Help me understand that switch/schematic Ibanez LF7

[lars-musik]

Hello folks,

the Ibanez LF7 seems to be a nice High- and Low-Pass-Filter pedal. The schematics online are the interpretation by PedalPCB (which are always very nice to read and understand) and the Ibanez service manual sheet which my eyes just refuse to follow and my brain to understand.


In the youtube videos there are hints that the three modes (guitar/drums/mic) which seems either to be just different in gain or maybe different voiced.

Can you help me understand what is what with this switch looking at the two schematics?

Thanks in advance, Lars

Factory schematic:


PedalPCB schematic:

[ElectricDruid]

Haven't we looked at this thing before? Seems awfully familiar. I'd do some searches here on the forum and see if there's a previous thread.

The gain switch is simple enough, at least. In the Guitar or Drums positions, it shorts out the R17/100K and C10/68p and turns that first stage into a buffer. In the Mic position, it leaves them in and connects up R18/4K7 and C9/10u making a non-inverting amp with a gain of (100/4.7)+1 = x21.3, +26.5dB.

Although you say the schematics are clear, they're more handy for debugging than understanding (the way the LM13600s are arranged with the pins like the IC on the board). But that means you can't see each separate amp or how it is arranged into a filter section. Sallen-Key? Maybe, but I'll probably have to redraw it to know for sure.

[Baran Ismen]

Out of context, I have the original pedal, which I got at a really funny price some time ago.  

If you need some gut-shots, let me know.

[lars-musik]

The gain switch is simple enough, at least. In the Guitar or Drums positions, it shorts out the R17/100K and C10/68p and turns that first stage into a buffer. In the Mic position, it leaves them in and connects up R18/4K7 and C9/10u making a non-inverting amp with a gain of (100/4.7)+1 = x21.3, +26.5dB.

Thanks a lot Tom,

that's exactly what I wasn't able to spot. I've searched the forum (plus tried my google-fus), but came up empty on the LF7. Maybe I've overlooked it or it was on another page where it was discussed.

Cheers, Lars