| miguel2 |
This is a bit over the edge but here it goes. I have this 800VA toroid with dual 67VAC secondaries. What you guys think about lowering the voltage to put it in a GC?
It will be with about 1/3 the original voltage and I guess with 1/3 the power (260VA?), so that would not be a problem. But it would be an enormous amount of unwinding. And the primary can become a mess. Is the primary located near the core or are these txs built by coats?
Miguel |
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| bigparsnip |
I'm sure you would be able to find someone willing to swap or buy this from you and you should be able to get more than enough money to buy a properly specified transformer for your needs.
Try putting it up on the trading post and see what you can get for it. |
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| SkinnyBoy |
| why do you have to live in Portugal?? wheres Portugal?? lol |
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| carlosfm |
| quote: | Originally posted by SkinnyBoy
why do you have to live in Portugal?? wheres Portugal?? lol |
In the centre of the world.:devily:
GMT time.
It´s in Europe, man!:bawling: |
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| miguel2 |
If you dig a hole I can offer you a beer at my place.
Miguel
PS: I am counting with engineering tolerances in that hole. |
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| Magura |
I may be mistaken...but im quite sure ill be the one getting guests if he digs a hole :)
Cheers
Magura |
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| Christer |
Doesn't any of you guys own a map? I am assuming we are
talking about a hole straight through the centre of earth,
since otherwise he may as well dig it anywhere he likes.
On my map Adelaide is at 138E 35S, which would mean he
comes up at 42W 35N, which I don't recommend. Our dear
friend will get very wet since that is roughly between the
Azoers and the Bermuda Islands. |
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| iCebReakEr409 |
talking about transformers...
i have this 300VA 2x30V one i bought a while ago. do you think i can use it for the national chip (3886, 4780, etc) ? it would probably exceed the 84V...:( |
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| Magura |
LMAO
Nope, i didnt check it on a map...it was off the top of my head.
Anyway, the azors isnt that bad...when he pops out, at least the water is warm :D
Cheers
Magura |
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| GregGC |
| quote: | Originally posted by iCebReakEr409
talking about transformers...
i have this 300VA 2x30V one i bought a while ago. do you think i can use it for the national chip (3886, 4780, etc) ? it would probably exceed the 84V...:( |
I wouldn't with 38XX, don't know about th other one. The voltage is too high. |
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| SkinnyBoy |
| ahuh.. well.. itds good to see we sorted all that out... :xeye: |
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| carlosfm |
| quote: | Originally posted by Magura
LMAO
Nope, i didnt check it on a map...it was off the top of my head.
Anyway, the azors isnt that bad...when he pops out, at least the water is warm :D
Cheers
Magura |
Talking of Azores...
That's Portugal.:D
Azores and Madeira belong to Portugal.;)
What did I tell you?
The centre of the world.:angel: |
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| Christer |
| quote: | Originally posted by carlosfm
Talking of Azores...
That's Portugal.:D
Azores and Madeira belong to Portugal.;)
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Yes, I know, so although he would end up quite far from the
Azores too, you were closest, at least. :)
Actually, when I checked up the coordinates of Adelaide and
checked where the "opposite" was, I hadn't expected it to
be that far off from mainland Europe. We learn in school that
New Zeeland is opposite from Sweden (haven't checkec how
accurate that is, I admit), but considering the distance between
NZ and Australia, and the size of Australia itself, I realized it
was probably quite difficult to make any good guesses.
BTW, Madeira is nice, and I have heard that the Azores are
similar or even more beautiful. |
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| carlosfm |
| Anyway, a guy will melt on the centre of the planet.:D |
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| Christer |
| quote: | Originally posted by carlosfm
Anyway, a guy will melt on the centre of the planet.:D |
Depends on how quick he is, but he will certainly need that
beer to cool down. :) |
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| joensd |
Miguel, you could rectify and smoothen each secondary, regulate it down to <80V and then use the chip in "single supply mode".
Of course this makes the gainclone quite complicate...
Just one solution.
I´d swap it as well.
Cheers
Jens |
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| miguel2 |
I guess I´ll give up on that tx.
I am not a civil engineer but I guess that when they make a bridge they multiply everything by some 20 to 50% more to make sure the whole thing doesnt break apart (any confirmations please?). So a hole with 50% to any side will be anywhere you want in this part of the world...
Miguel |
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| moamps |
| quote: | Originally posted by miguel2
I guess I´ll give up on that tx.
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Hi,
why?
Usually secondary windings are up and are usually bifilar wounded (both sec together). For test (how many windings for one volt) wound let say 10 windings with some spare wire on transformer, measure generated voltage. You will than find how many windings you must putting off. Your transformer will be 800VA with smaller sec. voltage too, only wires current capability will be smaller. In application where you don't need high current all the time (GC for example) this isn't so important.
Regards |
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| miguel2 |
Hi moamps,
I get the turns/volt part but the rest is confusing me.
You are saying to unwind x turns of the secondary, cut them off, and get the desired voltage right? So primary will be untouched (it is near the core?) and only secondaries will be cut off. But if current on the secondary is lower, how come the tx still has 800VA? How about noise, because the secondaries may not be as tightened as in the original pack?
