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Dual amp setup phase problems

Discussion in 'Amp Central Station' started by Doctorx33, Jul 10, 2018.

  1. Doctorx33

    Doctorx33 Tele-Afflicted

    Jun 8, 2014
    atlanta
    So I'm putting together a multi amp rig. If I can get it working it will be pretty cool:

    • Traynor YBA1A and AC30cc for dirt
    • BF Bandmaster and Bassman 100 in stereo for clean
    • BF Bassman driving a Leslie 16

    I have to build a new pedalboard too, my old one is over the hill.

    For the Traynor and the Vox, I either will build an A/B box or run them in stereo, not sure yet.
    So I was fooling with it last night, hooking up a Boss stereo chorus, and found out that the Vox and Traynor are apparently out of phase. I thought the pedal was screwy because the led wouldn't light up and the signal to the Vox was very faint. Something is getting grounded out. Experimentation proved the pedal was fine.

    So I'm guessing I need to build a phase inverter of some kind, assuming that it will fix the problem. I found this schematic online and will give it a try.

    Any comments or suggestions would be appreciated.

    26E01632-260E-4EAF-9381-5E25E128D5FF.jpeg
     

  2. Crobbins

    Crobbins Friend of Leo's Ad Free Member

    Jul 10, 2014
    Meiners Oaks CA.
    I use a Radial ABY pedal for my dual amp setup.

    [​IMG]
     
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  3. Papa Joe

    Papa Joe Friend of Leo's Silver Supporter

    Age:
    89
    Jun 30, 2007
    Swanton Ohio
    I'd first try inverting the speaker connections on one of the amps..
    That solved the issue for me..
     
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  4. Doctorx33

    Doctorx33 Tele-Afflicted

    Jun 8, 2014
    atlanta
    Don’t want to spend $$ for something I can build for under ten bucks.

    I’ll try the speaker phase thing but I think the issue is the input not the output.
     

  5. studio1087

    studio1087 Telefied Ad Free Member

    May 10, 2003
    Near Milwaukee
    Radial fixes everything. You can flip the electrical and you change the amps to make them "in phase".

    I have the smaller (Big Shot) Radial than Crobbins has but it still fixes everything - $99 new. I paid $55 or $60 on Reverb. It's a bulletproof box. The tuner line out is handy. The boost does look really sweet on the Pro model.

    [​IMG]
     

  6. luckett

    luckett Friend of Leo's

    Jun 14, 2011
    .
    Flipping the phase at the output is the same as doing it at the input.
     
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  7. ebb soul

    ebb soul Poster Extraordinaire

    Age:
    58
    Jun 7, 2016
    Smyrna georgia
    Fttt the Radial doesn't even light up to let you know where yer at.
     

  8. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    The speaker switch is a good suggestion. If you build an op amp phase inverter I'd suggest you don't use that diagram, it won't daisy chain with other effects because of its ground reference. It also could use a higher input impedance since inverting op amps have lower input impedances than non-inverting so I'd buffer the inverting stage first as well. It'd be convenient as most op amps are dual packages anyway.

    Try the speaker thing first and that should work, if you want a phase inverter just ask and ill draw you one up.
     

  9. Dacious

    Dacious Poster Extraordinaire

    Mar 16, 2003
    Godzone
    Just be aware that even phase reversal won't necessarily work 100% of the time. Like Strat pickups that in the 2 & 4 position in phase you can get phase cancellation occurring, especially at certain distances from the amps in between. Where soundwaves meet they can cancel at certain freqs. Same reason you have to be a bit careful pointing FOH speakers.
     

  10. Doctorx33

    Doctorx33 Tele-Afflicted

    Jun 8, 2014
    atlanta
    I have a speaker phase switch box and used it to swap the phase on the AC30, didn’t help. The inputs on the two amps are opposite each other, that’s where the fix must be applied, at least I think .

    I tested the amps with my Morley a/b/y box and the results were the same as with the boss pedals.

    Tomorrow I’ll try to do a video of what’s happening and post it somewhere for you to see.

    Asmith if you have a better phase reverser than the one I posted I would very much appreciate it. I have the parts for the one I posted.

    This is all assuming that’s the kind of gadget I need to fix this issue, if it can be fixed at all.

    Oh also I tested the traynor with a fender amp and it sounded fine.
     

