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Old 10th July 2005, 01:16 PM   #21
diyAudio Member
Join Date: Jul 2005
Location: england
"Technically, 24V should be ok"

Are you sure? The maximum supply voltage for the LM4700 is 66v; and when you switch the power on, the transformer output voltage will be some volts higher than its nominal rating. You'll lose about one-and-a-half volts through the rectifiers; but even so I'd have thought a 24v transformer with 5% regulation could generate at power-on a DC split voltage of 70 volts ... more if your mains power goes higher than its nominal value. (Perhaps someone with more experience of power supplies could comment.)

Anyway, you'd be better off with a transformer with 20v secondaries. That will give a split rail power supply of about +- 28 volts, which gives you a comfortable safety margin.

Are you using the same power supply capacitors for all the amplifiers? If not, you can have a regulated power supply for each amplifier chip, so each chip has its own supply voltage. But that's more expensive and complicated than simply using the same amp chip for each channel.

"I want to do (2) LM3886, (1) LM3875, and (1) LM4700 from one transformer ..."

It does seems complicated to use several different amplifier chips. Is there some advantage compared with using, say, 4 LM3875s? It's not as if the chips cost much.

Tim Martin
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Old 10th July 2005, 02:42 PM   #22
diyAudio Member
Join Date: Feb 2004
Location: North of Toronto
You could get the 25 volt Avel transformers and use 2 x LM338 with a 5 volt drop and this will give you about 30 Volts DC output,
this wil be a happy value for all of your chips.
use Carlos' suggestions for component values.
Sheldon D
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Old 10th July 2005, 03:27 PM   #23
DonoMan is offline DonoMan  United States
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Location: Massachusetts
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I have 68000uF caps, was going to put one of those per rail (so 2 per transformer) between the PSU and amps, and then put maybe a smaller el and a film cap in parallel at each amp
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