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Old 20th January 2007, 12:10 AM   #1
hotscot is offline hotscot  Scotland
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Default 2 Question on Gainclone voltage issues

Believe me thanks for the help. I'm trying to educate myself and the advice has been wonderful.

I've successfully connected my transformer to the rectifier board.
The rectifier is providing plus and minus 38 V which I believe is pretty good. I'm using Brians kit.

1.My first question relates to what happens when I connect the amp board to the rectifier. When I connect the amp board the voltage drops to zero across the two points where previously it read 38 V using my meter. ie the ouputs PG+ and V+ Is this normal, is it supposed to continue reading 38V or is it an indication of something wrong? If it makes any difference I don't have a load connected.

2. If I'm sending plus and minus 38 V to each amp board isn't that actually a voltage difference of 76 V?

Thanks for any input
Alan
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Old 20th January 2007, 12:24 AM   #2
hotscot is offline hotscot  Scotland
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Default Now that I think about it..

When the amp board becomes part of the circuit it now contains a capacitor, chip etc so a simple voltage test probably won't tell me anything.
I guess what I'm asking is this...how do I test my amp with a meter after turning on the juice..or do I need a load as well?

Alan
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Old 20th January 2007, 01:34 AM   #3
Leolabs is offline Leolabs  Malaysia
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One question:Is your transformer a dual secondaries or a single secondary but with center tap(ie 3 pins)???
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Old 20th January 2007, 01:38 AM   #4
hotscot is offline hotscot  Scotland
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Default Center tap...3 pins

But I connected it as directed from Brian and the rectifier board is outputting the required plus and minus 38 V
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Old 20th January 2007, 05:56 AM   #5
Nordic is offline Nordic  South Africa
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Not sure we are talking about the same thing...

But use a multimeter on the output to test for DC offset... should be way less than 100mv or so if all went well. Short the input during the measurement...
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Old 20th January 2007, 04:18 PM   #6
CarlosT is offline CarlosT  United States
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I believe that the rectifier voltage unloaded will settle down at a lower value once a load is added (an amp with an input signal [i.e., a CD player running] and driving a speaker, pilot lamp, resistive load, etc...anything resistive sucking up some juice). For example, my rectifier board was putting out like 31V unloaded but once I hooked up a pilot lamp, it went down to like 25V. This might be the nature of unregulated PSUs...?

Now showing 0V...I dunno...I'm not a PSU guru...yet

I'm still not crazy about your setup, hotscot...but it's cool...work with what you got. I woulda rather seen you use a true dual secondaries tranny and you populate the entire recitifier board with all 8 diodes and used all AC1 and AC2 holes BLAH BLAH BLAH

Keep going I say...
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Old 20th January 2007, 04:20 PM   #7
CarlosT is offline CarlosT  United States
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Quote:
Originally posted by Nordic
...use a multimeter on the output to test for DC offset... should be way less than 100mv or so if all went well...
I don't think that hotscot got this far yet...

Please don't tell him to short anything...
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Old 20th January 2007, 04:44 PM   #8
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Quote:
Originally posted by CarlosT
I believe that the rectifier voltage unloaded will settle down at a lower value once a load is added (an amp with an input signal [i.e., a CD player running] and driving a speaker, pilot lamp, resistive load, etc...anything resistive sucking up some juice). For example, my rectifier board was putting out like 31V unloaded but once I hooked up a pilot lamp, it went down to like 25V. This might be the nature of unregulated PSUs...?
It will show such voltage drop with 10uF capacitors on rectifiers board (only). But when amp board (with 1500uF caps) is connected, no drop should be observed.
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Old 20th January 2007, 04:46 PM   #9
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Default Re: Now that I think about it..

Quote:
Originally posted by hotscot
When the amp board becomes part of the circuit it now contains a capacitor, chip etc so a simple voltage test probably won't tell me anything.
I guess what I'm asking is this...how do I test my amp with a meter after turning on the juice..or do I need a load as well?
The quick test would be measuring DC voltage on the output. If it's approx 60mV, you have pretty good chances the circuit works fine.
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Old 20th January 2007, 04:50 PM   #10
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Default Re: 2 Question on Gainclone voltage issues

Quote:
Originally posted by hotscot
1.My first question relates to what happens when I connect the amp board to the rectifier. When I connect the amp board the voltage drops to zero across the two points where previously it read 38 V using my meter. ie the ouputs PG+ and V+ Is this normal, is it supposed to continue reading 38V or is it an indication of something wrong? If it makes any difference I don't have a load connected.

2. If I'm sending plus and minus 38 V to each amp board isn't that actually a voltage difference of 76 V?
After connecting amp board the voltage should stay the same, the reading between V+ PG+ shouldn't change, same for V- PG-

The voltage between V+ and V- is indeed close to 80V.

Attached is cuirciut wiring diagram.
Attached Images
File Type: jpg lm3875 wirig diag.jpg (53.7 KB, 240 views)
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