reading 226ohms vs 211ohms about 1/4 turn - at 0, it's 1.6ohm vs 0.4ohms. Is there a way to compensate for this imbalance in the pot somehow? Otherwise, I'll have to order another one hoping the new one will be better.
R39 and R40 are 2.2118Kohms and 2.2179Kohms respectively.
Also, I'm using 10K pot but this one is out of stock at Parts-Express. Would it be okay to use 20K or 100Kohms? -Max
R39 and R40 are 2.2118Kohms and 2.2179Kohms respectively.
Also, I'm using 10K pot but this one is out of stock at Parts-Express. Would it be okay to use 20K or 100Kohms? -Max
The schematic I have says 25K to 100K. I've used various things in there, and they have all been fine. I've also used some really high quality pots, like the Khozmo ones or the Audio Note pot from Parts Connexion, which is quite a bit cheaper. (They also have the ALPS pots.) This HPA is so good that it is absolutely worth spending a little extra for a great pot. It definitely improves the sound.
Measuring resistance isn't a reliable check surprisingly (and its not always accurate when done in circuit anyway) because it is the ratio of the two gangs that matters rather than absolute values.
To get an audible difference implies a large imbalance is happening somewhere. Just link the pins and test.
Another very good test if you have not got a scope and generator is to apply a low DC voltage to both inputs (say a 1.5 volt battery) and measure the DC voltage at the pot wiper which should be identical for both channels. Measure between the wipers and rotate the pot and you should always see zero volts DC if both track identically. Any voltage that appears is due to imbalance.
Any value from 10k to 100k will work but 10 or 20k are probably preferred. A lower value does load the source more but any modern kit has no issues with those values.
Linear pots tend to track better than log and its dead easy to fake a log law with the addition of one resistor.
See 'changing the law of a pot'
https://sound-au.com/pots.htm
https://www.ebay.com/itm/234034577366
I use this. It sounds great and the channel balance is impeccable. They come in various values from 10k to 250k.
I use this. It sounds great and the channel balance is impeccable. They come in various values from 10k to 250k.
... that does look good, especially at that price. I also like the split wiper contacts, for lowering the contact resistance. Nice.
There is also another one, which is sold like "ALPS RH2702". There are two problems with them, there is a lot of resistance to rotation and they crackle for a while until they work out. They sound just as great, and the balance is perfect. I use them on other devices, they replaced the ALPS RK27. Increased resistance to rotation is not a problem, if the knob is large. The fourth pin is for loudness control, performed at half-track (15% resistance). I don't use it, and it doesn't affect normal use.
https://www.ebay.com/itm/115257900615
The previous one has a 7mm thread, this one has a 9mm thread. And the Alps RK27 has an 8mm thread. 🙄
https://www.ebay.com/itm/115257900615
The previous one has a 7mm thread, this one has a 9mm thread. And the Alps RK27 has an 8mm thread. 🙄
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I wonder if the stepped EIZZ pot is actually SMD or just detents. I like their selector switches but don't know about the pots. TKD also makes some fine pots. Yup there are many choices, but quality is always important.
As stated above, small errors of a few ohms in pot balance will make absolutely no difference. A few ohms plus or minus in a 25K track isn't the problem.
As stated above, small errors of a few ohms in pot balance will make absolutely no difference. A few ohms plus or minus in a 25K track isn't the problem.
Some EIZZs I've seen on ebay have classic TH resistors inside. I don't think it can get any better than these SMD versions, but I could be wrong. More expensive and bigger definitely.
For the SMD ones that I gave links to, I can say that they sound better and cleaner than the original Alps RK27 (bought from RS Components).
For the SMD ones that I gave links to, I can say that they sound better and cleaner than the original Alps RK27 (bought from RS Components).
And just this, since I built both versions, the Whammy with the original Toshiba mosfets sounds brighter than with the IRF610/9610.
Hello again everyone, Thanks for the help with my Whammy, I still love it to this day. However, something happened recently. I was listening to music on my desktop and the sound cut out and the LED turned off. I removed 220uf 35v because they seemed to be the culprit as they looked bulbous. I installed 220uf 50v and plugged headphones in and tested it. At max volume I can hear music! But only on the Right ear cup....I turned it off and I can hear music on both ear cups.....what in the world? I got confused and to prevent further soldering and the like I figured I'd ask the forum what could be the problem?
If the problem is in both channels, that does suggest a problem with the power supply. Though the op-amp is also shared between the channels, so you might try replacing that. I doubt that's the problem, but it could conceivably have been damaged when the power supply flamed out.
PS Probably the first step, then, would be to re-test the power supply as suggested in the build guide.
The question is difficult, it can be anything. It must be opened and everything must be inspected and checked.
I do this to myself constantly when buying a new product. Lid comes off and I look at every tiny thing. This can lead to trouble folks, even with the best of intentions for people like me. In your case however, you really don't have a choice as to whether or not to open it up and take some measurements. As stated above, when both channels produce the same trouble, the power supply is a good place to start since it is in common with both channels.
So I opened it, sorry for the delay in doing that. I was able to get the meter out and check and it said -10 or -17 something like that with the amp turned on. I wasn't getting +17V and on the other check I was only getting -10v. So, it seems like it's a PSU problem? What parts exactly do I need to change?