  11. luckett

    luckett Friend of Leo's

    Jun 14, 2011
    .
    The inputs on an amp don't have a relative phase.
     

  12. Doctorx33

    Doctorx33 Tele-Afflicted

    Jun 8, 2014
    atlanta
    Ok then tell me what the problem is.
     

  13. luckett

    luckett Friend of Leo's

    Jun 14, 2011
    .
    I can tell you what isn't the problem, signal phase and changing the phase of the input signal isn't going to give you a different result than swapping speaker leads.
     

  14. telemnemonics

    telemnemonics Doctor of Teleocity

    Age:
    58
    Mar 2, 2010
    Maine
    Something seems off, the LED not lighting on a pedal that later tested fine, the signal to the Vox being "very faint", reversing the phase at the speakers didn't help, and an ABY didn't help.

    Two amps out of phase will not result in one amp signal being very faint.

    There will be a notable volume loss, but neither amp is right or wrong; one amps speaker cones move forward while the other amps cones move backward.

    Is the Vox the only amp of the four that sounds "very faint" when run with another amp?

    And does the Boss stereo chorus now work properly with the LED and both sides full power?

    I wonder if one amp has a failed or shorted component that's leaking some wall voltage to the guitar cord and screwing up your chorus?

    There is also the wall voltage phase in amps with vintage grounding and phase switches that change one or the other leg to ground, plus you'll get a ground loop if two amps are both grounded. This is obviously not the same as signal phase. Three out of your four amps were built with this problem AFAIK.

    I had an internal short send voltage down the guitar cable with both a BF Bassman and a Supro reverb unit. With the Bassman it stopped at a Rt66 which blew up.

    Just a guess because this sounds like something other than two amps out of phase.

    I have indeed run lots of amps in stereo, and a stereo chorus is a favorite method as well as a passive home made AB box.
    Whan an amp is out of phase with others i swap the speaker wiring and leave it that way.
    Back in the old days the phase was variable both in the amps and even the speakers were sometimes marked backwards, but modern amps are all phased the same.
    So if you have an amp that's OOP with your other amps, IMO you don't want to use a switch. Just fix it!
     
    Last edited: Jul 10, 2018

  15. Papa Joe

    Papa Joe Friend of Leo's Silver Supporter

    Age:
    89
    Jun 30, 2007
    Swanton Ohio
    Try this..Turn one of the amps around so that they face opposite of each other and see what that sounds like..
     

  16. Wyzsard

    Wyzsard Friend of Leo's

    Jun 22, 2009
    Falls City
    The current models do. They're awesome.
    http://www.radialeng.com/product/bigshot-aby/

    How do you like the Dragster ?

    I've got this model, and the stand-alone Dragster.

    BigShot-ABY-thumb-768x844.png
    Dragster-large.jpg

    Love both of them.

    I've got about 57 foot of cable on my 2 amp rig and the Dragster does the trick. Dials the highs the long cable runs reduce right back.
     
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  17. Asmith

    Asmith Friend of Leo's

    Age:
    22
    Nov 27, 2014
    Morley, England
    I'm agreeing with @telemnemonics on this one, if it's a specific amp you cant hear well rather than hearing both but with where a lot of the lower frequencies are missing and sounds thin in general. Also you can flip the phase at any point all you're doing is flipping the signal upside down and in some devices (pedals for example) the signal is flipped multiple times before it gets out the other end. It made modding my Boss CS3 the other day a real treat, I had to buffer and boost the dry signal so it would work well when being blended but I had a hard time deciding if I needed to flip the phase or not.
     
    Last edited: Jul 11, 2018
    telemnemonics likes this.

  18. srolfeca

    srolfeca Tele-Meister

    Exactly. Out of phase is very subtle, mostly heard as a loss of low end.

    If the Vox is literally “very faint”, and an LED diesn’t Light, it sounds like a bad cable, bad jack, or stray voltage on an input or output that shouldn’t be there...

    Got a multimeter?
     
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  19. Crobbins

    Crobbins Friend of Leo's Ad Free Member

    Jul 10, 2014
    Meiners Oaks CA.
    I haven't tried the "Dragster", but I set the drag on my Radial ABY pedal per the instructions, and have never changed it. In this pic I'm using a Marshall JMP 50 watt, and a Friedman 50 watt Smallbox. Sounds good to me. I use a Eventide H9 for my ambient effects, run it through the fx loop on the Friedman.

    [​IMG]
     
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