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Need help sourcing a power transformer

Gourockian

Nov 1, 2007
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Hi, I'm trying to find a supplier in the US where I can order a power transformer producing a dual output of [email protected] and [email protected] This is for building a PSU for a 1980's Yamaha AVS10 or CVS10 piano and organ expander. I currently have both units but only one Yamaha PA-W10 PSU and these are really difficult to obtain nowadays. The PSU's DC output is rated at [email protected] and [email protected]

Some years ago, a Yamaha engineer was kind enough to provide me with a hand drawn circuit diagram of the PA-W10 and I have all the components as well as the elusive 3-pin DC plug and cable. I've tried both Mouser and DigiKey's websites but have not been able to find what I'm looking for so any suggestions would be most welcome.

Thanks,

Al
 

Minder

Apr 24, 2015
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There is a Co. Antek that makes nice custom toroidal versions.
 

Gourockian

Nov 1, 2007
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There is a Co. Antek that makes nice custom toroidal versions.
Thanks for your response. However, although their site shows transformers with dual outputs, I wasn't able to find any with the voltages I need.
 

Gourockian

Nov 1, 2007
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No, unfortunately. I don't know what that is used for as it does not have a DC output.

This is a picture of the one I have, which is the UK version and is used it with a step-down power supply. The US one looks the same but has a different transformer with the same outputs.
Yamaha PA-W10 PSU.jpg
 

Minder

Apr 24, 2015
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Thanks for your response. However, although their site shows transformers with dual outputs, I wasn't able to find any with the voltages I need.
That is why I mentioned 'Custom' IOW they will build to your spec. !
In any case, a Toroidal type is very easy to modify/customize with a simple overwind.
 

Gourockian

Nov 1, 2007
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That is why I mentioned 'Custom' IOW they will build to your spec. !
In any case, a Toroidal type is very easy to modify/customize with a simple overwind.

Sorry, I did not notice you had said "custom". I'll contact them for a quote but I think the cost will be too prohibitive. Thanks again.
 

Martaine2005

May 12, 2015
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You may be able to rig something up fairly cheaply. There are DC-DC boost converters. And buck converters.
You could use an old laptop PSU or similar and then use two converters. One for 35V and one for 10V. House it all in one neat plastic container.
Without ever trying this, it might add noise to the organ. But I’d try it to see.
Failing that, there are 35V transformers on eBay too.
Might get you out of a tight spot while you keep searching for an original. I saw one sold for £5 (dollars).

Martin
 

kellys_eye

Jun 25, 2010
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A simple 12-0-12 transformer (i.e. centre-tapped) is easily available or even a dual 12VAC secondary (i.e. 0-12 and 0-12). Regulate one 'half' to the required 10V (use a 7809 regulator with series diode in the ground lead to 'boost' the output (although a 7810 might even be available to negate that issue).

Use a 'tripler' rectifier on the other half of the transformer to get approx 36V - which I doubt has to be regulated anyway.

A transformer of 12-0-12 (or 0-12 plus 0-12) rated at 1 or 2 amps is commonly available.
 

Gourockian

Nov 1, 2007
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You may be able to rig something up fairly cheaply. There are DC-DC boost converters. And buck converters.
You could use an old laptop PSU or similar and then use two converters. One for 35V and one for 10V. House it all in one neat plastic container.
Without ever trying this, it might add noise to the organ. But I’d try it to see.
Failing that, there are 35V transformers on eBay too.
Might get you out of a tight spot while you keep searching for an original. I saw one sold for £5 (dollars).

Martin
Hi Martin, thanks for your suggestion. I may need to try something like the laptop PSU idea although since my original post, I've managed to find a multi-tap transformer in the bottom of a junk box I had in my garage. I'll post further details in a separate post.

$5 for a PA-W10 is an absolute steal.........somebody got lucky!

Al
 

Gourockian

Nov 1, 2007
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A simple 12-0-12 transformer (i.e. centre-tapped) is easily available or even a dual 12VAC secondary (i.e. 0-12 and 0-12). Regulate one 'half' to the required 10V (use a 7809 regulator with series diode in the ground lead to 'boost' the output (although a 7810 might even be available to negate that issue).

Use a 'tripler' rectifier on the other half of the transformer to get approx 36V - which I doubt has to be regulated anyway.

A transformer of 12-0-12 (or 0-12 plus 0-12) rated at 1 or 2 amps is commonly available.

