Hot Rod Princeton/Blues Jr. Reverb - Scratch Build Amp

[TubeJunkie]

At the request of Papa Jim, here's the Meat and Potatoes:

▫   Building an ~18-20 watt EL84 British-voiced blues amp
▫   It's basically the pre-amp and reverb from a Princeton Reverb followed by the output of the Blues Jr.
▫   Design is based on a combination of various discussion groups, Doug's custom re-builds of a Princeton Reverb and a Blues Jr., and from
    Rob Robinettes various mods.

Mods included are:
▫   5Y3 full-tube rectifier
▫   Raw Control mod - a 250ka pot in place of the Middle pot
▫   Lead Channel Mod making it switchable;
▫   Modified MID pot to take amp to RAW (bypass tone stack)
▫   FAT switch to add bass
▫   Presence/Meat pot for the negative feedback
▫   Bias pot for the power-tube bias
▫   Doubled to 100uf the B+ capacitor to make the bass more beefier
▫   Would like to add a clean boost after the reverb

Looking for feedback/advice on the design – will it work, what looks wrong, what could or needs to be changed, etc.

Want it British voiced, with good bass, and going for a 1x12. Possible speakers include:
▫   Eminence Legend GB128 50 watt
▫   Weber Ceramic 1230-55 50 watt
▫   Supro BK12 - 50 watt (uses a special design ceramic magnet to mimic the response of the original field-coil speakers)

Speaker suggestions are also encouraged.

If it's not entirely Meat & Potatoes, it's probably because I prefer Surf & Turf!

Again, thanks in advance for all your help and input!!

Attached is the schematic of the project:

[Papa Jim]

Welcome TubeJunkie to the forum. It is jampacked full of knowledge. Thanks for the edit. 

[st]

I once built an amp with a Princeton Reverb frontend into an el84 p-p power amp, but kept the cathodyne PI. Didn't care for it much but that's a matter of taste.

Two questions/remarks from a quick glance at your schematic:
1. What makes yours British-voiced, except the el84 and smallish coupling cap in the power amp?
2. You kept the resistor in the third stage to connect nfb, which shifted to the PI. Are you sure this is what you want?

[tubenit]

I love creative ideas and will be interested in hearing how this sounds and works out.  I think it will work. Whether you like the EL84 tone or not with the PR preamp will be a matter of taste.

I personally would change the EL84's to 6V6's.

With respect, Tubenit

[Swampertech]

TJ, what cabinet and chassis do you plan to use? 12" Celestion Gold might fill the bill. Very interesting design.

[TubeJunkie]

ST . . .

I said British-voiced, but a more accurate term may be that I want to combine the somewhat limited (but with great potential when modded) British bluesy tone of the stock Blues Jr. with the Fender Princeton Reverb.  I’m hoping to blend the well-liked classic tone of the Princeton, it’s great reverb unit, and it’s additional 12AX7 gain stage following the reverb, all in hopes to push the amp to heavier saturation when played at breakup volume; and then putting this into the Blues Jr. power amp section, and adding mods like a MID/RAW that completely by-passes the tone stack, the NFB (negative feedback) mod, etc.

The NFB mod (what I’ve called Presence/Meat) is based on a Billm presence control mod and a mod Doug Hoffman incorporated into a Blues Jr. rebuild he did.  Billm’s mod replaces the negative 7k5 feedback resistor with a 10k pot, and Doug’s does the same thing, using a 1M pot.  In the words of Billm (RIP), “this lets you adjust presence from a brighter, louder tone that puts an aggressive edge on your pick attack to a more laid-back sound that is a warmer, mellower tone that swallows pick attack and lets the note bloom out.”  Billm and Doug have forgotten more than I’ll ever know about guitar amps, so I can’t argue with this mod.

However, if you see or believe there's a possible problem with the design, let me know, and give your reasoning - that's why I put it on here.  I am by no stretch of the imagination a guitar amp expert.

[TubeJunkie]

Tubenity . . .

I’ve got a home-built Fender Deluxe and a Fender Excelsior for that Fender-y 6V6 tone, and I have a couple of EL84 amps as well, including a Peavey Delta Blues 115.  However, I’m intrigued by the POSSIBLE tones that a hot-rodded Fender-EL84 combination could produce.  Could be great or could sound like I plugged a $25 guitar into an old mono-cassette tape player with a speaker that has a torn cone and a blown voice coil.  Whatever the outcome it’ll be fun finding out what it turns out to be.

