Converting a combo amp into a cabinet

Discussion in 'Amp Central Station' started by CaperDrag, Sep 21, 2012.

  1. CaperDrag

    CaperDrag TDPRI Member

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    Hello everyone,

    I know this topic has been covered many times, in many places (I have come across several posts, on various forums through my research), but I have not quite found an answer to my question.

    First some background information. I have an old solid state combo amp, and I am in the process of finishing up a DIY tube amp which I am hoping to use as a head. At the moment, however, I don't have the funds to buy or build a cab. My wish is to add a jack to my combo so that it can be used as a cab or as a combo. As I have been known to suffer from a condition commonly referred to as "cranial/rectal inversion", I'm looking to wire the jack such that when I plug in a speaker wire, the combo acts as a cab, and when I unplug the speaker wire, it goes back to acting as a combo. That way, I will have fewer worries about running either amp without a load. Would this be a relatively simple thing to do, and how would I go about it? I'm thinking I would need a 1/4" switched stereo jack (e.g. Neutrik NMJ6HF-S) and to wire that up appropriately. I should mention that I understand the importance of impedance matching, and that the speaker in the combo is rated such that it can handle the ouput from the DIY amp.

    Any help with this project is greatly appreciated. If this exact topic has been covered somewhere already, I apologize. I know how bothersome it can be to have duplicate threads!

    -Drag
     
  2. AirBagTester

    AirBagTester Friend of Leo's

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    Wow, I don't know how to do that, but I'm curious to know how also. I use my Pro Jr. as a cab all the time now, but I just unplug the speaker lead and use a connector and an extension speaker cable. I just try to remember to make sure it's hooked back up before plugging in the Pro Jr. amp!
     
  3. CaperDrag

    CaperDrag TDPRI Member

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    @AirBagTester: If I can't come up with a way to do this, that's the way I'll go. I'd like to pursue this avenue first because I have a pretty good memory, it's just VERY short, so I'm worried I would forget to switch cables or something, resulting in a very expensive burnt iron paper weight that used to be an OT haha!

    In my mind it should be wired up similar to the input jack on an effect pedal, such that (assuming the pedal is run only on a battery rather than a wall wart), when your instrument cable is plugged into the input jack, power flows, and when the cable is unplugged, you get no power from the battery, preventing someone from accidentally kicking on the pedal and burning through batteries.

    In my mind it should work, but I have been wrong before and just want some confirmation that I'm not way out in left field before attempting this haha!
     
  4. Vonduck

    Vonduck TDPRI Member

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    Would it be strange to assume that you could just run it directly to the input of the other amp?
    Kinda like a pre-amp...ran directly into the clean channel of your SS combo.
    That is assuming it's a standard SS combo and not a modeling amp.
     
  5. bdgregory

    bdgregory Tele-Afflicted

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    I don't think you need to make it as complicated as you're suggesting. First, it's almost certain that your Solid Stat amp will be just fine running without a load. Virtually all solid state's don't need a load when on. What I would do is install a standard non-switched jack that connects to the speaker in the combo, and add a phono plug on your speaker wires from the combo. This way, you can plug the combo speaker wire into the jack when you want to run it as a combo, and plug your tube speaker cable in when you want to run it as a cab. I've done this on a couple of my combos . . . works great.
     
  6. timbo_93631

    timbo_93631 TDPRI Member

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    Just use a Mono Cliff Jack for the speaker out. I drew up the little diagram below to show the connections. The lugs are shown as sticking out to the sides to make it easy to understand, but they really stick straight down as shown in the photo in the upper left. If you look at the way these jacks work the connection is made straight across the top with no jack inserted where the two sets of contacts touch. When you insert the jack the normal connection from the amp to the speaker is broken when the plug pushes the top contacts up thereby making the connection from the plug to the speaker.
     

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  7. bdgregory

    bdgregory Tele-Afflicted

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    I think this circuit results in power from the tube amp being applied to the SS amp output (ie when you connect the tube amp to the speaker).


    FFFZZZZZZTT !! not good . . .
     
  8. timbo_93631

    timbo_93631 TDPRI Member

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    No, that is not the way a Cliff jack works. When you insert the plug it breaks the connection between the SS amp and the speaker.
     

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  9. bdgregory

    bdgregory Tele-Afflicted

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    ahh, I see. Thought it was a standard shorting jack.

    by the way Timbo - how are things in Fresno? I was born/raised there.
     
  10. CaperDrag

    CaperDrag TDPRI Member

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    Thank you VERY much for all the help everyone, especially Timbo for taking the time to do those diagrams and pictures! I'll post again when I get everything wired up to let you know how I made out!
     
