Synthbox

[~arph]

I must have said this before in this thread. But no I actually have a diy roctave divider on my bench ( did not make it myself) but that has the NE750 trick in so one half is used as a compressor, then that halve also outputs the envelope on one of the pins, that is used with the other half to restore the envelope on the octave signal. Works great!

[Keppy]

Thanks liquids. I actually searched the gallery before posting, I just missed the little button that shows ALL results, so I thought it wasn't there. As far as the opamp version, I'd like to build it, but I didn't see a pcb layout (hope I didn't miss that too) and I haven't learned to make them yet.

Thanks for the fast response to an old thread!

[deadastronaut]

this has been on my 'definately to do list' for ages...sounds great, i would love to rip a few licks with one of these....

the one with the filter was very cool....nice....

[jdub]

As far as the opamp version, I'd like to build it, but I didn't see a pcb layout

I've started foolin' around with PCB layouts lately, so maybe I can fiddle with my perf layout for the opamp version and make it more PCB-ish.  I'll see if I can get it up by the end of the week.

This really is a great circuit- I use mine all the time.  It can be a little touchy tracking-wise sometimes, but some compression before it as well as the standard neck-pickup, tone-rolled-back octave setting on the guitar and can usually compensate.  I highly recommend it.

[liquids]

This really is a great circuit- I use mine all the time.  It can be a little touchy tracking-wise sometimes, but some compression before it as well as the standard neck-pickup, tone-rolled-back octave setting on the guitar and can usually compensate.  I highly recommend it.

Cool!  Yeah, I do still think the filtering can be improved.  My knowledge is sophomoric so the projects (and most of my mods/designs) continue to morph as I learn and understand more...

[Keppy]

I've started foolin' around with PCB layouts lately, so maybe I can fiddle with my perf layout for the opamp version and make it more PCB-ish.  I'll see if I can get it up by the end of the week.

That would be great! I've been attempting to do a layout for the last few days, but it's my first one and likely to be pretty rough.

[jdub]

OK, managed to adapt the perf layout for the Synthbox 2 (opamp version) to PCB (although can be used for either):
Project image w/component values is here: http://www.aronnelson.com/gallery/main.php/v/jdub/synthbox+2+project.png.html

And here's the PCB transfer image (will need resized, o' course):
http://www.aronnelson.com/gallery/main.php/v/jdub/synthbox2+opamp+pcb.png.html

In retrospect, my original perf layout was pretty crappy, so I modified it as much as I could without redoing the entire thing. This version is not verified by build, but I checked all connections so it should be good to go.

Note that this layout has a mod involving a DPDT with caps mounted on it for switching between the stock octave down and a synth-like same-octave sound.  If this is not wanted, simply use the stock caps (.22), one between pads C1a & C1b, the other between pads C2a and C2b.  If you do use the switch, I recommend using multilayer ceramics, simply because the smaller size is easier to mount.  You can also play around with the values for C21 & C22 on the switch- the .01s worked best for me.

Also, be sure to mount the jumper from -9V that runs under IC3 before installing the socket.  If there are any questions, or if you'd like the .diy to fiddle with, lemme know & I'll send it to you.  Enjoy!

[jdub]

Couldn't get the images to post before, but I figured it out  :

Layout/values:


PCB transfer:

[thedefog]

Couldn't get the images to post before, but I figured it out  :

Layout/values:


PCB transfer:

Lovely! Great job with the layout. I built the transistor version a year ago, but never got it to work entirely and scrapped it for parts. I'm thinking this is next on the bench! Thanks.

[Keppy]

Awesome, thanks jdub! This is my next build for sure. I'll post here once it's done, but it'll be a few weeks at least.

[Keppy]

I just put this on the breadboard. After mistakenly building it with 2N5087s in the oscillator (which resulted in a bad fuzz) I got it right on the second try. While I had it on the board, I tried a few of the suggestions posted in this thread:

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 found this to be no improvement - in fact it made the tracking and sustain both worse in my build.

