Boss Flanger Advice?

[dumbmonkey]

Hi y'all,
It's been a while since I posted anything, but here we go.  I just got a hold of a MIJ Boss BF-2 Flanger.  I checked the serial number through a lookup site, and I think it's dated from 1988.  Pretty cool; I was graduating from college then, lol.  Anyway, I'm planning on converting it for PSA (9volt) adapters, and changing the led for a blue one, but I was wondering if anyone has any thoughts or advice as to anything else I should be upgrading or replacing?  I don't think I want to do any major mods, but if anyone thinks I should replace electrolytic caps or anything else, feel free to let me know.
Thanks for being such a great resource!
cc

[ElectricDruid]

Ah, the classic purple flanger! It was the first flanger I ever saw or heard. I remember being amazed by the noiseless switching, which was the holy grail of that era. And the sound was something else - how did a little circuit *do that* to the sound?!? I was fascinated.

If it works nicely, I don't think I'd make any changes. You might find you need to tweak the Bias or Res trimmers. By now, it's highly likely that they've been messed with, and whoever adjusted it last might or might not have known what they were doing.

It's a stone cold classic. Other flangers might be more highly rated, but that bombproof purple box is the one that more people have actually owned.

[Mark Hammer]

I have little love for the BF-2.  It is severely limited in its width of sweep, and sounds metallic and "boxey" to my ears.

Having said that, when I have recommended a few mods to those who own them,  they reported being pleased with the outcome.

1) The annoying sound of the BF-2 occurs at the "bottom" of the sweep, in the bass range.  Remedying this involves trimming back on the bass in both the wet signal overall and the feedback path.  Stock, C7 (feedback) = .047uf and C20 (overall wet) = .22uf.  Reducing C7 down to something in the .015uf range will attenuate a lot of the annoying boxeyness as you turn up the feedback.  Reducing C20 down to .047uf (a way to put a removed C7 to use) will attenuate the bass in the wet signal for any feedback setting, including no feedback.

2) Stock, the BF-2 is spec'd to sweep from 1msec to 13msec, which is unspectacular.  This is a result of the limits of using an MN3207/MN3102 pair, which is only spec'd to clock the 3207 as high as 100khz in this configuration.  As with all such components, there is piece to piece variation, but the 1-13msec spec is what Boss assures and factory calibrates for.  Possible to clock it a little faster in order to achieve more "dramatic sweeps from delays shorter than 1msec?  Maybe, maybe not.  If you are willing to experiment, find and remove C30 (47pf) and replace it with 36-39pf.  In theory, that should nudge the shortest possible delay time a bit below 1msec.  It is the much shorter delays that yield the more dramatic "out of the stratosphere" sweeps we love flangers for.  Assuming you are careful in doing so, it should not damage anything in the pedal.

3) It is normal for pedal-tinkerers to want to convert a modulation pedal to produce vibrato.  In the case of the BF-2, and many similar pedals, the effect is produced by connecting the wet signal to a mixing stage, and defeated by lifting that connection, rather than fully bypassing the circuit.  If one lifts the dry signal to produce vibrato (wt only) and then steps on the bypass switch, you get neither dry NOR wet (i.e., dead silence).  In theory, one could convert the pedal to produce bypass or vibrato, but not without installing a little daughter board to accommodate different switching.

[dumbmonkey]

Thank you both for your replies!  It's funny to get two sides of the coin as far as this flanger is concerned!
Mark:  I've seen those mods before, especially the C7 and C20 one.  I'm thinking I want to at least check out the C7 one.  Someone mentioned using a .022 in there as well, what are your thoughts on that? Someone else also suggested changing C8 and C9 for filtering more like an MXR flanger, do you think that's worth it?
Thanks again for all your help!
cc

[ElectricDruid]

Don't get me wrong, I largely agree with Mark's criticism's of the pedal. But that doesn't change the fact that it's a classic.