[TubeJunkie]

Swampertech . . .

This is a complete scratch build, so I’ll be using a blank aluminum chassis and laying out all the holes and cutouts based on the final design and will be putting it into a custom-built open-back combo cabinet - this gives me the most flexibility.  As a combo, it’s a great grab and go (if it turns out), and then of course, there’s a reason God created extension cabinets.  Thanks for the suggestion, I'll keep the 12" Celestion Gold in mind, but then I do have "Alnico" tastes, yet have to live on a "Ceramic" budget (just ask the wife).

[st]

ST . . .

I said British-voiced, but a more accurate term may be that I want to combine the somewhat limited (but with great potential when modded) British bluesy tone of the stock Blues Jr. with the Fender Princeton Reverb.  ...

The NFB mod (what I’ve called Presence/Meat) is based on a Billm presence control mod and a mod Doug Hoffman incorporated into a Blues Jr. rebuild he did. 

However, if you see or believe there's a possible problem with the design, let me know, and give your reasoning - that's why I put it on here.  I am by no stretch of the imagination a guitar amp expert.

Hi,

I see no reason it wouldn't work. Like you said, Fender itself has coupled its frontend to an el84 power amp (both in the brownface era and more recently, as you said).
I was merely wondering why the 47r tail resistor is still present in the third gain stage when you no longer use it as the nfb injection point.

[TubeJunkie]

ST . . .

This is my understanding of how it works:

In the diagram below of the original Blues Jr. NFB design, R22, R21, and C12 work with the NFB to act as a fixed presence control. R21 and R22 form the first half of the NFB voltage divider, with R23 (the NFB resistor) being the other half.  An RC low pass filter is formed with the NFB resistor (R23) and C12.  Frequencies below the cutoff level are passed along, but high frequencies from the NFB signal are shunted to ground through R22.  This is what boosts high frequencies at the speaker.  R21 limits how effective the filter is – in other words, it controls the "volume" of the filter.

In my Modified Blues Jr. NFB design below, I’m adding a 1M pot and 22uf cap to allow for adjustment of the negative feedback, and as far as I know/understand, R22 – the 4.7k tail resistor you mentioned – is still necessary for frequencies below the cutoff level to be passed along, and the high frequencies to be shunted to ground.  At least this is how I understand what’s going on.  If I’m wrong, I’d more than appreciate someone explaining how/why it should/could be different.

Thanks for the feedback.

[sluckey]

The main purpose of R22 is to give the tube cathode a dc current path to ground. If you remove that resistor from the original you will strangle the PI tube. If you take it out in the modified circuit you will instantly kill the PI tube.

[TubeJunkie]

After input from Rob Robinette, I've made a small modification.  When I asked him about his "Lead Channel Mod" he said that this mod changes the cathode resistor R18 from 1.5k to 2.7k, the cathode bypass cap C7 from 22uf to .68uf, the load resistor R17 from 100k to 220k, and changes the coupling cap C13 to a smaller value.  He also told me that the coupling cap has the greatest effect on tone, the plate load resistor next, the bypass cap next, and the cathode resistor the least.  Originally I had only used the cathode resistor and cathode bypass cap mod, making it switchable between normal and lead.  I've decided to make all the changes, except the coupling cap, and see if I can wire it to a DPDT 2-position On-On switch - hopefully with little-to-none noise and signal loss.

[TubeJunkie]

sluckey . . .

That would certainly ruin my day, not to mention the tube.  Thanks for the info.

[DummyLoad]

100uF for a 1st filter could result in very short life of the 5Y3. suggest use of RC filter 32uF > 20R > 32uF > B+.

you could probably get away with 47uF/50uF but likely pushing the peak plate current spec of the 5Y3 with that 150mA PT.


--pete 

[Swampertech]

TJ, I used Rob's two preamps in my first build (5E3 Madzar Deluxe), and they both sounded great!! The Bright channel (Rk-1.5k, Ck-25uF, Rp-100k, Cc-.022uF) is Fender, and the Lead channel (Rk-2.7, Ck-.68 Tantalum, Rp-220k, Cc-.0047uF) is Marshall. Bright channel is warm, clean, and jazz voiced. That Lead channel has got some great crunch and overdrive. I'm using both in my second build, Mr. C-Verb SL, which is housed in a PR cabinet. I'm attaching the preamp schematic.

[st]

ST . . .

