Building the Tiny Giant amp

[PRR]

The symptom suggests over-heating. Either the chip or a dubious solder-joint. So I think it has to be opened.

[Moxienator]

Thanks PRR.
I'll open it up and triage. First I'll check and re-wet the joints, but as far as heat sink, any suggestions for a good one? I tried to look at Mouser, but there soooooo many, I don't even know where to begin. I figured the massive bar of brass would be enough, but obviously not. maybe if I used thermal compound as well? The thing is, The tabs are mounted to the enclosure, and the the bolts go through the brass bar, holding it on the outside. Transfer seems ok, though I haven't broken out the pyrometer yet...

The goal is to be able to crank this amp up for long periods of time. I plan on using it for small coffee-house type gigs and home practice at lower levels, but also to noodle about with the old bandmates (which is where the volume cranking comes into play). With this in mind, would it be better to use the TO-3 metal can version of the LM338 and just wire the leads into the board? It could then be externally mounted and use one of the larger heatsinks?

[Moxienator]

Got the Thermal compound in place. Amp didn't fart-out as much as before, or nearly as early. Will check solder joints and go from there. It is already better than it was. Temp of the casing and brass was at 77*F - ambient temp is about 75 or so.

[Taylor]

Thanks for that follow up, perhaps it will help others.

[Moxienator]

Hopefully I'll have more concrete data this weekend. Haven't had a chance to really blast it since the last post.
I did go over every joint though, and a few did seem suspect.
When I know more, I'll post some findings.

[Moxienator]

Vintage Handmade (strat-ish) with 3 Giant Single coils --> Neutron --> Azabache --> Tiny Giant 112.

TG Volume @75%, Tone @80%, Guitar Volume and Tone @10

Played with azabache on most of the time.

After about 30 min, casing and brass were merely warm. The heatsink is not the most efficient, and I have heard from other TG builders that a PC Processor Heatsink works very well (If only they could give me a part number! Argh!), but the brass seems to work. Haven't had to raise the TG volume more than 75% as I'm using the Aza as a boost/overdrive. It may be that putting the vol. at 100% would again make it cut-out. haven't tried, as the settings I used were LOUD. I will continue to search for a real heatsink (you know, with fins and whatnot) but until such time as I find one, this will do quite nicely.

Had some issues with my Neutron (who doesn't?), and the guitar needs some TLC in the electronics dept, but overall, played loud and proud w/o cutting out due to the amp. Success?.... Perhaps....

[Rock_on]

hi again! 1st sem's midterms is done. We are currently in Finals now. I have time again to do this.
i'm almost done and still my PS is my problem. our shop here does not have LM1084-85 (fixed or ADJ) and LM337-338.

ok, im done in power amp and preamp section. this is the last thing I need to do.

they also said that they have no 1n4004-4007 and they gave 1n540 instead which is according to them a 3A rectifying diode.

what IC is left for me now? I have 24V AC and needs 12-15V regulator.

[Moxienator]

So the evolution of the Tiny Giant continues! (and here you thought I was done...)

The goal is to build the GM/Cook spring reverb into the same chassis as the TG.
I located a 7 x 4 x 3" hammond enclosure that will fit everything, and will be mounted into the cabinet.
The reason for the 3" depth is due to the fact that I want to put in an actual heatsink to replace my hunk o' brass.

The heatsink I'm looking at is 2 x 1 x 2.5" (roughly), finned, large aluminum, and has a thermal resistance of 3C/W.
I plan on mounting it to the regulator only, using wire leads to attach the reg to the board, and attaching the power amp to the chassis itself.

Anyone have any idea if this heatsink will be enough? 3C/W was the lowest TR i could find, and from what I've been reading,
this should provide good heat transfer. I'm using a 16V 4A powers supply, and was thinking of getting a 15V one to reduce the
amount of heat on the Reg just to make the whole heatsinking thing easier/ more efficient. Am I correct in this assumption?

Should I mount a sink to the power amp as well? It seemed like only the reg was getting hot.

