Badmaster gain mod, hey Bob P :o)

[Satamax]

Hi everybody!

Just a quick gain mod easily reversable. You plug the guitar into the vib chanel. a jumper jack between Vib input 2 and normal input one

http://satamax.free.fr/bandmastermod.jpg

Guys, i love this daft simple mod. What do you think?

Bye.

Max.

[Bruce / Mission Amps]

I don't get it... what's the difference between this and the switch jack closed being the same as stock?
Do you put an on-off pedal in that jack in red so the two channels are in parallel with a jumper from the other channel?

[Satamax]

Hi Bruce!

For once it's me telling somebody else.

Basicaly output of vibrato chanel is on the tip lug of the jack, which has had everything else disconected. Then the grounding contact of that socket goes to the 220K mixing resistor. it's absolutely normal in this mode, exept that you can't plug anything in input two Then when you plug a jack in input two of the vib chanel, it makes a preamp out and disconects the link to the mixing resistor, giving no output into the PI. Take the other end of that jack into input one of the normal chanel, and you have 4 cascaded gain stages instead of two It's far too much, but can give some instruments some oomph that they lack. I love the simplicity of this Instead of jumpering the two chanels (which is still possible from the normal chanel) I have a gain machine. Without drilling any holes or anything. Ok it's not footswitcheable, but i could do a A/B box sending normal signal into normal input 1, or vib input one, and have the normal/high gain switching this way. I would need to find some way of taming the output of vib chanel before i send it to the normal chanel, may be a special jack vith a good shield (i have hiss probs at high gain) and a litle voltage divider inserted inside.

HTH.

Max.

[TD_Madden]

Maybe I don't understand...but jumpering the two channels has been well-known for a long time....

Am I missing something?

[Satamax]

Maybe I don't understand...but jumpering the two channels has been well-known for a long time....

Am I missing something?

Yes you obviously are. Guitar into vibrato chanel, then amplified by the two halves of the 12AX7, then it goes to the jack, which when a jumper lead is inserted, cuts the signal to the power amp, and sends it to whatever you plug the other end of the jumper lead into, in this case normal chanel, then the signal from the output of the vibrato chanel preamp is amplified again by the normal chanel two halves of a 12 ax7 before hitting the PI and power amp Clear???

[TD_Madden]

OK, I see now....I had misunderstood originally by thinking no circuit change was made...looking back at the schem I see where you updated.

[TD_Madden]

The mods I made on my Bandmaster were:

1. replace the tremolo intensity pot with one that had a switch. Taking the trem completely out of the circuit gives a VERY nice gain boost.

2. add a mid-control by putting a pot into the second speaker-jack hole and run a jumper from the existing tone controls....a very simple mod that gives the amp much more of a voice.

[Satamax]

Hi TD, thanks a lot for your reply! I gonna do the mid pot mod, but in the grounding switch hole. Grounding switch has to go. I gonna repalce the PT by this one http://cgi.ebay.fr/FENDER-EXPORT-POW...QQcmdZViewItem and add an octal socket so i can use a 5Y3 and drop the voltage a lot, in order to use 6V6 () and i'm searching for a way to have a variable NFB May be make a new cover for the second octal hole, with a pot hole into it. Th emod i've done, you could also do using the grounding switch hole and a DPDT. I've done this on sound cities

[TD_Madden]

I was going to use the groundswitch hole as well, but it made me nervous to put a pot there by the a/c.

By the way, I misspoke regarding the tremolo switch...I actually did that to a SFVR I have...I'm using the ground-switch on the bandmaster to do the tremolo switching (because I didn't have another switched-pot).

[Rick Erickson]

An interesting approach. I would try plugging the (preamp) output into the #2 jack of the Normal Channel. This will reduce the overall gain a bit and remove some of the Bass (probably a good thing) due to the loading on the .1uF coupling cap from the Vib Channel. For the record, you have 3 cascaded gain stages before the Normal Channel Volume control, which effectively becomes the Master Volume, and one stage after the Master. That's a lot of gain for an otherwise stock Fender. How does it sound? Is the distortion pleasant if you turn down the Normal Volume and drive the Vib Channel hard? I would think it would be rather harsh if you are using it this way. Looks like it might be prone to oscillation too - particularly because you are running the output of inverting stage #2 (180+180 = 360 Deg.) very near inverting stage #1's input jack on the Vibrato channel. Just my $.022, ymmv

RE

[stokes]

Yeah,but if you reverse it and try to sell it to a collector....just kidding,interesting looking mod,I cant wait to devaluate somebodies "priceless" Silver face,to check it out.Like Rick asked,how is the distortion quality?I am sure you could tweak the gain in each stage to tailor it,but that would really bring the resale value down.

[Satamax]

Hi everybody

Rick, well, i haven't tried to plug in Input 2 so far! The distortion is pleasant up to three on both chanels, it's hard to lower the "master" volume with the pre volume up without ending up sounding like crap, and i haven't been able to crank this thing up past something higher, i bet if one can whistand the acoustic presure, the solution is to crank the master, and use the pre as a gain boost of some kind. It gets square wavey extremely fast, hence i was speaking of making a voltage divider cable, which i might well do today So far i haven,'t noticed any oscilation.

Stokes, it's invisible from the outside, and from teh inside, there's no unreverseable wiring, just solder back the pre out wire where it ough to be, on the 220K mixing res. The 68K back on the tip lug of the jack and the 1M on the shorting lug, and it's back to completely original. And as far as tweaking the gain level, CF the voltage divider lead idea I should admit that in a silverface, i'd do this hardwired with a switch. If only i could find dpdt switches the same as the bright switches on the old fenders I'm trying to stay as sensible as possible on this one. Only thing, i want to use 6V6

[Satamax]

Hi everybody!

Well, tried the voltage divider cable 470K/220K to ground, this is not enough imho, but can be nice, still too loud for home use Could nail a cool early santana sound. Next step, using a pot on the cable to see how low i have to go I'm on my way to check a boogie schemo, see what they did

Something which crossed my mind, i could do a kind of sensitivity switch with teh ground switch, connecting a 22K or something like this, between common point of the two mixing resistors and ground

[stokes]

Max,I was just kidding about the "devaluation" and resale thing.I have no problem modding an amp I own and never think about what its value would be to someone else,I want it to sound or perform as I want and would not worry what a collector would or wouldnt pay.

[Satamax]

Cool Stokes! Ney bother

Well, i tried 10 times voltage divider today, far too much, so half is not enough, and ten times is too much! I gonna try a third tomorow.