FAT Freebass / MAM MB33 Problems + Midi channel settings

01012k7 · May 13, 2012, 08:12:41 PM

well i decided to give the thing one last go

to day i took out the chip 40 pin thing also clean the crap work i did before ok so i installed a metal case midi socket as the plasic one was bit knackered from when i got it also replaced the cny17-2 again just in case from over heating so installed a 6pin dip socket and also a 40 pin sockets here some pictures i also clean some of the pain off as the soldering was not great so wanted to make sure of some tracks

was please with the way the chip came out

think i may have a problem reusing this IC

Also with the ic sockets installed i done a route check to see if the links to other trackes work so just waiting for the main chip now if this don't fix it not much else i can do unless a dry joint on the board ..

Gordonjcp · May 13, 2012, 09:04:20 PM

To be fair, a dry joint would be the *first* thing to look for ;-)

If you don't get it going, can I buy it from you?

01012k7 · May 13, 2012, 09:48:40 PM

Quote from: Gordonjcp on May 13, 2012, 09:04:20 PM
To be fair, a dry joint would be the *first* thing to look for ;-)

If you don't get it going, can I buy it from you?

i been over it checking for dry joints but i be using the filter anyway so will not be selling it

Gordonjcp · May 14, 2012, 10:36:38 PM

Well if anyone else has a dead or dying FAT Freebase, MAM MB33 or similar they want to part with, I'll buy it. Ideally one with working analogue bits but a dead CPU, since what I want to do is gank out the old chip and devise a modern replacement, that eliminates the bloody stupid faulty dipswitch problem once and for all.

Circuitbenders · June 06, 2012, 12:39:05 PM

Heres something weird. We've had two Freebasses in for modding recently, both from Germany, which is pretty odd in itself as most mainland European Freebasses are MB33's. Whats strange is that both owners had complained that their units never sounded as good as the ones they had seen on Youtube videos etc.

Having checked out both pretty extensively i discovered that in both of them the 47K log pot for the cutoff (mysteriously labelled D47K) was only measuring to be around 40K. Thats measuring them with the pots out of the circuit. This gave a pretty feeble amount of response to the cutoff knob and you just couldn't get the filter even remotely closed

An attempt had been made on both to widen the cutoff response using the trimmer pots behind the cutoff knob. I assume this must have been done at the factory, but it was nowhere near as wide as is should have been. Replacing the cutoff with a proper A47K pot fixed the problem on both synths.

I've never seen this one a UK Freebass. I can only assume that MAM or whoever actually built these things must have got hold of a load of dodgy pots at some point and used them in units destined for mainland Europe. It would suggest that theres a whole load of people out there who are wondering why their Freebass sounds crap!

01012k7 · June 06, 2012, 06:24:56 PM

it sounds like the units were made in some one shed

also i going to be replacing the pots thxs for the info

01012k7 · July 30, 2012, 01:42:40 AM

i wound like to thx paul for helping me out with the tigger for the freebass ( i love this guy and not in a gay way

)

manneokoko · February 02, 2013, 09:04:06 PM

Hello, another MB33 mk1 owner here!
Ive read the whole discussion and can't find the answer to my problem:

Evertything works great except the auto tune button. When i press it the midi LED lights up and it stops reacting to incoming midi, nothing happens. Strangely enough the auto tune seems to work when i power up the unit: the Midi LED lights up for some time then its goes dark and the unit is running properly.

Any help?

Also it might be worth mentioning that i opened it up and changed one resistor to get some more resonance, this one. I changed from the original 2,2k to a 3,9k. Sounds great. But this shouldn't affect auto tune should it?

Gordonjcp · February 02, 2013, 11:09:38 PM

It depends on if it also tunes the filter. Does auto tune work if you swap the resistor back?

manneokoko · February 03, 2013, 05:03:07 PM

Ive tried changing back to the original resistor on the filter, the auto tune button still freezes it. Strange that the auto tune works when it is first turned on, but not when using the button.

manneokoko · February 03, 2013, 05:36:49 PM

I noticed when I accidentally used a 9V power adaptor that the midi LED stayed on/ freezed. So maybe the auto tune problems is related to voltage? According to the manual it needs 15V AC - but on the unit itself it says 12V AC...
What do you think, is it safe to try using a 15V AC adaptor?

Also, the resonance mod:
According to the instructions for the mod Im supposed to just bridge the given resistor. To my finding this result in decreased resonance, not increased. But when putting in a higher resistor than the original the resonance is boosted. Can this harm the unit in any way?

01012k7 · February 03, 2013, 10:04:26 PM

Quote from: manneokoko on February 03, 2013, 05:36:49 PM
I noticed when I accidentally used a 9V power adaptor that the midi LED stayed on/ freezed. So maybe the auto tune problems is related to voltage? According to the manual it needs 15V AC - but on the unit itself it says 12V AC…
What do you think, is it safe to try using a 15V AC adaptor?

Also, the resonance mod:
According to the instructions for the mod Im supposed to just bridge the given resistor. To my finding this result in decreased resonance, not increased. But when putting in a higher resistor than the original the resonance is boosted. Can this harm the unit in any way?

i my self would not play with the unit they they tend to die some times

Circuitbenders · February 03, 2013, 10:08:18 PM

Its 15v DC or 12v AC, either will work fine.

Bridging the resistor thats been removed on that link won't achieve that much as far as i recall. You want to go for the third one back from the rear of the resonance pot, not the second one. You don't need to take it out, just solder a switch to either side of it.

When you press the autotune button you won't actually hear it doing the tuning like you do on startup as it doesn't trigger the envelope. It takes about 40 seconds or so from when you press the button until the midi LED goes out again. While its doing the tuning the unit won't respond to midi.

Why do you even need to do the autotune?

manneokoko · February 04, 2013, 01:30:01 PM

When changing the resistor that is pointed out in the instructions on the net i certainly got a resonance boost.
But according to the instructions, the resistor should be bridged - I instead put in a higher value resistor.

I will try as you say bridging the third resistor instead.

Also, I have a MB33 newer version with green PCB - not the one shown in the modding instructions.

Well, i dont know if Im gonna need the autotune button, I just bought it. I just thought that since there is a button there, the machine will get out of tune every now and then.

manneokoko · February 04, 2013, 06:33:57 PM

OK, so i tried doing as you said and bridged the other resistor - it also made a resonance boost. I liked the res mod by changing the other resistor more, it gave another kind of resonance boost.. different sound. I guess it affects something else than just pure resonance, maybe accent or env amount or something.

So I will change back to the way i made the mod first - that is changing the second resistor back from the rear of the resonance pot to 3,9k and the third one I just use the original (or maybe I lower it a bit to have a little of booth resonance mods).

Can you please advice, will changing the second one back from the rear of the resonance pot give any damage to the unit?

And do you think its these resonance mods that damaged the autotune button?