This is my understanding of how it works:

In the diagram below of the original Blues Jr. NFB design, R22, R21, and C12 work with the NFB to act as a fixed presence control. R21 and R22 form the first half of the NFB voltage divider, with R23 (the NFB resistor) being the other half.  An RC low pass filter is formed with the NFB resistor (R23) and C12.  Frequencies below the cutoff level are passed along, but high frequencies from the NFB signal are shunted to ground through R22.  This is what boosts high frequencies at the speaker.  R21 limits how effective the filter is – in other words, it controls the "volume" of the filter.

In my Modified Blues Jr. NFB design below, I’m adding a 1M pot and 22uf cap to allow for adjustment of the negative feedback, and as far as I know/understand, R22 – the 4.7k tail resistor you mentioned ...

I was talking about r29... PI looks fine

[ac427v]

I'm thinking you may have too much transformer for a 2-EL84 amplifier. 310-0-310 at 150ma won't load down like a proper EL84 transformer so the real world B+ will be more than your goal of 340volts. How much more??? maybe too much.
If you're determined to use 100uf for your first power supply cap like the EL34 Marshall amps then you really should be using solid state diode rectification--and that would bump B+ way up there!

[TubeJunkie]

Swampertech . . .

I agree that Rob has a wealth of great information available on building and modding guitar amps.  I feel like when I was a kid and I would walk into the toy section of a large department store, and just spend all my time looking and wanting to try them out.
 
Interesting design.  You’ve run your signal through three triodes before the reverb, and then a fourth just before the trem.  Are you getting a lot of clean gain out of that design?  How does that 6GH8A work/sound in the reverb?  I’ve never seen/heard of that tube being used in a reverb before.  Not only that, you’re using it as both the driver and recovery.  Very interesting.

[Swampertech]

Swampertech . . .

I agree that Rob has a wealth of great information available on building and modding guitar amps.  I feel like when I was a kid and I would walk into the toy section of a large department store, and just spend all my time looking and wanting to try them out.

RR does have a wealth of knowledge and experience with tube amps, as does sluckey ( along with a lot of guys on this forum). My first build was using mostly RR's mods, since it was a Tweed based 5E3. I used the lead input voicing and the stock Fender 5E3 normal voice. I tried the Braxendall TB tone stack just to eliminate the interaction of the two channels sharing one tone control. Other mods I implemented were the FB bypass switch, hi/low power tube and rectifier ability (6L6/GZ34 and 6V6/5Y3), and a fixed/cathode bias switch.
 
Interesting design.  You’ve run your signal through three triodes before the reverb, and then a fourth just before the trem.  Are you getting a lot of clean gain out of that design?  How does that 6GH8A work/sound in the reverb?  I’ve never seen/heard of that tube being used in a reverb before.  Not only that, you’re using it as both the driver and recovery.  Very interesting.

TJ I haven't built this yet, still ironing out some parts. The Reverb circuit using a 6GH8A resulted from needing reverb, but only wanting to use one tube. So, a pentode/triode package provides the necessary drive for the tank, plus the recovery triode. Had to use sluckey's Tremor-lator, with the Mod#2 by 2deaf. The design uses only one triode, which left me with a mixing triode for Rev and signal wobbling by the Tremor-lator. Again, I don't know how it will sound till it's together. One thing I'm looking at is the PS filtering. Also, if I use this matched pair of British made Kt66's I've got , the tube data sheet says that I've got to have separate cathode resistors and capacitors. I plan to incorporate the fixed/cathode bias switch in this amp also. Keep up the good work on your amp.

[TubeJunkie]

ac427v . . .

After your post, and talking with others who know much more than I do, I'll be using the 47uf as first filter cap, and NOT the 100uf . . . something about overloading, blown tubes, smoke, etc.

However, I did find a great web site, “Tube Amp Power Transformer Current Draw Calculator” (http://thesubjectmatter.com/calcptcurrent.html) that calculates voltages at the first B+ filter capacitor, the 6.3v secondary filament current, and current draw.  The Allen Amps TO20B output transformer has a 6.6k primary impedance, and the specs for the Allen Amps TP25 power transformer are:

    Amp Power:        310V-0-310V @ 150ma
    Rectifier Heater:  5V @ 2A
    Filament Heater: 6.3V @ 4.5A
    Bias Tap:            50V

Using the calculator, the values I came up with for a 310-310 150ma power transformer are:

    First B+ Filter Cap Voltage:            376Vdc                         
    6.3V Secondary Filament Current:  2.84
    Current draw:                               138mA

The current draw calculation is based on all pre-amp tubes being 12ax7; except that for me, the reverb tube I’ll be using is a Mullard CV4024 (a military-spec 12AT7).   Therefore, I needed to add 7.5 mA to the current draw, making it the 138mA.

