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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Arcam AVP-600 humming
Arcam AVP-600 humming
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Old 17th October 2017, 02:12 PM   #1
GringoAudio is offline GringoAudio  Canada
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Default Arcam AVP-600 humming

I have a terrible hum, likely 60 Hz, on Zone 2 of my Arcam pre-amp with all Sources. It is also quite loud when FM is the Source on Zone 1. It is mildly audible on Zone 1 with all Sources but I can live with it.
I have ordered schematics. Anyone have any initial ideas on what it might be? Power supply leakage some how I guess. But with 4 layer boards it may be hard to work on this unit myself. I will open it up soon and poke around inside with a scope.
I bought it a couple years ago on EBay as refurbished but just started using it. Apparently a lot of Arcams from this period were flawed. One DIY fellow replaced 400 components in an AVR300!
Thanks.
Greg

Last edited by GringoAudio; 17th October 2017 at 02:20 PM.
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Old 17th October 2017, 10:39 PM   #2
MAAC0 is offline MAAC0  Portugal
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Does it hum with no cables and inputs grounded ? Check the PSU capacitors they could be suffering from the "capacitor plague"
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Old 18th October 2017, 01:36 AM   #3
GringoAudio is offline GringoAudio  Canada
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Interesting observation… If I leave it on all day the major hum in Zone 2 fades to the level of the quiet hum in Zone 1 by the time I get home from work. I unplugged all the sources etc and it still hums.
Do these clues help? ��
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Old 18th October 2017, 02:51 AM   #4
GringoAudio is offline GringoAudio  Canada
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AVP-700 I meant ...
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Old 19th October 2017, 03:50 AM   #5
GringoAudio is offline GringoAudio  Canada
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Hooked scope up to speaker and also rca prior to it entering power amp for Zone2. Nasty dirty noise with a 120 hz spike and noisy crap between spikes. So clearly the power supply. After the diode rectification and before the filter capacitor the double hump waveform is a 120 Hz DC wave. So that is where the 120 Hz is clearly coming from. The filter capacitor must be pooched. I will now open the box and put the scope to various points on the power supply. Seems to be a pretty wimpy 13v DC supply as it only has a 220 microF 25 volt cap.
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Old 19th October 2017, 05:28 AM   #6
GringoAudio is offline GringoAudio  Canada
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So .... there are four power supplies each complete with 4 diode rectifiers and filter capacitors(with a variety of values up to 1000mF) on the main board and one complete power supply on the so-called 'power supply board'. And it's hard to reach a probe to the DC outputs where ripple might be occurring on all five power supplies. Hmmmm.... harder than I thought! Which power supply is the culprit?

Last edited by GringoAudio; 19th October 2017 at 05:30 AM.
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Old 19th October 2017, 04:36 PM   #7
GringoAudio is offline GringoAudio  Canada
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I work with a talented electronics designer. And I studied EE for awhile and can analyze the circuit as well. We are going over the design of this Arcam. They should be called Arcane.
So weird to have 5 and 12 volt power supplies distributed all over the place with un-rectified AC running across various boards. Noise potential galore. I understand modularity but this is ridiculous. And a bunch of noisy zener diode regulators beside 5 volt chips when there are proper 5 volt regulators on the other side of the board. Just too lazy to figure out how to rout a properly regulated 5 volts over to the 74xxx series chips.
It is like different teams were assigned to different boards with no oversight to integrate the overall design. Even the design on individual boards seems to have been done ad hoc.
I completely do not respect Arcam anymore. The power of brand has sucked me in again. Much like with my poorly designed 2004 Ducati Multistrada. Again a product with a poor overall vision designed by disparate teams who kluged the various subsystems together at the end.
Is there no one with any Arcam repair experience out there? Tonight I will see if I can track done the ripple to one of the 5 power supplies.
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Old 20th October 2017, 05:16 AM   #8
GringoAudio is offline GringoAudio  Canada
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So there is a 1.5 millivolt noise that is a periodic hash of 100ghz spikes modulated by a slower wave of 20 MegHz an another at 120 Hz on the pos and gnd of the output RCAs on both Zones.
The main supply that sends 13 volts DC around the unit had a huge ripple of 1 volt. That was the supply with only 220 mF on it. I started there and upped the capacitance to reduce the ripple to negligible. Didn't help the output noise. The ripply 13 volt gets regulated to 12 volts and 5 volts in about 20 places throughout the unit so I guess the ripple gets rejected by the regulators. Seems crappy though.
Had to pull my old Hafler Pre out to listen to music. It sounds perfectly fine. Fantastic even but it has no modern features ...
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Old 20th October 2017, 02:27 PM   #9
GringoAudio is offline GringoAudio  Canada
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0.15 volts not 1.5 mV noise. The high frequency spikes must be digital related. THIS MIGHT BE BEYOND ME. I've read the digital section goes on these units. Lots of complaints online.
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Old 20th October 2017, 04:54 PM   #10
GringoAudio is offline GringoAudio  Canada
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100mHz spikes on a varying 20mHz wave form all modulate at 120Hz. Doh.
Anyway just RF crap I guess. But the voltage is high at .2 Volts so it manifests itself as a pretty loud noise floor with a 120Hz hum as well.
More probing around tonight after work.
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