Bought a couple of these little amp kits. I soldered one and it works good with a electret microphone. I 'm now trying to breadboard the second kit to make it more suitable for piezo disc pickup. My plan is to get the stock kit amp up and running on a breadboard, then experiment with various buffer circuits. Sounded easy, but for the life of me I can't get it up and running. Obviously fundamentally wrong with my interpretation of the schematic???
included a couple of pics..hopefully someone more experienced can spot what I am doing wrong. Disconnected the battery terminals to take pic (in case anyone spots that ??? I'm stumped.

heres the data sheet http://www.st.com/web/en/resource/technical/document/datasheet/CD00000118.pdf. kit looks pretty close to figure 2.
I swapped out the chip to rule that out, also done a continuity test on breadboard..it seems OK. Anyone got a suggestion.If someone could explain how I could test the amp with my dmm, and do continuity through the circuit. that would be appreciated too. For now I'll treat it as a good learning exercise.
cheers
Steve

 

Steve
What are the symptoms? Do you hear anything from the speaker??

 

hi,
Check pin #6, I do not see a +V power link, also pin #2 appears incorrect.
Its hard to tell from your rainbow choice of wire colours.
E

 

No real output from speakers. not even a crackle unless I play around with caps. Pin 2 in 33 ohm resitor and 100uf electrolytic going to ground. hidden behind the red lead.

 

ericGibbs....YES I had hooked power to pin 7..my eyes are shot: now when I hook up I get wild screaming feedback from my piezo pickup and speakers attached. Not controllable with the volume pot???

 

Update: piezo pickup doesn't have to attached...just acting like a tone generator..high pitched frequency continuously howling.

 

Hi,
I still do not see a wire in pin #6 on the amp, unless its hidden behind something else.??

EDIT:
You posted at the same time , so ignore this!

 

limited to just a couple of actual breadboard leads..the wild colours are actually paperclips. I don't have access to any electronics stores.
I measured the resistance on the paperclips and they were .9ohm...oddly enough i had some 0 ohm resistors and they have slightly higher resist than the clips..so I figured they would be ok to use here..a bit tight but they fit ok.

 

yep you right..there was no power on pin 6..I have attached and now getting a howling high pitched tone

 

It is possible by connecting +V to pin #7 has blown the TBA, try another IC.

EDIT:
I am still not convinced that pin #2 R1 and C2 are connected correctly.??

 

Heres a better pic. I have jumpered pin 1 to 5 instead of straddling over the chip with C3..

Swapped out a new chip. Back to being dead? Hmmm...the wild oscillationing noise..would that have come from a damaged chip?

 

Hi.
That R1 is short circuited by the board sockets.

 

Heres a better pic. I have jumpered pin 1 to 5 instead of straddling over the chip with C3..

Swapped out a new chip. Back to being dead? Hmmm...the wild oscillationing noise..would that have come from a damaged chip?

Hi.
That R1 is short circuited by the board sockets.
View attachment 92227

what do you mean ericgibbs?? Pin 2 shows a R1 followed by C2.. Do you mean i have laid it out wrong, or is their something wrong with the BB?.

 

R1 is not touching the pin 2. Still dead..rejiggled every component. This is my second attempt. Tried on a cheap breadboard, same result..thought the breadboard was faulty. Kinda giving up hope. Might be beyond my capabilities? Got no more chips ( just the 3) to try. Is there a way to check its functionality using my dmm. What info on the spec sheet should i look for?

 

Do you mean i have laid it out wrong

As Eric pointed out. Both legs of R1 are in row 6 of the board. All the sockets in a given row are connected together internally, so R1 is shorted. Likewise the small cap in row 5 is shorted.

 

Obviously fundamentally wrong with my interpretation of the schematic???

Double check your wiring - it is wrong.

 

OK the penny has dropped, finally figured out what you meant by "short-circuited by the board sockets" ...duh . That fixed it!!!! Amazing what a good nights sleep will do...Also the cap on row 20 was a short. Wow I really learnt something about the fundamentals of breadboarding... Thanks very much to all who replied, especially ericgibbs. No doubt I will have some more questions when I tackle the second part of my project..making the amp more suitable for capturing more bass frequencies of my ukulele via the piezo pickup. Its quite a tinny high-end sound and if I lay into the strings, quite a bit of distortion. Will now play with some buffers. If anyone has some suggestions on that subject..much appreciated.
cheers

 

Ok I have tacked this onto the breadboard, not getting great results...crazy distortions when turning the volume pot on the amp, there is a signal coming through on lower volume but slightly fuzzy. Can someone suggest a way to connect the output of the Tl072 R4 (220ohm)>10uf - - into the 1uf of the Tba 820m amp???

 

hi,
I would try a 'volume/gain' pot from the TL072 to the TBA amp, say a 25K pot.
One end of the pot to the 10uF and the other end to 0V, with the pot wiper to the TBA input cap.
E

 

Ok that sounds good. I don't have any 25k pots on had. Would a 10k pot work??? What would happen if a connected 2 x 10k pots in series?? Would that that get it close enough....would it even work..which one would you adjust??? Thanks very much.. When I get this working, will record and post a sample.
cheers