Hello,
I just finished constructing a k8084 preamplifier kit. I was delighted when I completed it. I plugged it into a tube amplifier kit I built a few weeks ago and it works…sort of.
The left channel works correctly. The left channel works much better than the tube based preamp and tone control kit I built and was using. I just think solid state does a better job as a preamp than a tube can. The whole reason I bought this kit was to replace the tube based preamp kit I was using.
When the preamp only worked on the left channel I made the following checks.
- I switched the outputs from the k8084 at the preamp. No Change. Left Channel works.
- I switched the outputs on the amplifier side to eliminate the possibility of the cable. No Change. Left Channel works.
- I switched the inputs on the preamp. No Change, left channel works.
- I checked the input signal level at the input cable. Signal level at about 100mv on left and right. Seemed ok to me.
- I disconnected the preamp from the transformer and checked the rca input jacks. It seemed fine at first but then I noticed that the signal on the right side is shorted to ground. I checked the solder joints and could find no problem.
- I desoldered the input jack from the board and checked the solder points for short to ground. No Short. I also checked to make sure the resistance measurements for the left side were identical to the right side. It seemed there was no problem on the board. So, I checked the jack and sure enough it still read short from the signal to the ground. Annoyed, I grabbed a couple of single rca input pairs salvaged from an old television. I soldered them in. Then I hooked the kit back up to the transformer turned it on and tried again.
- This time I am able to achieve sound from both sides of the preamplifier. However, there is an extreme imbalance and the left side plays much louder than the right side.
- I checked the input jacks for identical readings at the jack and all connection points from the jack. No difference.
- I’ve checked every component from the input jack to the volume pot on both the left and right channel and found no difference. I referenced every component to both the signal input point and the common ground.
- I have not verified if the volume pot taper differs from one side to the other.
- The next step after the volume pot is IC1. I have no way to verify paths as they take a seperate route through that IC and I don’t have the schematic for the IC anway.
I will test the pot taper tomorrow.
Do you have any suggestions for what could be wrong with this preamplifier kit? Should I return it since I have already discovered one bad component?
Thanks,
Jeremy Hedlind