Synthbox

[igor12]

Build Confirmed.  Tracks great, sounds great. Mine seems to sound a little more octave like than synth like.  PLease listen and tell me what you think.  The only thing I changed was to use a BC239 (Hfe=500) for the last buffer and I replaced 1N4148 with a 1N4517 which did improve tracking.  Blows away the shocktave and is better than Rocktave.
http://www.aronnelson.com/DIYFiles/up/synth_box.mp3

[liquids]

Build Confirmed.  Tracks great, sounds great. Mine seems to sound a little more octave like than synth like.  PLease listen and tell me what you think.  The only thing I changed was to use a BC239 (Hfe=500) for the last buffer and I replaced 1N4148 with a 1N4517 which did improve tracking.  Blows away the shocktave and is better than Rocktave

Cool sound clip!   

[tiges_ tendres]

Build Confirmed.  Tracks great, sounds great. Mine seems to sound a little more octave like than synth like.  PLease listen and tell me what you think.  The only thing I changed was to use a BC239 (Hfe=500) for the last buffer and I replaced 1N4148 with a 1N4517 which did improve tracking.  Blows away the shocktave and is better than Rocktave.
http://www.aronnelson.com/DIYFiles/up/synth_box.mp3

That definitely sounds more synthy than octave-y to me!

Like a blue box on steroids.

[liquids]

I replaced 1N4148 with a 1N4517 which did improve tracking.

1N4517 returned no results on mouser.   Do you mean 1N5817?

[thedefog]

No problem reviving this...it's still a 'work in progress.'  I may even have a 3rd version which is mostly op amp, and more user friendly in the near future.

Ticking? There is no LFO so I'm not sure I understand you....do you mean, when you aren't playing it is still 'making a note?'   If so, that should be fairly easy to resolve.

Following the layout, Check your traces for any stray solder connections especially around Q3.  Get your voltages on Q3. Either the base or the emitter - I can't recall which right now, but one of them should mostly be variable as you play a note.  The 'no note playing' voltage should be below .6 volts, which is a key part of the 'gating' and 'decay.'   Examine this area carefully, I suspect that is where the problem is.  Audio probe carefully here as well...it may give you clues. 

Also, the electrolytic cap that feeds that stage, right before the diode and Q3...you may want to reverse it.....and if you get it working, try replacing the 1uF and 47k pair with .1uF and 10k, you may like it better (maybe not!)

Good luck, let us know what you find.

Hey Liquids,

Thanks for the help. I'm going to try that out now. I have no clue why I said LFO. What I meant was that the oscillation kept going when not playing. I was a little drunk when I wrote that last night, so that explains that. 

[igor12]

I meant 1N457, sorry.

[thedefog]

No problem reviving this...it's still a 'work in progress.'  I may even have a 3rd version which is mostly op amp, and more user friendly in the near future.

Ticking? There is no LFO so I'm not sure I understand you....do you mean, when you aren't playing it is still 'making a note?'   If so, that should be fairly easy to resolve.

Following the layout, Check your traces for any stray solder connections especially around Q3.  Get your voltages on Q3. Either the base or the emitter - I can't recall which right now, but one of them should mostly be variable as you play a note.  The 'no note playing' voltage should be below .6 volts, which is a key part of the 'gating' and 'decay.'   Examine this area carefully, I suspect that is where the problem is.  Audio probe carefully here as well...it may give you clues. 

Also, the electrolytic cap that feeds that stage, right before the diode and Q3...you may want to reverse it.....and if you get it working, try replacing the 1uF and 47k pair with .1uF and 10k, you may like it better (maybe not!)

Good luck, let us know what you find.

Hey Liquids,

Thanks for the help. I'm going to try that out now. I have no clue why I said LFO. What I meant was that the oscillation kept going when not playing. I was a little drunk when I wrote that last night, so that explains that. 

I reversed the cap as you suggested, but it unfortunately made no difference. When it is powered on, even with nothing connected to the input, it sounds like a race car in pole position (which isn't a terrible thing, but not what I hoped for).

I guess I could try a different transistor for Q3. I have more MPSa18s laying around. I used alligator clips to probe at it, and before Q3 it just sounds like a fuzzy distortion, but the base and collector on Q3 has that race car sound coming off of it. Audio probe on the stages after that point still have it as well, just filtered differently and boosted. I checked all my components and soldering work, and I see no bridging or anything. The only thing I can think of is that I have the wrong resistor value somewhere in there. Voltages were variable on the base of Q3 when I checked that when I played notes (If I remember correctly, higher voltages around 6.8v when playing and drooping back down to like 4v when not).

[liquids]

 

I reversed the cap as you suggested, but it unfortunately made no difference. When it is powered on, even with nothing connected to the input, it sounds like a race car in pole position (which isn't a terrible thing, but not what I hoped for).

