Building the Tiny Giant amp

[potul]

I think LM317 does not provide enough current. Only 1.5A vs 5A of the LM338

mAT

[Rock_on]

LM317T?? Is that enough??

[potul]

this is 1.5 A as well. Not enough

[Jdansti]

If it is easier to get a regulated 12-14V/4A PS, you could omit the regulator.

[potul]

Ok,

After doing some tests with my Tiny Giant, I have some questions for you guys:

1- How do you know if the chips are getting "too hot"? Mines are attached to the metal keg, the problem is, it's not a flat surface, so the contact between the tab and the keg is not optimal. I want to be sure I will not fry them.
2-At what levels is it normal to start getting distortion? I can't crank it much without starting to get the sound distorted. I was expecting more clean headroom. At first I thought it was the small speaker, but I tried with a bigger one from another amp, and still distorts at around 25% pot rotation. I've used a linear pot I had, so this should be about 60% in a log pot. Do you see a similar behaviour?
3-If I crank the volume and specially if I feed a distortion pedal in front, sometimes the speaker seems to enter in an "oscillation". It just starts farting with a low freq noise (guitar signal is lost), until I mute the guitar, and then stops. To me it looks like it's a speaker issue, not the amp... but I've never seen this before. If I can I will record a video so you can see it. Any advise on how to avoid this? If I use a guitar speaker (like jensen MOD 5) may I get rid of this?

Regards,

Mat

[Rock_on]

If it is easier to get a regulated 12-14V/4A PS, you could omit the regulator.

I would like to put one so i can use any supply regulated or not..

Please help me

[garcho]

The TG is loud and clean, for what it is. Clean at levels much louder than conversation. It's not a 386, if that's what you're wondering. Think generic car stereo loud.

[garcho]

No point in omitting the regulator, just use any PS that is at least 2V higher than the regulator, which are easy to find and cheap. If you don't use the regulator, the power supply must be regulated. Don't forget it needs to supply a few amps, not 300mA or something.

[Jdansti]

Right-I misread when he said he "would have trouble with that". I was thinking that he would have trouble finding a regulator.  I've spoken with a couple of people who have trouble finding certain parts where they live.

Something to keep in mind is that the TDA amps are designed to operate at vehicle voltages, which are normally 12.6V when the engine is off and about 14V when running. It should even handle a bad vehicle regulator which would allow the voltage to go to 18V.   So if you have a regulated supply between 12-14V, you can omit the LM338T if you want.  On the other hand, if you've got one and a PS that is =/> 13.5V, you might as well use it. 

[PRR]

> How do you know if the chips are getting "too hot"?

How hot are YOUR chips getting?

I "like" to be able to hold my finger on it forever; but I'm old and conservative. Modern Silicon can be very happy when hot enough to boil flesh.

> metal keg, the problem is, it's not a flat surface

Bad Idea. A least try with chips outside the keg on a large flat hunk of metal.

Also I bet the keg skin is much too thin to spread heat. You want more like 1/8" 3mm. Small beer jugs are thin 'cuz the beer supports them.

> At what levels is it normal to start getting distortion?

20 Watts into a geetar speaker should get complaint from everybody in the house.

What *knob* setting that is, depends on too many variable to discuss.

> starts farting

Some chips do something like that when over-loaded or over-heated.

Use your finger. (If you can't type afterward, it's too hot.)

Read voltages while you play.

[potul]

Some chips do something like that when over-loaded or over-heated.

Use your finger. (If you can't type afterward, it's too hot.)

I think you are right, and the issue is what I was suspecting: over-heating of the chip. I did some tests, and if I leave it to cool down it stops "farting" until it gets hot again. So I will need to find a better way to dissipate the heat.

Thanks for the confirmation.

In this video you can see first how the "farting" happens, and see that it disappears when cool. Distortion is from a pedal, not the amp.

Mat

[artifus]

look at the charts on the datasheet. use your multimeter.

[psychedelicfish]

Kit arrived on Saturday, looks excellent. Might be nice to have all electrolytic caps 25v ones though, this would add a few cents to the cost of the parts, but then you'd be able to  raise the supply voltage for more power without having to go out and buy some 25v electrolytics. No biggie though.

[PRR]

> raise the supply voltage for more power

It's a "12V" chip. It will stand 16V and a bit more; but you can't arbitrarily jack-up the supply voltage or the chip will blow before a 16V cap does.

Also it's hard enough to heat-sink effectively at 12V-14V. Higher voltage would need heroic sinking, like old VW head castings.

If you are a hot-rodder, you'll take the 80% of a kit that suits you, buy heavy-duty tie-rods or capacitors as you think necessary, and hold the small parts for some other build.

[psychedelicfish]

The build document said you can squeeze a bit more power out of it by raising the supply voltage, on page 4. I was thinking of trying this. I started off building effects because I wanted to build an amp as a weekend project, which has been going for about a year now. The Tiny giant is what I have decided to use as the power amp, after a failed attempt at an LM1875 power amp, and before that a 386.
I do have a 1.1k/w heatsink, so excess heat is not much of a problem for me. Anyway, I'll give it a try.

[Rock_on]

I changed my mind can you guys help me how to make my own power supply for this and regulated already??

Cant find sub or LM388T so that's the last i think would work

[potul]

Have you tried to get a LT1084 (TO-220 package)?

I spent some minutes looking at the datasheets today, and to me it looks equivalent to LM388T, same pinout and specs. It should be a 1 to 1 replacement.

Mat

[Jdansti]

I changed my mind can you guys help me how to make my own power supply for this and regulated already??

Cant find sub or LM388T so that's the last i think would work

What kind of power supply were you going to use if you had an LM338T?

Voltage out?
Max current out?
Regulated?
I assume DC, but please confirm.

Do you have access to any other power supplies- AC or DC output?  If so please list the specs.

This information will help us zero in on a way to figure out how to get you going.

[Rock_on]

I changed my mind can you guys help me how to make my own power supply for this and regulated already??

Cant find sub or LM388T so that's the last i think would work

What kind of power supply were you going to use if you had an LM338T?

Voltage out?
Max current out?
Regulated?
I assume DC, but please confirm.

Do you have access to any other power supplies- AC or DC output?  If so please list the specs.

This information will help us zero in on a way to figure out how to get you going.

If i have LM338T then i'll just put it in my board and it's done.. I can use non-regulated/regulated now..

[Jdansti]

Sorry-I guess I screwed up again. When you said you wanted to make your own regulated power supply and asked for help doing that, and you said you couldn't find a substitute for the 338T (which the design calls for), it took this to mean that you couldn't get a 338T and were trying to figure out how to make a supply that would make the amp work without the 338T. That's why I asked you the questions about what kind of supplies you had to work with. So I'm a little confused by your requests and comments, and I don't mean that in an insulting way.  You're not my wife are you???

Either way, I'll step aside and let y'all figure this one out.