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SS Fx Loop schematic

Discussion in 'Amp Tech Center' started by GERPUD, Feb 20, 2015.

  1. GERPUD

    GERPUD TDPRI Member

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    Hi,
    I'd like to add an FX loop to my tube amp (I wanted first to add a reverb tank but I scaled down the project with an fx loop with a reverb pedal...)
    I don't want a kit. The goal is to learn and have some fun.
    I did my homework by looking around the web.
    I ended up with theses two schematics from two sources that I don't remember...
    Are they both going to work?
    Which one would be better and why?
    Comments, recommendations?

    Thanks!!

    Second picute link:
    http://imagizer.imageshack.us/a/img195/5981/4sloop.png
     

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  2. GERPUD

    GERPUD TDPRI Member

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    Little views no post reply....
    I guess fx loop isnt a sexy subject....
     
  3. Cleeve

    Cleeve Tele-Holic

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    It's a difficult subject- the effect loop for a guitar amp needs to take the guitar signal, I suppose post-eq of the preamp, then attenuate it back down to guitar pickup level, buffer the newly attenuated signal, send it out either a switched jack or a proper switch or relay so the loop can be bypassed, then with the return boost the signal back up to where it was.
    That's a lot of trouble for something that really does nothing.
    When I hear effect loop, I think of all the repairs to the switched jacks I had to do back when effect loops were a feature rather than a defect in amp designer's minds.

    Effect loops are further complicated by the multiple standards for signal level they may need to handle/provide depending on what one considers an effect. Floor stomp box? Semi-pro home recording studio level? Proper professional rack effects?
    I'd have to look up the nominal levels, but it's something like -20dB, -6dB, 0dB respectively, all incompatible with each other without attenuation pads and/or boosters.

    That's just me, there may be someone that has a different understanding of effect loops somewhere..
     
  4. GERPUD

    GERPUD TDPRI Member

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    Clint, interesting point of view. Here's how I see it:
    It is true that it is more complicated, but i can t see how to get a nice reverb sound on the drive channel.
    Anyway:
    I was willing to be in trouble first by having tube amp (4x bigger PT, need of a OT, lot of heat, a lot eavier, a lot more expensive, fragile tubes, expensive replacement tubes)
    I but myself a second time in trouble when i began to mod my amp.

    The secondary goal of adding an fx loop is to make it work well and get satisfaction from it.
    The primary goal of adding an fx loop is to waste time on a "healty" obsession.

    Having that said, would one of the two schematic would work with a reverb pedal?
     
  5. Cleeve

    Cleeve Tele-Holic

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    The thing with reverb is it has to be in the right place in the signal to do it's thing, which is to simulate the amp being in a big place. Mainly you want pitch bending effects before reverb, distortion before and tremolo after.. Since this amp is so simple I'm thinking about it like i think about my fender champ. I use a Holy Grail with my champ and use distortion and vibe before it in the signal chain.
    The trick is to make sure the champ is not distorting the reverberated signal, only the dry- but the signal going into the reverb that gets reverberated can be distorted, and sounds fine.

    I do think those circuits you posted would work with your amp possibly, but I think you'd be doing a whole lot of work for possibly little if any benefit.

    I have read good things about that belton reverb module which I assume has the IC used by many effect pedals.
    I think they have a schematic for adding reverb to existing amps I recall seeing that looked good.
     
  6. BartS

    BartS Friend of Leo's

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    Correct me if I am wrong but for an effects loop your only going to have to had an output right after the preamp and right after that before the power amp section. With Jacks the break the circuit when the cords are plugged into the jacks.

    Reason being any external effects you will be plugging in with have signal amplification already in the circuit. So it's not like adding an internal reverb to an amp where everything has to be amplified again.
     
  7. GERPUD

    GERPUD TDPRI Member

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    Here's what I have found.
    They show opamp on their schematic. I doubt that it would be suitable for a tube amp (between preamp and power amp) Also, since I don't want to add a 5V power supply, I don't know how to modify it to use 400V with lnd150 mosfets.
    (In the best case, it is possible to have oscillating 4.15-4.55V DC from the 6.3VAC, but they need 4.5V minimum)
    I would prefer a reverb pedal over the Belton Reverb because you can have more control and more choices on reverb type.

    I'll may give a try one of the fx loop schematic...
     

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