Building the Tiny Giant amp

[fatecasino]

getting back to the damaged tiny giant:
I replaced everything (tda, 072, lm338) + I didn't solder the tda7240 on the pcb directly but i used 7 wires of 5-6 cm as an extension (i was afraid that the pcb would be cooked)
Now...
It plays normally but in the background it whistles like a 50's AM radio!!
Actually, when I move my hands around it, without touching it, the whistle changes, something like theremin!
1. Is it the extension cables I used for tda7240?
2. Is there some capacitor that has to be replaced too?
I am writing all these just in case someone had had the same symptoms

[Taylor]

Is it in a grounded enclosure or otherwise shielded? If not it definitely could pick up and amplify radio frequencies.

[fatecasino]

yes, the enclosure is grounded.
I had faced that case in the past, when the amp was out of the box: I could hear clearly a radio station playing latin music all the time!
But now the case is different, I don't hear any radio station/music, the amp gives that theremin/am radio whistiling only

[PRR]

The power amp chip probably does not like those long wires.

[fatecasino]

just ordered new pcb and amp chip... I was that close to finish up a 4-year-project, my personal 3 channel battery powered busk amp!! I have to wait a bit more time probably

[fatecasino]

hi all,
i have another question to post, about the tiny giant power supply. I don't know if this is the proper forum, but I think it is close to the tiny giant amp topic.
I have built this power supply:


There is something magic happening here, when I follow the following scenarios:
SCENARIO A
1.Turn on SWITCH A(220V) Vmeter = 18V
2.Turn on SWITCH B(18V) Vmeter = 18V
3.Turn off SWITCH B(18V) Vmeter = 18V
4.Turn on SWITCH B(18V) Vmeter = 4V  and the amp of course doesn't power up!

SCENARIO B
But if
1.Turn on SWITCH A(220V) Vmeter = 18V
2.Turn on SWITCH B(18V) Vmeter = 18V
3.Turn off SWITCH A(220V) Vmeter = 0V, the amp makes a blip sound and its power led turns on (just for a moment) after 2-3 secs
4.Turn on SWITCH A(220V) Vmeter = 18V and everything works normally

SCENARIO C
Then, I have a 18V battery pack, I connect it in parallel to the exit of the power adapter, just before SWITCH B
1.Turn on SWITCH A(220V) Vmeter = 18V
2.Turn on SWITCH B(18V) Vmeter = 18V
3.Turn off SWITCH B(18V) Vmeter = 18V
4.Turn on SWITCH B(18V) Vmeter = 18V  and the amp of course powers up!

Obviously there must be some C1 capacitor disharge directly into my tiny amp (or into the battery pack in scenario C), and this probably damaged my tda7240a (could be)
I am missing out some theory around power adapters, but what could I change in my power supply circuit in order to make my first scenario work.

Thanks to everyone, I hope this post gives some knowledge contribution 

[steinbeck-il]

hey all,
i have built this little beauty for the second time now and still no success.
the thing works fine in very very low volume. but when i try to turn the volume up a bit or sturm a few strings together i get this repeating pop sound.

i build this with a vero layout and i have used monolithic capacitor for the 1u values.
i have switched the amp chip, the  power supply and received the same results.

any ideas what could have gone wrong ?

[bluesman69]

Taylor, this is one serious diy amp!  Love this thing.  Thank you for taking the time in your wonderful hobby to share and make this great little amp available to the rest of us, and at such an affordable working man's price.  I wanted to buy a few more of these because now I'm really hooked, but your website seems to be down.  Is there an alternative way that I can get in touch with you to order a couple more complete kits?  I plan to add a few pics here in the coming days of my build.  The chassis is an old metal Johnson and Johnson first aid case.  I built it into its own head cabinet and am working on two 8 ohm 112 cabinet wired in parallel for 4 ohms to get every ounce of sonic goodness out of your sweet creation.  I have noted that others here seem to not get much more in volume past about 9 oclock.  I don't know why, but mine is clean and mean with discernable volume gain all the way through to almost 2 oclock.  Very quiet (minimum him or noise).  I'm just loving this sweet amp Taylor.  Thanks a million and please let me know how I can buy a few more of these since your website seems to be down.  Also wanted to let you know that I am making a name plate for the head and speaker cabs that have my last name, but under that I'm giving you props and adding "Taylor's Tiny Giant".  Your work deserves at least that, for sure.

[bluesman69]

Thought I'd add a few pics of my build.  The head cab needs to have all edges routed and sanded, screw hoes filled and sanded and stain/ sealant applied.  Then I will finish the homemade speaker cabs to match.  If I can get a few more of these kits ordered I plan to do it all up with tolex for the whole shebang. ...hmm can't seem to add images using my smart phone.  Images will be added as soon as I can figure this out.  Sorry lads.

