Building the Tiny Giant amp

[Rock_on]

Hey, uhm...
What does the U1B do??

And where did 7v came from??

[Jdansti]

Hey, uhm...
What does the U1B do??

And where did 7v came from??

My guess is that the two 1M resistors on U1A form a voltage divider cutting the 14V in half. U1B shares this 7V.

[waltk]

What does the U1B do??

Nothing.  Taylor picked picked a dual opamp for the design just because they're more common than single op amps (maybe more easily found/available).

-Walt

[Moxienator]

Finally finished the TG today. It sounds great! Its mounted in a hastily put together cab of 3/4" plywood (and lots  of caulking). I have it hooked up to a celestion G12T and its got this great, light overdrive sound to it when its cranked. My Neutron Filter goes exceptionally well with this amp. Does get some hiss/hum when i fire it up in certain rooms, but not too terrible.

BUT!

Can't get the tone control to work. Has anyone successfully added a BMP tone stack into this build? If so, then how?

[Moxienator]

Got to play it today for about a half hour. It got HOT. its in a 1590BB (I think) its really roomy, and I thought the case would allow enough mass for good heat absorbtion. I guess not. I'm going to add a .25 X 1.25 X 8" bar of brass tonight, and hopefully will have solid results.

Would using an incandescent lamp instead of an LED help or hinder? I was thinking about trying to throw in some stuff before the giant to draw off some current.
Right now im powering the LED off the PCB's regulated output. Its a 16v 4a power supply feeding the thing, and I think it really needs to be taken down a notch.
I figure this will also clean up the sound a bit. It gets a bit gritty when you dime it. or really get close to dime-ing it.

Anyone use anything other than a 10k for the volume pot?

[Taylor]

I might be misunderstanding you but I think you have made some inaccurate assumptions about electricity. The amp will only draw as much current as it needs. Connecting something else on the supply like a bulb will draw more current from the supply but it will not divert any current from the amp.

The TG distorting when you crank it is normal. Some people like the way it sounds, others try to avoid it by turning down.

What effect are you going for by changing the value of the pot?

[Moxienator]

Yeah, the more I thought it about it, the less sense it made.

I was trying to clean up the sound a bit, as the amp was clipping when the volume was at 1/3rd rotation.
Then I figured out that the issue wasnt so much with the amp circuit as my tone circuit.
I've been trying to get the tone control to work, and with the many and varied permutations i've used I haven't gotten it yet.
The last one, wired up yesterday, is close. Its a modification of the 18w tone control found in this thread.
The sound is now MUCH cleaner. and yes, it clips when cranked, but not nearly as quickly as it was with
the last few bootleg tone circuits i had in it.

The issue now is that the sound is not completely cut out when the volume is at 0. I wired the lug 1 pad to the
tone control instead of the volume, and the output of the tone goes to the volume pot, which has lugs 2 and 3
going to the pads on the board. The tone works well, I used a 1n5 for the high end, and a .47 for the bass
(which needs to be smaller), so no worries there, but wiring it like that isn't quite right for this circuit.
I'm going to try putting the tone control on the output of the volume pot, which will hopefully allow the the signal to be
cut out when the volume is turned to 0. lugs 1 and 3 of the volume will go to the board, the wiper to the tone circuit,
and the tone's output will go to the vol 2 pad on the board. Keep your collective fingers crossed for me.

That's that for that.

The Large brass bar i put on as a heatsink seems to have worked. I only played it for a few minutes (maybe 10 or 15), but the bar was
only slightly warmer than room temp. A HUGE difference. Its about a pound, or pound and a half of brass, so we'll have to
see what happens after 30min to an hour of playing, but I have high hopes.

[Valoosj]

Taylor, don't you have heat issues with your small enclosure then? I remember seeing yours and it was only a 1590A enclosure.

