freestompboxes.org

Hey all,

I didn't see any solid threads out there for the blues junior. I only have 2 big questions, but, mostly, I just want people to post their ideas.

1. How would I go about changing the fat switch's capabilities. As far as make it boost more, or a different frequency.
- I'm looking to make it like the beefy midrange of the John Mayer Two rock amp. (I know that there's a lot more than different capacitors in the two rock

2. I don't use the spring reverb. What things could go in place of where that knob / circuit could be?? Any ideas??


Thanks

as far as reverb goes it's solid state so it won't leave you with a spare tube if you choose to remove it...not much you can do with it

I know you might not be interested anymore considering this thread is several months old, but who knows, maybe someone searching the forum will find this useful.

Bill M has some mods including adding a presence control and using the spare half of a 12ax7 to drive the tone stack. He also shares his findings on changing the caps in the tonestack. I decided to use tweed values for the presence circuit and tonestack in mine, which involved changing the slope resistor in the tonestack and slightly changing the feedback path. I did this several years ago, and thought it made it sound better. I also incorporated the spare 12ax7 to drive the tonestack, this change was very subtle, although worth a little time and wire. His new mod includes changing the coupling caps to 'higher quality' ones. I was never one to be able to tell between cap types and usually mix and match with whatever I have on hand. I used orange drops and mallory caps in different locations based on the value needed. One idea would be to incorporate the mesa boogie lonestar schematics presence control instead of the typical fender presence, which cuts off high frequencies which helping balance out the speaker's EQ. That schematic can be found here: http://schematicx.com/schematic/mesa-bo ... schematic/

Anything beyond these mods, I feel like you might as well rebuild the thing completely on point to point board, and create your own amp. Of course it would no longer really be a blues junior anymore.

Hope someone finds this helpful.

Now for the boost switch idea... I'm not sure there is a whole lot you can do with this. You could decrease the 22uF cathode cap that it engages, which could tighten up the low end and provide a boost. You could rip it out and use a different switch to bypass the tonestack 'dumble style' to get a boost. Rip it out and put a different switch in there to engage the spare triode in a gain stage configuration? To keep it footswitchable, I feel like there would be more work involved than its worth, and would probably be just as easy to take the whole board out and rebuild the amp point to point.

Anybody know what the Bill M mods are for this thing? Or any other mods? I have one of these things and I was thinking about trying Bill M's bias mod because the tubes get ridiculously hot on this thing. I also think that the eq knobs are pitiful. They don't really affect the overall sound very much. I want something more drastic when it comes to eq.

http://billmaudio.com/wp/

I did most of the mods:
-"Twinstack mod": One piece of wire, but very useful!!!
-"Improved green board reverb": Now it is really useable.
-Changed Caps in the Tonestack really improved the overall sound.
-added Presence control, and I added the little switch that gives a bit more highs (only needed for the green board version)
-shieldes input jack: a little less noise...
-lowered bias resistor: Much better sound and longer tube live! A fixed resistor works good, no real need for a trimpot there.

I didn´t do the "power stiffening mod" (larger filter caps), but I added a 500pF silver mica in parallel with each of those caps.

Maybe I´ll try the cathode follower mod and I´ll change the reverb IC to a NE5532AP, which has less noise.

Awesome ideas! I'll try some of this stuff

roseblood11 wrote:-lowered bias resistor: Much better sound and longer tube live! A fixed resistor works good, no real need for a trimpot there.

Aren't you supposed to raise the bias resistor to make it run cooler? Just want to check cuz I just did that mod yesterday and I raised it. I got my info from this page: http://home.comcast.net/~machrone/bjr/bjbias.htm (Bottom of the page)

I just got around to modding my Blues Junior a few days ago.
Here are the mods I did:

tone-stack
Cooler bias
Twin stack
Presence control

The mods sound very good. I like the Presence control a lot. I almost didn't do it because it was hard to find information on how to do it and I saw lots of reviews online where people said it didn't make a noticeable difference when they adjusted the knob. Then I watched the youtube demo where the guy demos the presence knob. There is a HUGE difference in the highs as the knob is turned. You can hear it really good even on a compressed youtube clip. So then I was determined to do it. I'm glad I did. Whoever can't hear anything when they turn the knob either did it wrong or they are deaf. I have the cream board version and all I had to do was replace R25 (I think) with a 10k linear pot wired as a variable resistor (it was around a 7k resistor prior to modding). Its a different resistor number in the green board version. Very cool little amp now.

Mine is a cream board. I like to tinker so.......

Tone stack mod
bias (fixed) mod
JJ tubes
Weber speaker
weber "beam Blocker"
doubled the filter caps
Ruby reverb tank, tank bag, and I also sprayed the exterior of the tank with
rubberized automotive undercoating.
and put in the bigger mercury magnetics output transformer.

I would really like someone to figure out how to do an effects loop.
And I'd love to make a custom cabinet out of some absurd exotic wood.

and....and....and....

