Twin-Like Clean Tone: TwinStack Mod
One of the easiest mods you can do your Blues Junior is to convert the tone stack from standard operation to Twin-style operation. Here’s the deal: The Twin is renowned for its bell-like clean tone. Part of that is having enormous power and headroom on tap, but the way the tone stack is wired contributes to the bright, Twin clarity. In the Twin, you can turn the bass, middle, and treble to 1, and get no sound out of the amp–all frequencies are cut off.
The Blackface tone stack, by comparison, started out with just treble and bass–and a fixed mids resistor. No matter how much you reduced the bass and treble, some mid-frequencies are always present. The Hot Rod series of amps, of which the Blues Junior is a member, added a mids control, but in a nod to earlier Blackface amps such as the Deluxe Reverb and Princeton Reverb, turning the mids control to 1 still left a basic amount of mids in the mix.
The surprising thing is how bassy the leftover mids are and how much they can muddy up your tone. Fortunately, it’s incredibly easy to modify the Blues Junior tone stack to work like the Twin’s. The reward is greater tonal flexibility and cleaner, brighter cleans and more interesting distortion tones. Of course, this works best with the tone stack mod, replacing the wimpy values in the Blues Junior stack with premium capacitors that give more solid bass–and mids.
This mod gives you all of your stock Blues Junior mids tones from about 4 and up on the control and fewer mids, down to none, from 4 and down to 1. It opens up the possibility of an ultra-scooped tone, with just treble and bass, as well as bass-only overdrive, which can be very effective by eliminating middle and high harmonics.
Don’t get me wrong–the Twin is still the King of Clean and no 15 watt amp can pretend to be something it’s not. But this mod is dead easy and opens up some very nice tone possibilities. It’s a popular mod on the Blues Deluxe, Hot Rod Deluxe and Deville, for the same reason. So try it!
All you have to do is connect the left and middle (looking from the back) terminals of the mids control together. This allows the mids control to fully ground out the middle frequencies. You can bend a short piece of wire and stick it into the eyelets in the back of the control. You don’t even need insulation. A piece of bare wire will do fine.
You must, however, make sure that the jumper wire is not longer than the eyelets’ depth, otherwise it could short against the metal portion of the control, which would remove all of the mids. You must also take care not to overheat the control. Use a deft touch with the iron–just enough to melt the solder and fuse to both the wire and the eyelet.
This mod is shown on a cream board, but it works equally well with the green board Blues Junior.
Just to restate one of the points above, the TwinStack will give you a noticeable improvement on any Blues Junior, but the tone stack mod brings out the best by providing more available bass and mids. With more mids on tap from the tone stack, you have more available when the control is wide open, down to zero when the control is at 1. So you improve on the stock tones at both ends.
When we do this mod in the shop, we bridge the center and left mids pot terminals on the back of the board. If you’re going to be pulling the board to install other mods, plan on doing it from the back; it’s faster and easier.
Here’s how: First, start with a short scrap of wire that bridges the two left pins of the mids pot. A thicker clipping from the tone caps or power supply stiffening caps is perfect.
Next, apply heat from your soldering iron to the middle of the wire. Add a little bit of solder if necessary to help the melt.
All done:
I can see the “offenders” on ebay selling the twin stack mod kit and when unsuspecting people buy it all they will get is a little piece of wire and instructions for $15. + $3. s/h . LOL
Dave
Have you done this mod to any other controls? If so what’s the out come
The TwinStack jumper is not a magic fix that works on other controls in some generic way. It’s specific to the mids control and changes its operation from a potentiometer to a variable resistor. It’s not appropriate for any of the other controls.
would be be ok to put a switch so i can go back and forth if i wanted to?
There’s no point to making the TwinStack switchable. The tone stack mod gives you more mids overall, and the TwinStack mod gives you the ability to remove all of them. So you create a larger range of adjustment — from none to more than stock — than you had before.
I was very pleased at how easy this mod was to do, especially for an amateur like myself.