The 11.6V out from the TG board will be the power for the reverb board. Is there a 'neat' way to connect the grounds?
My thought was to use a jumper to make two "lugs" off the power GND input on the TG and attach the GND's that way.

I was thinking of changing my tonestack, and instead using a modified version of a tonestack from an ROG effect I like.
I plan on adding a second stage between the preamp and power amp sections to power it, but I'm still working that one out.

The spring reverb unit is modified to only have 2 controls: Reverb and Level. The Input and Reverb drive pots were replaced with trimpots on a small board.
The reverb will not be bypassable, and I omitted the power switch. This will effectively give me 4 knobs on the TG: Vol, Tone, Rev, Lev. The circuit will run:
Input -> Reverb -> TG preamp -> tone stack -> TG Power amp -> Out

THEN by the gods, it will be finally done, and I can put it in a nice cabinet made from 1/2" dovetailed pine boards, 14 x 14 x 8" and have an amp I can actually carry without breaking my freakin back. Remember the days when you could carry your amp and guitar at the same time to a gig? I do... and they were long ago.

[waltk]

Wow - that sounds great.  Nice work!

Anyone have any idea if this heatsink will be enough? 3C/W was the lowest TR i could find, and from what I've been reading,
this should provide good heat transfer. I'm using a 16V 4A powers supply, and was thinking of getting a 15V one to reduce the
amount of heat on the Reg just to make the whole heatsinking thing easier/ more efficient. Am I correct in this assumption?

That heatsink sounds like more than enough.  I was using a very small heatsink that would get warmish, and then switched to a larger (but still fairly small) heatsink that I scavenged from a broken motherboard.  This heatsink was cooling the graphics chip on the motherboard, and was a perfect fit to stretch across both chips on the TG. It is blue anodized aluminum with some cool asymetrical fins.  Never had a heat problem with it.

Here's a better idea for you... instead of getting a lower voltage power supply, just change the TG (LM338) power supply to a higher voltage.  If you change one of the two resistors that set the output voltage of the LM338, you can make it put out 14 volts.  The TDA7240 can easily handle 14 volts (and might actually get you more output). The 2-volt difference with your 16-volt power supply means that the LM338 will have to dissipate less heat and is a sufficient drop for the regulator to operate.  It's win-win-win all the way around.

[Moxienator]

@ Walt - Wow, thanks man! Great idea on the resistor change! I'm ordering the heatsinks as soon as I finish typing! The ones I found at Mauser won't fit both, but I plan on connecting the LM338 to the board with wires, and leaving the TDA7240 on the board. This will allow me to have the two giant heatsinks mounted inside the chassis, and each IC will have its own heatsink. Thanks again for the info! I guess this means I'll need to order another kit from Taylor...

@ Taylor - My Norton Security thinks your site has been hacked. What gives? Is it just a fluke?

[Taylor]

The site did get hacked but it should be fixed now. AFAICT it's not anything dangerous to your computer, just spam that they insert into my header (oh my).

[Radcon]

I built a Tiny Giant amp a year or so ago, and I love it.  Use it more than any other amp.

(Runoffgroove Azabache -> MerlinB Solstice Reverb -> MusicPCB Tiny Giant)

I have started planning building another pair of amps with my brother.  Tiny Giant the obvious first choice.  But it looks like the TDA7240A might be hard to find.

Does anyone have a suggestion:

1. Where to buy the TDA7240A?

2. Similar solid state power amp to build instead?

Thanks

[garcho]

Check out a bunch of datasheets from various 'chip amps' (TDA blah, etc.) and look for their 'application circuit' examples. Here's a place to poke around for different chip amps.

[Moxienator]

Ok Kiddies. Its been a bit since I posted anything, and rest assured, its because I was in the a "lab" doing what Arcanists do best: Godless Tinkering.

So- I've been working on this tone control issue I've been having, to whit; I've tried NUMEROUS (I think the count is in the teens or so) passive tone controls, and none of them has reacted well to my ear.