  11. timbo_93631

    timbo_93631 TDPRI Member

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    Fresno is okay these days. Heat is trailing off, only 95-99 degrees this week. We had a long stretch over 110 this year with bad air in spades that was pretty unbearable in July. Harvest season for stonefruit is all but finished and was ok and most of the raisin grapes have been laid out and are drying or already dried. No freak rain storm to ruin the raisin crop so far! Pomegranates are just about in full swing. I should say I grew up down the road from Fresno in Kingsburg so I am a little more ag focused than your run of the mill suburban Fresnan. Anyhow, the big city is pretty good, too many forclosed houses everywhere though, same as the rest of the country. How'd you end up in Maryland?
     
  12. bdgregory

    bdgregory Tele-Afflicted

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    I went to college in San Luis Obispo, got a job in Colorado out of college, and gradually moved east until I landed in the capital area - and decided to finally put down roots here. Been here now for 22 years. I never thought I would live in one place longer than I did in Fresno (18 years in the same house), but now I have. You bring back memories - while in highschool, I drove tractor in the peach orchard in mid summer, and rolled raisin trays in the fall. I also worked in the orange packing plant in the late fall.
     
  13. jamesgmac

    jamesgmac TDPRI Member

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    i just found this post, and want to do the same thing. i've searched for mono cliff jacks, and it looks like them come either "switched" or "unswitched". which kind do you use for this type of application?
    thanks!
    jim
     
  14. ThomShivers

    ThomShivers TDPRI Member

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    After reading this forum thread and several other online sources i concluded that i should use a Cliff CL1160A S2/BNB mono switched jack socket.

    Today i built the socket into the back of my Fender Sidekick Reverb 65 combo amp, soldered the internal speaker wires to one side of the Cliff socket and soldered a pair of new speaker wires to the other side of the Cliff socket, connected the wire clips to the speaker and i was ready to go.

    First i tried the combo amp stand alone and everything worked fine as before. Then i turned of the combo amp, unplugged the power cable, put a speaker cable in the Cliff socket and connected it to the external speaker output of my Vox Pathfinder 15R. I plugged in my guitar and turned on the power of the Pathfinder, turned up the volume; no sound!

    What did i do wrong? The Pathfinder has its original 8'' Vox Bulldog 15W 8 Ohm speaker, the Sidekick has its original 12'' Fender Musical Instruments 65W speaker. I assumed the Fender speaker to be 8 Ohm as well, but now i'm confused. What if the Fender speaker is 16 Ohm, could that be the reason why i have no sound when connecting it to the Pathfinder? Or is the difference in wattage of both amps the cause of the problem?

    One thing i noticed is when i strum my guitar while the Pathfinder and Sidekick are connected to each other, the power LED light on the Pathfinder gets weaker. Maybe that might be a clue to the puzzle...

    Can someone help me with this please? Thank you in advance!
     
  15. Alamo

    Alamo Doctor of Teleocity

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    You just got out of the wrong side of the bed - no wait, of the jack. :lol:
    just swap & solder to the other side.
     
  16. ThomShivers

    ThomShivers TDPRI Member

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    Okay, I am an idiot, i though my first solder job ever was faultless, but this simple routing mistake i overlooked. Thank you Alamo for helping me out. I rewired everything and now it does work.

    Vox Pathfinder through Fender Sidekick sounds great! I bought the Sidekick especially for this purpose. The clean sounding speaker and the extra volume make a nice addition to the Pathfinder amp sound. It's only too bad that the internal pathfinder speaker is turned of when the external speaker is plugged in. I guess the Pathfinder external speaker output is a Cliff socket as well; it seems to break the signal to the internal speaker when the cable jack is plugged in...
     
  17. Alamo

    Alamo Doctor of Teleocity

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    Well you could easily daisychain the two amps.
    plug your guitar into input one of the Sidekick, another chord goes into input two and the other end into the Pathfinder input.
    voila, both amps are running independently and can be dialed in to complement one another.
     
  18. ThomShivers

    ThomShivers TDPRI Member

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    Daisy chaining the two amps doesn't seem to work. I plugged my guitar cable into Sidekick input 1 and plugged a second instrument cable into Sidekick input 2 running to the Pathfinder input. The Sidekick picks up the guitar sound but the Pathfinder doesn't. Maybe not all amps with two inputs are suitable for the daisy chain trick. I found some posts on the internet of people owning Sidekick amps that do the trick, but mine just doesn't.

    But i wasn't that interested in daisy chaning anyway, because then i have two separate amps with different tones that i both have to control. I rather change the external speaker jack socket on the Pathfinder into an unswitched version so i have the Pathfinder amp in control of both the internal Pathfinder speaker and the external Sidekick speaker.
     
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