Simple preamp and PSU for Amp3?

[Spasticteapot]

I have recently traded for an Amp3. It uses two output inductors (apparently, both "sides" of each channel share one inductor), but has Black Gate caps.

So, what do I do with it?I would like to use the amp in a small aluminum box, with a 14.4v (regulated to 12v) lithium-ion pack and some small portable speakers. (I've been spending a crapload of time on my GC design, and having some environmentally-friendly amp that costs almost nothing to build be my main amplifier would just be humiliating).

I have some 4-pole 12-throw rotary switches ( http://cgi.ebay.com/ws/eBayISAPI.dll...MakeTrack=true ) en route, so I figure I'll make up a small ladder attenuator. (3" long, or 2" without the shaft!). Should I use a buffer (op-amp?), or just the passive pre?

Also, what would you reccomend for regulation? It seems counterintuitive to use a regulator AND a battery, but lithium-ion cells are, if you can deal with the risk of explosion, much more convienent than SLA batteries.

[Spasticteapot]

Anyone?

Should I use a linear or (more expensive) switching regulator?

[BWRX]

Hi teapot.

You can actually use the amp3 with a 14.4V rail (14.6V is the absolute max, 14.2V is the max recommended by Tripath), but it will get hotter than usual so be sure to have a good heatsink.

You can use the in your main system while your gainclone is being built That's what I used it for when I was building my other amps, and it's well broken in. I hope I didn't mislead you to think it has Black Gate caps because it doesn't. It has the standard Panasonic FM supply caps and Panasonic FC input coupling caps. You can easily desolder the small FCs and put in whatever you'd like though. I've never heard Black Gate caps so I can't comment about them, but I have used Auricaps and found them to be very good. There are lots of opinions about what cap is best and it isn't really worth it to get all caught up in figuring out which cap is best. I actually have some small film caps that I used with my Ref-T amp (Tripath TA2021B based) that sounded fine, and I'd be happy to send a couple to you to try with the amp. Let me know if you're interested.

I also prefer linear regulation over a switch mode supply. I should note that my linear supply is just a tad overbuilt, very well filtered, and tightly regulated. A quiet SMPS will most likely sound better than linear supply that isn't well filtered or regulated. I believe that's what most people are hearing and is why they prefer switch mode supplies over linear ones. SMPSs are usually smaller and cheaper too, so those are some plusses.

[Fin]

Hi Brian

Originally posted by BWRX
I actually have some small film caps that I used with my Ref-T amp (Tripath TA2021B based) that sounded fine

What are they - these "small" film caps?

[Spasticteapot]

Originally posted by BWRX
Hi teapot.

You can use the in your main system while your gainclone is being built That's what I used it for when I was building my other amps, and it's well broken in. I hope I didn't mislead you to think it has Black Gate caps because it doesn't. It has the standard Panasonic FM supply caps and Panasonic FC input coupling caps. You can easily desolder the small FCs and put in whatever you'd like though. I've never heard Black Gate caps so I can't comment about them, but I have used Auricaps and found them to be very good.

Sorry about the shipping delay. It's getting UPS'd tomorrow. (End of quarter = half-day! Woot!)

You're right - they are Panasonic FC's. (D'oh!) Not necessarily a bad thing, and nice and small to boot.

Out of curiousity, can I just used a stepped attenuator with this amp, or do I need some sort of buffer or preamp with gain? And what values of pot does it "like"?

Finally, I was thinking of using a switching DC-DC regulator to step the 14.4v down to a nice, neat regulated 12v. This is going to be a portable amplifier, and I want to keep it nice and small. (An 8-cell battery pack of the standard-sized "18650" lithium-ion cells will only be about 2.7" x 2.7" x 2.7", and should result in 65 watt-hours of power, enough to run the amp at full blast for an hour.)

[BWRX]

Originally posted by Fin
What are they - these "small" film caps?

They're rectangular plastic case polyethelene film caps. 50V and 63V versions are usually small for the 1 to 2.2uF range and they're a lot cheaper and smaller than the "high-end" polypropylene film caps.

[BWRX]

Originally posted by Spasticteapot
Out of curiousity, can I just used a stepped attenuator with this amp, or do I need some sort of buffer or preamp with gain? And what values of pot does it "like"?

Finally, I was thinking of using a switching DC-DC regulator to step the 14.4v down to a nice, neat regulated 12v. This is going to be a portable amplifier, and I want to keep it nice and small. (An 8-cell battery pack of the standard-sized "18650" lithium-ion cells will only be about 2.7" x 2.7" x 2.7", and should result in 65 watt-hours of power, enough to run the amp at full blast for an hour.)

A stepped attenuator will work fine. Buffering it would be even better, in my opinion, but it isn't necessary. If you buffer the pot the value doesn't matter as long as your source can handle it.

You can use a DC-DC converter to get 12V but make sure the battery can provide enough input voltage for the DC-DC converter. The voltage will sag over time and can cause the output voltage to drop before the battery is fully drained.

[Pano]

If you think you need to regulate the battery volatge, why not just a standard regulator?

You could build your own circuit - simple - or get a kit like the TREAD regulator kit.

[Spasticteapot]

Originally posted by BWRX


A stepped attenuator will work fine. Buffering it would be even better, in my opinion, but it isn't necessary. If you buffer the pot the value doesn't matter as long as your source can handle it.

You can use a DC-DC converter to get 12V but make sure the battery can provide enough input voltage for the DC-DC converter. The voltage will sag over time and can cause the output voltage to drop before the battery is fully drained.

14.4v is the nominal voltage, down from a maximum of 16v fresh off the charger. In fact, it's not reccomended to discharge the pack below 12.4 volts anyway.

I wonder what the most efficient type of regulator would be?

[Pano]

Originally posted by Spasticteapot
I wonder what the most efficient type of regulator would be?

A switching regulator. But don't worry about it. Any normal "3 leg" linear regulator will be good enough for this use. Any losses in the regulator will be overwhelmed by the draw of the amp itself. A "low drop out" (LDO) type is what you want, because you need a small voltage drop. A 3 amp regulator is a good choice.

If the fresh charge is 16V, then you certainly need the regulator.