Interesting I came across this on Acoustica when modding naim power amps, I didn't think I will be taking apart 9 naim 135's not least because its just another can pop worms but I like the fact it can make a difference in a number of areas, so I have ordered some Panasonic FR 100uf 100v (The larger I can fit and the rails are +-89V.
Yeah add another variable before the issue is solved! Now suppose the issue is just caused by old age (and questionable cap quality) so simply dried out filter caps as often. Then the suggestion to use parallel fresh large value caps with crocodile clips to test if the issue becomes less was not a crazy idea. Those large cans should have been tested/replaced on day 1. Suppose this is the case then all the work and lost time was useless. It then also has nothing to do with PE.
IMHO 100 µF 100V caps in a +/- 90V rails device is too tight as you don't know what happens at power and power off.
IMHO 100 µF 100V caps in a +/- 90V rails device is too tight as you don't know what happens at power and power off.
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I hear you, stage one is the rewiring of the GND's as noted in Andrews note. With the chassis earthed the RCA GND connected to the chassis via a 0.01uf ceramic there is virtually no hum, its just the noise level when on I need to drop by a few db. So I will add in the decoupling caps suggested and take measurements before any other changes, agreed.
BTW, I don't need or want to have the signal GND connected to earth as every other unit is only connected signal GND to signal GND apart from the BluRay player which is tied to earth as well for the signal
Interesting point about the spike's on and off but the main card are 2x10,000uf 100v on both sides, will the transistors hold charge or encourage greater 'spikes' locally ?
BTW, I don't need or want to have the signal GND connected to earth as every other unit is only connected signal GND to signal GND apart from the BluRay player which is tied to earth as well for the signal
Interesting point about the spike's on and off but the main card are 2x10,000uf 100v on both sides, will the transistors hold charge or encourage greater 'spikes' locally ?
You add parts that were not there on another spot so the effects at power on/off are unknown.
We learned to choose caps rated for double the rail voltage but that is overdone. Power on/off phenomena are just like short circuit phenomena interesting and reality. Old ICs used to have latch up sometimes at power on which was also interesting but bloody annoying. I think it was in a Proton device where I actually saw double the rail voltage at one rail at power on.
So the hum is solved!? Good! If it hisses it would not be the first time that transistors have become noisy. Or oscillation as others have pointed out.
BTW it is V, mV, A, mA, dB, uF, L, N, PE etc. Hurts the eyes and gives doubt regarding technical abilities.
We learned to choose caps rated for double the rail voltage but that is overdone. Power on/off phenomena are just like short circuit phenomena interesting and reality. Old ICs used to have latch up sometimes at power on which was also interesting but bloody annoying. I think it was in a Proton device where I actually saw double the rail voltage at one rail at power on.
So the hum is solved!? Good! If it hisses it would not be the first time that transistors have become noisy. Or oscillation as others have pointed out.
BTW it is V, mV, A, mA, dB, uF, L, N, PE etc. Hurts the eyes and gives doubt regarding technical abilities.
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PS, my knowledge of audio gear as a user is quite extensive, I bought my first proper turntable in 1983 ( a Linn Sondek) and have listened to a lot of kit over the years, I still have 105db Horns, Vitavox drivers and valve amps I bought in the 90's. Most of my DIY and 'knowledge' has developed and is still very limited TBH. But I do like experimenting and I am quite vigorous about A-B listening and taking notes
It took many years of study, perseverance and many hours gaining practical knowledge but I can tell 100% for sure that the oscillation definitely will stop when disconnecting R29.
Still adding the input cap can be interesting. It has the bonus that the 7812 still has input voltage.
Still adding the input cap can be interesting. It has the bonus that the 7812 still has input voltage.
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Well, not having much luck....
I replaced all the small electrolytics and one film highlighted in green circles added the 0.47uF and a 0.1uF around 7812 and the diode. Removed the two power supply resistors to the VU meter and then powered up. All came on and then the amp turned itself off. I couldn't see anything obvious and tried again this time nothing. I stripped the units and checked and double checked then found a split on the track, the board is secured under the heat sink and then left unsupported out of the unit, near where the solder by the 22k resistor there was a crack and not contact (red X) I have desoldered and checked everything visually and can't see any damage. Is there anything I might check before powering up again as I think it was unhappy running with no signal out and 22k resistor in place
I replaced all the small electrolytics and one film highlighted in green circles added the 0.47uF and a 0.1uF around 7812 and the diode. Removed the two power supply resistors to the VU meter and then powered up. All came on and then the amp turned itself off. I couldn't see anything obvious and tried again this time nothing. I stripped the units and checked and double checked then found a split on the track, the board is secured under the heat sink and then left unsupported out of the unit, near where the solder by the 22k resistor there was a crack and not contact (red X) I have desoldered and checked everything visually and can't see any damage. Is there anything I might check before powering up again as I think it was unhappy running with no signal out and 22k resistor in place
After checking all looked okay and rebuilt again and retested it was fine. Good news it's the quietest yet. Very nearly okay regarding noise, a test using REW again shows the improvement. Green trace before the small cap changes, additional decoupling and a few signal resistors swapped out for metal film. Pink trace the latest variant. Black face the silent BPSP 500's
Ive yet to read my Oscilloscope manual so haven't tested for any oscillation or added to the 27pF ceramics (that did measure 27pF)
I was wondering what other resistors might be worth changing to 1% metal film ? Given the variable 1K resistor is set and I am unsure how to set any bias or make any adjustments I wondered what other carbon resistors I might change ?
Ive yet to read my Oscilloscope manual so haven't tested for any oscillation or added to the 27pF ceramics (that did measure 27pF)
I was wondering what other resistors might be worth changing to 1% metal film ? Given the variable 1K resistor is set and I am unsure how to set any bias or make any adjustments I wondered what other carbon resistors I might change ?
The beauty of applying several changes is that you never can tell what caused improvement. For me as someone that likes solving such issues quite dissatisfying as feedback is lacking/invalid. That won’t improve the quality of my advices.
Good that it is silent though.
Good that it is silent though.
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That's a fair point, but I did want to swap out the smaller electrolytics at the same time. I do suspect the decoupling has helped. It's time consuming to strip remove the board and then rebuild afterwards and that encourages me to do more than one thing at a time !
It is a mediocre way of troubleshooting and not giving anything in return to those that use their time to help out. One way trafic really. So ciao!
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I have some 100R 1% metal film resistors would it be okay to swap the carbon resistors here to see if this helps reduce the noise further, the later 500's are all metal film resistors ?
Well, I did swap out the carbon 100R resistors for some Ohmite WH small wire-wound and good news it sounds quieter and measures quieter. So I think I'll look at popping in a few other replacement resistors with either metal film or wire-wound
Pink before and green with 4 100R wire wound 1%
Pink before and green with 4 100R wire wound 1%
Have you done a loop back test with your sound card? make sure you have a grip on what your card is really capable of - you Dong want to go chasing your tail.
I’d be surprised if changing the resistors you indicate reduces the noise significantly.
I’d be surprised if changing the resistors you indicate reduces the noise significantly.