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Old 28th July 2010, 10:02 AM   #1
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Default DAR PLUS E-I transformer dead How to work out voltage?

Hi,

I have a Pioneer Powered Subwoofer HTP-200SWP with a Pioneer SA-50 65w plate amp.

The E-I transformer internal (one-time) thermal fuse has blown. I want to get a replacement transformer but I don't know the output voltage. Input is 240v. There are no markings apart from "DAR PLUS 9941" Tried searching on it but no specs came up.

is there a way to work out what the output voltage is?

cheers,
col.
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Old 28th July 2010, 11:32 AM   #2
AndrewT is offline AndrewT  Scotland
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look at the voltage rating of the various caps in the amplifier.
Compare the claimed output power into the specified load to other amplifiers of similar capability and see how their supply rail voltages compare to your capacitor voltage ratings.

Eg,
if the smoothing caps and the decoupling electrolytics are all 50V rated then you know that the transformer cannot be 35+35Vac . It must be significantly less.
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Old 28th July 2010, 02:20 PM   #3
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I don't know if my math is right, but from 65W into 4 ohms (assuming there, you should check!), I get about +/-22V DC, which comes out to a transformer of +/-16V AC secondaries. Given that you should probably pick the next higher voltage just to be sure you don't get early clipping, and assuming the capacitors are at least 35V rated, I would go for a 18V secondaries transformer.
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Last edited by Redshift187; 28th July 2010 at 02:28 PM.
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Old 28th July 2010, 10:05 PM   #4
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The amp is only one channel. Main power supply cap is chemi-con 63v 4700uf. The transformer only has one secondary. It has 2 x 6.5", 6ohm drivers in parallel. 3ohm load.

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Last edited by col; 28th July 2010 at 10:08 PM.
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Old 28th July 2010, 10:24 PM   #5
AndrewT is offline AndrewT  Scotland
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the absolute maximum voltage rating of the transformer feeding a 63V smoothing cap is 40Vac.
It is more likely to be 30 or 35Vac.

A +-28Vdc amplifier operating from a 20+20Vac transformer would push out ~35W into 8r0. Your 40Vac single secondary should be able to reach this maximum if designed for maximum power efficiency.
A 3ohm load could demand ~90W to 100W from the same 40Vac transformer.
That is maybe why it failed.
90W into 3ohm is a demanding load for a 1pr output stage. It may have taken out the output transistors and a low power transformer may have then overheated rather than blow a fuse.

You will need to check the amplifier on a temporary supply to see if this amp & transformer are worth repairing.
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Last edited by AndrewT; 28th July 2010 at 10:43 PM.
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Old 28th July 2010, 10:30 PM   #6
col is offline col  Australia
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OK, thanks for that. I will have a dig through the transformer box and see if I can rig something up temporarily to test the output stage. If it works will buy a new transformer.

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Old 29th July 2010, 10:42 AM   #7
col is offline col  Australia
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I hooked it up to a 36Vac small 10VA transformer and it is working. I'm considering buying an 80VA 36Vac Toroidal:

Altronics - Your One Stop Audio Visual & Electronics Supplier

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Old 29th July 2010, 10:45 AM   #8
AndrewT is offline AndrewT  Scotland
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36Vac should give about 80W into 3r0. Using an 80VA transformer is at the bottom limit of what is advisable. It should work but ensure it runs cool.
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Old 29th July 2010, 11:00 AM   #9
col is offline col  Australia
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Quote:
Originally Posted by AndrewT View Post
36Vac should give about 80W into 3r0. Using an 80VA transformer is at the bottom limit of what is advisable. It should work but ensure it runs cool.
They have a 160VA one for an extra $10, would that be more suitable?

Altronics - Your One Stop Audio Visual & Electronics Supplier

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Old 29th July 2010, 11:16 AM   #10
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does the bigger one fit the space available?
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