PSU suggestions for multiple LM4780s

[mctylr]

I am looking at building a multi channel (8 channels) amplifier based on bridged (~100W output into 8 ohm speakers using +/- 26V DC PSU) LM4780 chips.

I was wondering about affordable power supply units, either DIY or OEM, with enough current for either 4 channels ( 2 units of 4 channel each) or the a single 8 channel unit. It seems like a high efficiency switching mode power supply might be a wise (read: cheaper than multiple or large torrid transformers) design choice.

Any ideas or suggestions?

Thanks.

[youyoung21147]

Maybe I'm wrong, but switching PSU are more expensive than a good heavy 500VA troroidal trafo.

Switching PSU are said to produce supply noise and HF perturbations.

[mctylr]

But a single 500VA torrid transformer would be enough power for how many channels? (100W/channel using bridged LM4780) 1, maybe 2 channels based on most people are using 250-350VA torrid for a single stereo LM4780 unbridged.

So 4 or perhaps even 8 >= $100 torrid transformers at retail prices is not cheap either.

I was thinking a 1-2kVA switching power supply, with >= 50KHz frequency so any harmonics / noise should be above audio range, and with good filtering on output from the power supply, it should not be a problem, I assume.

Unless you know a source of large cheap torrid transformers with cheap shipping in/to Canada. I'm open to ideas.

[bogicp]

Originally posted by mctylr
But a single 500VA torrid transformer would be enough power for how many channels? (100W/channel using bridged LM4780) 1, maybe 2 channels based on most people are using 250-350VA torrid for a single stereo LM4780 unbridged.

So 4 or perhaps even 8 >= $100 torrid transformers at retail prices is not cheap either.

Probably you don't need 250-350VA transformer per channel .
If you go this way you must have a huge and very robust case, and this is an extra price.
One of ways to build your project is to use one 1.2kVA transformer for overall amplifier, or two 600VA.

I was thinking a 1-2kVA switching power supply, with >= 50KHz frequency so any harmonics / noise should be above audio range, and with good filtering on output from the power supply, it should not be a problem, I assume.

Unless you know a source of large cheap torrid transformers with cheap shipping in/to Canada. I'm open to ideas.

If PC power supply cannot fit to your needs, there isn't other ways (IMHO) to build SMPS cheaper than analog for this power. No matter about noise, hum and problems that SMPS may have with light loads.
I don't know where you can find smps modules in market for this amount of power, but cheaper than analog. If you look at prices of PC power supply, you have wrong example... PC power suplies is probably cheapest supplies on the world with this power.
Rule of the tumb is that (unregulated) analog supplies is always cheaper than (regulated) switch mode, or I missed something in today technologies, sorry if this is a true.

Best regards,

-boggy

[youyoung21147]

PC PSU only give 12V, so you 'd need 6 of them in series to get the power you need, but then, you won't have any problem with ratings if you use 400W supplies

I think you can find much cheaper trafos than 100$ for a 500VA. In my contry, everything is expensive in this domain, and I don't pay 100$ for a 500VA trafo.

I'd go for 2*600VA trafos with double unregulated PSU. You would use independant PSU for left and right, it has many advantages over one 1.5kVA trafo.

Maybe you will even spend more on capacitors than on transformers anyway.

[bogicp]

Originally posted by youyoung21147
PC PSU only give 12V, so you 'd need 6 of them in series to get the power you need, but then, you won't have any problem with ratings if you use 400W supplies

fully regulated power on PC supply is on 3.3V or 5V, 12V outputs is 5 to 15W only.

....
Maybe you will even spend more on capacitors than on transformers anyway.

Yes, (good) capacitors is more expensive than transformers.


best regards

boggy

[jackinnj]

Originally posted by mctylr
I am looking at building a multi channel (8 channels) amplifier based on bridged (~100W output into 8 ohm speakers using +/- 26V DC PSU) LM4780 chips.

I was wondering about affordable power supply units, either DIY or OEM, with enough current for either 4 channels ( 2 units of 4 channel each) or the a single 8 channel unit. It seems like a high efficiency switching mode power supply might be a wise (read: cheaper than multiple or large torrid transformers) design choice.

Any ideas or suggestions?

Thanks.

Power-One makes their "International Design" 24 and 26V switching supply at various current ratings -- so you need 2 of them and these are always for sale on EBay. They are compact and usually sell for $10 to $25.

PWER is one of Cisco's major power supply sources.

[youyoung21147]

fully regulated power on PC supply is on 3.3V or 5V, 12V outputs is 5 to 15W only.

Are you sure ? Under 400W or more, a good PSU will only have a few mV dropout and it delivers 30A or more. I am talking about ATX or so PSU, the standard ones. But maybe can't they be connected in series ??

[Tweeker]

Shipping might cost near what the parts did, but if your not averse to EIs you could get 16 18VCT Parts Express EI transformers for $80. Mono for every channel. Carefull not to throw out your back.