Power Supply for 40watt amp?

[kriista]

I plan on building four of these 1-chip 40watt amps (http://electroschematics.com/513/1-chip-40-watt-amplifier/).

The sound quality doesn't matter so much as I'm using them for an odd purpose (powering/driving computer hard drive voice coils...)(basically using an 'open face' hard drive as a 'speaker'. it sounds amazing!).
I've tested it with several home stereo amps (circa 40watts), and it's enough power to do what I want, so I found this circuit and ordered the parts to build four of them.

Here is the schematic:


Now the power supply looks like this:


In order to use these amps, do I need to build a power supply from scratch?
I can't see a regular 'power supply' rating on the page anywhere (like 12vdc 1000mA etc...)
It would be a pain to have to build a supply from scratch, much less four of them....

Can anyone tell something from the power supply schematic as far as it's output/rating?

[Rob Strand]

For power amplifiers you will usually need to build a power supply.  That means you have to do mains wiring (if you don't know how to do mains wiring safely you shouldn't do it because you could kill yourself or someone else!)

As shown the amp is running from an unregulated supply.     The chip can only handle +/- 30V max and recommended is +/-27.5V.  For this reason the recommended transformer is 36Vrms with a center-tap (18V+18V).

As for the rating of the transformer it's a little tricky because it depends precisely how you will use it.

For a basic rating you will need an 75VA transformer to drive one amp module.  With a 75VA transformer you can produce full sinusoidal output continuously without frying the transformer.  (Technically, If you intend of permanently clipping the amplifier you may have to bump the transformer rating to say 120VA.)  With the 75VA transformer you will only get about 30W output into 8 ohms because of transformer power supply regulation cause the power supply rail to drop.  It's probably unwise to increase the transformer voltage because you might over-voltage the power amp chip.  With a higher VA transformer you can get a bit more output, but not much, because it has better regulation - not worth the expense.

BTW:  An the PSU the caps should be 4700uF not 4.7uF.

[geertjacobs]

You could also go for the Tiny Giant.
20 Watts is not that much difference with 40 and it avoids the PS issue by using a laptop supply.

[kriista]

That's a bit of a bummer, as I've not done mains power before.

Is there a way to test the circuit (for a couple of seconds) without a from-scratch power amp, in order to see if it works and is loud enough, but getting/looking into a custom power supply(ies).

Also, is it possible to build a single supply that can power 4 of those amp circuits?

Something like the Tiny Giant would be great, but I think 40watts is as low as I can go. Rather, in the testing I've done (using a home stereo rated at 40w per channel) barely anything happens until it's cranked right up to maximum volume. So I worry that 20w would do nothing.

[iccaros]

That's a bit of a bummer, as I've not done mains power before.

Is there a way to test the circuit (for a couple of seconds) without a from-scratch power amp, in order to see if it works and is loud enough, but getting/looking into a custom power supply(ies).

Also, is it possible to build a single supply that can power 4 of those amp circuits?

Something like the Tiny Giant would be great, but I think 40watts is as low as I can go. Rather, in the testing I've done (using a home stereo rated at 40w per channel) barely anything happens until it's cranked right up to maximum volume. So I worry that 20w would do nothing.

40watts is  a lot,  way too much, really and 20watts will is not half the volume its only 3db volume as it takes doubling your output power to increase 3db..  so a 50watt is 3db lower than a 100watt, and a 25watt is only 6db lower than a 100watt.  Since you are using hard drives as speakers, I am not sure the goal of power @ 40watts, as I am sure the electronics in the hard drive is not rated for that..

you can use a computer power supply at 24volts. It should work in this case, just less volume, I have a few HP printer ones that are rated at 24v

[kriista]

It does seem crazy high to drive this. I'm accessing the voice coil directly, so it's literally just a magnet and a coil, like an actual speaker.

I'm basing the 40watt thing on the fact that having the volume at anything less than 95% of maximum volume literally does nothing. It's a tiny, muffled sound (making the arm move imperceptably). At full volume you actually get the arm bouncing around and you get the actual 'clacking' sound I'm looking for.

Computer power supply as in the thing inside a computer tower, or as in a laptop power supply?

[iccaros]

laptop supply, I buy them at Goodwill $3

[kriista]

Finally got around to make a video of the sound:

http://rodrigoconstanzo.com/hds/

(using just a home stereo at the moment)