The dialability/sound is great.
I got too excited with it and opened the back of my ‘06 Hot Rod Deluxe to do the mod there.
The C6 is right in front of the terminals on the mid and I don’t imagine it can be done at
this side of the PCB.
I imagine this mod should be done by a good tech who would remove the board to do it on the
other side.
(a man’s got to know his limitations!)
Hi
Thats interesting reading
If I get my amp tec to do this on my blues junior will I have the twin sound and also the stock sound available
Cheers
Frank
If you do the TwinStack mod, it works best with the tone stack mod and power supply stiffening provided in the basic mods kit. It gives you a very broad adjustment range, from less-than-stock mids and that Twin-like clean tone to more bass and mids.
I got a little confused when I was doing this one…I have a 2003 cream board, but the mid pot doesn’t have any pins to solder together, only eyelets. I did the solder connection on the green back, but do I need to do both?
Thanks
Jon
If you installed a jumper on the green side of the circuit board, there’s no reason to connect the eyelets together. It’s two ways of doing the same thing.
Hi Bill
When I bought my blues junior, last month I played it next to a new Princeton. I prefered the blues junior & half the price! Im interested in the mods but dont want to lose the sound of the amp, just to give the possbilities of extra sounds when I want them. Is that what will happen with the mods?
Thank for for your reply on 1’st July
Frank Swindells
England
Most people will agree that the modded amp sounds like a Blues Junior, but the best darn Blues Junior you ever heard. That’s always been my goal. I don’t try to change the basic tone, but improve it.
Which of the mods would most greatly get rid of boxiness?
The basic mods. That’s why they’re the basic mods.
I was attempting to do the TwinStack mod with PCB removed and I can’t help but notice the board in your picture is differant than mine. I have a 1998 Rev. C Green Board. Should I ignore the picture and connect the two terminals as shown?
No matter what board you have, the mids control has three terminals. If you connect the two terminals on the left, closest to the master volume control, you’ve done the TwinStack mod.
will I have to undo this if I install the presence control mod?
No, they have nothing to do with one another electronically. Tone-wise, they get along just fine.
Hello bill,
I have a DRRI amp. I modded mine with some features….
one of the mods, was the inclusion of a mid pot instead of the fixed 6.8 k resistor. I replaced that with a 25k mid pot. my question is, if i turn the pot all the way counter clockwise (minimum position) am i cutting all midrange freq like thw twin mod or am i leaving some??
thank u very much for your concern
To make the TwinStack mod work, you have to connect the wiper of the mids pot to the side of the mids pot that connects to the bass pot. This allows the mids pot to be bypassed completely for super-scooped tone. It also shuts off all sound when all three tone controls are turned all the way down.
Hi Bill,
Just thought I would update progress on my BJ’r. I did the tone stack mod, adjustable bias, power supply stiffening, twin stack mod and changed the volume control to an audio taper. The difference in sound was better but still did not make the amp gig worthy as the sound just kind of disappeared among the other guys, especially the drummer. Then I tried one more thing. I switched out the stock Groove Tube power tubes for 2 Mullard EL 84’s and what a difference! That one mod got rid of the the mushy tone completely and together with your mods, this amp has become one of the best small club amps I’ve ever played through, outside of a Princeton of course. The tone can go from crystal clear with my Strat to down and dirty Skynyrd type harmonics with my Les Paul. Of course it has excellent highs and, with the Mullards, some pretty decent lows now. In most clubs I never have to go above 3 and if I do watch out for your ear drums. It does start to distort around 4. Any effects can be achieved through my pedals. The only thing that might improve the amp at this point would be some 6L6 output tubes like the Princeton. But then if I did that and changed out the speaker I guess it would cost about the same as a real Princeton, cost wise. For no more money than I have in this amp though (I bought it used) it sounds great and solves the issue of weight when carrying it to a gig. I’ve also recorded with it and it does a superb job there as well. Thanks for the help.
