BAJA Black Toast

bajaman · Post by **bajaman** » 03 Jul 2008, 10:16

Hello international DIY freaks,
here is a little box i built today as a custom order for a customer of mine.
It is a jfet buffer and jfet boost in a Hammond 1590B case.
It uses three 2SK117 (surprise surprise

) - one for the buffer and the other two in the boost circuit.
It has a very low current draw and as such is extremely low noise.
The output of the buffer is sent to a 10k volume control and then via true bypass switching to the boost section, which consists of a single jfet gain stage followed by - you guessed it - another jfet buffer followed by the boost 10k volume control.
The frequency response is essentially flat across the guitar's range and the device is very transparent sounding in operation.
The boost section has a linear gain of 20 times the voltage or 13dB boost.
The buffer stage allows you to run your guitar on full and set the level for a clean rythmn sound without the traditional loss of high frequencies when you turn the guitar's volume control down. Then when you turn the buffer off the full signal from the guitar allows a boost in level to your amplifier. The boost - well it jut provides a super hot signal to the amplifier - if it is a tube amp, it will sound great - not sure with solid state though.

schematic details to follow and veroboard layout too.
in the meantime here are some pictures

cheers
bajaman

bajaman · Post by **bajaman** » 03 Jul 2008, 12:13

Here is the Label and schematic

Label is 1200 dpi
Schematic 300dpi

Cheers
bajaman

holio cornolio · Post by **holio cornolio** » 03 Jul 2008, 12:15

Looks sweet. If you want to send me one I'll tell you how it works with a solid state amp

gnognofasciani · Post by **gnognofasciani** » 03 Jul 2008, 12:41

Really cool, thanks

borislavgajic · Post by **borislavgajic** » 04 Jul 2008, 20:54

I respect You mister Baja...

bajaman · Post by **bajaman** » 04 Jul 2008, 21:46

bybass · Post by **bybass** » 11 Jul 2008, 06:01

bajaman wrote:Here is the Label and schematic
Label is 1200 dpi
Schematic 300dpi
members/bajaman/Baja/Baja%20Black%20Toast/Label.png
members/bajaman/Baja/Baja%20Black%20Toast/Schematic.png
Cheers
bajaman

Hi Baja.....

Do you have PCB layout for this ?

thxs

bajaman · Post by **bajaman** » 11 Jul 2008, 07:08

Do you have PCB layout for this ?

No - I built it on vero board - not a difficult circuit to build!
cheers
bajaman

Post by **modman** » 16 Aug 2008, 20:26

I was planning to build this, so I started a perfboard layout in the DIY Layout Creator. It's kind of tight and not yet verified, but it is a start.

bajaman · Post by **bajaman** » 16 Aug 2008, 21:04

IMPORTANT
Whoops

I forgot to mention a smal problem with this circuit.
In the boost stage the first 2SK117 should have a 10k trim pot fitted in place of the 5k6 drain resistor shown on the schematic. I found a drain resistance closer to 3k3 allowed the circuit to bias far better from memory, but you may have to go lower than this to achieve the best from this simple circuit.
The problem I encountered with the 5k6 resistor value, was that the sound would cut out when a Les Paul was strummed hard through the circuit - the fet was pinching off as the signal level attempted to drive the fet below it's source bias voltage point.
If you do not have access to a signal generator and oscilloscope, do not panic, just adjust the 10k trim pot until the circuit does not cut out the sound when you strum your guitar loudly into it. Once adjusted, you can measure the trim pot value and insert a suitable similar sized fixed value resitor if desired.
Cheers
bajaman

Post by **modman** » 17 Aug 2008, 07:29

Hey Baja,

I mounted everything up to R8 and then went to bed after watching Belgium get another beating in hockey after getting one from New Zealand. At least we did you guys in at soccer

So thanks for the swift reply, I will adapt the layout soon - intended to correct it after building anyway. It is economical but a bit clumsy with the 9V bridge wire. Note also that the LEDs and resistors are not shown on the layout. Couldn't find anything but a simple on/off switch in the layout library but that might be my inexperience, just downloaded it yesterday.

Also, for anyone wanting to build this with other fets, don't forget that 2SK117 has the wicked pinout DGS (left to right, when looking at the lettering pins pointing down. Not like J201 or 2N5457 which have DSG.

modman

PS: Just curious... why

the name black toast?

bajaman · Post by **bajaman** » 17 Aug 2008, 08:47

PS: Just curious... why the name black toast?

