Ibanez RC-99 Ticking with speed adjustment

[KaiApollo]

I have a pedal that even in bypass mode has a ticking that adjusts with the speed knob. I am currently assuming an issue with the clock for the BBD. Any ideas or suggestions? Thanks.

[Mark Hammer]

Ticking in LFO-modulated pedals is a topic that comes up often.  The problem is that the LFO is sharing the same power as the audio portion of the circuit and has current needs.  The ticking you hear occurs when the LFO produces the rising or falling edge of a square wave and there is a very sudden surge in current needs for that subcircuit. 

I used to use a different analogy, but I'll switch to a different one here.  Imagine two people share a bed.  When one of them gets up, the mattress moves and wakes the other person.  Now, if the one getting out weighed 80lbs and the one sleeping weighed 200lbs, perhaps the bed would stay motionless and the sleeper would continue sleeping.  If they roll out of bed gently, maybe the second person is not awakened, but if they leap out suddenly, the bed shakes.  And of course, if the mattress is large enough so that one sleeper is far away from the other,  none of the movement is transmitted.

This illustrates several principles used in preventing and curing ticking:

1) Use a low-current op-amp for the LFO (=lighter bed partner).  This is why you'll often see the LM358 or TL022 used for LFO subcircuits.
2) Make the LFO produce a trapezoidal, rather than square-wave (=slowly rolling out of bed), so that the rise time is distributed across a few milliseconds rather than all at once.
3) "De-couple" the LFO and audio portion (=larger mattress and isolation from vibrations) by running a small-value (1k resistor to the V+ input and a cap to ground (1-10uf) to provide a small reserve of stored current to "cushion the blow" when the LFO tries to suddenly suck current.

[KaiApollo]

1) Use a low-current op-amp for the LFO (=lighter bed partner).  This is why you'll often see the LM358 or TL022 used for LFO subcircuits.
2) Make the LFO produce a trapezoidal, rather than square-wave (=slowly rolling out of bed), so that the rise time is distributed across a few milliseconds rather than all at once.
3) "De-couple" the LFO and audio portion (=larger mattress and isolation from vibrations) by running a small-value (1k resistor to the V+ input and a cap to ground (1-10uf) to provide a small reserve of stored current to "cushion the blow" when the LFO tries to suddenly suck current.

OK Forgive my ignorance, I am new to modding, fixing and building. The circuit seems to already have the TL022, I am assuming that is the LFO because the only other op-amps I see are 4570's. So , I am not sure how to go about making the LFO trapezoidal, so I guess that I go with option 3. To accomplis this I can just rais the leg of the IC and adding the component.

Thanks for the advice.

[Mark Hammer]

The trapezoidal thing is nicely described and illustrated here: http://moosapotamus.net/IDEAS/stompboxology/Vol4No4/Page_02.gif
You can find that same circuit (with component value changes) in a number of Boss and other circuits.

[KaiApollo]

Thanks for the ideas Mark. I looked at the circuit and saw that the circuit was in place already for the trapezoidal wave. That plus the TL022 that was already in use left me only one choice. When I decoupled the LFO, I lost most of the effect, all the lush chorus was gone. That only left one thing to do. I replaced the TL022 with another from one of my "parts" pedals and like magic, the ticking is gone and the effect sounds great. Thanks for the assistance.

Darin