43v SMPS for dual bridge mono LM4780 - diyAudio
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Old 10th April 2007, 09:00 PM   #1
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Default 43v SMPS for dual bridge mono LM4780

Hello Everyone,

I recently purchased a SMPS from Ebay: http://cgi.ebay.com/ws/eBayISAPI.dll...1981&rd=1&rd=1

I was hoping to use it to power my two lm4780 boards from Chipamp.com.

Has anyone ever used this smps for the dual mono application. I also want to build a drv134 bridging module so that both boards will have a mono output. This is going to be used to power a bass guitar monitor speaker, probably an Omni 10, 12 or 15, for practice with my pc running guitar rig 2.

Thanks for your assistance.

Sincerely,

John
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Old 10th April 2007, 11:34 PM   #2
Minion is offline Minion  Canada
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Well First off that PSU will not supply enough Current for a 2 LM4780...Actually it will barely supply enough current for Half of a LM4780.....

Also +/-43v Rails is actually Too high of a Voltage for the LM4870, It states in the Datasheet that the Absolute Maximum it can stand (with a signal applied) is +/-42v and at that Voltage it will run very hot...+/-35V is Probably the Max that I would use but +/-28v what I aim for.....

If you had one of those PSU"s for each Half of the LM4870 (the LM4870 is actually 2 LM3886 in One Package) then it would work but you would probably have to regulate the Voltages down closer to +/-35v for best performance useing maybe an Off Board Linear regulator......


Good Luck
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Old 11th April 2007, 12:05 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
that ebay site is telling lies.

I see they cover themselves by offering a modifcation to get the voltage down to +-30V.

For 8ohm speakers (not 4 to 8ohm) you can run @ +- 35Vdc.
for 4ohm speakers you can use +-28Vdc.
for 6ohm or 4 to 8ohm probably some supply voltage in between.

You may be able to modify the SMPS to allow either 8ohm or 6ohm speakers to be used.
But the problems go on.

I think a 3886 has a peak output current of 7Apk.
A 4870 has two 3886 inside so the total output current is 14Apk.
Fortunately the supply pins for the two internal amps are separated so you can supply each chip separately.

So four of these SMPS can supply your two chipamps with less than half the peak current that they need.

I would suggest you try to sell on the SMPS to some unsuspecting purchaser, but try to be a bit more truthful.
Then go and buy a proper transformer/rectifier/smoothing capacitor PSU and do the job right.
Each 3886 can deliver upto 60W so the 4 chips need about 1.5Times (60+60+60+60) = 360VA @ 25Vac-0 & 25Vac-0 for 8ohm speakers or 360VA @ 20Vac-0 & 20Vac-0 for 4ohm speakers.
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Old 11th April 2007, 05:03 PM   #4
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Can's say much about the SMPS, through ignorance more than anyhting else. However I have used that particular E-bay seller without any problems. In fact just had some lm3875 chips delivered today. Its the second time that I ordered there. Stadholders prices were the best I could find. Got 4 for 9.18 this time, though I did win a pair in auction bought the other two buy it now.

The description does make it clear that the voltages are working at the absolute maximum for the chips.

I looked at this supply, but ended up going for four skynet 8080's.

I was more confident doing this as I could then use Decibel dungeons instructions to build an array i knew would work. I had my teething problems certainly, but i knew that I was not trying to achieve the impossible. I am very pleased with the SMPS amp, I have not built a transformer/rectifier/smoothing capacitor PSU as suggested by Andrew to compare with the SMPS but NUUK has tried both and recommends the SMPS.

Dont know if my experiance helps but I thought I would chip in.
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Old 11th April 2007, 05:19 PM   #5
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Thanks for all of the replys. I have spoken to a couple of members here about modifying this smps to work with a single board set, and getting a second smps for the other channel. I am sure it is going to be some work getting it all done, but I think that it is going to be fun to experiment with the smps, rather than the time tested transformer route.

Does anyone know of a good source for 1u and 2u rack mount cases? I am also building a dual channel tube blackface preamp and a acoustic 360+. I need 2 of the 1u for thoes and probably a 2u for the power amp. Has anyone ever made their own using steel from a hardware store cut to size? Mabey bolted to a frame of extruded aluminum?

Thanks again,

John
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Old 11th April 2007, 09:20 PM   #6
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I have never made a rack, but I have seen a DIY rack made from MDF on the internet somewhere.

It was months ago when I saw it. But a bit of googling might be worth it. It is likely I saw a link to it through hackaday, cause its the sort fo thing I would have come accross through browsing rather than by looking for. If I recall correctly it was used for mounting a server rather than audio equipment.

Sorry I dont have time to search it out again. I have some heavy work on right now. If you have no joy by hte weekend I will see if I can find it for you.

Blair
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Old 12th April 2007, 07:12 AM   #7
space is offline space  Norway
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With some hard work you probably can make the SMPS deliver lower voltages but you can't (easily and economically) make it deliver more current. I would drop that SMPS and look for something with the right spec (~+/-30V ~10A).

space
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Old 14th April 2007, 07:05 PM   #8
kscharf is offline kscharf  United States
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I don't know that I'd want to use a SWITCHING power supply in an audio amplifier application anyway. Asking for noise problems IMHO.
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Old 14th April 2007, 11:09 PM   #9
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Quote:
Originally posted by kscharf
I don't know that I'd want to use a SWITCHING power supply in an audio amplifier application anyway. Asking for noise problems IMHO.
No noise issues with mine, silent when its supposed to be. Very detailed, controlled sound.

I have 4 skynet 8080's in series and parrallell to give +/-24v 6a. I folllowed NUUK's advice to make it and I am very happy.
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Old 14th April 2007, 11:22 PM   #10
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I use two +48 VDC switchers and my own "secret sauce" humbucking torrid line filters to get a really nice quite source. Result is +/- 48 VDC rails driving two 500 watt modular MOSFET amps (into 4 ohms) with reduced power of ~ 220 watts per channel = a very cold running amp for 24/7/365 usage without ever needing a fan ... This one is a work in process ...
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