Tiny post-pedal-purchase surprises

[Mark Hammer]

A little over a year ago, I dropped by an out-of-town pawn shop on the way back from a trip.  I managed to score a nice old Guyatone guitar (at least judging by the pickups) for a song, and there was a Danelectro Fab Flanger sitting in the adjacent display case, which the guy was willing to throw in for another $10.  Bought them both, and when I powered up the Fab pedal and tried it out, was struck by just how bad it sounded.  Simply unusable.

I thought nothing more of it and simply put it back in the box and ignored it.  Stumbled onto it again the other day, and decided to plug it in again and give a listen.  Sounded just as bad as I remembered it.  Opened it up and was surprised to find not one, but TWO 3207 chips. ( )  Still don't understand the logic of that, but started to poke around online to see if there were any mods that could be done to redeem what was a bad-sounding pedal.  Now, understand that the Fab Flanger is a mixture of surface-mount and through-hole parts.  So it didn't particularly surprise me to find a 22pf ceramic cap soldered between two pins of the MN3102 clock chip.  But the images I saw online did not show such a chip.  When I looked a lot closer, it appeared the surface-mount cap that originally went between the same two pins had been removed, and the 22pf added instead.

The chief crime of the pedal was that it swept to too long a delay, such that the sweep was weird, and anything more than a touch of regeneration sounded abysmal.  I thought maybe someone had "experimented", made a bad choice, and passed the misery on to someone else.  So, I replaced the 22pf cap with 15pf, to shorten the delay range, and the sound and sweep is vastly improved.  I might go to 12pf later today (off to the local Mini Maker Faire momentarily), but it seems like I'm pretty close to what the pedal value was supposed to be.

Two questions:  1) Anyone know whatthe actual value is?  2) Anyone know how/why the 2nd BBD is used in the pedal?

[Jdansti]

I've got mine open now. I see the 3102 chip, but I'm not sure where the cap is that you see. Here are photos of both sides of the board:

[Scruffie]

Regards the dual BBDs... as the inputs are connected from what I can see, it's one of two reasons, differential operation or parallel multiplexing or both combined... can't think of any other reason for it.

[Mark Hammer]

The cap in question is on the underside, not the chip side.  It is the one between pins 5 and 7 on the 3102 inside the white outline by the screw hole.  It was removed in mine.  If there is a value visible on that cap, I can't read it on the pic.

[aron]

Mark, so someone modded yours?

[Jdansti]

The little caps don't have any markings on the three visible sides. If you'll confirm whether it's the one indicated by the arrow in the photo below, I'll pull it and test it tonight if I get a few minutes.

[analogguru]

.....
Two questions:  1) .....  2) Anyone know how/why the 2nd BBD is used in the pedal?

Nearly two years and 2468 Hammer-postings later, same question:
http://www.diystompboxes.com/smfforum/index.php?topic=100165.msg880419#msg880419

Why does a Fab Flanger have two BBDs?

.... and same answers:

Maybe one BBD is running on the half of the clock frequency than the other ?

Maybe, though I'm not sure what that would add, in terms of sound quality.

Think of a phaser: It gives a second time delay in an octave distance, therefore making the effect deeper.

....I'm sure eventually someone will pop up with some inside information.  I'll wait patiently until then.

Nearly two years are gone now and no inside information popped up.... Maybe you can do the following now - (while still waiting):

1.) Take a multimeter
2.) Turn it on and switch it to diode check (with sound)
3.) Connect one lead to pin 2 of the BL3102
4.) Take the other lead and tip to pin 2 and 6 of each BL3207 (note the result)
5.) Take the other lead and test if you hear a sound when you connect it to pin 3 or 11 of the 4013 (note the result)
6.) Connect one lead to pin 4 of the BL3102
7.) Take the other lead and tip to pin 2 and 6 of each BL3207 (note the result)
8.) Take the other lead and test if you hear a sound when you connect it to pin 3 or 11 of the 4013 (note the result)
9.) Connect the lead to pin 2 of the first BL3207
10.) Take the other lead and test if you hear a sound when you touch pin 1, 2, 12 or 13 of the 4013 (note the result)
11.) connect one lead to pin 6 of the first BL3207
12.) Take the other lead and test if you hear a sound when you touch pin 1, 2, 12 or 13 of the 4013 (note the result)
13.) Repeat the steps 9 - 12 with the second BL 3207

analogguru

[analogguru]

double post

[bluebunny]

double post

Nah.  "Echo".  Two BBDs...   

[Mark Hammer]

I thought my questions sounded sort of familiar!    And apparently the price I paid doubled in the intervening 2 years.  

I'll see if I can do the suggested tests, and get back to you.

[Jdansti]

I pulled the cap on mine and measured it. It was 29pF. Then I dropped it in the carpet!  I grabbed a 22pF disk cap and measured it at 28pF, so I used it to replace the SMD cap. It sounds the same as I remember it sounding, which isn't great. I might reduce the value of that cap like you're doing and see if it improves.

[Mark Hammer]

My workbench was painted/Varathaned solid white, especially to be able to spot things.  It's been chipped a bit over the last few years, such that I don't have a smooth white surface anymore.  I need to either install a white formica top, or give it a new coat of Varathane, because it's getting harder to find tiny things these days.

Dropping surface-mount parts on a carpet is not the sort of thing I would wish on anyone, unless I truly disliked them.

[Jdansti]

It started off over my bench, but the little bugger jumped over the edge and into the carpet like a little flea!