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Old 29th October 2012, 09:35 AM   #591
AndrewT is offline AndrewT  Scotland
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I did the mod on the DCB1,
Oh s....
just realised I need to go and look again at the driver circuit. I think I am on the wrong planet ... again !
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Old 29th October 2012, 09:48 AM   #592
AndrewT is offline AndrewT  Scotland
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I am trying to attach a pic of three different ways I modified the components & layout for the MyRefC. Don't have the schematics to hand since it was done about 18months ago. Never finished the PCBs after I heard the first one. Discrete wins every time.
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Last edited by AndrewT; 29th October 2012 at 09:52 AM.
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Old 29th October 2012, 10:11 AM   #593
AndrewT is offline AndrewT  Scotland
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finally got Irfanview downloaded to my new PC.
Sorry about the dust, just picked them up off the shelf.
Note the two Zeners for R19 on the left.
All the drivers have a Zener in the circuit to increase the triggering voltage.
The right shows a link below and slightly to the right of C16. This is an extra resistor that comes under the PCB from R23
Note the series Zener and diode across the relay coil for faster release.

How I wish when editing that the Forum software did not lose attachments. I have had to attach again during each edit.
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File Type: jpg MyRefC relay1.jpg (393.0 KB, 148 views)
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Last edited by AndrewT; 29th October 2012 at 10:21 AM.
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Old 29th October 2012, 10:28 AM   #594
bcmbob is offline bcmbob  United States
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Wow, Big differences from stock build. I hope someone with the right software can/will lay it out in a form to display the mod within the circuit. As usual, you have passed my pay grade.
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File Type: jpg 20121029_061713.jpg (179.5 KB, 128 views)
File Type: jpg MyRefC relay1a.jpg (141.4 KB, 123 views)
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Old 29th October 2012, 10:32 AM   #595
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Marra,

I like Andrew's idea,it is a good approach for more reliable triggering. But if you are looking for a quick diagnostic check and your relay appears to trigger, then drop out again, this might be a quick check.

R14 is 470 ohm in the BOM. Using the 470, the simulation suggests that the relay should trigger at about 1 second, then drop to 14 to 15 V once engaged (assuming 22V transformer in my simulation). If the problem is that your relay doesn't stay engaged at 14 to 15 V, then you can try reducing the value of R14. Try 220 or 330 ohms and that will increase the engaged voltage by a few volts without risking the DC protection. Actually, your DC protection may take a little longer to actuate, but it should still work.

Jac
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Old 29th October 2012, 10:52 AM   #596
bcmbob is offline bcmbob  United States
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Jac, That's the same advice I got from Siva when I had a similar problem in a V1.3 build. It worked.
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Old 29th October 2012, 01:17 PM   #597
Marra is offline Marra  United Kingdom
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Thanks for the pointers guys.I will check things out this evening.
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Old 29th October 2012, 04:48 PM   #598
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Yes, the smaller 220/330 ohm resistor works reliably with smaller transformers. I used one of those values (can't remember which) in my builds and I have NEVER had a relay fail to close or open at the appropriate time. My amps have been turned on and off every day for a more than a year.

My older MyRef's have the original 470 ohm value with 22v transformers, and they have worked reliably for more than two years.

If the amp is constructed properly, there should be no need to modify the protection circuit or cobble additional parts into it. A slightly smaller (than 470) value R14 probably will not hurt anything.

If your relay clicks repeatedly or not at all, you most likely have other problems.

Peace,
Tom E
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Old 29th October 2012, 07:49 PM   #599
Marra is offline Marra  United Kingdom
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I checked things out again this evening and have the following readings.
Good channel :-across main caps +- 28.5v C102 14.67v C202 -14.38v
across the relay diode 14.98v R14 is dropping approx 6v
With the input shorted ther is 1.5mv.
Bad channel :- across main caps + 28.25v - 28.34v C102 14.32v C202 -14.67v
Whilst checking these the relay starts clicking on and off before staying off;no led and I end up with 11v on the input and 26v on the output. I am at a loss as what to check!
Going to a friends tomorrow who has a good camera system I'll get him to take some high res pics to post maybe someone will spot something I've missed.
Forgot to say things are run from dual 20v secondaries just to check it out.
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Old 29th October 2012, 07:51 PM   #600
AndrewT is offline AndrewT  Scotland
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that sounds like DC detection and intermittent triggering of the relay to protect the speaker output.
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