Smack channel imbalance. [resolved]

[loudneighbor]

I got a Smack amp from a friend of mine and hooked it up tonight, I functions but there is a noticeable channel imbalance, the left channel is ever so slightly lower than the right. I swapped the tubes, no change, i have tried a different cable same issue. My other amp sounds fine so it's not my source. I read a few other threads with similar issues but for different amps. Aside from this issue it sounds very smooth I could get used to it.

Any suggestions would be appreciated.

[Paul Birkeland]

Are the switches on the impedance selector boards inside the amp set to the same settings?

[loudneighbor]

Yes they are, and an update, I got the imbalance with two different headphones. Tried my HD800s and it has all but disappeared. It still is there but my brain doesn't flag it instantly and demand i find a balance knob somewhere.

Also is there any documentation on this kit? I'd like to read up on what the different settings for the output switches do.

I've played with the switches if I set it to sw1 hi sw2 Lo there is no imbalance, if i flip 1 to low and 2 to hi or both to hi i get the imbalance.

[Paul Birkeland]

Is that good channel balance with SW1 HI and SW2 LO on both channels?  The BAL/UNBAL will also create a channel imbalance if they aren't the same between sides.

Your friend hopefully has the build manual for you.  If not, they are available for purchase from us. 

[loudneighbor]

 Yes the settings are the same for both channels. I don't believe he does have the paperwork anymore.

[Paul Birkeland]

Thankfully the impedance switching board tells you what transformer terminal number each wire needs to go to, so you can double check that wiring without the manual. 

-PB

[loudneighbor]

All The wires match the corresponding taps on the transformers, I reflowed some lees than beautiful solder joints on that board, but still have the same results, If that second switch is in the lo position it sounds fine, once it goes to hi in any combo the imbalance comes back. I Know enough of electronics to do some very basic trouble shooting and not kill myself.

I do have to say while the HD800s are pretty underpowered for my liking the Monolith M570 sound absolutely amazing.

[Paul Joppa]

...  If that second switch is in the lo position it sounds fine, once it goes to hi in any combo the imbalance comes back.  ...

That second switch selects whether the two secondaries are in series or in parallel, and it also shorts out the resistors. If one of the resistors is not shorted (or not soldered) when switched to high impedance, it will be in series, reducing HP output by several dB. If you have some good contact cleaner, I'd give that a shot. In any case, look closely at the switch and resistor soldering.

Posting late at night, so take the above with a grain of salt  :^)

[loudneighbor]

Cleaned the switch with some deoxit and the problem has vanished!!!!! Thank you kindly.

[Paul Joppa]

I'm glad to hear that! Enjoy ... :^)