Good evening (here) to all,
I’have two GFA 535ii’s, bi-amplificating my Tannoy’s. They are both perfectly working in terms of audio output quality but only one of them has a problem that I could not solve in any way.
The Power supply transformers of this one are audibly vibrating. There is no additional hum in the audio output signal but the chassis acts as a resonance box and when there is no sound in the room I distincly perceive its 50 Hz noise.
All electric parameters seems to be ok. The current absorbtion (signal inputs shorted) is the same, 360 mA, for both amplifier. The Transformers output Vac and the power supply board output Vdc are in line with the service manual. The Bias s ok for value and stability.
I tried removing the external metal (mu metal ?) band of the transformers with a little improvement. I placed a foam layer between transformers’ bodies and the chassis but this amplifier remains noticeably noisier than the other.
Has some of You solved a similar case ? I suspect that its transformer have been slightly damaged in the past (i bought them second hand).
Can someone give some advice ? Could someone, in case, supply me with couple of ‘new’ Adcom 535 Mk2 transformers ?
Thanks in advance to all for any help.
I’have two GFA 535ii’s, bi-amplificating my Tannoy’s. They are both perfectly working in terms of audio output quality but only one of them has a problem that I could not solve in any way.
The Power supply transformers of this one are audibly vibrating. There is no additional hum in the audio output signal but the chassis acts as a resonance box and when there is no sound in the room I distincly perceive its 50 Hz noise.
All electric parameters seems to be ok. The current absorbtion (signal inputs shorted) is the same, 360 mA, for both amplifier. The Transformers output Vac and the power supply board output Vdc are in line with the service manual. The Bias s ok for value and stability.
I tried removing the external metal (mu metal ?) band of the transformers with a little improvement. I placed a foam layer between transformers’ bodies and the chassis but this amplifier remains noticeably noisier than the other.
Has some of You solved a similar case ? I suspect that its transformer have been slightly damaged in the past (i bought them second hand).
Can someone give some advice ? Could someone, in case, supply me with couple of ‘new’ Adcom 535 Mk2 transformers ?
Thanks in advance to all for any help.
Adcom used cheap parts in general, so I don't think it's from past damage.
I've bought several used Adcom amps (5200 and 5400), some of which made more transformer noise than others. For one of mine which coupled noisily with the chassis (like yours?), I've separated the TX from the chassis by an inch, which helped a bit. But the 5200 and 5400 used toroidal transformers (unlike the 535, which uses two EI type) which are a bit more prone to hum.
I also made a DC blocker to stop some TX growling, but I don't think that's your problem.
I've bought several used Adcom amps (5200 and 5400), some of which made more transformer noise than others. For one of mine which coupled noisily with the chassis (like yours?), I've separated the TX from the chassis by an inch, which helped a bit. But the 5200 and 5400 used toroidal transformers (unlike the 535, which uses two EI type) which are a bit more prone to hum.
I also made a DC blocker to stop some TX growling, but I don't think that's your problem.
Check your power supply caps to see if they are bad or leaking. The transformer might be working hard to keep them charged due to age or a slight short within the caps. If you disconnect the output leads from the caps(tap off the ends) and turn on the amp does the transformer still buzz? If it does then it is a mechanical vibration issue due to mounting problems.
Thank you all for Your useful information and suggestions.
For my part, I decided to do the 'queen' test and, after verifying that the noise continued, even if slightly attenuated, even with the transformers unconnected and that the rectifier and leveling stages of the two amplifiers absorbed the same current, I replaced the transformers of the noisy amplifier with those of the other example that I already owned.
The noise disappeared almost completely!
At this point I found a US seller on the bay offering a pair of N.O.S. tx and I bought them. Let's hope the new Transformers, who are on their way, will behaved ok. I will keep you informed.
Thanks again
For my part, I decided to do the 'queen' test and, after verifying that the noise continued, even if slightly attenuated, even with the transformers unconnected and that the rectifier and leveling stages of the two amplifiers absorbed the same current, I replaced the transformers of the noisy amplifier with those of the other example that I already owned.
The noise disappeared almost completely!
At this point I found a US seller on the bay offering a pair of N.O.S. tx and I bought them. Let's hope the new Transformers, who are on their way, will behaved ok. I will keep you informed.
Thanks again