PGA2310 & NE5532 get hot?

[sergiusz]

Hello,

I built a small test circuit using a PGA2310 and a NE5532 input buffer. The analog part of the PGA2310 and the NE5532 are powered with +-15V using LM317/LM337.

When I touch the NE5532 it gets pretty warm, tha PGA2310 gets hand-warm.

Is this behaviour normal?

Thanks in advance,
Serge

 

[Netlist]

A schematic would be handy, if possible.

/Hugo

 

[sergiusz]

Sure,

attached is the schematic of the PGA and NE5532 part.

R3 & R6 are marked 0 and R4 & R7 nc (not connected), because I currently let the NE5532 run without any gain.

SV3 is the "bus" connector to the atmel controller. SV1 is the output bus for daisy chaining with a 74hc595.

Thanks !

 

[sergiusz]

And here is the PSU attached.

Nothing fancy at all

 

[Netlist]

Much depends on the environment and the definition of warm and hot.
Looking at the datasheet the dissipation is 1200 mW max.
I nothing is oscillating, I would believe this is fairly normal.

/Hugo

 

[sergiusz]

Hmm ... oscillation, that may be it ... I have to admit I have no bypass caps on the 5532, shame on me.

On another thread I read that a small series resistor may be needed on the output of the opamp too.

I did not assume oscillation because the sound is not distorted.

Thanks for the hint anyway. I'll rework my design and improve the buffer stage,

Sorry for the newbish questions ;-)

Bye,
Serge

 

[Jocko Homo]

Just because it doesn't sound distorted.............

Get your 'scope out. Hope you have one. "Sounds" like you will need it.

(Sorry.......that was too obvious a pun to pass by.)

Jocko

 

[sergiusz]

Hi,
Sorry .. I'm a pretty newbie at this. I put bypass 100n caps from the supply pins to ground as well as 250Ohm resistors on the output. Well, the ne5532 still gets warm.

I do not have a scope unfortunately. Is there any other method of detecting oscillation?

Thanks,
Serge

 

[Netlist]

A trick might be to calculate the power consumption at idle and look if it's within specs. If not…
Also, assuming you have taken the necessary precautions to prevent the circuit from oscillating you could be on the safe side.
But then again, you are never sure without a scope. Ebay might be your friend for your next investment.

/Hugo

 

[alfsch]

5532 gets warm, thats normal...30..35°
and the sound? idle noise?

 

[sergiusz]

I have to admit I still have to learn a lot ;-) I.e. power dissipation calculation and a scope is on my wishlist. Maybe I overestimated the heat, it is really all hand-warm, the NE5532 just a little warmer than the PGA.

The sound is just great! There is no idle noise on the speakers, no hum. I am currently working on the C code for the PGA, shift registers (74hc595 / 74hc165) and RC5 receiver.

I am also reworking the PCBs giving the opamp bypass caps. What I am still missing is some mute relais because the PGA gives some noise when powering on and off.

Attached is a picture of the prototype. All done with the maximum available PCB size of Eagle freeware version ;-) The enclosure is an old defect DVD player.

The shown prototype PCBs are:
1. The Power supply
2. The CPU
3. The shift registers
4. PGA & NE5532 input buffer

My goal was to create a "modular" design. The output of the PGA will feed a notch filter (also opamp based) for my W3-871S computer speaker. The digital part is also connected via a "bus" type connection so the modules can be always replaced for improvement or for playing around

There are still a lot of ToDos: Fuses for the power supply, mute relais, notch opamp, etc.

An externally hosted image should be here but it was not working when we last tested it.