BAJA Mini Juggernaut - Bass Rat with Blend and Boost section

bajaman · Post by **bajaman** » 22 Jun 2008, 02:49

As my 1st Anniversary present to the members here, I present this new DIY project - so new even I have not built it yet - I am off to the workshop to expose, develop and etch a PCB after finishing this epistle.
Before presenting this project, i would like to especially thank Dosmun (one of our newer members here), for the high resolution pictures he has provided, showing both sides of the PCB and identifying parts values. The pictures amongst other bits and pieces can be viewed in this thread: viewtopic.php?f=1&t=2652

Further thanks is given to Bernardduur and Analogguru for tracing and publishing schematics for this project.
There appears to be some doubt regarding the small ceramic capacitor (100p???) connected to the tone control, but i am sure someone will be able to verify this value in the near future.

Okay here are the files: http://www.student.ru.nl/r.kerkhof/Posts/Juggernaut.jpg
http://analogguru.an.ohost.de/001/schem ... ernaut.gif
members/bajaman/JUGGERNAUT/BAJA%20Mini% ... %20PCB.png
members/bajaman/JUGGERNAUT/BAJA%20Mini% ... verlay.png
members/bajaman/JUGGERNAUT/BAJA%20Mini% ... 0Label.png
members/bajaman/JUGGERNAUT/BAJA%20Mini% ... Label1.png
members/bajaman/JUGGERNAUT/IMG_6745.jpg

Some notes: this unit has 4 sockets: an input and output socket AND a send and return effects loop, to allow other devices to be connected between the distortion stage and the boost stage.
You could simply connect the effects loop wires together if you do not want to use the effects loop feature.
You should have just enough room to mount the sockets under the component side of the board. Dosmun's picture of the ProCo juggernaut shows the method of mounting the board and controls, leds, and footswitches. i will post photos of my Mini Juggernaut in due course.
In the meantime - Happy soldering
bajaman

bajaman · Post by **bajaman** » 22 Jun 2008, 05:14

IMPORTANT
Do NOT build this one just yet - I made a major error - I did not allow for the case screw mounts.
I will redesign the board etc. in the next few days and then it will be buildable - my apologies

bajaman

stay tuned

bajaman · Post by **bajaman** » 22 Jun 2008, 09:45

Okay - redesign complete - go ahead and build it - just refresh your browser for new images (F5).
There may be a problem sourcing the long collet type alpha pots - futurlec's are two short to go through the board with a spacer and still hve enough thread for the shaft on the outside of the case. Perhaps Digikey, Mouser, Allied, MCM etc. will have the long threaded collet pots required - please let us know if you locate a good cheap but reliable source.
Maybe Mike Fuller can help us with this one - was't he the one that "invented" this method of board and pot attachment.
(Or did Sola Sound have a Time Machine - Back to the Future)

Apart from this small obstacle the Mini Juggernaut is good to go

bajaman

bajaman · Post by **bajaman** » 23 Jun 2008, 07:14

Well - I built one of these and discovered that one of the electros was reversed polarity (now corrected in picture files).
I used a 10n tone capacitor - I see Dosmun has verified this today also.
I think the Mix or Blend control should be a 100k lin poti, because the two 47k resistors are in series with each other and paralleled across the poti - this would give a 50k reading. With a 100k lin poti, the master has a lot more effect due to the higher signal level being fed to the opamp inverting virtual earth mixing stage. (1.3 times the signal voltage at mid rotation)
I tried it with my bass and it sounded hopeful - not boxed up yet, but with this type of construction almost every part mounts on the board with the plastic insulated sockets under the potis. I ran a length of 30 amp fuse wire across the back of the potis and connected it to the ground track on the board, so no hum.
Although this type of construction looks nice it does have it's pitfalls - you have to file all the solder joints flat to stop them from shorting against the inside of the case, and there is still a lot of wiring to do to the footswitches and to the potis - my pins were not long enough to be bent at right angles and still go through the board to the solder side - I had to use pieces of 30 amp fuse wire as connector links for them.
more later plus build pictures etc.
cheers
bajaman

bajaman · Post by **bajaman** » 23 Jun 2008, 10:50

bajaman

ps: spot my favourite jfet - the 2SK117 being used as a buffer here.

and the cut out corner pieces to allow the original board to fit in the NSC1290 case.

Post by **modman** » 23 Jun 2008, 18:08

Wow, Baja, looks terrific even without the case -- love the replica switch mounting.
And if people think there's nothing left to be said about stompbox building, But it's only when you create integrated pcb's like this that modding and servicing afterwards could be a joy. I think where a lot of DIY pedals fail, is always in the "off-board" wiring.

modm

chicago_mike · Post by **chicago_mike** » 24 Nov 2008, 01:36

Hey gang,

Im close to having a inished unit, I had an origional a long time ago, but forgot something basic, like way retarded basic...

where in the signal chain is the effects loop? Pre or post distortion. And is it buffered?

I told you is was retarded basic stuff!

mikebike · Post by **mikebike** » 10 Jan 2009, 16:55

i think bajaman said the loop is post distortion, pre-boost.

bajaman, do you have pcbs for sale?

i dont know how to etch boards yet

chicago_mike · Post by **chicago_mike** » 10 Jan 2009, 21:22

This was the first board I etched and it went very well.

