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]

Version 4
SHEET 1 4004 1244
WIRE 1168 -752 816 -752
WIRE 272 -736 272 -768
WIRE 1472 -736 1232 -736
WIRE 1168 -720 1104 -720
WIRE -208 -640 -240 -640
WIRE -80 -640 -128 -640
WIRE 48 -624 -16 -624
WIRE 64 -624 48 -624
WIRE 144 -624 128 -624
WIRE 160 -624 144 -624
WIRE 272 -624 272 -656
WIRE 272 -624 240 -624
WIRE 384 -624 272 -624
WIRE 416 -624 384 -624
WIRE 528 -624 496 -624
WIRE 624 -624 592 -624
WIRE -80 -608 -112 -608
WIRE 144 -592 144 -624
WIRE 272 -592 272 -624
WIRE 720 -592 720 -624
WIRE 816 -592 816 -752
WIRE 848 -592 816 -592
WIRE 960 -592 928 -592
WIRE 1200 -592 960 -592
WIRE 1296 -592 1200 -592
WIRE 1472 -592 1472 -736
WIRE 1472 -592 1376 -592
WIRE 384 -544 384 -624
WIRE 480 -544 384 -544
WIRE 624 -544 624 -624
WIRE 624 -544 544 -544
WIRE 816 -544 816 -592
WIRE 960 -544 960 -592
WIRE -112 -496 -112 -608
WIRE -112 -496 -160 -496
WIRE -64 -496 -112 -496
WIRE 48 -496 48 -624
WIRE 48 -496 16 -496
WIRE -160 -480 -160 -496
WIRE 144 -480 144 -512
WIRE 160 -480 144 -480
WIRE 272 -480 272 -512
WIRE 272 -480 240 -480
WIRE 272 -464 272 -480
WIRE 384 -464 384 -544
WIRE 464 -464 384 -464
WIRE 624 -448 624 -544
WIRE 624 -448 528 -448
WIRE 640 -448 624 -448
WIRE 720 -448 720 -528
WIRE 720 -448 704 -448
WIRE 848 -448 720 -448
WIRE 960 -448 960 -480
WIRE 960 -448 928 -448
WIRE 992 -448 960 -448
WIRE 1104 -448 1104 -720
WIRE 1104 -448 1072 -448
WIRE 1200 -448 1200 -592
WIRE 1296 -448 1200 -448
WIRE 1472 -448 1472 -592
WIRE 1472 -448 1360 -448
WIRE 464 -432 384 -432
WIRE -112 -416 -112 -496
WIRE -64 -416 -112 -416
WIRE 48 -416 48 -496
WIRE 48 -416 0 -416
WIRE 1472 -400 1472 -448
WIRE -160 -384 -160 -416
WIRE 720 -368 720 -448
WIRE 816 -368 816 -480
WIRE 144 -352 144 -480
WIRE 176 -352 144 -352
WIRE 272 -352 272 -400
WIRE 272 -352 240 -352
WIRE 1104 -352 1104 -448
WIRE 1200 -352 1200 -448
WIRE -112 -336 -112 -416
WIRE -64 -336 -112 -336
WIRE 48 -336 48 -416
WIRE 48 -336 0 -336
WIRE 1472 -304 1472 -336
WIRE 1664 -304 1472 -304
WIRE 1792 -304 1664 -304
WIRE 144 -256 144 -352
WIRE 160 -256 144 -256
WIRE 272 -240 272 -352
WIRE 272 -240 224 -240
WIRE -160 -224 -160 -304
WIRE 160 -224 -160 -224
WIRE 384 -224 384 -432
WIRE 720 -224 720 -288
WIRE 720 -224 384 -224
WIRE 816 -224 816 -288
WIRE 816 -224 720 -224
WIRE 1104 -224 1104 -288
WIRE 1104 -224 816 -224
WIRE 1200 -224 1200 -272
WIRE 1200 -224 1104 -224
WIRE 1664 -224 1664 -304
WIRE -160 -208 -160 -224
WIRE 384 -192 384 -224
WIRE -544 -96 -640 -96
WIRE -464 -96 -544 -96
WIRE -320 -96 -400 -96
WIRE -176 -96 -320 -96
WIRE -16 -96 -96 -96
WIRE 528 -96 -16 -96
WIRE 736 -96 528 -96
WIRE 784 -96 736 -96
WIRE 912 -96 912 -128
WIRE 912 -96 864 -96
WIRE 1600 -96 912 -96
WIRE 1664 -96 1664 -144
WIRE 1664 -96 1600 -96
WIRE -544 -64 -544 -96
WIRE -320 -64 -320 -96
WIRE -16 -48 -16 -96
WIRE 1264 -32 416 -32
WIRE 1600 -32 1600 -96
WIRE 912 0 912 -96
WIRE 1264 0 1264 -32
WIRE 1664 32 1664 -96
WIRE 1696 32 1664 32
WIRE -544 48 -544 16
WIRE -320 48 -320 0