[Taylor]

Cool, thanks for the props and the first aid kit enclosure sounds really cool. Glad you're enjoying the amp! A simple website for uploading images is imgur.com.

Right now the MusicPCB site is down while I switch to new domain name servers and a new platform. The site will be all new so anybody who previously had issues getting onto the site should have no more issues. It may take another day or two before everything's setup.

[bluesman69]

Thanks Taylor, you deserve all the props anyone here can give for sharing this with us.  This is the first amplifier I have built.  Granted, it's not "from scratch" but it's as close as a newb like me can get on a first build without feeling way out of their depth.  Anyway, thank for the info on your website.  Can't wait!  I'm still having trouble posting pics.  When I kit the "post picture" icon, it only adds the img/img text in my text box, can't seem to get it to do anything else.  By the way Taylor, any plans for another tiny giant style amp with a bit more power?  I was wondering if two of these in a kind of AC/DC or push pull (wrong term) could be chained together to create an amp with around 35-40 watts at 4 ohms?  Anyway, I was planning on originally building this with some kind of preamp in front, but after building it stock, I really love the tonal qualities of this amp clean, as well as the fact that with my boss GE7 eq and Ibanez tube screamer in front for just a little bit of warm breakup, it is sweet, sweet, sweet!

[Taylor]

This forum doesn't allow you to upload attachments directly, so you need to upload it to another website like imgur.com, then once it's uploaded, there will be some code on the Imgur site that you can copy and paste into this forum using the [img] tags.

The amp chip used in the TG is a "bridge-tied load" configuration, which means it's actually two channels bridged already. For this reason you can't bridge two TGs to get more power, and because loudness is on an exponential curve, doubling the power actually only gives 3dB more volume, which is a barely noticeable difference. You need 10 times as much power to double loudness, and at that power the build is necessarily much more expensive, difficult, big, dangerous. So the TG exists kind of in a sweet spot. If I needed 200+ watts I would definitely purchase a commercial amp rather than try to build it - companies like QSC are really good at what they do and I couldn't build a better amp for the same price.

[bluesman69]

Thanks Taylor, that's good to know.  If need, I can just mic this sweet little baby up.  When I get off work, I'll try to get images up.  One other thing I wanted to try to do on top of the power on/ off switch I added, was to add a led on/ off light.  I tried with a 12v led light from radio shack.  The light came on nice and bright as I had hoped, but for some reason I could not get any sound signal through.  I wired it up with the power switch to go directly between the power in and the board.  When I disconnected the led light and tied the power on/ off spst switch back direct, it works just fine.  What gives?  I'm wondering if the 12v led light is chocking the rest of the amp.  Should I use a larger v led light?

[bluesman69]

pics of my head cab, not completed, just fit together for testing out!  I will be completing it with stain/ finish and building 2 112 cabinets to be wired in par.  Hopefully I can find some good realistic basketweave or similar for the grill clothe

[Taylor]

Cool, it looks good!

[fatecasino]

hi all,
I just received the replacement parts (pcb, tda chip, etc) and:
1)getting back to the power adapter problem, I fixed it with a help of a friend,
it was the LM7818, which on switching back on the amp, it couldn't actually stabilize the voltage and it was giving 4volts instead of 18V.
I added 470 uF in parallel at the output and it works fine now!

2) adding extension wires to the TDA chip does not generate any annoying noise

3) All works fine now, EXCEPT (as usual), after the increasing the volume to 70% I get some ugly bass fuzz/synth noise. I changed a couple of caps, but with no results. Any ideas on that?

[PRR]

Many builds of this work fine without the 470uFd.

I wonder if your 16V power supply is weak?

If it is barely weak, for a bridge-mode power amp like this I would be thinking a BIG cap, 2,000uFd to 5,000uFd. But that is a band-aid for power supply wobble.

[fatecasino]

ok, I think everybody here has paid intention to what is called...Murphy's law
Which part burns first if the two wires of the speaker output created a short circuit?
I suppose the tda...do you know any reliable store in the internet to get some of them?

[Taylor]

According to the datasheet of the TDA2740, it's protected against output shorts across the speaker or if one or both speaker connections shorts to ground. In these cases it will shut down until the short is fixed but should not be permanently damaged.

[PRR]

What Taylor said. This is a CAR audio chip. Car speaker wires sneak under carpet, through door hinges, and over sharp edges inside the body. And in my Honda, if I put a metal case in the trunk, it hits the naked speaker terminals.

Shorts happen. A lot. Far too often to be replacing a chip inside the radio every time.

Car-sound chips "must" self-protect against shorts; either to-ground or to the other live wire. It isn't a very complicated problem. It's more parts, but once the chip-designer is done, they can make millions of chips that don't fail in every-day car wiring mistakes and accidents.

If you shorted and it is NOT working, you have an odd problem. Look for solder joint that did not hold-up under the momentary strain. Then use general debugging process; link in one of the top topics of this forum.