With an output of 376Vdc and a max 138mA current draw, the PT should be just fine.  I’ll need to add a step-down resistor before the first filter cap to bring it down to the 340Vdc, but everything looks like it should work.

I feel like I'm getting close, and I've updated my schematic (below), but I'm still working out some values for the step-down resistor, and the resistor and cap values for the adjustable-bias.  Any insight here would be appreciated, and if anyone sees a mistake, please let me know.

[ac427v]

Lookin good! I had never seen that calculator before. Looks like a keeper. I like that it includes all the important factors in figuring B+ without being complicated to use. Sorry I don't understand the math enough to help with the size of the dropping resistor before the reservoir cap. Hope I can learn more from your experience.
A previous poster mentioned that R29, the tail resistor on the third stage is not needed. Doesn't hurt but would be a little simpler to build if omitted. It's original purpose was to provide an insertion point for negative feedback with the Princeton Reverb phase inverter. The Blues JR phase inverter has its' own insertion point.

[TubeJunkie]

Okay, so more research has revealed that the 5Y3WGTB rectifier has a 1.1Vdc increase, and not a 1.25Vdc as originally used for calculating.  This means that my B+ voltage will be

     310Vac * 1.1 = 341Vdc

This is right where I need to be for the B+ of 340Vdc I was looking for, so I won't need the step-down resistor.  I also made a couple more changes:

    1. I moved the Standby Switch to just after the filter reservoir cap and added a 47k 2W trickle resistor.  This will slow the current as the capacitors "fill up,"
        placing less strain on the rectifier tube, and will make the 47uf reservoir cap more "bearable" to the rectifier.

    2. I'm contemplating a Reverb Dwell Control to be able to tweak how the reverb sounds.

    3. I could replace the .01uf C11 cap with a .1uf cap to tighten up the bass even more.  I'll probably wait on that one to see how the .01uf sounds first.

I think I may have finalized everything, but as always, I'm still looking for feedback, suggestions, and someone to point out the too often over-looked glaring mistake.  Thanks for the feedback so far . . . now off to convince the wife how much I really need to build this amp.

[PRR]

> suggestions

The Lead/Normal switch will POP bad. I think after the first time, you won't do that while the amp is turned up. It might work as a Saturday/Sunday switch (louder than the drunks in the tavern, then softer than the preacher). I doubt it can be used chorus-bridge-chorus, unless you can blame your drummer for the POP.

C11 larger has about no effect. Even a somewhat smaller value has no effect.

R29 does nearly nothing; is probably left-over from something you stole.

[galaxiex]

I have nothing meaningful to contribute.... but here's my Blues Junior that I hand wired.

Very similar to what you are doing.

[TubeJunkie]

galaxiex . . .

It's very similar, because you're design is one of the inspirations I had for this build.  After deciding I wanted to scratch-build a modded Blues Junior, I started searching the Web.  I have taken ideas from you, Doug Hoffman, Rob Robinette, Bill Machrone, and several forum members.  I'm by no stretch of the imagination an amp design guru, and so have relied on others for more knowledgeable advice . . . so THANKS!

How does yours sound?  It looks like you opted for the smaller reverb tank.

[TubeJunkie]

PRR . . .

I knew from the beginning that the Lead/Normal switch would probably pop, but what I was thinking was that for the DPDT switch I would use an ON-OFF-ON, and not just an ON-ON.  This way I could wire in a 1MΩ pop-stop resistor between each side of the Normal and Lead channels.  I don't know if it will work, but this was my initial idea to get it to work, and prevent the pop when switching – similar to a Standby pop-stop.  Any feedback/recommendations to this idea would help.

Can't remember where I found/saw the C11 mod. It sounded interesting, and so was contemplating on whether or not to do it.  I'll try and find the reference to better understand the reasoning – but I remember it having an effect on the bass response.  Perhaps you could elucidate for me as to why it's not worth changing, and make some suggestions, which would be greatly appreciated.

R29 is in there because as I made perfectly clear, I "stole" many design ideas from several sources, including Doug Hoffman.  The reason Doug kept it there is something Doug would have to address.  The reason I have it there is because who am I to argue with someone who has probably forgotten more than I'll ever know about guitar amps?  What your reason for your position that it does nearly nothing?  I would very much appreciate the edification.

