Building the Tiny Giant amp

[Scheissami]

Sorry, summer has been nuts and crushed my productivity, just got around to this.

Checked the supply voltage while testing the amp, stays stable at 15V without fail.

Could I have fried the chips while soldering them in? The TL072 is socketed but I didn't socket the LM338T or TDA7240A (I don't think they would have fit in the enclosure if I did). Or is it more likely a capacitor that's not working (like it can't hold it's charge appropriately?)? I checked all of the resistors before installing them but can't remember if I checked all of the caps.

Any further help appreciated!

[Taylor]

It sounds to me like the amp chip (TDA7240, the one with 7 legs) is going into its automatic protective shutdown. I don't think it would work even for those few seconds if the amp chip was damaged, and if you're getting steady voltage then you know the regulator (338) is fine.

One thing you didn't mention: what sort of speaker are you connecting to it? Impedance? Can you check the speaker pads on the board with a multimeter to see if one is somehow getting shorted to ground?

[caveDog]

Hello All,
I come seeking help with my Tiny Giant. I new to this forum and new to electronics for that matter. I have built a few projects and I am hooked, but still getting my head around some of the basics.

So, I bought the Tiny Giant kit and put it together. When I fire it up I get no signal - but - if I jumper the input jack directly to the in of the volume pot I get sound  out the speaker. So if I skip everything before the volume pot including the TL072, it sort of works. Its a little scratchy because the jumper connections are poor. The standby toggle works and I ultimately get sound, either a hum or the guitar if I use the jumper, so I believe the TDA7240A is working properly.

I tested the leads on the TL072 and this is what I got:
1: 0
2: 0
3: 3.95v
4: 0
5: 3.95v
6: -0.05v
7: -0.01v
8: 11.75v

I also confirmed that I didnt have the 10uf cap in backwards.

Any help is appreciated.
Thanks.

[Taylor]

The bias voltage at pins 3 and 5 looks a little off. It should be around half the regulated supply voltage, so closer to 5.8 or 6V. Check the two 1M resistors to make sure they're the right value and there aren't any solder bridges to adjacent parts.

Other than that, it looks about right, so you may just have a cold solder joint around the input, like the 100N cap right by the volume pot pads. Often just reflowing all your solder joints (reheat, allow to cool without letting the parts move) can solve problems like this. Also, apologies if this is too obvious - it can get the best of us - but make sure the TL072 is in the socket the right way round - the notch or dot near one end of the part should be facing towards the 100N and 220N caps.

[ginomolinari]

Hello everybody. First of all thank you for the great posts and information. I have built my tiny giant and I get a very low volume on a 8ohm speaker. Barely audible. Before I get to measure things maybe somebody can take a look at my built and see if there is something clearly wrong. Any input would be much appreciated. Thank you.

https://drive.google.com/file/d/0B_EO7EHMDw6XMFpaaDEzSXNqbFU/view?
https://drive.google.com/file/d/0B_EO7EHMDw6XVkpEWVpFQVBKQ2s/view?usp=sharing
https://drive.google.com/file/d/0B_EO7EHMDw6XNWYzRkhnODFtRmM/view?usp=sharing

[tonyharker]

How about a picture of the bottom. Some of your solder joints don't look very good.

[ginomolinari]

Thanks. Here is a pic of the back and off board wiring. Also, the amp makes a loud buzz when I touch the volume.

https://drive.google.com/file/d/0B_EO7EHMDw6XNDBJZ2o0ekxXbzg/view?usp=sharing
https://drive.google.com/file/d/0B_EO7EHMDw6XTkx2d1pvZUM3cGs/view?usp=sharing

[Taylor]

Might be a good idea to scrub the bottom of the board with rubbing alcohol - your solder probably has no-clean flux (though you should check if you don't know for sure - I once had a month's worth of projects not working because of this) but there could be bits of solder in the flux shorting things together.

