Building the Tiny Giant amp

[MDK002]

ok... I separated the input and speaker wires from each other....just moved them around inside the chassis.   problem is still there.   sounds like a heartbeat almost.
when the volume is increased, it clips on each "heartbeat" and also when a note is played with any force.
I only had the amp on for about 10 or 15 seconds total...the problem started as soon as I turned on the amp.
would shortening the input and out put wires make any difference?   There is some extra length there that is not needed.  Also,  I can't figure out why the standby switch has no effect.
I'm going to work on getting the heat sink issue fixed.   
Any other ideas?

[Jdansti]

I wouldn't short the output. Even if it were safe to do so, it's not a good diagnostic technique because you would expect your speakers to be silent if you did this.

The next step that I would do is build a simple audio probe and follow the signal starting at the TGA input. See: http://www.diystompboxes.com/pedals/debug.html The only deviation from the instructions would be to stop probing after you check the input of the TDA7240. No need to probe the output of the chip and it could potentially damage whatever you have the audio probe connected to.

[Jdansti]

One other thought. You might have already said, but have you checked that the speaker works with a trusted amp?

[MDK002]

I have checked the speakers....I've used 2 different cabinets that work great with my other amps.
I'm going to put together an audio probe and start looking for the problem.    I'll take the time to clean up the wiring to make it fit the chassis better.
Might be a week or so but I'll post my findings as soon as I can.  Lot's of other projects on my honey-do list. 

[Jdansti]

Lot's of other projects on my honey-do list. 

I know the feeling!

[Taylor]

John, thanks so much for helping folks debug in this thread. Most of the time you've helped somebody before I even see their question.

[Jdansti]

I enjoy solving mysteries (or at least trying to)!

I remember what the owner of a hobby shop told me when I bought my first RC airplane kit. He said to make sure I get help from him or someone knowledgable, because if the plane doesn't fly, or if I crash it on the first flight, I'll be less likely to continue the hobby.

[jakobmagnusson]

Hi,
Trying to finish off my, Tiny Giant Combo..

Question: I will add the line describe mod as described here http://i.imgur.com/Uill1.gif

Is it really correct to add a 10k resistor in series after the 10k volume pot? Wouldn't it decrease the signal very much?

Or did I get something wrong?

Edit: I put it together now and it works ok, both the guitar and line in amplification..

Regards,
Jakob

[Rock_on]

Hey guys it's me again

I dont know if i asked this one before but

What if i have a preamp already (jokerx's blackforest, or jcm2000).... Do i need to remove the stock? Or stack it?? I mean just put my preamp in my pedal board..

[MDK002]

I wouldn't short the output. Even if it were safe to do so, it's not a good diagnostic technique because you would expect your speakers to be silent if you did this.

The next step that I would do is build a simple audio probe and follow the signal starting at the TGA input. See: http://www.diystompboxes.com/pedals/debug.html The only deviation from the instructions would be to stop probing after you check the input of the TDA7240. No need to probe the output of the chip and it could potentially damage whatever you have the audio probe connected to.

Alright, I've got good news. After probing the circuit I found that the TDA7240 was the problem.  I have replaced it and the amp is now functioning properly.   And it's mighty loud for it's size.

Paul, I took your advice and removed the puny little heat sinks and dug up a very chunky piece of aluminum from my pile of stuff I've collected over the years.   I've got it bent into shape and will have it attached to the chips as soon as my little bushings get here from China.   I'll post some photos once I have it together.  
I'm building a cabinet for it to match my Marshall 4x12.  

John and Paul, thanks for your help...and everyone else that posts on here to help us beginners out.   You guys make this enjoyable.

[Taylor]

Hey guys it's me again

I dont know if i asked this one before but

What if i have a preamp already (jokerx's blackforest, or jcm2000).... Do i need to remove the stock? Or stack it?? I mean just put my preamp in my pedal board..

You can leave the stock preamp; it's totally clean so there should be no issue stacking them. Just watch the levels going into the TG preamp as it's not the most thrilling sound when the opamp is overdriven.

[jogina111]

I prefer removing the stock preamp and rebuilding the poweramp from the  7240 datasheet...  I have made an amp using a wampler plexidrive to the tda 7240 and  I'm keeping it to myself. Love how it sounds...

