I want to build an EH Zipper, but I have a question...

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2/18/2000 4:11 PM
Rob	I want to build an EH Zipper, but I have a question... I have a Q-tron, and heard the zipper is much better, so I really want to build one of these!   Anybody built one with good results?   My question is: What are the guys marked Q1, Q2, and Q3 on the schematic? Are they FET's? If so, what should I use? Weird how there's no info on them on the schem...   Thanks!

 

2/18/2000 6:02 PM

Mark Hammer

Unless there is something really quirky about the Zipper that we don't know about, or something truly undesirable in your Q-Tron, I don't know why you would want to waste your time on the Zipper. The number of options, and degree of control available on the Q-Tron, far outstrip the degree of control available on the Zipper. That doesn't mean it is a lousy pedal, just that it is less than what you currently have.     Yes the transistors in question are FET's, and no nobody seems to know what they are.

 

2/18/2000 8:40 PM

Rob

Mark, do you really think the Q-tron is that much better?   I've heard of several people say that the zipper completely   blows it away. Supposedly it's much more controllable? I DO like the Q-tron; it is a very flexible filter, but I   always seem to end up with the same settings.   It's like I can only get one sound I really like with the filter in the 'up' direction, and one I really like with it   'down'...   I play bass, too, so I think it might be a little more limited for use with bass as opposed to guitar.   I'm just hoping maybe the zipper would allow me to get more than two sounds I really like...   As i sit here looking at the zipper schematic, I'm not sure   that I want to build it without being positive of all the   components anyway - the thing looks a bit complicated!   I'd hate to spend hours putting it together and not get it to work.     Rob

 

2/22/2000 9:53 PM

Mark Hammer

Half of what makes an envelope-controlled filter make you want to keep using it is the dynamic responsiveness of it. Often, this is a function of the envelope detection circuitry, and any add-ons that can add some lag to the envelope. I'm not saying that lag is better, merely that having a choice of faster and slower response times can lend a better match to the particular hunk of music being played. This is one reason I always loved the MXR envelope filter: it has an attack time control. I added two decay-time settings to my Dr. Q, and that improves its usability noticeably.     So where am I going with this? The Zipper (and remember, I haven't ever heard one) appears to have two major differences between itself and the Q-Tron. One is the control element being varied. In the Q-Tron it is optical. In the Zipper, it is FET's, which may introduce some distortion that adds a bit of character to the sound (more harmonics leads to a more pronounced filtering effect). The other major difference is that the Zipper has two attack-time settings, and that may be part of what seems to make it more playable to many users; i.e., better matching to the music through greater flexibility.     Not to fret, it IS possible to add envelope variety to the Q-Tron (assuming it isn't too far removed from the Mutron design), and I gather someone with access to more technical info will tell us how.     In the meantime, I suggest you check out the Craig Anderton Retro-Stereo that Stellan Lehrberg has posted at his site. Build one and plug your Q-Tron into it. You'll never go back to playing without one when you realize how great filters sound when combined with straight signal. Stereo effects ain't too shabby either.

 

2/23/2000 3:18 PM

Rob

Mark,   I appreciate all your input! I think you're right- I bet the switchable attack rate quality of the zipper has a lot to do with why people rave avout it. That's one thing I noticed about my Q-tron - the attack seems too fast for me.   I would like to be able to slow it down, maybe even have a pot to fine-tune it. The thing that's odd is that: when you put a distortion pedal in front of the Q-tron, the attack is much slower and more controllable and you can adjust it by tweaking the gain knob on the Q-tron. I'm guessing it's because the Distortion compresses and clips the signal?? (making it more useable by the filter?) When you play straight into the Q-tron, it seems to "wah" too fast for my taste, I want it to drag out and go "waaaaaaaaaaaaaaaaaaaaaaaaaaaaaah".     Ahhh.... but wait!!! They just came out with a "Q-tron +",   it adds an attack rate switch as well as a separate effect loop! Maybe this will solve my quest for the killer filter!     But in the meantime, I got some input on the zipper schematic and it looks like I might be able to build it afterall...     Rob P.S. I'll check out that retro-stereo, thanks!

 

2/23/2000 4:30 PM

Mark Hammer

If you look at the schematic for the Mutron III, you will see an RC combination at the output from the envelope detector (the op-amp with two diodes connected to it). On the schematic I'm looking at, it's a 330-ohm resistor and a 4.7uf cap. These set the rise (attack) and fall (decay) times of the envelope voltage going to the photocells. If you increase the resistor value, the attack will be slowed down. If you increase the capacitor value, it will take longer for the fall (or "swing-back") to occur. If you can identify their equivalent on your Q-Tron, and don't mind popping a hole in the chassis, replace the 330 ohm with something smaller (say 100 ohms), and run a larger value pot (500R to 1K would be about right) in series between the fixed resistor and the positive end of the cap. This will allow you to vary the attack time. The simplest way to vary decay time is to patch another electrolytic cap in parallel with the existing one. If the one on the Q-Tron is also 4.7uf, try sticking a 6.8-10uf one in parallel, using a chassis mounted SPST toggle to select it. This will give you plenty of lag.     One of the nice things about long lag/decay time is that you can turn down the Q and sensitivity, and get a randomy-sounding soft filtering. Running this ahead of a distortion is VERY nice. Not as pronounced as using a wah or regular setting Mutron-like device, but definitely adding some motion and animation to the sound. If you stick a compressor ahead or it, and set it for heavy compression, it becomes even less in-your-face, and more of the kind of thing you can leave on for longer periods, without it seeming gimmicky, especially since you can keep it riding just below threshold most of the time, and then just inject a little flick of the wrist now and then to open up the filter more.     I made myself one of those Craig Anderton Bi-Filter followers, and it has a fairly sizable decay-setting cap. I added a toggle for selecting three different ranges of the upper filter section (it uses two swept filters, much like the EH Bassballs), resulting in a selectably bigger and narrower spread between the two filter sections. When set for low sensitivity, longer attack and longer decay, with the filter sections spread out, you get something very much like an envelope driven phaser sound. Great for rhythm guitar.     I'm a firm believer that there is a lot more in your Q-Tron than you give it credit for. Indeed, there is more in MOST envelope-controlled filters than most owners give them credit for. You just have to get inventive. I'm not sure if the Q-Tron gives you the choice of notch filtering (highpass plus lowpass), but if it doesn't, the design makes it feasible to do so, and that would be a definite addition to consider.

 

2/25/2000 4:49 PM

Rob

thanks for the info Mark!   I'm going to order parts to build the zipper today - hopefully I can get it to work after I build it!   Yep I agree, I'm sure there is more in my Q-tron than I have found up until now. I don't really want to get into   modding it, but maybe I'll change my mind.   One thing I definitely want to try is to put a compressor in front of it. I don't have one, though, gotta build one!   I may take the Q apart this weekend and see if I can find the RC filter combo you spoke of, just for kicks. This is assuming, of course, the Q-tron uses the same basic design principle as the Mu-tron.   I also won a 70's bassballs off of ebay last week for $150, can't wait to try that puppy out!   Love them filters...   Rob

 

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