Specific Power Supply Question...

[Ben78]

Hi All!

I have been putting together a 2.1 chip amp system together. I have the 2 channels sorted but am now working on the .1 for sub.

The 2 channels are LM3876 and kit calls for 25-0-25 secondaries at 80VA per channel (I am using a 22-0-22 160VA currently)

I am looking at a ebay BTL LM3886 or TDA7293 prepopulated board for the sub channel. Most of these are asking for 24-28V CT AC at 300VA with one dual TDA7293 asking for a 700VA 35-0-35 supply

I have found some 30-0-30 300VA toroids at prices too good to pass up and was wondering if this would be suitable to power chimpamp kits. According to datasheets LM3876/86 can handle +/- 42v DC as a max so I accept that this toroid would be pushing the limit. TDA7293 is +/- 60V. Load will be strictly 8ohm so am ignoring the lower voltage requirements of 4 ohm loads.

I can change my 2 channels to TDA7293 based amps if required due to the increased voltage.

Is my train of thought heading in the right direction?

Ben

[Ben78]

I didn't realise I could run a regulated psu for amps, this makes it a bit easier!

LM338 regulated snubberized PSU for audio amplifiers

[pacificblue]

Using a regulated power supply for a power amp is like buying a car with 500 HP and then filling it with weight to avoid passing the speed limit. And it doesn't make it easier. On the contrary it adds more complexity, more heat to be sunk away and is a waste of power.

The transformers you quote for the kits are recommendations, not requirements.

30-0-30 is pushing the LM to the limits, although AN-1192 describes such a setup, too. The biggest issue will be heatsinking. The ±60 V for the TDA are only valid with no signal and correspond to ±47 V for the LM. The ±42 V with signal of the LM correspond to ±50 V for the TDA. The TDA has a current limiter with lower threshold than the LM. Both ICs have the same heatsinking area, so you should expect a similar performance.

Why don't you just connect the subwoofer amp to the power supply you already have? Check, if that setup satisfies you and if not, you can still add another power supply for the sub.

[!]

I built a regulated +-35V PSU for a pair of LM3886 with a 28.5-0-28.5 transformer, yes it uses a little more power than an unregulated setup would, but on the other hand I so often see people using several thousand uF of capacitance instead raising the cost and size about as much without reducing the ripple as much, though as PB mentioned, it's up to you which path to take with overbuilding a PSU or trusting the good PSRR figures for these chipamps.

Some say there is a sound difference. The only way you'll know for sure with your build would be to try it both ways. I think mine built that way sounds less lively but more accurate, like it's a much more powerful amp than it is even at middling output power if that makes any sense.

Another idea is whether you can unwrap the transformer and take some windings off to reduce voltage if it isn't potted. On a tight budget I'd consider PB's suggestion to share the existing PSU with all three channels, BUT with it only a 160VA transformer, it seems like you're cutting it close unless the L&R channels are just satellites not needing much power or you don't much listen to loud music.

Regarding heatsinking, something about the size of a CPU, early socket 370 heatsink should suffice, I used something about like this except without a fan, choosing one with a thick enough base that I could tap holes into the side of the base to screw it onto the PSU PCB: