Fun with T-amps - I didn't know what I was missing.

[cowtown]

Itching for a project, I was reading up on amps like the gainclone, and stumbled into the whole "class D" cult. On a whim I bought two of these little 2x100watt amps from China, and I've got to say they sound just great. The rating is optimistic - realistically, they put out 2x40W @ 8Ω, < 3% THD.

For $40 each, I thought these would be toys and would just keep me occupied for a few hours, but they have a surprising amount of power. I'd say they sound at least as good as my Denon 90WPC AVR (of course, they don't offer SPDIF, DTS, and all that other stuff). The t-amp's noticeably better in the mids and highs than my Nady pro amp.

I've been running one in my garage with my Statements Monitors, and they do an easy 80-85db without the heatsink going over about 110F on a 70 degree day. I'm running it off a 24V lead acid battery, but the board will accept anything from 12-26V.

The only problem I'm running into is kind of tangential - the switched-mode power supplies I've tried all seem noisy and send a whine through the amp. I've tried a 19V 6A, 12V 11A, and 24V 11A bridged supply, and they are all noisy to some extent (these are notebook PC power supplies). On the battery, the amp is nearly silent.

Are there any standard ways of cleaning up the output of switching power supplies with some filtering caps? I can't find much on this subject beyond "buy a higher quality power supply."

I've attached a few pictures of the amp just to show how small it is. The loose speaker grill covers an RS180 woofer, so it's 7" in diameter for size reference.

[Pete Schumacher]

Re: (ignore - posted to the wrong forum)

(sorry-I posted to the wrong forum)

Too bad.

I love the driver covers . . . where'd you get them!!!

[cowtown]

Re: (ignore - posted to the wrong forum)

Too bad.

I love the driver covers . . . where'd you get them!!!

Well, that was just me getting confused. I think I got my post straightened out....

The covers are home-made from tackboard sandwiches, grill cloth and small magnets. I'll see if I can dig up a picture.

[philiparcario]

Re: Fun with T-amps - I didn't know what I was missing.

get a better made power supply. there are a lot of good ones. if you have a noisy one that switches it is designe wrong and filters and shields may not help.

[meep]

Re: Fun with T-amps - I didn't know what I was missing.

you seem to have some electronics chops... build a regulated linear supply-- old school with a transformer. circuits aren't that difficult.

[cowtown]

Re: Fun with T-amps - I didn't know what I was missing.

get a better made power supply. there are a lot of good ones. if you have a noisy one that switches it is designe wrong and filters and shields may not help.

you seem to have some electronics chops... build a regulated linear supply-- old school with a transformer. circuits aren't that difficult.

Thanks - I was thinking that was going to be the answer - either higher quality switched or just regulated. Never any magic bullets when you want them. :D

I love the driver covers . . . where'd you get them!!!

Pete, I've attached a few photos of the covers. The magnets are hotglued into the grill frames' holes, and clip to the bolts holding the driver in.

Magnets are PE #320-012 and the grilll cloth is PE #260-335. Those little magnets are very strong, and only 2 per cover were needed.

[charlielaub]

Re: Fun with T-amps - I didn't know what I was missing.

I think things will only be improved with a new power supply if you can shut the existing one off completely. Otherwise, the amp circuitry may just continue to pick up the noise you are hearing now...

Now that you see how fun chip amps are, I suggest that you revisit the LM3886 "gainclone". You can buy them assembled, as mono boards without onboard power supply, for around $15/channel shipped. Build a simple linear power supply and you will have more power and cleaner output than the class-D amp that you have now.

-Charlie

[cowtown]

Re: Fun with T-amps - I didn't know what I was missing.

I think things will only be improved with a new power supply if you can shut the existing one off completely. Otherwise, the amp circuitry may just continue to pick up the noise you are hearing now...

Now that you see how fun chip amps are, I suggest that you revisit the LM3886 "gainclone". You can buy them assembled, as mono boards without onboard power supply, for around $15/channel shipped. Build a simple linear power supply and you will have more power and cleaner output than the class-D amp that you have now.

