Boss BF-2 trim pot calibration

[beedoola]

I need to know the procedure for how to calibrate the pedal with the trimpots and oscilloscope.

I found this alleged link here on the Boss Area forum but it takes me to nothing.

Anyone happen to know the procedure?

Thanks!

http://www.bossareaforum.com/Forum/viewtopic.php?t=390

[Mark Hammer]

1) The resonance/regen trimmer is set to be able to achieve the highest possible feedback without tripping into oscillation.  So, set the  Res to max, the Depth to min (so it doesn't sweep and make things a moving target), the Manual to Min OR Max, and tweak the feedback trimmer until the howling just barely stops.  You will now have a Res control with usable settings over 95% of its range.

2) Bias:  All bucket brigade chips, regardless of capacity or brand, require a DC bias voltage for the audio signal to "ride in on".  Optimal settings will vary by individual chip and circuit board, which is why there is a trimmer rather than fixed components.  The audio signal will not pass through the chip if the bias is set too high or too low.  Fortunately, fiddling with the bias trimmer will not damage the delay chip, so you can twiddle away without fear. (although such trimmers are usually cheap and don't hold up well to a LOT of twiddling).  While in a perfect world, you'd use a scope to measure signal quality, it CAN be set by ear.  Set your Res to maybe halfway, Depth to maybe 2:00, and Rate to maybe 12:00.  Starting from fully counter-clockwise, you will hear no flanging as you gradually turn the trimmer clockwise, bit by bit.  Eventually, you will hear a distorted delay/flanging sound, which becomes clearer as you continue rotating, becoming dirtier, and then disappearing again.  Once you have an idea about what trimmer range provides audible - if not perhaps cleanest - delay sound, you can pay close attention and gently adjust the trimmer to nail the optimum bias.

3) Clock frequency: The clock that steps the signal through the stages in the delay chip can't be too low or too high.    Most dramatic flanging occurs when the shortest possible delay times (i.e., highest clock rate frequencies) are achieved.  Set your Res to max, your Depth to min, so that you have an audible, but non-moving, delay time.  Set your Manual to Min and gradually sweep it.  You should hear manual flanging.  If the last bit of its sweep does NOT result in any audible flanging/notch-filtering, then the clock freq has been set too high.  I honestly don't know aht trimmer direction provides faster or slower clock speeds, but again, you won't break anything; you'll just either get better or worse sweep than you want.

[ElectricDruid]

Here's the relevant page of the service manual - I nicked this from a Reverb listing where they're selling two old bits of paper for $18!



With the Depth at Zero, you're looking for 40KHz to 500KHz clock frequency at TP1 by adjusting VR7.

The other trims are easier, more obvious.

[Rob Strand]

With the Depth at Zero, you're looking for 40KHz to 500KHz clock frequency at TP1 by adjusting VR7.

That's the main one.

On one unit I measured:
f(kHz): 37kHZ to 425kHz

The range varies from unit to unit but traditionally the lower frequency is the one used for calibration.

[beedoola]

You all rock!!

What does "rotate manual PCW" mean for the clock calibration? "Pointer clockwise?"

[Fender3D]

I think it's FCW, fully clockwise