| fireman |
As I said in another post, I will probably try my hand a building a GC pretty soon. This is gonna be my first try at this and I don't want to break the bank. I'm thinking about building 5-7 monoblock amps for our home theater in the future but first I need to show my wife that I can do it within a relatively low budget.
Will there be a big difference in the sound of my amp if I choose to use a "regular" cube style transformer instead of a toroid one ? It seems to me that toroid transformers cost quite a bit more than the regular ones. For this first project, I guess it would probably make sense to buy a regular transformer. It would porbably be cheaper and easier to source in Canada.
BTW, any good tips on where to find affordable transformers in Canada ? |
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| joan2 |
| in manila, torroids are almost non-existent, but we manage to build gainclones using e-i cores with good results.... |
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| mrskinny |
| I have tried both EI core and toroid transformers with my LM1875 NIGC. Toroids do sound better-smoother,clearer sound.I was surprised that there was a difference at all,but there is. Keep in mind that most EI cores have only a single secondary winding+center tap,which means using a single bridge rectifier with the center tap hooked up to ground for a balanced supply.This was my initial setup,and I can tell you that this is a BAD idea.If you want to keep your costs low,use a single power supply for two channels,there is not much of a difference between this and a dual mono supply. |
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| skyraider |
| In malaysia most of the EI transformers are cheap and bad.... I have to use toroids through mail order. For me, toroids dont create humming as much as EI transformers. |
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| joan2 |
| quote: | Originally posted by skyraider
In malaysia most of the EI transformers are cheap and bad.... I have to use toroids through mail order. For me, toroids dont create humming as much as EI transformers. |
cheap ei trafos can be made to behave, if you mean humming by the trafo itself, you can tighten the screws on the mounting brackets, or you can put wooden shims wedged on the center legs, then polyurethane bath should fix your problem....
on the other hand, if humming is comming from the speakers, then you have ground loop problems....
torroid cores are prone to saturation easy..... |
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| fireman |
I found these for sale on the Net. Would they work ?
As you can see, they are 115V for the primary and 20 V 2.5 amps for the secondary. Is it enough or would I need a beefier transformer ? |
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| Sherman |
| quote: | Originally posted by mrskinny
Keep in mind that most EI cores have only a single secondary winding+center tap,which means using a single bridge rectifier with the center tap hooked up to ground for a balanced supply.This was my initial setup,and I can tell you that this is a BAD idea. |
You can use a ct transformer with dual bridges without problem. I've built three different power supplies with ct transformers and all of them use dual bridges.
Just hook it up like this if using Brian's board- use the first AC secondary to connect to AC1H on the board, connect the ct to both AC1N and AC2H and connect the other AC secondary to AC2N. Try it, it works. |
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| fireman |
| quote: | Originally posted by fireman
I found these for sale on the Net. Would they work ?
As you can see, they are 115V for the primary and 20 V 2.5 amps for the secondary. Is it enough or would I need a beefier transformer ? |
Don't even bother answering it. I just realised that there is only one secondary. So that won't work... Too bad. At 3.50 $ US that would have been interesting. Oh well !!! |
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| skyraider |
Joan,
"or you can put wooden shims wedged on the center legs, then polyurethane bath should fix your problem...."
mind to elobrate further? I have lots of cheap EI trafos around.. Would be nice if I can use it.
Thanks. |
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| joan2 |
| quote: | Originally posted by fireman
I found these for sale on the Net. Would they work ?
As you can see, they are 115V for the primary and 20 V 2.5 amps for the secondary. Is it enough or would I need a beefier transformer ? |
if you have them on hand, might as well use that, you can use a full wave voltage doubler, and your rails will be at +/- 28 volts which is quite good...
go ahead and do it!!!
tony |
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| mrskinny |
| Actually, those cheap transformers you found on the net would work- just use two of them and you will have your "dual" secondaries!At that price (and considering the kinda low VA rating), why not buy four of them and use two transformers per channel? |
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| joan2 |
depending on the slack found in the center leg of your traffo, wedge wooden shims, about a 16th of an inch thick and width about the size of the tounge, between the core and bobbins..
this is to compress the laminations at the center legs of your traffo, you have to use rubber mallet to push that shim in...
once done, preheat the traffo in an oven about 50degrees above ambient, them dip it in a container filled with electrical grade insulating varnish, (polyurethane)....once the bubbling subsided, lift it out and drip dry..
an oven can speed things up, i use air drying type of varnish so i never had to oven bake my traffos...
good luck
tony |
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| Elkaid |
I wouldn't even bother using them since they're only 2.5A.
