Building the Tiny Giant amp

[KF5TJC]

What kind of foot switch would I need in order to turn this thing on and off without having to bend over?

[Jdansti]

What kind of foot switch would I need in order to turn this thing on and off without having to bend over?

Just a SPST latching foot switch to break the power. If you've got a DPDT or 3PDT, those would work too, you'd just have extra poles that wouldn't be used.

[niopren]

exists PCB for transfer?

[Taylor]

This PCB is double-sided and not the type of layout that could be etched at home, but the schematic is available on the musicpcb site.

[KF5TJC]

I'm wanting an on/off switch with an led. Would I jumper where the standby switch would normally go and just put a 3pdt switch in between the ac jack and pin 6 on the tda7420 chip? Just wire the led and resistor in parallel?

[Taylor]

Just leave the standby pads empty, and then put your switch between the power jack and power inlet on the PCB. Then I'd take the power for the LED from the regulated voltage pad near the TL072 - check the build doc for a drawing.

[KF5TJC]

Got mine built today. Things didn't work out like I'd wanted with the on/off toggle and led. The push button doesn't work either. So, my amp is always on. I mounted it to the side of my cabinet to keep it handy but out of the way. I ordered two at the same time, so I still have one left to build. Someday, I'll either do another one or rehouse this one in a better enclosure that looks a little better.

[arkham00]

Hi,

I'm fairly new to the DIY world and I've just build a few pedals from kits and recently my first veroboard following tagboard blog layout.
I really want to build this tiny marvel but I have a big dilemma, I live in Europe and the shipping cost for the PCB from taylor is higher than the board itself (13$), it really bothers me.
So I found a veroboard layout on tagboard http://tagboardeffects.blogspot.fr/2014/06/tiny-giant-amp.html
The problem is that the regulator and the amp are not aligned like on taylor pcb, so I can't screw them on the side of the enclosure for heat dissipation.

Can you link me some valid heat sinks that I could use ?
Is there anything in this list that will fit the purpose ? https://www.musikding.de/navi.php?qs=heat+sink

In the case I use separate heat sinks I do not need the insulator,  I can just screw the chip on the heat sink. is that right ?

Another question, I'd love to wire an accutronics spring reverb tank to the circuit, reading the thread someone did it, but how ?
I suppose I need to cut the rca plugs and solder the wires somewhere on the circuit, and add another potentiometer, can you guide  me through the process pls ?

Thank you very much

[alltrax]

I there, if I use a 12VDC@5A power supply I guess I can omit the 338 and it's 2 resistors and capa ?

[Taylor]

Yes

[alltrax]

Thanks !

[alltrax]

Pin 5 is actually connected to pin 3 and therefore driven by the input signal and biased to the center of the power supply. That opamp is not being used and this is just a way to hold it near the center of the supply to avoid drawing a lot of current.

So, that's a mistake in the schematic. There was an error in the voltages at one point, which I corrected, but it looks like in correcting that I created a new error. In other words, there should NOT be 11.6 at pin 5.

I don't see anything obviously wrong in your voltages, so my guess is that there is just an open circuit somewhere in your audio path. I would recommend audio probing to see where the signal is getting stopped.

Hi Taylor, would you mind clarifying in you schematic the pin numbering ?
This is my guess but since you say that there should not be 11.6v at pin 5, which is actually connected to pin 3 I must be wrong

That would help me a lot
Thanks

[bluebunny]

Pin 8 is the power for the TL072, so that's the only one with 11.6V on it.  The opamp at pins 5, 6 and 7 is the one being used as the "preamp" before the TDA7240A power amp.  As Taylor says, pin 5 is also connected to pin 3 - the non-inverting input of the other opamp on the chip - to bias that opamp, which is otherwise wired as a buffer (pin 1 connected to pin 2) but unused.

[alltrax]

Thanks bluebunny, I did the modification on my build (on veroboard from my own layout), that didn't change anything but at least now I know it's correct 

I still have an issue, when the volume pot is cranked, it seems the chip gets overloaded, notes attack sound farty but become normal when I let ring. If I push it with an overdrive in front, I don't have this problem and it sounds great, I mean really great, and loud !
If I don't go over about 50% on the pot course, no problem and nice clean sound, very well balanced. But I want volume
I built it without the 338 and its resistors and cap because I power it with a 12v@5A PS
Any idea ?

[potul]

I don't know if this is going to help, but in my case I had farting noises due to the improper cooling of the chip. What kind of heatsink do you use?

[alltrax]

I don't know if this is going to help, but in my case I had farting noises due to the improper cooling of the chip. What kind of heatsink do you use?

Pics of my build



And my power supply, which I modified to make it 2.1mm center negative

[potul]

Ok, heatsink seem to be enough...

Just to be sure, you could try to force some cooling (using a fan pointing to the heatsink), and see if this reduces the farting.

[alltrax]

I can try that but the problem starts with the first note when the chip is still cold

[bluebunny]

Farty sounds like mis-biasing.  Double-check the two 1M resistors at the input to the opamp.

Edit: actually, scratch that: I hadn't spotted your comment about driving with an overdrive pedal.   

[alltrax]

ok I solved the problem by lowering the regulator output voltage down to 9V using a 160 ohms resistor intead of 120.
Now the amp works like a charm, sounds very good on all the volume pot course.
I'm gonna try a bright cap on the volume pot to try to avoid losing highs at low volume. Has anyone already tried that with this amp ?