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Old 12th July 2012, 04:45 AM   #1
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Question Anyone here understand volt-amps?

I hate to admit it, but itís something I donít have a firm grasp of. I bought a 2.1 Yuanjing amp kit. I think itís 28 X 2 and 68 X 1. I want to use a toroidal transformer for power.

I donít have much info on the amp, I want to use the right transformer. I would like at least 26 volts, that's the max the amp is rated for.
Hereís the amp Yuanjing



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Old 12th July 2012, 07:22 AM   #2
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Quote:
Originally Posted by JohnDeaux View Post
I hate to admit it, but itís something I donít have a firm grasp of. I bought a 2.1 Yuanjing amp kit. I think itís 28 X 2 and 68 X 1. I want to use a toroidal transformer for power.

I donít have much info on the amp, I want to use the right transformer. I would like at least 26 volts, that's the max the amp is rated for.
Hereís the amp Yuanjing




If you need 28VDC you need a transformer that delivers about 30VDC peak because you lose about 2V in the rectifiers.
30V peak is about 30*0.707 RMS which is about 21VRMS. Standard transformers are avialable for 20V or 21V sec which would both be OK.
Does the amp include rectifiers and reservoir capacitors on the board?
I guess it needs pos and neg 28VDC so you need a transformer with 2 sec windings or a center tapped 20V-0-20V secondary.
BTW This amp uses what is known as a 'chip amp' and there are many threads here about chipamps which includes supply designs and even PCBs.

Whats that '68V-1' thing?

jan didden
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Old 12th July 2012, 08:52 AM   #3
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Right behind the capacitors is a 25 amp bridge rectifier. The 26 volts comes from where the A/C goes in. I donít know what the 68v-1 thing is that you speak of.
So the input voltage multiplied by the A/C RMS value will give me the true input voltage? What about the current needed?
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Old 12th July 2012, 09:04 AM   #4
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Well you mentioned '68 X 1', just curious.

Assuming this is an amp for an 8 ohms load, which is about 35-50W per channel, a 200VA transformer would be adequate.
Does the board have connections for 2 sec windings or for a center tapped sec winding?
Do you have a schematic?

Edit: the board looks like it has 2 chipamps for L and R plus a bridged pair of chipamps for a (sub)woofer?

jan
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Last edited by jan.didden; 12th July 2012 at 09:07 AM.
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Old 12th July 2012, 11:02 AM   #5
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Quote:
Originally Posted by JohnDeaux View Post
I bought a 2.1 Yuanjing amp kit. I think itís 28 X 2 and 68 X 1....
Maybe 2x28W (SE) and 1x68W (bridged)?
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Old 12th July 2012, 11:12 AM   #6
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Like Jan I too see 3 outputs on the PCB. L, R and Bass.

Without much more info and/or a detailed photo of it all we are guessing. Maybe if you could post a picture of the other end of the amp showing the transformer connections etc.

When you say the amp is rated for "26 volts max" where has that info come from as it doesn't mean anything as such ?

More helpful info would be the device numbers of the 4 power IC's and the type number of the 2 regulators ???? that look to be screwed to to small heatsinks. Also the voltage rating of the 6 large caps.
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Old 12th July 2012, 11:43 AM   #7
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It has 4pcs TDA7294; two parallel for the sub channel. Supply caps are 63V 2200uF. Regulators are for the pre-amp op-amps.

Board silkscreen says "26V-0-26V". Seller recommends 18-22VAC secondaries.
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Old 12th July 2012, 02:09 PM   #8
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It has 4pcs TDA7294; two parallel for the sub channel. Supply caps are 63V 2200uF. Regulators are for the pre-amp op-amps.

Board silkscreen says "26V-0-26V". Seller recommends 18-22VAC secondaries.
So you have all the answers then, don't you?
Why ask again here?

jan
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Old 12th July 2012, 03:06 PM   #9
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Jan, take that blindfold off man.... I'm not the OP.
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Old 12th July 2012, 04:37 PM   #10
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Jan, take that blindfold off man.... I'm not the OP.
Uhhh....
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