Miguel |
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| SkinnyBoy |
| its a perfectly good transformer, please leave it intact.... |
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| bigparsnip |
| quote: | Originally posted by miguel2
I guess I´ll give up on that tx.
I am not a civil engineer but I guess that when they make a bridge they multiply everything by some 20 to 50% more to make sure the whole thing doesnt break apart (any confirmations please?). So a hole with 50% to any side will be anywhere you want in this part of the world...
Miguel |
For civil, that would be more like 200-500%, they generaly like there things to be BIG. |
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| Christer |
| quote: | Originally posted by miguel2
Hi moamps,
I get the turns/volt part but the rest is confusing me.
You are saying to unwind x turns of the secondary, cut them off, and get the desired voltage right? So primary will be untouched (it is near the core?) and only secondaries will be cut off. But if current on the secondary is lower, how come the tx still has 800VA? How about noise, because the secondaries may not be as tightened as in the original pack?
Miguel |
It won't be 800VA anymore. The core will, but not the entire
transformer. If you take off the secondaries completely and
wind new ones with thicker wire you could get a lower
voltage 800VA one. |
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| SkinnyBoy |
| speaking of toroidals... how can I work out the power rating of the primary? cos I have these transformers which are only rated at 250VA, but the cores are almost as big as 500VA ones.... any ideas? lol any chance of rewinding the transformers to get higher VA? |
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| millwood |
| if the transformer has dual primaries and you live in a 110v country, you can put the primaries in serial and get the voltage down to 67v/2. Not exactly what you want but closer. |
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| carlosfm |
| Mains here is 230v... |
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| moamps |
| quote: | Originally posted by miguel2
How about noise, because the secondaries may not be as tightened as in the original pack?
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Hi,
Leave rest of secondary intact and wound plastic isolation back. This will not be so tightened like original but will works. Or do nothing and sell them for small amount. And learn nothing.
Your choice. | quote: | Originally posted by SkinnyBoy
its a perfectly good transformer, please leave it intact.... |
And useless too.| quote: | Originally posted by Christer
It won't be 800VA anymore. |
Theoretically correct, application depending no. This tweaked transfomer will be in classA application much better than originally 300VA, in class AB application will be same like ca originally 500VA, and in GC application (about 200W audio power) like originally 800VA. This transformer will be able to produce about 800VA but not all the time. This IS 800VA transformer in some condition.
| quote: | Originally posted by SkinnyBoy
lol any chance of rewinding the transformers to get higher VA? |
No.
Regards |
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| Christer |
| quote: | Originally posted by moamps
Theoretically correct, application depending no. This tweaked transfomer will be in classA application much better than originally 300VA, in class AB application will be same like ca originally 500VA, and in GC application (about 200W audio power) like originally 800VA. This transformer will be able to produce about 800VA but not all the time. This IS 800VA transformer in some condition.
|
It will probably be able to take peak loads similar to the original
version, so in that respect it is better than a smaller one.
It will have a lover average VA rating due to the size
of the secondary wires, which is important to note. So yes,
I think we agree. |
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| millwood |
| quote: | Originally posted by Christer
It will have a lover average VA rating due to the size |
I didn't know that you guys rate lovers in sweden by size, :) |
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| Christer |
| quote: | Originally posted by millwood
I didn't know that you guys rate lovers in sweden by size, :) |
Sure, and if you use one with too low rating it gets too hot. :)
We'd better stop here before the mods catch up with us. :)
(In case somone missed it, there was a typo in my previous
post. It should read "lower" not "lover".) |
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| moamps |
| quote: | Originally posted by Christer
It will have a lover average VA rating due to the size
of the secondary wires, which is important to note. So yes,
I think we agree. |
:up: :) |
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| miguel2 |
| quote: | | Leave rest of secondary intact and wound plastic isolation back. This will not be so tightened like original but will works. Or do nothing and sell them for small amount. And learn nothing. |
I already done it from a 50VAC to 40 with other tx. But this one requires lowering around 40 VAC, that is why I have doubts. But I guess I will try it.
Puting back the the plastic isolation is a real mess (at least it was in the other one). Are there any alternatives, like some glue or adhesive tape?
Miguel |
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| phase_accurate |
Hi Miguel
Would a dual 20 Volts xformer be O.K. (even if it isn't a toroid ?).
Regards
Charles |
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| moamps |
| quote: | Originally posted by miguel2
Puting back the the plastic isolation is a real mess (at least it was in the other one). |
Hi,
use-make the tool (allu or pcb piece) on picture below. Wound isolation tape first on it , than wound tape from tool tape on transformer.
Regards |
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| miguel2 |
Thanks moamps, that will be useful. Yesterday I saw in Maryland transformers that for a VA rating of 800VA the Volts/turn is around 0,5. So I will have to unwing around 80-90 turns on each secondary. Ugh. Good news is that I can turn it on without any inrush limiter necesssary.
