Boss Tremolo TR-2 schematic and help

[nothingMaker]

hi, I've a new Boss Tremolo TR-2 (board pb-free with internal trimpot).

I have a problem, there is a ticking sound in time with LFO, greater with high value of depth.
I need some help or a schematic...

Thank you so much

[Mark Hammer]

Just do an image search, and you'll find it. It helps to do a Google image search and specify "black and white" over on the left options list, since most schematics will be in black and white. We'll use this one: Boss TR-2 Tremolo Pedal Schematic Diagram

The TR-2 already employs a clever trick that Boss came up with to virtually eliminate audible LFO ticking. The ticking results from the traditional 2-op-amp comparator/integrator LFO producing a square wave first, then smoothing that out to be a triangle wave. That initial sharp rising edge on the square wave results in a sudden instantaneous current draw that produces a spike on the power line shared by the audio and and modulation/control path.

There are a few ways to address that:
- Use separate devices for the audio and modulation portions of the circuit (Boss has done that) so they can be electronically isolated;
- Use as low-power a device as you can for the LFO so that it doesn't need the amount of current that would produce an audible spike (hold that thought);
- Decouple the device/s used for the LFO from the rest of the power line (hold that thought too);
- Make the sudden rising edge less sudden.

Using the referenced schematic, the circuit built around IC4b produces not a square wave, but a trapezoidal wave that introduces juuuusssst enough time to the rising edge of the waveform as to "spread out" the current draw. You can read more about it here: http://moosapotamus.net/files/stompb...-mo-tremlo.pdf

Normally, one tends to see such LFOs using either a TL022 or LM358, both of which are low-power chips. The M5218AL that the schematic shows IS a nice dual op-amp for audio, but I don't know how its current-draw compares with others. It may or may not be worth replacing with a lower-current type.

C25 provides some decoupling and smoothing of the reference voltage to IC4, but IC4 still shares the direct connection to the power line shared with the audio part of the pedal. It would be useful to smooth out the 9V power line to IC4 as well. The simplest method would be to insert a small-value fixed resistor (<47R) between V+ and pin 8 of the chip, and run an electrolytic cap (e.g., 22uf-47uf) to ground from pin 8. That added cap will work like a "micro-battery" for IC4, providing a teeny amount of reserve current to get it through those sudden rising edges without needing to pull so much current from the rest of the supply.

Of the various factors to consider, inserting the decoupling resistor/cap is likely the first thing to attempt since it does not require outright removal of a chip. If that doesn't do the trick, THEN consider swapping out the 5218 for a 358 or TL022 or whatever else you can identify that has low current draw.

[nothingMaker]

thank you so much Mark, you're very helpful.
I'll try some trick.

The schematic, unfortunately, is different in the new version, there are some NJM14558 instead of M5218AL, and the VCA is a THAT2181.

[Mark Hammer]

Interesting. I wasn't aware of that change. If anyone has a schematic of that issue, I'd certainly be interested.

I don't know that the NJM14559 is, or isn't, a lower-current chip.

[nothingMaker]

I've solved replacing the IC4 with a TL022, low current chip.