Hi all,
I just bought a KSA80 that according to its former owner, had intermittent bursts of popping sound (crackling, static like sound) in one channel. I took the thing all apart and reflowed every solder joint. Plus I replaced every plastic TO220 MJF15030/15031 power transistor I can find, including the actual power drivers. I put it back together, adjusted the bias and played it for almost 3 hours before a burst of popping sound came and then went. Does anyone have any hints where I should look at?
Thanks!
UPDATE -- I just got done replacing all the power supply caps with 100V 105C 40,000uF caps and all the board mounted 100V 470uF with 100V 1000uF ROE caps and the DC cap with Mundorf 10uF cap. The one channel still exhibits popping and crackling. What should I be looking at now? Any hints?
I just bought a KSA80 that according to its former owner, had intermittent bursts of popping sound (crackling, static like sound) in one channel. I took the thing all apart and reflowed every solder joint. Plus I replaced every plastic TO220 MJF15030/15031 power transistor I can find, including the actual power drivers. I put it back together, adjusted the bias and played it for almost 3 hours before a burst of popping sound came and then went. Does anyone have any hints where I should look at?
Thanks!
UPDATE -- I just got done replacing all the power supply caps with 100V 105C 40,000uF caps and all the board mounted 100V 470uF with 100V 1000uF ROE caps and the DC cap with Mundorf 10uF cap. The one channel still exhibits popping and crackling. What should I be looking at now? Any hints?
Last edited:
Are you sure it's not snap, crackle and pop?😛
Any multiconnectors on the pc board? Clean the contacts, how old are the pc board electrolytics ? Change them all if thier old, or it could be a bad device , try freeze mist on each one in turn while listening on a cheap full range speaker.
Any multiconnectors on the pc board? Clean the contacts, how old are the pc board electrolytics ? Change them all if thier old, or it could be a bad device , try freeze mist on each one in turn while listening on a cheap full range speaker.
I have a KSA80 that developed a DC offset after being on for anywhere from 5m to 3 hours. the following is from Krell technical on the possible cause:
With regards to your DC problem, if you have already replaced all of the capacitors on both the driver boards in the unit in question then you might look more closely at the nylon (hard plastic) hardware on these same driver boards. We find over time that this gets hard and brittle and that the connections get compromised and it can sometimes contribute to increased DC. Check also the capacitors on the protection board on the rear panel of the unit as well.
With regards to your DC problem, if you have already replaced all of the capacitors on both the driver boards in the unit in question then you might look more closely at the nylon (hard plastic) hardware on these same driver boards. We find over time that this gets hard and brittle and that the connections get compromised and it can sometimes contribute to increased DC. Check also the capacitors on the protection board on the rear panel of the unit as well.
@Dr H -- thanks for the input.
I have had the unit on couple more times, each about 3 hours per session and the noise did not come back. The first burst lasted maybe a couple minutes. Currently the DC offset readings are about 5mV. Does the above correlate to what you observed on your unit?
I have had the unit on couple more times, each about 3 hours per session and the noise did not come back. The first burst lasted maybe a couple minutes. Currently the DC offset readings are about 5mV. Does the above correlate to what you observed on your unit?
In my case, the DC came through briefly and then the relays kicked in to protect the speaker. No crackles, just a bzzz, clack (relay).
It,s a good time to replace the power supply caps as well considering the age. My Synder amps (Krells production manager at one time) own design went almost 15 years before the same conditions you describe started in one channel. Turned out one of the big computer caps started to nuke internally.
I replaced all 4 and alls well
Regards
David
I replaced all 4 and alls well
Regards
David
@avwerk, what was the noise like in your amp when it was acting up. Was it a steady condition or did it come and go? How often did it happen?
What caps did you end up buying and where did you source them? I imagine they are quite expensive if one wants to buy good stuff.
What caps did you end up buying and where did you source them? I imagine they are quite expensive if one wants to buy good stuff.
It was similiar to what you described. What you need to do is spend the money amd buy new power supply caps.
Call Steve at Apex since he has the best prices if the voltage is the same or greater than what you have.
Your unlikely to find the same MF as what you have, but you can increase it a little without to much penalty.
I,m not saying this is Your problem but if your going to keep it and fix it regardless, this procedure comes with the territory even if something else is wrong.
