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Old 25th April 2003, 01:31 PM   #1
Paulr is offline Paulr  United Kingdom
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Join Date: Nov 2002
Location: S.Yorks, UK
Default Gainclone on a shoestring

Hi All,

Given my limited experience (& budget) I decided to have a go at a clone using what I had laying around & 2 sample 3886's.

So far I have one chanel built & working, loosely based on Thorstens Inverted Gainclone. Impressions on sound are useless at this point as I have only been testing on an old 4Ohm car speaker.

Cost so far has been a whopping 11.50 as all but the 1uF, 2,2uF & 1000uF caps are from the scrap bin. Including the transformer from a 600VA UPS that had gone south. A worthy sum for an amp if you ask my wife .

My main problem is that the transformer only has 1 secondary. Currently I am using 1/2 of a bridge to get + & - at 28.5V (at no load), with the the other side of the secondary tied to ground. I am pretty sure it won't drop too much under a normal amplifier load given the size of the damn thing

Is there a better way to use this transformer i.e. with 2 half bridges & still create a ground? Is it even wired correctly as it is?

Thanks in advance

Paul
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Old 25th April 2003, 06:40 PM   #2
joensd is offline joensd  Germany
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Join Date: Dec 2001
Location: Germany
Hi Paul,
you mean the "one way symmetric" from the picture?
Its not the usual way to get dual voltages and is not recommended if you still have to buy a transformer but as it was lying in your scrap bin Id say use it.
The following filtering has to be quite on a large scale to get you almost the same smooth voltage as with dual secondaries but fortunately the LM3886 has got a good PSRR value so it wont matter that much.
Mostly people go for rather small capacitors with their gainclones anyway.

If you got more caps in your scrap bin Id put them in as well to compense your "one way rectifying".

Just listen to the amp when its done. You might be happy with it like it is.

Jens
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