Part one can be found here: I’ve been doing some research on this beast and it’s been really hard to track down service info for this model Crumar in particular. The Crumar Bit 01 is the rack mount version of this box and i have that service manual but it includes no info on how to properly calibrate the oscillators or filter board. I’m also not sure if the parts naming even matches really because the boards are not identical within each box.
So with some hunting i found that Bob at Tauntek had posted some info on his site about the Bit 99 that was very helpful. I don’t have a scope here so i am unable to check the digital side but the analog side it starting to make a lot of sense after a few poke and prod sessions with the tweaker!
1, I fixed the velocity sense on the key bed and it’s back to 90% of feeling good. It’s still a little clunky in spots and i am attributing this to smoker musician damage at the moment. I cleaned the springs and rails on the key bed with vinegar and it made a great improvement on the keys that were not striking well or without useful velocity info. I replaced any springs that were distorted or broken with a set from an old deceased mirage key bed. So all the keys work and behave much better. It was hard to get the springs soldered into the right position with the right amount of tension on them. The mirage key bed has little loops that hold them in so there’s no need to solder them.
2, I am still trying to get the scale and tuning of everything right on. If i get the oscillators tuned nice with each other the pitch bend scales incorrectly between the two voices and sounds bad. I can get one range ( up or down ) to work but not both together while the oscillators are scaled properly. It’s a bit whack a mole at the moment.
3, The mod wheel is working now. I’m not sure what was up with that before but that gremlin moved out…
4, All of the filters are matched decently and sound great! I will do one more round of adjusting once i get a better feel for how it sits best and sounds the most even. If i under cal the VCA the oscillators sound better but they leak a lot when the key board is idle. So i tweaked it back until they just barely disappeared.
5, On other quirk is that it seemed like there was some awkward voice stealing or filter triggering problem at first but i realized that it’s only apparent at the upper / lower 1/4″ outputs. I figured out that the headphone jack actually mutes the other outputs ( much like the juno 106S and the internal speaker muting ) and the jack / switch is dirty and sometimes doesn’t make great contact. The Crumar Bit 99 sounds really great in stereo mode when the voices are all panning around within chords.
6, I also epoxied the right end of the key bed as it had cracked. This should help it from getting any worse.
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- 01 Crumar Open View 1
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- 02 Crumar Open View 2.JPG
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- 03 Crumar Open View 3 Filter Board.JPG
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- 04 Crumar Open View 4 Voice Board.JPG
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- 05 Crumar Open View 5 Keybed 1
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- 06 Crumar Open View 6 Keybed Hinge
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- 07 Crumar Open View 7 Keybed springs 1
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- 08 Crumar Open View 8 Keybed springs 2
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- 09 Crumar Open View 9 Replacement springs 1
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- 10 Crumar Open View 10 old mangled springs 1
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- 11 Crumar Open View 11 unattached springs 1
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- 12 Crumar Open View 12 old and new springs 1
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- 13 Crumar Open View 13 Replacement spring fitted 1
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- 14 Crumar Open View 14 Replacement spring fitted 2
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- 15 Crumar Open View 15 cracked keybed mount
Side note: There is also a soft version of the Crumar Bit series Here: I haven’t tried it though…
::: IF :::
xbs111.wordpress.com 
i need to replace both volumesliders and thought i found a good replacement in some Alpha’s but the pin config is not fitting and can not be made to fit.
Do you know of any modern replacement?
i’ve seen them for sale on ebay before.
sometimes they show up on ebay!
Thanks for all this info.
I was wondering how exactly the symptom manifested regarding your 5th observation (dirty headphone jack)? I just picked up a Bit99 and I’ve been getting intermittent crackling noise coming from the upper/lower outputs. It’s been in with my tech guy 3 times over the last week and he cannot reproduce the crackling noise symptom. Although he’s replaced one of the output connectors and 2 mute chips which he thought may have been on their way out. After replacing the mute chips I experienced no unwanted noise for a couple of hours before it started up again. I haven’t been able to get a hold of him to ask if he cleaned the headphone jack switch so just wondering if that might be responsible for the unwanted noises coming from the upper/lower outs. I think he’s feeling somewhat haunted by it at this stage… As am I. It would be nice if it was as simple as cleaning or replacing a dirty jack/switch.