WIRE 528 80 528 -96
WIRE 1792 80 1792 -304
WIRE 1792 80 1760 80
WIRE -240 96 -240 -640
WIRE -208 96 -240 96
WIRE -96 96 -128 96
WIRE -16 96 -16 32
WIRE -16 96 -96 96
WIRE 144 96 -16 96
WIRE -16 128 -16 96
WIRE 144 128 144 96
WIRE 224 128 144 128
WIRE 912 128 912 80
WIRE 1008 128 912 128
WIRE 1040 128 1008 128
WIRE 1136 128 1120 128
WIRE 1168 128 1136 128
WIRE 1264 128 1264 80
WIRE 1264 128 1248 128
WIRE 1280 128 1264 128
WIRE 1440 128 1360 128
WIRE 1600 128 1600 32
WIRE 1696 128 1600 128
WIRE -96 144 -96 96
WIRE 304 144 304 112
WIRE 640 144 640 112
WIRE 1600 160 1600 128
WIRE 416 176 416 -32
WIRE 1008 176 1008 128
WIRE 528 192 528 144
WIRE 528 192 448 192
WIRE 912 240 912 128
WIRE -528 256 -656 256
WIRE -240 256 -240 96
WIRE -240 256 -464 256
WIRE -208 256 -240 256
WIRE -16 256 -16 192
WIRE -16 256 -128 256
WIRE 80 256 -16 256
WIRE 224 256 80 256
WIRE 304 256 304 240
WIRE -96 288 -96 224
WIRE 1008 288 1008 256
WIRE 1008 288 976 288
WIRE 1264 288 1008 288
WIRE 1440 288 1440 128
WIRE 1600 288 1600 240
WIRE 1600 288 1440 288
WIRE 640 320 640 224
WIRE 1136 320 1136 128
WIRE 1440 336 1440 288
WIRE 528 368 528 192
WIRE 576 368 528 368
WIRE -96 384 -96 368
WIRE -16 384 -96 384
WIRE 1264 384 1264 288
WIRE -16 400 -16 384
WIRE 80 400 80 256
WIRE -336 416 -336 400
WIRE -256 416 -336 416
WIRE -96 416 -96 384
WIRE 736 416 736 -96
WIRE 1008 416 1008 288
WIRE 1600 416 1600 288
WIRE -656 432 -656 256
WIRE -336 432 -336 416
WIRE 1440 432 1440 400
WIRE 1440 432 1328 432
WIRE -256 448 -256 416
WIRE 640 464 640 416
WIRE 672 464 640 464
WIRE 1440 480 1440 432
WIRE -96 512 -96 480
WIRE -16 512 -16 480
WIRE -16 512 -96 512
WIRE 80 512 80 480
WIRE 80 512 -16 512
WIRE 160 512 160 480
WIRE 160 512 80 512
WIRE 208 512 160 512
WIRE 336 512 288 512
WIRE 640 512 640 464
WIRE -656 528 -656 512
WIRE -336 528 -336 512
WIRE -256 528 -256 512
WIRE 80 528 80 512
WIRE 160 528 160 512
WIRE 640 608 640 592
WIRE 736 608 736 512
WIRE 736 608 640 608
WIRE 912 608 912 336
WIRE 912 608 736 608
WIRE 1008 608 1008 480
WIRE 1008 608 912 608
WIRE 1136 608 1136 384
WIRE 1136 608 1008 608
WIRE 1264 608 1264 480
WIRE 1264 608 1136 608
WIRE 1440 608 1440 560
WIRE 1440 608 1264 608
WIRE 1600 608 1600 496
WIRE 1600 608 1440 608
WIRE 80 624 80 608
WIRE 160 624 160 592
WIRE 912 624 912 608
FLAG 80 624 0
FLAG 912 -128 9V
FLAG 160 624 0
FLAG 336 512 9V
FLAG 160 480 Vr
FLAG -336 528 0
FLAG -336 400 9V
FLAG -656 528 0
FLAG -544 48 0
FLAG -640 -96 OUT
FLAG 912 624 0
FLAG -160 -208 Vr
FLAG -48 -592 9V
FLAG 272 -768 9V
FLAG 384 -192 Vr
FLAG 1200 -768 9V
FLAG -48 -656 0
FLAG 192 -208 0
FLAG 192 -272 9V
FLAG 496 -416 0
FLAG 496 -480 9V
FLAG 1200 -704 0
FLAG -256 528 0
FLAG 720 -624 9V
FLAG -320 48 0
FLAG 304 112 9V
FLAG 304 256 0
FLAG 640 112 9V
SYMBOL res -32 -64 R0
SYMATTR InstName R1
SYMATTR Value 47k
SYMBOL res -112 128 R0
SYMATTR InstName R2
SYMATTR Value 75
SYMBOL cap -32 128 R0
SYMATTR InstName C1
SYMATTR Value 560p
SYMBOL res -112 272 R0
SYMATTR InstName R5
SYMATTR Value 270
SYMBOL cap -112 416 R0
