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Old 24th April 2001, 12:55 PM   #11
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Quote:
Originally posted by Evaas
Ok, so I'm getting the feeling that this is a bad idea. I definitely want to stay away from the restistor and diode ideas, and even the thin wire inductor, as those are very inefficient. However, I thought that inductors that are wound with low resistance wire will not dissipate much heat, but this does not seem to be what you guys are saying. Let me walk through an example:

I have a transformer with 8.5VAC secondaries driving a bridge rectifier(assume 2v loss through the rectifier), so the rectifier has 10v peaks. (8.5*1.41-2=12-2=10v). If I then use a large capacitor bank, my dc rail will be close to 10VDC. However, if I use a choke between the rectifier and the capacitors, then it will serve to lower the peak voltage out of the rectifier, and raise the bottom voltage. Whereas the peak was 10v and low was 0v without the choke, the peak my be, say 8v, and the low will be 2v with the choke. Is this basically correct? Furthermore, the area under the curve of the circuit with the choke will be similar to the area under the curve for the circuit without the choke. That is to say that the average voltage in both scenarious will be similar, but it is distributed differently. Based on this, the power dissipated by the choke should be small because in essence, its chopping off the peak voltage and distributing it later on (90deg later) rather than wasting it as heat. While the average voltages may be the same, what matters to me is the peak voltage, since that is what my caps will hold and the peak voltage of the inductor circuit will be lower.

Since nobody else seems to think that this is a good solution, can you tell me what I'm missing?

as for getting the right transformer, I'd love to Unfortunately in two months, and with trips to all the local surplus stores and all over the web, I still haven't found a good one less than $70, and I need two because I'm building monoblocks.

Grataku, yes I'm thinking 4 caps (actually 4 banks of caps) and two inductors

Robert, when you refer to difficulty of driving 4Ohm loads with lower current, you're talking about current limited by the power supply and not about bias current, right? I don't see how bias would affec tthe ability to drive harder loads, but I know it would be a problem if the psu ran out of steam


Evan

Go look at standard toroids at the Plitron site.
http://www.plitron.com/

300Va are selling for around $45, 500Va for $60.
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Old 24th April 2001, 02:37 PM   #12
grataku is offline grataku  United States
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jbateman,
I don't mean to start a flaming war but can you avoid quoting someone's message for no particular reasons other than wasting server space? All the relavant info in your post was contained in one line and there are other ways to "beef up" one's postings.

grataku

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Old 24th April 2001, 10:19 PM   #13
Evaas is offline Evaas  Canada
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Unhappy accepting defeat

Well I guess I can't use my surplus transformer, so I'll just bite the bullet and buy one. Are there any real differences between the major brands? Avel, Plitron, and Toroid of Maryland?

Avel - I like the Avel Y236801, and I'd go for even more power if I could. However I couldn't find prices on the web. Do they sell direct, and if not, where can I get it?

Plitron - hmm.. it looks like the 750VA transformers are only 6 bucks more than the 500VA, and they have the same voltages for each. $66.85 for 750 VA, 25V secondaries

Maryland - the only ones they have with similar ratings are > $100

Surplus - $40, 750 VA but the voltage is too high - 33v <sniff>...

I've also decided that I'm going to have to simulate the whole circuit, because there are still a few things that I don't understand. Can anyone recommend a good free simulator? should I stick with spice, or is there something thats graphically oriented? that would be nice..

I did a little checking before sending the message and I found this: http://www.duncanamps.com/psud2/index.html
Its a power supply simulator and it looks pretty good. Has anyone used this? I'll let you know what happens after I try it out.


Evan
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Old 24th April 2001, 10:39 PM   #14
rljones is offline rljones  United States
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Evan,

I gave you Avel's phone number in my previous post; it is: 860-355-4711. They do sell direct and typically ship the same day you order by whatever method you wish to pay for. My guess is that it'll run you around $75 apiece for a 500VA transformer, but give them a call. I've found them very helpful.

I now only buy from Avel. Plitron seems to have nice stuff but EVERYTIME I've tried to place an order they have no stock and lead times are 6 to 8 weeks. Forget it.

Maryland seems a bit overpriced. Like I said, I buy from Avel. You'll save a couple of bucks on shipping if you buy both transformers at the same time.

Good luck,

Robert
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Old 25th April 2001, 12:02 PM   #15
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It was inadvertent. Sorry!
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Old 28th April 2001, 06:55 PM   #16
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Smile Duncan can tell you all you need to know

http://www.duncanamps.com/psud2/index.html

A side effect of using inductor loaded supplies is to increase the charge period and thus make the transformer and look bigger than it is (more iron if you wish).

Watch out for resonances, though.

In tubed circuits, some people use a smallish cap at the front of the inductor to adjust voltage upwards. Others use pi filters which are not really choke loaded at all. The more current you have passing, the smaller the choke you need (Energy=.5L*I^2)

http://www.transcendentsound.com uses something in the range of 50mH for an OTL tube amp. I plan to use 150mH custom gapped toroids.

Petter
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