Problem with DS1802 digital volume control IC

[some0ne]

Hello everyone. I've been trying to build a simple volume control circuit using the DS1802. I have built a circuit almost identical to the circuit mentioned in Maxim's appnote. The only difference is the opamp. I've used a NE5532 in unity-gain configuration instead of the MAX4167. I'm powering the circuit with a 5 V supply and as a signal source I've been using a line level source, but also tried to further attenuate the source with a voltage divider. In either case the circuit basically works (without any clipping), but the attenuation of the DS1802 is very unsatisfying. While the upper 32 steps or so work as I would expect it, the rest barely makes any difference and even with mute enabled (which is said to attenuate by at least 90 db) I still can clearly hear the audio. Does anyone have an idea what I might have done wrongly or how to improve the circuit to get a better attenuation?

[Leon08]

NE5532 needs dual power supply.This means at least +5V and -5V.

[some0ne]

Thanks for the reply. According to the datasheet the NE5532 should work with +/-3 V, which is basically the same as single supply +6 V. You are right though, that 5 V is below the rated minimum of 6 V, but it seems that this is not the problem here. I have noticed that the maximum attenuation improves when I reduce the values of the R2 resistors. Using 1 Kohms for each of the resistors (instead of 2 Kohms) reduces the volume at the lowest value considerably. Using 470 ohms reduces it even more. Of course this increases the current flowing through the resistors. :/

[Bonsai]

Can you post up your circuit then we can give you some advice.

[Leon08]

If you want to operate the NE5532 with single power supply then you must make some changes to the circuit in the appnote.You need to make the virtual earth, wich will be at the middle of your supply voltage of +6 V.In your case it will be at +3V and then you need to block the DC at output.
Look here: Basic Op Amp Design

[some0ne]

As I said, it is exactly the circuit from the applicagtion note, except for the opamp, where I have used a NE5532 instead of the Maxim opamp.

[some0ne]

Originally Posted by Leon08

If you want to operate the NE5532 with single power supply then you must make some changes to the circuit in the appnote.You need to make the virtual earth, wich will be at the middle of your supply voltage of +6 V.In your case it will be at +3V and then you need to block the DC at output.
Look here: Basic Op Amp Design

There is a virtual ground in that circuit already. That's what the wheatstone bridge is for. The signal is aligned at VCC/2 through the whole signal path.

[Leon08]

I don't know why it does not work.It's hard to say because I don't know how this DS1802 works inside.You can experiment with it.Try without the opamps or another type.
I would measure the voltage on output of the opamp and if it's 3V DC then they are working and the problem is somewere else.

[some0ne]

Yes, the opamp outputs are at half the supply voltage. Also, there is no audible distortion in the signal. The opamps after the DS1802 are neccessary because the DS1802 can drive very small loads only.

[Leon08]

Then the problem is somewhere in the DS1802 or faulty connections.