One of the problems with Blues Juniors (as reported on Bill M's site - and probably elsewhere) is hum, induced into the output transformer by the nearby mains transformer.

Bill M shows a simple mod with a folded piece of metal (he didn't specify what metal) between the two transformers (http://billmaudio.com/wp/?page_id=882).

I've got a Carling On/Standby/Off switch fitted to my BJ, and as soon as I go to standby, there's noticible hum coming out of the speaker. So I thought I'd try Bill's simple mod. Aluminium didn't seem to do the trick - but the steel (?) bottom off an old, unloved Boss pedal worked wonders !

I decided to make it a permanent fixture, by stripping off the rubber 'foot', drilling a 4mm hole in the centre of one end of the plate, then bending it in a vice.

The part with the hole, I made about 10mm wide - and this bit fixes under the nut of the output transformer. I bent the plate upwards, about 90 degrees from there, to the approximate height of the transformer (as Bill recommends), then on a downward slope towards the mains transformer. For a photo, visit Bill's site - my plate is similar - but much neater.

It doesn't remove every trace of hum, but it certainly reduces it to a more acceptable level. Definitely worth a try if you've got a hummy amp.

I replaced C2 with 500pF in my Blues Jr for a chimy-er sound. Now the fat boost is more of a Top Boost-ish thing.

Bill M's Clean Boost module adds a similar (but linear...) circuit to the last preamp stage. I just made a small vero layout that fits directly to the place where the original cathode resistor was, I'll post it in a few days, when it's definitely verified.

Here's the Bill M 'anti-hum' plate that I referred to above.

I haven't got round to taking a pic of mine yet, but this one gives you the general idea.

What kind of metal works best for this?

I think Bill's metal plate is steel.

I tried aluminium, but it had no effect. But the base plate from an old Boss pedal really cut the hum, so that's what I used. I think it's steel.

It's a bit ugly, but once the amp is back in the cabinet, no-one will see the metal strip. It's doesn't remove all the hum, but it's much cheaper than a fully-encased output transformer.

I would be interested to hear if anyone else has success with any other metal (eg, copper or brass) - or a different shape or thickness.

Interestingly, Andy from RAT Electronics in the UK, replaces the output transformer in Blues Juniors with a Hammond 125E, which he reckons gets rid of all the hum - though I'm puzzled how it does this when it's the same size and shape as the original, and sits in the same radiated hum field. If anyone can confirm the suitability of this transformer, I'd be tempted use one instead of the metal strip.

roseblood11 wrote:What kind of metal works best for this?

It needs to be steel (or other ferrous metal) to block/absorb the radiated magnetic field. The stuff Bill M has used looks like galvanised steel sheet. The shape looks a bit odd to me, as though that was a piece that he had lying around and had nothing to cut it with so bent over the surplus.

If I were doing it I would make the steel barrier "L" shaped, with the lower portion bolted to the chassis, almost the width of the chassis and as high as you could to fit in the case while still allowing air to flow to any important parts.

Thanks for your wisdom, Deltafred.

As an alternative to the bent plate recommended by Bill M, I tried a straight plate (actually the base plate of an old, knackered, DOD pedal) - and it reduced the hum FAR MORE than the Bill M's plate. Thanks again Deltafred.

I then adapted an L-shaped bracket to mount it with.

The attached photos show the bracket, plus the plate. There's an extra hole in the plate, as I originally had it too far forward and it fouled the loudspeaker (Vintage 30). I also found that I needed to lop off a corner, for the same reason. These changes did not adversely affect the hum reduction, so I am well chuffed !

I've also attached a picture of the insides of my Blues Junior, showing that it is now a hand-wired beast. Vyse Amps (the UK branch of Torres Amps) ripped out the circuit board, mounted the tube sockets on the chassis, then rebuilt the amp using whatever parts were salvageable (mainly the transformers). They fitted full-size pots, and put in a toggle switch for the 'FAT' option. They call the model a BBQ Blue, and it's a far bluesier amp than the original Blues Junior.

I retro-fitted a Carling Off-Standby-On switch, changed the footswitch socket to an Fx send/return, and used the other half of the FAT switch to alter the feedback. In 'THIN' mode, I've got maximum negative feedback (NFB), giving a compressed, clean sound, great for Jazz. In 'FAT' mode it has less NFB, more gain, and more bass - and it is SUPERB !

Looks good Lucifer, glad you got the hum tamed.

You could use an opened out (and washed out) bean tin (can - USA) that you can cut with kitchen scissors (as long as your wife/GF/mum doesn't see you), but it wouldn't look as good as a pedal base.

Yes, Deltafred, the INDUCED hum is pretty much tamed - still a little bit there, but way down on what it used to be. No longer intrusive in a quiet room, so it's at an acceptable level.

Just got to get rid of some hum pickup around the input - plus a little bit of 'beehiving' in the background which is puzzling me (maybe the amp is picking up WiFi !)