[QQQ]

I mean if the pot is 20k, adding 20k resistors will result in 50% gain drop, right? What resistors i must use if i want to get 25% gain drop? 10k?

Is power rating of resistors important here? 0,25w will be ok?

Can i put resistors either side or i must them in specific position?

 

[n0ll4k]

You could do that but the gain ist set with the resitors in the main circuit. The volume pot is basicly a voltage divider and you could build another one at the input with 2 resistors.
voltage divider @wiki

Which amp did you build pherhaps someone could tell you which resistors to change to lower the gain.

 

[QQQ]

Yes, i'm talking about voltage divider.
It's more of a theoretical question.. What resistors i must take in case of 20k pot to reduce maximum volume 50%, 25%...

 

[n0ll4k]

You need at least two per channel because the pot ist basicly a voltage divider and you have to build a second one behind the input.

Too get 50% you need 2 with the same value, 25% for expample 1 25Ohm and one 75Ohm.

 

[ericj]

you're increasing attenuation, not decreasing gain. It decreases the overall gain, but it's a bad way to do it.

 

[dgbiker1]

It's not a great way to go about reducing gain. It will attenuate the signal to a certain degree, it will have a lower limit. At a certain point the bias current for your opamp will drop below threshold and you don't get sound. If your gain was much too high to begin with, the minimum volume will still be too high. Reducing the ratio of the feedback resistors is the right way to do it.

 

[QQQ]

Quote:

Originally Posted by ericj It decreases the overall gain, but it's a bad way to do it.

what's the good way?

Quote:

Originally Posted by dgbiker1 Reducing the ratio of the feedback resistors is the right way to do it.

Please explain...

 

[Polaris111688]

Do you have a schematic of the circuit? If it's a non-inverting amplifier, there will be (assuming it's a CMoy) 2 resistors that determine the gain of the amplifier. One goes from the output of the opamp to the inverting (-) input of the opamp. The other one goes from the inverting input to ground. To lower the gain, lower the value of the resistor from the output of the opamp to the inverting input.

 

[dsavitsk]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif you're increasing attenuation, not decreasing gain. It decreases the overall gain, but it's a bad way to do it.

Have you tried? It's actually, often, a pretty good way to do it, particularly in circuits with no negative feedback where there isn't an easy way to reduce gain. You will attenuate the signal by 6db, double the input Z, and use a, generally, better matched portion of the attenuator. Also, the resistors you use will almost always be of higher quality than the pot, and this seems to translate into better sound.

Now, of course, the actual best way to do it is with a step down transformer on the input, but this is considerably more expensive than the resistor attenuator method.

 

[dgbiker1]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif Have you tried? It's actually, often, a pretty good way to do it, particularly in circuits with no negative feedback where there isn't an easy way to reduce gain. You will attenuate the signal by 6db, double the input Z, and use a, generally, better matched portion of the attenuator. Also, the resistors you use will almost always be of higher quality than the pot, and this seems to translate into better sound. Now, of course, the actual best way to do it is with a step down transformer on the input, but this is considerably more expensive than the resistor attenuator method.

That doesn't fix cases where your gain is WAY too high (2-3X+ a comfortable setting). The op-amps need a bias current to function properly, I've run into cases where the minimum voltage needed to produce that bias current was too loud with the given gain. So adding resistance to the pot just meant I had to turn the volume knob more to reach that bias point, then the amp was too loud right off the bat.
And I'm not sure it would have a huge impact on input impedance since I think you also have to consider the (very high) input impedance of the op-amp relative to the (ideally) near zero output impedance of the previous stage.
BTW: I'm curious about which amps don't use negative feedback. Why would you want an open loop amp since they're inherently unstable? Is it for the open-loop gains of 1000's of V/V?

 

[dsavitsk]

Quote:

Originally Posted by dgbiker1 /img/forum/go_quote.gif BTW: I'm curious about which amps don't use negative feedback. Why would you want an open loop amp since they're inherently unstable? Is it for the open-loop gains of 1000's of V/V?

Sorry to not explain. I don't use opamps. Here's what I am using right now (complete w/ shunted pot): ecp.cc