FAT Freebass / MAM MB33 Problems + Midi channel settings

[Circuitbenders]

To be honest i'm not entirely sure why the autotune button is there. I've never needed it, and even if you did, you could just restart the thing and it'd go through the autotune sequence anyway.

Without a schematic of the filter it'd be difficult to tell exactly what the second resistor is doing, but i can't imagine increasing it would cause any issues, especially not by such a small amount.

I don't think the filter tracks the keyboard so its unlikely to have any effect on the tuning.

[manneokoko]

I bow down in thanks for your support!

[01012k7]

not shure if i ask you guys before any one know if you can connect a midi to cv adaptor to the VCO of the freebass i know you can do if for the vcf and have info was thinking ( and yes it does hurt to think) if this possable was thinking maybe using one ...

[01012k7]

I bow down in thanks for your support!

Paul great ..

[darkest_star]

First of all: This is a really great threat. Never get so much troubleshooting information about the great MB33.
My MB33 MK1 has the following behaviour:

After switching on I can hear a bass sound which is slowly getting quiet after 1-3 seconds. After about 5-10 seconds the midi-LED goes out. But if I send midi data to the device I NEVER see a flashing midi-LED or hear any sound of my MB33. I have checked a lot with my oscilloscope. The DIP-switch seems to be ok. For testing I have measured the voltages on the CPU pins where the DIP-switches are connected: All DIPs work fine. Further I have seen a perfect TTL signal on the midi-input at the CPU while playing a midi song. So, optocoupler and midi-input socket should also to be ok. During the "warm up phase" (midi-LED on) I have accidentlly touched pin4 of the CPU and have heared a bass sound, which can be manipulated by the knobs on the front. Perhaps pin4 is the gate signal?
Therefore I would like to ask, if someone could send me the schematics of a MAM MB33 or FB-383 MK1? It would be very helpful for me.

Could it be, that my EPROM has partially lost it's memory? Or wouldn't then go my midi-LED not off after some seconds? I have a EPROM programmer available and would like to try to program a another EPROM chip for a retest. But unfortunately the posted link to the EPROM dump of a MB33MK1 (many threads before) isn't working anymore. So, if someone could send my this dumpfile, it would also very helpful for me to investigate respectively isolate the problem of my MB33.

Thank you very much in advance for support!


Regards,
Uwe

[Circuitbenders]

I've just uploaded the EPROM firmware again. You can fin it here http://www.mediafire.com/?u4kkx9659e9tk6r

I've never found the schematic for the mkI anywhere. I asked Touched By Sound a while back and they said they were in the process of uploading them, but then they stopped answering emails. The schematic might be out there, but i've never seen it.

I'd be willing to bet that you have a problem with the CPU, they seem to die on a fairly regular basis.

[01012k7]

cheers for that! ive had a search and cant seem to find one anywhere!

can only find AC/DC!

anychance you would know where id be able to get one?

cheers again, muchly appreciated

lots on ebay

[darkest_star]

@crustypaul: Thank you very much for uploading the EPROM file! I will reprogram a second EPROM on Monday.

But, if the midi-LED goes off after some seconds I assume, that the autotune procedure was successful. Which means, the CPU has already a working program in EPROM. Changing one of the ICs (e.g. CPU) would no problem for me. I've done this a lot in my life (the first time in the 80s for my C64). But doing this without any success in sight I wouldn't do this. :-)
Probably it is one of the multiplexers (4051, 4053)?

But I could really remove all IC's from digital part, solder for each a IC socket and then retry with replaced ICs.

If you send me the email address where you have tried to get the schematic I could retry to get it. I think there are a lot of MB33-hobbyists around which would be happy with that schematic.

Thanks very much!

[Gordonjcp]

Don't just shotgun-replace parts.  It's worth checking the outputs of the multiplexer with a 'scope to see if they seem sane.  They do fail, quite frequently.

[01012k7]

Don't just shotgun-replace parts.  It's worth checking the outputs of the multiplexer with a 'scope to see if they seem sane.  They do fail, quite frequently.

going to have another look at the unit after reading your post.

[darkest_star]

Unfortunately still had no time to reprogram the EPROM because I'm on business trip.
I will check the outputs of both multiplexers too. But this is also a kind of reversal engineering due to missing schematics. 
But back to the symtoms: My mb33 seems to perform a succesful autotune because the midi-LED goes off after some seconds. As I understand the posts in this thread the LED would stay on if an error occurred? Further I can press the autotune button without any reaction. Not during running device and not while swithing it on (where it should play a demo melody).

Very strange... 

[darkest_star]

After the hours I've spent trying to find the error I really assume to "disable" the digital part, add CV and gate input sockets and connect it directly with my Doepfer Dark Time. 

[01012k7]

After the hours I've spent trying to find the error I really assume to "disable" the digital part, add CV and gate input sockets and connect it directly with my Doepfer Dark Time.  

i had an idea with adding a meeblip  this what they told me

_______________________________________________________________________________
My question to one of the guys

can another filter be connect to a Meeblip like anther vcf filter as i have korg ms 20 vcf clone i am making ..
_________________________________________________________________________________
Reply
Yes, it's possible to drive an analog filter from Meeblip. There are two 8-bit outputs on the DAC chip - they're currently both used to generate the audio waveform. It's possible to use just one output to generate an 8-bit waveform. That leave the other output to provide 0-5V cv to control filter cutoff on an analog filter.

It works even better with a higher resolution DAC. Or so a little bird tells me
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any idea if this would work for the freebass

[Circuitbenders]

I've just checked a Freebass. Pin 4 of the CPU does appear to be the gate signal. You should see pulses of about 750mv whenever you play a note, for the duration of the note. Pin 14 drives the transistor for the Midi activity LED, and pin 10 is the midi input.

The pitch CV seems to appear at pin 13 of the 4051 behind the autotune button. It seems to be some kind of an inverted log scaling with around +5v at the lowest C and about 80mv at the highest C.

If the midi is getting to the CPU and it looks fine, but you aren't seeing the gate signal on pin 4, then i guess you have a CPU issue, or possibly an EPROM problem, but as you say, if the EPROM was corrupted i doubt it'd even get past the startup sequence. If you are seeing the gate signal but no pitch CV, then the first thing i'd try would be replacing the 4051.

[01012k7]

i am going to have a go and  trying to get the vcf to work with my 8 Step  Analog Sequencer if no joy i decided to give up with it and break it still worth a bit to me as i can use the 2SC2291 2SC1583 out of it for x0xb0x think this the way forward.

I do have 2 cpu think 16mhz and 12 mhz which is a old one none have been solder into boards just installed in ic sockets also i guess knobs , and some of the plastic pots