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Old 8th August 2006, 10:14 PM   #1
matt09 is offline matt09  United Kingdom
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Default Transformers...

Hello,

I found the following transformers avalable cheap for 5, however I dont know how many amps on each of the two taps the amps take?

I can get a 2 x 100 va transformer at 18 volts ac
or 2 x 20 volts ac at 6-7 amps.

Which is best out fo those 2?

What is really need to know is how many amps does a gain clone need? bare in mind I doubt I will drive it past 40 watts per channel.
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Old 8th August 2006, 10:29 PM   #2
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I hardly know anything about Gainclones, but AFAIK, the amperage required depends on the load impedance. If you know it, I suspect you'd get better answers if you post the info.

For fun:
The <20W 41hz Amp6 Tripath-based amp I'm building comes with a recommendation of 15V 50-100VAC transformers. [edit]The transformers you mention[/edit] might make sense for a 40W amp, based on my ignorant guesstimate.
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Old 8th August 2006, 10:31 PM   #3
Sherman is offline Sherman  United States
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I just put together another GC and three different power supplies to try out. First was a toroid 20V, 4A, second was another toroid 24V 5A and third was dual EI transformers 24V 5A.

Both higher powered trafos sounded better to me than the 20V 4A toroid. The dual EI setup won the day because it fit in the box I wanted to use for my PS! The difference in sound between that setup and the similar toroid was minimal at best and neither was "better".

All that to basically say more available current seems to sound better to my ears.
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Old 8th August 2006, 10:38 PM   #4
matt09 is offline matt09  United Kingdom
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hello,

thanks for your info, i forgot to mention i will be driving a 4 ohm load on each channel!

it looks like that 20 volt one rectified to 30 is ideal then. However how much current will be needed for 4 ohm loads on each amp?
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Old 9th August 2006, 08:09 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
20Vac might just give you 29Vdc unloaded, falling to 26 to 27Vdc loaded.

If you can source some enamelled wire you can add secondary windings to convert the transformer to 2*22Vac or even 2*24Vac.

Scientific Wire Co. (SWC) are good suppliers.
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Old 9th August 2006, 01:55 PM   #6
Sherman is offline Sherman  United States
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Quote:
Originally posted by matt09
hello,

thanks for your info, i forgot to mention i will be driving a 4 ohm load on each channel!

it looks like that 20 volt one rectified to 30 is ideal then. However how much current will be needed for 4 ohm loads on each amp?
Four ohms is a tougher load for an amp than eight ohms and more current is better than less. If you are looking at getting 30-35 WPC I would think 200 to 250 VA would be OK.

I've built GC with as little as 120 VA and think they sound fine at low to medium volumes.
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Old 10th August 2006, 12:31 PM   #7
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edited:

The 2x20V is much more powerful ? (2x20Vx6.5A=250VA)
It should be twice the weight.

The 18V 100VA may be slightly more suitable voltage for 4ohm eg with LM3886 (check the specs). But 100VA is marginal for 2x40W.

At that price I would go dual mono (assuming you can buy 2 trafos the same).

PS: If these are toroids and there are more available I'm sure other members would be keen to get hold of them.
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Old 10th August 2006, 03:56 PM   #8
cpemma is offline cpemma  United Kingdom
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You can download an Overture Design spreadsheet from NS that covers most "Gainclone" chips, and input your DC supply voltage, speaker impedance, etc. A warning will pop up if you exceed any safety margins. Very useful tool.
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Old 10th August 2006, 04:30 PM   #9
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Am I just slow in finally noticing the 2nd tab in that design guide where it shows a graph of power dissipation vs. output power? How long has this been there? Interesting. Not sure it is of much use to me .

-SL
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Old 10th August 2006, 05:08 PM   #10
cpemma is offline cpemma  United Kingdom
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Could be new? I've just got 'Calculations', 'Empty' & 'Empty2' tabs

Yup, new to ver.1.5, I had 1.4
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