I really like the sound of a vibrato control and have been looking at a possible add-on mod for the loophole. I just don't see any way of making it simple. I am looking at porting the clock and voltage controller from the Payback project. In theory it is simple, turn the unused logic gate into a clock and have it modulate the power supply voltage on the ISD chip through a 2n5088 transistor. Here is Tonegod's site on the payback.
http://tech.thetonegod.com/payback/payback.html (http://tech.thetonegod.com/payback/payback.html)
What does everyone think? too complicated? Routing everything looks pretty messy and a few traces need to be cut (including those grounded gate inputs on the CD4001!) The transistor board itself will be very tiny though.
Another thought is that you could just use another dual gate chip (CD40107) to avoid having to reroute the CD4001. It would still be pretty darn small.
Hmmmm... I wonder. :D
Now I just need to get the balls to cut up my board and test it out.
Sorry about the MS paint blobs, just trying to simulate what my solder joints are going to look like ;D
(http://i693.photobucket.com/albums/vv299/pnordeen/VibratoMod.jpg)
Cool! 2 more knobs would make this pedal a tweak-beast! :o
Would you have the the Vibrato on/off switchable too?
Quote from: nzCdog on July 04, 2011, 05:28:35 AM
Cool! 2 more knobs would make this pedal a tweak-beast! :o
Would you have the the Vibrato on/off switchable too?
You could. It would just be switching the green line between the vero and the blue trace (constant 5 volts to modulated 5 volts). That probably doesn't make any sense but I can draw it up later. I definitely want to see what the depth range is. I like the vibrato because it sounds (well in the PGS vid) like a really old/warped tape playback, sort of driving home the low fidelity thing this effect has.
The PGS demo does sound awesome
did I miss something? what PGS video?
Here is the one of the Zvex lo-fi loop junky with vibrato.
Hmmm, Tonegod is using a Schmitt trigger action NAND gate, I cannot find an 8 pin - 2 device Schmitt trigger IC. I wonder if the vibrator will work normally with just a normal comparator IC.
Update: yeah I am pretty sure that oscillator needs a Schmitt trigger, shame to use a whole cd4093 for just one logic gate...
Updated to CD4093. Also need some filtering now that the post regulator cap has been spliced off. Move C17 to where R15 is, jumper the de-tune switch, put a 22uF electro where C17 is and the wiring should be the same as before! To add a vibrato on/off switch just add a switch that opens/closes the "To REC switch" connection. That should do it.
(http://i693.photobucket.com/albums/vv299/pnordeen/VibratoMod2.jpg)
Wow! that didn't take long Paul. I'm excited to see how his works out. Are you gonna have to ditch the detune function to pull this off?
Quote from: cjkbug on July 04, 2011, 01:34:44 PM
Wow! that didn't take long Paul. I'm excited to see how his works out. Are you gonna have to ditch the detune function to pull this off?
Yeah I really want to see if it works. It is so simple I don't see how it could go wrong. I am pretty sure you could maintain the de-tune function by moving the filtering cap to the Vero and just wiring up the switch normally, I am not sure how it will react with the vibrato though...
Would this work maybe for a modified de-tune feature? The base bias for the 2N5088 is still controlled by the depth pot to the 5 volt source. The collector voltage is varied to a specific value (between 0 and 5 volts) using the pitch knob. When the NC switch is pressed it switches the 5 volt collector connection to the voltage selected on the pitch knob and if the depth knob allows a significant conduction between collector and emitter the ISD supply voltage will be set specifically to the de-tune value and the pitch will go to a specific value. Of course I have no idea if this will work or not but that seems like overkill with knobs and switches to me... awesome 8)
(http://i693.photobucket.com/albums/vv299/pnordeen/VibratoMod3.jpg)
Dude you NEED to proto these, I'l drooling at the very idea of these cool mods! Let us know how you get on!!! ;D
Quote from: nzCdog on July 06, 2011, 10:12:54 PM
Dude you NEED to proto these, I'l drooling at the very idea of these cool mods! Let us know how you get on!!! ;D
Yeah I am definitely including these on my loophole build. It might be a while before I get to it though.
I'll be building mine next week. I definitely trying this out. can you draw a working schematic to go with the vero layout Paul?
Here we go. Someone should definitely double check this to make sure I am not crazy. It is a direct copy of the vibrato section in the payback with the additional voltage drop switch on the collector supply of the transistor. You could also couple the base bias supply (now just 5 volts) to below the pitch pot to see what effect it has on the vibrato on low depth settings. Remember that R15 is now a 10uF elecro cap and C17 is a 22uF electro cap.
BTW: Purple are jumpers and blue are trace cuts.
