Building the Tiny Giant amp

[potul]

Aha!

This explains pretty well what I see in mine. My voltage is still higher than 11 so even with the drop out of the regulator the TDA7240 is still able to work.

Thanks for the clarification, this opens up some more options in my plans.

Mat

[9aul]

As a bit of an amateur, im always posting asking for help, so for once I thought I'd post about a finished and successful project.

Just want to say, this amp is great! Finished this a good while ago now and it hasn't failed me yet. I use it as a practice amp (the case is just an old wine crate), its loud and at higher volumes distorts nicely (nothing glitchy or harsh sounding). At first I was getting loads of motor boarding at high volumes but this was solved when I changed the power supply. I didn't have enough power (I thought I could get away with lower than the recommended spec) but now I've switched to  15v 5 amps and haven't looked back.

anyway here it is:




I was going to cover it in some cream vinyl and bling it up with some sexy retro chrome, but i've got used to it looking this rustic and kind of like it now.

Great PCB, an easy build, packs a punch and sounds amazing!! Thanks!

[bluebunny]

Looks great - keep it rustic!

[Jdansti]

+1!

[Harry]

awesome job i like it

[ginomolinari]

Would love to be able to have a line in to connect an mp3 player or iPod. Anybody have an idea where to tap into the circuit, maybe after the volume pot?
Thank you!

[mth5044]

I would try to add a line in after the buffer with resistors for mixing.

[mth5044]

Any chance the kits will come back? Tried building my own, but I get a lot of squeals and throbbing.


Squeals and throbbing  

Forgot to add some voltages:

LM388T
Adjust (1): 10.83
Vout (2): 12.03
Vin (3): 19.41

TDA7240A
1: 5.55
2: 5.58
3: 5.48
4: 0.00
5: 5.58
6: 11.93
7: 5.59

TL072
1: 5.71
2: 5.51
3: 5.53
4: 0.00
5: 5.75
6: 5.83
7: 5.84
8: 11.65

It seems strange to me that pin 3 of the TDA has 5v on it, as it's the input, but according to voltages  posted a while ago in this thread, my voltages look good. I've checked that both the LM338T and the speaker out are electrically isolated from the chassis, which they are; however the speaker isolation is a bit strange.

One speaker connection is isolated around 8k from ground while the other is about 440ohms. That seems strange, but it might be something internal to the TDA causing those readings.

I fixed both TDA and LM338 with brass screws to the chassis, but I've isolated the LM338 using rather heatshrink and rubber washers. Head shrink around where the screw meets the LM338 tab and the rubber washers on either side. Seems to work well.

I can't seem to think of anything else! Thanks

[mth5044]

I've audio probed the circuit (using a sick keyboard drum track) set up with the output of the keyboard into the input of the tiny giant. I severed both output wires to the speaker from the circuit and probed around with a 0.1u cap on the tip and the sleeve to ground of a jack.

I good audio (quite, but that's expected from this keyboard going into a passive speaker) all the way through into the TDA chip on pin 3. I then probed the output pins. From each pin I get a very distorted signal. Might this be due to the large output of the keyboard? It is a output/headphone jack, which I suppose is very large.

I reconnected the circuit and it works(ish). Not sure what happened. Now, I get very hot audio coming out, most likely due to the hot audio coming in, but it cuts out every 5-6 seconds to for half a second then comes back to normal audio   

Tried it with guitar and the same thing happens, but when the volume is turned up anywhere past a whisper, it distorts, tremolos, throbs, sputters, throws a tantrum. Oi.

[Taylor]

Some people had similar trouble when using noisy and/or underpowered supplies - what kind are you using?

Kits for this will be back at some point but I'm not sure when.

[StarGeezers]

  Not sure when Hubig pies come back either ... 

Still thoroughly enjoying my TG , which now lives in the gig bag as a backup/spare  amp !!!  Works Great for that too !!! 

[mth5044]

Some people had similar trouble when using noisy and/or underpowered supplies - what kind are you using?

Kits for this will be back at some point but I'm not sure when.

I will look forward to their return!

The supply I have is spec'd at 19V (19.41V) and 4.74A. It has three prongs, although based on PRR's way of seeing if the third prong is actually earth grounded (some 1ohm from the third prong to dc out), it seems it is not.

I had throught that was enough amps/properly grounded, but I suppose I will find another one and see what happens! Thanks for the reply.

[mth5044]

Is it odd to have voltage on pin 2 of the TDA? There are two voltages posted in this thread, supposedly ok, one having voltage there and the other have none. 

[PRR]

> strange to me that pin 3 of the TDA has 5v on it, as it's the input

The input circuit has to be "somewhere".

The LM386 managed to get its inputs to ground, but that is unusual.

Mostly, all signal pins should be at "half supply".

You've seen 9V pedals with a lot of stuff biased to 4.5V.

Here we have 12V so you expect 6V. Somehow everything is 5.5V. I believe this is normal. We say "half supply" but it really depends on the pull-up pull-down transistors. I can easily believe there is a half-volt difference between them, and that the 5.5V bias point has been carefully designed-in.

> odd to have voltage on pin 2 of the TDA?

If it is below 1V, the chip goes to StandBy and won't play. "Normal" is to let it go loose and it will find its own level, which IS the 5.5V bias point.

[waltk]

One speaker connection is isolated around 8k from ground while the other is about 440ohms.

That's about what I have on mine, and it's working fine.  I would say this is normal.

[mth5044]

> strange to me that pin 3 of the TDA has 5v on it, as it's the input

The input circuit has to be "somewhere".

The LM386 managed to get its inputs to ground, but that is unusual.

Mostly, all signal pins should be at "half supply".

You've seen 9V pedals with a lot of stuff biased to 4.5V.

Here we have 12V so you expect 6V. Somehow everything is 5.5V. I believe this is normal. We say "half supply" but it really depends on the pull-up pull-down transistors. I can easily believe there is a half-volt difference between them, and that the 5.5V bias point has been carefully designed-in.

> odd to have voltage on pin 2 of the TDA?

If it is below 1V, the chip goes to StandBy and won't play. "Normal" is to let it go loose and it will find its own level, which IS the 5.5V bias point.

I knew that, and I knew I knew that, but I don't know what I didn't know it when I was debugging. I guess I have bias blindness  Thanks for the info!

One speaker connection is isolated around 8k from ground while the other is about 440ohms.

That's about what I have on mine, and it's working fine.  I would say this is normal.

Good to know! Looks like most things are checking out and leading up the power supply. Off to scour amazon. Thank you all very much.

[seadi123]

Can't wait for the kit to be in stock

[smurfedelic smurfberry]

Can't wait for the kit to be in stock

ditto

[smurfedelic smurfberry]

according to the guy who runs that store it'll be abt 2 months or so

[Ben N]

Gotta get rid of those USC athletes, if you know what I mean.