Synthbox

[Nalo1022]

I'm really digging this project, but I was wondering how tracking was with quicker licks? When I get the time and money I am definitely going to build this. I love synth sounds from guitar but find when playing faster leads things tend to get a bit messy.

[isildur100]

As with most octave down pedals, the tracking issues are more with the lowest notes. Playing fast licks on higher frets will track ok. Anyways, it depends on what you mean by fast If you accidentally hit more than one string it will surely mess with the tracking.

[kdowqo]

i think the caps on the DPDT is mounted wrong on your pref layout jdub
it should be like this

i can be wrong but i don't understand how it would work in any other way

[jdub]

It works- that method was copped from a Mark Hammer post, and operates by shunting.  When the common lug of the switch is connected internally to one of the outside lugs,  current essentially takes the path of least resistance (i.e. the internal contact) and bypasses the cap mounted between those lugs. So in the layout, for example, if current enters the switch through C1a, if the common is connected internally to that outside lug, the cap between C1a and the common (C19) will be shunted (or bypassed) and the current will pass through the cap C21.  If the switch is pressed, and the internal contact is now between the common and the other lug, C19 will become the effective cap and C21 will be bypassed.  I didn't get it at first either, but then I used that method for Univibe mods to a Phase 90, and it worked like a charm; makes sense to me know.  At any rate, that's how I have it wired on my Synthbox and it does work, even if it's a bit puzzling at first.  It's cool, though, because it allows the caps to be mounted compactly on the switch with a minimum of flying leads... 

[kdowqo]

ok, thanks, now it makes sense 

[kdowqo]

ok I have built this circuit now but it doesn't work properly
first it made no sound at all then i removed the max1044 and the thing started to work... well not actually work because it sounds far from the sound-sample
it sounds like the octave is missing and the pots doesn't seem to do much either
the sound is kind of swelly and after being on for a couple of minutes it started to hum
I'm going to look through my soldering again but i thought it was strange that it worked without the charge-pump but not with

maybe i should mention that i used mpsa18 for all the npn transistors and LM833N for all the op-amps, is it crucial to use those specific op-amps TL072 and LF353?

[jdub]

Any dual opamp will work; I just used those cuz I had 'em.  As for the transistors, I'm not certain what effect using MPSA18s would have- what confuses me is the MAX1044 situation.  Since the opamps are running off a bipolar supply, removing the 1044 removes the -9V supply which should render the opamps inoperable.  Are you sure you have the -9V going to the right places?  Is the MAX1044 even producing the negative voltage as it should?  Also, be sure the MAX1044 isn't toasted- it has a max supply voltage of 10v.  If you can take some voltage measurements (with the 1044 in place) for the opamps and transistors & post 'em, and verify that the MAX1044 is putting out + and -9V, I'll check the voltages on mine as soon as I get a chance & we'll see if we can get it happenin'... 

[kdowqo]

i did some voltage tests not completely certain haw and witch pins that should be tested but i got these results and the max1044 seams to operate properly

+Vcc +9V
-Vee approximately -9V (-8.65V)
on all op-amps

Q1 & Q2 drain +0.5V
Q3 collector +9V
Q4 & Q5 collector between +0.2 and +0.1 V (volume-knob set to max)

I have looked through my soldering searching for mistakes but havent find any but thers probbably a verry good chanse there is some error hiding there

[jdub]

Best to check all pins of all opamps and all leads of all trannies.  Check out the debugging thread here:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0 for detailed intructions, if you've never done this before.  Follow the method & post the results- best way to find the problem.  

