Building the Tiny Giant amp

[Colonel Angus]

Could you use the GGG charge pump to power the TG off a 9V wall wart? Obviously I still haven't built mine, other stuff came up... and I still can't get my gristleizer to 100% function

[slacker]

No, the TG needs way more current than the charge pump can provide.

[slacker]

Plan now is to build a stompbox type preamp to run off the regulated 16.69v and put in the same case, any recommendations for one which will clean right up, but still get to a decent classic rock sound?

Mine sounds really good with a Colorsound Overdriver as a preamp, gets you everything from clean to a nice amp like bit of distortion.

[Colonel Angus]

Got it, thanks Slacker!

[Taylor]

I'm using a scrounged PSU from a defunct laptop that gives 20v at 3.5A (Dell) so set it up using the 1.5K resistor on the regulator and got 16.69v on my meter.  Two niggles when building, the ic socket had got it's legs mangled in the post, pity it wasn't stuck into the other side of the foam the tlo72 was in, and one of the screw and nuts wouldn't go together I figured a damaged thread: replaced both the socket and the screw/nut and had no further problems: except how small and fiddly it is to solder up ( hey I'm over 40 and my eyesight isn't what it was!

Hi Avulon, thanks for the feedback on the kit. Glad you're liking it!

[Avulon]

I've now managed to test using a 4 ohm load (two paralleled celestion 10 inchers) and it still sounds good - until I hit max vol then it cut in and out before cutting out completly, rolling the volume back a hair and waiting a moment and the sound came back. I guess I pushed one of the chips into shutdown.  My gut feeling is that it's the power chip as I'm running it at 16.69v, there was no discernible heat from either chip when it did this. I've still to put in a regulated voltage take off.  when I do I'll push it into cut off and check what the voltage does, that should tell me whether it's the regulator or the amp chip.  I'll also test with an 8ohm load (single speaker) and see if it still does it.

As far as a preamp, I took a look at the coloursound overdrive, which seems like a fuzz circuit, but am leaning more towards an English Channel or BSIAB,  I'll try and get one on the breadboard to feed the amp and see how I like it.

[YouAre]

The best power supply I could find was 19v and 4a. Would you guys think it's beneficial at all to use a voltage divider to bring it down to 16v (1v higher than the recommended 15v to leave some wiggleroom)? 

I'm assuming if I were to, 1/4w would not be a sufficient size. Another consideration is the heat from these resistors offsetting the reduction in heat from the lm338, negating the idea of doing this in the first place.

Any thoughts?

Thanks,
Murad

[waltk]

The best power supply I could find was 19v and 4a. Would you guys think it's beneficial at all to use a voltage divider to bring it down to 16v (1v higher than the recommended 15v to leave some wiggleroom)? 

Nope. Just leave as is.  As long as the LM338T is properly heatsinked (?), there isn't a need to use an additional voltage divider.  It's also OK to change the resistor(s) that set the output voltage of the 338.  The rest of the circuit will handle 16V, so you might as well run it at that voltage. (I wouldn't go any higher though).

[YouAre]

Nope. Just leave as is.  As long as the LM338T is properly heatsinked (?), there isn't a need to use an additional voltage divider.  It's also OK to change the resistor(s) that set the output voltage of the 338.  The rest of the circuit will handle 16V, so you might as well run it at that voltage. (I wouldn't go any higher though).

Groovy, thank you! Much appreciated.

[garcho]

I play electric mandolin in a strange band that is occasionally mobile. The guitar, violin, accordion and myself play through smokey amps taped onto helmets with speakers bolted on top. Obviously, those little 386s are no match for trombones, trumpets and drums, and although I love the "tone" of the smokey, it'd also be nice to have something with higher fidelity than a speaker phone. The tiny giant would be perfect, but so far the best thing I can find is a pricey cordless drill battery, 18V @ 3 AH. Is that enough amperage for the Tiny Giant? When we're mobile, we usually play less than 30 minutes. Also, we don't have to be super loud, just audible. Any other ideas? Thanks dudes!

[Taylor]

That drill battery should work - WaltK has done exactly that with a similar amp design. I can't speak to the battery life (maybe he can weigh in) but if the batteries you're looking at are new, I bet you could get an old cordless drill for fairly cheap. The motors on the cheap ones wear out, probably a while before the battery's recharge lifespan is out, so people are often throwing them away anyway.

Cool photo! Would like to see you guys sometime. Sort of reminds me of a crazy DIY marching band I saw in San Francisco once.

[waltk]

That drill battery should work - WaltK has done exactly that with a similar amp design.

Yea - works great.  I use 18V lithium batteries (I think they're 3.0AH).  They are very pricey, but since I already had some for my power tools, it was a low-cost proposition for me.  Plays for hours.

Haven't tried this, but I think a 12-pack of (high-drain lithium rechargeable) AA batteries might also work.  Most power tool power packs just contain sub-c size individual cells.  The TG draws a bunch of current when you first turn it on, then settles down to a reasonable current draw, so I would expect you could easily play for 1/2 hour with a double-A pack - maybe even triple-As.  Just wire e'em up in series (maybe with 3 standard 4-cell battery holders).  In a pinch, you can then power the thing from disposable batteries too.

The speaker(s) you use makes a huge difference, and it's not easy to find efficient small speakers.

