First Gainclone. AX-730 Transformer Question. - diyAudio
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Old 12th January 2006, 07:41 AM   #1
bezel6 is offline bezel6  Australia
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Default First Gainclone. AX-730 Transformer Question.

Hello,

I have decided to have a play with a LM3875 and make a gainclone to experiment with.
I have been given a Yamaha AX-730 which has had a repair attempt on it but don't know who tried the repair or what the orig problem was, most of the O/P trannies are missing and other mods done..
Anyway i was thinking about using the transformer from this to experiment with the LM3875. I measured 2x17v ac and 2x46v ac secondaries but have no idea what the amp rating of either is..

I was thinking of using the 17v lines for the amp...

Does anyone have any info on this transgormer...???

Thanks..

David... BD
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Old 12th January 2006, 12:34 PM   #2
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I don't know anything about that amp, but I would suspect that the 17V rails are a low-current output intended for the preamp. As such, I'm afraid the transformer wouldn't be suitable.

Still, judging by the 46V windings, I bet it's got some impressive heatsinks!

Cheers,

Mark
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Old 12th January 2006, 07:07 PM   #3
bezel6 is offline bezel6  Australia
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Hello,

Thanks for the reply Mark. I will be recycling the heatsinks onto the gainclone, plenty of room on the heatsink for 2 gainclones.. I checked the back of the Amplifier case and it has 600Watts rating for the Amplifier but the heatsinks look a bit too wimpy for that sort of heat dissipation.
Maybe they were being a little optomistic or a little loose with their power ratings.

The wire used for the 17v & 46v taps are the same guage so I was hoping that maybe the 17v rails were being used for more than just the preamp.

Does anyone know of a method of testing a transformer for current rating..???

Maybe I should use the transformer and create a bench powersupply so I can regulate it from 0 - 50 volts DC and once I have tested the gainclones and played for a while buy a Transformer for it...

Just musing here....

Have a great day.

Regards,

David... BD
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Old 13th January 2006, 01:16 AM   #4
bezel6 is offline bezel6  Australia
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More reading, more thoughts.....

I have been reading in this forum and others regarding rewinding Microwave Oven Transformers ( MOTs ) to use in a powersupply. Now I just happen to have some dead microwaves I have been cannibalising for other projects ( a magnetic flux accellerator ) and have some MOTs sitting around...

I might have a play at winding a transformer and see how that goes...

I think I read too much, I get too many ideas... heheheh..

Have a great day..

David... BD
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Old 15th January 2006, 10:49 PM   #5
bezel6 is offline bezel6  Australia
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Hello All...

Ok Transformer update.....

I have decided to use recycle a Microwave Oven Transformer for my Gainclone powersupply during testing. I may purchase another transformer later depending on the sound of this one.

I have removed the secondary ( 2000v ) and wound my own secondary, I decided on +/- 20 Volts center tapped...

If anyone is interested in how I did it let me know and I will give a little info and some photos if needed...

Just need to settle on my gainclone circuit and start putting it together....

Take care..

David.. BD
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Old 16th January 2006, 09:18 AM   #6
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Quote:
Originally posted by bezel6
I have removed the secondary ( 2000v ) and wound my own secondary, I decided on +/- 20 Volts center tapped...
Wow - that sounds like you put in a lot of effort

Did you have to remove the EI laminations? I have tried this before, and always found it hard to get them all back together again afterwards! Mind you, I haven't tried this since I was a kid...

I'd love to see some pictures if you have them...

Should someone mention electrical safety at this point?

20-0-20 is a good choice - should be good for around 30W per channel
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Old 16th January 2006, 10:03 AM   #7
bezel6 is offline bezel6  Australia
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Hello mhennessy,

I have gone to a bit of trouble, but seems to have worked out nicely. Finished winding it tonight.

Here is the first pic I didn't dismantle the laminations as they are welded along the sides so would have to grind out the welds to remove the E I Laminations so I cheated by using a hacksaw to cut the end off the 2000v windings ( you can see some marks in the photo which hopefully attached ) I knocked the rest of the coils out with a hammer and lump of wood, I then took some of the insulating material and glued it back into the vacent holes.

I had some enamelled wire, too thin for what I want but good for a test wiring, I calculated I would need 12 loops in the winding to get 10v so tried 12 loops passing through one hole and back through the other, didn't take very long.

Put the multimeter on the ends using alligator clips stood back and plugged in and switched on. I got a touch under 10v so switched off unplugged and wound 1 more loop on, tried again and got 10v exactly. So I would need 26 loops for each 20volt winding.

More to come next post..

PS, I am very careful around mains etc... Worked for a couple years repairing video games, pinball machines and Jukeboxes about 15 years ago... Actually I am thinking about using the Gainclones in a Jukebox I am building....

David... BD
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Old 16th January 2006, 10:09 AM   #8
bezel6 is offline bezel6  Australia
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Next I unwound the 13 loops and measured some .8mm enamelled wire twice the length of the .5mm.

I then passed this wire through the holes to give 26 loops, not this took a while.. I superglued the coils in, stripped the ends put on multimeter and tried again, as you can see in attached photo I have 20v ac....

Pic of other side in next message...

David.... BD
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Old 16th January 2006, 10:17 AM   #9
bezel6 is offline bezel6  Australia
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Here is the pic of other side...

That was the last pic I took so far, needed more wire for the second winding so bought some more tonight and did the second winding, took measurements and got 20v from both windings and when I join the center 2 together got 40v on the ends...

Took a little while but very happy with the results and should be good for testing.

Most of my first gainclone will be from recycled parts or stuff I have around here..

I started putting my Gain together tonight, I usually prefer using PCB's but decided to try P2P...

Will take some more photos as I go so if people want to see how things are progressing I'll keep posting...

Catch ya..

David.... BD
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Old 16th January 2006, 10:19 AM   #10
Nordic is offline Nordic  South Africa
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Oi that seems easy enough!!!!!!!!!!!!!!!!
will give this a shot some day.

BTW, it would be great if you could start a how to build a jukebox thread... don't think the forum has one of those yet!
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