Synthbox

[igor12]

SOUND CLIPS PLEASE!!!

[~arph]

Ok, I will give this a go as far as designing a PCB for it.
Let me try to fit it in a 1590B 

[~arph]

Question, what is the value of the resistor coming of the positive input to ground on the last opamp stage (ic 1b)?
My guess is 1M-3.3M, but I thought I'd better verify.

[liquids]

Question, what is the value of the resistor coming of the positive input to ground on the last opamp stage (ic 1b)?
My guess is 1M-3.3M, but I thought I'd better verify.

I'm not in front of the breadboard, but if I recall, right now I have it connected right to ground with no resistor.  I'm pretty sure that, since it's off a bipolar supply, it doesn't matter. ...?   

I don't have my op amp book in front of me, but the last thing I think I read, said that the value in these situations is generally negligible, something small will do. But hopefully someone more savvy can chime in.

And, why is that particular op amp stage labeled 1b?     Yes, the schematic is not only bare bones, it is a bit rough. I do things as time permits.     

Any luck breadboarding it?

[~arph]

Ah yes, I was just tracing the circuit into eagle without paying a lot of attention. It seems it is a normal non inverting stage so a straight ground connection seems like the right thing as we're on a dual power supply.

Haven't breadboarded it, but I can't spot any mistakes after completely redrawing this into eagle. I think I might be taking the bold route and build this from PCB directly.. It's about time I made one for real.

[Badside]

This looks rather interesting and I'm adding the necessary parts in my current Mouser order to have a go with this!

But I was wondering: is it possible to feed various types of oscillators? I like doing synthy sounds (I play in a rock cover band, but we do some dance and techno songs for fun) and I'd like to be able to do sawtooth waves as well, perhaps square waves too. I don't care if the pedal has to be huge.
And mostly I'd like to add a high-resonance variable low-pass filter controlled with a wah-type pedal (I love that effect).

I'm not looking for someone to feed me a nice schematic, but rather maybe brainstorm with me on how to implement this kind of stuff, or perhaps point me to a DIY resource that deals with analog synth filters and oscillators?

And mostly, I still have trouble wrapping my head around this one, but from what I understand, what comes out at the output of the pedal is really an oscillator that is pitch-controlled by the input signal. Is that correct?
If that is correct, am I correct in thinking I can feed various types of oscillators? (Octave effect not always required, but appreciated)
Or perhaps just run the signal through an extra circuit node that would reshape it? I can build a tube amp no problem, but I have no idea how analog synths work!

Thanks

Yannick

[Jimi W]

Help!!!!!
I've just finished building this on Perfboard using the layout by isildur100. When switched on all I get is a sort of pulsating sound. Kind of machine gun sound. The bypassed signal is fine, the volume pot works fine and controls the level of machine gun, the bass switch also thins or thickens the sound so thats working. The shape pot does seem to make it a bit thinner and hissier.

This is only the 6th pedal I've built and so far they've all worked first time so I'm new to the de bugging lark.

I'm going to make an audio probe tomorrow but for now I've checked all transistors are correct, the right way round and have I've also tried different transistors.

The voltage on the trannies are as follows

            E             B            C
Q1      5.60        5.69        8.78
Q2      2.06        2.60        4.41
Q3      0.25        0.46        8.74
Q4      0            0.26        0.18
Q5      0            0.43        0.61
Q6      5.59        5.69        8.78       

The power supply is a soundlab GO25M and is kicking out 8.78 V

Is there anything obvious to anyone? I'm pretty clueless, I just follow other peoples layouts at the mo!

Thanks for your time guys,
Jimi

[isildur100]

Hi,

The best thing to do is to use an audio probe. That way you will see up to where the signal starts to act funny. Basically you should have a very loud signal right after Q2.

Did you match Q4 and Q5? What trannies did you use exactly?

[liquids]

It's not quite so simple to audio probe due to what happens in the circuit as compared to most distortions and fuzzes, but audio probing does help, to a degree.  Some of the voltages need to be variable when notes are played, etc.  And There's other places in the circuit to compare voltages than just the transistor pins as well.  I believe I have posted some info about voltages in this thread a way back.  

You should indicate if playing notes has any affect on the 'machine gun' better known as the oscillator triggering- or at least that is what I call it.... Anyhow, it sounds like playing doesn't 'override' the machine gun, which is one problem if so.

