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
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
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
Check C62 on the relay board.
Here's the Hifi engine link. http://www.hifiengine.com/manual_library/bgw/410.shtml
Here's the Hifi engine link. http://www.hifiengine.com/manual_library/bgw/410.shtml
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
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
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?
You should make sure the speaker relay actually opens when powered off too. Maybe one set of contacts is welded shut?
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.
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.
Hi Folks and Thanks, jwilhelm;
The BGW is working perfectly! I replaced C3, but this had no effect. There where only 2 other electrolytics on the board, C8 and C9. I replaced them they were beside some higher wattage resistors that showed some minor signs of heat. The relay pulls in silently now. Are these caps for coupling to the drivers or would they be called 'pre' drivers?
Thanks so much for pointing me in the right direction, jwilhelm and all. Thanks to everyone at diyaudio for the satisfaction of repairing this nice amp, and the a little more knowledge and experience!
The BGW is working perfectly! I replaced C3, but this had no effect. There where only 2 other electrolytics on the board, C8 and C9. I replaced them they were beside some higher wattage resistors that showed some minor signs of heat. The relay pulls in silently now. Are these caps for coupling to the drivers or would they be called 'pre' drivers?
Thanks so much for pointing me in the right direction, jwilhelm and all. Thanks to everyone at diyaudio for the satisfaction of repairing this nice amp, and the a little more knowledge and experience!
If it's the same VAS design as the 500, they are bypass caps that AC couple the signal from the op amp to the VAS. Without them, the AC open loop gain would be reduced. If they are not identical (out of balance) there is a hell of a turn on thump -probably a lot more than what the relay circuit was 'expecting'. If one were bad, it could even force enough voltage at the op amp output to damage it or cause an uncorrectable offset. I would think about doing the other channel as well, to avoid trouble in the future.
VAS is "voltage amplification stage". In a normal amp design, input signal gets a small current boost in the input stage, the op amp here. Next it gets a voltage boost to near output voltage in the VAS section, Q1 and Q2 here. Then it goes to the output stage for the big current boost.
I think wg_ski is correct about the ac coupling thing.
I think wg_ski is correct about the ac coupling thing.
Thanks jwilhelm and wg ski
I am literally learning something every day. My next project (yes, I'm drowning in broken stuff!);
My soundcraftsmen tg-3044-r equalizer, one channel dead. Its for my backyard system, stored in the garage and I suspect affected by the humidity.
I will start yet another thread and hope to hear from you there.
I am literally learning something every day. My next project (yes, I'm drowning in broken stuff!);
My soundcraftsmen tg-3044-r equalizer, one channel dead. Its for my backyard system, stored in the garage and I suspect affected by the humidity.
I will start yet another thread and hope to hear from you there.
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