Elephant SFL5 Flanger (BOSS BF-2 clone?)

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ChopSauce
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Post by ChopSauce »

(Request for comments)

Hi!

I've been given that

Image

which looks like
DSC08463.JPG
a clone of the Boss BF-2

Image

yet some caps seem to be missing.

So, I am pretty please with the FX with all the knobs set at noon but the thing squeals once the RES pot is maxed.

I was suspecting the messy wiring but the wiring of the BOSS doesn't look much better... :?

Any question/comment/criticism?

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ChopSauce
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Post by ChopSauce »

The pedal has been unused during several years and the effect is somewhat weak, so I plan to change all the electrolytic caps.
(plus the trimmers for horizontal/more usable ones)

I'd like to push the revision a little further, though.

I tried using the pedal unboxed (deployed wiring) but she still squeals. The (VR5/RES) trimmer is already dimmed. The only way to stop it was using another (bias) trimmer but once she stops to squeals with the RES pot maxed, the Flanger FX stops as well.

From the schematic
BOSS BF-2 Flanger-schematic.jpg
and a view of the BS-2 guts (vs SFL5 one, above)
BOSS BF-2 Flanger-IMG_0109.jpg
I am tempted to conclude that the SFL5 is missing C34 & C35 (470pF), C36 & C37 (220pF) as well as one of R57 & R58 (100k) but:

- I haven't checked for other discrepancies yet (so will it work if I had the above components as is) ;

- I am not sure it will solve the squealing issue (yet the corresponding network is related to the RES pot).

Any clue?

I can trace a circuit (with time) but I am far from understanding its subtleties.

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ChopSauce
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Post by ChopSauce »

One more question, maybe:

- how about the JRC 062D (SFL5) versus the 022CP (BF-2)... :?:
(might the JRC be more prone to oscillations, for example?)

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ChopSauce
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Post by ChopSauce »

60 views, no questions - so far. I wish things were as obvious to me... 8)

I wish I could read some comments before I order some parts to include that in the list possibly.

Three more observations:

1. the BOSS BF-2 I could see all show a (Q6 bias?) network (R46, VR7) of (100k, 1M) instead of the (330k, 470k) of the schematic

2. the SFL5 embeds the "C6 (15nF) mod" - see: viewtopic.php?t=307

3. there seem to be several minor changes of resistor values spreaded all over the circuit... :?

NB: afterwards, I think I won't change the trimmers. Also, I don't really want to mess with the ICs - but maybe the JRC 062D (IC5)... :?:

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Post by deltafred »

ChopSauce wrote: 25 Feb 2021, 18:36 Also, I don't really want to mess with the ICs - but maybe the JRC 062D (IC5)... :?:
Sorry I can't help on the squealing problem, I would need it on my bench for that.

I would carefully remove the ICs and fit sockets. That way you can try other opamps and put the originals back if you so desire (after cleaning any excess solder from the pins).
Politics is the art of so plucking the goose as to obtain the most feathers with the least squawking. - R.G. 2011
Jeez, she's an ugly bastard, she makes my socks hurt. I hope it's no ones missus here. - Ice-9 2012

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Post by ChopSauce »

Thanks, anyway!

I'll change the electrolytic capacitors and hopefully this will solve the issue. I remember having some parasitic oscillations with one amp whose filter caps had bad grounding, but I am a bit troubled with the fact that the (VR5) RES trimmer already was on the lower setting.

I'll report and will manage to trace the network around Q9 and Q10, for this seems to be the major deviation from the BOSS BF-2 circuit, in the interval.

EDIT/For the record, the planned mods:
  • C27, C38 (22uF)
  • C6 (47uF) back to BOSS values (from 15uF, stock), eventually something inbetween
  • C7 (33nF)
  • non electrolytic 220nF caps
  • (Q9, Q10) network back to BOSS values

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Post by ChopSauce »

So, I had some time to have a look at it.

I was a bit anxious and possibly made some mistakes, but the (Q9, Q10) network should look pretty much like
SFL-5 flanger-detail.jpg
with the close neighboor (I haven't been farther) components being just the same.

Not sure how this "section" compares to the BOSS BF-2 one... :?:

Image

In extenso: could it be a good idea to convert the circuit to the BOSS version?
(for the PCBs are the same and all the missing components can be simply added)

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The G
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Post by The G »

Sorry, didn't have time to look closer to your posts, so I apologize if I'm stating the obvious.
Q9, Q10 and the associated parts are the Boss flip-flop switching circuit, which is described here or here. If the switching works even with C34, C35, C36, C37, R57 & R58 missing, then there is a posibility that your pedal is using a 3PDT switch for true-bypass switching. So it doesn't need the missing parts. The standard Boss pedals use buffers that make the whole pedal chain more oscillation resistant, as oposed to true-bypass pedals. Try inserting a buffer or a buffered pedal in front of the SFL5, it might stop the oscillation. Then you can decide if you'll alter the pedal chain or the pedal itself.

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Post by ChopSauce »

Thanks a lot!

