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Old 16th September 2001, 04:38 AM   #11
hifiZen is offline hifiZen  Canada
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Wow, I'm glad to see more young people getting involved! I was about 15 myself when i first started getting serious about audio electronics, but back then the closest thing to this forum was the usenet (gee, i almost feel old talking about the pre-mosaic era...). The newsgoups were populated mostly by scientists and engineers who were very patient with all my absurd questions, but didn't really have too much DIY- or even audio-specific info to offer up. So, take full advantage of this forum... i'm sure you've already found that your most valuable resource is right here! (thanks again to Jason for so kindly maintaining this site)
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Old 16th September 2001, 05:17 PM   #12
Super is offline Super  United States
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Trust me, I'm milking these forums for everything they're worth . I've found them to be an invaluable resource thus far, and perhaps the best audio forum I've ever been to.

As for power, the current speakers I have are about 92db efficiency, but I'd still like a good deal of power, since I (obviously ) have plans to build more speakers in the future. I would have liked to try for the full 50 watts if it weren't for funds and the monumentous heat, but I'm thinking that somewhere along the lines of 30 watts would be a good place to start.

There are a few things that I'm relatively unclear about after visiting the pass site. If I were to go for 30 watts power, what values should the resistors and other components be? (I'd be willing to run several resistors in series or parallel for heat dissipation if necessary.) I have a general idea, but would like be a little more definite in my assumptions, so that I can start pricing some of the parts and get a head start on the PPM (Parental Persuasion Method).

Also, it appears that Holco's resistors with heatsinks appear to be quite popular. Are there any other heatsinked alternatives to these?

Thanks, thanks, and thanks some more

Bryan
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Old 16th September 2001, 11:48 PM   #13
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Bryan,
I'm assuming that you're talking about building a SOZ, yes?
You don't need to change the resistor values, only the rail voltages.
Caddock resistors would be a decent alternative to the Holco, but you'll have to keep an eye on the wattage ratings. Your best bet will be the big Dale aluminum body (gold anodized) power resistors. They're 1% tolerance and capable of taking quite a bit of punishment.

Grey

P.S.: For what it's worth, I've been doing this since I was about six or eight years old, but that was long before the advent of the PC. Having no money--not even an allowance--I was forced to scrounge parts from any old junk I came across. That led to a lifelong obsession with seeing how much I could do with how little money. On the other hand, perhaps it's just my frugal Scottish ancestry coming to the surface.
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Old 17th September 2001, 12:02 AM   #14
Super is offline Super  United States
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Yes, I am referring to the SOZ. Rather than cramming it all into a single chassis, I'd be making a pair of monoblocks. As for the resistors, any ideas as to the quantity I should use and the wattage ratings? Also, any suggestions as to where I should start looking for MOSFETS?

By the way, my current preamp is unbalanced single end. If I recall, the SOZ is designed for balanced XLR types? Is it difficult to change the design over to a single ended unbalanced, and would it be easy to change back if I ever needed to do so? Thanks again
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Old 17th September 2001, 01:29 AM   #15
PassFan is offline PassFan  United States
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Cool Unbalanced Input

In order to use the SOZ unbalanced all you do is ground the unused input. You could even use a switch to make it selectable. The big dale power resistors you can get from
Vishay Dale Electronics Inc.
1122 23rd Street
Columbus,NE 68602-0609
(402)563-6308
For around $32.50. If you can spring for the 250w version you can always increase your output wattage down the road. You'll need 4 of these for each monoblock . The mosfets I use are IRFP240 n-channel purchased from digi-key. About $3.00 apiece . I bought ten and got two matches (maybe lucky) because you'll want to match them pretty close.
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Old 17th September 2001, 01:34 AM   #16
paulb is offline paulb  Canada
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Super,
Read Nelson Pass' article on the SOZ at http://www.passlabs.com (I just re-read it). It should tell you everything you need to know.
Not a practical design for high power, except for folks who are really out there (you know who you are). The sizes of everything get out of hand very quickly. For a 10 Watt output, you need 200 Watts from the power supply and a 400 VA transformer - that's one channel. At least 190 watts get turned into heat.
To scale to different power levels, you just change power supply voltage and power rating, and the resistor's power ratings.
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Old 17th September 2001, 02:28 AM   #17
arnach is offline arnach  United States
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Default Bah


Bah, I've never found the SOZ to produce as much heat and draw as much power as people say it is. Maybe because it was my first DIY project, im just used to it?

I'm the guy with the 50w/ch stereo SOZ.