Thanks for the suggestion but since my original post, I've managed to find a possibly suitable transformer in one of my junk boxes. i'll post further details separately.
 

73's de Edd

Aug 21, 2015
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Sir Gourockian . . . . .

I see that your owned and currently used power supply is for 220VAC and Florida USA is 120VAC,how are you presently solving that voltage disparity . . .an additional , intermediate step down transformer ?

And you would be building up the additional power supply for 120VAC operation . . .correct ?

And . . . . .. can you give us the schematic provided for thee construction of that additional power supply.

My preference . . . . if building such . . . . would be to use a 120 vac in and 12vac @2 A output, transformer and an additional 120VAC in and 24VAC A 1/2 A output and then connect series aiding secondaries and then adequately filter both the 12 V out and the 12+24=36 V and regulate down, if necessary, since they are so darn close.

73's de Edd . . . . .
 

Gourockian

Nov 1, 2007
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After a further rummage in my garage, I found a long-forgotten 120V transformer which might work out. It was soldered onto part of a circuit board which already has fuse-holders so I think I can customize it by breaking some of the copper tracks and adding wiring as required.

The secondary has eight pins and after removing it from the pcb, I checked for continuity and measured resistance between them and found what seems (to me at least) to be an unusual setup. Pins 1 and 8 are connected as are 2 and 3, 4 and 5 plus 6 and 7. This basic graphic shows the winding resistance figures along with the no load voltages when 120v AC was applied to the primary.
Transformer outputs.png
My plan is to use pins 4 and 5 for the 10V and 1 and 8 for the 35V supplies and the windings look as if they can handle the currents involved.. I'm not too worried about the voltages being a little higher as the Yamaha PSU I currently use pushes out approximately 13.35v and 39.0v (both DC) under no-load conditions.

Incidentally, one thing I don't quite understand is that this PSU provides 30.0v AC, measured, at the secondary output but after rectification and smoothing, it gives 39v DC. It's many years since I did electronics theory but I seem to remember that the bridge rectifier causes a slight voltage drop but that's not the case here. Any thoughts on this?

Hopefully, this will resolve the problem and allow me to use both expanders at the same time.

Thanks to all who took time to respond.
 

Gourockian

Nov 1, 2007
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Hi, I did mention in the post with the picture that I was using a step-down power supply, which of course was wrong. It is a step-up PSU.........120VAC to 220VAC. I'll see if I can edit that post.

Yes, the plan is for a 120VAC supply for the new one.

Here is a copy of the schematic supplied by Yamaha, with a few of my added comments.
Yamaha PA-W10 Schematic.jpg

I don't think I would want to use two transformers, etc. due to the resulting size and weight but I appreciate you taking the time to respond. Actually, I was typing up my earlier post as your's came in, where I shared that I had located a somewhat suitable transformer, so hopefully this will meet the needs.
 

kellys_eye

Jun 25, 2010
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Using a bridge rectifier the DC output will be 1.414 x the AC input so for the 30VAC secondary this will be 42V ;less the diode drop (call it 2V to be easy) then the UNLOADED DC output will be around 40V - as stated on your drawing. This drops under load to the required 36V DC - it doesn't have to be that accurate.
 

Gourockian

Nov 1, 2007
13
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Nov 1, 2007
Messages
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Using a bridge rectifier the DC output will be 1.414 x the AC input so for the 30VAC secondary this will be 42V ;less the diode drop (call it 2V to be easy) then the UNLOADED DC output will be around 40V - as stated on your drawing. This drops under load to the required 36V DC - it doesn't have to be that accurate.

Ah, yes, I forgot about the 1.414 multiplier. Thanks for the explanation but what seems strange is that the 10VAC output does not seem to have the same increase ratio, except unloaded. Would the diodes in that part of the circuit have a higher voltage drop?
 

Gourockian

Nov 1, 2007
13
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Nov 1, 2007
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Replace triac I physically broke the triac on my drilling out rivets on a cheap router speed control trying to improve heat sink. info on triac is; ST phil e3, BTA41600B, 7SACF VU, PHL 7S 004. I am totally IT and electronic illiterate so out of desperation I am replying to this post in the hope of obtaining assistance. I am so bad and now i even cannot upload a picture. Not sure I will be able to find this thread again but I would greatly appreciate all assistance in learning what and where to obtain replacement

Yep, you sure messed up loading the picture.....it is a pdf of your AARP insurance cards! Suggest you delete this post as it has your home address showing.
 
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