distortion+phaser or synth type diy pedals?

[FutreBen]

Hello, my name's Ben. I've never posted here before. I'm pretty green with this electronics business, I hope to try something new though. I play bass and would like to build a unique pedal, although from the looks of the experimentation i've watched go on in this community, nothing I have in mind is probably unique. If there are there any schematics for the Pnp type of etching to build something like a distortion/phaser or a bass synth pedal i'd like to give it a go. i would be using a Tonepad phototutorial i found here for the etching. I also just downloaded Slade's tut.
Right now i'm running my bass through a q-tron plus (downward sweep) with an old boss HM-1 in the effects loop so I end up with a low passed, fuzzy, vowelly effect to kind of simulate the modulation i'm looking for (note: I don't want to try to build an envelope filter). I also bought a $20 phaser pedal to put at the end of the chain. Unfortunately it turned out to be garbage, but hey, for $20 you can't lose right?

So really I'm just wondering if there's any directions for building any distortion+phaser or synth type pedals I could build with the pnp etching system, or if I need to know anything before trying something out.
Thanks! 

[kaycee]

Hi, feel free to etch a board if you wish,  but for an easy life, there are plenty of people supplying kits or circuit boards for phasers and distortions. You could build stand alone pedals from kits, or get two boards, source your parts and put them both in a single enclosure, a 2 in 1 . Depends on your experience building which option to take.

[Mark Hammer]

I think the first helpful step is to think in terms of analog modular synthesis.  That is, start by imagining the sounds you want to produce, then deconstruct that into the specific signal-modification building blocks, and what would patch into what in what order.  And then move to the closest effect approximation of that. 

Certainly the availability of the send/return loop in the Q-Tron+ is a great starting point.  One of the weaknesses of the older folded-metal chassis Q-Tron+, and to a lesser extent the cast aluminum chassis issue, is that decay time is not directly controllable..  You'll find that faster decay time tends to make both guitar and bass sound more "synth-ey".

I am naively assuming that the circuit of the Q-Tron+ and non-plus models is the same, but for the external loop.  My schematic of the non-plus model shows a 47k resistor to ground, in parallel with a 4u7 cap. in the rectifier section (the part that tracks pick attack).  Making that resistor lower in value quickens decay time, and making it higher extends decay time.  If you want to test out whether altering decay time produces something like what you imagine, I would recommend doing the following:
1) get a 500k pot (linear or log, doesn't matter at this point)
2) identify the pads on the copper side of the board where that 47k resistor is
3) using the wiper and one of the side lugs on the pot (doesn't matter which), temporaily wire up (solder) the pot to those two contacts points on the board

This will put 500k in parallel with the 47k pot.  It won't let you make the decay time slower, but it will let you hear what "faster" sounds like to you.

Note that, past a certain point, the pot will make all audible sweep tend to disappear..  Why?  The 4u7 cap stores up the voltage/current that the envelope follower "captures".  The 47k resistor lets that stored energy drain off, at a certain rate/speed.  If the rate that it is drained off is too fast, it never really gets a chance to "store". 

So, with the temporary pot set to max resistance, 47k+500k in parallel produces an effective resistance of 43k.  With the pot set to half of its resistance (47k+250k), that drops to 39.5k, and with the pot reduced to 50k (47k+50k), we're down to 24k.  Once the pot is at 10k, that parallel resistance is 8k2, and you won't likely hear any sweep.  Still, this is a temporary non-intrusive way of seeing if a decay mod wuld be useful to you.  YOu don't need to cut anything, and you don't need to remove anything.

Needless to say, if you have the cast-aluinum chassis model (which I gather is mostly surface mount) you need to consider a different strategy.

[FutreBen]

Thanks for the feedback! Buying a kit is definitely an option. If I did buy a distortion kit and a phaser kit, could I blend the sounds somehow? And also, would it be cheaper than making it myself?

I am naively assuming that the circuit of the Q-Tron+ and non-plus models is the same, but for the external loop.

Needless to say, if you have the cast-aluminum chassis model (which I gather is mostly surface mount) you need to consider a different strategy.

Mark,
The Qtron+ has a feature that lets you switch between "slow" and "fast" sweep. The slow sweep supposedly makes the pedal sound more like the Mu-tron, and the fast sweep sounds more like an auto wah when the sweep is set in the up direction. I'm not sure if this is the change that you're talking about, this board is beyond me. I think it might be easier to read on the other side, but it won't come out of the case. I'm going to make some statements to try to explain the circuit that you will probably laugh at now, if these components appeared to be visibly connected i could probably determine what path the electricity was following and figure something out, but they're not.

I found some capacitors that said 4.7u/25v in various places and also some that said 10u/25v. I'm under the impression that capacitors are the cylinders? I'm not going to try to interpret the labels, i'm just going abandon my shallow electrical experience and copy them.

There are also blue plastic boxes that say 47n/63v, one is right by a wire that says ground. Some blue boxes say 0.1u and 0.1u/63v.

It would be really interesting to swap the 2 option fast/slow response knob to an actual pot.

My q-tron's chassis is die cast aluminum.

[Mark Hammer]

There will be a few "cylinders" in there.  You are correct in assuming that most of them will be electrolytic capacitors.  The "boxes" are also capacitors, of different material (box shaped so that industrial robotic arms can easily grab and stuff them into boards).  The unit uses two photocells to sweep the filter.  I haven't seen any gutshots of the cast-aluminum box version, so I don't know if it uses two single optoisolators or one dual.

I wasn't sure if the slow/fast control was a variable control or simply a switch.  As you can tell, the feel of the sweep can be very different, depending on the setting of the slow/fast switch and the direction of sweep.  Since it is a switch, I'm fairly confident that it simply swaps a few resistors or adds one or two resistors in parallel.

Forgive my rather paternalistic view here, but based on the questions you're asking, I fear you may be wading into deeper waters than you're ready for...yet.  A year from now, this may be a simple mod for you, but given the newness of the device, and the risk of buggering up the board, I'd either hold off, or find someone skilled enough to do the mods and I'll happily guide them through it.  The goal here is for you to have a more usable pedal, not a heap of regrets.

Here is an illustration of what the differing decay settings can sound like.  It's a heavily modded Bass Balls circuit.  The sound samples really don't start until the 7:00 mark, with everything before that a discussion of how the circuit - modded and original - works.  http://www.youtube.com/watch?v=eoAIKHFGOcQ  You'll have to forgive the hum from the fluorescent lights.