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Old 15th April 2006, 05:28 PM   #1
Thunau is offline Thunau  United States
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Default Parallel a dual power supply or two power supplies?

I have a dual 12V linear power supply. Each side is rated at 5A and has a trimmer pot for fine adjustment.
With a meter I see 12V on either output and 24V when I measure from neg. on one side to pos. on the other side. (see attached graph)
Can I wire it for 12V at 10A?
The reason I'm asking is, I bought a 4 channel Tripath car amplifier on ebay that is rated at 100W per channel @ 4 Ohm. I wanted to use it for my home speakers. I know that 120W power supply is small, but a 60W is even worse. Not looking for a lot of SPL- just trying a Tripath.

I also bought two 12V, 100W SMPS for possible use with the amp (too cheap to pass up).

Is it safe to parallel those for double the current?

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN%3AIT&rd=1
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Old 15th April 2006, 06:34 PM   #2
Eva is offline Eva  Spain
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Given the 85% or better efficiency figures of class D amplifiers and the inherently low power content of music signals due to their high peak to average ratio, a single 100W PSU may suffice to power a 4x100W amplifier as long as it's used for listening plain full-range music.

Also, you can parallel independent 12V switching power supplies, but due to their regulated nature and their very low output impedance, the one producing a slightly higher output voltage will supply all the current until it folds back, then the following unit will start providing current also (if the PSUs shut down instead of folding back in case of overcurrent, then they are not suitable at all for paralleling). There is no general rule about paralleling two 12V outputs from the same PSU, some designs allow to do that while others doesn't, so you will have to study the circuit and find out.
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Old 15th April 2006, 07:53 PM   #3
Thunau is offline Thunau  United States
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Quote:
Originally posted by Eva
Given the 85% or better efficiency figures of class D amplifiers and the inherently low power content of music signals due to their high peak to average ratio, a single 100W PSU may suffice to power a 4x100W amplifier as long as it's used for listening plain full-range music.

Also, you can parallel independent 12V switching power supplies, but due to their regulated nature and their very low output impedance, the one producing a slightly higher output voltage will supply all the current until it folds back, then the following unit will start providing current also (if the PSUs shut down instead of folding back in case of overcurrent, then they are not suitable at all for paralleling). There is no general rule about paralleling two 12V outputs from the same PSU, some designs allow to do that while others doesn't, so you will have to study the circuit and find out.
Thanks. That is a very concise answer.
I thought that a single 100W PS would do OK as well, but bought two just in case.
I will try to parallel them if I notice distortion in peaks. If not, I'll stick to one.
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Old 16th April 2006, 07:21 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
what voltage does a Tripath need to produce 100W into 4r?

Surely not 12Vdc.
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Old 16th April 2006, 07:28 AM   #5
Eva is offline Eva  Spain
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He said that it was a 4 channel car amplifier, so it's supposed to have a SMPS inside to provide the required voltages. Otherwise it would be a bare 4x15W amplifier with a lot of hype in it.
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Old 16th April 2006, 08:01 AM   #6
AndrewT is offline AndrewT  Scotland
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Silly me.

What about the possibility of getting inside and feeding the amp +- Vrails directly?

That would improve efficiency compared to SMPS down and SMPS back up again.
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Old 16th April 2006, 01:46 PM   #7
Thunau is offline Thunau  United States
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Yes, there is a switching PS inside the amp. I also thought of bypassing it and using another PS to just run the amp. But after I opened the amp it became obvious that it's not a good idea. The circuit board is all integrated and tightly packed (most likely multi layered as well). The internal PS produces at least a couple of voltages and trying to figure out where to cut traces and inject voltages would be very hard.
It works just fine on a 12V external PS. Considering how cheap those are- it's a no brainer. Yes, there is some energy wasted going to 12V and back up to the internal operating voltage, but neither the PS nor the amp get warm at normal levels. So far it all sounds great.

I paid only slightly more for the 4x100W Tripath car amp and power supplies than I would have had to pay for a 2x15W Super-T. It's definitely a deal!
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Old 16th April 2006, 02:10 PM   #8
paulb is online now paulb  Canada
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Quote:
Originally posted by Eva
...Also, you can parallel independent 12V switching power supplies, but due to their regulated nature and their very low output impedance, the one producing a slightly higher output voltage will supply all the current until it folds back, then the following unit will start providing current also (if the PSUs shut down instead of folding back in case of overcurrent, then they are not suitable at all for paralleling). There is no general rule about paralleling two 12V outputs from the same PSU, some designs allow to do that while others doesn't, so you will have to study the circuit and find out.
Normally you would put in low-valued resistors in series with each before parallelling them; this will help to share the current. I wouldn't connect them together directly (or, actually, even with resistors) unless they're so cheap you don't mind the risk of blowing them both.
I'd use one supply for now, then look for a cheap surplus transformer to build a higher capacity supply like this one:
http://sound.westhost.com/project77.htm
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Old 5th October 2006, 10:26 AM   #9
diarav is offline diarav  India
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Hi,

On similar lines, I am planning to parallel two transformers (24-0-24 V, 5A ), both same type, same manufacturer, same specs to increase the current . Attached is the possible schematic. I did not find a transformer greater than 5A. This would feed a 6 (5.1) channel gainclone amp (with preamps etc).

Any suggestions, pitfalls , precautions would be appreciated.

Thanks
Din.
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Old 5th October 2006, 10:59 AM   #10
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Quote:
Originally posted by diarav
Hi,

On similar lines, I am planning to parallel two transformers (24-0-24 V, 5A ), both same type, same manufacturer, same specs to increase the current . Attached is the possible schematic. I did not find a transformer greater than 5A. This would feed a 6 (5.1) channel gainclone amp (with preamps etc).

Any suggestions, pitfalls , precautions would be appreciated.

Thanks
Din.

Same problem. They will never be EXACTLY the same. If one gives out only a fraction of a volt more than the other, this will set up a high current through the very low resistance windings of the other. Not a good idea.

What you CAN do is put a rectifier on each transformer and feed a common reservoir cap. The load will then balance out.

Another option is (if you need dual +/- supply) to use each transformer for a supply and connect them in series, midpoint to gnd.

Jan Didden
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