PreAmp Boost controls

[shebbycaster]

Have any of you circuitry tech gurus experimented with some kind of controls over the sound of the PAB?  Maybe along the lines of the Tw@ R@ck Lead Gain and Lead Master controls?  Maybe changing components on the PAB board so that the change is not so drastic when the PAB is Engaged.

[bobgoblin]

Is this what the "HRM" stuff is?  Internal trimmers beyond what's available in the OTS (which is a "non-hrm" design).

[mcinku]

I didn't try this but maybe some EQ pedal into the loop would do the job...
 

[shebbycaster]

I'm thinking in terms of something that would not affect the sound of either channel with the tone stack engaged but would allow you to dial in the tone and amount of boost that happens when the PAB comes on.  Seems like the first step would be to be able to decrease the amount of boost somewhat.

[mcinku]

I'm thinking in terms of something that would not affect the sound of either channel with the tone stack engaged but would allow you to dial in the tone and amount of boost that happens when the PAB comes on.  Seems like the first step would be to be able to decrease the amount of boost somewhat.

I wrote in the other thread about that mod...


There is a way to reduce PAB boost jump. You can try 4.7M resistors instead of 22M on the switch. This lowers the amount of boost and fattens up the bass while still keeping the overall character of the normal PAB...

 

[shebbycaster]

Thanks.  Correct me if I'm wrong here before I solder anything.  One 22M resistor is on the small board behind the switches and the other is behind the Treble pot.  Both connected to the switches.  There is already a 4.7M resistor connected to the ground buss.  Leave that one as is.

Thanks for taking the time to weigh in on this.

[mcinku]

Thanks.  Correct me if I'm wrong here before I solder anything.  One 22M resistor is on the small board behind the switches and the other is behind the Treble pot.  Both connected to the switches.  There is already a 4.7M resistor connected to the ground buss.  Leave that one as is.

Thanks for taking the time to weigh in on this.

Sorry I was out of town and didn't see this...

Attached schematic is V1 stage from #124 with OTS values in red (first layout values).
You can see from this which resistors are related to PAB.

If you do this please report back, I didn't do this mod yet.
 

[shebbycaster]

OK,  I changed both PAB resistors to 4.7M.  Thanks to mcinku for the help.  I would have missed the fact that there are two resistors to change.

It's tighter than it looks getting a soldering iron in there behind the switches so think twice about doing this and mask things off so you don't burn adjacent wiring.  I disconnected the Orange Drop from the switch, moved it out of the way temporarily to put in the new parts and then re-connected it once the resistors were in.

My first impression is that with the 4.7M resistors I get less of a volume boost from the PAB and more of a mid boost than with the original 22M resistors.  However, your mileage will vary depending on how you set up your amp.  All the controls in and on the amp play a part in making this work.

The jump in volume from disengaging the Tone Stack with the PreAmp Boost depends on how you set your Treble, Middle and Bass controls.  What I mean is, if the levels on the ToneStack controls are set low and then you disengage the ToneStack by clicking on the PreAmp Boost, you get a big jump in volume.  If you have the controls up a bit there is less of a volume boost when the tone stack is bypassed.

My goal was to get all four functions (Clean, Clean + PAB, Overdrive, Overdrive + PAB) to be relatively close in volume with the Boost being a little louder but still similar in tone to the regular channel with the ToneStack engaged.  It's a balancing act that includes all the controls and switches, but I feel like with the 4.7M resistors I'm closer to having four useable functions than I was before.

I listened to each channel with the PAB on and used the Bright, Deep and Rock/Jazz switches along with Volume, Level, Ratio and Presence (basically everything but the tone controls) to get a PAB sound that worked with both channels.  Keep in mind that the Volume and Level controls are key to setting the both overdrive characteristics and the relative volume of the PAB.

Next I tried to get close to that basic tone in each channel using the ToneStack controls.  I ended up with the Volume about 6, Bright on, Deep off, Rock on, Treble 8, Mids10, Bass 8, Level 4.5, Ratio set so Clean and OD channels are consistent in volume, Master fairly low, Presence 8 to 10.  I play blues in the low to medium gain range and I like some chime on the top end.

I haven't played very loud with this yet and I'm not positive that the character of the overdrive has not been affected by the change of resistors.  I'll have to see as I play it more and play it louder.

But I have played both my number 1 Strat (Rocketfire pups) and my Les Paul (WCR American Steel Set) without changing settings on the amp and have gotten good tone from each guitar.  I mean, these amps sound pretty darn good no matter what. 

This amp had all the Zucker Mods when I got it but I put back the small bright cap on the Master Vol.  My internal Gain Trimmer is set at around 9:30. 

Right now my favorite all around speaker set up is a Hellatone 30 (G12H-30) together in the same cab with a Hellatone 60 (Vintage 30).  That's all I've had a chance to play through so far.

Hope this info is useful and thanks for the help.
Rich

[mcinku]

Thanks man, for this detailed report
 

I'm glad it works for you.