Using a car amp in the house?? - diyAudio
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Old 7th February 2007, 03:59 PM   #1
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Default Using a car amp in the house??

I was looking through some stuff that was in storage in my basement and I came across my old car amplifiers from about 10 years ago. I have three amps
1.
Orion HCCA225r

2. Pheonix gold M25

3. Pheonix Gold m100

I know this has been covered in other threads before, I searched and found some info, but not all the answers to my questions. Im interested in possibly using one of them in the house Could I just build a simple 12vdc power supply to power the amp?? I will probably try the m25 first since its the smallest. If so about what size transformer would I need??? I was hoping to get by with a 12v 250va torriod that I have. Im planning on using the amp to drive a small sub. Any ideas??
thanks
Frank
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Old 7th February 2007, 07:54 PM   #2
jaycee is offline jaycee  United Kingdom
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You'd need quite a hefty amount of current for this. The amps have a switchmode supply inside which converts the low voltage, high current supply from a car battery, into something more appropriate for the amplifiers.

You might want to consider using the 12V as a test, then open the amps up and find where the output from the supply is. Then disconnect it, and build a standard mains power supply to replace it.

On the M25, you can see a small transformer at top right. This is the output from the SMPS (driven by two MOSFETS, on the heatsink just above it). Try looking around there. My guess is the output will be something like +25V/-25V.

The M100 looks similar and may even be easier to adapt. The two large blue capacitors will be across the power supply rails. probably +40/-40V in this case.

The Orion looks much more complicated. I'd avoid fiddling with that one - consider selling it on eBay
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Old 7th February 2007, 09:09 PM   #3
Limhes is offline Limhes  Orkney Islands
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Quote:
Originally posted by jaycee On the M25, you can see a small transformer at top right. This is the output from the SMPS (driven by two MOSFETS, on the heatsink just above it). Try looking around there. My guess is the output will be something like +25V/-25V.
You might check the large reservoir caps too. Supply voltage is most likely on them too - easier place to start from I'd think...

Fantastic page by the way
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Old 7th February 2007, 11:13 PM   #4
CBS240 is offline CBS240  United States
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Hi

I did this type of mod once in a cheap optimus amp. I remember that it had 2 smaller front channels that are chips run from the 12V B+ and that the 2 larger channels with the SMPS, ect. I had to add some PS filter caps(obviously, since the freq. 60Hz instead of 30-40KHz) and also connect the input and remote to a 12V source in order to get it to turn on. I left the original caps connected to the SMPS since it was still running and used seperate ones for the new PS. The 12V source I used was small though since it wasn't really driving anything heavy anymore. Because the SMPS was still running, I had to break the copper traces for the +/- Vcc so it would run from the 60Hz power source. I also added a couple of power resistors to load the SMPS slightly just in case the no load situation might screw it up. I wanted to use this amp in the car again later. Different amps may have different configurations, so I recommend maybe looking at a schematic first. In the case of this cheap POS, I really didn't care much if it exploded or not.

The Vcc was like +/- 28V. I cranked it up about 4 or 5V once and it had more power. After a while it blew a small signal driver on one channel. So I fixed that and continued to use it at 28V, but now it is back in the car.
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Old 8th February 2007, 02:15 PM   #5
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never mind.


==edited due to me actually reading the original post all the way through==
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Old 8th February 2007, 04:33 PM   #6
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Ive been playing around with a cheap Kenwood 4x25w amp that I have, I was thinking of using it to make a small 2.1 system for my dads PC. Ive been powering the amp with a 500w PC power supplies thats rated at 20a on the 12v rail. I connected a pair of bookshelf speakers and a small 8in sub and it playes fine. Actually sounds half way decent too. I was wondering what I could do to improve on this. How could I clean up that 12v before it enters the amp?? I was think of a pair of 2200uf/35v caps and maybe a small choke inline with the 12v. What do you guys think??
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Old 8th February 2007, 04:45 PM   #7
poynton is offline poynton  United Kingdom
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My wife objected to the fumes from the car engine so I had to build a power supply !!

I used the guts of an old UPS to form a basic battery charger / battery combination. (removed the DC-AC inverter )

Andy
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Old 8th February 2007, 05:38 PM   #8
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thanks for the idea. Im going to stick with the PC power suppluy for now since it was free and easy to implement. I added a 10000uf cap from 12v+ to ground right before the amp and a small choke inline with the +12v. I pulled the choke from one of those car audio hookup kits, it was used inline with a fuse. Any other ideas how to quiet down the 12v even more?? There is some noise when no music is playing if you put your ear to the speaker, it sounds like it may be noise from the fan in he power supply, but I could be wrong. Any ideas to get rid of this?
thanks
Frank
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Old 9th February 2007, 04:25 AM   #9
jaycee is offline jaycee  United Kingdom
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Bear in mind that you will be putting power through two switchmode supplies so supply noise is pretty much unavoidable. I'm not sure what switching frequency is typical for a PC PSU but in a car amp it's only going to be around the 40KHz mark.

Also, you may find that hanging a load of smoothing on the output of a PC PSU will trigger it's protection circuit when the capacitor(s) are empty.

If what you want is a quiet amp, you would be best to do what I initially suggested which is to bypass the amp's own switchmode supply, and make a linear supply that will provide the voltages needed by the actual circuit itself.
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