Conn Multivider Repair

[DrGonz78]

Anyone ever work on one of these ocatve pedals before? I have one right now where it is cutting out on higher frequencies and even some low frequencies get cut off. The unit passing the main signal through the unit but the wet effected signal is cutting out. Actually now the main dry signal is way way quieter, so something else must have went out. Anyone have a schematic? Thanks.

[DrGonz78]

You know what? Nevermind on this one the circuit board is really too hard to even get it off. The dry signal is still coming through but whatever was still making the octave effect come through at lower frequencies finally went out completely. Can't really fix it if I can't get it apart... I give up on this one! Perhaps this is why there are basically no threads repairing these units online?

[big_teee]

Don't Force it, Get a Bigger Hammer!
GL,
T

[52 Bill]

You know what? Nevermind on this one the circuit board is really too hard to even get it off. The dry signal is still coming through but whatever was still making the octave effect come through at lower frequencies finally went out completely. Can't really fix it if I can't get it apart... I give up on this one! Perhaps this is why there are basically no threads repairing these units online?

I've seen a couple of different versions of these. One had a red control panel and the other one had a black panel. I think that the black one was the later version and was made by Jordan in California. They used to make the BossTone fuzzes.

How hard can it be to take it apart? Post some photos and somebody here will tell you how to do it.

[DrGonz78]

So here are some pics...




Basically the on/on switches are latched like a cage nut would be in an amp chassis. It looks like it would be easy enough to use a pair of pliars and squeeze them to remove. Only thing is they are not easy to squeeze and scraping up the front is not a good idea. So I elected to try remove the solder at all twelve points that connect the switches to the circuit board. Well got the solder off and the pads are not that strong. I also think that the plastic standoffs on the switches are somewhat fused to the board as well. So even after removing the solder it was still too tight to feel comfortable pull it apart. It is a double sided board so yeah I think there are pads even on the other side, but I did get a good amount of solder out. At this point it feels like I am gonna just break the thing to remove the board. I think the 2n2924 transistors are actually all working and my main problem might have to do with the flip flop CD4013A IC chip that is the flip flop circuit. So what do you guys think is best way to get it apart?

[52 Bill]

Basically the on/on switches are latched like a cage nut would be in an amp chassis. It looks like it would be easy enough to use a pair of pliars and squeeze them to remove. Only thing is they are not easy to squeeze and scraping up the front is not a good idea.

Are the mounts part of the switch or are they just holding the switches in place? The small bent spring tabs on the underside of the panel look to me like the mounts were inserted from the front side. If you press in the spring tabs do the mounting tabs move up and out the front side? If you push up on the back side of the switch, do the mounting tabs move enough away from the front panel to allow you to get a small screwdriver under it?

If you do get the switches unsoldered, you will have a better idea and view of how to get them removed from the panel. Use Chip Quik if you have it, to make removal easier.

[Mick Bailey]

I've seen that type of switch before (though not on an FX unit) and it was inserted from the front and the board soldered on afterwards.

[Jazz P Bass]

I agrre that the switches must be desoldered to remove them from the front panel.

[DrGonz78]

Well I finally used some chip quick and some finesse to get the circuit board off. What a beast! Anyway I have managed to get some of the octave functionality back but basically I am back to my original problem. The octave effect signal fizzles out at lower amplitudes and the higher frequencies just give popping sound. So basically if I feed a strong sine wave signal at 300hz it works great, but if I turn the volume down 2-3 decibels it fizzles out ending up with only a dry signal.

I have changed out all the electrolytics except that silver one that you can see in the pic(that silver one is not the problem). It is not any of the transistor as I have replaced those too. I also have replaced the CD4013A flip flop as I was suspicious that it might be the problem. I hate this shot gun approach and am strongly thinking I will order the schematic. There are two tantalum caps that could be in question as well as a few ceramic caps. So far I am not doing so well with this repair, but there is light at the end of the tunnel. I am now able to trace out the effected signal so now I am learning how the circuit works better.

I have another one to repair too and it has the same problem. At least to say I have not tortured that one in any way, yet... Once I go to repair that one it will hopefully go much smoother.

[cjlectronics]

Thanks for being the guinea pig on this unit. I've never worked on one but now I know what you have to do to get the board off. I know the trouble you went thru de-soldering the switches from a double sided PCBA, it's a tedious job. If at all possible, I cut components out before de-soldering them. These parts are cheap.
I didn't see where you verified the supply voltage is good throughout the circuit. Is it clean at the 4013?
When I start seeing issues with frequency stability, I focus my attention on filter circuits. What's the RLC circuit doing at the 4013? Does it decay or react like the output signal? Make sure the inductor is original and someone didn't swap it out thinking it'll make it sound better.

[Mark Hammer]

You've pretty much described how the preponderance of analog flip-flop-based octave dividers work and sound...well, with the exception of the "popping" n response to higher-amplitude inputs.

The 4013 treats signal above some threshold as valid positives, and below another threshold value as valid negatives. The usability of flip-flops for octave division depends on the envelope qualities of the input signal. Reeds are decent because they can provide a robust steady signal. Plucked strings, like guitar or bass, not so much, since they have an initial supra-threshold peak, followed by a rapid decay; i.e., an unstable input. When Craig Anderton eventually incorporated a 570 compander into the PAiA Rocktave Divider to provide a more consistent input signal, and quickly fade it out when the signal sank near the lower threshold, that improved the performance of such analog units measurably for application to guitar and bass.

[DrGonz78]

Well thanks for the feedback you guys! Apparently my client has even one more of these pedals that they say works flawslessly. At this point I have no idea what a working unit should behave like from the very start. I figured they would have given me the working one to make comparisons, but unfortunately I only got the two that needed to be repaired. The voltage is regulated to 12 or 11.96v DC to be exact and I have clean power all through out the unit. The 4013 chip gets that 11.96v clean all the time whether or not signal is applied. I did some voltage observations of that flip flop circuit and understand better what the circuit does based on input voltage. The inductor is the original one just to answer that question. I did signal tracing of the flip flop chip and it appears to work pretty good. Actually if the input volume is not pushed hard enough it does not activate the flip flop effect, as Mark had pointed out.

On the upside the unit that I repaired would not work very well with my guitar and before replacing the 4013 chip it stopped working all out. I finally realized that putting an overdrive pedal in front of one of these units gets the input signal to a more workable level. In fact, even without the overdrive pedal I am now getting higher notes to consistently trigger the flip flop effects. So, it is as fixed as it is going to get and it sounds pretty damn cool. At no time had I ever gotten high frequencies to work and now they are working. The overdrive pedal really makes the multivider come to life and that is the only way I see this type of pedal working with the use of a guitar. That all makes sense figuring this circuit is really designed for reed and horn players where there is a very strong input signal. As always I really appreciate all the help and advice I find here at MEF!! Thanks guys!

Now onto fixing the other one so it plays as good as this one!