9v Battery in 1w Power Amp (TDA7052) :: Voltage drop issue..

[chptunes]

Hey folks.. been striking out these past few weeks.  I'm trying to get a simple <1w Power Amp working in a 1590B enclosure.  The Ultra Class A Superdrive Power Amp did not have enough output (softer than my plucked strings, even with a cranked Fuzz).

So, I've built tca's 1w Punch amp on Perfboard.  Just a Switchcraft 12B Input Jack [with 9v battery switched by the sleeve contact] and an Insulated Output Jack for connecting an 8 Ohm speaker.  I laid out the components like tca shows them on his PCB artwork.. see page 3 here:  http://www.diale.org/pdf/punch-v1.pdf

I'm getting audio through my 12" Ceramic Weber, but it's nasty distorted and chopped off!  The problem is, my 9v battery is only sending 1.9v to Pin 1 of the TDA7052.  Disconnected, my battery measures 8.9v.. but when I connect it to the battery snap of the circuit, it measures 1.9v. ..disconnected = 8.9v and connected = 1.9v ..what type of problem could this be?  Grounding scheme?  I've verified my wiring against tca's schematic and artwork several times.


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Thanks for the help..

-Corey

[tca]

Some high resolution pics, both sides, of your build would be nice for debugging.

Cheers.

P.S.(edit)

Is it a fresh battery?

[chptunes]

Hello again tca.. I'm at work now, but I'll snap some pictures tonight.  As you and I discussed earlier, I'm wondering about the 220µf Cap.

Also, I just noticed something interesting on the Manufacturer's Data Sheet.  In the Block Diagram, they indicate Pin 3 as the "Signal Ground" and Pin 6 as the "Power Ground".  Right now, I have Pin 6 connected to Pin 3 and the other "Signal Ground" connections.  Should I move Pin 6 to the Input Jack's sleeve contact (where the battery's return voltage is connected)?


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Thanks for the help..

-Corey

[tca]

The datasheet that you show is for the TDA7052A.  Check the IC. Is it really a TDA7052 or a TDA7052A, they are different although with the same pins number. I've done this mistake before  , using a version A instead of the correct one. Use your finger as a temperature probe, if there is something wrong you will feel it

The TDA7052A does not like that 10k input resistor to ground it needs a smaller value resistor, 5k. The TDA7052 is ok with it!

Just put all ground pins together.

[R.G.]

Also, I just noticed something interesting on the Manufacturer's Data Sheet.  In the Block Diagram, they indicate Pin 3 as the "Signal Ground" and Pin 6 as the "Power Ground".  Right now, I have Pin 6 connected to Pin 3 and the other "Signal Ground" connections.  Should I move Pin 6 to the Input Jack's sleeve contact (where the battery's return voltage is connected)?

The symptoms you describe fit best with one side or the other of the speaker jack being accidentally grounded.

The first step is to check the wiring with an ohmmeter, not just visually, with especial attention to the wiring of the speaker leads.

Having all the leads marked "ground" connected seems to be OK in concept at least from the datasheet.

Switching power to a power amp by using the input jack switching trick is in general a Bad Idea. It's something you can get away with, maybe, but it is getting away with something, not doing it right. The problem is that all of the return current from both outputs to the battery has to run through the input signal ground lead and a possibly-dirty/intermittent contact on the input plug sleeve.

[chptunes]

Thanks a bunch guys.  I appreciate your quick and expert advise.  Tonight, I will change the 10k Resistor to 4.7k.. and I will carefully inspect the speaker outputs.

..ah shucks, I need a dedicated switch for interrupting the Power Supply?  Alright..    

-Corey

[Gurner]

one other thing to add to the list of 'things to do' tonight  ....if you've used an  IC holder (vs soldering the TDA7052 direct to your circuitboard) try pulling the actual IC out of circuit....then measure pin 1 again (with the battery connected)  & report back.

This is not a power/signal ground type issue (or cap issue), but a shorting type issue....either you've a solder bridge somewhere or the IC itself is stuffed or what RG said earlier.