Also, wouldn't it be easier to instal a small fan such as these to dissipate heat?
http://rato.e-nitiative.eu/product/details/velleman/electronic-components/bsspc1/M640E442?flang=en
http://rato.e-nitiative.eu/product/details/sunon/electronic-components/bsv1225/S8042006

Or would it cause extra noise? I'm thinking of having a go at it with this fan.

[Moxienator]

the fan would definitely add noise.

mines in a taiwanese 'B' i think. it might be a 'BB' though. In any case, its roomy. it just didnt have enough mass for heatsinking.
It has more to do with the power supply than anything. With a 12v power supply, you should be good. Mines a 16v, so there is
quite a bit of heat. Just use the screws that secure the tabs to mount a decent sized piece of scrap metal. It works.

[Taylor]

I've never had any problem with mine and I use it all the time with guitar, bass, and synth. I also seem to rattle it off the cab a lot so it gets beaten up and handles it well. It does get warm but never more than that. However, I always use it in its clean range of volume, never distorting.

[Moxienator]

Worked out the Tone control problem.

I used the modified marshall 18w posted by PRR a while back, and in order for it to work properly, it needs to come AFTER the volume control, so the wiper of the Volume is the input of the tone circuit, and the output of the tone circuit is wired to the pad on the PCB marked '2'.

I used a small piece of perf board to mount the components, as the only 1K resistor i had was HUGE! it fits nicely into the amp though, and if you ever wanted to tweak the circuit, the small board makes it very easy. I suggest using a B10K pot with center detent for the tone knob, the build just seems cleaner this way.

After a few tweaks, the modified 18w tone works great! It dials in a really clean sound, and allows me to push the volume much further before it distorts.
Thanks PRR!
Much thanks to everyone else who contributed their wisdom/advice for this build as well. Your comments and of course your math were greatly appreciated!
Thanks to Taylor also, as this is a great amp!

[Taylor]

Glad you sorted it out. Enjoy!

[Moxienator]

Thanks Taylor! LOVE IT!

P.S. - finally got a multimeter. You know, in celebration-like.

[patricks]

Just stumbled across this thread, the TG looks like a great build! Does anyone know what its input impedance is?

[psychedelicfish]

Just stumbled across this thread, the TG looks like a great build! Does anyone know what its input impedance is?

Probably ~500k

[patricks]

Cool, thanks! I'm planning a microamp build and was wondering whether I could just connect the output straight to the TG but I'll just make sure to build in a "pre out" and a dummy load.

[Moxienator]

Ok guys, Its 99% finished. I installed a speaker out jack, a DC in jack, made plugs for each ( love right angles! ), re-worked and cleaned up the insides (shortened wires, removed remnants of old configs, et cetera), and put it all back together in the "sheissbox". So-named due to the odd shade of brown used for the caulking, as well as the lack of any sort of care given to its construction. Its spot on. Everything works, The heatsink is perfect (I can play LOUD for a long time.), and I paired it with the azabache to see how it would sound.

Amazing.

It really goes great with the aza in front. The next foray into tiny giantdom will be the full custom amp, with switchable "lead" channel and a reverb.
Has anyone tried that spring reverb pedal? It takes 12V to power it so....

Thanks again to everyone!

[Moxienator]

Hey guys... yeah I'm back.

SO my TG is acting up when the volume is at or above 3/4. The sound cuts out, and or volume goes way down for a second or two, has this kind of overworked-tired-fizzy type of sound, and then it comes back. It happens mostly when I bang out barre chords at this level. I added a Tone control on the output of the volume pot, but other than this, the build is stock.
Any ideas?
should I nix the tone control?
I feel like when I first made the amp it was able to go to max volume without any issues, but can't say that I really remember.

[PRR]

> The sound cuts out

Do that, then put your finger on the chips.

Can you hold it? Or does it burn you?

[Moxienator]

PRR,

The outside of the enclosure and the brass bar were "decently warm", not "fry an egg". The Chip was probably very hot, but due to the massive brass bar I attached to it, Its a bit of a process to open it up. Could this be caused by over heating? Should I work on finding a more efficient heat sink?