The sweep range is only 12.5:1, 40KHz to 500KHz, which is not that wide, so you don't get huge sweeps. It's not bad given the MN3207 BBD, since as Mark said the specs on that suggest 200KHz as the max frequency, which is nonsense. The clock chip at least can get up to 700KHz (check the datasheet).
Mark's idea of trying to push it a little bit faster is probably a good one, and the trick of reducing the bass in the feedback signal is one that I used myself in my Flangelicious design. It enables you to increase the resonance without causing runaway oscillations, which helps the sound.

[Steben]

It's a great side kick chorus alternative.
I do remember I had one long ago and swapped the chip to 512 stage.... less chorus, but shorter delay and more "jet edge"

[dumbmonkey]

Steben,
I really like the idea of using flanger as a chorus.  I used to do that with an A/DA PBF flanger I had, although I was an idiot and sold it.  That's the main reason I got the BF-2.  I have an Ibanez FL9 as well, so I can compare the two, lol.

[Steben]

Steben,
I really like the idea of using flanger as a chorus.  I used to do that with an A/DA PBF flanger I had, although I was an idiot and sold it.  That's the main reason I got the BF-2.  I have an Ibanez FL9 as well, so I can compare the two, lol.

The Police is full of electric mistress chorus

[Mark Hammer]

Steben,
I really like the idea of using flanger as a chorus.  I used to do that with an A/DA PBF flanger I had, although I was an idiot and sold it.  That's the main reason I got the BF-2.  I have an Ibanez FL9 as well, so I can compare the two, lol.

I must have at least a dozen flangers of various forms: MXR, Yamaha, Alesis, PAiA,  Boss, Chase Bliss, and flanger settings on various rack and pedal multi-FX.  I like the effect, but find one generally has to "go Reticon" for a dramatic sound. 

Tom/Druid is quite correct that the Panasonic chips CAN be pushed to go somewhat faster.  Mike Irwin once demoed for me, in person, an MN3007 unit he made that he could clock up to 1.5MHZ  .  The limitation of the 3x07/310x pair is that the clock chip is unable to push enough current to easily overcome the capacitance of the clock-input pins on the BBD.  The MN3007 and 3207 have a 700pf capacitance on those pins, where the Reticons are 110pf.  HOWEVER, much the way long cables and their capacitance can be overcome by feeding them from a higher output-current buffer, inserting a suitable clock buffer between the clock generator and BBD overcomes the clock-pulse corruption that occurs at higher clock frequencies in the absence of that buffering.  Stated another way, it's not that the 3207.3102 pair CAN'T be clocked much faster than the BF-2 permits.  Rather, the signal quality degrades substantially if one tries to push harder.  BBDs  need a relatively seamless "handoff" from one bucket to another to sound decent, and that requires nice crisp clock pulses.  The high clock pin capacitance on the BBD turns those crisp pulses into something more like a trapezoid with highly sloped sides (essentially "rolling off the treble" on the pulses).  This results in a bit of a gap between bucket-to-bucket handoffs.

The "Panasonic pair" (MN3101/3007 or 3102/3207) makes for a nice compact and convenient chip pair for producing a variety of effects.  They just have their limitations as a "complete" solution, even though they yield a nice small footprint and cheaper production cost.

[ElectricDruid]

Incidentally, does anyone know *why* exactly the Reticon chips had such a much lower clock input capacitance than the Panasonic MN series? There must be some significant silicon difference between them, but I have no idea.

It's a pity that the recent clones all share the same defect - high capacitance, mostly. V3207 is as bad or worse than MN3207. Couldn't we have had a modern "clone" with some miniscule capacitance? That would have been nice...

[Mark Hammer]

Well, I'm assuming some fundamental design difference, but that's not saying very much.  I will say that technical info for the Reticon chips often makes mention of video production applications (something one tends not to see in the Panasonic chip info), so clearly it anticipates the need for much higher clocking frequencies.