Building the Tiny Giant amp

[carlosfilipe]

Not forgotten, but having a hard time building it. 

Disassembled it and trying again...

[sevrien]

Am I correct?
When using a different voltage supply than 19,5V.

I need to adjust the resistance (1K original) connected to leg 1 (adjust)of the LM338?
Perhaps a trimpot to make it a bit easier?

greetings

[potul]

As far as I know you don't need to adjust anything. The adjustment is needed if you want to provide a different voltage to the circuit (output from regulator)

the voltage should be:

Vout = 1.25 (1+R2/R1) = 1.25 (1+1000/120) = 11.6666

which does not depend on Vin if you get a high enough voltage.

FYI, I'm powering mine with 12v bypassing the regulator.

[tpb03]

I finally got around to putting my Tiny Giant Kit together after it sitting in its little yellow envelope for the past 8+ years. I made a mistake soldering in a resistor and borked up the pcb when I desoldered said resistor and solder stayed in the mounting hole which I couldn't remove. I truly borked up the PCB when I tried to drill out the hole!

I have a stack of perf board lying around and all the components from the original kit (including the now desoldered transistor!). I remember that Taylor said he had a perfboard layout when he was prototyping. Is this perfboard layout available? I could put together a layout myself, but I don't want to reinvent the wheel if one already exists.

Tim

[bluebunny]

Welcome to the forum, Tim.

I've not seen any perf layouts, so I can't help you there.  Be aware that the amp chip has pins which don't fit on a regular 0.1" grid, so you'd need to bend half the pins to fit.  So far as dealing with a PCB hole filled with solder, just heat the pad with your soldering iron and poke though a cocktail stick while the solder's still molten.  No need for a drill.   

[PRR]

I use a steel needle to open clogged holes. Heat, poke, done. Hot solder won't stick to cold steel.

If you have only borked a few holes and traces, it is surely easier to stick with the PCB and patch-up. If a hole-pad is gone, extend the part lead or a jumper wire to the next healthy part of the trace.

[Ben N]

I never thought this guy would turn up here.

[tpb03]

I never thought this guy would turn up here.

Wrong Bork!

Thanks for the tip re: using a hot needle to free up the solder pad/well. I'll see if I can salvage the PCB. If I can't I'll plan out a perfboard layout.

Thanks again
Tim

[PRR]

> using a hot needle

I use a hot soldering iron and a cold steel needle.

A hot needle, if it cools a bit, will freeze solid in the hole.

[blues_mang]

Hi, I know this is an old thread, but I'm hoping maybe Taylor will see this. I just found the Tiny Giant amp and built it. It's working for the most part, but if I turn the volume knob up half way or more, all of a sudden the speaker starts vibrating and freaking out until I dial it way back again. I checked and I have 14.6VDC coming into the amp. No grounding on the LM338T or the speaker jack and I use a 1.2K resistor, so I'm getting about 13.8V on pin 8 of the TL082 (I used TL082 because I didn't have a TL072). Anyone have any ideas of why this happening with the amp?

[PRR]

Anytime an audio amp freaks-out at high volume, suspect that the output signal is leaking-back to the input circuit.

Taylor's PCB and suggested wiring? Perfboard and haywiring?

Photos?

[blues_mang]

Yes, Taylor's PCB and suggested wiring. The only addition was I added a TMB tone control between the input jack and In on the board. I'll try and post some pictures later. What would be the best way to check to see if the output is leaking back to the input?

[Taylor]

Could it be the input jack wires crossing near the speaker wires? Or possibly even regular old acoustic feedback from the speaker to guitar?

[PRR]

I would take that tone network out for the moment. That's a lot of parts/area to catch signal from speaker wires.

[blues_mang]

Just got back from traveling for the holiday. Haven't had a chance to take pictures yet, but yes, the wires going from the board to the speaker definitely cross the input jack wires inside the enclosure. Didn't think it would cause an issue. I don't think it's the acoustic feedback. I'm actually using this as a preamp for a Leslie speaker and so the speaker is fully enclosed. I also tried it with just a bare speaker that had lying around thinking maybe it was a problem with the impedance of the speaker. I'll try re-routing the speaker wires to keep them away from the input wires and see if that helps. Is there a way to isolate or insulate the input wires to keep from picking up signal from the speaker wires?

[bluebunny]

You could try using screened wire for the input (connect the screen to a suitable ground point at one end only), but you'll probably find re-routing the input and output wires away from each other will be more effective (and quicker).