Electro-Harmonix XO Q-Tron Plus Envelope Filter Guitar Effects Pedal

Perfect for the Jerry Garcia sound as well as funk.

So I'm an engineer and I design audio circuits. I've owned the original mutron and many clones. This qtron is somewhat faithful to the original design with a few exceptions. However some of those exceptions make it considerably worse. And furthermore, a bit of fine tuning and improved parts would make it much better. The biggest problem is volume, the output is overly loud. From a design perspective this is sort of like the original in that they're over-driving the circuit, particularly the optical section, but in this qtron it means you get a bit of that overdriven charm, but even more volume. More than the original which was also quite loud. This pedal has several IC stages all built around the old 4558 op-amp and a couple optical sensors, controlling which will dictate the envelope effect. The 4558 was about all there was in the early 1970s but terrible by 1980s standards and it's still terrible now. BUT it's also true to the original and Musitronics used a ton of them. The qtron is SMD (surface mount) so good luck swapping them out without a pro smd rig. All said, any op-amp would be better, even just a TL072 would be a nice improvement BUT they're low-fi grimy in a similar way to the original so no major fault I suppose. The big failing in my opinion are the ultra-cheap electrolytic capacitors. They're so bad that swapping just the NP signal ones is a big help and swapping all the electrolytics for competent audio caps made a HUGE difference in my pedal. Because fundamentally it's a well tested, very nice envelope design....just poorly executed. Many people want to do a volume mod on these. It's probably easiest to cut in on the cabling around the foot-switch. But really EHX should have gained down the final stage, or at least included an internal trim pot or even switch to swap in different resistors around the final gain stage. Doing this and using better caps would have cost them maybe $1 a unit. So frankly it's just negligence this pedal is borderline un

I waited for one on back order which made it especially disappointing when it broke immediately. I suspect a power issue.

The amount of knobs May intimidating but it is great because I can nail down what I want with each of my guitars by fiddling with the settings. The effects loop is pretty darn useful too. It's a bit large and requires a dedicated 24 volt power supply but I love this thing.

It took me a little time to get the gist of how the pedal works, Guitar input volume has a great effect on the pedal sound. But, i think I was able to capture the essence of Garcia's tone after some fiddling.

I combine it with a mild compressor and overdrive to get that great wah sound. Couldn't be happier.