Regards
David
Call Steve at Apex since he has the best prices if the voltage is the same or greater than what you have.
Your unlikely to find the same MF as what you have, but you can increase it a little without to much penalty.
I,m not saying this is Your problem but if your going to keep it and fix it regardless, this procedure comes with the territory even if something else is wrong.
Regards
David
@AVWERK, thanks for the advice. I am going to talk to Steve at Apex.
@AVWERK or @Dr. H, do any of you know the power supply cap ratings (uF, V and maybe even size)? I just put the whole thing back together so was trying to avoid to take it apart...
@AVWERK or @Dr. H, do any of you know the power supply cap ratings (uF, V and maybe even size)? I just put the whole thing back together so was trying to avoid to take it apart...
@Dr. H -- thanks. Where did you buy your caps. My contact at Apex does not have something this large in capacitance at this voltage level.
I have seen this brand Kendeil (or something like that) advertising large caps on eBay. Are those caps good quality?
I have seen this brand Kendeil (or something like that) advertising large caps on eBay. Are those caps good quality?
I think Mouser.com; I got the 40,000 at 75V (IIRC). the line voltages are around 40V on those caps.
UPDATE -- I just got done replacing all the power supply caps with 100V 105C 40,000uF caps and all the board mounted 100V 470uF with 100V 1000uF ROE caps and the DC cap with Mundorf 10uF cap. The one channel still exhibits popping and crackling. What should I be looking at now? Any hints?
My KSA-250 has the same problem. but no pops, just a very faint crackly sound when cold. once it warms up it goes away. I suspect a input stage transistor!
I think I did all the key ones, all the bulk output supply caps, the input section power supply caps on board and the big 10uF cap on board. Nothing else in the signal path except the small mica caps left.
Mine does the sound after it warms up and it has pops and crackle. Initially I thought it was my Martin Logan arcing but I verified by switching speakers and sources and etc that it was the power amp. Any thoughts on how you are going to solve your issue? Are you thinking of replacing the input transistors (I assume you have to replace the in matched pairs)?
Why not cool them with freeze spray or freon base aerosol first before using the shotgun approach. It's a thermal problem, so an abrupt change in temp. will find most semi. culprits.
It may not actually be the input transistors but other(s) that may not require matching.
Edit: I should add that using hydrocarbon based aerosol is not a good idea in a powered amplifier - don't try it
It may not actually be the input transistors but other(s) that may not require matching.
Edit: I should add that using hydrocarbon based aerosol is not a good idea in a powered amplifier - don't try it
Last edited:
Why not cool them with freeze spray or freon base aerosol first before using the shotgun approach. It's a thermal problem, so an abrupt change in temp. will find most semi. culprits.
It may not actually be the input transistors but other(s) that may not require matching.
Edit: I should add that using hydrocarbon based aerosol is not a good idea in a powered amplifier - don't try it
@Ian, sorry for a dumb question, I bought some R134a based freeze spray. Is there a reason that would not be prudent to use, given your comments? Care to expand a bit? Thanks!
Hi all,
An update -- I tried freeze spray and could not find conclusive evidence so I started poking around the board. When the popping started, the DC offset went from 1mV to 35mV. I measured all around the input stages and could not find a smoking gun in the input stages. When I got to the MOSFET differential stage, I touched the drain of one of the diff pair, the noise went away and the DC offset was able to be re-adjusted to 1mV. The noise has not returned after another hour or so. Question is -- should I replace the MOSFETs (VP210N5 and VN210N5) or was that just an indication of something else wrong in the circuit? Can they be sourced or substituted with better types? Thanks in advance!
An update -- I tried freeze spray and could not find conclusive evidence so I started poking around the board. When the popping started, the DC offset went from 1mV to 35mV. I measured all around the input stages and could not find a smoking gun in the input stages. When I got to the MOSFET differential stage, I touched the drain of one of the diff pair, the noise went away and the DC offset was able to be re-adjusted to 1mV. The noise has not returned after another hour or so. Question is -- should I replace the MOSFETs (VP210N5 and VN210N5) or was that just an indication of something else wrong in the circuit? Can they be sourced or substituted with better types? Thanks in advance!
- Status
- Not open for further replies.