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Thread: How to best split audio output signal into two to feed separate Amplifiier and Reverb

  1. #1
    pp Pianissimo Eric Mack's Avatar
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    How to best split audio output signal into two to feed separate Amplifier and Reverb

    Currently, my Alesis reverb units obtains its signal from the "reverb out" that comes from the "EN-II Entertainment Center" in my my Rodgers 340 Organ. (Basically, the headphone out)

    For various reasons, I no longer want to do this. Instead, I would like to tap off the audio signals before they go to their respective speaker channel amplifiers.

    So you know where I am going with this: I have 5 channels on my Rodgers 340. These go into amplifiers and end up at speakers. I want to tap off 3 channels and the combine them -- these will become the input to the LEFT REVERB channel. Then, I will tap the two remaining channels and combine them -- These will become the input to the RIGHT Reverb Channel.

    What is the correct way to do this?

    One option I can think of is to use a "Y" adapter at the RCA jack though, based on what I learned earlier this week, I suspect there is probably a better way to do this...

    Another option might involve some passive resistors to do this? If It used Potentiometers I could even adjust the mix level into the reverb units, but that might require more circuitry. I am weak in this area, so I am not sure where to start to think about this.

    I like to avoid adding active mixers and more components to the organ if possible.

    Any thoughts?

    Eric


    FYI: This new question is a follow-up to a similar question I posted the other day on how to combine two audio signals to feed into an amplifier. LINK I learned a lot from that thread and I was able to successfully implement the changes and now my organ sounds so much better. (Thank you to those who responded)
    Last edited by Eric Mack; 07-11-2018 at 10:28 PM. Reason: Clarity
    Eric Mack
    www.ThisOld340.com
    Rodgers 340 S/N 34341
    Los Angeles, CA

  2. #2
    Administrator Admin's Avatar
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    You can split signals using a standard Y- adaptor. It's combining them that requires the use of summing resistors or an active mixing circuit. The more channels you wish to combine, the more attractive using an active circuit becomes, especially if you want to control the individual mix levels. For passive mixing, you can start with 10k resistors as you did previously.

  3. #3
    pp Pianissimo Eric Mack's Avatar
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    Quote Originally Posted by Admin View Post
    You can split signals using a standard Y- adaptor. It's combining them that requires the use of summing resistors or an active mixing circuit. The more channels you wish to combine, the more attractive using an active circuit becomes, especially if you want to control the individual mix levels. For passive mixing, you can start with 10k resistors as you did previously.
    That's great news, it will allow me to take the reverb from a clean signal for each channel. As for combining these, I will take the passive resistor approach and will probably use 10K pots so that I can adjust levels of mixing, At what point would you say that I should consider active mixing? Is combining 3 or 4 channels to many to do passively?
    Eric Mack
    www.ThisOld340.com
    Rodgers 340 S/N 34341
    Los Angeles, CA

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    fff Fortississimo toodles's Avatar
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    I believe, as you indicated in your other post regarding combining the signals, each of the Rodgers outputs has a 4.7k ohm series resistor from the output drive transistor. It's best to connect your 10K mixing resistors directly at that output transistor rather than after the 4.7k resistor. The reason is to prevent the mixed signals from leaking back into the other channels--the transistor output itself is a lower impedance point.

    Make sure your reverb system is actually a stereo unit before going to the bother of isolating some of the channels into the L signal and some into the R signal. Many of the lower cost reverb units (meaning under, say, $500) combine the L and R signals to process the reverb in mono, and then provide the reverberated signal to both L and R outputs.

    I really don't think that processing reverb in stereo is worth doing--in an actual reverberant environment you really don't hear a significant stereo effect on the reverb--it's much more obvious on the source than on the echoes.

