Ibanez DL5 schematic

    

     I've been looking at various delays, digital and analog. I came across the Ibanez DL5, from their "Soundtank" line. There is a reverse-engineered schematic, but it just didn't make sense to me.

Tic Toc, Ya Don't Start

    The thing that I was most interested in was the clock source for the delay chip. It vaguely looks like an oscillator, but not really. There are two inverting stages made from IC6. You need an odd number of inversions to make an astable oscillator though. Also, what is TR6 doing? It has two fixed voltages going into it, and a current flowing into C29?

Bad clock schematic

    I wanted to validate this, so I opened up my pedal, took some pictures, and started tracing.

Traced PCB

    It turns out that TR6 was labeled incorrectly, and it's actually TR3. R28 is actually R26. R24 and R25 don't go to different voltages; they both connect to what is probably +5V.

    The key mistake was the omission of R23. This connects TR6(TR3) to the second inverter, and totally changes what's going on.

    Here it is redrawn. TR5 helps to bias the CV going into TR4. TR4 acts as an exponential current sink, pulling current out of C29. The inverters monitor the capacitor voltage at pin 1, and use TR3 to recharge the capacitor when it gets low.

Corrected clock schematic

    I made a version of it in Falstad, so you can experiment with it. Link here

Falstad simulation

    It's actually very similar to the Monotron's VCO that we looked at previously. 

Monotron VCO

I Can't Be Your Lover

    The number of mistakes in this one area calls into question the whole schematic. What else can we find wrong?

Incorrect schematic

    The "Ref" pin (24) of the M50195 delay chip is incorrectly labeled "OP1+", making it look like it's an input for one of the internal opamps. It's acutally a reference voltage that's used by the opamps.

    The opamp on the delay's output (IC5B) is connected backwards. What should be its output is instead its input.

    Long story short, I decided to redraw the schematic. This let me make some more conventional layout choices too.

Redrawn schematic

    I skipped a few things that didn't interest me, like the LED, some power filtering, and jacks.

    Now we can see what all the blocks of the circuit are, and how the signal flows through them.

    At the top left we have an input buffer, and a preemphasis filter that feeds into the delay line. We also have a deemphasis filter that mixes the dry and wet signal together.

    Below that is a lowpass filter that cleans up the wet delay signal. After that is a FET that bypasses the effect. Then comes the repeat control that mixes the signal back into the delay line.

Input, filtering, and mixing

    At the bottom left is the delay line itself. It has a similar lowpass filter that's built using one of the M50195's internal opamps.

Delay line and RAM

    Bottom right is the latch that controls the FET. Pressing the tact switch toggles the state of the latch, and the FET, turning the effect on or off.

Bypass Latch

Bonus

    Here are the traced and redrawn boards. It's not a faithful recreation, but good enough to make a schematic from. The 70mil-spaced 36 pin DIP was "fun" to recreate.