BAJA Black Toast

Original effect designs complete with verified schematics, layouts and instructions. All project were freely contributed by members and cannot be used for commercial purposes without consent of the respective owners of the copyright.
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bajaman
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Post by bajaman »

Hi all
They are two separate effects in one pedal. right handed guitarists have always had the input on the right - all my designs read from right to left - a Chinese throwback I guess, but more logical signal flow wise.
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Post by modman »

I see Baja, on the inside it works from right to left, but on the outside to the guitarist it read right to left.

Still, I dug into DIY Layout creator some more and succeeded in cooking up a pcb layout with mounted pots en LEDs, I used Bajaman's label as a drilling template. The pcb would be sitting up inna Zvex 1590B style, except that the board is in the middle of the box.

Image
  • Yes, I did move the buffer pot to the right on the input side.
    Going to and fro in DIY Layout Creator R7 =1M
    Resistor 56k should be replaced with a trimpot (not shown) between Q2 drain and the red power rail
    Grey wire = input of buffer part (come from switch)
    Brown wire = input of booster part (from switch)
    Green & Orange wires = ground for the LEDs (go to switch)
    Red traces are +9V, Blue traces are Ground
    Wipers of the pots are the outputs of the two parts, and go to the switches
    I haven't boxed it up yet, but it is tested and works. According to my calculations it should fit, but I haven't tried it yet.
    The pcb will span the depth of the 1590B, so it wil be necessary to cut out the space between R14 and R15 to lead the wires to the switches. I'm more concerned about the postion of the jacks, but it should be ok.
    The PCB is designed for the more common fets, i.e. fets with the pinout DSG or GSD when looking at the lettering: J201, 2N5457, BF245, MPS-A18. SK-fet all seem to have DGS or SGD pinout. Just tried the J201s for now, but will be testing some more later. Sorry Baja, i'm loving the sk117 in this one, but my stash is gone!
    LEDs are 3mm and mounted on the solder side, so they can be bend down and squeezed into the drill holes (I stopped using LED bezels and never regretted it)
Some pictures of the clean PCB untrimmed - finished pcb component side and solder side

PCB transfer file - board should measure 92mm by 24mm
PCB component placement file - same as above
Bajaman's original schematic

more later!
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Torchy
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Post by Torchy »

My small contribution ...
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Black Toast.PNG

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bajaman
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Post by bajaman »

:D Torchy
That looks just like my build :hug:
cheers
bajaman
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Post by modman »

I have to retract my advice on the 2N5457 and this fet just doesn't have the gain the SK117 seems to have. I didn't like the SK117s in my minibooster, but here they are the a perfect choice.

I'm having doubts about the real necessity of two switches though...

thanks for sharing that layout Torchy!
Did you built it yet?
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Post by bajaman »

I'm having doubts about the real necessity of two switches though...
That is ahat my customer wanted - I built what he asked for :wink:
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rocklander
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Post by rocklander »

I've had a go at a PCB. unverified at this stage - the 2nd switch can be jumpered if one deems it unnecessary, or used if necessary.
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Post by modman »

Great work, Rocklander, but don't forget that when using an SK117 fet you really need a trimpot where you have the 5k6 resistor, because I found something strange.

SK117 + 10k trimpot allows you to bias the circuit, I mean: no sound at 0k and no sound at 10k, with a 'sweet spot' with maximum gain and clean sound in between.
J201, 2N5457 + 10k trimpot works like a unnecessary gain control, only gradually increasing volume. So it could be jumpered -- until somebody corrects me and says it's 10k :scratch: :mrgreen:

But still, there is something very different about SK117s when compared to these 'standard' fets.
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Post by rocklander »

modman wrote:Great work, Rocklander, but don't forget that when using an SK117 fet you really need a trimpot where you have the 5k6 resistor, because I found something strange.

SK117 + 10k trimpot allows you to bias the circuit, I mean: no sound at 0k and no sound at 10k, with a 'sweet spot' with maximum gain and clean sound in between.
J201, 2N5457 + 10k trimpot works like a unnecessary gain control, only gradually increasing volume. So it could be jumpered -- until somebody corrects me and says it's 10k :scratch: :mrgreen:

But still, there is something very different about SK117s when compared to these 'standard' fets.
thanks very much. it's really my first completion of a PCB and as I said 'unverifried' so would love it if someone who understands this stuff better than I can verify that it looks right.