[tca]

I bet you have the TDA7052A. Both can deliver 1W but the A version has 36dB of gain and the TDA7052 has more gain, 39dB. If you have the TDA7052A you can add a voltage divider to put pin 4 at 2V and then you can have 40dB (see fig.3 of the datasheet (http://www.nxp.com/documents/data_sheet/TDA7052A_AT.pdf).
Something like R1=24k, R2=100k, this will give 9*24/124=1.7V at pin 4. Don't forget the 5k input resistor to ground.

Cheers.

[R.G.]

Thanks a bunch guys.  I appreciate your quick and expert advise.  Tonight, I will change the 10k Resistor to 4.7k.. and I will carefully inspect the speaker outputs.

..ah shucks, I need a dedicated switch for interrupting the Power Supply?  Alright..    

No, you probably don't. See the index page at http://www.geofex.com , first entry from 12/11/2012, on using PNP transistors to switch power to FX circuits. This circuit is specifically designed to sidestep the issue I outlined. There is a little more current in the input ground line, but it's both much smaller and constant. It may take a little tweaking to get to the higher currents, but that's not really a big issue.

[chptunes]

I will change the 10k Resistor to 4.7k.. and I will carefully inspect the speaker outputs.

I did this.. but, now I get no output through the speaker.  Snap!!  I'm going backward!

one other thing to add to the list of 'things to do' tonight  ....try pulling the actual IC out of circuit....then measure pin 1 again (with the battery connected)  & report back.

This is not a power/signal ground type issue (or cap issue), but a shorting type issue....either you've a solder bridge somewhere or the IC itself is stuffed or what RG said earlier.

Did this too.. see the readings below.  Also, what do you mean by "..or the IC itself is stuffed..."?

Here are some fresh readings with a guitar lead in the Input, and an 8 Ohm speaker in the Output:

MPF102
Drain: 2.3v
Gate: 0.0v
Source: 1.5v

TDA7052A
Pin1: 1.9v
Pin2: 0.0v
Pin3: 0.0v
Pin5: 1.1v
Pin6: 0.0v
Pin8: 1.2v

Speaker Output
Tip: 1.1v
Sleeve: 1.2v

IC Socket (with IC removed)
Pin1: 7.4v

I also tried a different TDA7052A IC, but all of the measurements were basically the same as above.

Any further assistance is greatly appreciated. ..how likely is it that one of my Jacks is faulty/compromised?  My cables and speaker cabinet are known to be good.

-Corey


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[tca]

Aren't those jacks earth connected to the enclosure? (just guessing know) Remove everything out of the box and test it.

Cheers.

[chptunes]

Aren't those jacks earth connected to the enclosure? (just guessing know) Remove everything out of the box and test it.

Cheers.

The Input Jack is, yes.. it's a Switchcraft 12B.  The Output Jack is NOT.. it is a Switchcraft Insulated type (black plastic thread area).

..tonight, I can lift the jacks and circuit from the enclosure.

I've successfully built and modified a PT-80 Delay circuit, but this 7 component power amp is kicking-my-behind!

-Corey

[Gurner]

I also tried a different TDA7052A IC, but all of the measurements were basically the same as above.

You schem is for a TDA7052, but you're using a tda7052A (which has a volume control pin...pin 4)...I know from experience that a TDA7052A should have about 2.5V at the input pin (pin 2) with a 9V supply, so if your's is at 0V, then that's not good & will be a contributing factor to your problems.

In my opinion, you need to have a look for a short to ground in or around the TDA7052A pin 2 area...I think it's biasing your IC very wrong (is your IC hot to touch?). ...try taking a DC resistance from pin 2 to ground.

If there aren't any shorts to ground, then I think your TDA7052A might be Donald Ducked.

Basically, you aren't gonna progress until you get pin 2 to float in or around its normal level of about 2.5V.....while sitting at 0V it's gonna strain that IC something rotten.

[chptunes]

I also tried a different TDA7052A IC, but all of the measurements were basically the same as above.

You schem is for a TDA7052, but you're using a tda7052A (which has a volume control pin...pin 4)...I know for a fact that a TDA7052A should have about 2.5V at the input pin (pin 2) with a 9V supply, so if your's is at 0V, then that's not good & will be a contributing factor to your problems.

