Building the Tiny Giant amp

[fatecasino]

thank you!! I'll check it out. I had just put together the newly arrived pcb+parts..it was working like a charm. I think, it's the 3rd or the 4th time I am attempting to fix this amp. They always work perfectly at the beginning, but then always something goes wrong until I put it in the enclosure. The tda has very sensitive legs, you can easily loose 1-2 legs by just moving it. Well, it's a matter of honour, I have decided to finish this project, no matter how much it will cost.

[fatecasino]

well, the things go like this
1.after power up, the amp sounds like a distorted 2-stroke-scooter which accelerates and de-accelerates randomly
2.The volume pot does not influence this sound at all, it is steadily loud
3.the tda7240 gets too hot in very short time 4-5 secs
4.The voltages are:
input 18.5v
tl082 pin8 16v
tda7240a pin6 16v
lm338 Vin 18.3V
lm338 Vout 16.1V


Any suggestions?
@taylor: have you thought of selling extra tda7240a pieces in this combo?(http://www.musicpcb.com/pcbs/tiny-giant-amp-pcbcomponents-kit)

[tombaker]

Heya,
What voltage and amperage is your power supply?
Is the TDA chip heatsinked in anyway?
You could use a multimeter to check whether the pot is faulty.
The fluttering is consistent with the amp not getting enough current I believe. I could definitely be wrong, but I've made one before and it works great and I've never had any motorboating issues.

[fatecasino]

Hi!
the power supply is 19.5V/4A, I tried with another power supply, same results thought.
The tda is heatsinked with a really big heatsink. Otherwise it would explode with all this heat that it produces now.
The pot is OK.
It's not exactly a motorboat sound, like some faulty pt2399s, it's much more distorted and loud.
Is there a reliable seller for trying with a new tda?

[Taylor]

The parts kits are put together by forum member Waltk, but I'm not sure where he is currently purchasing the TDA chips. I have exactly one per kit so I can't sell extras myself, but he may either have extras or could post the most recent retailer for them. Maybe posting some pictures of your build could help, since you mentioned it was working fine until you boxed it up.

[bluebunny]

I got my first TDA7240 from xiaobao_semi on eBay.  Turned out to be garbage.  Thankfully, they appear not to be selling anything these days.  My working replacement came from swle2000 on eBay.  They're in the UK and they still have parts available, going for £4.51.

[fatecasino]

thanks bluebunny! just ordered 2 from swle2000. let's see 

[bluesman69]

Preparing to build two 12 inch cabs using Jensen mod speakers, 8 ohm each.  They will be in two separate cabs.  My plan was originally to have one of the cabs with two jacks so that I could run a cable from the amp to the first cab, another from the first cab to the second having everything wired in parallel for 4 ohms.  Now I'm wondering if maybe I should put two output jacks in the back of the amp coming from the pcb. If I did that how would I wire them to the pcb/ each other for parallel so that the 2 speakers (8 ohms) can become 4?  Thank you.

[Taylor]

You would connect one of the SPK pads to the tips of both output jacks, and the other SPK pad to the sleeves of both jacks. Physically, it would generally be better to join the wires at your jacks' lugs rather than soldering multiple wires to a single PCB pad.

[bluesman69]

Thank you Taylor for your reply, that makes sense.  I momentarily forgot just how small the pcb pads are lol

[bluesman69]

Another quick question.  I was thinking of doing something similar to what tech 21 did with the power engine 60.  Use the runoffgroove professor tweed as a preamp (similar to sans amp character pedal) with two outputs rather than one and run that preamp to two tiny giant (each in a 212 cabinet).  I don't think it will actual be louder per say, but perhaps using that will push more air and the ear will perceive it to be louder...I guess it would essentially be modular amp setup, a couple of power amps feed tone from a preamp.  I guess it would be similar to using an aby pedal.  Any thoughts on how this may be perceived louder by the ear?

[Taylor]

Yeah, that seems a good way to do it. If I'm remembering correctly, you'd get approximately 3dB more from doubling power, and 3dB for doubling speaker area.

[bluesman69]

Thanks Taylor.  I guess now I need to try to figure out how to wire in an additional output Jack to whatever preamp pedal I chose.  The only way I can think to do it without significant signal loss between guitar-preamp-tiny giant amps is to maybe wire the two output jacks of the prof tweed in parallel?  Or does it really matter all that much going with this type of signal chain?  Anyone have thoughts?

[PRR]

> 3dB for doubling speaker area

It's never that simple; but it is a good general rule that more paddle makes more push.

I like to work in quads. Four speakers gets 6dB more bass efficiency due to better air-load, and 6dB more mid-bass level on-axis due to narrower pattern. That's why a Champ or a Giant will BLOW-AWAY many "mighty" amps if fed into a Full Stack (eight 10s).

The two-12" array on the ground (many Fender Twins) is also significantly louder per electrical Watt than any single 10" box. By the logic above, 3dB better bass efficiency and 3dB extra on-axis (better projection to the far corner).

That's assuming "guitar" speakers, and not the highest-power g-speakers. Light cone is also part of the formula. Hi-power speakers have heavy coils and cones to hang-together at 200 Watts. Sub-woofers have heavy cones to leverage against air stiffness in the lowest octave of bass.

