[bradmill]

I just finished my first META... a basic portable 9V configuration based around the AD8620 opamp (I also tried the AD823).

I now want to build a better quality wall powered unit, but I am not sure what to use for a power supply. I have a couple different wallwart supplies already:

Ault Inc P57181111A010G - 18V 1111mA unregulated linear power supply.
Phihong PSA-30U-24-0 - 24V 1.25mA switching power supply.

Both of these are likely too noisy to use directly. However, would it be cheaper to build a circuit to regulate one of these, or just buy a regulated ELPAC WP12 (or something similar). If regulating one of these myself is an option, I would appreciated it someone could give me some hints on the best way to do so.

I do have access to a scope... so I suppose I should take a look at the outputs of these and see how bad they are.

Off topic... I haven't really tweaked my first META much yet. I haven't stacked the buffers, haven't added a current source, and I also left out C4, and it still sounds great! What tweak would get me the best improvement, but not drain my battery too fast

Thanks in advance,
Brad

 

[tangent]

I never really understood the term "linear unregulated". Ault charges a lot for them, so they probably don't completely suck, but their linear regulated ones cost more so there's got to be a drawback. It would be very educational to look at its outputs with your scope.

If you find that the unregulated linear supply is fairly quiet, it's probably the one to use. But if it's noisy, especially in the audio frequencies, the switcher will probably work better. I've not bothered to try and find the cause of this, but the META42 can couple power supply noise into the amp output if there's enough of it. It's important to use a fairly quiet power supply with this amp board. The switcher might have a fair bit of noise, but it'll be up in the hundreds of kilohertz to low megahertz range, which is usually harmless. Please post your findings -- I'm really curious as to how a $40 "unregulated" supply performs.

Quote:

regulated ELPAC WP12

That's another switcher, for what that's worth. "Regulated" can mean switchers, since all the word means is that the output voltage is independent of the input voltage. Allied mistakenly calls these linears, but they're not. See my second post in this thread for ways to identify switchers when the datasheet doesn't say.

Quote:

I haven't really tweaked my first META much yet. I haven't stacked the buffers, haven't added a current source, and I also left out C4, and it still sounds great!

Yeah, it's kind of unfortunate that some people are under the impression that a META42 will have sucky sound if you don't max the thing out.

What next? Well, adding the current source is fairly inexpensive in all senses of that word -- $1 in parts, easy to install, and usually under 2 mA additional current drain. It's not going to totally transform the sound, but it's a foundational kind of upgrade -- a good one to do before you start making the rest of the amp sound better, since the op-amp is the source of all the sound.

You might also consider adding a second level of buffers. This will draw an additional 3 mA or so if you use EL2001s. It's a bigger sound improvement than the current source, but of course it's more expensive, harder to add, and it's a bigger battery drain.

C4, well, that's kind of a "if you've got the money, what the heck" kind of upgrade, especially if the amp is behaving well without it. I think the other two upgrades are bigger improvements.