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Old 14th March 2010, 11:25 PM   #1
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Default Buy new or reuse transformer

Hi, I used to be a member here a long time ago but chickened out of building a gainclone... but now parts are on order. Connectors from parts connextion, kit from audiosector, and now comes the transformer issue.

I have an old Pioneer amp which the GC will replace. It has an STK4141 IC. The amp has some connector issues and volume control issues. I'm thinking on reusing the transformer in it. It measures 27.05v (120.1V on the mains measured) on each of the secondaries and after the rectifier in it, it measures 35V and holds very steady when the amp is playing at 10-15 watts (just a guess, no UV meter) or just sitting idle.

Speakers are PSB Alpha B1's which are 6 Ohm nominal impedance.

All the charts in the datasheet put 35V rectified on the limit so inclined to think I should be looking at another chunk of change to get a new transformer. I don't plan to push this hard as these are my computer speakers essentially and in a small room. I'd like to save a little money on this if I can as I'm in Canada and shipping a transformer will tend on the expensive side.

Should I order a new 18V or 22V transformer or just use this one? Will the added voltage be an issue with noise / sound quality. Any risks assuming I take all precautions (IEC plugs, Fuses before and after transformer stage, large heatsink, etc). Is it worth the 60-80 dollars to get a new transformer is what I am getting at?

I just spent about an hour or so looking to try and find this issue already without posting, but so much to wade through since the inception of the GC years ago. I've read threads and links on the PSU side of this and from my electrical understanding the chip should be fine at this voltage.

Thanks in advance
Keith
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Old 15th March 2010, 01:30 AM   #2
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I would go with a new one to be sure. You wouldnt wanna blow it. I used a 300VA 2x22v toriod, cost £38 delivered here in UK. Search for a local supply, you may be able to collect.
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Old 16th March 2010, 06:00 AM   #3
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Quote:
Originally Posted by kwakeham View Post
All the charts in the datasheet put 35V rectified on the limit so inclined to think I should be looking at another chunk of change to get a new transformer. I don't plan to push this hard as these are my computer speakers essentially and in a small room. I'd like to save a little money on this if I can as I'm in Canada and shipping a transformer will tend on the expensive side.
I wouldn't bother with a new transformer if you already have one. The data sheet specifies +/-40V DC as maximum, but I've heard about guys using even higher voltages and chips not failing.

I've been using GC with batteries for almost a year supplying +/-39V (amp permanently on), so your transformer is more than fine
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Old 16th March 2010, 06:53 PM   #4
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Thanks, This should save me a little bit of cash. It might not look as nice as a new torid but so long as I do go frying chips I'll be happy.

Cheers
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Old 16th March 2010, 07:32 PM   #5
faiyaza is offline faiyaza  United States
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Quote:
Originally Posted by Peter Daniel View Post
I've been using GC with batteries for almost a year supplying +/-39V (amp permanently on), so your transformer is more than fine


Almost a year on batteries? That's really surprising. I'm wondering how green these little wonders are if they can go a year always on with batteries. What's the idle current of the GC? Better yet, how big are your batteries ;-)?

Thanks!

F
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Old 17th March 2010, 04:07 PM   #6
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The batteries were being constantly charged, except when I played music.

On idle, they can last few days ( 6x 12V. 7.2Ah ea.)
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