Thought: Rane SM26 as preamp switcher...

Discussion in 'The Rack Space' started by Lavely, Aug 3, 2018.

  1. Lavely

    Lavely Silver Supporting Member

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    I have a few preamps I want to hook up to one power amp...any reason to NOT just feed each preamp into an SM26, jack up the volume of the one I want so use, feed the power amp from the SM26? Seems like an easy solution to the issue - just to have them all hooked up at once so I don't need to unplug stuff. I'm a home player only...
     
  2. jb4674

    jb4674 Member

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    It could be done. How many preamps do you have and what are they?
     
  3. Lavely

    Lavely Silver Supporting Member

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    MP-1, V-Twin, PSA 1.1
     
  4. jb4674

    jb4674 Member

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    He could use cables with the ground lifted on one end to curve the problem IF it happens...
     
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  5. jaykay73

    jaykay73 Member

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    Ground lifted power cables is not a great solution unless you want to ride the lightning one day.

    You have to make sure each preamp has ONE and only ONE path to ground - this should be the ground of the power cable. One option is to have each unit electrically isolated from each other and the rack rails. Then you need a guitar level signal splitter with transformer isolation between each preamp input and BEST to have one which will maintain high impedance at its input. Radial JX44 or JD7 will get you there in style. Then you can run the outputs of each preamp into a simple switching system like a Rocktron Patchmate or Voodoo Lab GCX, to select which preamp you want to be "active". Or if you really wanted to blend preamps you could run the outputs into any line level mixer, such as the SM26 as mentioned above.

    JK
     
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  6. jaykay73

    jaykay73 Member

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    I beg to differ about the Patchmate. It worked in my rack for a long time. A switcher is dumb. All it has to do is decide to pass the input to the output of each loop, or not. It does not care what level the signal is running at and on the original Patchmate, at least, all loops are electrically isolated from each other.

    The key is splitting the signal BEFORE the preamps, not after and then switching each preamp in or out of the chain. There is a good diagram in the original Patchmate manual for how to do it with a daisy chain cable. But a daisy chain cable is not enough as the inputs need to be electrically isolated from each other.

    JK
     
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  7. Lavely

    Lavely Silver Supporting Member

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    Another twist - what if I turn on only one preamp at a time and use the Rane simply as a utility box so I can keep them all patched in without having to change cabling? If only one is on, does that eliminate ground loop concerns?
     
  8. jaykay73

    jaykay73 Member

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    Well, not only should you have only one on at a time but you should also just plug your guitar into just one and that way you could avoid needing a splitter. The low tech method always works! But if you're going to do that, why even bother with the Rane? Every time you go to play your toys just plug the inputs & outputs of the preamp of your choice. Works for Leon Todd :)

    JK
     
  9. Lavely

    Lavely Silver Supporting Member

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    Leon Todd does kind of rule...I'm just a little lazier than him, I believe.
     
  10. stickyFingerz

    stickyFingerz Supporting Member

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    I had an SM26 and I found it noisy and cruddy sounding.
     
  11. jaykay73

    jaykay73 Member

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    @Man with Gas please explain why "it doesn't work with preamps". Have you used it in the scenario where you split your signal using transformer isolation BEFORE the preamps then used the Patchmate to switch the preamp outs in or out of the chain? Or did you use it the way you SHOULD NOT use it, by connecting each preamp to a loop and switching the loops in & out?

    Seriously this discussion is high level and comments like "it doesn't work" require some example or justification. Otherwise we'll never escape from the dark ages.

    Please provide more detail. Thank you.

    JK
     
  12. Slicklickz

    Slicklickz Member

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    I've been using Ibanez EPP-400s to switch preamps for over 30 years,never had a problem.Pics:

     
  13. jb4674

    jb4674 Member

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    @OP, why not get an RJM mini amp gizmo used?
     
  14. jaykay73

    jaykay73 Member

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    @Man with Gas I used a Patchmate to switch preamps for a few years. The way I ran it I split my guitar signal with a daisy chain cable. Each limb of the cable fed a channel of an Ebtech hum eliminator which is an isolation transformer. Then each isolated signal fed a preamp and each preamp output went to a Patchmate loop. It worked with zero ground loop issues. The only thing was there was slight tone loss because each transformer in the Ebtech is a cheap item compared to the Jensen transformers in the Radial gear which are $70-100 per piece. If I were to do it again I'd get a Radial unit or any other higher quality isolation transformer unit. Edcor makes some reasonable ones too.