I'm a 'paint by numbers' kinda guy. I have no idea at all about theory :oops: so I just followed the schematic.
I'm happy to adjust and add the trim if that's necessary, but should I just add it to the 5K6 on q2 or should I also have them on q1 and q3? and if so, what resistor(s) should I be replacing?
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Post by bajaman »

Hi guys
Thanks Ivan
Only the 5k6 on Q2 needs a trimpot to bias the fet correctly.
cheers
Steve
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Post by bajaman »

Some mistakes on the board layout/PCB.
The junction of the 33n and 1 Meg resistor on Q2 should connect to the gate of Q2 - NOT the junction of the 10k and 33n as drawn, and Q3's drain needs to connect to the +ve rail ( shown disconnected).
Apart from these errors the board layout should work very well.
cheers
bajaman
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rocklander
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Post by rocklander »

bajaman wrote:Hi guys
Thanks Ivan
Only the 5k6 on Q2 needs a trimpot to bias the fet correctly.
cheers
Steve
bajaman wrote:Some mistakes on the board layout/PCB.
The junction of the 33n and 1 Meg resistor on Q2 should connect to the gate of Q2 - NOT the junction of the 10k and 33n as drawn, and Q3's drain needs to connect to the +ve rail ( shown disconnected).
Apart from these errors the board layout should work very well.
cheers
bajaman
thanks to you Steve! :applause:
adjusted (and size reduced to fit the page layout better)

can one of the MODs please remove the image from my previous post (if it matters)? I've deleted the wrong image from photobucket anyways,
Image
larger version available here
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rocklander
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Post by rocklander »

been working on this tonight. the board is pretty tight - I may have to redo it to make more room between the components, but the reason I wanted it so is that it fits east/west across a 1590b and also fits inside the depth.
I have adjusted it a bit since (even tighter than what I have posted here) but am a 3M3 resistor short (and no local store with the component) so am waiting for parts to arrive.

would substituting the 3M3 with a 3M9 make a significant difference Bajaman?

and biasing.. should that just be by ear or am I looking for a particular voltage on one of the fet pins?

cheers
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Post by bajaman »

would substituting the 3M3 with a 3M9 make a significant difference Bajaman?
yes, but you could still use a 3M9 in it's place IF you add a 680k resistor in series with the OTHER 3M9 (it then becomes a 4M58 resistor)
Cheers
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rocklander
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Post by rocklander »

hmmm.. might just wait a week for the spare parts then thanks.


and biasing.. just 'to taste'?
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Post by modman »

rocklander wrote:hmmm.. might just wait a week for the spare parts then thanks.
and biasing.. just 'to taste'?
What Fets will you be using? I noticed the below:
modman wrote: SK117 + 10k trimpot allows you to bias the circuit, I mean: no sound at 0k and no sound at 10k, with a 'sweet spot' with maximum gain and clean sound in between.
J201, 2N5457 + 10k trimpot works like a unnecessary gain control, only gradually increasing volume. So it could be jumpered -- until somebody corrects me and says it's 10k :scratch: :mrgreen:

But still, there is something very different about SK117s when compared to these 'standard' fets.
Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

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rocklander
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Post by rocklander »

I used the 2sk117 (that's the pin config on the pcb I drew too by the way).
and I have the 10K trim, so I guess you're saying that I just bias it by ear somewhere in the middle of the 10Ktrim?

the only reason I ask is that the only biasing I've done was on the runoffgroove pedals and they had fairly specific voltages to look at on the FETs....
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Post by bajaman »

bias the drain of the fet to just over half voltage - for a 9v supply , bias it to 5 volts
cheers
bajaman
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rocklander
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Post by rocklander »

sweet as.. thanks a heap.
world's greatest tautologist ...in the world
Ronsonic wrote:...the lower the stakes the more vicious the combat.

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rocklander
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Post by rocklander »

okay.. here's the final layout because (as I said) I'm not much for the stripboard things - I find it easier to use etchant [I know - I'm weird]..
.. I've tested using this layout (board built and running, but waiting for my enclosure at this stage). it's set up so that it can fit across the narrow part of a 1590b box, and should also be shorter than the height (if you trim the FETs appropriately). printed for UK/NZ paper A4 size (not US 'letter') but may fit on that too.

I don't have the rights to remove my earlier posts.. Mods - can you please do that?

thanks heaps Mr Bajaman for this unit! :applause:



thanks
Ivan
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pcb-schem-layout-tested.pdf
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world's greatest tautologist ...in the world
Ronsonic wrote:...the lower the stakes the more vicious the combat.

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