Building the Tiny Giant amp

[PRR]

Those are wonderful speakers, but one or even two will NOT take the full output of a 20 Watt amplifer doing overdriven guitar.

Two in *series* makes about 12 ohms and with this amp will absorb 5 Watts total, 2.5 Watts each. A good rating for these speakers on _RAW_ (overdriven) audio is 3W each, so 2.5W each 5W total is just about spot-on.

Two dinky speakers is not going to give the chest-pounding Authority that a proper Guitar Twelve will. The pair has about 1/10th of the air-pushing area of a Twelve. Like paddling a canoe with a large salad-spoon. It will go. It may go good enough for canoeing a swimming-pool or playing a workbench. But a Twelve (or similar) will give a lot better grip on thin air, and a much bigger sound.

[jakobmagnusson]

When you say increase the volume, where on the dial do you have it when it starts distorting? What kind of instrument and effect chain are you using?

Hi,
Did some more testing, separating the TG from the combo. It drives my 10" well and loud, the distortion is gone. In my "combo" I have a 3,5" speaker (a quality Peerless speaker with high wattage etc, 8 ohm) in a 2 litre cabinet. Either the cabinet which is not 100% finished yet caused some distortion/noise or the that the TG was inside the cabinet without proper shielding... I'll rethink and put the the TG in a separate box...

=> Where do I buy a suitable metal box? Like the one in very first post in this thread?

There is still some small noise/hum which increases when I turn the volume up. Maybe a shielded box will help? Or can it be my HP laptop power unit?

Regards,
Jakob

[psychedelicfish]

"=> Where do I buy a suitable metal box? Like the one in very first post in this thread?

There is still some small noise/hum which increases when I turn the volume up. Maybe a shielded box will help? Or can it be my HP laptop power unit?"

https://www.smallbearelec.com/home.html is a good place to buy most guitar related electronics, and they sell boxes just like the one in the first post, in different colours too. I suggest you also buy some other components for any other projects you have going, to save on shipping (the prices are comparatively low for most components at small bear)
As for hum, it wont be the power supply for the TG, because it uses a voltage regulator, which gets rid of nearly all power supply ripple. It might be power supply ripple from something else you have between your guitar and the TG, but it's probably hum from your leads, your guitar and the TG not being shielded.
I hope that helps

[jakobmagnusson]

Hi,
Thanks psychedelicfish for answer, it helps. I found a case locally here in Sweden, not as neat, but with some extra space for 9V regulator etc.
Let's see if the hum disappears when I get the TG boxed.
Thanks,
Jakob

[gcme93]

I'm a novice jumping into this one a little bit, my electronics has only been going about a year:


FIRST - 20W output means roughly 30W input for a solid state amp like this?

SO - Running off 18V, the amp would draw about 1.7A?

THEREFORE - if I wanted this to be a portable amp, I'd be looking to have two lithium 9V batteries in series, but lasting less than an hour, (Lithium 9V ~1200mAh)

Are my rough calculations about right on this, and if so, what other battery/cell solutions could I use?


I know i'm being ambitious with a wireless Tiny Giant, but I'd like something a bit more than a 'noisy cricket'. Is there an intermediate stage, perhaps 8W to 15W?

[Pyr0]

I know i'm being ambitious with a wireless Tiny Giant, but I'd like something a bit more than a 'noisy cricket'. Is there an intermediate stage, perhaps 8W to 15W?

I've built this one for use with a 12v sealed lead acid battery, great for busking.

http://xtronic.org/circuit/amplifier/audio-amplifier-potency-circuit-tda2030/

It's around 12 Watts into 4 ohms, or 8 watts into 8 ohms speaker.
It uses a TDA2030, which was designed for car radios, so works great from 12v. It's just a power amp, so you will need to add a preamp to it.
I actually used a Colorsound Overdriver pedal as the preamp, so I can use it clean or add some overdrive/distortion. And it all fitted quite nicely into an old Squire 10w amp that I gutted. I'm running it with the original 8 ohm speaker from the Squire, and it sounds good, if I can find a nice 6" 4 ohm speaker I'll upgrade to that for more oomph.

[PRR]

> Are my rough calculations about right

Yes.

But... the chip is really made for 12V (car) battery. The 17V was just a handy (cheap) plug-in supply, which has to be dropped for the chip. That's a waste. You want a 12V battery.

As Alan says, there are many good choices around 12V 2AH. Fire alarms and exit lights often use such a size so they are available at home-stores. The smallest motorcycle or lawn-tractor battery may busk all day, though the cheapest types are prone to spill acid.

[gcme93]

Thanks a lot Alan and PRR!

One last thing, am I now okay to leave out the LM338T altogether now? I understand exactly what you mean about the excess voltage being a waste! The rest of the schematic only runs off 12V! I was planning to create my own vero layout, so I'll just have the 12V hooked straight up as written in the schematic.

Again, sorry for the ignorance on my part, but do I need any protection on this V+ line to stop chips frazzling? I was thinking that a battery doesn't have the same potential for power surges like a wall supply, but I can never work out on my own where the random RC filters and things are needed...

Then again, I may also add in a power supply option as I have some 12V/13.5V plugs around (yes I'll check they'll supply enough current!), so if I do, I'll just add in the regulator as on the schematic


Thanks again for the help,

George

[garcho]

Something I'd like to try but haven't got around to, is using a cordless drill battery. Rechargeable, small, cheap enough to buy two and always have one going. I'm probably missing something obviously wrong with that set up, but might be worth noodling around with.