Stolen, schmolen . . . like the guy who "stole" the design idea of the Fender Bassman, and then eventually came up with the JTM45 . . . if only I could be so fortunate . . . (sighhhhhhhhh) . . . oh well, I'll just keep smiling, and move on to another amp project . . . which always makes me smile . . .

[galaxiex]

galaxiex . . .

It's very similar, because you're design is one of the inspirations I had for this build.  After deciding I wanted to scratch-build a modded Blues Junior, I started searching the Web.  I have taken ideas from you, Doug Hoffman, Rob Robinette, Bill Machrone, and several forum members.  I'm by no stretch of the imagination an amp design guru, and so have relied on others for more knowledgeable advice . . . so THANKS!

How does yours sound?  It looks like you opted for the smaller reverb tank.

Thanks for the kind words.  ...and you are very welcome! :)

I also am no amp guru...
This was my first "build" and no one is more surprised than me that it came out so good.

To me it sounds awesome, very usable tones at almost any knob settings, very easy to dial in...
whereas before, the stock BJ seemed to have *one* setting that sounded ok
and it seemed like the slightest bump of a knob and it was gone...
Very much a one trick pony...

I used the small tank cuz the BJ cab is just a hair too small for a full size tank.

The small tank sounds ok, but a big tank does sound better.

Could squeeze a big tank in with some cutting....

A better (solid wood) and sightly bigger cab would be an improvement, but mine sounds great as is,
So I'm in no hurry to buy or build a new cab.
Maybe someday...

Cheers!

[PRR]

Larger cap with same resistor load is a path to deeper bass, yes. C11 appears to drive a 1Meg load. 0.01u and 1Meg is a common combination and gives -3dB at 17Hz, far below guitar or even bass. But the 1Meg is actually "bootstrapped" from the cathodes tail and acts-like roughly 2Meg. Response is -3dB @ 8Hz. -1dB @ 16Hz, -0.5dB @ 32Hz, insignificant effect even for bass's 42Hz low-note. Changing from 0.01uFd to 0.1uFd moves this down a decade (3 octaves). But 0.01u was already ample, 0.1u won't be more ample.

That's for clean signal. In heavy overdrive V4 grid tries to go positive, which really puts charge on the cap to de-bias V4, "blocking". This may be insignificant because the 220k in series limits the charging current. But if it does "block", it recovers according to the cap. A just-big-enough cap may recover very fast, before the next note. A real-big cap may cause sound to "faint" for several notes after a big hit.

I think your on-off-on scheme will still POP. You cut-off tube current. Plate node sits at 175V then *jumps* to 250V, then back to 170V. 75V jumps at a point where signal levels are few-Volt. I'll be curious to hear what you think when you try it.

[sluckey]

R29 is in there because as I made perfectly clear, I "stole" many design ideas from several sources, including Doug Hoffman.  The reason Doug kept it there is something Doug would have to address.  The reason I have it there is because who am I to argue with someone who has probably forgotten more than I'll ever know about guitar amps?  What your reason for your position that it does nearly nothing?  I would very much appreciate the edification.

That part of the circuit was stolen from the Princeton Reverb which uses a cathodyne PI. The top of R29 was the injection point for the NFB loop. But your BJ uses a LTP PI and it's NFB loop injection point is at the second grid (and cat tail) of the LTP PI. All this makes R29 useless. Just remove it and connect R28 directly to ground. R29 also is causing no harm in case you want to leave it there so you can have these little chats.

[galaxiex]

R29 is in there because as I made perfectly clear, I "stole" many design ideas from several sources, including Doug Hoffman.  The reason Doug kept it there is something Doug would have to address.  The reason I have it there is because who am I to argue with someone who has probably forgotten more than I'll ever know about guitar amps?  What your reason for your position that it does nearly nothing?  I would very much appreciate the edification.

That part of the circuit was stolen from the Princeton Reverb which uses a cathodyne PI. The top of R29 was the injection point for the NFB loop. But your BJ uses a LTP PI and it's NFB loop injection point is at the second grid (and cat tail) of the LTP PI. All this makes R29 useless. Just remove it and connect R28 directly to ground. R29 also is causing no harm in case you want to leave it there so you can have these little chats.

Which R29 are we talking about? 

I see 2 of them.... and one of them is a plate load on the LTP...

[sluckey]

Which R29 are we talking about? 

