Flanger - Reduce Speed

[Zipporello]

Hi all,

recently i've build an Ibanez FL301 Flanger.
It works, but i want to reduce the speed of the pedal.

http://elektrotanya.com/PREVIEWS/63463243/23432455/ibanez/ibanez_fl301_sch.pdf_1.png

I think i have to reduce the value of the resistors R151 or R155: is it right?
I don't want to reduce the range, so i'll not reduce the speed pot, but i want to decrease the maximum and the minimum of the speed value.

Really thanks to all.   

Stefano Giordano

[armdnrdy]

Raise the value of C125 and C126 for a slower speed.

[Mark Hammer]

Depends how much he wants to slow it down.

Larry is absolutely correct that the value of the capacitance in the feedback loop - in this case, the combined series value of C125/C126 - determine the overall range of sweep speeds that the LFO produces.  But the speed is a function of both that feedback capacitance and the resistance between pins 1 and 6 .

The pot setting determines the max resistance (and slowest speed).  The value of R151 determines the minimum resistance and fastest speed.

It would not be unreasonable to replace the 500k pot with a 1M pot and a parallel fixed resistor to provide a max resistance of, say, 600-700k.  The trouble, as I see it, is that it is a trivial matter to get a 1M pot and adjust its effective value with parallel resistance.  Caps, on the other hand, do not simply increment in the values you want.  The pair of back to back 10uf caps gets you a non-polarized series value of 5uf.  If you can find a pair of 15uf caps to fit the available space and give you 7.5uf, then that presents a reasonable compromise.  Moving up to a back-to-back pair of 22uf, though (the typical next-common-value), gets you a halving of the speed range.  The effectsdatabase shows the stock sweep rate ranging from 0.057 Hz - 11 Hz.  Replacing 10+10 with 22+22 would shift your range to .025-5hz.  The .025 may be to your liking, but not the 5hz.

So, my take would be to use the pot value route, allowing you to keep the fastest rate, but maybe extend the slowest speeds a bit.

Alternatively, since using one pot to cover an even broader range of speeds than it currently does might make that pot "twitchy" and hard to adjust, the value of R151 could be switched with a toggle.  So, stock, the resistance ranges from 1k8 to 501k8.  replace R151 with a 150k resistor, and use a SPST toggle to add a 2k resistor in parallel with the 150k.  That will get you faster and slower ranges, without having to change the pot, play around with parallel resistance values with the pot or taper issues, or sacrifice your fastest speeds.  It won't drop your speed quite as much as going 22+22 instead of 10+10, but it may end up being more convenient.  Plus it will fit the available space on the PCB.