[jakobmagnusson]

Hi,
Finally ready with my Tiny Giant Combo. Some pictures and spec:
Tiny giant - standard PCB etc
Power feeding: HP laptop charger, 18V / 3.5 A

Speaker element: Faital Pro 4Fe35
Nominal Impedance: 8 Ohm
AES Power Handling: 30 W
Maximum Power Handling: 60 W
Sensitivity (1W/1m): 91 dB
Frequency Range: 90-20000 Hz

Speaker cabinet:
Birch plywood 14 mm
Outer size:
Height: 220 mm
Width: 120 mm
Depth: 95 mm
Volume 1,77 litres
Bass port: diameter 24 mm, length: 42 mm

Additional features:
- 9 V output (for pedals etc)
- Line in

[jakobmagnusson]

Hi again,
My Tiny Giant Combo sounds quite good, but it has some distortion. Not so much at lower levels byt when volume is at 11-12 o clock, its quite bad. Especially since I'm after a clean tone. When I play through a larger cabinet (10" Eminence speaker), it's mucher better.

How come the sound gets distorted with the small speaker (the 4", as describer in earlier post..)

Here are som sound clips at different volume levels. (The is recording as such is not generating any clipping)

I used a Les Paul, neck pickup, full volume.

Youtube clip: http://youtu.be/Q3Ux4wj8sHE

Comments and advice welcome.

[Taylor]

The sensitivity of your 4" speaker is a lot lower and therefore it doesn't get as loud at the same low settings on the knob. It's true that this amp will distort at higher volumes. To get more clean headroom a higher-sensitivity speaker is needed.

There is a loose rule in speaker design that you can have two of the following, but not all three: low (frequency response), loud, and small.

[jakobmagnusson]

Hi Taylor,
I think I see what you mean. So to improve this set up I either need

1) a speaker with higher sensitivity. But I think it's difficult to find a 4" with at least some response below 100Hz with higher sensitivity than 91 dB(?)
2) Use a more powerful amplifier. But then it would be a more complex design I suppose, with large transformer etc. Or is there any similar (=simple) amplifier to Tiny Giant with say 60-80 watt?

Regards,
Jakob

[jakobmagnusson]

The sensitivity of your 4" speaker is a lot lower and therefore it doesn't get as loud at the same low settings on the knob. It's true that this amp will distort at higher volumes. To get more clean headroom a higher-sensitivity speaker is needed.

There is a loose rule in speaker design that you can have two of the following, but not all three: low (frequency response), loud, and small.

Having thought a little bit more.. It seems like the amplifier distorts more at say 11oclock with the small speaker compared to the larger one. (irrespective of the dB output from the speaker). Does it make sense? If so, why?

Regards,
Jakob

[Valoosj]

There is a loose rule in women that you can have two of the following, but not all three: ...

Fixed it for you 



(And fill in the dots for yourself. We all know how it goes)

[Jdansti]

There is a rule in loose women that you can have two of the following, but not all three: ...

Fixed it for you 

[PRR]

> to improve this set up I either need

A 4-inch just can't make room-filling power.

I have a 4-inch speakered amp but it is only 1 Watt and was probably $12.95 when new.

The TG is *not* a "tiny amplifier". It makes 10 or 20 Watts. Much more than a Champ, more than a Princeton or DeLuxe. Not a whole lot less than amplifiers sold with two-10 even two-12 speaker systems. (I had an 18W with four 10s, lovely amp.)

10-20 Watts is a LOT for just 3 inches of air-paddle with any bass.

While the speaker specs may say "30 Watts!", that's a melt-down rating. The coil won't burn from electrical heat, even though the cone is slapping like mad. The "60W" rating is more to the point: it is comfortable *in hi-fi use* with a 60W amp NOT clipping, implying more like 6 Watts average.

It helps to get in a *small* room. Like a car. Even then, 4-inch car-speakers usually distort when fed the full 16W-20W that most car-audio amps give. I have 5-inch in front, 6x9 in rear, of a small sedan, and the speakers "sound stressed" somewhat before the amp does.

OTOH, you can use a proper size speaker which will move a proper amount of air.

Look at commercial amps. The small Champ is still a 6-inch (and only 5 Watts). 8-inchers are popular for low-price amps in the 10W range.

Eminence 820H or Jensen MOD8-20 or Jensen C8R would be sweet good-size cones. The MOD is also low-price. A 12"x20" sheet of plywood with 1x4 sides is good baffling for Eights in guitar-duty.