Boss BF2 IC mods completed!

[Steben]

Now maybe some tweaking I guess.

I subbed the MN3207 for a MN3204 as you all might know. Great improvement in getting Jet sounds.
Now I placed a TLC2252 rail-to-rail "almost NO power"  opamp in for the LFO with subtle change, but still "improvement".
I noticed before that the metallic resonance has gone with the MN3204.

I think the clock trimmer needs some re-trimming to get the most out of it.
Any suggestions? Maybe the LFO circuit needs a mod too to increase amplitude even more?

ASAP I will produce sound samples!

[stm]

Did you swap the 180k and 220k resistors in the LFO as I mentioned previously?  That change PLUS the rail to rail amp is what should extend the sweep ratio.

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!)

[Steben]

Ok. thanks for the reminder, stm 

[Gila_Crisis]

hi! i've done this mod on my bf2 and:
- the mn3204 seams to work fine,
- i remplaced the TL022 with a TLC2262 and swapped R36 and R37, but the LFO is dead!

I tryed also a TLC2272, but same results. i tryed to measure the volteges on IC5, i'm getting:

1: 5.53V
2: 0V
3: 2.79V
4: 0V
5: 2.42V
6: 2.76V
7: 5.56V
8: 5.56V

i noticed also a voltage drop on the power supply, from 9V to 7V!!
what can i do?

[Gila_Crisis]

no ideas?

[Mark Hammer]

There's five and a half volts on too many pins.  If this is a perf or stripboard build, you need to check your wiring.

[Gila_Crisis]

it's not a perfboard, i'm modifing an original one

[Mark Hammer]

Well, looking at the schematic, a reading of zero volts on pin 2 will definitely mean that the LFO ain't gonna have any sweep.

For the time being, I would suggest setting R36/R37 back to what they were.  While you have them out and have a clear space to work in, I would strongly recommend cleaning up all the flux residue with a cotton-tipped applicator and some alcohol or methyl hydrate.  Once the non-solder crap is cleaned off, you'll be better able to see if there are any unintended solder bridges. If the problem does not go away following resistor reversal, then clearly what you have is either a solder blob somewhere, or a fried op-amp.  While reasonably robust, keep in mind the TLC2262 is a CMOS device, and should be handled with the same care you'd apply to any CD40XX type chip or BBD.

[stm]

OK, I verified the circuit in the sim and indeed swapping R36 and R37 stops the oscillation.  Sorry about that!  Don't know what lead me to conclude at that time it was a good idea. 

Now I've already simulated the circuit and can speak with a bit more authority.

The original circuit produces a triangle wave that varies approximately between 2.2 and 3.3V (Vref in this case should be close to 2.8V).  Changing the TL022 by a TLC2262 (ceteris paribus) does extend this range perhaps too much (from 0.6V to 5.0V).  So, it is likely you might want to reduce the range if it is causing some artifact.  This can be done by reducing R36 (180k) down to 100k.  In this case the triangle range will vary from 1.6 to 4.0V, which should be noticeable.  Just see which you prefer.

Finally, if you find the LFO frequency range shifted too much (towards high speeds), you could try replacing C27 and C28 (33uF) by two 47uF or 68uF.

Hope this does it!

[Gila_Crisis]

ok thank you very much! i'm gonna try this, maybe with a trim pot in place of R36

[Gila_Crisis]

so, i swapped back R36 and R37 like before and now the LFO works again.

well, i'm really happy now with it, with the MN3204 (i got this for the other flanger i have, an old Arion Stereo Flanger) and the TLC2262 it works a lot better!
more swooshy and "flangerish" sounds than before!

if you can't find the MN3204, just make the LFO mod with the TLC2262, really a keeper mod