Another car amplifier at home thread...

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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
 
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.
 
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....
 
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
 
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
 
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
 
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
 
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/steven_mantz_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
 
adding a transformer

Hi,

Assuming the transformers are all identical, I simply parallel them after the rectifiers. The sharing isn't perfect, but it's close enough, basically because the one that hogs the current heats up more and as it's resistance increases it will compensate for the imbalance.

I could be wrong, but I think you are better off making huge capacitors from many parallel smaller values. I use paccom 4700uF/50v guys, each has a ripple current of something like 10a, by the time I parallel a bunch no single cap will ever come close...and I have hundreds of them...I designed a really simple PCB layout approx 10x12 and simply covered the entire sheet with them...each serpentine trace is about 3/4 of an inch wide and gets an 8 gauge wire to the rectifiers and another to the battery.

Stuart
 
Adding a trans makes much more sense now...thanks

The caps I was thinking of using(I have 4, though one's dented, not sure if its still good) are 1,000,000 uf @20 VDC. Im not sure how the voltage differential affects its "stiffening" capabilities at 13.8v. I picked these up from a partsexpress closeout a few years back and was going to use them to beef up the charging system on a competition auto sound system. I obviously never got around to that.....:(, but If I could work them into a PS to "help" out that would be cool too....... watcha think?

Nathan
 
big caps...

If you already have them, they'll help and you can't go wrong...hmm, well no, thats not strictly true, actually...

You will have to figure out a way of gently charging them when the power is applied, or you run the risk of blowing things. Car alternator diodes are very tough hombres, rated for the alternator they are attached to (100+ amps), plus they share the duty with a battery of huge capacity...the power is never really off...

I played with a 0.5F cap for a little while and while it held the correct amount of charge, there was no way it had an esr < 1 milliohm, so it didn't function like a bank of capacitors of even 1/10 of the nominal value.

At their normal price, and in the context of a car, I think perhaps the money is better spent on a bank of caps, more battery, more alternator, better cables etc.

Stuart
 
Reliable commercial power supply

Look for a ham radio power supply. They are rated for continuous duty at high power levels, which is what you really need.
A 600 watt amp would run on the average much lower power and only use full output for short periods, unless you are driving a sirene...
In my experience, the most reliable (reasonably priced) regulated ham supplies are made by Astron (US). You may want to pay another $20 for meters on the front-panel. For this application I'll buy the RM-50 or the next one up in their line of fixed 13.8V supplies.
They show up on eBay but they're not expensive new and they last a lifetime or two. Look for your local supplier of ham gear.
 
In that case..

You guys are all impressively overthinking this situation. Converting 120VAC down to 12VDC then back up to 60-80VDC in the amp is ridiculous. If you want to get the most performance out of your permanent installation in your home, simply build a standard amplifier power supply, remove the rectifier diodes, bypass the protection circuitry (if it's involved) and blast away.

I also repair car amplifiers professionally...and build them. No, they're not for sale. :)
 
;)

I'll try to draw up a schematic soon..

After I built it,I told my friend about it,and suggested he build one for his car amp (an older 150x4) to use with some B52 bandpass boxes he has.(anybody know anything about these?)
We went out one day and found 4-5 big caps at the surplus place(~$10-15),and he built it up..I think he has close to a half Farad of caps. (0.45F,or something,I forget) connected together with aluminum bars.
He's got the same dual rectifier setup,but I think his bridges are rated for a bit higher current.

He was showing me how well it would work for light welding too.. :hot:
Be careful about shorting it out! (theres alot of energy in those caps!)You can easily blast the tips of screwdrivers away,and weld them across the bars...(Don't try this! :whazzat: ) Be very careful!

On my supply I only have about (hmm,lessee..) about 0.11F..but it still makes the light dim for a split-second when you first turn it on.. It does run fairly warm due to the magnetic shunts on the MOT core. I've heard it's possible to remove these,but havn't tried it yet. The shunts might actually help to regulate the voltage a bit,so I figure I'll leave them for now.. Using a metal enclosure,with a fan would be a good idea. (My friends PS actually has forced air cooling for the rectifiers,with a little sheetmetal duct.He used large CPU heatsinks also..)
I also suggest a fuse,or circuit breaker on -atleast- the primary side.(I used a 15A breaker from an old 6-outlet strip.) I don't have any fuses/breakers on the secondary,but it might be a good idea. (couple of 30A 12V breakers,or something?) and use a heavy 3 conductor power cord and plug.(I snagged it from the same 6-outlet strip.) grounding the tranny core is a good idea.


But-I have to agree that bypassing the SMPS in the car amp is probably a better solution.I actually did that with the 200Wx2 amp before I built the 12V supply. The tranny was slightly small for the job,but I never really cranked the volume much.. I think the rails were +/-35V..
But it's always nice to have a decent high current bench supply for testing car equipment,or recharging car batteries,etc. :D
 
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