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Stereo Preamp Question

Started by duclon, April 19, 2007, 09:10:12 AM

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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

#2
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?


Quote from: syndromet on April 19, 2007, 09:39:06 AM
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?

Quote from: teemuk on April 19, 2007, 09:42:35 AM
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.


Quote from: teemuk on April 19, 2007, 11:04:01 AM
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.