Loud hum from SSM2166

[Forummonkey1]

I am getting a very loud hum from my SSM2166 breadboard project. I followed the standard "debugging" methods. I also added a DC blocker capacitor at the SSM2166 output, before feeding the signal to the power amp. I also used the capacitor-on-a-cable method to check where the hum is coming from and it seems like it is coming from everywhere. I am using 4 AA batteries to power the SSM2166. Have you experienced anything similar? Any tips on how to troubleshoot?

[PRR]

Welcome!

Picture!

[antonis]

Welcome, also..

Breadboard isn't the ideal "layout" for such device including circuits..



P.S.
I presume you did put the optional 10μF capacitor from pin 4 to GND..

[amz-fx]

Loud hums frequently come from a bad ground connection or a bad cable.

Check that all ground points have essentially 0 ohms to all other ground points. This includes the breadboard as well as the input and output jack grounds. Check that the negative wire from your battery pack has essentially 0 ohms to the breadboard ground and to the jack grounds.

Then use a meter and check the cable to see if it has good continuity.

regards, Jack

[Forummonkey1]

Thanks for your inputs. It was a bad chip. Luckily, I bought a 2nd chip!
I am using the default circuit diagram from Analog Device's data sheet.
Breadboard may not be ideal, but it should be OK for testing the basics of SSM2166.
I am getting oscillation when bringing my fingers close to the wires as it changes the capacitance. I need to house the finished circuit inside a metal box or deploy a Faraday Cage around it.
I am using the optional 10uF capacitor from pin 4 to ground, which reduces random oscillations, but I am not using the 1000pF capacitor for input pin 7 as it sacrifices some high frequencies.
I am pleased with the SSM2166 chip's audio quality.
I am using regular 0.1uF (104) ceramic capacitors for input and output DC blocking purposes. Do you have any suggestions on what value and which type of capacitor to use in order to get better performance?
All of my potentiometers in this circuit are linear. I have a bag full of high value, such as 500k and 1M pots, and I bridge a fixed resistor across to achieve whatever value I need.

[ElectricDruid]

I am not using the 1000pF capacitor for input pin 7 as it sacrifices some high frequencies.

This is risky and very likely to increase the chance of oscillations. They didn't put that 1000pF there for fun - it's there because it *needs* to be there.

Also the datasheet says "A capacitor with a value of 1000pF is a good starting value and sets a lowpass corner at 31KHz for 5K sources", so you're not losing any high frequencies unless you're feeding it from a *very* high impedance, like 10K or so.
Even if it were true that you were losing some high frequencies then the solution would be to reduce the cap's value,not remove it. Taking it out altogether is asking for trouble, which is exactly what you've got.

[amz-fx]

Thanks for your inputs. It was a bad chip. Luckily, I bought a 2nd chip!

Thanks for reporting your findings!

Here is some reading you may enjoy: http://www.muzique.com/lab/compw.htm

Best regards, Jack