Building the Tiny Giant amp

[Jonsuit]

Having fried one, I got a new TDA chip and have it installed. This seems to resolve one issue, however I have a new problem. I am not getting guitar signal through.



To the best of my limited knowledge continuity looks good as I followed along with the schematic and checked bit to bit.

My adjusted voltage coming in is right at 11.5v

I have 11.5 on pin 8 of the TL chip and I have 0v on pin four, as expected. I am curious about the other values though. 

On the remaining  sets of pins I am showing around 3.3 at the + inputs, and 1.6 on the outs and - inputs.

I am very new to this and don't really understand how the audio signal works in relation to these other measures, but I feel like these low voltages might be indicative have some problem that corresponds to my not getting audio through?

As a side note I believe my volume pot amplifier and speaker are all working as I can get an amplified hum from holding the volume pot in a certain way and adjust the volume of that hum.

[PRR]

> I can get an amplified hum from holding the volume pot

Input jack wiring error is a very popular mistake.

[jeffiswrong]

I've been looking at getting some of taylor's boards for a while, and I have a buddy who's looking at getting his first amp. He got interested when I mentioned this. The plan right now is to build a 1x12 with a matching head. The idea is to house the board and power supply in the head, as well as an eq and a distortion circuit. I read through quite a few pages of this thread and skimmed some more but didnt find anything like what I'm attempting. I know there's an 11v tap on the board and I intend to use it.

Basically my question is how I would go about doing it? Would it be as simple as getting a schematic for a 3 band eq pedal, then wiring the output of that to the input of the tiny giant with both boards sharing a ground? Same thing with the distortion, wire that in before or after the eq with a pre/post volume and a true bypass? Would all 3 boards then share a ground? I don't imagine the difference between 9v and 11v would matter if the components were rated for say 18v

And something I know nothing about, how could I wire a bypass for the distortion switch that would allow it to be foot controlled at some point? Any help would be appreciated.

[Taylor]

It pretty much is as simple as that, although that's a tall enough order if it's your first electronics project.

So, yes you'll be connecting power and ground from the amp board to your EQ/dist circuits, and then you'd just connect the output of one stage to the input of the next.

You're right that you won't damage anything on 11v if it's rated a fair bit in excess of that voltage. Depending on the circuits you choose, you may even like the sound of the distortion better at that higher voltage, although it could go the other way. Generally any circuit can be tweaked to get it functioning the same at a few extra volts, if need be.

The footswitch thing can be approached many ways. Maybe the simplest, especially if true bypass is a must, would be to use a DPDT relay. The relay is inside your enclosure and does the bypass switching. The footswitch is just a latching SPDT that connects the relay's coil to power when the footswitch is pressed. This lets you connect the footswitch to the amp with just a regular mono 1/4" cable that you would already have if you play guitar/bass.

There are some relay bypass kits available, maybe somebody else can pop in with a recommendation for one.

[StarGeezers]

  Taylor, we've had the TG for some time now and it's really Great !!!  ( JMHO)

Question is , can we adapt the circuit to amplify a Piezo pickup .....do we need some kind of Z buffer ...

[Taylor]

Great, glad you're still enjoying the TG!

You could connect the piezo straight to the amp input, but the sound will not be great. Piezos sound best going into a very high impedance preamp. Connected to a regular instrument input, the piezo forms a highpass filter with the the input and all the low end is removed, leaving a tinny, brittle sound.

Here's a piezo buffer that would work. I built one of these years ago for an electric upright bass I used to have. This was before the TG existed, so I never used them together, but I recall having good results with the buffer going into a tube amp.

http://www.scotthelmke.com/Mint-box-buffer.html

[StarGeezers]

  Taylor , THANKS !!!   Just like what we were looking for !!!   Much appreciated ...   !!!!

[crxeffect]

I bought a board awhile back, finally got around to testing it. Doesn't work.... I have around 11.5 at the regulator and power amp supply pin. My meter is slow but i'm showing 300-400mv to the power amp input when I strum. So the TL072 is working. The thing I can't figure out is, there is 20-30M ohms between ground and speaker jack terminals. I don't have this in an enclosue so it is something on the board. At this point I can only assume the power amp is fried/shorted. Any other ideas?

Also realized the power supply I grabbed is only 2A. I'll use a different one but can't think that would matter for a short test?

[Taylor]

The power supply is probably sufficient. Did you get the parts kit too or did you supply your own components?

I just measured my TG and had around 8k and 400 ohms, respectively, from each speaker jack terminal to ground. I'd be out of my depth speculating as to why they're not approximately equal, but yours being effectively infinite resistance in comparison definitely would seem to point in the direction of a problem at the TDA7240.

You mentioned no enclosure, do you have heat sinks on the amp chip and regulator, and are they electrically isolated from each other?