My customer chose the name - the concept for a buffer and booster in one box was his idea too.
Hey Modman, have you guys won any medals yet at the Olympics - did you see how our girls - the Evers Swindell Twins robbed the Germans in the double Sculls - beat them by 1/100 of a second!!!!!!!!
Soccer - forget it - in NZ - we are the pits, but Rugby football - well that is a totally different matter - we (THE ALL BLACKS) just whipped the South African Springboks 19 - 0 this weekend (not at the Olympics though)

cheers
bajammin'

Post by **modman** » 17 Aug 2008, 12:04

No metal yet and I'm pretty sure there won't be any for us Belgians. Perhaps the soccer competition -- mind you these are not the national A team, but the B team, the A team didn't qualify for World or European championships, so the B guys are kind of overmotivated. Anyway, we're only good at soccer, cycling and billliards -- the kind of sports where there's a lot of beer around.

Anyways, put in the trimmer in, I'll see how it goes...

floris · Post by **floris** » 17 Aug 2008, 13:20

Hi Baja,

Thanks for sharing your design, much appreciated! A buffer combined with a booster to me is always interesting for my "bluesy tube-amp" sound.

A few questions if you please:
- Why the preference for the 2SK117 JFET? Is it particularly nice for some reason?
- The boost is a "clean" boost, so it is not designed for nice clipping but mainly for a linear gain?
Btw, this is what triggered my last question:
Guys at diystompboxes are having a discussion on JFET clipping and the usage of drain trimpots for setting the bias. Interesting if the boost is designed to be a "clipper" instead of a clean linear booster:
https://www.diystompboxes.com/smfforum/ ... ic=70065.0

Post by **modman** » 17 Aug 2008, 18:29

It worked, did have to change the pots and there was a jumper missing.
Might clean this up even more later, but for now just go by this AND THE SCHEMATIC above! It sounded as promising as it could on a shitty solid state cheapo amp that I use for rough work bench testing.
Biased up ok - with trimpots it's never easy.

thanks BAja!

bajaman · Post by **bajaman** » 17 Aug 2008, 21:41

Why the preference for the 2SK117 JFET? Is it particularly nice for some reason?
- The boost is a "clean" boost, so it is not designed for nice clipping but mainly for a linear gain?

first question - I do not know why - I just find them to be very clear transparent sounding fets - not muddy like j201 for example.
The boost is designed for linear gain when fed from the output socket of an electric guitar - how it behaves when fed from a higher signal voltage may not be quite as linear though

cheers
bajaman

floris · Post by **floris** » 18 Aug 2008, 00:40

Thanks for the reply!
I wonder what makes one type of JFET sound transparent and another more "muddy". Would the biasing have much influence on that, perhaps even more than the type of JFET? I assume it is only the booster JFET that influences the sound here, not the buffer JFETs?
"Muddy", to me, indicates a non-flat frequency response... hmmm, this JFET stuff is all very interesting...

bajaman · Post by **bajaman** » 18 Aug 2008, 01:20

sound is so subjective and we all hear things slightly differently.
I have had good results with the Toshiba 2SK117.
Incidentally this is the fet that Roland use in their early jazz chorus 120 and cube 60 amplifiers - they have an excellent sound reputation and are in my humble opinion, far nicer sounding than the later IC op amp versions.
cheers
Steve

Post by **modman** » 19 Aug 2008, 19:51

Some remarks on building this great circuit:

Biasing: I didn't take out the trimpot -- did measure the voltage on the drain of Q2 -- it should be around 4,5V when running on 9V. If you have a good ear, that's where you'll end up. I used a 10k trimmer
220uF power filter cap: is missing from my layout, I realised.
+9V: When correctly biased, you seem to win little by running it at 12V or higher

Bajaman, I think you label is great, but

wouldn't it make more sense to put the buffer part at the right (at the input) and the booster part left?

Maybe you made it for a left handed guitarist and the input is left?

floris · Post by **floris** » 19 Aug 2008, 20:09

In my opinion, we read from left to right so it makes sense to present the user interface (the "label") in such a manner that signal flow goes from left to right also.