[kdowqo]

I'm using a power-supply because the cheap 9v batteries I have measure about 7v

Q1
D = +3-0 *
G = +3-0 *
S = 0

Q2
D = +3-0 *
G = +3-0 *
S = 0
*(started at about 3v and then dropped to 0)

Q3
E = 0
B = +0.2 **
C = +9

Q4
E = 0
B = +0.42
C = +0.42

Q5
E = 0
B = +0.42
C = +0.42

D1
A = 0
K = +0.2 **
**(started at a higher value but dropped to +0.2)

IC1
P1 = +9
P2 = +4.45
P3 = 0
P4 = -4.36
P5 = -8.65
P6 = +4.45 (not connected)
P7 = +6.67 (not connected)
P8 = +9

IC2
P1 = +0.86
P2 = +0.86
P3 = +0.65
P4 = -8.65
P5 = +0.86
P6 = +0.87
P7 = +0.87
P8 = +9

IC3
P1 = -0.05
P2 = -0.05
P3 = +0.87
P4 = -8.65
P5 = +0.6
P6 = 0
P7 = 0
P8 = +9


IC4
P1 = +0.14
P2 = +0.14
P3 = +0.13
P4 = -8.65
P5 = 0
P6 = 0
P7 = -0.93
P8 = +9

thats the values i got but some of them where tricky to read because of the changing values

edited the values now in proper order , i hope  

[jdub]

OK, I'm a bit puzzled- are you numbering the pins of the ICs in standard fashion (e.g. looking top of IC, notch at top, pins 1-4 on left from top down, pins 5-8 on right from bottom up)?  If so, something is way off.  It seems that you may have your pin numbering reversed- are you calling the tip pin on the right pin 1?  That's the only way +9V across pin 1 and -9V across pin 5 of ICs 2-4 makes sense...

[kdowqo]

well i was a bit unsure about how they are numbered but i went in this order
- 1 - 8 -
- 2 - 7 -
- 3 - 6 -
- 4 - 5 -

but now i see that i reversed it  

remeasured everything and edited the list

[jdub]

OK, checked my voltages and they are pretty much in line with yours (my battery is only putting out about 8 volts, but voltages are relative to yours).  You may wanna check closely for solder bridges (it's kind of a snug layout) and/or check the circuit with an audioprobe.  Is it still not working with the 1044?  Did you try it with 5089s & TL072s?

[kdowqo]

the problem remains and I get no sound at all with the 1044 in place, I thought, but actually there is some oscillation sounds or something in some knob-configurations
it seems likely to be a soldering-bridge somewhere but when I tried to get some information on the LM833N I read that people had oscillation-problem with it so I'll get new op-amps on my next order end see if it solves the problem

[isildur100]

I suggest you build it on a breadboard and make it work there first. It is not a very complex circuit to breadboard and it will be a lot easier to debug.

John

[jdub]

+1.  I had mine on the breadboard for a couple weeks before I perfed it, especially since I had never played around with bipolar supplies before. 

[Keppy]

Sorry about the zombie thread, but I want to build this on pcb. The pcb layout on the thread is for the transistor version, and the link to that schematic is dead. Anyone have the old, transistor-based schem, or a pcb layout for the opamp version? Liquids?

Man, I gotta learn to do my own layouts...

[liquids]

Search the gallery.

[frequencycentral]

Ah! That reminds me, I did a layout for this a while back, forgot all about it. It's unbuilt, untested, unverified. I haven't added the component values yet, but it's based on Naz's layout, just more compact, so most of the values should be obvious. If anyone's interested I'll revisit it and add the values. It really needs checking over by someone before being built though:

[liquids]

Keep in mind that the transistor version works, for some, but it's primitive compared to the op amp versions. It's more complex, less consistent/controllable results, less precise filtering, slightly less idiot-proof, and I dare say more trouble to build than an op amp version, if you're going through the trouble of building one...

I'd probably even continue updating the op amp version to be honest  - the tone controls are especially screwy, but I keep learning... http://www.aronnelson.com/gallery/main.php/v/liquids/Synthbox+Op+Amp.JPG.html

The thing is really amazing if I do say so myself...I don't know how I've not housed one yet. In addition to my 'ADD,' I keep wanting to perfect an envelope filter to joint house it with...haha.  Yeah, that is, when the planets align!