MXR Envelope Filter circuit boards for sale on ebay!!

[StephenGiles]

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3768381043

There is a reduced circuit diagram on the ebay page with factory notes, perhaps someone with a razor sharp screen can decipher - the notes that is!

[slacker]

Interesting, if I save the imges and then zoom in on them they are readable. I'll have to see if there's any useful info in there.

[StephenGiles]

Interesting, if I save the imges and then zoom in on them they are readable. I'll have to see if there's any useful info in there.

It's a pity there are so small. The circuit is well known of course but it's interesting to have the notes and the setup instructions.

[skiraly017]

Looks like same schematic with notes can be found here.

[StephenGiles]

Looks like same schematic with notes can be found here.

So it is - the plot thickens. I can't get deeper into that site, maybe a more readable version of the setup procedure is there somewhere!

[Mark Hammer]

I actually have all that stuff from my 1978 EF.  I photocopied the copper side of the board and drew the parts side layout.  I just don't have the file with me here at the moment.  I know that one of the board layouts posted around (not the Tonepad layout)  is precariously close to the original layout.  Fits in a 1590B and everything.

[skiraly017]

1977 PCB Layout

1976 Schematic

[skiraly017]

Looks like same schematic with notes can be found here.

So it is - the plot thickens. I can't get deeper into that site, maybe a more readable version of the setup procedure is there somewhere!

If you want, download the picture and mark/circle what's difficult to read in red and email it to me. I'll take a crack at it over the next few days.

[Dragonfly]

I thought about just buying one of the boards for the heck of it, but he doesnt take paypal...oh well.

[Mark Hammer]

Looks like same schematic with notes can be found here.

After loving this pedal for 30 years, I've never seen that drawing until today.  Lucky I haven't started eating because I would have choked on my lunch.  I draw your collective attention to the notes surrounding the filter portion of the circuit.  Am I to understand that one could derive highpass, bandpass and lowpass outputs simply by redirecting C2 (.05uf) to either pins 6, 2, or 12 of the CD4069 (leaving R12 as is)?  If so, this is BIG news.

[mdh]

Looks like same schematic with notes can be found here.

After loving this pedal for 30 years, I've never seen that drawing until today.  Lucky I haven't started eating because I would have choked on my lunch.  I draw your collective attention to the notes surrounding the filter portion of the circuit.  Am I to understand that one could derive highpass, bandpass and lowpass outputs simply by redirecting C2 (.05uf) to either pins 6, 2, or 12 of the CD4069 (leaving R12 as is)?  If so, this is BIG news.

Isn't that feature common to state-variable filters such as this one and the Neutron?  I mean, I realize it's not a standard mod for the MXR EF, but if I'm seeing this correctly, it would be pretty much the same arrangement as in the Neutron if you just tapped high-pass and band-pass outputs.

[soggybag]

I thought about buying a board. But changed my mind when I realized the price $21. I think I could get something from TonePad or GGG for less.

[Mark Hammer]

Looks like same schematic with notes can be found here.

After loving this pedal for 30 years, I've never seen that drawing until today.  Lucky I haven't started eating because I would have choked on my lunch.  I draw your collective attention to the notes surrounding the filter portion of the circuit.  Am I to understand that one could derive highpass, bandpass and lowpass outputs simply by redirecting C2 (.05uf) to either pins 6, 2, or 12 of the CD4069 (leaving R12 as is)?  If so, this is BIG news.

Isn't that feature common to state-variable filters such as this one and the Neutron?  I mean, I realize it's not a standard mod for the MXR EF, but if I'm seeing this correctly, it would be pretty much the same arrangement as in the Neutron if you just tapped high-pass and band-pass outputs.

Perhaps.  But the use of the CMOS invertor sections, and the way it was drawn prevented me from actually recognizing it as a SVF all this time.  I always thought it was simply a 2-pole lowpass.

[slacker]

Tapping the high and band pass outputs work pretty well, I played around with the idea a while ago but it never came to anything.  If I'd have realised I was on to something of interest I'd have posted about it.

I found you need to buffer the outputs though which I did using the spare CD4069 section with 1M input and feedback resistors.

[jefe]

mostly just bookmarking this page

I think I'm gonna but this on the breadboard again.

[Mark Hammer]

Tapping the high and band pass outputs work pretty well, I played around with the idea a while ago but it never came to anything.  If I'd have realised I was on to something of interest I'd have posted about it.

I found you need to buffer the outputs though which I did using the spare CD4069 section with 1M input and feedback resistors.

Excellent tip!  many thanks

[StephenGiles]

Whilst breadboarding this it would be interesting to wire up 3 filters wired as HP,BP and LP and observe the sounds when mixed together.

[StephenGiles]

Whilst breadboarding this it would be interesting to wire up 3 filters wired as HP,BP and LP and observe the sounds when mixed together.

I'm working at home today due to serious refurbishment happening in the house where I work, and I don't have any 4049s or 4069s. That was not good planning!