decreasing gain using an op-amp?

[any]

Hi there,

I have stried some different approches to this, but somehow I am missing it... 
I've built Tim Escobedo's PWM and it sounded awesome with the output going directly to
the switch and output jack, however it was way too loud.
After installing a 500k log pot in the usual "volume control" way, the sound was completely
different! With volume turned down the low frequenties disappeared and became really thin.
(like putting the pulse width on "10") a larger output cap (15uF) helped a bit, but the sound
wasn't quite as fat and nasty as my first set up.
I've also built a simple unity gain IC buffer after the PWM but then even a 1k pot was useless in
controlling the volume. (only the first 10% of the turn would attenuate the signal)

So basically I'd like to know how to make a "simple" single op-amp active volume control
with a pot controlling the op-amp's gain from silence (infinite attenuation) to unity gain.

Any explanation would be greatly appriciated!

[rockgardenlove]

Look around...find a circuit with an op amp and see how the gain is controlled. 

Personally though, I prefer the sound of the post opamp volume pot.  You can bypass some highs with a resistor and a cap, works good.

[any]

Look around...find a circuit with an op amp and see how the gain is controlled. 

Personally though, I prefer the sound of the post opamp volume pot.  You can bypass some highs with a resistor and a cap, works good.

I did look around, but all i could find was unity to +*dB, thus increasing gain and not attenuating it.

[Seljer]

If you want to attenuate a signal with an opamp you need to have it set up as an inverting amplifier (which can also attenuata signal, not just amplify it)
http://en.wikipedia.org/wiki/Operational_amplifier_applications#Inverting_amplifier

[any]

If you want to attenuate a signal with an opamp you need to have it set up as an inverting amplifier (which can also attenuata signal, not just amplify it)
http://en.wikipedia.org/wiki/Operational_amplifier_applications#Inverting_amplifier

I've looked at that but don't quite understand yet how I can use a pot to get the gain from zero to unity...
(should Rf simply be the pot in the above example?)
I guess I'm not that smart at some subjects... 

[d95err]

If you want to attenuate a signal with an opamp you need to have it set up as an inverting amplifier (which can also attenuata signal, not just amplify it)
http://en.wikipedia.org/wiki/Operational_amplifier_applications#Inverting_amplifier

I've looked at that but don't quite understand yet how I can use a pot to get the gain from zero to unity...
(should Rf simply be the pot in the above example?)
I guess I'm not that smart at some subjects... 

Gain is -(Rf/Rin). Replace Rf in with a variable resistor. . When Rf is at zero resistance, you get gain 0 (no sound). With Rf = Rin, you get gain 1 (unity).

I'd give the regular volume pot a few more tries first though. 500k could be way too much and 1k way too small. Try a 10k or 100k pot and make sure its logarithmic (audio) taper.

[Gilles C]

Check this article

http://focus.ti.com/lit/an/sloa058/sloa058.pdf

Fig 4-5-6

Gilles