(http://i693.photobucket.com/albums/vv299/pnordeen/Vibmod.png)
(http://i693.photobucket.com/albums/vv299/pnordeen/Vibmodlayout.png)
Final revision. I tested this vero layout today. The vibrato section worked like a charm good sweep from 5 volts to about 2.5 volts. The detune works but the vibrato kind of goes nuts at certain settings and doesn't work exactly like I was hoping. Redesigned the detune to ground out the Schmitt trigger oscillator when in detune mode. Needs a momentary DPDT (SB carries one). The switch does a few things:
1) Switches one of the gate inputs between ground and the record switch (5 volts in REC mode), this just stops oscillation while the detune switch is working.
2) Switches out the depth (base bias) pot, this will give us singular control over the gate voltage with the pitch knob.
3) Switches in the pitch knob. This pot places the gate anywhere from about 1 to 5 volts, which varies the emitter voltage (ISD Vcc) from 1 to 4.5 volts. Bump up the 4.7K resistor in case 1 volt is too low for the ISD to handle.
The layout turned into a rats nest, sorry about that. This is semi verified then. Everything operates as it should but I still want to test it with the actual loophole.
(http://i693.photobucket.com/albums/vv299/pnordeen/LoopholeVibMod.png)
and the schematic
(http://i693.photobucket.com/albums/vv299/pnordeen/Vibmod-1.png)
compared to the layout. the schem looks pretty simple. still waiting for my pcb. but I'll probably stary messing with the vero tonight. super excited 'bout this one.
Quote from: cjkbug on July 12, 2011, 12:53:17 AM
compared to the layout. the schem looks pretty simple. still waiting for my pcb. but I'll probably stary messing with the vero tonight. super excited 'bout this one.
Yeah it is all off board wire routing that makes it kind of jumbled. I should have spread it out a little more. I am excited about this too. Ever since I sold my RC-20 my jam skills have gone out the window. I just bought an ISD2560 from a dude in Italy! Stoked :D
*cough*
Whoops I bumped it... love to hear how this went (or goes) ;)
Man I was really hoping to update this one too. My SB order for this was delayed by a day (which means Monday because of the weekend). Ill get this mod tested (and an ISD2560) in the loophole on Monday night hopefully. I still have the Bajaman Compulator to build and test that day too so it may be done very early in the morning.
:D!
Alright. This mod works. But...
2.5 volts is way to low for the ISD to handle (at least the isd2560). The isd just goes into warp/glitchy mode after about 3.5 volts. I would say a little over 1 volt drop is okay. I would bump up the 4.7K to 33K.
I am not sure how to lower the bound of the oscillator though, maybe lower the base bias (depth) pot to 5k?
Another wild little quirk of the oscillator is because it is smoothed through a cap faster speeds wont be as deep and need i little extra on the depth knob to sound "full". I don't see any way of getting around that...
Other than that, mod away. It is pretty jumbled as far as wiring goes but with a decent sized enclosure you can fit everything. I also included a little effect bypass toggle on the side of mine to keep everything TB.
Very nice work! I have not had a chance to try this out yet, but my interest is piqued. Perhaps a future revision of the Loophole could incorporate this (with Paul's permission). I'm thinking also it would be nice to have the option for the ISD2560 on board.
Yeah of course you can include it. I would definitely test some values to try and get the voltage drop a little lower but it is pretty much exactly like tonegod's payback mod. It sounds very similar to the demos of the loop junky.
Oh yeah and to get the ISD25xx series to work it would only be an additional jumper to ground out two of the pins.
I was playing with this more today and also noticed that the speed knob sort of bunches up all the speed up on the last rotation of the pot. The lower speeds aren't very useable. I would try something like a reverse log taper 50K speed pot. Also the higher depth settings are useful at max speed so for depth I would use either a 10k or 5k pot depending on how extreme you want things to be (10K being more extreme)
Hey, could you use this to detune a PT2399 delay? Similar to Madbean's detune idea, where you starve the regulator, but instead of a steady voltage starve, use this instead to get a regular sweep... could that work? If so, how would you go about wiring it up? Say, for a Sea Urchin (DBD)?
I'm not quite sure if this would work with a PT2399. It works in the ISD chip because our sampling frequency is dependent on the chip's supply voltage. As we starve the chip supply we cause sampling rate modulations which cause the wavelength of our recorded guitar signal to expand and contract.
But the exact same idea is used for existing modulation schemes for the PT2399s and I am not sure why you just wouldn't use that. This also allows for the direct modulation of sampling frequency using the built in delay time control.
Bumping an old thread...
At the risk of sounding stupid, for your standard Loophole build (no vibrato mods), what if you replaced the momentary Detune switch with a potentiometer. Would this allow you to apply a detune to the playback that is not constantly falling but is "fixed"?