What might cause this amp (A23+) to go staticky on the right channel after about 15-20 minute warmup?
I swapped inputs and it stayed on the right channel, there were no previous power spikes/issues (Furman power surge/conditioner)
No protection circuit tripped just gradually built static on the right channel until it was as louder than the input music playing.
This was repeatable (let it cool and it started out fine until it warmed up) three times before deciding there was definitely a problem and took it out of service.
Lastly what might cause the problem to mysteriously disappear (all conditions same)?
Thanks, Bob
I swapped inputs and it stayed on the right channel, there were no previous power spikes/issues (Furman power surge/conditioner)
No protection circuit tripped just gradually built static on the right channel until it was as louder than the input music playing.
This was repeatable (let it cool and it started out fine until it warmed up) three times before deciding there was definitely a problem and took it out of service.
Lastly what might cause the problem to mysteriously disappear (all conditions same)?
Thanks, Bob
Thanks profi,
Would that problem induce the static gradually on warming, as in no noise just normal music from cold start then gradual increase after 10 minutes to full static after 15-20 minutes?
Turning the input pots up and down increased/decreased the static along with the music but did not act as a bad pot i’m used to where the static crackles with wiper movement.
Would that problem induce the static gradually on warming, as in no noise just normal music from cold start then gradual increase after 10 minutes to full static after 15-20 minutes?
Turning the input pots up and down increased/decreased the static along with the music but did not act as a bad pot i’m used to where the static crackles with wiper movement.
No Pavel, unfortunately I do not…….and with the problem seemingly resolved for over two weeks of daily use without a hint of issue it seems that under testing it might not show up?
It would need long time monitoring, during normal listening operation.
The pots have double elements and control both inverting and non-inverting (differential) stages. The amp basically operates in balanced input mode all the time, but in rca inputs mode it only attenuates the rca input signal and the other pot section just loads the inverting stage with 100k to keep the input offset balanced.
Your issue as described points to the input pots. More than likely you have one resistive pot element going open circuit and making the input differential stage bias fluctuate from the loading resistance changing. Do you see the woofers in your speakers moving in and out slowly with the static noise? If so, that points to the problem i described. If its only static you're hearing without fluctuating DC at the output, the wiper on one of the pots is intermittent.
Either way, you likely have a bad pot. Its common. The only other likely culprits are the switches selecting xlr/rca mode or bridge/stereo mode, but thats much less likely. I'm pretty sure its the input potentiometers. If the noise gets worse with a higher input level setting, it points towards the pot, given your source (preamp) is fine.
I always replace the xlr input jacks and pots at the same time when I'm in there, but if you only use single ended inputs, then just replace both pots. Parasound sells them for about 8 bucks a piece. They're just carbon element dual 100k log taper pots. Nothing special. I bought mine from Mouser and cherry picked the best matching/tracking pair from several pieces I ordered, which were less than 3 dollars a piece.
Your issue as described points to the input pots. More than likely you have one resistive pot element going open circuit and making the input differential stage bias fluctuate from the loading resistance changing. Do you see the woofers in your speakers moving in and out slowly with the static noise? If so, that points to the problem i described. If its only static you're hearing without fluctuating DC at the output, the wiper on one of the pots is intermittent.
Either way, you likely have a bad pot. Its common. The only other likely culprits are the switches selecting xlr/rca mode or bridge/stereo mode, but thats much less likely. I'm pretty sure its the input potentiometers. If the noise gets worse with a higher input level setting, it points towards the pot, given your source (preamp) is fine.
I always replace the xlr input jacks and pots at the same time when I'm in there, but if you only use single ended inputs, then just replace both pots. Parasound sells them for about 8 bucks a piece. They're just carbon element dual 100k log taper pots. Nothing special. I bought mine from Mouser and cherry picked the best matching/tracking pair from several pieces I ordered, which were less than 3 dollars a piece.
There’s a bit more to the story,
The problem started about a month ago and considering the amp is under warranty (for another 2 yrs) I contacted parasound…..danced around with a few emails got a RMA and sent it to one of their ‘authorized service centers’ to be checked. It struck me funny that included with the RMA email there was a disclaimer saying that if there was No Problem Found I’d have to pay a $200 ‘NPF‘ fee along with return shipping…….after going over every warranty agreement on their website and also my printed version that came with the unit I found no mention of this NPF fee but was so sure there was a problem I just ignored it and sent the unit to the service center.
About a week goes by and I get a call from the service tech saying they let it play for hours with no problem, so i asked them if they scoped it with a dummy load and he acted like he was the only dummy involved in the testin, then he tried to sell me a $500 power cord insinuating maybe my power source was the issue! I‘m rather infuriated at this point but didn’t lose my cool…..asked him if he could please dig deeper, assuring him there is a problem.
Few days later I get a invoice email from parasound asking for (you guessed it) $200 NPF fee + $65 return shipping.
Tried calling parasound to no avail (they only communicate in emails now) and after some more dancing around they flat out refused to talk to me over the phone…….parasound did offer for me to have the amp shipped straight to them from the service center for more ‘testing’ but with the same caveat that if no problem was found there would be another $200 NPF fee assessed on top of all the shipping costs!
