Practice Amp?

[E]

Well after i've built a battery amp odds are i'll be looking for a 'budget' practice amp. I'd say between 10 and 30W, but quality is more important than volume. Essentially can you spec me everything please? Speaker, Power Amp, Preamp... whatever. I've had a look around but without much success...

It's worth noting though that i'm in the UK, cheers in advance

[dan stanton]

I don't know how to post links. Look up epemag.com. They've got a good practice amp there.

[J M Fahey]

http://www.ssguitar.com/index.php?topic=1524.msg9719

[E]

Hmm, thanks. Just because you said that was better suited to bass i thought there might be a better option. But looks good, you think a Celestion Super 8 would be a good match? I could use my woodwork skills to make a cabinet. Would this transformer work, assuming it's a good idea to go for the 2050 over the 2030?

http://www.djsoundkit.co.uk/proddetail.php?prod=P037A

Thanks

[dan stanton]

The Celestion would be good. If you can get 12+12 out of that transformer, should give you 15V. Also look at the tl082 datasheet. There's a good tone control you could replace the tl081.

[J M Fahey]

*This* one: http://www.djsoundkit.co.uk/proddetail.php?prod=P034A , 12+12V, 45VA will give you nominal +/-16V rils, +/-15V in practice, good for an around 15W/8ohms power amp
That 8" Celestion is fine and the +/-15V rails, with a little extra filtering, will power any preamp you build.
You can later build another TDA2050 on that chassis, and hook it to an external speaker jack, to borrow any 8 ohm speaker you find where you play, or you can later build an extension cabinet.
You will be loud.

[E]

That's great, thanks. Since i've got two weeks off i'll probably have a go at it... if anybody's interested i made a copy of the PDF without the giant 'www.epmag.com' in the middle of every page so you can actually see the diagrams.

http://www.mediafire.com/?mmmvn4rft2k

[tonyharker]

i made a copy of the PDF without the giant 'www.epmag.com' in the middle of every page so you can actually see the diagrams.

So How did you do that then? Huh!!

Tony.

[E]

i made a copy of the PDF without the giant 'www.epmag.com' in the middle of every page so you can actually see the diagrams.

So How did you do that then? Huh!!

Tony.

Open original PDF
Print to file - PDF (gets rid of the permissions)
Open with PDF Editor (Linux)
Select watermark
Press delete
Repeat for every page
Save
Host



Oh, and will using a 12v transformer instead of a 9v one work?

[J M Fahey]

Yes, it gives you more power ; with 12VAC windings you'll end with +/-15V rails, as datasheet says.

[E]

Okay, so replace the TDA2030 with a TDA2050 and the TL081 with a TL082. Anything else i should know?

I've got a heatsink here, pulled it from an old PSU. Was cooling a few similar looking chips, but i think it would be okay for the 2050? Roughly 3cmx3cm on one side, 5cmx3cm on another and 4cmx3cm on the oposite one. Not counting the fins. Nearly 2mm thick and aluminium as far as i can tell.



Sorry for the quality, phone camera doesn't do macro very well.

[J M Fahey]

Tha heatsink will do.
You can't replace TL081 with TL082 but with TL071.

[E]

Tha heatsink will do.
You can't replace TL081 with TL082 but with TL071.

Yeah, i wondered because one sais 'dual' and the other 'mono' in their descriptions. Kinda being newbie here and assuming that a higher number is better but which of the two (81/71) would be better? Thanks

Oh, and i'm having a bit of trouble finding a 470k Carbon Preset Potentiometer, could i replace it with say a 500k one? Sorry to be such a pain...

[phatt]

A 500k pot can be anywhere from 300k to 550k.
This is called, tolerance window.  most stuff like this is general/ kinda/ about.

Same with caps where you see a value 50nF but the closest you will find on the shelf is 47nF.
don't worry you will catch onto all these little quirks soon enough.
Phil.

[E]

Okay, thanks for your help - you learn by making mistakes so i'm just going to go for it. Little update - PCB arrived today, i love how the dog only seems to destroy the non important mail.



Again, sorry for the image quality. I would have used a better camera but i'm having problems with ISO and the flash casting shadows of the lens. Anyway, looks good. Home etched as far as i can tell, as you would expect. Not the most pleasing of colours but that doesn't really matter. It's smaller than i thought it would be, which will help with the plan i've got to make a small, portable enclosure.