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Input 2 on Deluxe Reverb

Discussion in 'Amps and Cabs' started by GBStratman, Mar 10, 2008.

  1. GBStratman

    GBStratman Member

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    I've had a SFDR with a weber 12F150 that I've always had trouble getting to the sweet spot, mainly because it's too loud. On a whim, I tried plugging into input 2 of the vibrato channel, and voila, I could finally turn the volume up to 6. I finally found the tones I was looking for! By dropping the input signal a bit, I figure this avoids any preamp distortion and just gets the power tube distortion. Is anyone else doing this?
     
  2. Guitar Josh

    Guitar Josh Resident Curmudgeon

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    It's a well known "more headroom" trick in two input blackface amps.

    Try also swapping V1 and V2 with AT7s rather than AX7s. You can probably squeeze additional headroom if you need it by doing that.
     
  3. Blue Strat

    Blue Strat Member

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    Lowering the input signal takes you further from power tube distortion too. It's like turning a faucet open all the way but turning down the water flow into your house with the shut off valve.

    The only way you get power tube distortion is to play LOUD or crank the amp into an attenuator.

    If you like the effect of what you're doing that's all that counts.
     
  4. GBStratman

    GBStratman Member

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    I see the analogy. But what is the difference between plugging into Input 1 with the Volume on 4, vs. plugging into Input 2 with the Volume on 6? Even with the actual loudness the same, it sounds different. Just curious as to why.
     
  5. Blue Strat

    Blue Strat Member

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    Several possibilities including less preamp distortion, lower input load impedance of the #2 input (which will result in different frequency response....probably less highs) and others I'm not thinking of.
     
  6. Guitar Josh

    Guitar Josh Resident Curmudgeon

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    Mike, that's exactly why I don't like input #2. I don't care for the freq response and the highs just drop off the planet. All the shimmer disappears.
     
  7. Blue Strat

    Blue Strat Member

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    I'm with you on this.
     
  8. vibroverbus

    vibroverbus Member

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    sounds like he's saying he gets less headroom and that's why he likes it? I know normally what you say is correct (that's how my traynors work as well)

    to the OP - first I agree Mike about impedance and various subtle RC cutoff differences - change the volume pot and all those tone-network 3db points will change a bit. i'd also suggest the difference is because you are putting mainly the first preamp stage at into different operating characteristics by changing the point on the curve that they are operating at.

    the volume pot is just a voltage divider / attenuator that comes after stage 1. as is the resistor that causes Input 2 to have a lower input level. by switching inputs, you are essentially moving the attenuation location. by giving the first stage a lower input level, operates at a slightly different point on it's performance curve and produces some different harmonic characteristics.

    but beyond that, keep in mind all simple gain stages always amplify at fixed ratio regardless of 'volume knob' settings (at least for simple tube amp circuits like this). all the volume pot does is to 'thrown away' excess gain through a voltage divider afterwards. so unlike what people think, you're not 'revving the engine' so to speak, by turning the volume up.

    once you turn up the volume to accomodate for the lost signal at the front-end, you are pretty much by definition (assuming equal output volume) driving the other 2 voltage gain stages and then the power amp, with about the same signal you had in the first place.

    as Mike says, you can't be driving the power amp any harder (again, amplifying at a fixed rate, so the only way to drive it harder is to be louder or 'throw away' some of the gain after the fact).

    so bottom line is the tone preference is either through some interaction around the volume pot / tone stack, or, from not driving the first gain stage as hard so it is at a place that you like better.

    with time I know a lot of guys who find lowering their pickup height and/or going for lower-gain pickups ultimately end up sounding a lot better than jamming the hottest signal possible into the amp... could be the same effect...
     
  9. GBStratman

    GBStratman Member

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    No, I just like the quality of the distortion better -- less buzzy.

    This makes sense. Although I notice on the schematic that the resistor on the input is before the 1st gain stage, while the volume pot is after the 1st gain stage. I was thinking that what I was hearing was coming from not driving the preamp into distortion (which would get amplified by the 2nd stage and power tubes, each adding their own distortion). But maybe it is all from subtle differences in RC as you suggest.


    Could be!
     
  10. in a little row

    in a little row Member

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    Clear this up for me...dont V1 and V2 have different wiring (caps) from each other, just like main and vib channels are wired differently...this would contribute to the effect you describe...

    FWIW you can get a quicker breakup by cranking the volume to whatever channel you arent plugged in to...

    j
     
  11. Blue Strat

    Blue Strat Member

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    V1 and V2 are virtually, not completely, isolated from each other in Fender 2 channel amps like the DR. The OP is talking about plugging into the 2nd input of a particular channel (there are 2 inputs per channel) so only V1 or V2 is in play for both inputs being discussed.

    Your statement about the alternate volume control is definitely not true of all amps. Which amp are you referrring to specifically?
     

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