SYMATTR InstName C2
SYMATTR Value 150n
SYMBOL res -32 384 R0
SYMATTR InstName R6
SYMATTR Value 27k
SYMBOL res 64 384 R0
SYMATTR InstName R7
SYMATTR Value 2k7
SYMBOL res 64 512 R0
SYMATTR InstName R8
SYMATTR Value 39k
SYMBOL cap -464 240 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 100n
SYMBOL res 880 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 2k7
SYMBOL res 1280 96 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R11
SYMATTR Value 12k
SYMBOL cap 144 528 R0
SYMATTR InstName C4
SYMATTR Value 10µ
SYMBOL res 304 496 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R13
SYMATTR Value 47k
SYMBOL voltage -336 416 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL voltage -656 416 R0
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 0
SYMATTR Value2 AC ac 1.
SYMATTR InstName V2
SYMATTR Value wavefile=d:\bas.wav
SYMBOL res -192 -80 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R14
SYMATTR Value 10k
SYMBOL cap -400 -112 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 100n
SYMBOL cap -304 0 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C6
SYMATTR Value 22n
SYMBOL res -560 -80 R0
SYMATTR InstName R15
SYMATTR Value 470k
SYMBOL res 896 -16 R0
SYMATTR InstName R16
SYMATTR Value 1k
SYMBOL pnp 976 336 R180
SYMATTR InstName Q1
SYMATTR Value 2N5087
SYMBOL res 992 160 R0
SYMATTR InstName R17
SYMATTR Value 47k
SYMBOL cap 992 416 R0
SYMATTR InstName C7
SYMATTR Value 1µ
SYMBOL res 1136 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R18
SYMATTR Value 1k8
SYMBOL res 1264 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName UD1
SYMATTR Value {Rsw}
SYMBOL res 1376 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName UD2
SYMATTR Value {100k-Rsw}
SYMBOL cap 1120 320 R0
SYMATTR InstName C8
SYMATTR Value 1µ
SYMBOL npn 1328 384 M0
SYMATTR InstName Q2
SYMATTR Value 2N5088
SYMBOL res 1456 576 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R21
SYMATTR Value 1k
SYMBOL cap 1424 336 R0
SYMATTR InstName C9
SYMATTR Value 1µ
SYMBOL res 1648 -128 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R23
SYMATTR Value 10k
SYMBOL cap 1616 -32 M0
SYMATTR InstName C10
SYMATTR Value 10µ
SYMBOL res 1616 256 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R24
SYMATTR Value 1k8
SYMBOL res 1584 400 R0
SYMATTR InstName R25
SYMATTR Value 10k
SYMBOL res -224 -624 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R26
SYMATTR Value 1k
SYMBOL res -80 -480 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R27
SYMATTR Value 390k
SYMBOL diode 0 -432 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode -64 -320 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL cap -144 -416 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C11
SYMATTR Value 22n
SYMBOL res -144 -288 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R28
SYMATTR Value 4k7
SYMBOL cap 128 -640 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C12
SYMATTR Value 100n
SYMBOL res 144 -608 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R29