[Pyr0]

The problem with most cordless drill batteries is that they are designed to connect to the cordless drill, and don't have an easy way to hook up wires to connect it to something like an amp. Whereas a 12v Sealed Lead Acid battery normally comes with lugs so a standard connector can be used to make a cable to power your amp. They are also available in a range of amp/hour ratings.

[garcho]

12v Sealed Lead Acid battery

are they rechargeable?

[Jdansti]

Yes. That's what you normally get in an uninterruptable power supply (UPS/battery backup).

[waltk]

The problem with most cordless drill batteries is that they are designed to connect to the cordless drill, and don't have an easy way to hook up wires to connect it to something like an amp.

I like Lithium power tool batteries.  They are light-weight, and have high energy density (lots of power for the size).  You might be able to build a connector for one by scavenging it from a dead tool or charger, but I just do this - a couple small pieces of PCB cut to the size of the contacts with wire soldered on - an o-ring or two (like a rubber band) to hold them in place - and a couple small pieces of wood glued on so the o-rings can exert some pressure.  Works very well.

[Pyr0]

Good idea Walt. that would also give you a much higher range of voltages to use, could build a nice powerful battery amp with an 18 or 24 volt one.

[PRR]

> are they rechargeable?

Lead-Acid is the ordinary car battery. Play the radio until the battery is flat, get a jump and run the engine a while, the battery is full again. Without an engine you can use a battery charger from a wall-outlet.

Yes, it is nasty technology. The acid will rot your shirt and your skin. (In a dead-short, a car battery can boil your face off.) When the lead cruds-up and we throw it in the woods it poisons the earth.

But it is also reasonably good energy density, and fairly inexpensive for the energy.

And there are versions which do not leak acid. An EXIT sign or underdesk UPS should not be dripping scuzz, those cells are totally sealed. We have a car with battery in the trunk, sealed so it won't soil the luggage. Motorcycles used to use a vented battery where outgassing was less likely and if it happened it all came out a tube you could aim away from the frame or your leg. Lawn-tractor batts are this type.

Ni-Cads served us well for 70 years but are going out of style in a hurry.

> I like Lithium power tool batteries.

Yes, now that production is mass and prices have come down, I use Lithium more and more. I do wonder about the long-term effect of concentrated Lithium trash on the earth (we have not yet trashed as much Lithium as Lead). I do worry that the rush to high energy at low prices encourages marginal construction (cell-phones burning backpacks, etc). I'm actually still using Ni-Cad tools but it is clear the tool makers are discontinuing that and moving us to Li-Ion.

[gcme93]

I'm looking at something like this:

http://gb.dinodirect.com/rechargeable-lithium-battery-12v-4800ma-cctv-camera-d-12480.html?vn=RGlub2RpcmVjdEZ1Y2s&AFFID=33

Seems to fit the bill? and a normal size, connector, even includes a charger!


Final question is this:

Do I need any capacitors or anything to protect my circuit from current surges, too high a voltage from battery etc? I'm planning on using a simple diode setup to protect against connecting the battery the wrong way around.

Sorry if this is a beginners question, but I would definitely count myself as a beginner - only one pedal and a small radio to my name


Thanks for all the information on this topic!

G

[antigluten]

Hello everyone: First time poster - long time lurker

I purchased this kit with the components about a week ago now. Soldered the board no problem (really nice PCB!) have how I have only had marginal success getting it to work properly. I've read through the posts here and done as many tests/fixes as are recommended now but I guess it's time to bite the bullet and ask for help.

SYMPTOMS: When I first fired it up, it sounded fine except it would cut out slightly when the guitar's volume was down almost like it had a noise gate. a little crunchy when cranked which was cool but I had wired the pot backwards too so I opened it up. Resoldered the pot the correct way and put it back together. The same 'noise gate' type effect was significantly more pronounced as well as some very nasty clipping. I double checked for grounding between the case and the LM338 and confirmed there was no issue there (also no issues grounding on the speaker jack.

It worth noting that both of the SPST switches ive tried have done absolutely nothing. Not sure why... maybe this is a clue to my problem? I've also tried it with nothing in the bypass slot with no changes to my problems.

The voltage coming out of the hole following the "MUSICPCB.com" print measures 15.5v

Thank you all for looking at this

[waltk]

Welcome!  You came to the right place for help.  We're gonna need a little more information to help you figure out what's going on.

Can you measure the voltages on the opamp pins?
Can you post some good pictures (top and bottom of the PCB and how it's connected in the box)?

-Walt

[antigluten]

Firstly, here are pics - my wires are a bit long still - once i get it working I'm gonna tighten them up a bit.

Back of the PCB


The Enclosure (the two white wires lead of to the SPST)


So, I'm assuming the opamp is the 8 pin chip that plugs into the 'holster'? Thanks, Walt

[antigluten]

Ok, so I measured both. The TDA is the opamp and the TL is the regulator?

TDA7420A shows all 0v except for pin 2 (2 pins from the big capacitor) with read 15.6v

The TL072 reads (not sure how the pins are numbered so this is the side facing the voltage in/load out):

pin1: 7.7v
pin2: 7.7v
pin3: 7.3v
pin4: 0.0v

other side (side facing capacitors):
pin5: 15.6v
pin6: 7.7v
pin7: 7.7v
pin8: 7.3v