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Old 22nd September 2004, 05:06 PM   #1
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Default CG Distortion Issue

Hello all... village idiot here.

I was looking for a low-cost, high performance amp for my system and came across the Gain Clone. With all the positive feedback I read I felt I couldn't pass it up.

So, I ordered the boards from Brian Bell (BrianGT) and gave myself a weekend project. Fast forward to the finished product, and I've found I have an issue with some unwanted intermittent distortion bleeding into the output signal... a steady "pulse," almost if there was a switch being turned on and off.

I thought it may be a grounding issue, so I went back and checked everything out and it seems to be correct. Another thought is that I may have incorrectly wired one of the xformer leads. Perhaps it's something that your experienced eye could spot immediately. Me, on the other hand, have very little electronic engineering experience and I'm learning as I go along (if that wasnít obvious).

I've attached a couple of diagrams outlining exactly how the amp is wired. One is a PS schematic (in this post) and the other is the GC board schematic (in the following post). Iím hoping that itís an obvious and easy fix. BTW, I used an AVEL Y236750 330VA 25V+25V TT.

Any help is greatly appreciated!!!!

Cheers,
Hat
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Old 22nd September 2004, 05:07 PM   #2
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Default GC Distortion Issue (pt. 2)

Here is the GC boards attachment.

Danke!
Hat
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Old 22nd September 2004, 07:50 PM   #3
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it loks like the output from PS out is wrong I have older PS pcb but on mine the outputs are grouped as V- first 2 and second 2 are power + (this is for -ve supply) thiss is marked PG-.

the next set of 2 is PG+ but this is really the -ve of the plus power supply lastly the V+ is the positive of =ve supply

these 2 supplies are seperated until the amp board

look at the small cap each side has 2 connectors

Each amp board going from left to right V+ as the first and second PG+ these match exactly to PS board
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Old 22nd September 2004, 10:09 PM   #4
moamps is offline moamps  Croatia
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better grounding scheme, IMO:
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Old 22nd September 2004, 10:17 PM   #5
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I may go to Texas just for saying this (it has happened before), but here it goes:

Try the amp without earth, disconnect the cable from the plug.
Anyway, it's better to use it with a 0.1uf cap parallel with a 100R resistor, not directly to star ground as you have.

And you should rearrange those grounds, as moamps says.
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Old 27th September 2004, 07:54 PM   #6
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I wanted to thank all of you for your replys. Unfortunately, after taking the suggestions and trying them, and variations of them, on my gc, i've found that i'm still plagued by this distortion problem.

i've gone as far as replacing the amp chips and still, nothing.

i'm considering starting the boards from scratch again and see if i have the same problem.

if anyone has any other suggestions before i begin again, it'd be greatly appreciated.

best,
hat
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Old 27th September 2004, 08:11 PM   #7
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Are the chips getting hot? -- Thermal protection could be kicking in if you haven't out heatsink on the chips.

Steve
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Old 27th September 2004, 08:22 PM   #8
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actually, they are. but i've mounted the chips to a 7" x 1.5" x .5" heatsink (it runs along the length of the chassis. i used artic silver when mounting them as well. i would think they would be pretty well protected, but i could be wrong...
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Old 27th September 2004, 08:41 PM   #9
Nuuk is offline Nuuk  United Kingdom
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Quote:
actually, they are. but i've mounted the chips to a 7" x 1.5" x .5" heatsink (it runs along the length of the chassis. i used artic silver when mounting them as well. i would think they would be pretty well protected, but i could be wrong...
Just checking - are you using insulated chips or are you insulating the non-insulated versions from the heatsink?
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Old 27th September 2004, 08:46 PM   #10
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I'm using the insulated version (LM3875TF)
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