avalon Posted November 12, 2019 Posted November 12, 2019 I have a Marantz PM7200 that I have had since new. Recently, the transformer hum (common with this amp, apparently) seems to have gotten louder. So much so, that I can hear it between tracks from my listening position 3.5 metres away. I took the lid off to check the source - definitely seems to be coming from the transformer. Plugged the amp into another power point away from everything else... same hum. Does anyone have experience with this amp, or thoughts on a solution? Repair? Replace the transformer? Put up with it? Cheers
avalon Posted November 12, 2019 Author Posted November 12, 2019 6 minutes ago, Muon N' said: Is there DC on the mains? Crikey... I wouldn't know. How do I ascertain that?
Guest Muon N' Posted November 12, 2019 Posted November 12, 2019 (edited) 5 minutes ago, avalon said: Crikey... I wouldn't know. How do I ascertain that? I have never tested for it, but I had a double C Core transformer in a piece of kit that buzzed from the transformer and it went away after i installed a DC Blocker in it, if you can borrow a CD Blocker (I know @mwhouston ) Mark makes these, you could see if that is the cause. BUT, you say it is a common issue with these amps? Edited November 12, 2019 by Muon N'
avalon Posted November 12, 2019 Author Posted November 12, 2019 2 minutes ago, Muon N' said: I have never tested for it, but I had a double C Core transformer in a piece of kit that buzzed from the transformer and it went away after i installed a DC Blocker in it, if you can borrow a CD blocker (I know @mwhouston ) Mark makes these, you could see if that is the cause. BUT, you say it is a common issue with these amps? Okay, thanks mate. It is a common issue with these amps, but the reports I've read suggest that you have to virtually put your ear to the amp to hear it.
Guest Muon N' Posted November 12, 2019 Posted November 12, 2019 (edited) 1 hour ago, avalon said: Okay, thanks mate. It is a common issue with these amps, but the reports I've read suggest that you have to virtually put your ear to the amp to hear it. All I'm suggesting is that DC on that mains could be the issue. But without ruling out every other possibility first I couldn't say it is this for sure. The EI transformer in my valve amp has a buzz ever since they corrected the high mains voltage in my local area, was always 250vac all the time, now 237v to 241v, but with the change this buzzing has come, I suspect it is DC on the mains, but I can't be sire until I remove that possibility and see if that is the cause. Edit: funny enough, the DC causing the double C Core that was fixed with a DC blocker was previous to this, that was in a valve phono stage I had but now I don't use, was thinking about transplanting the internal blocker into the CD player I now use as a source. Apparently this issue is more of a problem with toroidal transformers. Edited November 12, 2019 by Muon N'
Guest Muon N' Posted November 12, 2019 Posted November 12, 2019 Does the level of the transformer buzz or hum vary at different times of the day, day to day? Or is it same level all the time regardless? If the former it could be DC on the mains, if the later it may be the amp itself.
avalon Posted November 12, 2019 Author Posted November 12, 2019 10 minutes ago, Muon N' said: Does the level of the transformer buzz or hum vary at different times of the day, day to day? Or is it same level all the time regardless? If the former it could be DC on the mains, if the later it may be the amp itself. It does seem to be more prominent at night time. Not sure whether this is just because there is less ambient noise at that time of day. I will pay more attention.
mwhouston Posted November 12, 2019 Posted November 12, 2019 8 hours ago, Muon N' said: All I'm suggesting is that DC on that mains could be the issue. But without ruling out every other possibility first I couldn't say it is this for sure. The EI transformer in my valve amp has a buzz ever since they corrected the high mains voltage in my local area, was always 250vac all the time, now 237v to 241v, but with the change this buzzing has come, I suspect it is DC on the mains, but I can't be sire until I remove that possibility and see if that is the cause. Edit: funny enough, the DC causing the double C Core that was fixed with a DC blocker was previous to this, that was in a valve phono stage I had but now I don't use, was thinking about transplanting the internal blocker into the CD player I now use as a source. Apparently this issue is more of a problem with toroidal transformers. Generally with toroidals because there is not a lot of metal in their cores. It ‘tends to saturate very easily with only a few miliamps of DC. Initially I never promised my DC blockers would stop Tranni hum but on about half a dozen cases it has. It even stopped hum for a member’s power conditioner. Without the hard sell, money back of it doesn’t do what you think it should. Out of a few dozen sold one was returned which re-sold the next day with an additional order. Win-win.
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