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.

I had a similar problem, but with the treble pot all the way down. Your fix worked like a charm. 

I also tried jdub's mod for synthy same-octave sound, using .01uF caps in place of the .22s. It worked, but the tracking on the attack of each note was glitchy for me. Values from .0047 on down worked, but exhibited a buzzy quality I didn't like. Using .0068s yielded an effect which I liked a great deal. It's basically a tracking glitch that is consistent and predictable, giving an interesting sound to the attack of each note. I will use this value when I box up the circuit, switchable with the stock caps.

Also, I jumpered the input of the last opamp section to ground, leaving out the unlabeled resistor. For the rest of the unlabeled values in the schematic, I used those suggested in jdub's build file in the gallery. I tested it with a guitar loaded up with an assortment of Seymour Duncans. It has a Duckbucker (supposed to be a Strat sound) in the neck, a Hot Stack rail pickup in the middle, and a Custom 5 humbucker in the bridge. The circuit reacted similarly to all three of these very dissimilar pickups.

Before I take this off the breadboard, I want to see if I can make it work for bass. It seems like this should be possible with some tweaks to the filtering. The problem is, I know nothing about filters. Suggestions would be appreciated!

[Keppy]

I found a couple of errors in the PCB layout. There is a pad missing for R22 on the trace between gain pot pin 1 and IC3 pin 2. Also, the trace connecting R5 & C11 on the vero layout was moved, and now incorrectly connects to C5 as well, causing the opamp to short. So far, the only other issue I've found with it is that the lead for pin 2 of the bass pot moved from its spot on the vero layout, but it's not hard to figure out where to attach it on the PCB.

I'm planning to correct these problems with a marker and etch another board to finish my build, so hopefully I can verify the rest of the layout by the end of the week. Wish me luck!

In other news, the box worked better than I expected for bass when I had it on the breadboard, so I made no changes to the filtering. I did, however, change the 47k resistor in the clipping stage to 10k, which enabled me to get some lower-gain settings (which seemed to track a bit better on bass) without sacrificing much gain when the pot is maxed. I also changed the capacitor to ground in that feedback loop from 2.2uF to 100uF. While I was still testing with guitar, this seemed to improve tracking on the lowest notes by a small amount. Values higher than this yielded no change on either guitar or bass.

[auden100]

Nice work, Keppy. Are you going to post any final schematic or layout as well?

[Keppy]

No, the schematic is liquids' and the layout is jdub's. I just wanted to build one myself and thought I'd share what I found since it's still an evolving project.

[jdub]

Dudes, sorry about the biff on the PCB. The connections I checked were on the layout; when I rendered the PCB I musta moved some stuff.  Anyway, here's a corrected version: http://www.aronnelson.com/gallery/main.php/v/jdub/synthbox2+opamp+pcb.png.html

Keppy, I'm sorry if my errors messed with your build. 

[jdub]

BTW, does anyone know how to correct images in old posts? 

[isildur100]

BTW, does anyone know how to correct images in old posts? 

You need to replace the old image with your modified one having exactly the same name and link address.

[jdub]

That's what I figured.  Can this be done in Flickr?  That's where the original image is stored- tried to change it last night but couldn't see how to replace the image with a new one without changing the link address...

[Skruffyhound]

Good work guys, like Rob, I've been looking at this for a very long time. Maybe with the layouts all done and tested I'll finally get off my arse and build it. Thanks

[Keppy]

Sorry I'm taking so long with this. I (mostly) built this back in March, but noob that I am I didn't plan my enclosure well, and every time I try and assemble the thing something shorts. When I fire it up outside the enclosure, though, it works except for one thing: When I turn the treble knob below about halfway, there's a pop followed by noise. The noise does not go away if I turn the knob back up. It does go away when I bypass the pedal and unbypass it again, but only if the knob is above halfway. Any ideas what could be causing this? Other than this issue, I can verify that jdub's pcb layout works.