I'm considering going with 8 toroidal tranformers in one box, 4 50w/ch SOZs, two in parallel, but currently have inadequate funds. That's gonna be interesting...

-- Finley, who will be 17 tommorow, dang, losing the real-young advantage thing.
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Old 17th September 2001, 02:29 AM   #18
Super is offline Super  United States
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I must have read that article about 25 times by now . The more I read it, the more I understand it. I'd like to go for the 250 watt resistors, but if I can afford it, I'd probably get 8 with half the wattage for better heat dissipation. As for the MOSFETS, at only 3 bucks a piece I'll probably buy quite a few and try and get at least 4 matched pairs. That way, if one pair fails over time, I can easily replace it. All in all, things are looking as though I should make it under budget.

Theres still a few parts that I need to source out. I still need to find the toroids, the transformers, and the capacitors. I'd much rather use a variac instead of a soft-start circuit, so that I can keep the heat and voltage to a minimum when just listening to some background music. Also, I understand that since this is all point to point wiring, the type of internal wiring could play a big difference. Anyone have any suggestions as to brand, gauge, or type of conductor that I should use for wiring? If I'm reeeally lucky, I'll be able to get some freebies (maybe even the air core inductors) from Alpha-Core, which just happens to manufacture Goertz cable. Their production facility is about 15 minutes from my house, and my dad, being a UPS man himself, knows the man who delivers there. I guess I'll just sit here and hope for some interconnects and speaker cables while I'm at it

Anyways, thanks to everyone again for all of the help you given me thus far, including Mr. Pass himself. And thanks again to Jason for maintaining this site. If he didn't, I'd have way too much free time on my hands

Oh, just for the heck of it, what size transformer and torroid would I need if I managed to spring for the full 50 wpc?

[Edited by Super on 09-16-2001 at 09:31 PM]
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Old 17th September 2001, 03:29 AM   #19
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Paul,
I've got this *MONSTEROUS* transformer I pulled out of a defunct mainframe tape drive that will do something like +-55V at infinite current (okay, okay...maybe something like 25A...ahem, close enough to infinite for our purposes). I keep eyeing that with Evil Intent, perhaps for a SOZ variant.
Definitely a candidate for a water-cooled heatsink.
I suppose I might as well put in my application for membership in the Out There Club. If I'm lucky, they'll grandfather me in, seeing as how I've been a bad, bad boy for many years now, and have the projects to prove it.
Bryan,
As a rule of thumb, take the quiescent dissipation (how much heat the critter puts off while idling) and double it. To the extent that Nelson says 1200W for a 50W amp, plan on a 2kVA transformer, and expect it to run warmish. Depending on how warm, you might consider running a fan on the transformer. Now, that's assuming that you don't go for the current source version...
Plitron (www.plitron.com) has good prices on transformers, but they tend to make you wait a few weeks before they wind your parts. I'm patient when I can save a penny, but others are more in the gotta-have-it-now mode. There are plenty of other suppliers, but not all of them have heavy iron in the 2kVA range. Surplus is always an option, but it's really difficult to find the right thing, although the prices are better when things are available.
Have you filled out the paperwork for your Out There Club membership, yet?

Grey
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Old 18th September 2001, 02:35 AM   #20
Super is offline Super  United States
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After some talk with the owner of an electronic repair business to whom my father delivers, he suggested that I try my hand at practicing some other hands on work before I dive into the amps. I have no problems with this, and I may even try to grab a part time job at his place to learn some tidbits, all while making some money for these projects.

Anyways, he thought that it may be a good idea to try and repair or upgrade an older amplifier, before diving into the SOZ's, which he is familiar with, seeing as he is into audio himself. While strolling along the internet, I came across a Mark Levinson ML-9 amplifier for about 500 bucks, but with some damage to it. A friend of the owner took a peek inside, and said that some of the parts on the power supply board had overheated and would likely need replacement. After taking a look at some of the pictures, the board appears to have a fairly simple layout.

A good picture of it can be found here: http://marklev.com/marklev/ML9/img/_back.html

Its the board mounted to the rear of the front faceplate. Does this appear to be a simple enough circuit to repair, and is the amp worth anything near the $500 bucks? My parents would not be objectionable to buying it. They'd just consider it a birthday present, and my dad really wants me to gather some experience with soldering and electronics before diving in the SOZ monoblocks. The owner of the electronics company said he'd be willing to help me with the project (SOZ's and the ML) in any of his free time as well. Any thoughts or ideas? As always, all of your help is greatly appreciated. Thanks again.
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