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Old 9th November 2015, 07:58 PM   #1
Peter S is offline Peter S  Canada
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Default BGW 410 turn on 'POP'

Hi All;
I was just about to sell a BGW 410 power amp. It has had a small 'click' as the speaker relay pulled in, for some time. On testing this amp, once more before placing the add, the 'click' has gotten worse and actual blew a diaphragm in my Cerwin-Vega PD-18.
The pop is just on one channel, and once the amp is on, there is very little DC offset. This is consumer model, RCA inputs, Speaker A/B selector, and headphone jack, but has a modular design like the BGW 750. The amp has been driven hard (run hot, may have even shut down) on occasion, it was loaned to some musician friends. Could someone direct me to any known related trouble spots. I will try to attach the schematic, included in owners manual.
Sorry, the pdf is too large to attach, but I would more than willing to email it to you, I'm at hennioriginals@gmail.com
Thanks for any help, Peter
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Old 9th November 2015, 08:19 PM   #2
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It looks like there is a DC servo. Can you monitor the output voltage before the speaker relay at startup? Maybe the amplifier isn't finished settling down from power up by the time the speaker relay engages.
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Old 9th November 2015, 08:41 PM   #3
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Check the feedback decoupling capacitors. If they are leaky, the DC offset will be too high.
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Old 9th November 2015, 09:25 PM   #4
wg_ski is offline wg_ski  United States
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It's probabaly whatever 10 cent capacitor is supposed to be responsible for slowing down that relay isn't slowing it down (enough) anymore. So the turn on pop that's always there gets through. Beginning to se a pattern?

"No! Shut them all down ! Hurry!" - C3PO
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Old 9th November 2015, 09:49 PM   #5
Peter S is offline Peter S  Canada
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I thought the relay pulled in quickly, replaced what I thought was a leaky cap on the relay board, but the pop is only on one channel. Just learned how to separate one page from a pdf. I will try attaching the amp module schematic page only. If the schematic loads, could you point me to the caps that are likely suspects? Thanks again, all
Attached Files
File Type: pdf Heat Sink Module.pdf (586.6 KB, 31 views)
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Old 9th November 2015, 09:52 PM   #6
Peter S is offline Peter S  Canada
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Well, at least I've learned how to break down a large pdf, thanks again for the help, sorry it has to be downloaded, I'll try to attach jpegs next time!
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Old 9th November 2015, 09:54 PM   #7
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Check C62 on the relay board.

Here's the Hifi engine link. http://www.hifiengine.com/manual_library/bgw/410.shtml
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Old 9th November 2015, 11:24 PM   #8
Peter S is offline Peter S  Canada
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Hi again, jwilhelm! and everyone;
Someone here gave me the link to hifiengine, regarding a schematic for my Yamaha 2200 and 2201. I am actually the one who uploaded the 410 manual to the site! I got the pdf directly from BGW, a few years ago.

Next coincidence, I found C62 (330 ufd) to be leaky yesterday. I replaced it with 1000 ufd, thinking it would slow down the relay delay time. ..Nope, relay pulled in immediately, then fluttered, then pulled in again, lots of noise. I should use a dummy load but the tweeter is blown anyway.
I replaced C 62 with the same value new (newer) cap. Relay pulls in with reasonable delay, but one channel still clicks, the other is quiet. Is there another cap that could slow down the relay pull-in time? Again, it's only one channel, what caps would you suspect in the amp module? Once a load is connected there is no serious offset IMHO, less than 10 mV. But with no load, the led VU meter was 'pegged' on that channel, only half scale on the other channel.
Thanks guys, Peter
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Old 9th November 2015, 11:31 PM   #9
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If they are both engaging and only one is noisy I would be inclined to check what the amp outputs are doing on power up. You may have a similar problem there causing the amp to settle slower than it should.

You should make sure the speaker relay actually opens when powered off too. Maybe one set of contacts is welded shut?
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Old 9th November 2015, 11:49 PM   #10
Peter S is offline Peter S  Canada
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Hi jwilhelm,
I am sure the relay is good, the noise is exactly when the relay pulls in, a second or second and a half after the power is switched on, as if a residual DC offset is is being discharged through the speaker. I suspect that more time is needed, as mentioned, for the amp to settle. But the other channel is fine.
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