Stereo Preamp Question

[duclon]

I've built a small amp based on the Ruby. I added a tone stack between the input and amp and it works well. what I need to do is have stereo inputs as I have a stereo instrument. Both need the tone stack. I tried just adding another input with a tone stack and it lost a lot of volume and didn't sound very good.  It hadd some weird issues when I adjusted one the other would drop in volume. that may have been a wireing error.
So can anyone advise me how to place the tonestacks.  and combine the 2 signals.
Do I need some boost on each signal.
Do I need a resister inline of each input signal beore the tone stacks.
The pickups I have a passive.
Mike

[syndromet]

In order to have true stereo, you need two sepparate tonestacks and amps. If you just want to blend both signals before it hits the preamp, you need a buffer for the signals before you blend it. Sorry for the short answer, but I have don't have a lot of time right now. Let me know if you nedd a "fuller" answer.

[teemuk]

You can, for example, try something like this as input or mixer:
http://www.art-sci.udel.edu/ghw/phys245/05S/classes/images/opamp-adder.gif
And configure it for gain of 1.

[duclon]

Well I just need the stereo to have the separate tone for each side of the instrument. One side is bass, one is melody, after I get by the tone I can use mono or it can be mixed. It will end up going through one speaker. And I guess one amp?

In order to have true stereo, you need two sepparate tonestacks and amps. If you just want to blend both signals before it hits the preamp, you need a buffer for the signals before you blend it. Sorry for the short answer, but I have don't have a lot of time right now. Let me know if you nedd a "fuller" answer.

[duclon]

Thanks, would I go from my inputs to my 2 tone stacks then to v1 ad v2?

You can, for example, try something like this as input or mixer:
http://www.art-sci.udel.edu/ghw/phys245/05S/classes/images/opamp-adder.gif
And configure it for gain of 1.

[teemuk]

You can do it with so many ways... For example, see how the outputs of each module are summed in this:
http://www.schematicheaven.com/voxamps/sspa50.pdf

I assume you have nearly identical scenario (two "channels" feeding their individual tonestacks - output signals from the stacks are summed together). In the example only simple "mixing resistors" were used but for better result I would separate each tone stack from the "mixing" circuit by using a buffer in between.

The simple configurations always have some problems like the one described in http://www.best-circuits.com/booa.htm (See the section about "inverting adder").

How you want to do this is entirely dependent on how complex you want to make the circuit.

[duclon]

Thanks this is helpful. I think I can get it to work now.
 

You can do it with so many ways... For example, see how the outputs of each module are summed in this:
http://www.schematicheaven.com/voxamps/sspa50.pdf

I assume you have nearly identical scenario (two "channels" feeding their individual tonestacks - output signals from the stacks are summed together). In the example only simple "mixing resistors" were used but for better result I would separate each tone stack from the "mixing" circuit by using a buffer in between.

The simple configurations always have some problems like the one described in http://www.best-circuits.com/booa.htm (See the section about "inverting adder").

How you want to do this is entirely dependent on how complex you want to make the circuit.