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Neat, I'm interested to here how this build goes. Let us know how it turns out!

More build photos.

I finally had the chance to finish my SFT modded like i showed previously.
Well, it works very well. Unfortunately the PCB I produced contains a few mistakes (including the footprint of the transistors... doh!) so I need to modify it before posting it. Unless someone who uses kicad wants to do it by him(her?)self.
I find it not hissy at all, but I didn't have the chance to compare it with an original one. I may post a sample (using a bass guitar) so people can refer to it and tell me if there's something wrong, or not.

Here's a picture of my build (it fits a B enclosure with a 9v battery)

That'd be great. I was going to make a layout from your modded schem but I was having a hard time reading the values because a bunch of them are crammed over each other, so I'm excited to see your layout.

I will. I will probably build another, so I'll need to correct that stupid layout.

Meanwhile, here's a sample of my build, so people can confirm it sounds right to their ears compared to the original one?
http://rapidshare.com/files/446188174/sample_svt.mp3
It's recorded this way : fender jazzbass > "modded" SFT > some transistor-based bass amplifier using a 1x15 speaker > beta 52 + sm57 > motu soundcard > ableton live. No effect used, no compression, I just mixed both microphones without panning and there you go.
I was just tweaking knobs while my bass-player friend was playing. The sample begins with the effect disengaged.

OK, I build one and must say I am so unimpressed.........

So I got one in for repair (AC instead of DC, etc) and noticed some other things:
- The 'weird' connection on the gain pot was not there. When I disconnect this connection the gain pot worked like a charm!
- the output was quite low. I had no time to check the output resistors (those 2x 100k) but when I removed em on my build I got approx the same output as the original!

Hope it'll add to the discussion!

my build has got an huge output level, I barely cross noon to match the output level of my jazz bass. Are you sure you're build is right ?
Also, the whole sound of that thing seems to rely on the last gain stage.
I think the "weird" connection on the gain pot allows for less bass when the latter is maxed out, which is probably a good idea given the following gain stage. That's to be verified though, I didn't check it on ltspice.

Just a quick Q for confirmation. This thing has an inverted output right? Three muamps andtwo source follower buffers.
I need to build a clean blend for this, so I have to make sure I invert the clean as well.

Any smart suggestions on matching the clean level with the huge output level of the effect?
What is best practice, lower the fx signal level or boosting the clean?
Latter option does not require an extra boost section to bring the output level back up, but it might be noisier?
I know it is a bit tricky as the output volume of the fx also changes with the gain.

Cheers!

Arnoud

the output was quite low. I had no time to check the output resistors (those 2x 100k) but when I removed em on my build I got approx the same output as the original!

i also experienced the same thing on my build (i used the vero layout). i checked over and over again and again, and found no mistakes. i even used my scope to check all the waveforms after every stage etc

in the end i removed the 100K thingamajigg, just like bernarddur.
i only noticed the difference in volume when i compared knob settings with sound samples on the internet.

cheers,
lohstah

Lohstar - Did you also have to fiddle with the gain pot connection like Bernarduur to get it up to snuff?

Bernardduur wrote: - The 'weird' connection on the gain pot was not there. When I disconnect this connection the gain pot worked like a charm!
Hope it'll add to the discussion!

I am glad that you checked that on an original, it has bothered me since it was first traced. It makes no sense at all to wire it as it was.

When I built mine I missed the 'weird' bit off.

I also added noiseless biasing as my breadboarded version had lots of hiss.

This is definitely one pedal that benefits from 18v.

On the gain pot I ended up setting it up as a regular divider and bypassed the stopper resistor going to ground for better clean sound when set at minimum. Only problem is I can't figure out how the 47pf should be configured on the lugs now.... is it needed and what is it for?

gkoerselman wrote:Here is the PCB (300dpi) and layout that I used to build mine (plus a build picture). I think it looks pretty ugly, but it does work and I got it to fit in a B type enclosure (without reserving room for a battery). Note that I didn't include the 47 Ohm resistor to +9V or the 1N4001 protection diode in this layout.

PM me with your e-mail address if you want my Eagle files. Comments and or corrections as always appreciated!!!

Hi Gkoerselman,
It's me again...

I have a question about the SFT schematic/layout that you posted.
You've highlighted that you didn't include the 47ohm nor the 1N4001 protection diode.
I would like to know, what are the risk if leaving out the 47ohm resistor?
I know the protection diode is there to protect circtuitry from wrong polarity, but how about the 47ohm resistor?
Will it be ok if I left it out altogether?

Thanks in advance, and sorry to keep bugging you from time to time

That resistor helps prevent or eliminate power supply noise.

[quote="greenskull"]On the gain pot I ended up setting it up as a regular divider and bypassed the stopper resistor going to ground for better clean sound when set at minimum. Only problem is I can't figure out how the 47pf should be configured on the lugs now.... is it needed and what is it for?[/quote

I also missed out (R8) 22k resistor, mainly because when I breadboarded the circuit I was using 2N3819 FETs and I needed to get the gain down a bit more than the resistor allowed.

I forgot to fit the 47p capacitor to the gain pot. I have been gigging it (on bass) for 4 months and not really missed it. It is to give a bit of treble boost when you back the gain pot off.

It should go between the wiper and the hot end of the pot, the end that is fed from the previous stage by (C3 on my schematic) 0.1uF. If you view the pot (back) with the legs facing down it will be across the centre and left side legs.

greenskull wrote:On the gain pot I ended up setting it up as a regular divider and bypassed the stopper resistor going to ground for better clean sound when set at minimum. Only problem is I can't figure out how the 47pf should be configured on the lugs now.... is it needed and what is it for?

I also missed out (R8) 22k resistor, mainly because when I breadboarded the circuit I was using 2N3819 FETs and I needed to get the gain down a bit more than the resistor allowed.

I forgot to fit the 47p capacitor to the gain pot. I have been gigging it (on bass) for 4 months and not really missed it. It is to give a bit of treble boost when you back the gain pot off.

It should go between the wiper and the hot end of the pot, the end that is fed from the previous stage by (C3 on my schematic) 0.1uF. If you view the pot (back) with the legs facing down it will be across the centre and left side legs.

Hey folks, long time listener, first time caller. Used Mike's vero layout (thanks Mike!) and very pleased with the results.





Only had to order one part that I didn't have in my parts bins- the C taper 1M gain pot. That happened to be the one component that was faulty post build when I was trying to debug it So now I'm back to a 1M B pot with all the gain bunched up at about 8



Used a charge pump type circuit to bump the voltage up a bit before the circuit. A tad disappointed it's only pumping out 15 volts as opposed to 17/18 but there you go.
Very pleased with the sound on guitar- definitely going on my pedalboard. On bass though, can't quite put my finger on why, but the sound is a bit "blown out" like there is too much gain or something- a bit fizzy and farty. The decay is quite gated too. Reduced the (circa 600hfe) transistors down to around 400, not sure what else to try...

Many thanks to Mike for the ver0 layout and rcubed and the original tracers who put the hard yards in.

Nice build

+1
makes my builds look like I did them with oven mitts on..Ha
I love building the boards hate putting everything in enclosures. At least this inspired me.
nice graphics too.
cheers

Hmm, just got back from hols and had a good session with this tonight- did anyone have an issue with HUGE volume with the vero layout for this?

The volume pot is basically barely doing anything and, stock, it's (probably rightly) running so much louder than when in bypass