Here's some quick help: Audio probe at the capacitor before the diode/Q3, around where the 22n caps go to ground.   It should sound like a semi-muffled, distorted fuzz type tone without too much gating if any.  If that is all good, than you are good up to there (at least for this issue). If not, stop right there and audio probe where the signal dies from the input to this point.   Up to Q3 it's just a filtered fuzz.

As for the cause of the machine gun sound, my though is you have a problem around Q3, possibly Q4/Q5.   Something is causing stray voltage in this area that is causing the oscillator to remain open, and respond to the voltage like a note....otherwise your Q3 E and base would be resting above the diode drop....other have suggested using other types of diodes, but if you have a germanium or schottky diode there, use a silicon for now until you get this resolved...I prefer it anyhow.   The silicon diode drop/silicon transistor (.6v to turn on or so) helps it gate  so that at your said voltages (.25 E .46 B) it reads 'no signal' and gates off.  I don't have voltages for Q4/5 but I find it odd that Q5 C is at about .6v....

Also check your values, correct part types, make sure you've got everything correctly oriented, crossed traces, etc.  Look it over with a magnifying glass. You'll learn a good amount from the debug.  It's usually something small and embarrassing if you had so much success in the past.  Good luck.

[liquids]

SOUND CLIPS PLEASE!!!

With all the building blocks this is a fragile monster that spans 4 breadboards currently, and over 10 pots!  But I finally got back to the workbench this week, and got it all working again on the board.  I'm tinkering still, and sorry for the delay, but I did record some sloppy clips for you. 

Also, my original Synthbox demo was (as noted in that post) recorded with a poor setup involving an awful recording program and a cheap computer mic, put at a distance to avoid distortion.  It definitely colored the tonality of the recording a bit.... 

These samples should be a bit more realistic, as now I've got Audacity, a SM57 in front of the amp with a cable that goes from xlr->1/8", all that into the same cheesy sound card.  So I recorded a short snippet of the 'current' Synthbox '2' on the breadboard (but with the active EQ disconnected), and also a few sloppy phrases of the synthbox-->rather modified MFOS envelope filter.  But The envelope is generated using a buffered, high passed-filtered version of my clean signal as the 'trigger.'  See these dead threads for some of the basics, if you happen to be interested in that part:
http://www.diystompboxes.com/smfforum/index.php?topic=81140.msg671699#msg671699
http://www.diystompboxes.com/smfforum/index.php?topic=78325.msg671598#msg671598

So, the new clips are in the gallery.  I may eventually remove the old clips...Enjoy!

Brief demo of the Synthbox 2 in the same vein as the original clip:  http://www.aronnelson.com/gallery/main.php/v/liquids/Synthbox+2+Demo.mp3.html
Some sloppy phrases of synthbox-->down sweep envelope filter:  http://www.aronnelson.com/gallery/main.php/v/liquids/Synthbox+with+Filter.mp3.html

[~arph]

Nice that sounds really neat!
I still intend to do a PCB layout for the latest version, but time is not on my side.
You could also try to run this into a Snow White autowah (schem at the other forum)
That looks a bit like the MFOS. Just a bit simpler I believe.

[mantella]

I've tried to download the vero layout file a few times, and it always tries to save as an Adobe After Effects file. Is there a straight-up image file (jpg) of that vero?

And has anyone built the vero layout yet?

Thanks!

[~arph]

As far as I am aware there is no vero layout for this?
Can you give me a reply# in this thread where I can find the file you're trying to save?

The Adobe Effect problem is probably a setting on you personal computer. Adobe must heve registered image file extensions to Adobe Effects.
(I currently endure the same problem but then it wants to open in adobe image ready, which su#ks)

Regards,

Arnoud

[Jimi W]

Thanks for the help guys, it's very much appreciated! I didn't get much time lastnight to do much but I did make some progress! 

Firstly I've confirmed the transistors are MPSA18 for 1 and 6 the rest are 2N5089s. Qs 4 and 5 are perfectly matched 2N5089s and they are all oreintated as per the layout with Ll the emitters going to ground.

I've made an audio probe and after finding a dodgy solder joint on Q2 (looked fine but slightly on the lean side) after checking components around it. After I'd resoldered that I am now getting the correct synth sound but the machine gun/oscillation is still present. The pots and bass switch all do as they should. 

