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Quad 2805 power supply malfunction?
Quad 2805 power supply malfunction?
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Old 19th May 2019, 09:11 AM   #61
clog is online now clog  Netherlands
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Sheldon thank you again. One moment I pondered about the idea that a small piece of tape could solve my problem fast and easy. But no, I think it would an unwise move now that I've come so far and having the panels spread out for me. So I will replace the membrane and why not doing it myself after all it's DIY here. At first I will try to get the necessary parts nearby in Holland, mylar, coating and glue. As for the tensioning of the mylar. As a newb particularly the method with tape and a spring balance seems promising to me. If I can't get parts locally I will contact ER audio in Australia.
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Old 1st June 2019, 11:13 PM   #62
malthuse is offline malthuse  Canada
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Can someone please explain to me the different protection circuits the quad 2905 would have. I see two different effect. One is the speaker distorts but doesn’t shutdown and my amp protection doesn’t kick and shut it down (quad artera). The second is no sound and the amp shuts down. Are these two different causes? Is one a spark and the other too much power going to the speaker?

Thanks
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Old 2nd June 2019, 03:07 AM   #63
stokessd is offline stokessd  United States
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There are two different clamping mechanisms in any of the modern quads (63's and newer; inside they are the same). There is an overdriving clamp circuit that was originally more sophisticated with a soft clipping and then a hard clipping, but that was replaced in the later 63's (about SN30000) and newer with a set of stacked diode bridges with zeners across them. This new circuit clamps at ~7000v. In theory that is before the panels arc.

The second circuit, which is effectively identical in every modern quad, is a RF receiver that triggers a triac that shorts the input of the speaker (because screw your amp) if the circuit senses an arc. This one is triggered by bad panels and typically sounds like the speaker got quieter and is distorted.

The clipping circuit would only be active on very loud peaks. But the arc clamp can happen anytime if you have a bad panel. I can imagine that if the amp is playing a quiet passage and the clamp fires, it may not trigger the amp's shutdown circuit. But if the passage is over some current sensing threshold, then it shuts down.

Sheldon
quadesl.com
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Old 2nd June 2019, 04:28 AM   #64
malthuse is offline malthuse  Canada
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Great thanks Sheldon. If one speaker is triggering the overdrive circuit too early, ie at loud, but not too loud music, where do you think the problem is?
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Old 2nd June 2019, 12:44 PM   #65
stokessd is offline stokessd  United States
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Quote:
Originally Posted by malthuse View Post
Great thanks Sheldon. If one speaker is triggering the overdrive circuit too early, ie at loud, but not too loud music, where do you think the problem is?
Obviously it's hard to diagnose without seeing the speaker, but my money is on a bad panel. The clamp circuit is really simple (and assuming the power supply filter cap is good), there's not much to go wrong. Because it's doing the clamping, people naturally gravitate to thinking something is going wrong there. It's a classic case of shooting the messenger.

Sheldon
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Old 2nd June 2019, 02:06 PM   #66
malthuse is offline malthuse  Canada
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sorry, I’m a little slow on the uptake.

Two,circuits, clipping and clamping.
Clipping due to overdriving
Clamping due to sparking

Clamping causes distortion
Clipping causes the speaker to shutdown??? Could it also trip my amp off? Can a spark cause the speaker to shutdown?

Some background:
1) It does clip on loud but not too loud music
2) I’ve heard clamping on these speakers due to sparks and fixed the issues with failed panels. They’ve all in tip top shape now and I no longer get clamping from sparks.
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Old 4th June 2019, 12:05 AM   #67
stokessd is offline stokessd  United States
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[QUOTE=malthuse;5810239]sorry, Iím a little slow on the uptake.

Two,circuits, clipping and clamping.
Clipping due to overdriving
Clamping due to sparking

Clamping causes distortion
Clipping causes the speaker to shutdown??? Could it also trip my amp off? Can a spark cause the speaker to shutdown?
[/qoute]

Clipping only happens are very high volumes, and will make the speaker seem like a lower impedance during peaks. No idea whether that would cause your amp to shut off, but intuitively it seems like the spark clamp shorting the input would be more likely to shut off your amp.

Quote:
Some background:
1) It does clip on loud but not too loud music
2) Iíve heard clamping on these speakers due to sparks and fixed the issues with failed panels. Theyíve all in tip top shape now and I no longer get clamping from sparks.
Do you have a very large room? I can't stay near the speakers when they are loud enough to clip.

Sheldon
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Old 4th June 2019, 12:50 AM   #68
malthuse is offline malthuse  Canada
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Not really no, but I listen quite loudly. Always have. It’s definitely the clipping. I’ve heard the speaker when it clamps due to a spark and it distorts but doesn’t shutdown the amp. This only happens during big loud music. In your experience is it possible for something to fail that could cause the clipping circuit to kick in too early? Is this where that 25v capacitor comes in?
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Old 4th June 2019, 02:39 AM   #69
stokessd is offline stokessd  United States
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There could be a problem with the zener strings or rectifier diodes in the clamp circuit, such that one of the bridge rectifiers is essentially shorted out. That would make the limiter run at 2/3 of the normal level. I've not seen that behavior before personally, but anything is possible.

The service manual is on my website, if you look at the schematic, you can see the three stacked rectifier bridges with zeners in them: http://quadesl.com/modernRefs/ESL2905.pdf


Sheldon
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Old 5th June 2019, 03:48 AM   #70
bolserst is offline bolserst  United States
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Recall that the 2905 service manual has some errors in the schematic.
Corrections posted here: Parts for the Quad ESL 63

Quote:
Originally Posted by stokessd View Post
...Clipping only happens are very high volumes, and will make the speaker seem like a lower impedance during peaks. No idea whether that would cause your amp to shut off, but intuitively it seems like the spark clamp shorting the input would be more likely to shut off your amp...
When the zener string clipper activates, it effectively shorts the secondary of each of the transformers so the amplifier is being asked to drive 2.5ohm below 100Hz, dropping to around 1 ohm above 1kHz. While this is 1 ohm higher than when the SCR spark detector activates, it is still pretty brutal. The early ESL-63 clippers that operated on the primary side of the transformer were much gentler on the amplifier...dropping the impedance to 5 ohm below 100Hz and 3.5 ohm above 1kHz. Most amplifiers would handle that just fine. Makes we wonder if the newer zener clippers were intentionally made to drop the impedance lower to encourage people to NOT overdrive their speakers.
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