Building the Tiny Giant amp

[mindpunk]

Thanks Paul,

From a year or more of lurking, I knew if I was lucky enough to get an answer from you it would help get me out of the head scratching fit I've been in for a week now and into a fresh perspective to fix and finish this thing.

I hadn't thought about bypassing the tube as it seems to be working well as I scoped and probed a signal all the way through it and it amplified and looked and sounded great.  But pulling the tube and going direct into the PA will be the next step as it could rule in or out a bad TDA and might identify some bad interplay issues with the tube.  As it stands now my volts look fine based on your off the cuff numbers.  I have the 338 biased closer to 12.5 volts and I'm seeing 12 volts, 0 volts and around 6 volts on the various pins.

I'll bypass the tube and see where I stand.  I've been resisting the idea that the TDA is bad because I've already changed it out twice.  But like my mechanic brother says, "When a customer tells me it can't be the alternator because they've already replaced it; it's usually the alternator..."

I wonder if I have a bad cap on one of the PA legs, that could throw the IC into shutdown, right?

BTW Paul, I'd love your take on the schem I linked to and my dumb questions about the filtering bits from the Tube Cricket if you get a chance.  How does a fella send you a beer anyway?  You do a lot for this community...

[butch199]

I am building a second tiny giant amp, I am currently using a 16 volt 4 amp power supply, can I power both tiny giants with this 1 power supply?
thanks in advance for assistance

[PRR]

> a 16 volt 4 amp power supply, can I power both

If both speakers are 8 Ohm, it should be fine.

If both speakers are 4 Ohm, it is right at the edge of punking-out.

[butch199]

thanks for input, actually 1 cab is 8 ohm and the second cab is 4ohm,,what do you thing of using single power supply in that case?u

[PRR]

Fine.

[butch199]

I have not seen this answered on the thread, can the tiny giant handle a 2 ohm cabinet?
Thanks

[Taylor]

The datasheet for the amp chip doesn't list a minimum output load resistance but all of the ratings and charts are for 8 and 4 ohm loads, so I think they don't intend for 2 ohm loads. I'm guessing the chip will just mute itself and shut down with 2 ohms as it sees it as a short but I'm far from sure about this. Could kill the chip for all I know. If it works the amp is going to be more likely to overheat so you'll want a much bigger heat sink.

[PRR]

Peak output current (repetitive) is 3.5 Amps.

Skipping math, this does not support 2 Ohm loads at any reasonable supply voltage.

IMHO: in 2 Ohms it will play softly for a short while, but any serious use will be grossly distorted at a level less than you'd get in 4 Ohms, and then it will over-heat and shut-down. Some rough calculations say it would need an infinite heatsink to stay barely-safe at high output in 2 Ohms. A heatsink from a 100W amp might not be infinite-enough.

[sizzlemeister]

Would anyone who has ordered the kit from MusicPCB tell me how long it takes to receive it?

[psychedelicfish]

Depends where you are. It took a couple of weeks from memory, but I am in New Zealand, so you'll likely get much shorter shipping times if you live in/closer to the US.

[butch199]

I am in the process of building second tiny giant for stereo and to support keyboard on some tunes. This is a great little amp and is perfect for me to play my line6 x3live thru. I use it to gig and mic the amp, much better than x3 live direct to board. My question is the amp does get warm when play at gog level(I have mine in 125b size box). Is a heat sink needed or is the alim box enuf to dissipate heat, when played for extended periods, say gig set of 1 hour at a time, or is it likely to shut down?
thanks in advance and what a great project

[PRR]

> Is a heat sink needed

Yes!!

It is a car-radio chip. Typically it uses most of the back-side and other surfaces of the car-radio as a heatsink. Bolted to a 125B box may be a minimum-size (unless you have radio factory testing chambers).

It can run HOT. Too hot to hold. It probably should not boil spit. Somewhere in that area it will turn itself off, cool, and go again. No harm is done to the chip (unless it happens thousands of times); however the show won't be the same without you.

[butch199]

thanks for the input
I have found heatsinks at this site http://www.heatsinkusa.com/
can be cut to size will but 1 on top of my 125b alum enclosure, I would think this should keep it cool

[Heemis]

Hey all,

Built my Tiny Giant a year or so ago in a recycled Yamaha combo enclosure and I love it!  However, there is a spare hole in the chassis and I would love to add a headphone out jack.  I wasn't able to find any info regarding a headphone out on this thread, so I was wondering: Is it just as simple as adding a switched, padded output, or will the chip have an issue with headphone impedance??

[PRR]

The headphone problem is that headphones are grounded-jack, the TG output is _NOT_ grounded.

Other problems being far too big a signal, forcing us to waste-away some.

All problems can be attacked. However at the moment I need to attack my bed.

[Heemis]

I did figure that the amount of output the tiny giant can provide might be too much for phones, and yeah, that's a lot of wasted energy if it's padded down. 

What about tacking a simple 386 headphone amp onto the circuit?  Would it be an issue to share the 12v power coming off the regulator to power the 386?  Would it be ok to drive the 386 right off the output of the TL072 with a separate cap and volume control?

[PRR]

If you did not already have a Tiny Giant, yes the LM386 is a good way to go.

Tapping from the Tiny Giant is practical, but we have to take care.

There is 6 Volts of DC at either TG output pin. This will cook most headphones. We need a Blocking Cap. (The '7240 chip will shut-down if it sees a heavy to-ground load; I'm not sure it would see a headphone as a problem.) This cap needs a bleeder.

The ground return should go to the '7240's ground pin. If it goes to some random groundy point, the headphone current in the small wiring resistance is liable to make trouble.

The one-output audio level is 4V, which is fine for 150 Ohm phones but too much for common 32 ohm cans/buds. Basically we add a series resistor, 33 to 22 Ohms.

The TG output is mono but cans/buds are usually stereo, we need to feed both HP jack fingers (L and R).

The '7240 chip can drive low-low impedance at either pin, so you "could" feed many friends from the one TG. If you are just using it as a silent practice amp, I suppose that is no use.

[Heemis]

PRR, as always your wisdom is greatly appreciated!

I highly doubt I'll ever use anything but a pair of Sony MDR 7506 cans, which are 63 ohms... does the math still work out?  If so, 22r is pretty specific, could I get away with a pair of 10r in series for each lug of the stereo jack?

[PRR]

Design headphone jacks for "any" impedance. Today you have 63 Ohms, many cans are 32 Ohms, some 16 Ohm, and some very fine cans are 100-300 Ohms.

> 22r is pretty specific

If you read, I did say "33 to 22 Ohms". 10 Ohms is pretty risky on lower-Z phones and this much voltage, IMHO. 47 Ohms is fine if you do not require Very-Loud in low-Z phones.

[Heemis]

Ah, I meant two 10 Ohm resistors in series on EACH lug of the stereo jack, for 20 Ohms per side, but I'll just go ahead and get some 47 Ohm resistors and be done with it.

My main issue now is with design: trying to figure out a way to wire up a switching jack so that the plugging in headphones will mute the output from the speaker, but I don't think that's going to fly with this arrangement.  I guess I'll just wire up a switch to go back and forth... thanks again for the help!