I carried on probing and it does seem to start at Q2 very quietly where the 2.2 cap meets the collector. Its more of a flutter here than machine gun. This carries on until the diode where it dramatically increases in volume. I replaced the diode with another 1N4148 and it's not cured it. The strong noise starts where the diode meets Q3. 

Reading your previous posts it seems that I have a voltage on the 1k resistors after the 2.2 cap that comes off the collector of Q2. You mention these should be close to ground voltage. Mine start around 2.6 and slowly decrease untill you play a note and they hit 2.6 again. I've replaced this cap and it's still the same. The - side of the cap is connected to the resistors and the + to Q2 collector. I've also changed the 2.2 before the diode and the diode itself. 

Any more clues as to what could be causing this?

Must say that I think I'm gonna love this pedal, sounds great (from what I can hear!) and also tracks well with my 67 SG Special with P90's just a shame it sounds like Im jamming with a machine gun!

Thanks again for your help guys, I'm trying my best to absorb all the info and learn, so hopefully I won't be pestering you too much in the future.

Jimi

[liquids]

Some of what you are saying seems odd, but it would indicate that the stray voltage is most likely coming into the signal after Q2...it may be that some is 'feeding back' into that area, but not where it starts, since there is no aplification going on between Q2's collector and the diode. 

Theoretically, there should be no voltage between the cap coming off Q2 and the cap that connects to Q3/Diode as those caps are there to take DC off that whole section, so that DC stops at the Q2 collector, and likewise does not 'feedback' from the voltages on the diode/Q3. Hence t that whole resistor-capacitor network in between should be very close to ground.

Check and or replace both of those caps if it's reasonable, to ensure they are not faulty. I'd suspect the one closest to Q3 is the cuplrit, of the two.     Also, it may help to reverse the orientation of that 'second' cap anyhow since it's presumably electrolytic and polarized.  The side that is facing the Q3/diode junction will have some level of varying voltage on it (positive), while the other should not have much or any voltage (negative)....

These are semi-informed shots in the dark, but keep trying, you're getting there, and learning a bit about debugging in the process! 

[mantella]

here's the link I was referring to:
http://www.aronnelson.com/gallery/main.php/v/liquids/SynthboxLayout_diy.html

maybe there was a layout there at one time?

EDIT: ah, just had to download the DIY Layout Creator (http://www.softpedia.com/get/Others/Home-Education/DIY-Layout-Creator.shtml) to get the download to work.

[Jimi W]

Hi,
Well this evening I have replaced 7 Caps and its still doing it! Grrrrr!!!!!!

I've replaced the 2.2 polarised cap before Q2, the 3 polarised caps between Q2 and Q3 and also the 2 non polarised caps between Q2 and Q3. I reversed the 2.2 just before the diode too. I also changed the 1 u polarised cap that goes from the Q3 Collector to ground.

I've also triple checked all joints for solder bridges and have scored between each 'close' joint with a small screwdriver to confirm that they are not touching.

If the DC was bleeding back, how far could it bleed back from?

I'm thinking about just scrapping this and starting again, it'd probably be quicker!....no..... its doing me good to learn about debugging and looking into what is actually happening in the circuit, I'm not really in the right frame of mind tonight though!

Any thoughts guys?

Cheers once more,
Jimi

[TrentC]

Has anyone built the op amp version? If so what op amp did you use?

[liquids]

Nothing special needed here.  Common Jfet input types should work quite well here if not best--such as TL072, LF353.  Standard 4558 type should work well too. 

[isildur100]

I have the opamp version on my breadboard right now. It works pretty good. I used TL072 for the opamps and a max1044 to obtain +/- 9V.

The tracking seems to be better than with the original version. The only thing is that I had to replace the 100nf cap with a 10uf cap where that transistor and diode section is. Doing that gave a lot more sustain which helped the tracking at the same time.

I also used the tone stack at the end which is not bad at all. However, I had to change a 10k resistor to a 15k value for the treble because with a 10k, when the treble was maxed I had a loud squeal. The 15k got rid of the problem.

Oh, and there is a resistor with no value in the tone stack going from the + input of the opamp to ground. I put a 470k there but I don't know what value should be there optimally.

All in all, I really like this circuit. I will try to make sound clips very soon.

cheers

John