Power Supply for 5 channel Gainclone

[Gcollier]

I'm looking to build a 5 channel Gainclone based on the LM3875. I'm hoping to get at least 30-40W per channel into 8ohms. Id like to stuff all this and the power supply into an old Carver M1.0T Chassis (may it rest in peace ). Since I have no experience with power supply design (or much else for that matter) I could use a little help. I was considering using a single 750VA Plitron for the transformer, with either 25 or 30V secondaries (I think this would be in spec for the LM3875). I've also got a fistfull of parts from the old Amp I could reuse (if possible) including:

2 Nichicon 6800uF 110V Caps
2 Rubycon 3300uF 63V Caps
2 Rubycon 3300uF 35V Caps
2 Good Sized Heatsinks
1 Transformer (120V primary, +/- 60V secondary also with 2 120V secondaries)

I'm not sure whether this Transformer would be suited to the project or not but it would save me $100 bucks on the Torroid.

Any help with a PS for this project would be greatly appreciated!

[rick57]

Not a quick answer: may have to trawl through the thread
This is not just another gainclone

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[rick57]

Transformer: How large?

[UrSv]

Originally posted by Gcollier
I'm looking to build a 5 channel Gainclone based on the LM3875. I'm hoping to get at least 30-40W per channel into 8ohms. Id like to stuff all this and the power supply into an old Carver M1.0T Chassis (may it rest in peace ). Since I have no experience with power supply design (or much else for that matter) I could use a little help. I was considering using a single 750VA Plitron for the transformer, with either 25 or 30V secondaries (I think this would be in spec for the LM3875). I've also got a fistfull of parts from the old Amp I could reuse (if possible) including:

2 Nichicon 6800uF 110V Caps
2 Rubycon 3300uF 63V Caps
2 Rubycon 3300uF 35V Caps
2 Good Sized Heatsinks
1 Transformer (120V primary, +/- 60V secondary also with 2 120V secondaries)

I'm not sure whether this Transformer would be suited to the project or not but it would save me $100 bucks on the Torroid.

Any help with a PS for this project would be greatly appreciated!

All the caps can of course be used just fine providing the rails ar lower than the 35 V for the last pair. Wether you like the set-up is a personal preference. I myself would prpbably try with a little more for this set-up but would most likely be perfectly happy with it and you could always try to use more (or less). As for the transformer you mention with 60 V secondaries that will not be useful as it would give way too high rails. You mention a 750 VA Plitron with 25 or 30 V secondaries. The 25 VAC secondaries will give you something like 36 V rails which would give you the power you're trying to get. Most people seem to use something between 18 and 24 VAC secondaries and I am using 25 vac myself which seems to work just fine with 8 Ohm speakers. Do NOT choose 30 VAC secondaries as that would give you a higher rail voltage than the chip is speced for and would most likely ruin it sooner or later. The heatsinks could obviously be used.

As for the rating of the transformer I think that 750 VA would absolutely do no harm but you could easily get away with a little less depending on your preferences. It is music and you don't plan on running all channels flat out all the time. Say 300 VA minimum and you'd most likely be very happy.