[PRR]

The TDA7240's outputs don't go to-ground. Only to each other. Conceptually they could be infinity from ground, but that's certainly wrong. There will be at least the internal NFB resistors from each output to a groundy inside node.

One reason for a "difference" is that there are parasitic diodes everywhere in a chip. If you flip the ohm meter leads you may get a different reading.

But my first guess is bad connections, at chip, PCB, or jack. Get it out in the light and eyeball those solder joints.

[KF5TJC]

I've got through 10 or 15 pages reading, looking for pics, etc. So, if the answer to my question is in one of the pages I skipped, please don't be too upset with me. I'm a bedroom player with no interest in playing in a band. I've got a Line 6 Pod XT Pro that I intend to use and I want a simple, low power amp that can cleanly get loud enough to be annoying. How loud can these little amps get before starting to distort? I'd like to get two and have two 10" or 12" speakers. I've got some experience with a DIY ham radio, so doing a kit like this isn't foreign to me.

[Taylor]

It gets pretty darn loud for playing in a house without an audience. Two sounds like a lot to me if I wasn't trying to be heard over a drummer, but we probably all have a different definition of "annoyingly loud" 

I play bass, modular synth, and electronic drums more than guitar, and have used the TG for those purposes quite a lot. Those would all be more demanding in terms of clean power than guitar because of the frequency ranges involved.

[KF5TJC]

What about one amp and two speakers? Would that cause any problems? Not sure whether the output jacks should be parallel or series.

[Taylor]

One amp, two speakers would be fine. Parallel/series would depend on the impedance of the speakers you use. You want the total impedance at 4 or 8 ohms generally (check the build document though for details). So if you have two 16 ohm speakers then wire them in parallel for 8 ohms total, etc.

[crxeffect]

Taylor, I did buy the kit. So the isolators are used between the heatsink. I did try and reflow all the joints to no avail. I just ordered a couple more 7240's so I'll just try and replace it. keep ya posted! thanks for the help

[KF5TJC]

I ordered two of them, just in case.

[Scheissami]

Noob here, having trouble with my TGA.

I bought the kit, so have all of the appropriate spacers/electrical insulation.

The power supply I found is actually a selectable supply, with the option of 15V at 6A; I wired the amp center positive because the connector for the PS is actually 2.1mm.

I double checked before powering up that the 338 is electrically isolated from ground, as well as both poles of the speaker outs. I'm getting 11.6V at pin 8 of the TL072. It's in a Hammond 1590BB enclosure with the chips heat-sinked into the side.

When I fired it up, I got about 1 second of a clean sounding guitar chord before it fuzzed and farted out. If I mute the strings and wait a few seconds, I can get another second of clean before fuzzing out.

Any ideas?

[Taylor]

The symptoms sound like the amp chip overheating, but from your description it seems like you've got your bases pretty well covered on that front. Could you post a picture of the guts? Might help spot something that's keeping the enclosure from doing a good job as a heat sink.

After it cuts out, does the amp chip feel really hot? (Obviously, use standard "touching a thing that may or may not be really hot" procedure for safety's sake)

[Scheissami]

https://dl.dropboxusercontent.com/u/23281298/IMG_3328.JPG
https://dl.dropboxusercontent.com/u/23281298/IMG_3329.JPG

Sorry, tried to link the pics themselves but they were massive, not sure how to reformat them on this board. The reason some of the solder joints look odd is that I trimmed them down significantly to remove excess wire (despite the huge enclosure, vertical space is actually pretty tight), but looking over the joints none of them are loose or dull. As an aside, since I mentioned that space is tight, the dysfunction I describe happens while the lid is off, so that's not shorting the chip.

The amp chip is specifically the 338, right (sorry, as I said, I'm quite new to this)?

The chip stays cool even once it starts to fart out and go mute. It only takes a second before it starts to cut out, then it's completely quiet, not even the usual 60 Hz hum getting through. If I mute the strings and wait 3-5 seconds, I can begin to hear the usual slight background noise, then can play a few notes until it fuzzes out and dies again. I get essentially no real time of significant consistent sound, and the chip isn't warm to the touch in the slightest. Seems like it should take longer to heat up/cool down?

I'm happy to entertain other thoughts. I bought two kits at one time so I can always try replacing the 338 chip and seeing if that solves the (short-term) problem, though I'd prefer to see if there are other trouble shooting options before pulling it apart.

Thanks again for your help! I'm excited to get this working, I built it inside a larger enclosure with the eventual goal of adding EQ and gain stages if I can get them all in there.

[duck_arse]

can I suggest: measure the supply voltage, while good running and stop running. does it change when the sound goes? is it possible the supply is overloaded/ing and doing a sputter shutdown?