I reloaded factory patches last night via your link on gearslutz and the problem ceased for several hours… but persisted again this morning. Another thing I noticed is the output signal is quite low even when upper/lower faders are at full. However after I reloaded the factory bank, the output signal was almost double what it had been before, although still quite low relatively speaking.
I would be grateful if you could offer any suggestions on cause/solution.
Many thanks,
S
the headphone jack interrupts the outputs i believe. so if that jack is dirty or broken the main outputs will be unreliable. are all the voices behaving similarly? loud soft etc? the main volume faders may be broken or sloppy inside so that they behave badly.
Or the DAC is out of calibration and the patches load improperly in random ways because the DAC is telling the voices inconsistent info.
Thanks for getting back to me.
The faders seem to work fine and to be honest the crackly noise has become much less persistent than it was before the mute chips were replaced. I’ve had it on for most of the day and only observed the crackle a couple of times over several hours. Much less frequent and severe than previously. It seems to occur more or less at random, with the faders in any position, and can happen whether keys are depressed or not. It might just be my imagination but it appears to happen more when a deep brass or pad is selected or any patch with a long release. Having said that, I’ve also observed it occurring on a short decay patch. Actually, right now it’s started crackling away again, no keys pressed (Lower Prg 25 Upper Prg 24).
I couldn’t say whether the voices are behaving oddly or not. The soft patches sound soft, the louder ones loud. Kind of as I would expect them to, but I don’t really have a great frame of reference for how this machine should sound. Overall everything sounds a little bit distorted if anything but, like I said earlier, the output signal is actually quite low when I view the input signal through the sound cards display. Baffled.
I’ll ask my tech guy about the DAC calibration. Thanks for all the suggestions. Just another thought; would it make any difference to reliability whether the factory patches are loaded up though WAV tape method as opposed to a Sysex dump?
Thanks so much for your help.
S
It could be a similar problem to what happens with Roland Juno chips.
they start to fail and make strange sounds.
there’s lots of CEMs in there ( if i remember correctly ) and i wouldn’t be suprised if one is grumpy. or not soldered well.
Cleaned the outputs and phone jack with isopropyl and so far so good, several hours use with no crackling. Thanks for your help. I’ll post any developments.
I spoke to soon. Crackle just started up again with a vengeance.
Whether this is of significance or not, I don’t know, but I noticed where the ribbon connectors joining the filter and voice boards, on the filter board side of the ribbon connectors there is a whitish deposit like something leaked and dried. I tried removing the connectors with the white dust around it so I could clean properly but they had seized. Could this be responsible perhaps?
i would suggest trying to discern if it one voice or a global issue.
this is very hard to tell unless you have a service manual. i wish i had the service manual myself…
;-D
Thanks, I’ll have to find someone with the right electronics skillset to make that determination as its beyond my expertise. My tech guy is not responding to my calls or texts which accentuates the frustration. Shame there’s no trace of the service manual floating around anywhere.
I managed to disconnect and clean of the white deposit at the ribbon connectors which seemed to help the noise issue become less severe and frequent although didn’t eliminate it by any means. I had it off for a few days and only turned it on this morning to see what the status was and, to add to my distress, a new symptom has presented; the tune of all patches are off, ie everything sounds like an out of tune bell.
Sigh, think I’m gonna have to shelve it and the associated frustrations till after Christmas.
Have a good one, chat to you in the new year.
