Parallel transformer wiring for Aleph30???

[hifimaker]

I bought 2 Antek 2x22vac 400va transformers I'd like to use with BrianGT's mini-Aleph PSU board.

I've successfully hooked up the primaries and get 22vac at each of the secondaries.

My question: Is this the correct way to parallel these 2 400va transformers together for a single 22vac secondary with an 800va rating?

Thank you!

-David

 

[mpmarino]

I would just 'dual mono' it with 2 bridges and 2 sets of cap banks. It'll keep you out of trouble and a dual mono 400va each chan on an aleph at those voltages would be better than needed. IMHO those trafos are not EXACTLY matched and they won't play equally in parallel (load share) as you would like.....

regards...

edit: oh...but your schem does seem to be correct if you wanted to..

 

[tja]

Only one secondary?

What are you going to use for the other secondary?

Take

 

[hifimaker]

I was hoping to use a single powersupply with one bridge rectifier. Is this practical? The other option is to use 2 PSU boards, but given space limitations I was hoping to get away with only one.

Thank you,

-David

 

[tja]

You need both +22V and -22V. The scheme you cooked up above delivers just one of them. If you want to use one bridge parallel each transformers secondaries and use one transformer for the positive side and one for the negative.

In the attached picture break connections at the red crosses, join the green connection and attach it to ground

Be sure to verify this with someone who knows a heck of a lot more than I do.

Take

 

[mpmarino]

Take is right..your orig. schem is wrong. But I think you would want it as below. I would still go dual mono or at least use 2 bridges and parallel the dc after the bridges.....

 

[hifimaker]

Take is right..your orig. schem is wrong. But I think you would want it as below. I would still go dual mono or at least use 2 bridges and parallel the dc after the bridges.....

mpmario and Take,

Thank you so much for your help!

I'm looking to get 22vac at the input of the rectifier. Would this design give 44vac or 22vac?

Thank you,

-David

 

[mpmarino]

44 vac total , or in other words, +-22vac referenced to the ground shown in my schem. If your building a traditional aleph 30 type amp you need about that voltage before rectification.

someone please flame me if i'm wrong so dw doesn't blow himself up. 🙂

 

[hifimaker]

I hooked it up as diagramed in post #1 and I'm getting +-15.6 volts after the rectifier. I was hoping to see 25vdc.

What's wrong here?

Thanks!

-David

 

[Zen Mod]

I hooked it up as diagramed in post #1 and I'm getting +-15.6 volts after the rectifier. I was hoping to see 25vdc.

What's wrong here?

Thanks!

-David

you need caps after the bridge.

 

[hifimaker]

Thanks Choky,

I'm actually using BrianGT's PSU board in a CRC configuration. So far I only have the bridge rectifier and caps (44000mf per side)installed.

-David

 

[mpmarino]

I hooked it up as diagramed in post #1 and I'm getting +-15.6 volts after the rectifier. I was hoping to see 25vdc.

What's wrong here?

Thanks!

-David

post 1 has no ground for the secondaries (aka:center tap)...where are you seeing +- voltage?
if you are measuring from mains ground to your bridge I'm sure your measurements are erroneous.

 

[hifimaker]

mpmarino,

Yes, I was measuring the output of the rectifier to ground, and getting the same voltage from both sides with the right polarity.

I think I'll try your idea in post #6 and rewire the primaries to 220vac to get 22vac with 120vac input.

-David

 

[mpmarino]

DW,
I am under the impression you are building an aleph 30. If I'm wrong tell me and then ignore everything I have posted. If you are building an aleph keep in mind that you will need a positive (+) secondary and a negative (-) secondary...not a single secondary. I believe the stock a30 used a dual secondary 21v trafo (if memory serves) so you would be right in the ballpark with DUAL 22v secondaries. That's a total voltage swing of 44vac with a tap dead center as the ground. a single 22vac sec. is useless for an aleph. Therefore I think you want to use the 120vac primaries.

I still think you should go dual mono😀

Edit: Oh...and be careful!

 

[DSP_Geek]

Let me add my voice to mpmarino's and say that paralleling transformers is a BAD idea. Why? Imagine that one transformer has one less turn on the winding than the other as a result of normal manufacturing variance, and as a result it runs at 21.8 volts instead of 22. With a secondary resistance of 0.2 ohms (not atypical), there is a 1 ampere current flowing from the higher voltage unit to the lower voltage one. This current only serves to heat up the windings: it's pure wasted energy, doesn't go to the load.

Now, the analysis is simplistic, and there are a number of second-order effects I haven't touched, but the gist is there: if you have two transformers, by far the better solution is dual-mono.


Cheers,
Francois.

 

[hifimaker]

Hi Francois,

Thanks for the help. I'd like to stay with the 1 PSU board I have. I think I'll scout around for another transformer.

mpmarino,

I was able to successfully hook-up both transformers as you and Take suggested. After the rectifier and caps I measured a steady +- 31.7vdc without a load.

-David