Gain Stage Added to Deluxe Reverb

[Sasquach]

I have been thinking about how to do this for a while now without adding another 12AX7.  If you ask why I want to do this then my answer is to see if it will work.  After seeing the AA864 Musings on Sluckey's page, I came up with the following idea.
 
Take the output from the Normal Channel (V1) and feed it to the volume pot of the trem channel (V2).  That way, the Trem Volume pot acts as a Gain pot.
 
In order to do this I use a TPDT switch.  When in Gain mode, the switch will:
Disconnect the trem channel at the tone stack (which disables the trem channel)
Change the cathode resistor at V2B to 1.5k with no bypass cap.
Disconnect the normal channel which allows trem/reverb on both channels

I haven't done this yet but I simulated it using the LTSpice model for a Deluxe Reverb from Jim Ryan.  Attached is the LTSpice Schematic with an input of 50mV at 1000Hz.  I have a VVR in the amp which explains the 0.047uF and 1M at the channel inputs and volume pots.

With both pots at 50%, the signal shows no clipping.  With either pot at 40%, the clipping starts. See attached

What problems do you see in doing this.  Popping from the switch?  Horrible sounding output?

EDIT:
I hardwired this to add the additional gain stage to see if there are any problems and it works well. 


 

[Sasquach]

Bump

I hard-wired this and it works well.  I'll add the switch to see if that causes any issues (i.e., popping, etc.)
I'm not sure why there are no comments/criticisms

[sluckey]

EDIT:
I hardwired this to add the additional gain stage to see if there are any problems and it works well.

I assumed this statement to indicate it was a done deal, case closed.

 

[Sasquach]

Schematic update to show switch pinouts.

[acheld]

With regard to folks not commenting -- this topic would normally generate good discussion. 

But, speaking for myself, it is not easy to read LT Spice schematics without some orientation -- such as where is HT1 coming from, etc.  I have just enough LTS experience to know what to look for, but it is not the same as our usual classic Fender (or Hiwatt, or ) schematics.

Just a thought.  I've just bought Kuehnel's Guitar Amp Circuit simulation book, but haven't had the time to dig in . . . 

[eggbert]

why not just lift vibrato ground to get that extra gain ? And /or tone stack lift (both with switches and resistors.  ( i get no popping ) and the guitar still responds.  I also found pushing the front end too much causes a lot of oscillation a cant control with snubbers.  Just a thought.

[Sasquach]

With regard to folks not commenting -- this topic would normally generate good discussion. 

But, speaking for myself, it is not easy to read LT Spice schematics without some orientation -- such as where is HT1 coming from, etc.  I have just enough LTS experience to know what to look for, but it is not the same as our usual classic Fender (or Hiwatt, or ) schematics.

Just a thought.  I've just bought Kuehnel's Guitar Amp Circuit simulation book, but haven't had the time to dig in . . .

I didn't think of that.  The schematic was mainly to show the switching.  I guess I should have just zoomed on the switching part and showed that.

[Sasquach]

why not just lift vibrato ground to get that extra gain ? And /or tone stack lift (both with switches and resistors.  ( i get no popping ) and the guitar still responds.  I also found pushing the front end too much causes a lot of oscillation a cant control with snubbers.  Just a thought.

I did this mainly to see if it would work, which it seems to.  I have a tendency to tweak just about everything I own, sometimes with unintended results (usually bad).   

I already have a switch to lift the vibrato ground.  With this mod and the vibrato ground lift, you can almost go from clean to overdrive or from overdrive to fuzz with the flip of a switch.  I'm still playing around with it.  The VVR prevents my wife and the neighbors from complaining.

I ordered a 3PDT slide switch from Mouser to replace the bright switch (DPDT) on the front panel.  Now I don't have to do any drilling. 

[Sasquach]

Update: Replaced the Normal Bright switch with a 3PDT switch and this mod seems to work well for my un-trained ears.  I'm getting some popping when switching though.  I'm going to try to add some 1M resistors to reduce this.

[Sasquach]

The switch is causing popping and I'm trying to reduce the effect.  In the schematic, I have added 1M resistors across select terminals of the switch to precharge caps and prevent popping.  See attachment. I've only included the relevant portion of the schematic to show caps that are involved in switching.  Do you see any that I am missing?  Taking the switch in and out is a real pain so I only want to do it once.

[PRR]

Wasn't there a 47k to ground after that 3.3Meg?

[Sasquach]

Wasn't there a 47k to ground after that 3.3Meg?

I only included portions of the schematic related to the switching.
I attached the Weber Schematic and it shows a 220K to ground after the 3.3Meg.