If I was you, I would look for a 2 X 25V AC transformer rated at least 200VA for a 2 channels gainclone. |
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| sam9 |
I don't know if this is germaine or not regarding the original question but here goes. I just faced the same question sort of. I recently designed (sort of) and built a headphone amp. The first version used rather crude single sided pcbs that weree easy to work on and modify. Once I thought they were in a state to actually start listening to them, I suffed them into a cheapo project box along with a $9.00 unshielded E-I transformer. Something you would more likely use to run toy motors. The power supply was an equally simple unregulated supply. I just wanted "proof of concept" before spending much more money. I made little attempt to optimize the wiring in the box.
I fully expected some kind of noise from the transformer and supply. What I gor was total silence - except for music. The point is that I would expect a headphone amp to be especially vulnerable shortcommings in a power supply/trandformer due to the low signalk levels and the fact I'm using isolating headphones.
The upshot of this is that I'm more respectful, now, of "square" transformers than previously and I'm not as certain about the benefits of toroids beyond those of size and weight. |
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| Magura |
Ive had a similar experience on more than one occasion. Back when I was a teenager I never had much money, so all of my projects back then were built from salvaged parts and components and a minimum of el cheapo parts. Transformers being relatively expensive, were usually salvaged from anything from matrix printers to photocopy machines. All of them being EI type. They do just fine. The only limitation is high power applications where their shortcommings are obvious.
Magura:) |
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| sam9 |
| But then what is high power? I know some people think it begins at 25W and other think it begins at 250W.:scratch: |
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| Magura |
| quote: | Originally posted by sam9
But then what is high power? I know some people think it begins at 25W and other think it begins at 250W.:scratch: |
In my book EI transformers are fine at any power level, the problem is that they become expensive and not very common around 250-300 VA.
Magura:) |
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| joan2 |
| quote: | | I wouldn't even bother using them since they're only 2.5A |
don't give up easily, this torroid is good for one chip, monoblock if you may....so two can be used for stereo....
you may be in for a surprise.... |
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| joan2 |
| quote: | Originally posted by Magura
In my book EI transformers are fine at any power level, the problem is that they become expensive and not very common around 250-300 VA.
Magura:) |
agreed!!! i have done a lot of ei's and in my country, these are cheap to make...
tony |
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| joan2 |
| my traffos, big one is a 3kva one for a leach amp cost at around U$105, smaller one is suitable for a gainclone amp up to 4 chips and costs around U$10. |
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| JasonL |
| If i were to build any thing these day's if it to be a cheap project to a hi end thing i would invest in a toroid in any chance i got.. Why.. just because i want the best : O ) and really there not that expensive until you get into the 1kva and up range.. |
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| djQUAN |
tama. walang toroid dito. :P
I couldn't find toroids here locally so I went to hongkong and got a 225VA for a pair of P3A's and a 500VA for a pair of N channel amps.
I guess it'll be a very long time before I could get my hands on new toroids.
as far as cheap EI core trannys go, locally, we can only get those under rated ones that get hot even at idle (I assume those are run well near core saturation to get better regulation to make up for voltage drop due to underrated-ness). I had one that was rated at 1.2kVA and is only about the size of a 300VA EI. for lower voltages, the real ratings are closer to that specified. |
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| joan2 |
| quote: | as far as cheap EI core trannys go, locally, we can only get those under rated ones that get hot even at idle (I assume those are run well near core saturation to get better regulation to make up for voltage drop due to underrated-ness). I had one that was rated at 1.2kVA and is only about the size of a 300VA EI. for lower voltages, the real ratings are closer to that specified.
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the heat is due to the fact that locally available iron require more turns than goss types...besides local winders tend to everrate their traffos...your observation is on the dot...
i take this into consideration whenever i design a traffo for my own use..... |
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| dhenryp |
Try Apex Jr. I bought a half dozen 350VA El XFormers a few years back for ~ 8$ a piece. They are very good quality and I am, in fact, I'm in the process of using most of them for a & Channel Chip Amp HT setup. These are gone but Apex does have a 55V CT 7+ amp El for 7.95
Fender 55 Dual 55V power transformer @ 7.12 Amp
http://www.apexjr.com/miscellaneous.html
I think El's and Torroids both have some plusses and minuses. I'm not convinced that a properly sized transformer of either type is going to affect your sound, all other things being equal (i.e. same bridge, caps amps). If there is a difference, it is debatable, (and has been debated here before) which type is better. |
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| jinkuchi |
it harder to find.
normally they use rectangular transformer.
I have big one, it work very perfect (with ELNA 20000 MFD 50V CAPACITORS).
but..
I need teroid because it gonna looked beautiful.
it thin too!
and it not hot!
3 things is enough
tiger
:smash: |
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