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Just wanted to report that I boxed this up a week or so ago and everything works perfectly. My main hiccup was in missing those 2 cuts and one jumper and also in not setting the trim pot correctly. The boxing up stage was actually quicker and easier than I expected it to be.

Anyway, it's been a positive experience building my first pedal. If i were to do it again I would make more effort to source metal film resistors just to get the hiss as low as possible (I'm gonna buy one of those packs with like 10X30 different MF resistors) and I would also socket the Jfet and try out a J201 as well as the 2n5457 which I ended up using (because bitsbox was out of J201s). Also I've heard that you can get less noise by using the correct resistor instead of using a trim pot so I might have done that too. It's too much effort to go changing it now and I'm 90% happy with how it turned out so I'll just leave it as is.

Here's a summary of the mods I did to the original circuit:
Notch: replaced a 100k with a 47k for a shallower cut at 600hz instead of the deep cut at 400hz.
HPF: Jumpered 2nd cap (47nf) and replaced 1st cap (47nf) with 18nf for a shallower bass rolloff.
LPF: replaced one of the 4 22k with a 13k for more top end.

The overall result sounds more 1 by 12 inchy, and less 4 by 10 inchy.

Next build will probably be an EP preamp/boost which I'm considering putting in a smaller enclosure.
The voltages on Q1 are a bit odd. Pin 3 (Collector? ) is OK but pin 2 (Base? ) is at 0V. It should be about 4V
Pin 1 (Emitter? ) is also too low but that is due to the absence of bias volts on the Base.
Find out where those volts have disappeared to. Check the board for any solder bridges that may be causing short circuits. Also make sure that the resistors R3 and R4 are the correct value.
Hi everyone,

So the IC LM13700 first....
Pin 1  1.33v
3  4.07v
4  4.07v
5  1.6v
11 8.29v
all other pins including pin 6 are zero volts

Q1  pin 1= 0v  pin 2 = 0v  pin3 = 8.27v
Q2  pin 1= 1.09v  pin 2 = 1.63v  pin3 = 7.17v
q3   pin 1= 0v  pin 2 = 0v  pin3 = 8.23v
Q4  pin 1= 0v  pin 2 = 0v  pin3 = 8.23v
Q5  pin 1= 7.68v  pin 2 = 0v  pin3 = 8.28v

Hope this proves meaningful to you. Not so much for me except pins 6 and 11 on the IC :)


Building your own stompbox / Re: Two band Parametric EQ
« Last post by antonis on Today at 05:48:06 AM »
IMHO, for such a wide frequency spectrum, a 3 band parametric EQ should be more appropriate choice..
(by narrowing range you can be more flexible in Q setting and cap/res values..)
Building your own stompbox / How to beef up your drummachines?
« Last post by FUZZZZzzzz on Today at 05:38:31 AM »
Hi Guys!

I've been looking for a good way to beef up my drummachines. I've collected a few over the year which I use on a regular basis. I've tried a couple of different pedals and some seem to work and others dont (obviously). I thought a compressor could do the trick, but the normal compressor pedals dont seem to give enough result. Also, maybe something with tubes to colour the sound. Maybe a preamp of some kind. What do you guys use (if any at all?) preferably DIY

Also, I wont mind if it works on old synths as well ;)
Building your own stompbox / Re: Volume pot to VR with signal bleed.
« Last post by antonis on Today at 05:34:48 AM »
mostly the reason fro taking the bottom of the pot to Vref not ground would be to avoid the need to put a DC blocking cap in before the volume control.

I might get you wrong, Tom, but connecting the bottom of the pot to Vref doesn't avoid the need of DC blocking cap..
(DC flows through voltage divider lower resistor to GND - by doing that you simply "offset" bottom lug voltage..)
Building your own stompbox / Re: J201 discontinued?
« Last post by POTL on Today at 05:34:35 AM »
I don't know why anybody hasn't started using these? :icon_confused: I prefer them over the J201

VGS Off 0,5-4
quite a large spread of values

The 2SK208 datasheet can be misleading if you don't read the "Note" under the electrical characteristics. 
There are 4 different variations of this jfet that are identifiable by the marking JR, JO, JY and JGR
Those are the IDSS classifications: 
2SK208-R = JR = 0.30 to 0.75 mA < Not that far off from the beloved MMBFJ201
2SK208-O = JO = 0.60 to 1.40 mA
2SK208-Y = JY = 1.2 to 3.0 mA
2SK208-GR = JGR = 2.6 to 6.5 mA

So, when you are looking at the IDSS and you see the min 0.3 mA and the max 6.5 mA that is the range of all 4 combined.
The same goes for the VGS Off −0.4 min / −5.0 max.  The VGS Off for the 2SK208-R should be in the ball park of -0.4 to -1.5

If ya ask me, it's kinda stupid how they combined them all together like that...  :icon_confused:  But, if you can get past that they are really consistant, easy to work with and sound damn good!

Another stupid Toshiba trick I noticed, check the specs for 2SK879 :-\

It's funny, but my supplier has 208-R for sale, I hope that he indicates the correct marking)
You obviously refer on series resistor, don't you..??

Check between the leg with signal and the tip where resistor should be connected (not on resistor's actuall leg..)
It's an odd schematic since mostly the reason fro taking the bottom of the pot to Vref not ground would be to avoid the need to put a DC blocking cap in before the volume control. But in this case they seem to have done that anyway, so there's no reason why they couldn't have taken the bottom of the pot to ground.
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