I guess I could try a different transistor for Q3. I have more MPSa18s laying around. I used alligator clips to probe at it, and before Q3 it just sounds like a fuzzy distortion, but the base and collector on Q3 has that race car sound coming off of it. Audio probe on the stages after that point still have it as well, just filtered differently and boosted. I checked all my components and soldering work, and I see no bridging or anything. The only thing I can think of is that I have the wrong resistor value somewhere in there. Voltages were variable on the base of Q3 when I checked that when I played notes (If I remember correctly, higher voltages around 6.8v when playing and drooping back down to like 4v when not).

Yeah, it's all right there.  You got it, even though you didn't 'get it'.  I just tested mine, and when rigged off a 9v (one spot = 9.4v) supply, the emitter/base hover around .2v, and when I play a note it gets up to about 2.5v.  Q4 and Q5 also seem variable voltage with note played (?) but stay pretty low, from a quick look - below a volt even?

That transistor stage crates a voltage which acts in one way or another like a gate, in response to the 'note signal' of which the oscillator responds to.  Any voltage above the diode drop (.6v) = the gate is open.  Likewise, I don't totally understand it, but if there is enough voltage, it somehow triggers the oscillator to create a frequency - how or what frequency is determined, I don't know, but that little bit I know.  Hey, I'm still just an amateur hack, as I've said many times.   

Following the layout you said you are using: first off, make sure there is no voltage on those 1K resistors.  everything should be very close to ground between the 2.2uF capacitor off of Q2 and to the 'inside' of the following 2.2uF capacitor.  This ensures that the Q3 is not being fed any DC from the previous stage. 

At that point, make sure Q3 is what it says it is, and that it's oriented properly.  Again, you should be at or below .6v , where you reading 4v (the emitter), to keep the oscillator from ringing.   Check this whole area around and after that very closely with your DMM and find out where the voltage is coming in.  Since nothing outside of the collector of Q3 (which should read about the voltage of the power supply) has much voltage on it, you should be able to track down where the 'stray voltage' is coming into play around Q3 or afterward pretty clearly....you may even be 'backfeeding' from Q6 if there is a bad cap somewhere...

Hope this helps!

[~arph]

I believe 89 is higer gain too.. EDIT:   where did the post go that I replied this too?? 

I've had some oscillations too during the experimentation phase. This is the flipflop arrrangement oscillating. This means it is getting the wrong voltage from the frequency to voltage converter.

[igor12]

OK, I tried with all 3904 and it works fine. Just match the gain in the flip flop section. This opens up the choices if you want to use a transistor-array IC.  I also tried setting Vref to 4.5v using 2 15k resistors and that works fine also. Now how can I get second octave? Cascading 2 synth-boxes?  I still can't figure out the theory behind the F-V and flip-flop section. But I will. 

[liquids]

http://www.diystompboxes.com/analogalchemy/sch/shocktave.html

"The circuit consists of a high-gain preamp stage, followed by a frequency-to-voltage convertor, which in turn drives an oscillator. The oscillator is tuned so that it can only keep up with every other cycle, resulting in the octave-down effect..."

[earthtonesaudio]

http://www.diystompboxes.com/analogalchemy/sch/shocktave.html

"The circuit consists of a high-gain preamp stage, followed by a frequency-to-voltage convertor, which in turn drives an oscillator. The oscillator is tuned so that it can only keep up with every other cycle, resulting in the octave-down effect..."

This part still eludes me.

[isildur100]

igor, the sound clips are very cool!


what type of guitar pickups are you using, humbuckers or single coil?

[liquids]

http://www.diystompboxes.com/analogalchemy/sch/shocktave.html

"The circuit consists of a high-gain preamp stage, followed by a frequency-to-voltage convertor, which in turn drives an oscillator. The oscillator is tuned so that it can only keep up with every other cycle, resulting in the octave-down effect..."

This part still eludes me.

If you use your DMM at the base/emitter of the transistor paired with the diode...you see that as you pluck a note, voltage varys...so I'm assuming thats the f-v part.  How it works?   NO idea...

[igor12]

humbucker, neck pickup.  IBANEZ LR110 (ES335 Copy)

[thedefog]

I reversed the cap as you suggested, but it unfortunately made no difference. When it is powered on, even with nothing connected to the input, it sounds like a race car in pole position (which isn't a terrible thing, but not what I hoped for).

I guess I could try a different transistor for Q3. I have more MPSa18s laying around. I used alligator clips to probe at it, and before Q3 it just sounds like a fuzzy distortion, but the base and collector on Q3 has that race car sound coming off of it. Audio probe on the stages after that point still have it as well, just filtered differently and boosted. I checked all my components and soldering work, and I see no bridging or anything. The only thing I can think of is that I have the wrong resistor value somewhere in there. Voltages were variable on the base of Q3 when I checked that when I played notes (If I remember correctly, higher voltages around 6.8v when playing and drooping back down to like 4v when not).