  5. #5
    pp Pianissimo Eric Mack's Avatar
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    Quote Originally Posted by toodles View Post
    I believe, as you indicated in your other post regarding combining the signals, each of the Rodgers outputs has a 4.7k ohm series resistor from the output drive transistor. It's best to connect your 10K mixing resistors directly at that output transistor rather than after the 4.7k resistor. The reason is to prevent the mixed signals from leaking back into the other channels--the transistor output itself is a lower impedance point.

    Make sure your reverb system is actually a stereo unit before going to the bother of isolating some of the channels into the L signal and some into the R signal. Many of the lower cost reverb units (meaning under, say, $500) combine the L and R signals to process the reverb in mono, and then provide the reverberated signal to both L and R outputs.

    I really don't think that processing reverb in stereo is worth doing--in an actual reverberant environment you really don't hear a significant stereo effect on the reverb--it's much more obvious on the source than on the echoes.
    Thank you, I will plan to approach this in the way you suggest.

    As for reverb units, I presently have an Alesis 2 channel unit, which I believe may in fact mix the two as you suggest. It supplies its own amp and speakers which was a big improvement.

    ROOM REVERB OUTPUT PLAN:
    My plan is to purchase a Lexicon MX400 and supply it with 4 independent channels of audio coming from the 340:
    LEFT
    - Main #1 RW3 (Which includes tuned percussion and traps for now)
    - Main #2 RW3 (Which has my Bourdon and String Celeste)
    RIGHT
    - Tibia/Solo Rodgers Small Speaker Array
    - Brass Rodgers Small Speaker Array with the JBL Bullet Tweeter

    - PEDAL: Using a BSR 15" speaker for now. It's what fits and what I had.

    As far as feeding the Lexicon reverb, my pedal channel is independent of the above four, so I would probably mix that into Main #2.

    PRACTICE HEADPHONE OUTPUT PLAN
    CONCURRENTLY with that, I would also take the 5 signals above into a separate mixing circuit, which I would use to drive a headphone for practice. I might reuse the Aleses reverb in front of the headphone preamp. This will allow me to completely disconnect all of the Entertainment center circuits - which is simply unplugging from main mixer board and jumpering pins.

    I found a number of threads on setting up the Lexicon MX400 on this forum, so when I get one, I will study those. Until then, I will experiment with the Alesis, mindful of your point about mixing channels.

    That's the plan, at least.

    Thank you Toodles, you are among the champions on this forum, without whom many of us would be lost. I don't know if my private messages or emails reached you, but thank you. (You are welcome to reach out to me)
    Eric Mack
    www.ThisOld340.com
    Rodgers 340 S/N 34341
    Los Angeles, CA

  6. #6
    ppp Pianississmo csw900's Avatar
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    1 members found this post helpful.

    Combining Audio Signals using resistors

    Quote Originally Posted by Eric Mack View Post
    Thank you, I will plan to approach this in the way you suggest.

    As for reverb units, I presently have an Alesis 2 channel unit, which I believe may in fact mix the two as you suggest. It supplies its own amp and speakers which was a big improvement.
    I am a retired electronic design engineer with an interest in organs. I have just joined this forum and this is my first post so please excuse errors if I am pushing the wrong buttons.

    When combining audio signals using resistors you must remember that the combiner is also an attenuator which will reduce the levels of the combined signals.

    If the source resistances are high e.g. 4K7 (4.7Kohm) then you can safely combine signals just by connecting the outputs together. There will be much less attenuation this way.

    The attenuation can be calculated from knowledge of the source resistance and the destination input resistance.

    In most situations where a formal resistive combiner is useful the source resistance is low and the destination input resistance is high e.g. 100K

    csw900

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    ff Fortissimo Hamman's Avatar
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    Harrison Labs makes a mixer on a "card" that has 8 or 12 channel inputs each with parallel outs on each channel (Bypass-direct out) that will mix down to 2 channels. I currently use this on my Allen set up.

    http://harrisonorganworks.com/index_files/Page784.htm
    Allen 5300-DK, Hammond A-105, Conn Custom 905-DK

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