"Big Muff's" (and the myriad variants) need boosters, buffers, and power. I like my muffs trim and shaved thank you very much. 
The "18 watt" (posted somewhere by PRR I think) was close, but horse-shoes and hand-grenades come to mind. 
The "top boost" (Also by PRR, I think) wasn't quite how I wanted to approach things. 
The SWTC (Jack Orman) didn't appear to do anything, but I like its' simplicity. 
I've been messing with values, and as of today (TG Tone Control #17ish) have stumbled close to the right track. 

The TG with a 12" Yngve Malmstein Celestion G12T has great bass response, so I figured, the "tone" would really involve a control for treble boost without attenuating low end. I'm currently playing a heavily (body) modified SSH MIM strat through an Azabache, into a Forrest Cook spring reverb, into the TG. 

Using Jack's SWTC #2 as a guideline, and based on the brightness of the maple/alder strat,
I've soldered up a B5k pot with a 1N on lugs 2&3 that occurs AFTER the volume pot of the TG.
The Volume pot's lug #1 and #3 connect to the "1" and "3" pads on Taylor's PCB, and the wiper goes to lug #1 of the tone control.
Tone pot lug #3 (connected to the 1N) goes to the "2" pad on the PCB.

Technically, this is Bass Ackwards to the original schematic, but it is the ONLY way I could get zero interaction between the volume and tone pots.
The effect using a 102 (1N) cap on the tone is fairly subtle, but definitely "boosts" high end.
I'll continue tinkering, but I REALLY wanted to share this breakthrough with you guys.
My plan is to go down to a 151 or .15N cap next and see where that goes.
TTFN - Moxie

[garcho]

Why not use an active filter? You're already using a chip amp and an op amp, so not much mojo left.

The effect using a 102 (1N) cap on the tone is fairly subtle, but definitely "boosts" high end.

I'm assuming the quotes mean you understand that's impossible.

[Moxienator]

Figured it would be easier to use a passive tone control. If I can't get this right, I may have to go the active route.
I've already got the TG's power supplying the GF Cook spring reverb, would adding another "power tap" be an issue?
The PS I'm using is 16V 4A. Not sure if I need something with more juice or not.

"boosts" is a term I used for lack of a better one. I'm still not exactly fluent in the electronics lexicon.
The control brightens the sound without cutting the bass response. That was the point.

[potul]

Hi everybody,

How much tolerant is the tiny giant with the input voltage WITHOUT the regulator?

I bought a 12v lipo battery to transform my tiny into a "portable tiny" with the idea to plug it after the regulator. But I just received the battery and I see it outputs almost 13.6V when fully charged.... Will this damage the chip?

Thanks for the help!

Mat

[Taylor]

That should be fine, but if you're worried always check the datasheet for the chip.

[potul]

Thanks for the help.

On the other hand... I just was impacient and I did a quick test plugging the battery into the regulator (the same place I plug my 25V laptop PS), thinking that it would not work. I had the idea that the regulator needed at least 15 or more to work properly.
My surprise was that it worked fine... I left it running during 2 hours with my Ipod in, to test the voltage drop of the battery, and I was even more surprised to see that even at voltages of 11.5 from the battery, the amp was still running.

I was assuming that if the regulator does not receice enough voltage it will not provide output, ... but maybe I'm wrong and the only issue if you feed low voltage to the retulator is that it will not "regulate", and simply pass the input voltage... But I have no clue.

Do you know what happens if you feed 12 volts or less to the regulator?

[waltk]

Do you know what happens if you feed 12 volts or less to the regulator?

If the regulator is set for 11.6V output (as it is in the TG), you need an input voltage of 12.85V to get it (11.6 + 1.25).  At any input voltage less than that, you'll get (Vinput - 1.25).  So a 12V input would produce 10.75V output.

The TDA7240 is pretty tolerant of different supply voltages (as it was intended for car use).  There are graphs in the datasheet showing Output power vs. Supply Voltage.  The graphs show the supply voltage down to 9V, and the output is fairly linear for the whole graph. 

I think you can take that to mean it would be safe to power the TG (including the regulator) with any voltage greater than 10.25V (although your output would be reduced accordingly).