Hey Liquids,

Thanks for your help. I really appreciate it. I'm going to take another look at it tonight.

Yeah, it's all right there.  You got it, even though you didn't 'get it'.  I just tested mine, and when rigged off a 9v (one spot = 9.4v) supply, the emitter/base hover around .2v, and when I play a note it gets up to about 2.5v.  Q4 and Q5 also seem variable voltage with note played (?) but stay pretty low, from a quick look - below a volt even?

That transistor stage crates a voltage which acts in one way or another like a gate, in response to the 'note signal' of which the oscillator responds to.  Any voltage above the diode drop (.6v) = the gate is open.  Likewise, I don't totally understand it, but if there is enough voltage, it somehow triggers the oscillator to create a frequency - how or what frequency is determined, I don't know, but that little bit I know.  Hey, I'm still just an amateur hack, as I've said many times.   

Following the layout you said you are using: first off, make sure there is no voltage on those 1K resistors.  everything should be very close to ground between the 2.2uF capacitor off of Q2 and to the 'inside' of the following 2.2uF capacitor.  This ensures that the Q3 is not being fed any DC from the previous stage. 

At that point, make sure Q3 is what it says it is, and that it's oriented properly.  Again, you should be at or below .6v , where you reading 4v (the emitter), to keep the oscillator from ringing.   Check this whole area around and after that very closely with your DMM and find out where the voltage is coming in.  Since nothing outside of the collector of Q3 (which should read about the voltage of the power supply) has much voltage on it, you should be able to track down where the 'stray voltage' is coming into play around Q3 or afterward pretty clearly....you may even be 'backfeeding' from Q6 if there is a bad cap somewhere...

Hope this helps!

[liquids]

I did a major overhaul to the op amp version that I've been working on again recently   I wanted something that might offer a little more consistency and flexibility in terms of input signals and other users, and more so, more ideal filtering for myself. 

The links for the 'op amp' or synthbox 2 will show this new schematic, the original version which used all transistors, so to speak, is still up since there are projects that people occasionally seem to be building and working on with the original version.

http://sites.google.com/site/liquidselectronics/synthbox-2

While the output sound is nearly identical with this version, I think this one is by far the best one to build for anyone interested.  The op amps offer consistency in impedance, gain, and filtering, while the active filter at the end offers some cool tonal flexibility.

I didn't originally work on this design with filters in mind, so it stands alone,  but I've been expirimenting with using it with envelope filters.  I do plan on integrating it/housing it with other builds, in particular an envelope filter that will probably be a modified version of the MFOS EF.  With the synthboxes active treble boost filtering in particular, when it is combined with an EF, it gets some of the best synthy filter sounds I've heard yet, and gets a sound that rivals my favorite setting of my my Microsynth!  Cheers!

[isildur100]

Hey that's cool!

I need some clarifications. What are the mosfets models used (Q1, Q2)?

What voltage is it run on, +- 9V ?

Are the "grey" grounds the negative voltage or they are the ground?

There seems to be only one V- connection (in blue). You should show where V- is to be connected elsewhere too, if any.

thanks

[liquids]

I need some clarifications. What are the mosfets models used (Q1, Q2)?

Use whatever mosfet you like, but follow the datasheet and this site: http://www.muzique.com/lab/zenmos.htm
Both BS170 and 2N7000 have worked for me.  Zeners and LEDS can work too...tweak away.   The schematic is a bit open ended in some places on purpose....

What voltage is it run on, +- 9V ?

Any bipolar supply from any charge pump should work about the same for this circuit, but I've currently used something close to +/- 9v from a one spot PS and a LT1054 charge pump, currently.  V+ and V- can be whatever pubolar supply you like outside of the the limitations of the parts you use, most likely.

Are the "grey" grounds the negative voltage or they are the ground?

The ground connects are ground, and ground is typically identified with something like this symbol  Power is listed as generated of a bipolar supply (which can be gotten via a charge pump or otherwise).  

There seems to be only one V- connection (in blue). You should show where V- is to be connected elsewhere too, if any.

The only other thing that connects to the rails of the bipolar power that isn't shown, are the op amps.  I'm under the impression, from some recent reading, that typically that power connections for op amps are not included on most schematics, especially with a bipolar supply?  I'm going to leave that as is.   The  only thing outside of the op amps connected to power is liste -- the red arrow is shown as connecting to V+ and the blue arrow as connected to V-.  Again, it is left a bit open ended on purpose.

[isildur100]

Ok that's what I figured but just wanted to make sure, thanks!