Understanding the EHX Y-Triggered Filter

[Scruffie]

That's quite a nice filter there. Thanks for the vid Mark.
I noticed the envelope detector didn't trigger every time.

When you play it, it kinda keeps triggering and triggering and then just jams up, before starting again, you have to adapt your playing a lot and even then it's not particularly consistent.

Having said that, Mark isn't wrong, studying it more might lead to it being developed in to something more useful and yeah the filter itself is quite pleasant, it's the same type as found in the mini (not micro) synth.

[Mark Hammer]

Yep. Not your basic Doctor Q variant.

[Kipper4]

I might have to reread that a few times, but yer 4046 pll right.

[rankot]

This is ltspice model of a filter, hopefully w/o errors. Fixed so it can use LM13700 OTA, simulation works fine.

Code Select Expand


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TEXT -592 -320 Left 2 !;.tran .2
TEXT -584 -352 Left 2 !.ac oct 32 10 30k
TEXT -664 -384 Left 2 !.step param Rsw 10k 90k 10k


[rankot]

This is the final corrected schematic. There are still some parts (marked with ?) for which I'm not sure if they are really necessary, but this one works fine, at least in ltspice.

[Mark Hammer]

As much as I appreciate it, and the work involved, I am confused by your drawing.  Are you subbing a 13700/13600 for the original 3094/1048?

[Scruffie]

As much as I appreciate it, and the work involved, I am confused by your drawing.  Are you subbing a 13700/13600 for the original 3094/1048?

He is, the current source/sink darlington from the 3094 is in the bottom right corner of the schematic with the "P1, P8" connections.

[rankot]

As much as I appreciate it, and the work involved, I am confused by your drawing.  Are you subbing a 13700/13600 for the original 3094/1048?

Yes Mark, since I can't find CA3094, I decided to recreate this using LM13700. Also, I confirm that R21 and R37 on my schematic are not necessary - they're present in the "official" schematic, but not on the PCB photos you've shared. But I'm still not sure about C23 (10u), it's not present in original schematic, but I believe I saw it on the PCB. It definitely affects operation.

I must ask Mark or anyone else having an original pedal, to check out R2, R4, R5, R6 value. They seem as 1k to me (if photograph colors are right), not as 10k as shown on original schematic.

[StephenGiles]

I echo Mark's appreciation, but I'll have to restate the 13700 rectangle with usual triangles to get my head around this!!

[rankot]

OK, like this:



Just have in mind that this is the same as the previous schematic, just replaced LM13700 symbol. Also, previous schematic uses both halves of LM13700 in parallel.

[PRR]

I have not digested plan in #49. But it appears if you use LM13700, then the two NPN between R42 and R43 can be done by the buffer inside the '13700, and IAC R42 should not be needed. Saves 3 parts.

[Scruffie]

I have not digested plan in #49. But it appears if you use LM13700, then the two NPN between R42 and R43 can be done by the buffer inside the '13700, and IAC R42 should not be needed. Saves 3 parts.

There's no access to the collector on the 13700's internal darlington.

You can do it with just one transistor if you want and then ignore R42.

[rankot]

I have not digested plan in #49. But it appears if you use LM13700, then the two NPN between R42 and R43 can be done by the buffer inside the '13700, and IAC R42 should not be needed. Saves 3 parts.

I tried that in ltspice, but it doesn't work as expected.

[StephenGiles]

OK, like this:



Just have in mind that this is the same as the previous schematic, just replaced LM13700 symbol. Also, previous schematic uses both halves of LM13700 in parallel.

Many thanks!

[rankot]

I have not digested plan in #49. But it appears if you use LM13700, then the two NPN between R42 and R43 can be done by the buffer inside the '13700, and IAC R42 should not be needed. Saves 3 parts.

There's no access to the collector on the 13700's internal darlington.

You can do it with just one transistor if you want and then ignore R42.

Like this? This seems to work in ltspice.

[Scruffie]

I have not digested plan in #49. But it appears if you use LM13700, then the two NPN between R42 and R43 can be done by the buffer inside the '13700, and IAC R42 should not be needed. Saves 3 parts.

There's no access to the collector on the 13700's internal darlington.

You can do it with just one transistor if you want and then ignore R42.

Like this? This seems to work in ltspice.

Yes, but I have had more consistent results with a discrete pair of transistors, but it will work like that.

[rankot]

In that case, I will stay with a few extra parts

Did anyone with an original pedal had time to check values of resistors mentioned above?

[rankot]

I'm finally done with the PCB for this. I need some help - is this ground plane done well or not? I don't have ground loops, but I wander if it is OK regarding current flow. Please help!



Single layer, with two SMD capacitors (for PS filtering right under ICs).

[PRR]

> There's no access to the collector on the 13700's internal darlington.

Duh. Sorry, brain fart.

[rankot]

Both sides separated: