Building the Tiny Giant amp

[waltk]

The TL072 is the opamp.  The TDA7240 is the amplifier chip.  The LM338 is the voltage regulator.

The dot on the opamp is on the top-left, and the top-left pin is pin 1.  The pins are numbered from 1 to 8 down the left side and up the other side, so the pin numbers you gave for 5-8 are reversed.

You substituted a 1500-ohm resistor for the 1k resistor, so the voltage regulator is trying to put out 16.88V.  To get that much voltage out, the power supply must be about 1.25V higher than the output voltage you are trying to get.  It looks like your opamp is getting 15.6V, so that means your power supply must be putting out about 16.8V.  That's not likely to be a problem.

Your opamp is biased at about half the supply, so that looks good - and the other voltages on it look about right.

Your pot is wired correctly.

I don't see anything obviously wrong in the photos, but it's a little hard to make out the details on the solder-side shot, and to see where everything is connected.

It's kind of fishy that the switch connected to the white wires doesn't mute the amp.  With no power applied, can you verify that one of the white wires is connected to ground, and the other is connected to pin 2 on the TDA7240?

-Walt

[antigluten]

You substituted a 1500-ohm resistor for the 1k resistor, so the voltage regulator is trying to put out 16.88V.  To get that much voltage out, the power supply must be about 1.25V higher than the output voltage you are trying to get.  It looks like your opamp is getting 15.6V, so that means your power supply must be putting out about 16.8V.  That's not likely to be a problem.

My power supply is rated at 16v 4.5a so I guess this may be an issue. My desire for gain gets the better of me sometimes I'll swap this with a 1k resistor when I get home today and see what changes.

As far as the SPST goes, I can confirm continuity with both the ground and pin 2.

[jogina111]

the circuit is designed to work perfectly on 12v , 11.6v to be precise. Subtituting the values of the resistors on the regulator section will change the voltage  and may damage both power and preamp sections of the amp.

[waltk]

My power supply is rated at 16v 4.5a so I guess this may be an issue. My desire for gain gets the better of me sometimes  I'll swap this with a 1k resistor when I get home today and see what changes.

You can try that.  It definitely won't hurt.

As far as the SPST goes, I can confirm continuity with both the ground and pin 2.

Hmmm. That's puzzling.  If pin 2 is grounded, the chip should be in standby - and no sound should be coming out.  If it's true that the switch has no effect, and you still get sound output, then I would think that there's an open circuit somewhere between pin 2 and ground.  When you checked continuity, were you testing pin 2 from the top side of the board?  The reason I ask is that if you have a cold solder joint, it might not be making contact with the pin (and if you have one cold solder joint, you might have others.) ...or maybe the switch itself is bad.

Your original description of symptoms (noise gating/nasty clipping) makes me wonder about the preamp section.  Did you ever put the opamp in the socket backwards and apply power?  Do you have another opamp that you can try in place of the original one?  Did you ever try running it outside of the box?

[meffcio]

1. I have a 8Ω/15W practice cabinet. In a normal situation the Tiny Giant outputs 12W at 8Ω. Is it maximally safe then, or shall I lower the supply voltage a little, to gain something like 10W at 8Ω output? I'm asking because of component's tolerance. You know, the 120R and 1k resistors that control the supply voltage can differ from the desired values, making the voltage higher, etc.

2. It's said that TG needs a 4A or more PSU. Isn't it like ~2 times the real value? I was once playing with a 2xTDA2003 kit, and it was supposed to draw as much as 2,5A.

3. If I have a decent 12V regulated supply I can omit the LM338 part, right? But what is better? Additional security(?) of double regulation, or just getting rid of another heat generator? Also, wouldn't powering the amp from 12V (not the usual 11.6V) raise output power too much for my cabinet?

4. I was thinking of packing the TG in an enclosure along with some sort of preamp, but I might as well stick to using stompboxes. However, I've heard people complaining about the flat response, or the TG not being guitar amp-like. Would adding the classic tone stack as once suggested by PRR deal with that issue?

Thanks in advance.

[PRR]

If the "15W" rating is for Guitar Amp Use, you are fine. Guitar speaker makers have learned to build strong and rate low, or else guitarists kill them too often.

5% resistor tolerance or 11.6V:12V difference is not a big deal.

You can't "double regulate" 12V then 11.6V because the on-board regulator needs a volt or two of excess to do its regulation duty.

If you are still very concerned about speaker blow-up (or it is just a bit too loud?), put a 4 ohm 10W resistor in one of the lines from PCB to speaker jack. This will cut power to around half, and also lighten-up the speaker damping giving a more lively sound from the speaker (more bottom thump, more scream).

Yes, the 4A spec for power is very generous. That comes from Tayor finding Laptop PC power supplies at VERY low prices, and these are usually 4A or more. I doubt it really eats 2A, but the extra does not hurt.

[meffcio]

If the "15W" rating is for Guitar Amp Use, you are fine. Guitar speaker makers have learned to build strong and rate low, or else guitarists kill them too often.

The speaker is Celestion Super 8, so it speaks for itself.

You can't "double regulate" 12V then 11.6V because the on-board regulator needs a volt or two of excess to do its regulation duty.

Ugh, of course, I just forgot about that. So let's put it like that - is it better to buy bigger voltage PSU and use the onboard LM338, or is the regulation in those chinese power supplies good enough for TG thus allowing to omit that specific part in TG, so less heat is generated during operation? Price is the same for 12V and other voltages PSUs, but most likely I'd find some kind of laptop PSU at my house.

If you are still very concerned about speaker blow-up (or it is just a bit too loud?), put a 4 ohm 10W resistor in one of the lines from PCB to speaker jack. This will cut power to around half, and also lighten-up the speaker damping giving a more lively sound from the speaker (more bottom thump, more scream).

Good to know. Will consider doing.

Yes, the 4A spec for power is very generous. That comes from Tayor finding Laptop PC power supplies at VERY low prices, and these are usually 4A or more. I doubt it really eats 2A, but the extra does not hurt.

Just as i thought. As I said, most likely I already have that kind of PSU. Asked just from curiosity.

Anyway, I'm still concerned about the tone stack that you mentioned earlier in the thread.
http://www.diystompboxes.com/smfforum/index.php?topic=89687.msg768743#msg768743
Will it make TG sound more like a guitar amplifier? I'm pretty sure it will, but what's your opinion?

[EDIT]
Here's something that I think would make a better use of the dual opamp in TG.
http://deanmarkley.com/Info/LegacyAmps/Schematics/D1508.pdf
I have heard it sounds good, so I want to try it. It's also paired with a chip power amp, so if I wanted to use it permanently, shall I omit the buffer/preamp part of TG, and connect it directly to 1uF cap just before the TDA's input?
As you can also see it's meant to be powered by dual rail supply. How to deal with this? There's a kind of DC version of this combo (http://deanmarkley.com/Info/LegacyAmps/Schematics/D1536.pdf), but it uses a sh*tload of additional components, and I prefer the simple ideas.. Would the old resistor trick be any good for this?

[Supakas]

Hei,
i finally got my kit, and this little amp is amazing.
i made a rehersal with that, and it sounded quite good with my mxr stomps.
Heres my build, not ready jet.

[Taylor]

Whoa! I love the look of that, seriously. Really cool.

[Supakas]

Still one question.
if i use this heat sink.
Should i use vent? or isit okei.

[PRR]

> Should i use vent?

Play hard. Put your finger on the heat-sink.

If you can hold it as long as you like, it is fine.

Looking at that one, I think it is entirely fine if you mount it upright, so both sides have a free flow of air.

[ajb]

This was a great build.
The PCB was excellent and great to work with.

The local Radio Shack had a 10K audio pot with a switch.  This seems to work great.
The Pilot Light was also from there and it would handle the voltage range from stock to enhanced.

I put in a toggle switch to flip between the 1k and 1.5k resistor for a "boost" feature.
future builds will keep the 1K and simply mount the Input Jack on the front of the case.

[Supakas]

Here is my new build, its a birthday persent.

[Skruffyhound]

Beautiful box!

[Skruffyhound]

I'm looking to make a pretty small amp with a few simple effects in for acoustic guitar. Actually I will make two of them eventually. I'm hoping to encourage two different girls one in England and one in Denmark to invest more time in their guitar
playing, they both have excellent voices but could play better.

