Any Pass amps use a higher supply voltage? - diyAudio
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Old 16th May 2011, 03:01 AM   #1
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Default Any Pass amps use a higher supply voltage?

I ask as I have a variety of toroidal transformers... two of which came from a "killed" ML No27 amp. But, they all have much higher supply voltages.

I have two toroids, from an old Optonica amp, at +/- 45. The MLs seem to be about +/- 65.

I thought about building DC-DC converters to use them but to create one to handle the dissipation of a BA-2 might be insane.

Or, maybe a Pass design is not what I need...
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Old 16th May 2011, 03:52 AM   #2
godfrey is offline godfrey  South Africa
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If they have two 120V primary windings, you could connect those in series instead of in parallel. That will halve the output voltage. The VA rating goes down though, since you don't get double the current.
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Old 16th May 2011, 04:21 AM   #3
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I wish...

But, wait... that made me think... the ML might be able to be used abroad. I know they had US and EU versions at the time it was built. It could be separate transformers for each area or it could just be taps.

Thanks!
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Old 16th May 2011, 04:23 AM   #4
3GGG is offline 3GGG  Australia
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Or you could unwind or "cut in to them" at the desired output voltage. But your VA will go down aswell.
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Old 16th May 2011, 05:27 AM   #5
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I thought about that as well. However, they are fairly well made and I am hesitant to do that at the moment. I think the ML ones are entirely custom but I'll take a peek underneath the wrapper and see if there is anything else.
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Old 16th May 2011, 05:55 AM   #6
godfrey is offline godfrey  South Africa
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If they have separate secondaries (e.g. two times 0-45 windings instead of one 45-0-45), you can connect the secondaries in parallel to make a single-ended supply.

Or... desperate last resort:
Use two transformers together, with the primaries connected in series and the secondaries in parallel. They don't even have to be the same. e.g. With a 45V transformer and a 65V transformer, the voltages work out like this:

45v xformer:
primary voltage: 120*65/(65+45)=70.91V
secondary voltage: 45*70.91/120=26.6V

65v xformer:
primary voltage: 120*45/(65+45)=49.09V
secondary voltage: 65*49.09/120=26.6V

Heheh - I'm starting to like this idea. It sounds like you have enough to make a pair of monoblock amps, each with two power transformers.
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Old 16th May 2011, 06:08 AM   #7
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I like that idea as well. But, there is a massive difference between the 45v and 65v transformers. The 45v are like 8 pounds and the 65v is more like 25 pounds.

Also, I am not too sure on the wiring diagram for the ML ones. They must have peeled the original manufacturer labels off of them and the voltage readings are not really making sense. Unless, I have two primary, CT'ed windings. But, when I connected what I though was the second primary it did not work at all.

If anything, I can sell these and buy the proper transformers for BA-2. However, I am having a tough time finding those as well. I am in a pretty good transformer rut today.
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Old 16th May 2011, 08:05 PM   #8
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Quote:
Originally Posted by godfrey View Post
Or... desperate last resort:
Use two transformers together, with the primaries connected in series and the secondaries in parallel. They don't even have to be the same. e.g. With a 45V transformer and a 65V transformer, the voltages work out like this:

45v xformer:
primary voltage: 120*65/(65+45)=70.91V
secondary voltage: 45*70.91/120=26.6V

65v xformer:
primary voltage: 120*45/(65+45)=49.09V
secondary voltage: 65*49.09/120=26.6V
It's still a bit early in the day for me, but why does this work? (since it seems to open up many possibilities for my transformer collection)
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Old 16th May 2011, 08:42 PM   #9
godfrey is offline godfrey  South Africa
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The way I see it... If you force the secondaries to be the same voltage (by connecting them in parallel), then the primary voltages must be different, so the mains voltage is shared unequally between the two primaries.

edit: Just make sure you get the phase right or you'll be boosting the primary voltage on one or both of the trannies to higher than mains voltage.

Last edited by godfrey; 16th May 2011 at 08:45 PM.
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Old 16th May 2011, 09:17 PM   #10
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But with the current the same in both primaries (in series), doesn't it possibly force one transformer into being over- (or under-) worked? What are the shortcomings?

I'm surprised I haven't seen this trick before....
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