I did the ammonuim persulphate method:

1 part Murcaic Acid..available at homo depot
2 parts Hydrogen Peroxide

I mixed the solution in little tupperware trays..like the 4 in a package kind at homodepot.

as the board etches, the solution turns a flouresent green color..

to print the board, this part is cool and it works great...

Cheap gloss photo inkjet paper. But you print the pcb layout with a laserjet printer. Now be careful cause it can smear easily.

I used this method for all my pedals, the brassmaster, mxr envelope filter, mcmeat, polyphase, etc...

youtube has a good supply of videos on etching

bajaman · Post by **bajaman** » 10 Jan 2009, 22:02

bajaman, do you have pcbs for sale?

Not as such, but I suppose I could etch a board for you - I just hate drilling all the holes - my eyesight is not what it used to be.
One of the difficulties associated with this project is the requirement for potentiometers with long collars.
the standard alpha pots are no use as their collars are two short to allow two nuts and separation between the inside of the case.
Really - etching a board is not too difficult to do.
I personally use a black laser (not inkjet) printer and print the PCB tracks mirrored onto transparent laser overhead projector type film.
I then use Kinsten brand coated PCB material.
Remove the protective plastic film from the Kinsten board and lay the laser printed transparency onto it with the ink surface contacting the coated board. I place a small sheet of glass on top of the transparency to provide a good even contactwith the board.
Next, i take my ultraviolet sun lamp and after it has warmed up (goes greenish light) I carefulyy move this back and forth across the glass top sheet, until the coating on the board changes from green to blue - usually about 30 seconds.
Then I turn the light off place the exposed board in a black bag and take it to my kitchen.
Using a pyrex dish, I mix a small amount of Kinsten developer crystals with cold water and insert the exposed board - after a few seconds the unprotected coating dissolves and I am left with a very sharp green coloured tracks image on a bright shiny copper board.
After I have rinsed the board under cold running water, I mix up some ammonium persulphate crystals with hot water and place the board face up in this solution - depending on the temperature of the water it takes about 5 to 10 minutes of gently swilling the solution back and forwards over the board until all the unprotected copper is etched away. I am then left with a perfect green tracks board. A quick scrub (after rinsing in cold water) with a goldie (kitchen pan scouring thingy)
And I now have a shiny copper tracks PCB etched.
Not difficult to achieve, but like with all things, practice makes perfect. So, I would advise practising with something smaller than this project if new to the world of PCB etching

What comes next - back to the workshop and the tedious task of drilling all those 1mm holes with my cheap chinese drill press. A few minutes later and it is component insertion time - this is the most enjoyable part of the build process.
Give it a go - my way is not neccessarily the cheapest way, but I do get very high quality results.
cheers
bajaman

chicago_mike · Post by **chicago_mike** » 28 Jun 2009, 22:05

Hey Baja

I need some jfets for this juggernaut...

which ones could I try out and does anybody here have any they could sell me?

bajaman · Post by **bajaman** » 28 Jun 2009, 23:02

Only one fet used as a source follower (buffer) so any n channel jfet should work in this position - J201, 25457/8/9, 2SK 30/117, 2N3819, MPF102 etc.

chicago_mike · Post by **chicago_mike** » 28 Jun 2009, 23:18

coolies!

chicago_mike · Post by **chicago_mike** » 08 Jul 2009, 20:12

Hey Baja!

are the pinouts of the 2SK117 and the J201 different?

Sorry for such newbish questions.

bajaman · Post by **bajaman** » 08 Jul 2009, 20:22

Yes

J201 = DSG
2SK117 = DGS
When looking at the flat face of the fet with the writing on it and the pins or legs at the bottom.
Cheers
bajaman

clintrubber · Post by **clintrubber** » 27 Sep 2009, 22:42

Nice to find this thread, good info, thanks !

With all the LM308-hype-or-non-hype for the 'normal' Rat,
I was a bit surprised to see the Juggernaut using 1458 opamps...
might probably not matter much, but has anyone perhaps tried a '308 in the pre-clipper location ?

Thanks,

Peter

roseblood11 · Post by **roseblood11** » 12 Nov 2009, 10:25

Hi,

Bajaman, where did you buy those alpha-pots? No european supplier seems to stock them... Do you have parts numbers? They are from Alpha-Taiwan, I suppose?

regards, Immo

bajaman · Post by **bajaman** » 12 Nov 2009, 10:31

Hi Immo
I just told Uwe

sorry, i never did box this one up because I could not find the long collar pots

.
Can anyone help with a source for these???
cheers
Steve

rbstep · Post by **rbstep** » 12 Nov 2009, 15:21

I got some long collar pots from Antique Electronic Supply. I think they were made by Kustom. Marshall makes some pots that will work also.......

ron

chicago_mike · Post by **chicago_mike** » 15 Nov 2009, 02:10

Umm...

Question. I finally got mine "finished"

The master volume and blend controls work, but the other 3 pots dont. THe leds light up.

Right now I have tl072's in her...is this as simple as putting in 4558's or 1458's?

Thanks!

I currently use regular 16mm pots and they seem to be long enogh to poke thru a 1590BB.