SYMATTR Value 1k
SYMBOL res 128 -608 R0
SYMATTR InstName R30
SYMATTR Value 1k
SYMBOL res 144 -464 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R31
SYMATTR Value 1k
SYMBOL res 288 -496 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R32
SYMATTR Value 4k7
SYMBOL res 288 -640 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R33
SYMATTR Value 10Meg
SYMBOL diode 288 -400 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL diode 176 -336 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value 1N4148
SYMBOL res 400 -608 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R34
SYMATTR Value 1k8
SYMBOL diode 528 -608 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D5
SYMATTR Value 1N4148
SYMBOL cap 544 -560 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C13
SYMATTR Value 3n9
SYMBOL cap 704 -464 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C14
SYMATTR Value 1µ
SYMBOL res 704 -384 R0
SYMATTR InstName R35
SYMATTR Value 3k3
SYMBOL res 944 -464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R36
SYMATTR Value 470k
SYMBOL res 1088 -464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R37
SYMATTR Value 470k
SYMBOL cap 976 -480 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C15
SYMATTR Value 6n8
SYMBOL res 832 -576 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R38
SYMATTR Value 18k
SYMBOL cap 832 -480 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C16
SYMATTR Value 10µ
SYMBOL res 800 -384 R0
SYMATTR InstName R39
SYMATTR Value 12k
SYMBOL cap 1120 -288 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C17
SYMATTR Value 6n8
SYMBOL res 1280 -576 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR InstName R40
SYMATTR Value 270k
SYMBOL cap 1360 -464 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C18
SYMATTR Value 10n
SYMBOL cap 1488 -336 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C19
SYMATTR Value 4µ7
SYMBOL npn 576 320 R0
SYMATTR InstName Q18
SYMATTR Value 2N5088
SYMBOL npn 672 416 R0
SYMATTR InstName Q19
SYMATTR Value 2N5088
SYMBOL res 624 496 R0
SYMATTR InstName R44
SYMATTR Value 47k
SYMBOL res 624 128 R0
SYMATTR InstName R45
SYMATTR Value 2k
SYMBOL Opamps\\LT1057 -48 -560 M180
SYMATTR InstName U1
SYMBOL Opamps\\LT1057 192 -304 R0
SYMATTR InstName U2
SYMBOL Opamps\\LT1057 496 -512 R0
SYMATTR InstName U3
SYMBOL Opamps\\LT1057 1200 -800 R0
SYMATTR InstName U4
SYMBOL cap 544 80 M0
SYMATTR InstName C20
SYMATTR Value 2n2
SYMBOL cap -272 448 R0
SYMATTR InstName C22
SYMATTR Value 470µ
SYMBOL cap 736 -528 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C23
SYMATTR Value 10µ
SYMBOL pnp 1760 128 R180
SYMATTR InstName Q3
SYMATTR Value 2N5087
SYMBOL AutoGenerated\\LM13700_NS 336 192 R0
SYMATTR InstName U5
SYMBOL res -112 80 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 47k
SYMBOL res -112 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 47k
SYMBOL res 1184 -368 R0
SYMATTR InstName R10
SYMATTR Value 100k
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: