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Old 6th November 2004, 10:20 PM   #1
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Default Another car amplifier at home thread...

After much searching ad reading, I still have a few questions concerning the use of a car amplifier in my home stereo.

The largest factor seems to be the power supply. I plan on using a "test bench" supply. Its a Sorenson 13a, 0-40v. Using the 13a I figure(13a=170w/13.8v) that I can use about a 170W amp. What would happen if I used an amp rated at a higher output, say 600W....{evil grin}? Would the low amperage just "limit" the amplifier, or would there be damage or other negative side effects? I plan on getting one of those monster(100+amps) power supplies, with 220 three phase mains, but not for a while.

Since the voltage is adjsutable, what would be the ideal value? I used 13.8 for calcs, but would increasing the voltage increase the performance/output?

Are there any issues with input impedance(preamp to amp)? I seem to remember hearing something, years ago, about a converter being needed, but havent seen mention of one in any other threads.

Can I "parallel" power supplies' outputs to increase amperage? If not, can I increase amperage by using multiple power suplies with car battery isolators(used for multiple battery setups in competition auto sound charging systems)?

Would auto sound "stiffening" capacitors (1 farad each, and also found in competition auto sound charging systems) help the power supply?

Any "constructive" ideas/comments welcome......

Thanks,

Nathan
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Old 6th November 2004, 10:29 PM   #2
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Default Why??

When you can buy a really big pro audio amplifier from QSC or Crest that will kill your weakly powered car amplifier?

Besides, the best way to power car amplifiers is to remove their switching power supply and drive the amplifier's voltage rails with a "Standard" amplifier power supply.
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Old 6th November 2004, 10:41 PM   #3
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If you wanna buy me a Crest or a QSC....hell, buy me both...., I'll give ya my address...hehe. But seriously I have an old favorite amplifier of mine (Autotek 7600BTS by Zed Audio...IMHO, one of the best car amps ever made) that I dont realistically want to put in a car anymore. So why not bring it indoors(harder to steal that way too). In fact I have several of the AutotekBTS amps that I want to use for a complete HT/HI-FI setup someday(hence the need for the 100amp plus PS of the "future"). For now I have to make use of what I have.....exceptional car amps and decent power supplies(neither of which I plan on parting with).

I'm not positive what kind of PS is onboard the BTS amps, "regulated" sticks in my head though.

Thanks for the input....
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Old 7th November 2004, 12:29 AM   #4
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Default big power supply...

Hi,

I've recently been fixing dead car amps I've been buying on ebay. In order to test them at a good level I made a pretty big power supply, basically a 500va, 12v transformer, 35 amp rectifier and 100,000uF...17v rectified and smoothed, I used a variac to lower the ac in to get 15v on the cap, then 12" of 8gauge to get it to the amp...

It didn't work well enough, at full power an amp rated at 2x200 into 4 ohms would shut itself down erratically. I had to use my scope to figure out what was going on, though the average draw was as predicted, the peaks were making the voltage droop, only for a few millisecs, but it was triggering the undervoltage shutdown on the amp, making for lousy musical performance.

The answer proved simple enough, add a battery, I used an old 7ah unit I had spare when I replaced the batts in my UPS.I actually have 4, though I can't imagine a scenario where I'd need all of 'em...Though I am upgrading this to a pair of the transformers, bigger rectifiers and more capacitance, basically so I can drive the sort of amp you are describing...

Biggest amp I've run at full power is 2x250 into 4, and in doing that I've popped two 35amp rectifiers so far, both mounted on a big heatsink, my next stop is a pair of IRF 160a diode blocks I found on eBay...

If you have an old battery of some sort use that, it makes for an infinitely better musical experience...beware of the huge current, it breaks things...

Stuart
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Old 7th November 2004, 12:56 AM   #5
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Thanks for the info, I'm trying to stay with a "commercially available" ps though, as I'm sure you know they are all over ebay, its just the shipping that kills ya(and the 220 three phase restrictions). I agree with your "backup" battery idea, I was hoping that the stiffening capacitors that I have would act in much the same capacity(no pun intended). Do you remember the brand of the "250x2" amp that you had on your bench? Some brands rate different that others.

And BTW im very good at breaking things, thank you very much......heheh......

Nathan
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Old 7th November 2004, 01:08 AM   #6
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Rewind a MOT

I did,I can easily power both of my car amps at the same time with it.
(an old 200Wx2 Majestic (sic) and a Kenwood KAC-645 70Wx4)

http://www.users.qwest.net/~ptaylor/...MOTPSpage.html

Plenty of current available there...
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Old 7th November 2004, 01:09 AM   #7
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Hi,

I think it was an earthquake, or maybe the big pioneer, not sure too many amps...

I've been buying and fixing these things at a prodigious rate, and by chance I actually have a handful of the zed audio amps. I didn't know who they were until sdoom, one of the other guys here, clued me in. Apparently they designed amps for a couple of different companies. As I was fixing I was seeing virtually identical amps, so I began to suspect a common designer, then I noticed the zed audio branding on the boards and it all made sense...

If you need a 12v/100amp supply, it will only pull approx. 10 amps from the wall, so why would you need 3 phase...I made a 70amp supply for less than $100...adding another transformer would cost $30 and I'd have 100amps easy...

Stuart
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Old 7th November 2004, 01:21 AM   #8
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DigitalJunkie, nice job on the transformer. I cheated and bought mine, they use a gauge of wire about 3mm in diameter for the secondary, the place I bought them from didn't know the rating, only the application they were used in, one of those 35/120amp car battery chargers...

I suspect if you had a test load and used your amps at full power into it you'd pop the rectifiers, you'd need an average of 65 amps, it has to pass through 2 diodes, each of which will drop about 1-1.5 volts, so the bridges will have to dissipate 30-50watts each...poof, been there done that...and let me tell you those extrusions that pretend to be heatsinks are nowhere near adequate for the sort of power these amps put out, 10 mins at 1/2 power and all of them are 60c or hotter...fans anyone...

I'm gonna rewind me some transformers...

Stuart
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Old 7th November 2004, 01:35 AM   #9
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DJ......Thats cool, SCARY, but cool.....I might have to do some playing with that idea, Do you have a schematic, I can see alot from the pics But if I do attempt this, I would want to be sure I have everything right.......Thanks


Stuart.....if your interested, there's a good "fan" site of zed audio and its main man Steve Mantz....

http://www.members.shaw.ca/pferlow/s...tz_history.htm

cool stuff if youre into it. The three phase PS stuff is relatively cheap and available on ebay(several thousand dollar power supplies for basically the cost of shipping). How does your PS compare with DJ's? Again I'd like to ask for a schematic....if you have one available for your PS. Also, how do you "add" a tranformer to a power supply? Sorry if thats a "dumb" question.....

Thanks again......

Nathan
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Old 7th November 2004, 01:50 AM   #10
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Oh yeah....I forgot to ask about the "shorted penny"..........sounds like a good show.......heheh
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