Synthbox

[gigimarga]

The soundclips inspired me to draw up this, based on the schematic from page 1 ... at least I found a use for my insomnia, right?  
.........................................................................................
... not verified, but it looks ok AFAIK.

Very nice your work...thx for sharing it!
Can you post the PCB, too?

[mantella]

awesome job Isildur100. Thanks!
Looking forward to this one...

[kristoffereide]

Any replacement transistors? Or do I have to order those exact ones?

[liquids]

Any replacement transistors? Or do I have to order those exact ones?

Please read the whole thread.

[kristoffereide]

oh now I found it

[Naz Nomad]

Very nice your work...thx for sharing it!
Can you post the PCB, too?

LINK TO PnP DRAWING

Print size ... 2.7" x 2" ... 600 dpi (I think ... lol)

I realise now that I've left 2 pads for the trimpot, thinking it was an offboard pot.

I'm sure it'll still fit on the board with no problems, but there's only holes for the 2 legs that are used.

[Naz Nomad]

For the record, this is what I did to the schem so I could draw the PCB ... The layout mimics the schem pretty closely, so should be easy to follow ...

[Cliff Schecht]

That's one of the hardest to follow schematics that I've ever seen.

[Naz Nomad]

Naaah, it's easier to folow than the original if you take it as 2 separate schems ... the top half is one, the bottom half is another ... it's just that the bottom half was flipped to join the grounds together and make the board more square, instead of  6 inches long.

[bluesdevil]

Thanks a lot Naz! I should have all parts on hand to build this on PCB... can't wait!!
By the way, if anybody  needs  a board I can do it while I'm etching mine within the next couple of days... drop me a PM.

[gigimarga]

Very nice your work...thx for sharing it!
Can you post the PCB, too?

LINK TO PnP DRAWING

Print size ... 2.7" x 2" ... 600 dpi (I think ... lol)

I realise now that I've left 2 pads for the trimpot, thinking it was an offboard pot.

I'm sure it'll still fit on the board with no problems, but there's only holes for the 2 legs that are used.

Thx a lot Naz...you're great!

[Jimi W]

Hi,
I'm new around these parts!
I'm in the middle of doing this on perf. What would you guys recommend for the non electrolytic caps? Metallised Poly film or multilayered ceramic? Looking at the perf layout I'm following it looks like ceramic is the way forward. Would using one make a noticeable difference to tracking/sound?
Sorry if this is obvious but I am new to all this!
Thanks for your time,
Jimi

[~arph]

I used poly on the breadboard and that worked fine.. I don't think the difference will be that big.

[gigimarga]

I've just finished it using BC549C for all transistors...it works poor, far from the soundclip...can somebody to post some good voltages?

Thx a lot all!

[~arph]

You need transistors with higher gain. The BC549 is typically 270, the 2N5089 is around 800.

[gigimarga]

Thx ~arph for your answer!

All the BC549C that I used had the gain over 600 and instead of MPSA18 I used two with gains around 700.
Anyway, I will try to found some MPSA18 here.

[liquids]

Are you using a power supply?  Check your battery for one...

This is one circuit where I think that an audio probe will be far more useful than measuring voltages.  Your transistors should be fine, by the way.

Describe what you mean by 'it works poor,'  that might help...as I've messed with this quite a bit.  

Do be sure to read this entire thread.  It has some useful bits.

That being said, from my recollection, using a 9.43v supply:

The first and last transistor are buffers, and base of each should be around 5-6v.  Following, the emitter will be a silicon diode drop (.7 volts) below the voltage you get there, and the collectors should read whatever voltage your voltage source is.  Easy enough, but if not, something is wrong.

The second stage, the base should be about 3.3ish volts, if I remember correctly. Audio probe at the collector, though, and you should get a fairly loud and overdriven/fuzzy sound.

Measuring voltages at the next transistor--in conjunction with the diode, you should find, will actually be somewhat akin to measuring the voltage of an envelope signal at some points (base and emitter?), and vary according to input signal...that much I remember.

The oscillator transistors, I don't recall ever checking their voltages...hmm.

I'm sorry I don't have more exact voltages, but even so, I do believe this is one where audio probing and careful checking of your values will be far more helpful in solving the problem.    And as I said in posts previously, be careful looking at the schematic on the bottom half, around the 'third' transistor and the oscillator (two transistors with emitters to ground).  Check out the 'original' Joe Davisson's schematic which is the springboard and which I find is a clearer visually for this part of the schematic, due in part to the limitations of what I used to draw my schematic: http://www.diystompboxes.com/analogalchemy/sch/shocktave.html.  

[gigimarga]

Thx a lot liquids for your answer!

I will check the voltages as you indicated above.

By "it works poor" I understand that it sounds farty and unclear (I can't hear the octave), as opposite in your demo where it sounds metal-ish and very sharp!

The trimpot seems to do nothing, but the other pots works OK.

Thx again!

[liquids]

From that description it sounds like something is wrong in the frequency to voltage or oscillator sections....oftentime it won't octave due to a bad connection there, a missing connection there, or having mismatched values in caps, etc...  

Also, note that the trim is for improved tracking - it shouldn't make much difference to the tone, more so to compensate for how you play and maybe assist a very bright guitar and/or bridge pickup to have cleaner tracking.  

[gigimarga]

Thx a lot liquids!