[bluesman69]

Thanks Paul.  I sort of figured that, but not in exactly such an eloquent and technical way.  I already have the two 8 ohm 12 inch speakers, so that's what I will use for the first build.  But I have received my second kit from Taylor and am thinking of using four 10 inch 16 ohm speakers wired in parallel to get down to 4 ohms.  Sure I could use four 12 inch speakers, but I love the bassman speaker setup and I'm wondering if four 12 inch speakers would be overkill.  Also, I like the idea of a slightly smaller cabinet.  I would like to play the two amps together to get a fuller sound, hence the "modular" idea of using the amps similar to the tech 21 power engine 60, and using a rog preamp pedal in the same fashion as a sansamp character pedal to run into both the amps.  I'm beginning to wonder if it would just be better to go ahead and use the active aby pedal route.  I think it would be more versatile because I could load a preamp pedal after the aby pedal into each amp to give them slightly different tones from each other.  Also, as this tiny giant is my first actual build of any electronic (and I'm hooked now) It will give me a reason to build yet another kit. 

Taylor, one of the things I really have come to love about your amp design is how uncolored the tone is.  It's great for running my various pedals through it and getting great tone.  I have one of the first production runs of the Peavey Classic 50.  Love the amp and the tone, but it's WAY too much power for what I'll probably ever need, and I can't get it up to saturation volume without tearing up the neighborhood.  I also have the Orange Micro Terror, which I really also like, but it does have it's own tube preamp which significantly colors any preamp pedal tone, So it's kind of a one trick pony in my mind.  I just have to say, I play the Tiny Giant almost exclusively now for that reason (and also because I put it together myself).  Have you toyed with the idea of designing and supplying something similar but a bit bigger like say 40 or 50 watts capable?  If so, I would be the first in line to order a few of them.  Thanks again.

[bluesman69]

I am curious that if I wanted an amp with a bit more wattage if I could swap out the LM 338 for an LM3886.  I would have to look at the data sheet for that to see what kind of power supply I would need...I'm sure I'd also need a significant heat sink as well, but would the rest of the supplied components and the pcb work fine with an LM3886, an appropriate power supply and heat sink as is?  Or would resister/ capacitor values need to be adjusted as well?

[Taylor]

The LM338 is a voltage regulator, whereas the LM3886 is an amplifier chip. The amplifier chip in the Tiny Giant is the TDA7240A. These amp chips are different electronically and are physically in different packages with different pins, so they are not compatible and can't be substituted for each other within a pre-existing circuit.

You definitely can make an amp with the LM3886, and there are schematics and kits for them out there, but it would be a different circuit entirely. I bought one of those kits a few years ago but ended up not building it and came up with the TG instead, based on datasheet designs and posts by WaltK. You need to build your own more serious power supply and will have to do mains voltage wiring, which can be deadly dangerous if you don't do your homework on safety.

This is why the TG came about: it's pretty easy to build and pretty loud and pretty clean. Since 40 watts is just barely louder to the human ear than 20, and considering the expense, difficulty, and danger in building a significantly more powerful amp, making the TG seemed a better option to me at that time than building the 3886 amp kit I bought. But that's just me and other people do build very nice high power amps. Check out the DIY Audio forums for gobs of info.

Actually, if you really want more volume you should also turn your attention to speaker designs such as those of Bill Fitzmaurice. You can get a good 5 more dB in the relevant frequency ranges (better than doubling watts) by just building your cabinet in a different design.

[bluesman69]

Thanks Taylor.  The high voltages is what put me off of tube amp kits.  I will certainly take a look at the cabinet designs you suggested.  I'm still thinking of aby pedal or some sort of modular setup.  I understand that I can find speakers with different db ratings per watt and that makes a big difference.  Thanks again Taylor.

[mindpunk]

Can someone please post the pin voltages from a working TG?  I have a version with a tube pre I am working on that has signal getting to (and even through) the TDA but there is no amplification (I can hear the signal when I probe pins 5&7, but nothing on the speaker).  The vero prototype worked and sounded real nice, but moving the design to PCB has me stuck.  I want to rule out circuit design problems as I have already desoldered 2 suspected TDAs and my traces are starting to melt.

If someone wants to look over my design it is here: https://drive.google.com/file/d/0B_Sh_vDhJkMqWVJ4cU45WGZCY1U/view?usp=sharing

I know the protection diode is in a weird place (it's where it ended up on the vero prototyping madness).  I'd also be interested in knowing people's thoughts about removing all of those filtering bits taken from the Tube Cricket (Diode through 220uF cap) as I assume those would be unnecessary with a switch-mode PS and the LM338.  Although I've been wondering if they don't provide some protection (load) to isolate the Vout on the 338 from the ground potential on the cold heater elements on the 12au7.

My PCB has the diode before the 338 and all the filter bits in place FWIW.

Any help would be appreciated but pin volts are really needed, thanks!

[PRR]

There should be 11.5V from the '338. All the power-amp and opamp pins should be 11V, zero V, or half of 11V (5V or 6V).

Which ones are not right?

Adding a hot bottle is outside the original design, and should probably be diagnosed separately. i.e., feed signal to *just* the TG and see what comes out. If that works, problem is around the tube.