Building the Tiny Giant amp

[waltk]

I do not know the temperature limits of the components. I do have room to add a fan to cool the amp, but do I really need it?
I am also not averse to scrapping the entire Radioshack box idea for a better one, but it does seem that it may work. 

The datasheet for the chip says it can handle a junction temperature of -40 to 150 degrees C.  It seems you are easily within that range.  Were you measuring the temperature of the chip, or the air in the box?  Also, the chip has a built-in thermal shutdown.  So if you like that particular enclosure, and you didn't encounter the thermal shutdown with an hour of hard playing, go with it.  It sounds like you have plenty of thermal headroom and wouldn't need a fan.

[firebird8600]

Were you measuring the temperature of the chip, or the air in the box?

I was measuring the aluminum plate behind the chip, not the air. I held the box shut with masking tape while playing. Then about every 10 minutes would grab my infrared thermometer, take the plastic cover off, and aim just behind the two chips. It leveled off at 104 after 30 minutes, and stayed there for another 30.

[squigglefunk]

Anyone tried running this amp kit off a 12 volt battery?

[waltk]

Yep.  Works great.  If you want to do this, you should bypass the onboard LM338 voltage regulator.  You can just leave out the LM338, the two (120R and 1k) resistors, and the associated 100nF cap.  Hook up your 12V input to the middle pad for the LM338.  If you want to also run it off of a higher-voltage power supply, you can leave the parts in place and hook up an external switching arrangement.  Caveat: we're talking about a large 12v battery - right?  It needs to supply enough current.

[squigglefunk]

Yep.  Works great.  If you want to do this, you should bypass the onboard LM338 voltage regulator.  You can just leave out the LM338, the two (120R and 1k) resistors, and the associated 100nF cap.  Hook up your 12V input to the middle pad for the LM338.  If you want to also run it off of a higher-voltage power supply, you can leave the parts in place and hook up an external switching arrangement.  Caveat: we're talking about a large 12v battery - right?  It needs to supply enough current.

yup, I was looking at compact deep cycle batteries?

do you have any battery suggestions?

[waltk]

do you have any battery suggestions?

Nope.  Any car battery would run it for a long time.  I'm not sure how big a compact deep cycle is, but if you wanted to go lighter-weight, you can also power it with a rechargable (lithium?) tool battery.

[myramyd]

Hey Taylor,

I put together my TG yesterday. Hooked it up this morning and the LM338 (literally) exploded immediately.

Here is some more info:

Before I connected the offboard wiring, I checked the heat sinks and speaker jack lugs for continuity with ground (the enclosure). None of them showed continuity. I did not recheck after I connected the wires to the jacks (I know). But when I check them now, both heat sinks, both speaker wires, and all 3 pot wires show continuity with ground. I disconnected the speaker jack and heat sinks from the enclosure and they still show continuity with ground. So the continuity is somewhere on the board. With a visual inspection I don't see any problems that are immediately detectable. There may be a cold joint somewhere but it's hard to see any off hand.

The PS is 15V 6A if that helps.

Two questions:

1- Will I just need to replace the LM338 or would you guess more components are also fried?

2- Any thoughts where I should check on the board for problems? i.e. how everything seems to be connected to ground? Any particular spots I should check first?

Sorry for the incoherence. My brain is going nutty trying to figure this out.  

Thanks in advance.
J

[Taylor]

Hmm. Can you post a photo of the build? Maybe that will have some clues.

If the regulator blew, perhaps it took the amp chip down as well, in such a way that the amp chip shorted its outputs to ground. I think it's got to be something along those lines unless you just have a solder bridge somewhere.

[myramyd]

Okay, here we go: (note that the screw is only there to hold it in place for taking photos)

[Taylor]

And you've got some kind of velcro or foam under the PCB to keep the bottom from shorting out against the enclosure, right?

[myramyd]

Yeah, I had some cardboard underneath it and was going to replace that with foam tape. I just plugged it in so I could get a voltage reading on the TL072 and it exploded immediately.

The continuity checks where I noticed the heat sinks and speakers connected to ground were with it detached from the enclosure (as it is now--but without the screw).

J

[Taylor]

It's weird because I can imagine ways in which the speaker jacks could short to ground, but the fact that all of those things including all three pot wires are connected to ground is completely strange and I honestly can't think of how that could happen, other than a short on the board or conductive flux.

I would go through and reflow all of those joints. Most look fine, a couple look iffy. Since you have to replace it anyway, I'd pull the regulator out of the board, may fix something if it's internally shorted in death. If you haven't desoldered from a double sided board before, go slowly and make sure that the solder is liquid all the way through and on both sides before pulling.

[myramyd]

Okay, I can do that.

I figure worse case if I can't figure it out I can just order another kit and start over! Hopefully I can salvage what's already been done though.

I was having trouble getting some of the joints to flow they way I wanted them to so it could be a problem there. If I manage to find something that works I will report back.

Thanks for your help,
J

[Clarke]

First post!

bought the kit today, its going to get my second project.

can i just ask if this would be ok ?

http://www.ebay.com.au/itm/16V-4-5A-72W-F-AC-adapter-IBM-A-R-T-X-I-series-08K8204-/230569983399?pt=AU_Laptop_Accessories&hash=item35af0abda7#ht_4082wt_1139

Thanks guys! and Taylor it looks great!

[myramyd]

Hello,

I just ordered two of these--hopefully these are the correct replacement?

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_192284_-1

Thanks,
J

[Taylor]

Clarke: yes that will be fine.

myramyd: yes that's the right one.

[haroldjenkins]

After reading the last few posts in this thread, it brought to mind a little would-be problem I came across while building this amp. I had to drill holes in my heatsink to accept the screws for the chips. When I got it assembled, I did the continuity test and found that both ic's backs were shorted to the heatsink, and therefore ground.

I double checked the insulators and bushings and they were straight and looked good. I even tried nylon screws and nuts, still shorted. After scratching my head for a while I checked the heatsink and found just a little bit of burr left over from the drilling and it was poking through the insulators.

It doesn't look like this would be myramyd's problem, but I'm just throwing this out there.

[Bham Dave]

Hello to all. Been lurking a while, but took the plunge.

So, I'm pretty much a noob. Done some modding and work on guitars, and built with moderate success the Noisy Cricket. Just ordered the TG and am going to put it into a gutted combo.

I'm interested in putting the BMP tone stack into it. My question is this: where does it go? Does it attach to the input jack and then into the circuit, or should it go before the vol pot, as described earlier? I searched a few places for the answer, but it seems to be obvious to most people. Just not me.

I'm excited to do more builds and keep learning. Reading schematics alone is still very challenging and tortuous for me. Pictures and layouts are my friends at this point. But it's coming along.

Thanks for any insight and tips.

Cheers!

[Taylor]

This post has a 3-band tone stack:

http://www.diystompboxes.com/smfforum/index.php?topic=89687.msg768743#msg768743

If you just wanted the one-knob BMP control, that's still a good spot for it.

[Bham Dave]

Thanks. That's what I thought, and was referring to in my post, but just wanted to clarify. This will be going into a gutted Traynor TS-15. Will connect the speakers to a jack, so I can use the onboard TG, or connect other little amps to it. Stoked.