In my opinion, you need to have a look for a short to ground in or around the TDA7052A pin 2 area...I think it's biasing your IC very wrong (is your IC hot to touch?).

If there aren't any shorts to ground, then I think your TDA7052A might be stuffed.

Basically, you aren't gonna progress until you get pin 2 to float at its normal level of about 2.5V.....as while sitting at 0V it's gonna strain that IC something rotten.

Define "stuffed", please.

Ys, I was only able to procure a TDA7052A.. I'm just ignoring the DC Volume Pin.  Is this OK?

-Corey

[Gurner]

Define "stuffed", please.

This is probably one of those English terms that doesn't exist over the pond... "stuffed" = not working!

Ys, I was only able to procure a TDA7052A.. I'm just ignoring the DC Volume Pin.  Is this OK?

Probably. The vol control pin (pin 4) DC will likely float up...and ultimately sit at maximum gain...better to put a Pot (aka the TDA7052A datasheet) from pin 4 to ground...at least then once you do sort your problem, you'll have a degree of control over the gain (I'd imagine you'll get terrible clipping without a volume control)

[tca]

Hi Corey,
I've just breadboard the circuit. The PUNCH as is does not work with the TDA7052A. In my previous posts I said to put a 5k input resistor to ground, I said that from memory... and, sorry about my bad memory, as you confirm that does not work! But I did put my breadboard version running: remove this input resistor (you can also put a 1M resistor from pin 4 ground). And it works!

My question is: why is there a 5k input resistor to ground in the datasheet for the TDA7052A???

Hope to ear from you soon. Cheers.

[Gurner]

Hi Corey,
I've just breadboard the circuit. The PUNCH as is does not work with the TDA7052A. In my previous posts I said to put a 5k input resistor to ground, I said that from memory... and, sorry about my bad memory, as you confirm that does not work! But I did put my breadboard version running: remove this input resistor (you can also put a 1M resistor from pin 4 ground). And it works!

My question is: why is there a 5k input resistor to ground in the datasheet for the TDA7052A???

There is one, but it's on the left hand side of the input cap...





this is the problem (& like I said in my last post, pin 2 should not be at ground, the 5k resistor is pulling the pin down to ground). As you say,  remove the 5k resistor & that should stop the biasing chaos.

[chptunes]

Hi Corey,
I've just breadboard the circuit. The PUNCH as is does not work with the TDA7052A. In my previous posts I said to put a 5k input resistor to ground, I said that from memory... and, sorry about my bad memory, as you confirm that does not work! But I did put my breadboard version running: remove this input resistor (you can also put a 1M resistor from pin 4 ground). And it works!

My question is: why is there a 5k input resistor to ground in the datasheet for the TDA7052A???

Hope to ear from you soon. Cheers.

tca, YOU ROCK!!  Thank you for the big effort to help me succeed.  I will remove this input resistor, and install a 1M Resistor from Pin 4 to Ground (if needed).

And thanks for the confirmation Gurner!

After I get it working, I'll tackle the PNP Power Switching scheme that Mr. RG linked above.. versus the "ring" contact trick that I'm currently employing.

Thanks folks.

-Corey

[Gurner]

 I will remove this input resistor, and install a 1M Resistor from Pin 4 to Ground (if needed).

Better to use a 1M pot, then you'll have full control of the TDA7052A gain range.

[tca]

Hi Corey,
I've just breadboard the circuit. The PUNCH as is does not work with the TDA7052A. In my previous posts I said to put a 5k input resistor to ground, I said that from memory... and, sorry about my bad memory, as you confirm that does not work! But I did put my breadboard version running: remove this input resistor (you can also put a 1M resistor from pin 4 ground). And it works!

My question is: why is there a 5k input resistor to ground in the datasheet for the TDA7052A???

There is one, but it's on the left hand side of the input cap...

this is the problem (& like I said in my last post, pin 2 should not be at ground, the 5k resistor is pulling the pin down to ground). As you say,  remove the 5k resistor & that should stop the biasing chaos.

oh I forgot about that cap! There is none on the TDA7052.