Hi all,
Long time lurker but admittedly, not many posts. Sorry for the long post but the testing and analysis should make it easier to answer my questions.
Quite a while back, I picked up a nice Kenwood KA-88 integrated amp (100 w/chan of Class A power). I didn’t need it but it was a nice price (I don’t remember what I paid) but while testing after bringing it home, I noted some turn on issues (what I thought was popping through the speakers). That destined it to the end of my quite deep “to-do” queue and I put it aside what turned out to be a few years. It’s finally made it to the top of my queue.
With some extended testing, I found that it wasn’t popping. A more precise description is that at turn on, right after you hear the speaker protection relays kick in, you would hear crackling type noises come from the speakers. It was sharper and peakier than say a white noise kind of thing. It’s loudness would depend on where the volume control was at turn on so it could be quite loud but it would dissipate after a second or two. It was independent of which input the input selector is on or any other control. However, it was most pronounced after I pulled the amp out of storage. The more testing I did, the less noise it made. It’s to the point now where it doesn’t make the noise at all.
So, the first question is what everyone thinks is the cause. My guess would have been that it was corrosion on the contacts in the relays themselves based on the fact that it went away with repeated use. It bothers me a bit that it was affected by the volume control. I’m not sure how my surmise fits the scenario because aren’t speaker protection relays at the output of the amplifiers, not the input? If so, then the crackling noise should be independent of the volume control, no? The second question is, should I even bother with it? If repeated power cycling can eliminate it, it doesn’t seem like it would justify a major repair. Sub-question: if it is the relays and the repair is justified, how hard is it to replace the relays (or fix whatever the diagnosed cause is)? I have never really dabbled much in used equipment mostly because I haven’t had much time. Between work and other hobbies (my wife says I have too many), I haven’t much time to devote to significant repairs, let alone restorations. Light repairs including soldering are okay. Eventually, I’d like to up my game some and get into serious repairs and restorations as time permits.
Final question on a slightly adjacent topic. Just recently, I recently found a companion Kenwood KT-88 tuner from the same era (part of why I was spurred to work on the KA-88). It works fine but it’s not in as good shape aesthetically. Specifically, it has a not insignificant scratch in the Lucite (or whatever it is) plastic area covering the tuned frequency display. Had anyone had any luck polishing out such scratches and if so, how? I tried polishing compound and polishing with toothpaste (from online recommendations) and not had much luck.
That’s all for now. Thank you kindly for any advice offered
-Rocky
Long time lurker but admittedly, not many posts. Sorry for the long post but the testing and analysis should make it easier to answer my questions.
Quite a while back, I picked up a nice Kenwood KA-88 integrated amp (100 w/chan of Class A power). I didn’t need it but it was a nice price (I don’t remember what I paid) but while testing after bringing it home, I noted some turn on issues (what I thought was popping through the speakers). That destined it to the end of my quite deep “to-do” queue and I put it aside what turned out to be a few years. It’s finally made it to the top of my queue.
With some extended testing, I found that it wasn’t popping. A more precise description is that at turn on, right after you hear the speaker protection relays kick in, you would hear crackling type noises come from the speakers. It was sharper and peakier than say a white noise kind of thing. It’s loudness would depend on where the volume control was at turn on so it could be quite loud but it would dissipate after a second or two. It was independent of which input the input selector is on or any other control. However, it was most pronounced after I pulled the amp out of storage. The more testing I did, the less noise it made. It’s to the point now where it doesn’t make the noise at all.
So, the first question is what everyone thinks is the cause. My guess would have been that it was corrosion on the contacts in the relays themselves based on the fact that it went away with repeated use. It bothers me a bit that it was affected by the volume control. I’m not sure how my surmise fits the scenario because aren’t speaker protection relays at the output of the amplifiers, not the input? If so, then the crackling noise should be independent of the volume control, no? The second question is, should I even bother with it? If repeated power cycling can eliminate it, it doesn’t seem like it would justify a major repair. Sub-question: if it is the relays and the repair is justified, how hard is it to replace the relays (or fix whatever the diagnosed cause is)? I have never really dabbled much in used equipment mostly because I haven’t had much time. Between work and other hobbies (my wife says I have too many), I haven’t much time to devote to significant repairs, let alone restorations. Light repairs including soldering are okay. Eventually, I’d like to up my game some and get into serious repairs and restorations as time permits.
Final question on a slightly adjacent topic. Just recently, I recently found a companion Kenwood KT-88 tuner from the same era (part of why I was spurred to work on the KA-88). It works fine but it’s not in as good shape aesthetically. Specifically, it has a not insignificant scratch in the Lucite (or whatever it is) plastic area covering the tuned frequency display. Had anyone had any luck polishing out such scratches and if so, how? I tried polishing compound and polishing with toothpaste (from online recommendations) and not had much luck.
That’s all for now. Thank you kindly for any advice offered
-Rocky