Also, possible short on one of the 22uf caps?

There's one part where it looks like the pad got overheated and pulled up (pic 5, bottom right). This is OK because that part doesn't connect on the bottom, but make sure there's some solder connecting it on the top.

[ginomolinari]

Thank you for the reply. I have scrubbed the PCB, nothing. The burnt spot has some good solder on the other side so that's no problem. Do I have to take the caps out to test them?

[Taylor]

I would recommend just reflowing all of the solder joints (heat them back up and let them cool without moving the part/wire). Then measure voltages with your multimeter on all the pins of the 3 ICs while the TG is powered up, and post them here.

You probably don't need to test the caps, just make sure that the 22uf cap farther from the edge of the board is not shorting its two contacts together. In your picture there looks like a possible a solder bridge.

You didn't mention or show a heat sink or enclosure, but you've got those, right?

[ginomolinari]

Thank you! I will do that! Be posting asap.

[Ben N]

Question for Taylor, or anyone else: I am putting together an order at Tayda, getting ready to tackle a few long awaiting projects, so the question is what heat sink (x2) would be sufficient? Here is the Tayda heatsinklink. I haven't really settled on an enclosure yet, so I'd like to be able to dissipate enough heat regardless. TIA for your thoughts.

Ben

[bluebunny]

I used one of those extruded aluminium enclosures and bolted the power amp chip to it.  Gets mildly warm.

Paul will be along shortly to advise you how to do the maths to work this out correctly!   

[Ben N]

Hey, Marc, you mean one of the little ones? (or two of them, I guess--one for the regulator, too) That's really my question, I guess--would those small ones (17mm x 17 mm x 26 mm or so) do.

[Taylor]

I built mine way back when to use the enclosure it's in as the heat sink - it's a 1590A. But, I've never tried to gig with it, so that might be insufficient for playing with volume up fully for a long set. I wouldn't use one of the smallest ones on that page. Maybe one of the 14 fin ones, since they're all pretty cheap.

When I first built it, I bought an absolute monster heat sink - about 11 x 9 x 2 inches. That was absurd overkill, but some day I'm going to find a purpose for that thing. It makes a lovely bell sound if you suspend it on a string and hit it with a hammer.

[bluebunny]

Hey, Marc, you mean one of the little ones? (or two of them, I guess--one for the regulator, too) That's really my question, I guess--would those small ones (17mm x 17 mm x 26 mm or so) do.

I meant this kind of thing - an enclosure, not a heatsink:

[duck_arse]

When I first built it, I bought an absolute monster heat sink - about 11 x 9 x 2 inches. That was absurd overkill, but some day I'm going to find a purpose for that thing. It makes a lovely bell sound if you suspend it on a string and hit it with a hammer.

ahhh, the stashed heatsink. how many of us [older types] don't have at least one big heavy heatsink 25 or more years old, "I might use in an amp one day"?

[Ben N]

ahhh, the stashed heatsink. how many of us [older types] don't have at least one big heavy heatsink 25 or more years old, "I might use in an amp one day"?

That reminds me, I have a couple of old desktop computer power supply cages with fans that I always figured to stick something like a Firefly in--the Tiny giant could go in one, although it does seem kind of overkill.

Anyway, thanks, everyone. I think I will order a couple just to be safe, and, as Taylor says, because they are so cheap.

[Taylor]

ahhh, the stashed heatsink. how many of us [older types] don't have at least one big heavy heatsink 25 or more years old, "I might use in an amp one day"?

Nah man, I'm totally gonna get around to using this thing... 



Edit: Y'know, I was being facetious, but I just noticed there are 4 sets of holes spaced just right for the TG. Since I'm into modular synth stuff these days, a quadraphonic amp is something I could actually use. I could finally experience electro-fart noises whirling around me.

[duck_arse]

you would have to paint it, black (you devil!) if you wanted to mount four amps on, just to shift the heat.