This looks like the perfect answer. I am totally new to the subject and couldn't expect much better, does it seem ... :)

I'll have a look at those links - thanks again -

EDIT: for the sake of completion...

The SFL-5 has no 3PDT switch and inserting a BOSS (buffered) pedal in front of it didn't help at all.

So I'm back to my plans, but now a bit less ignorant about what I'm doing... :)

EDIT2: I see the R54(?) noted as 1k from the common point between C36 & C37 (flip-flop net) to ground (connector 18) being 100R, both on my SFL-5 and the pictures from the Wampler book ... (for what's worth.)

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Post by cjonesplay »

BBD Flangers tend to have clock trimmer that needs to be set verrrry carefully, and there is also usually a trimmer to adjust feedback of the resonance. Instead of replacing things, try moving the trimmers around. Technically you need an oscilloscope for the clock, but I’ve done it by ear plenty and you can usually get it close. Just a suggestion:)

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Post by ChopSauce »

I've seen that, thanks!

I have already tried setting the trimmers / in extenso: struggled to have the thing back (almost) working as it used to.

So, it looks like I should have a look at it again... :?

Note that the pedal is a survivor from the punkest years of one of my brothers, which has been carelessly stored a few decades & which has at least the power supply jack not switching to battery power, so it's not really like I'm messing with a working thing... :wink:

EDIT: forgot to link to https://www.hobby-hour.com/electronics/ ... langer.php

Image

Note that the above layout mixes the position for (R60, R56) with that of (R59, R55), & vice-versa.

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Post by ChopSauce »

In case that can be usefull: the trouble rather stands near the bias pot.

Either I set the bias so the Flanger FX exists, and oscillations start, either I stop the oscillation but the FX vanishes - roughly.

Actually, I can set the pedal to something in between but (the FX is somewhat disapointing) & the clock (VR7) trimmer couldn't help at all with the oscillations, anyway.

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Post by ChopSauce »

So, I changed all the electrolytics for I had them already. Few ones were slightly leaking. The pedal squeals less and the FX is stronger. I'll manage to set the trimmer better, now. Maybe this slight improvement will suffice...

Note: this pedal already has some mods amongst these suggested by Wampler, that is (C6,C7) = (10n,15n). These values tend to reduce the squealing: my intention was to mod the pedal to Boss values as much as possible but the squealing went worse, so I went back.

However: I assembled the whole flip-flop circuit as per the BOSS schematic and now the pedal always stays on. Whatever you're doing with the switch you can't stop it.

- any suggestion but going back to the above original circuit?

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Post by The G »

First of all, the flip-flop circuit was working before it was modified, so it makes sense it will not work after. Also, chances that the flip-flop circuit will have anything to do with the squealing are slim to none.
Then, basic debugging rules would recommend to not change working systems and to not make multiple changes at a time. So not much success will come from asking to provide modifications over yours.

Obviously, there are differences between SFL-5 and BF-2, so a good start would be to know what are those. I'm interested to trace it, so if you provide one good well-lit picture for the parts side of the PCB and one for the copper side, I'll have time next week to do that. Having done that will get us a schematic to refer to and to justify having this topic in the Modern Stompboxes forum and not in the Pedal Debugging one.
Also, a recording of the squeal would be useful, just to be sure we're all thinking of the same sound.

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Post by ChopSauce »

I could get rid of the oscillations/squealing by tunning the trimmers by ear, now that I have changed the electrolytic caps. I'll have to do that properly though(*), but it already is more usable.

I'll revert the pedal back to its initial state - but the new caps - and post a couple of pictures, as soon as possible, thanks!
_

(*) as per the instructions below, I suppose(?)
https://www.hobby-hour.com/electronics/s/boss-bf2-flanger.php wrote:
Adjustment procedure:

1.) Clock frequency adjustment:
Set MANUAL and DEPTH knobs to full counterclockwise. Connect an oscilloscope to TP-1 test point. Adjust VR7 for T=25us (40kHz). Rotate the MANUAL knob fully clockwise. T should be 2uS +/-20%.

2.) BBD bias:
Set DEPTH and RES. knobs full counterclockwise. Feed a 200Hz, sine wave, 0dBm signal into the INPUT jack. Connect the oscilloscope to Q3's emitter. While turning MANUAL across its entire rotation range, set VR6 for a clip-free waveform at the peaks.

3.) Resonance:
Set MANUAL, DEPTH knobs full counterclockwise and RES. knob full clockwise. Plug short circuit into INPUT jack. Connect OUTPUT jack to an amplifier and speaker. While touching a screwdriver to TP-2, set VR5 to the point where oscillation begins.

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Post by ChopSauce »

I managed to shot best views with the daylight, this morning, but couldn't do better than the attached pics.
top1.JPG
bot1.JPG
I can't believe this will suffice. Please let me know if you need further views, informations, etc.
Attachments
bot2.JPG
top2.JPG

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Post by ChopSauce »

Just in case ...

NB in its pictured state, the LED can be switched on/off again, but not the signal.
Attachments
top4.JPG
top3.JPG

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