I see 2 of them.... and one of them is a plate load on the LTP...

I'm betting you can figure this out. Read my post again for clues. 

[TubeJunkie]

Sluckey/PRR . . . 

Ohhhhh, THAT R28 & R29 . . . NOW I see the confusion . . . I haven't had the time to go back and check the numbering of caps and resistors due to the mish-mashing (stealing ) of different designs and mods, and so there are two R28s and two R29s.  The whole time I was looking at the PIs R28/R29, since that's where the Blues Jr. injects the feedback; completely forgetting that the PR injected it back at the gain stage BEFORE the PI between that R28 & R29.  Now I need to find the time to fix the cap and resistor numbering.  Thanks guys for the help and insight – Doug was right, this is where I need to be to get help with this project.
 

Also, I found this on the Aiken Amplification site:

"The input coupling capacitors: Too large of a coupling capacitor will increase the tendency for the phase inverter input to generate "blocking" distortion.  If C1 (C11 on my schematic) is made small (less than .01uF or so, with 1Meg grid resistors), it will improve the low frequency response balance between the two output phases if the second coupling cap, C2 (C12 on my schematic), is made at least ten times larger than the first cap, C1."

C11 = .01uf
C12 = .1uf

So, it looks like the C11 .01uf coupling cap (I think it's the only C11) going into the PI will stay how it is.

No, the numbering isn't fixed on this one yet . . .

[galaxiex]

Which R29 are we talking about? 

I see 2 of them.... and one of them is a plate load on the LTP...

I'm betting you can figure this out. Read my post again for clues. 

Yup, I had already figured it out... 

I was posting for the benefit of others that might not.... 

[PRR]

> Which R29 are we talking about?  I see 2 of them....

Larry Daryl and Daryl.

George Foreman's sons (all "George").

[TubeJunkie]

> Which R29 are we talking about?  I see 2 of them....

Larry Daryl and Daryl.

George Foreman's sons (all "George").

Who's on First
https://www.youtube.com/watch?v=kTcRRaXV-fg

[pullshocks]

For your V1A cathode circuit, an alternative that might not pop as much would be to have a 2.7k wired permanently and switch a second 2.7 k resistor in parallel to get close to the normal Fender RK value of 1.5 K.  You could include the larger cathode bypass cap in this switching setup.

[TubeJunkie]

For your V1A cathode circuit, an alternative that might not pop as much would be to have a 2.7k wired permanently and switch a second 2.7 k resistor in parallel to get close to the normal Fender RK value of 1.5 K.  You could include the larger cathode bypass cap in this switching setup.

I like that idea.  I'm going to draw something up and see where it leads . . .

THANKS!!

[TubeJunkie]

Okay, so thanks to pullshocks I've re-designed the Normal – Lead switch.  Instead of a DPDT, I'm using a 3PDT.  This switch allows me to put everything in series.  This means with a single flip of the switch I can go from 100 kΩ to 220kΩ to the plate (100k + 120k in series), and go from an RC of 1.5kΩ and 22uf, to an RC of 2.7kΩ and .68uf on the cathode.  For the lead cathode, the resistance in series (1.5K + 1.2K) gives me the 2.7k, and for the capacitance of 22uf and .68uf in series, I get:

                     C1 * C2
        Ceq =  ------------
                     C1 + C2


                     22uf  * .68uf
              =  ------------------
                    22uf  + .68uf



                     14.96uf^2
             =  -------------------
                      22.68uf


             =  .66uf

This is well within the 10% tolerance of the .68uf cap value.

I'm hoping this will minimize, if not eliminate, a nasty pop when switching, and so I'm also considering a 1MΩ pop-stop resistor between lugs 1 & 3 on the switch, just to keep a little current flowing when going back and forth between 100kΩ and 220kΩ.

As always, comments and suggestions are welcome and appreciated (this means I can use all the I can get).

[DummyLoad]

> suggestions

The Lead/Normal switch will POP bad. I think after the first time, you won't do that while the amp is turned up. It might work as a Saturday/Sunday switch (louder than the drunks in the tavern, then softer than the preacher). I doubt it can be used chorus-bridge-chorus, unless you can blame your drummer for the POP.

R29 does nearly nothing; is probably left-over from something you stole.

Like BANG pop bad! turn vol all the way down before switching... add a 10Meg across the anode R switch poles MAY help some, 100K across the cathode R/C poles would work. i'd compromise on the anode R at 150-180K and ditch anode R switch.


--pete