[PRR]

Echoing Walt:

> cordless drill battery, 18V @ 3 AH.

At HIGH volume in 4 ohms, most of an hour. Much longer at lazy level, but competing with brass I bet you'll have to slam it hard.

A 12V lead/acid alarm or motorcycle battery would work. Omit the TG's regulator, go right into the power amp chip. This does add danger of acid-burn, and may not be lighter, but is cheaper if you get lucky.

Speaker size and selection is VERY important. The 4-inch horns are a good deal for the mandolin, and the squeeze-box if it doesn't expect full bass. The 8-inch is a bit better. Either would be better with a cardboard extension to flare-out to a larger mouth. 250Hz needs at least 10 inch diameter mouth or sound waves don't happen. $1 of posterboard may be enough for two shows, affordable for an occasional gig.

I would not like full-bodied guitar through either speaker, but I admit that any "decent guitar speaker" will be too big and heavy to ride on your head for 30 minutes.

[Avulon]

I've now managed to test using a 4 ohm load (two paralleled celestion 10 inchers) and it still sounds good - until I hit max vol then it cut in and out before cutting out completly, rolling the volume back a hair and waiting a moment and the sound came back. I guess I pushed one of the chips into shutdown.  My gut feeling is that it's the power chip as I'm running it at 16.69v, there was no discernible heat from either chip when it did this. I've still to put in a regulated voltage take off.  when I do I'll push it into cut off and check what the voltage does, that should tell me whether it's the regulator or the amp chip.  I'll also test with an 8ohm load (single speaker) and see if it still does it.

Now tested into 8ohm load, this time it didn't cut out at full vol.  When connected to the 4ohm load it also seems to depend on the input signal level, e.g rolling back the vol on the guitar also made it stop cutting out, which makes me more certain it's too much current in the amp chip (due to running at the higher 16.69 voltage). So at some point I'll have to replace the 1.5k on the voltage regulator with a 1.2 to lower the voltage a little.

I've now also heard the Catalinbread RAH pedal and am set on building this for the pre-amp - parts collection has already started - maybe I'll need a bigger box! medium sized giant anyone?

Avulon

P.S it seems almost as loud into 8ohm as 4ohm - but only tested in my workshop which isn't that big a space.

[garcho]

Thanks for the replies y'all! I can't wait to try those ideas out.
PRR, I am a little scared of the acid burn, I guess just cause it sounds really scary. Also, when we play, we move around a lot, so weight is an issue. But we do have a couple motorcycle geeks in the band, I'll talk with them. Great suggestion!
I plugged a few gigs I have next weekend on this wax cylinder post in the Lounge if you're interested and available. Can't wait to have a Tiny Giant on my head!

[Taylor]

P.S it seems almost as loud into 8ohm as 4ohm - but only tested in my workshop which isn't that big a space.

Sounds about right. Most amps will put out less than double the power into half the load, and double the power is approximately the threshold of an audible change in volume. Speaker sensitivity is a more important factor if you're trying to get as much volume as possible out of it, as well as EQ.

[parra]

Ok, so i'm new in this forum but i have built the tiny giant a couple of months ago and it's still working perfectly (awesome little amp by the way, Taylor!), but from the beginning i don't know why, i feel that it is missing some highs, maybe because i mounted it in a home made pine cab with a 10'' 4ohm speaker (jensen mod10-35)?

if i change the cap to the volume pot maybe i can get more treble? i don't want to put another pot for the tone, cause i'm planning to add a professor tweed as a pre amp and power it with the regulated 11.6V from the TG, and it has already a tone pot, but i think that if i leave the TG as it is, i will still have problems with the high frequencies not passing through...

PS: sorry for comming only now into this discussion, cause i've been reading this entire thread and others also and learned a lot in the process, so thanks to everyone who's posting their knowledge and experiences in this forum, and major thanks to taylor for this cool project!

SeeYa
Parra

[PRR]

> problems with the high frequencies not passing through...

The TG passes highs just fine.

Changing the cap to the volume pot won't get more treble. (It affects bass-drop, but you don't want to cut bass SO much that only the highs are left.)

However: The TG is a "flat" amp, what you put in is what you get out. Most guitar amps have some or a lot of Treble Boost. So compared to some "typical guitar amp", the TG may be less bright. TG=vanilla, 5F6a=salsa.

There's many thing you can put in front for tone-shaping.

[trem7]

Hi, I've already successfully built one of the tiny giants and recently finished my second. This time I wanted to add a switch volume pot and led. I've gotten the led to light up and turn off when the switch is switched however there's no sound at all. At first I had the power wired wrong but fixed that. Any tips?

[parra]

thanks for the reply PRR

> problems with the high frequencies not passing through...

yeah, i didn't explain myself there right, it's true, the TG really gives what you send to it, i just wanna get a bit more treble without changing the TG circuit with tone stacks and eq, so i was thinking if i add a preamp circuit this will fix my problem or not?

By the way i'm not sure if i should try the ROG professor tweed (and power it from the 12von the TG) or the ROG supreaux deux and if this one can be powered by the 18 v from the laptop power supply or if i need some sort of regulator, or to the 12 v with a charge pump. what do you think? (to many questions i know sorry! =])

PS: when i get the camera i'll take some photos.