Charles, I believe I am gonna stick with this one to see what I can do. |
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| carlosfm |
Migueeeeeeeeeel!:eek: :D
It just hit my head.
What about a little 230-110v transformer?
They are cheap.
It would lower the voltage of your toroid.
:angel: |
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| miguel2 |
Nah! I am gonna squeeze that toroid...:devilr:
That would give around 35VAC, which is too high still.
Miguel |
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| miguel2 |
After extensive unwinding I have now a toroid with about 40º of wire, being the rest unused. Quite strange. Maybe I rewind a part so I can use it for the psu of the sub amp...
Now I have one secondary with 25.3 VAC(unloaded) and one with 26.5VAC - close enough to do some thinking. So I have to decide:
- which voltage should I choose? As the original tx is 800VA, maybe I can go with some higher voltage and stay with 24-25VAC. I guess it wont run out of juice, so it is not necessary to lower the voltage more, and I can get a bit more power from the GC.
- And how close should the secondaries voltage be? For example, 24,5 and 24,8 is acceptable? Or they should match exactly? I can make half a turn if I want:)
Miguel |
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| darkm4n |
Hm ...
If you want to lower the voltage just wind some wire on the toroidal , put it in series with the primary output .
I wind about 50 times to reduce the voltage from 40 V to 30 V |
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| carlosfm |
Miguel,
If you can go a little lower, the ideal voltage would be around 2x22v AC. |
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| miguel2 |
That gives around 28VDC (if the 1000u caps can maintain the voltage...) or 38 W according to the spreadsheet of National. Sounds good to me.
| quote: | | If you can go a little lower |
I can go to 0 VAC, I am becoming a pro in unwinding:)
Miguel |
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| carlosfm |
| You'll have around 30v, the limit for 4 ohms speakers and the ideal voltage for a GC.;) |
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| miguel2 |
Its done! I have now +/-28.5 VDC on the rails. The transformer secondary covers only a bit less than half the core but the sound is now much better than with the other small EI tx.
The problem now is that the tx hums and the speakers go along too:mad:. Man, it took me two years to teach my kid how to speak :).
I have to reinforce the expanded plastic/rubber sheet under that transformer to get more damping. Maybe the unbalanced covering of the secondary has something to do with it. And then I have to convince my speakers that the star ground I made is awesome.
Just one thing that worries me is that the volume pot is around 3 cm away from the tx.
Miguel |
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| carlosfm |
| quote: | Originally posted by miguel2
Just one thing that worries me is that the volume pot is around 3 cm away from the tx.
Miguel |
Ouch!
That may be the problem...
Use shielded cable.
And a mouse mat on the toroid.:D
Miguel, you can wrap the toroid with aluminium tape.
I buy it on AKI.;)
Can you post picture of the whole thing?:) |
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| millwood |
| quote: | Originally posted by carlosfm
Miguel, you can wrap the toroid with aluminium tape. |
does the tape conduct electricity? if it does, wouldn't that form a shorted secondary? |
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| Philo |
Miguel,
Before you go after the transformer for your speaker hum, make sure you didn't induce a ground loop somehow. Is the new TX connected to the bridges the same way as the EI or did you do some rerouting. If the pot is Al bodied, is it grounded? Peter had an original problem with hum (especially when he touched the pot) until he grounded the case of his pot with a small wire. If the pot is wirewound the close proximity to the Tx could be inducing the hum. If all the above is good, how tightly did you tape up the remaining secondaries? I have reduced transformers a couple of times and have used clear packing tape with good success.
Philip |
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| miguel2 |
I use shielded cable (microphone) for the inputs but the outputs of the pot are cat-5. The pot is an Alps blue, which is made of metal, and is connected to chassis, being the chassis connected to the star ground via 100R/.22uF.
The EI tx was center tapped with only one wire (the secondaries were connected) while this new one has two independent secondaries. The difference in cabling is that I route the two secondaries to the star ground separately, while in the other I had only one wire.
I finish wraping of the secondaries with some strenght, using cloth adhesive tape and the plastic tape that came with the tx. So I guess that the secondary wires are not vibrating. Maybe it is from some unbalance between the two halves of the core.
Carlos, I though of wraping with Al but I am thinking of making another set of secondaries for the sub amp. I have half of the tx for that. Oh, and my thrusty conventional Canon still has around 20 photos to go...
I am going to try a piece of metal between the pot and the tx. And use shielded cable on the pot instead of cat5. BTW, the shield of the cables is connected to chassis or to the star ground? As I don't have a ground connection in the plug (just hot and neutral) I dont know if this even makes sense.
Miguel |
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| carlosfm |
Miguel, you can use shielded cable on the pot out, but connect the shield only on one side of the cable, anywhere.
Just for shielding. |
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| miguel2 |
Hi,
In the unwinding process I just took off the sleeves from the secondaries. So after this step I just saw with DMM which were the wires from each secondary and plug them into the bridges. But now I understand that there is only one way to connect them, and the center tap must be well chosen. As I do have the right voltages, is there any chances I had swap the secondary wires?
I still have hum that I cant get rid off, so I am checking all possibilities.
Miguel |
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