I found this today:

Speaker                      Dual cone type
                                 Woofer 13 cm, polypropylene cone type
Max input power         120 W
Rated input power      30W
Impedance                4 ohms
Sensitivity                  90dB/W/m
Frequency response   40-22,000Hz
Mass                        Approx. 590 g per speaker.

I know nothing about speakers, would this be useful in this context? It is a car speaker with a plastic cone which sounds dubious, but it looks cool and what do I know?

[gcme93]

I'm not a speaker expert, but the specs definitely match up to what you need. From what I've heard (excuse the pun), you can't really tell until you hear them. If they did have too much response in certain areas, and not in others, you could always compensate with your EQ design?

It's likely that a speaker designed for Car HiFi audio is going to have a bright response throughout, not a mid focused response like guitar speakers, so you might be able to find a simple cab emulator circuit to play around with in front of it?

As I said, I think you can't really know unless you've tried them

[waltk]

Speaker                      Dual cone type
                                 Woofer 13 cm, polypropylene cone type
Max input power         120 W
Rated input power      30W
Impedance                4 ohms
Sensitivity                  90dB/W/m
Frequency response   40-22,000Hz
Mass                        Approx. 590 g per speaker.

I've tried a few car audio speakers.  They'll probably sound tinny and underpowered unless you mount them in an appropriate enclosure.  I was kind of shocked when I first figured out what a huge difference the speaker cabinet makes.  If you build/test without putting them in an enclosure, be prepared for them to sound awful (until you get them mounted).

The Tiny Giant itself has full-range response, so you might want to put a simple low-pass filter in front (or a cab sim as already mentioned).

[PRR]

> an appropriate enclosure.

A 5-inch speaker, just naked, has bass roll-off of everything below 1,300 Hz.

(Not _so_ bad on larger cones.)

It is a car door speaker. Put it in a 2-foot panel of heavy cardboard, it has bass to 250Hz. Put that panel in a door, so the back-wave hardly comes out, it has pretty-much all the bass the speaker can give.

You can also start with a 3-foot panel and bend the edges back. It becomes basically a Twin Reverb size. Makes sense when you want two 10"-12" cones. And that rig would make good sense for the Tiny Giant.

If you want a bedroom rig: multiply speaker size by 1.1. About 5.6 inches. Imagine a closed cube 5.6" inside. But when you build it, stagger the dimensions 1.2 or 1.5. Since 3.5" is a common size for window trim lumber, perhaps 3.5" * 6" * 8" inside. Don't be exact. Smaller will bump-up the midbass, which may be nice in a gut-less speaker. Bigger will slump the midbass and extend the deep bass.

> put a simple low-pass filter in front

First off: if it sounds wizzy, use a sharp razor and cut off the wizzer cone. They don't work for guitar. Not just IMHO, look at "real" guitar speakers. Even though the E-V SP-12 had a half-good whizzer, the EVM-12 derived from it does not. Wizzers are for complex mixes, FM pop-music, not simple clean tones fresh out of your hands.

The "120 Watts" is totally bogus (so are the other numbers, except size). However it is designed for 12V-14V bridge-mode car radios. The Tiny Giant is a car-sound chip working at 11.5V. An exact fit with a little slack so that crazed guitar solos won't burn the speaker any more than crazed road-trip do.

[Skruffyhound]

Thanks guys.
Paul, a closed cabinet 3.5" * 6" * 8" right, but what about the thickness/type of material.
What is optimal? I'm toying with the idea of welding a cabinet out of sheet steel.
I've made similar things before, but I'd probably need to damp the box internally I reckon.
Is it a dumb idea?

[PRR]

> What is optimal?

Whatever is laying around the shop.

For this purpose, 1/4 hardboard would be fine.

In my shop, scraps of 3/4"x3.5" trim are everywhere. I'd do four sides of that stuff, and whatever thin plywood is hanging around the shed for front/back.

> I'm toying with the idea of welding a cabinet out of sheet steel. ...Is it a dumb idea?

Yes. But don't let that stop you.

Are you clever? If you can roll the sides as one strip more/less curved, no flat areas, the ringiness of steel will be moved well above troublesome frequencies. Additionally curving the front/back might be terrific. Think of the oil-tank on a Harley motorcycle.

Just welding six flat slabs together won't suck, but some tones may be over energetic.

It all sounds like more work than whacking some wood.