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Just purchased a B&K ST-202 amp through craigslist for $180. Did a listen before purchasing, but unfortunately the seller did not have very nice speakers to audition with, very little bottom end. But acoustic tracks sounded very good -- detailed, warm, lots of life.


Bought the amp, got it home, connected it to the line level output of my mixer (I'm an aspiring DJ) and my JBL Studio Monitor 4406's, and started jamming. Sounded good, but I expected...well, more. I'm coming from a very midrange Kenwood from about 1995 w/ 60wpc output, so I was expecting a huge improvement, but it wasn't materializing. There was more headroom, for sure, but I thought almost certainly bass response would be dramatically improved. But I thought, well, maybe I just need to get to know the amp, etc.


Well, then after a few minutes of listening I noticed that the woofer on my right speaker was moving A LOT more than the left. Played some hip-hop to confirm, and there was a very visible difference.


At first I feared I'd damaged the drivers with the newfound wattage. To test, I swapped connections left and right on the output of the amp, and now the left channel was really moving. Then I tried disconnecting the other speaker, and with just one speaker connected, moved the connection back and forth.


Well, turns out that the "left" (there is no left and right, but for simplicity's sake I'll use those terms) channel has no "oomph" -- it's not that it's quiet, per se, and it sounds fairly decent when listened to by itself, maybe a TOUCH of distortion and a sort of weak low end, but the midrange and up volume is more or less the same as the R channel. But in terms of fullness and richness it simply pales in comparison to the R channel which has so much more output and headroom, with bass response being the most obvious and dramatic difference. MASSIVE difference in cone movement and airflow from ports, and R channel sounds sooooooo good.


I have also noticed that the "left" channel heatsink is a fair bit warmer to the touch than the right, regardless of load (i.e. nothing playing it's still warmer)


What I've checked so far:

- Tested multiple RCA cables and audio sources

- Tested different electrical outlets in room, always plugged directly into wall

- Opened case and used compressed air to remove dust, unscrewed and rescrewed connections

- Checked over boards / fuses, everything looked good / normal, no obvious signs of issues or repair of any kind, fuses all good, RCA connections looked good

- Left amp on for several hours before playing


Any ideas what the problem might be? Suggestions? I have tried calling the seller, and he appears to be avoiding my calls. I love the sound of the R channel and would like to fix the amp if it's not going to cost a fortune.
 
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