Arcomatic Rosinator - bowed string effect

[anotherjim]

So, my first design post here - about time too.

Here is the Arcomatic Rosinator...



And here's some short demo tracks.
https://soundcloud.com/ashdalestudio/arcobass1
https://soundcloud.com/ashdalestudio/arcoguitar1
https://soundcloud.com/ashdalestudio/arcoduetdemo1

The idea was to reproduce the sound of a String Machine keyboard such as the Arp/Solina.
These instruments were basically organs using digital dividers for the tone BUT the basic square wave is high pass filtered and rectified making a kind of sawtooth wave highly reminiscent of a bowed string.

In the Arcomatic Rosinator the input is amplified (a lot) and squared by a schmitt trigger, then high pass filtered (variable by the tone control) and then fed to a simple "swing" type VCA (Q1). The preamp also feeds the envelope circuit which contains an Attack control.

Pretty simple. It can sound too raw heard dry. It is meant for playing through a guitar cab. Also, you do need to articulate in a string player way or it sounds synthy - but it can be synthy if you want. It's a very rich sound which works well  with many modulation type effects and
really does need at least some reverb.

Hope it finds some favour
Jim

[duck_arse]

one sounds like a cello, the other like a stylophone (!) thru slow gear, and both sound spooky/creepy.

nice work, looks like a few wrinkles in that circuit.

[alparent]

This is very interesting.
What do you mean "a few wrinkles in that circuit"?

[duck_arse]

tricks, new building blox, things I haven't seen, different ways to do things. wrinkles. the diode clamps, the zener diode, the swing vca.

[alparent]

OK got it. I'm French, so sometimes I miss things.  
So wrinkles in schematics are good, in my clothes it's bad, but in designs it's good.  

Is a layout of this coming? Or should I work on my own? 

[DougH]

Sounds cool! Good job!

[armdnrdy]

Yes...Sounds great!

A couple a questions:

Most analog effects such as this don't track very well when played at a fast rate. I've found that one must adjust their playing and choose "passages" that will "work" with the effect.

How does this design track at faster speeds? Also, how is the tracking when playing higher strings/notes?

I don't know if you designed this effect with simplicity/low parts count in mind but...I feel that a mix control would be useful.
Also, if a decay control were added, it would open up the effect for different percussive synth/steel drum sounds.

[~arph]

Nice! Somehow I was expecting a divider in there 

[jdub]

Very nice indeed!  I'm curious about the tracking, too...

[Luke51411]

I like it! Sounds very good!

[slacker]

Sounds great, nice work.

[Keppy]

Excellent!

[anotherjim]

Thanks for the comments all.

It was very much designed with simplicity in mind.

To list the limitations involved...

Tracking - it depends. Nearest possible to neck pickup. Tone rolled off. A stable neck. If humbucker, then turn down a bit or reduce gain in first amp. I find finger picking (traditional bass style) near the neck joint very beneficial too.

Technique - Well, even a perfect trumpet sample on a synth won't sound like a trumpet if you play it like a piano. Legato with finger vibrato is the way. I hope to hear much better example than mine! I haven't been playing axes much lately and my finger tips have gone soft.

Speed  - you lose the slow attack if you play fast. Envelope detector not sophisticated enough to snap off on short "note offs".

Range - First amp loses gain noticeably due to poor GBW of single high gain amp at higher frequencies - so the envelope level falls. Again, not sophisticated enough for more than 4 octaves.

Range (again). The wave out is actually a single positive "pip" per cycle. This is the bowed sounding part. There is an optimum range  duty cycle for this. Too narrow a pip (HP filter cut off high) and it starts to sound like brass (note - you may want that). Too broad a pip (HP filter cut off low) and it starts to sound square wave (you may want that too!). Ideally there would be a pitch tracking element to the HPF.

Notes on circuit...
The Zener is to limit the amplitude. With a slow attack, it takes a lot of judgement to know how hard to pick, this removes the doubt. 2 green LED's in series would probably do instead.

Swing VCA was used in several of Rolands better known analog drum machines. It is very simple BUT it rectifies the output - I wanted that.

LM324 ( or 2 LM358) I wanted output & input to ground and cheap. More expensive rail to rail types might well give better response on high notes. Or, just more stages.

Input clamp diodes - these may be useless -  just that I had read they can keep an opamp out of latch-up when it's gain is trying to send the output beyond the rails. They don't cost much so they're there!

No layout sorry. I can supply the Eagle scheme file  if anyone wants to work one up? Mine is made up in my usual "make it up as I go along" fashion on perf-board.

Next...

You should hear it with a complex chorus - scarily like a Solina. I have a plan to cook up a string machine style triple, dual lfo chorus using PT2399's

Octave divide - yes, that's to come. I left it out of this build to easily fit a standard stomp box and keep it simple.

Octave up - that too appears possible followed by 2 octaves down.

Blend - definitely. Guitar and strings go very well played note for note together.

Other instruments. Brass appears to be possible.

[Mustachio]

Man that sounds awesome! Nice work Jim!

Wow sounds like you got a bunch of stuff cooking up! I need to get out of my funk and build some stuff! This sounds like a fun pedal to play with

[DDD]

Beautiful sound, uncommon design.
Great!

[bluesdevil]

Very cool!! I have a feeling there will be a super duper deluxe version with all the bells and whistles soon... you are on to something really great.
Looking forward to seeing how it progresses.

[tubegeek]

And, a cooool name!

[Zool]

I've tried to make a veroboard layout for this, but I'm not too experienced in drawing layouts from schematics. So if someone could verify it, that would be great 

[Luke51411]

I'm a little confused by the schematic so here is a noobish question. What is Vcc as it seems to just be +9v and Agnd and Vee seem to be the same am I missing something?

[deadastronaut]

love it...great work jim..