    I really don't buy your logic of "just because Rocktron put out a dedicated preamp switching unit the Patchmate can't work". You need to appreciate the science behind how a pro preamp switcher works - I explained that in detail for the OP but you appear not to be open to scientific rationale which IS required when it comes to discussing these high level technical issues.

    When you say "the more obvious the problem" can you please enlighten us on what you allege the "problem" actually is.

    Pro preamp switches like the Bradshaw / CAE, Egnater SS4, Mesa high gain switcher are simply boxes that have quality isolation transformers to split the input signal while retaining input impedance and then switching the preamp returns with a simple loop switcher. The key is "quality" transformers and "quality" filtered power supply for the whole enchilada.

    JK
     
  15. Coalface1971

    Coalface1971 Member

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    Hi there,

    I like this sort of stuff, One of the sad things about HRI going down is you could readily run a search on this stuff and get an answer or suggestion or two. Not being mean, but there needs to be be a lift in the technical side of this board. Many reason's guys get rid of rack gear and pull down its reputation, is through misuse or misguidance concerning its implementation.

    Really the issue with multiple amps/pres and other equipment is buffering and ground/earth loop issues which have existed since the beginning of time.

    Plenty of ways to do this, but reckon what you are talking about Lavely could work as described in your OP, with a little more additional stuff.

    If you can handle the sound of the buffer required to drive them (all buffers color the sound, I don't care who makes them), transformer isolation between the inputs of each pre, like an old Axess BS2/RJM equivalent etc. basically feeding the preamp's front ends a signal at all times is a method.

    The ground loop will be broken here by the isolation transformers, the buffer will drive them and present the impedance required to stop pickup loading. Each pre after the first one needs an isolation transformer (or cascaded BS2, Mario offered a 2nd isolated output at one point, transformer was a common Mouser 10k/10k from memory).

    An old GCX or equivalent then can be used just to handle the outputs of each preamp. Plug the preamp output's into each a GCX loop each, then just use send output of each of those GCX loops into the a channel each of the mixer. Mixer is connected to power amp and cabs of course.

    You can turn the preamp's on/off individually then, or mix them even. If they aren't in phase, stuff like the old BS2 and most of those buffers have a phase switch, which basically flips the phase of the isolation transformer inside. I think the later version of the RJM Y-Not allows that to be automated via MIDI, if you want to run it live. Or if you are keen, that could be patched into a GCX loop with a phase reversed isolation transformer, giving automated phase flip that way. There was a video of super tech and rig builder Lonnie Totman showing this automated phase flip method, on a comprehensive video as he described the construction of Barry Stock's touring rig. it was out at HRI if you can still find it.

    If you'd like to avoid buffering before the inputs of the preamps, a possible solution is to use a switcher as described, but have them handle switching you guitar inputs on each preamp individually. The preamp outputs go straight to the mixer.You'll probably still need to deal with the ground loops, however.

    The "ground lift" mains cable method is not recommended of course (despite the fact that all of the major rack builders either still do this or have done so in the past). If you understand why it gets done fair enough (I'm an electrical tech with 28 years experience, so I've got the idea, let's just say), but as mentioned it still may not solve ground/earth loop issues.

    I think jb4674 was suggesting lifting the audio cable screens (ground) at one end as a way of breaking the ground loop. This is a method commonly employed in studio wiring. If you you are going to lift the audio screens, I'd have a tendency to do it on the preamp output's. What end doesn't matter, as much as they are still attached at the same point (CGX or Mixer).

    The signal is line level here and has better noise rejection properties than the instrument level cabling before the preamp inputs.

    Otherwise, if you like DIY, you can buy individual line level isolation transformers and break the ground loops with them on the line level side. The Behringer and Ebtech ones are commercially available variations. Just keep them away from any transformer power supplies or sources of magnetism as they are prone to induced hum.

    Chris.
     
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  16. jaykay73

    jaykay73 Member

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    Hey Chris,

    "There needs to be be a lift in the technical side of this board" is a serious understatement.

    The method you described is what I've been doing for years...



    Thanks for expanding on the technicalities.

    JK
     
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  17. Coalface1971

    Coalface1971 Member

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    Hi Jeremy,

    Nice rig, mate.

    Chris.
     
  18. iam_krash

    iam_krash Supporting Member

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    Ummm, the original red Rocktron Patchmate(Bradshaw designed) was indeed designed to run preamps. It's been the mainstay of my preamp and processor switching forever...
     

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