Bill,
Got the parts today, did the work and just finished “test driving” the Blues Jr. You’re right, the mod opens up the tone of this amp fantasically! It went from that tone that some call boxy or muffled (to me, it made my Tele sound like a Strat in switch position 2 or 4) and has really opened up. Plenty of bass and the power to project it but most importantly the ability to adjust the tone for a wide range of choices.
My motovation for doing this mod was to be able to play my pedal steel through it for my solo/midi and coffee shop type gigs. Before the mod, the mids were untamed and I wasn’t able to get a useable steel tone (E9 tuning and 18.5k single coil pickup). I put the BJ and steel through the test this morning and was pleasantly suprized! It sounds like a mini twin reverb. High end sparkle, sufficient bass and most importantly control of the mids from none to plenty.
I will have no trouble using this for steel/Tele on my small gigs and for a “no hum” recording rig. I don’t think I could use it for a steel gig with a drummer (maybe brushes though or miked…depends on the drummer) but for sure with my Tele. This Blues Jr is now a very useable and just the ticket for those “in and out” light-duty gigs.
My voltages for plates (11.74) and bias (2.42) came out just as you suggested and the mod was a fun way to spend the evening. Your instructions were very detailed and easy to follow.
This thing sounds like a Fender,
Tom
A friend and I just did the tonestack capacitor mods and the twin-stack jumper mod to a newer Blues Junior. The owner liked the amp because of size and weight but thought it could be more like a “Fender” amp. He was thinking about buying a new speaker, and I’d read quite a bit about Blues Junior’s needing a new speaker, so that was my first inclination, but then I remembered reading about your tone stack mods. To make a long(er) story short(er), the combination of the tonestack and twin-stack mods made the amp sound like it was an entirely new amplifier, it sounds like a real “Fender” amp now!
Bill,
I’m a blues harp player in China.Last year I bought a NOS Blues Junior from the States.It’s really hard for me to fight with the feedback in gigs.Does this mod help to eliminate feedback?Thanks.
Best Regards
BlueSimon
Some harp players say they get better headroom before feedback with the Twinstack because it makes the tone controls less interactive and they can pull out more mids. I think that the best solution for harp is a 10-band graphic equalizer pedal. With it, you can pull down the main feedback frequency and leave the rest of your tone intact. More bands equal more precision, but then you’d need a piece of rack equipment, not a pedal.
Bill,I did your twin stock mod today,my junior sounds really good cant wait to do your basic mods.I want to do a twin stock mod on my hotrod deluxe.Is there anything i need to know about flipping the circuit board to get at it.I assume every thing else is similiar to working on blues junior.Or is there a site as good as yours with illustrations.I am new to all of this.Thanx for your help. Todd
Unfortunately, the only good Hot Rod Deluxe site disappeared a few months back and its former host (Eastern Kentucky University) blocks access via Archive.org. So you’re on your own with the HRDx.
Bill,
I did the twin stack mod, and did not notice much difference. I was careful to make the wire only go barely into the pot’s holes and was also mindful of overheating of the pot. Is it possible that I did it wrong, or is it more likely that the difference is subtle to my ear? I guess what I really mean is if I did do something wrong, would there be a symptom that would be so overt that I could not miss it such as amp simply does not work or explodes or something?
The mids pot does still function (if it’s on one and I turn it to 11 I can hear a subtle change in tone) and I am sure that I put the wire in the correct holes.
I have not done any of the other mods yet but plan to, and I am just hoping that the twin stack mod is so subtle because I have not yet replaced the caps with orange drops yet.
I am very interested in your prices for mods actually done by you as well but when I sent you an email requesting prices a few weeks ago, it was not answered.
Is there a way to contact you for this or should I just email you again?
Thanks for all your info, you provide a wonderful cornucopia of information fir Blues Jr owners and we are grateful for your passion for amp modification
You can verify the correct operation of the TwinStack by turning off all three tone controls. If you’ve done it right, no sound comes out of the amp. You can then turn up the bass and treble for a super-scooped tone.