I just went ahead and paid the first $265 ransom and told them I was not at all a satisfied customer.
The amp has been playing flawlessly for two weeks now since its return, which can mean one of only two things…….the jarring around of the shipping process ’fixed’ a loose connection, or they actually fixed it and use this NPF to help recoup some losses on the repair.
Whats your thoughts on this? I’m under the impression they know of this problem you describe and came up with this BS to limit losses.
Another part of this paranoia stems from the fact they would not let me send it to Deltronics in Chicago (another parasound authorized service center) after asking twice! They are just about as close to me as ‘Just Audio’ in Maryland who they had me send it to…….and if I would have known who they were I never would have sent it there. They are that bearded feller all over you tube peddling spit shined Sansui recievers with ‘pretty lights’ for twice or even three time what they’re worth!
thanks,
Bob
The problem started about a month ago and considering the amp is under warranty (for another 2 yrs) I contacted parasound…..danced around with a few emails got a RMA and sent it to one of their ‘authorized service centers’ to be checked. It struck me funny that included with the RMA email there was a disclaimer saying that if there was No Problem Found I’d have to pay a $200 ‘NPF‘ fee along with return shipping…….after going over every warranty agreement on their website and also my printed version that came with the unit I found no mention of this NPF fee but was so sure there was a problem I just ignored it and sent the unit to the service center.
About a week goes by and I get a call from the service tech saying they let it play for hours with no problem, so i asked them if they scoped it with a dummy load and he acted like he was the only dummy involved in the testin, then he tried to sell me a $500 power cord insinuating maybe my power source was the issue! I‘m rather infuriated at this point but didn’t lose my cool…..asked him if he could please dig deeper, assuring him there is a problem.
Few days later I get a invoice email from parasound asking for (you guessed it) $200 NPF fee + $65 return shipping.
Tried calling parasound to no avail (they only communicate in emails now) and after some more dancing around they flat out refused to talk to me over the phone…….parasound did offer for me to have the amp shipped straight to them from the service center for more ‘testing’ but with the same caveat that if no problem was found there would be another $200 NPF fee assessed on top of all the shipping costs!
I just went ahead and paid the first $265 ransom and told them I was not at all a satisfied customer.
The amp has been playing flawlessly for two weeks now since its return, which can mean one of only two things…….the jarring around of the shipping process ’fixed’ a loose connection, or they actually fixed it and use this NPF to help recoup some losses on the repair.
Whats your thoughts on this? I’m under the impression they know of this problem you describe and came up with this BS to limit losses.
Another part of this paranoia stems from the fact they would not let me send it to Deltronics in Chicago (another parasound authorized service center) after asking twice! They are just about as close to me as ‘Just Audio’ in Maryland who they had me send it to…….and if I would have known who they were I never would have sent it there. They are that bearded feller all over you tube peddling spit shined Sansui recievers with ‘pretty lights’ for twice or even three time what they’re worth!
thanks,
Bob
Would the bias fluctuations possibly result in a warmer running amp?
Because before it ran quite warm borderline hot now its just normally warm even under heavy use.
Yes, it could. Bias on the A21/A23 is high compared to other class AB amps. This was intentional to give the amp a higher percentage of class A operation in the lower power range, where it really counts.
You can adjust bias yourself, but its critical to get it close for lowest THD. You'll be looking for at least 7mV across the emitter resistors. It won't be exactly that on each resistor but an average across each channel. I wouldn't exceed 10mV, otherwise it will overheat. The amp needs to be on for at least 30 min and you need to allow a minute or two between each adjustment to get a stable bias reading. It will read almost 3 times higher on first turn on and gradually drop down during a 10 to 15 min period. Don't make large adjustments at once, just small ones inching up to the desired level. An infrared temp gun will help verify the actual balance between both channels. Aim for about 100 - 110 F on each heatsink when it's all said and done, then double check voltage drop across all emitter resistors.
You can adjust bias yourself, but its critical to get it close for lowest THD. You'll be looking for at least 7mV across the emitter resistors. It won't be exactly that on each resistor but an average across each channel. I wouldn't exceed 10mV, otherwise it will overheat. The amp needs to be on for at least 30 min and you need to allow a minute or two between each adjustment to get a stable bias reading. It will read almost 3 times higher on first turn on and gradually drop down during a 10 to 15 min period. Don't make large adjustments at once, just small ones inching up to the desired level. An infrared temp gun will help verify the actual balance between both channels. Aim for about 100 - 110 F on each heatsink when it's all said and done, then double check voltage drop across all emitter resistors.
I feel your pain with the experience you had. This isn't an easy amp to service. You need to know its quirks. They likely dropped the bias setting on both channels which will ruin the sound. I own several A21s, A23s and a JC5. They're some of the best sounding amps for what they cost.
If you want to have me look at it, PM me and I'll work it out with you. I've been a service tech for about 40 yrs and have seen this industry go down hill steadily. The old timers are all dying off and the new guys just use YT videos as their guide to everything. Its pathetic and sad.
If you want to have me look at it, PM me and I'll work it out with you. I've been a service tech for about 40 yrs and have seen this industry go down hill steadily. The old timers are all dying off and the new guys just use YT videos as their guide to everything. Its pathetic and sad.