-Charlie

Thank you Charlie. I live in East Davis, and was going to try to get to the event last Saturday but my son's T-Ball took priority. It is nice to see locals on this board.

[Pete Schumacher]

Re: Fun with T-amps - I didn't know what I was missing.

Pete, I've attached a few photos of the covers. The magnets are hotglued into the grill frames' holes, and clip to the bolts holding the driver in.

Magnets are PE #320-012 and the grilll cloth is PE #260-335. Those little magnets are very strong, and only 2 per cover were needed.

Ingenious!! Love the idea. I'm not a fan of grills, but those things are just too cool.

[philiparcario]

Re: Fun with T-amps - I didn't know what I was missing.

I think things will only be improved with a new power supply if you can shut the existing one off completely. Otherwise, the amp circuitry may just continue to pick up the noise you are hearing now...

Now that you see how fun chip amps are, I suggest that you revisit the LM3886 "gainclone". You can buy them assembled, as mono boards without onboard power supply, for around $15/channel shipped. Build a simple linear power supply and you will have more power and cleaner output than the class-D amp that you have now.

-Charlie

Aw charlie I was just hoping to get him to use a good power supply. Gainclones are an amazing amp. I have 4 or 5 and sold a few on the board. dead quiet clean clean clean sound.

[johnnyrichards]

Re: Fun with T-amps - I didn't know what I was missing.

Aw charlie I was just hoping to get him to use a good power supply. Gainclones are an amazing amp. I have 4 or 5 and sold a few on the board. dead quiet clean clean clean sound.

How friendly are they for a "newbie" to DIY amps?

[Mike E]

Re: Fun with T-amps - I didn't know what I was missing.

How friendly are they for a "newbie" to DIY amps?

i guess this depends, you could follow the LM diagram of the LM3886 in the tech doc. you could go a more pre-tweaked route with www.chipamp.com, a BrianGT kit stereo+unregulated psu is $70. if i recall right i think i paid $80 for mine along time ago. if your lucky and wait, brain does do sales on all the boards/kits. I got the whole thing built in less then a hour. tested one channel without really paying attention to grounding. i had no humm or hiss or noise in the background from the amp at all. the noise i had in the amp was from the cd player i was using, using the headphone out as a volume control since i didnt have a pre-amp at the time. played it safe and not to much volume on the cd player, really great amps from BrianGT.

[pypes]

Re: Fun with T-amps - I didn't know what I was missing.

Ingenious!! Love the idea. I'm not a fan of grills, but those things are just too cool.

The magnets really do work great, my buddy did something similar but inset the grills so that they sit flush with the baffle... from a couple feet away it looks like they're painted on. These gents are onto a neat trick for grills with the magnets holding to the screws, that's for sure!

[john trials]

Re: Fun with T-amps - I didn't know what I was missing.

Cowtown, I know it's a little OT, but those grills are really cool.

1) What's tackboard (is it cork, or is it stronger)? Sandwiched? Are you gluing layers together for thickness and strength?
2) How do you cut such nice circular shapes (the overall shape of the grill frame...I assume the small holes are done with a punch)?
3) Statement Monitors in your garage?!?!?!??!

[jclin4]

Re: Fun with T-amps - I didn't know what I was missing.

Aw charlie I was just hoping to get him to use a good power supply. Gainclones are an amazing amp. I have 4 or 5 and sold a few on the board. dead quiet clean clean clean sound.

I have one of Phil's gainclones and I can confirm it is both very quiet and clean sounding. Sounds much better than the Dayton DTA-1 t-amp.

I can't say from experience how difficult it would be to DIY, as I only rebuilt the exterior case and added an LED power indicator.



But looking at the innards, this one seems to be based on chipamp.com parts, at least the rectifier if I recall. The two LM1875 chips use the bottom of the case as a heatsink. The only other parts are the toroidal power supply, volume attenuator and input/output jacks.