Boss BF2 mods

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Boss BF2 mods

Postby Gila_Crisis » 02 Aug 2007, 13:53

a) C27 and C28 make up a non-polarized 16.5uf capacitor which sets the speed range. If the capacitance value is reduced, the speed range goes higher. Faster speed can produce an effect that sounds very much like a ring modulator. I would suggest a pair of 4.7uf caps, back to back, as a suitable replacement.

b) Maximum flanging effect needs a 50/50 balance between delay and clean signal, but sometimes you want just a taste of flanging. If the value of R29 is increased, the balance is shifted in favour of clean. If you replaced R29 with a 22k fixed resistor, and a 100k pot, wired as a variable resistor (2 lugs, not all 3), you would be able to get everything from a *perfect* 50/50 balance to a much softer flanging effect, even with very high regen/res.

c) R11, D3, and D4 form a soft limiter, to keep high regeneration/resonance signals from overloading the delay chip. If you shunt/short R11, the clipping of D3/D4 becomes "harder" and introduces more harmonic content. If you want to experiment with more interesting high regeneration signals, solder in a wire bridge across R11 on the copper side of the PCB, turn up VR5 a bit higher (VR5 is normally set so that turning up the RES control all the way puts you just below the point of oscillation).

d) C7 sets the lower bandwidth point (bass rolloff) of the regeneration signal. If you make it smaller in value, this will make high regen/res settings sound less metallic. A value of .01uf might be a good place to start.

e) The depth contol (VR2) adjusts the balance of voltages coming from the LFO and the Manual control to drive the clock (IC4). VR7 is used to adjust or fine tune the delay time by adding (or maybe subtracting) a small DC voltage on top of whatever comes through VR2/R48. C30 sets the delay range of the clock circuit. Values larger than 47pf will set the minimum delay time much longer. Smaller values will reduce the minimum delay time. You can change the sound of the pedal by changing the range of delays it can produce. Try a cap of 39pf and see if you like it. If there are problems with the sweep, you may be able to fix them with VR7. Alternatively, if you are able to find an MN3209 chip somewhere, you can take the MN3207 out and replace it with the MN3209 for shorter (X/4) delay times and more of a "jet plane" sound.

f) Vibrato is created when you use ONLY the delay signal, and leave out the clean signal. If you lift one end of R28, that will prevent the clean signal from being mixed in with the delay signal, and give vibrato. Unfortunately, because of how bypass is done in this pedal, this means that when you try to bypass the pedal, there will be NO sound coming out.
Solution: In modulation effects where dry and wet are combined, you can cancel the effect bi simply lifting the connection between the wet path and mixing stage. In the BF2, Q4 fulfills this function.

This means that while the "flip" part of the circuit is used to enable/disable the gate of a FET and an LED, the "flop" part of the circuit does nothing. We *can* put this section to work, though.

To produce vibrato, lifting one end of R28 will kill the dry signal and get you vibrato. When you hit the footswitch, though, there is no "flop" action to restore the bypassed/clean signal....but there COULD be..

Imagine that there is a second 47k resistor and a FET in series with each other, and in parallel with R28. Now, also imagine that there is a 1M resistor, .047uf cap, and diode connecting the gate of that FET to the junction of R55 and Q9, exactly the same way a resistor, cap, diode combo connects the gate of Q4 to the junction of R56/Q10. Step on the footswithc once, and the led comes on and Q4 goes low resistance. Step again and Q4 and the LED go off and our new added FET turns on and provides a low resistance path for the clean signal to the added parallel resistor and the mixing stage. More importantly for our purposes, that path exists independent of the toggle switch. So, if the toggle is closed, the added FET/resistor simply duplicate what is already there when you step on the footswitch. If the toggle is open, then cancelling the wet signal also results in providing a dry signal.

FYI, the C7, C21 mods have no effect at all when the res/regen is off.
I suggest you look at the BF-2B which does have less metalic sound. Roughly,
- a delay chip with less (512) stages. this reduces the delay time
- C7 mod (47nF to 10nF)
- C6 is reduced from 47nF to 15nF.
Now reducing the delay time can significantly reduce the metalicness. One way to approximate this is to reduce C30 (47pF). Unfortunately the clock frequencies are already pretty high so it's probably unwise to use a small C30 like 22pF to drop the delay to the BF-2B level. You could try 33pF and cross your fingers.
Tune the C6 mod first to your taste with res/regen off - try say 22nF or 33nF.
Then Tune C7 using some res/regen.
Another mod is to play with C8 and C9. For example you can get the filters to be quite close to the mxr flanger by changing only two caps: C8 from 12nF to 2.2nF, and change C9 from 150pF to 1nF.