Sam
Sorry to bother you again… Just an afterthought… hypothetically, if it is a single voice or perhaps a global issue, what might that mean with regards to a successful repair? ie Would repair be possible in your opinion? Would I have to source new voice chips and are these even available anywhere?
the tuning regime is very odd inside. it’s not like a normal analog synth because the oscillators are tracked to each other in an obtuse way. my bit 99 can be tunes and will be happy ( play in tune, patches make sense ) but i can’t get the pitch wheel to track equally on both oscillators. again, without the service manual it’s been hunt and peck…
Just thought I’d close this one in case anyone has a similar issue with their Bit99…. Good news at last. After 4 trips to the synth doctor and a couple of weeks of crackle free use it would seem the problem has been resolved.
On top of aforementioned work, my tech guy replaced a bunch of tantalum capacitors (I think with electrolytic), replaced a voltage regulator which appeared to have a dodgy middle leg, and replaced the headphone chip.
As you’ve mentioned he had no service reference material so in a sense was working blind. Thank God he’s a genius! Well I think so anyway 🙂
Thanks for all your help,
Sam
Hi, Thanks for documenting your Bit, nice to see some interest these days!
I’m a Bit 99 owner .. picked up mine in 1996. And it’s always been bit sick, mostly at first drifting out of tune then strange random missing voicing problem which seems to be a common issue. I used to take a hairdryer to it to help keep it in tune!
I digged it out the other night and its still working partly , actually the best in tune sounding ever. Definitely think there are some voicing issues and biggest problem is it seems like only one or two voice chips are working as in single mode you have to hold down 3 keys then the 4th pressed will sound, so it kinda works monophonically but you have to wait for the note decay to finish to play the next note. Now in double mode it plays the weird mono style as well, (without having to hold down any extra keys) and if you overlap your playing you won’t get new overlapped note.
I’d be really interested to find out how to start testing all the chips and calibrating it. Unfortunately I don’t have much experience of synth boards but I’m sure I can learn.
Would you be possible to help , and maybe make a photo of the boards annotated with what sections and adjustment screws do what?
I think I have recognised the NEC voice chips and the filter cem3328s.
I have in the past tried taking a screwdriver to many of the adjustment screws inside , I think last time a couple of years ago I managed to get it mostly in tune with itself, without really having a clue what I was doing.
I am still amazed at how raw and deep it can sound, as someone mentioned it does seem to overdrive itself a lot but this could be an adjuster is set too high.
I remember getting a Juno 6 and was disappointed on how thin and tame it sounded in comparison, and swapped it shortly after for DX.. doh!
So i’d love to get it working in full poly and get using it again as has a special sound.
Any help would be greatly appreciated 🙂
this is the main issue with working on Bit series synths.
without the service manual it’s impossible to do basic troubleshooting.
there is undoubtedly a startup key command that allows one to hear each voice. without this it’s hard to see what voice is having what problem…
etc.
i agree it’s a truly unique design and sounds HUGE.
Do you know if you should hold the load button, when restoring it to factory settings, while playing the sound?
there is no factory restore for patches. they must be reloaded from a tape or sysex.
I know, I meant do i hold the the load button while playing the tape?
I recently aquired a Unique DBK, the US version of the Bit 99 which came with a set of schematics. These have no factory test procedures etc just layouts and circuits. I’d be happy to scan and make these available.
Oh Boy!!! can you please! this would rule! can you email me a link to them at: newallianceeast @ gmail.com
Had my bit one for a little over a week and now there is no audio output. At loud volumes I can hear some sort of oscillator very faint in the background, but nothing significant is coming through. Should I look to replace the Amp T8350 6N137 chip?
Hello! you should check the audio / headphone jacks first. if they don’t make good contact they can sometimes mute each other by accident
Very helpful all this info 🙂 Im restoring a few BIT MIdi Master Keyboards and i have a few issues with those troublesome springs as well..and a few of the tactileswitches as well.. still searching for an exact match to them. A bunch of the 1/4″ phonejacks on the back are beeing replaced as well when they due to age and fatique came right of. I am for sure going to try the trick with wineager. Wbr Per from sweden.