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Parallel Effects Loop Recovery Mixer Dry Signal All Resistive

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  • Parallel Effects Loop Recovery Mixer Dry Signal All Resistive

    I'd like to build a solid state parallel effects loop that runs inside the chain of my serial tube effects loop. I'm planning on using it for delay and reverb in 'kill dry' mode. I use a volume pedal in the loop as a master volume and want to split the signal to go to the effect and then recover and mix it in with the dry signal. My goal is two-fold: 1) nice sounding parallel loop and 2)minimize the impact of the loop on the dry signal. I would like to maintain a purely resistive/capacitive dry circuit in the recovery mixer, so I'm thinking I will need some sort of hybrid mixer that is resistive on the dry side but can be solid state on the effects side. I've got a LOT of signal to work with so I can withstand about 6dB of insertion loss on the dry side of the mixer.

    What is the best way to approach this? Can I simply amplify the return from the effects and feed one side of a resistive mixer? What are the sonic considerations with this approach so that the dry signal maintains its transparency?

    What are the preferred resistive mixers for guitar signals in the 10 volt range? Which aspect of this circuit trumps other aspects? I'd love to use lower value resistance in the mixer to maintain signal quality but don't want to load down the return path in a way that will affect the dry tone.

    The output of the mixer will be sent to a long tail pair phase inverter connected to the return jack with a capacitor, so fairly high impedance load... upwards of 20 feet of high impedance guitar cable...

    I'm not looking for a simple schematic (but, hey, if this wheel is already invented...) but an identification of the problems that exist with this approach and some suggestions on how to best handle them.

    Thanks, guys.

    In the interest of full disclosure I may commercialize my design.

  • #2
    Resistive lossy mixer = crosstalk between mixed signals.
    Your design objectives 1 & 2 are mutually exclusive in a passive mixer.
    Virtual ground mixer is the way to go.
    There are ready made designs out there.
    Some are by our own R.G.Keen
    Aleksander Niemand
    Zagray! amp- PG review Aug 2011
    Without the freedom to criticize, there is no true praise. -Pierre Beaumarchais, playwright (1732-1799)

    Comment


    • #3
      Let me add a third objective

      Alex,


      You've identified a potential issue, but I would like to pursue my original objective which is to maintain an all-non-solid-state-non-digital circuit from guitar pickup to speaker. I do not want the dry signal to go through a solid state device. I would like to prototype a best effort here and compare sonics to devices like a Suhr MiniMix II which has a VE mixer but has the dry signal traveling through three SS devices.

      So let's say I have some cross talk. Are you saying I may get some effects return signal flowing back into the send-side splitter of the parallel effects loop through the passive/dry side of the circuit? Are there other issues I may encounter besides insertion loss and crosstalk?

      Given my application I may be able to tolerate some crosstalk because I'm using it to mix delay effects back into the dry signal in a passive/dry solid-state/wet parallel effects loop.

      So back to my three original questions. Who has a point of view on:

      1)What is the best way to approach this?

      2) What are the preferred resistive mixers for guitar signals in the 10 volt range?

      3)Which aspect of this circuit trumps other aspects?

      Smitty

      Comment


      • #4
        Did I say Solid State? I mentioned R.G.Keen only for reference of principle.
        VG mixer is very easy to implement with single triode or you can pull all plugs and do it with a 12DW7 or an ECF82.
        Sorry for not showing schematics of my VE all tube loop....on the other hand you will find several designs in Merlin Blencowes book.

        As for issues with passive mix.
        - signal crosstalk
        - mix level controls on return interactive, adjust one and level of the other changes too. Not so important as loop levels are usually "set and forget"
        - what about source impedance of SEND drive?
        Aleksander Niemand
        Zagray! amp- PG review Aug 2011
        Without the freedom to criticize, there is no true praise. -Pierre Beaumarchais, playwright (1732-1799)

        Comment


        • #5
          Limited use but might be effective

          Alex,

          OK. Probably me not being clear. Really want passive dry. Here's why. I'm building amps with a built-in tube-buffered (12AX7 cathode follower) effects loop. I really like the sound of a parallel loop for time-based effects but I want to use it within a serial loop so I can control overall volume with a pedal. Sort of a master volume pedal.

          Essentially I just want to hang a solid state parallel loop off of a volume pedal without the dry signal going through anything active. I'm trying to avoid a tube parallel loop on the pedal board. I'd like it to be a solid state unit run from 9 volts for convention. I'd also like it to be a stompbox size device so it can live on a pedal board. I'm looking to get the benefit of loop level/location time-based effects without rack gear. Think TC Electronics Repeater. I really would like to try to keep the dry signal all passive if I can. As you point out the interactivity of a passive mixer isn't a deal breaker in this context.

          How would you approach this task if you couldn't suggest a different alternative? Let's say I can afford 6dB of insertion loss. What does the most transparent device look like and what are the most elegant solutions ? Any neat tricks?

          I'm thinking the send side of the ss parallel loop can be a simple source follower so it won't load down the dry side.

          Thanks.

          Smitty

          Comment


          • #6
            Originally posted by Smitty View Post
            Essentially I just want to hang a solid state parallel loop off of a volume pedal without the dry signal going through anything active.
            Why? "I want" is not an answer unless you're 4 year old at the candy shop window.
            Originally posted by Smitty View Post
            I'm trying to avoid a tube parallel loop on the pedal board. I'd like it to be a solid state unit run from 9 volts for convention.
            Didn't you mention a 10V signal level? 9V supply is a guarantee for clipping....I wouldn't go less than 18V supply.
            Originally posted by Smitty View Post
            I'd also like it to be a stompbox size device so it can live on a pedal board.
            I think you will find something suitable at Lehle.com
            Originally posted by Smitty View Post
            How would you approach this task if you couldn't suggest a different alternative? Let's say I can afford 6dB of insertion loss. What does the most transparent device look like and what are the most elegant solutions ? Any neat tricks?
            I'd go active buffers + crossfade VG mixer. 0db total chain gain. Low noise studio quality stuff.
            Aleksander Niemand
            Zagray! amp- PG review Aug 2011
            Without the freedom to criticize, there is no true praise. -Pierre Beaumarchais, playwright (1732-1799)

            Comment


            • #7
              Chocolate Factory

              I like to think I'm more like Willy Wonka and my bench is the Chocolate Factory. Which means that I don't have to convince anyone but myself that I have a good reason for designing and building this loop. It seems that convincing you is either a requirement for your input on the subject or you just don't have a developed point of view on the matter. That's OK. Please no more recommendations for active mixing. Thanks.

              I was thinking of using a DC/DC converter to get a +/- 15 volt dual rail from 9 volts. 9 volts is kind of qwerty on the pedal board and if I want to make these for customers they will play nice on existing boards.

              Comment


              • #8
                In this case, being a chocoholic myself, I can only wish you best of luck and success with your chocolate business.
                Aleksander Niemand
                Zagray! amp- PG review Aug 2011
                Without the freedom to criticize, there is no true praise. -Pierre Beaumarchais, playwright (1732-1799)

                Comment

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