In case you are still interested in attemping the mod on the BF-2, I studied the schematic available from the Free Information Society and came to the following changes in order to achieve the increased sweep after replacing the BBD for a 512 stage MN3204:
1) IC5 needs to be replaced with a full rail-to-rail output opamp like the TLC2262, TLC2272 or MAX492, to name some.
2) Then, resistors R36 (180k) and R37 (220k) need to be swapped with each other to increase the output voltage range of the LFO.
The use of a rail-to-rail output opamp is necessary, otherwise the LFO won't work with the extended output voltage range. Eventually, but not necessarily, VR7 might need a slight adjustment in order to center the new range of the sweep.
In summary, the required changes are pretty simple, except for the difficulty in getting the MN3204 and TLC2262 ICs (WHICH YOU HAVE ALREADY DONE!)
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Re: Boss BF2 mods

Postby Gila_Crisis » 26 Aug 2009, 20:39

if you do the last mod (with the TLC2262) don't swap R36 and R37, otherwise the LFO won't work no more.
instead you can try a lower value for R36 :wink:
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Re: Boss BF2 mods

Postby CHEEZOR » 26 Aug 2009, 20:52

Awesome post! Thanks. It would be nice to have info like this for more pedals! :thumbsup
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Re: Boss BF2 mods

Postby Rocker8229 » 08 Nov 2009, 16:13

I was wondering if anyone else has noticed the level increase when kicking in the BF-2 and if there there is a way adjust this?

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Re: Boss BF2 mods

Postby pedal pusher » 03 Apr 2010, 13:47

I myself would love that mod too. A little help out there on this one please.
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Re: Boss BF2 mods

Postby Seven64 » 10 Mar 2012, 11:34

the monte allums bf2 kit comes with 2 germanium diodes (which of their kits don't, i know). I tried putting them at d3/d4, but it basically made the effect not work anymore. it was extremly subtle at best. put si back in, and its back to normal. i figure the germanium would warm it up a little more, but where should i put them?
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Re: Boss BF2 mods

Postby phibes » 10 Mar 2012, 19:25

Read "C" up in the first post.

You'll probably need to tweak R11 if you put those diodes in. Looking at the Monte photo it looks like there's a 2K2 resistor as well. That might go there. Put the didoes in, and put a 3K9 resistor in parallel the 4.7K resistor (that'll give you 2K2) and see if it helps. Did you try tweaking VR5 too?
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Re: Boss BF2 mods

Postby Seven64 » 11 Mar 2012, 06:10

yea, i need to wire up a pot for it. i tried the 2.2k resistor, and it didn't do anything. put the silicon back in and it works fine.
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Re: Boss BF2 mods

Postby phibes » 11 Mar 2012, 07:58

You matching the polarities when you put the germanium diodes in? You should still be getting something with them in.
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Re: Boss BF2 mods

Postby Seven64 » 12 Mar 2012, 00:10

yea. i would have thought i would be getting something too, but it basically sounds like a clean signal. maybe 10% wet at best.
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Re: Boss BF2 mods

Postby Seven64 » 19 Apr 2012, 17:07

apparently monte allums doesnt offer the germanium with their mod anymore. anywhoo, i have an idea for that that i might try later. put each germanium in series with an LED to give it a little more umph.

onto my more serious question, i figured the mxr filter mod would be nice, so i decided to put it on a switch. its a dpdt on/on switch, but there is BARELY any difference at all. half the time i am convinced its in my head, but the other half i just think it sounds mildly smoother and my pick is not as harsh when i am strumming hard.

what purpose does this filter area serve, as so i can understand it better and maybe that will help with my experimentation.

and fwiw i played with the internal trimmer but still couldnt get it to do much.
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Re: Boss BF2 mods

Postby euronymous0001 » 25 Jul 2012, 02:16

hi all!

how can i increase the volume. am i correct that changing resistor (R31) in the feedback loop on the last opamp from 47k, maybe to 100k, will increase the volume and would not change the tone? thanks in advance :applause:
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Re: Boss BF2 mods

Postby roseblood11 » 25 Jul 2012, 21:04

Does somebody have a layout for a BF-2 clone? I know that it's (still) quite easy to find a used pedal, but I'd prefer a true bypass version with some of the mods included on the pcb (better: veroboard...). I had a BF-2 for many years, but I was so stupid to sell it when I got my first digital multiFX unit.
MN3207 and 3102 are still available quite easily, so it would make sense to have a diy project, as the original pedals are out of production for 10 years now...

Maybe I could try to do a vero layout myself, if someone has a readable schematic, preferably with the fet bypass switching removed.
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Re: Boss BF2 mods

Postby Beedoola » 01 Oct 2013, 01:54

anyone try the Wampler BF-2 mods in the Wampler book?

I have a MIJ BF-2 I'm thinking of modding
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Re: Boss BF2 mods

Postby roseblood11 » 01 Oct 2013, 04:37

please post them here...
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Re: Boss BF2 mods

Postby Beedoola » 24 Nov 2013, 02:13

I got the books from here in the resources section:

viewtopic.php?f=70&t=16716&hilit=wampler+books
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Re: Boss BF2 mods

Postby Beedoola » 14 Aug 2017, 00:33

Does anyone know of an effective way to reduce the overall volume of the circuit? I tried making the 100k output resistor variable - which works - but it affects the bypass volume as well.

From the OP post, the R29 pot addition won't fix the volume boost. I like the way the flanger is currently mixed, I just want to be able to adjust the effected signal.
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Re: Boss BF2 mods

Postby EmmG » 07 Sep 2017, 04:50

I'd like to know this too. I'm about to just replace the switching with a relay board and 100k trimmer. The slight boost is not working for me.
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