OB-Xa Problem With Envelopes

Hello. The envelope times on my OB-Xa do not match between the upper and lower control boards. It is particularly noticeable with sounds that decay quickly after their initial attack. If the first four voices triggered (from board one) decay after say 250ms, the next four voices triggered (from board two) will decay after say 400ms. In the technical manual I cannot find anywhere to calibrate envelope response between the upper and lower control boards. Has anyone else experienced this with an OB-Xa? Is there anything I can do about it? Thanks in advance.

This will most likely have something to do with the common analog part of the instrument. If you do not have fairly significant troubleshooting skills, you will probably need to take it to a technician such as myself.

Thanks, Wes. It's an honor to have a technician of your stature answer my post! I will take your advice and have a professional take a look at it here in Germany, where I'm located.

Can you make sure the problem is with the DECAY and only the decay ?

Which is the problematic section ? the upper or lower board ?

Try to make the diagnosis more focused...

Gilwe

I think your quest for the Polysix stuff will only be possible by aquiring a Polysix in better condition than the one you have now.

Endbells alone are not really possible on a Polysix. The cabinet is a complete assembly which includes two sides, the front rail, and the bottom. To make the instrument look right, at minimum you would need 2 endbells and a front rail, and considerable modification to the bottom to attach these parts securely. A considerable project, that if left to a professional cabinet maker, such as myself, would cost about as much as a Polysix on the market today.

Sorry, I'm not much of a technician. I have an 8 voice OB-Xa, so if I understand it's architecture correctly the upper board has four voices and the lower board has four voices. The problem is that the envelope response times do not match between the lower and upper boards... not just decay times, rather the entire ADSR envelope is slightly different. It's hard for me to say which of the boards has a problem, since I can only use my ears, and it's a relative question: is the shorter envelope correct, or the larger?

If I play four notes in a row, they all have the same VCA ENV ("Loudness Envelope" on the OB-Xa front panel). Once I hit the fifth note, the envelope changes: the entire ADSR response time is shorter, quicker, as if it's been somehow compacted -- only slightly, but enough to cause problems on some patches. As a work around, I've been using split mode whenever I can. At least then the envelopes are consistent for half the keyboard -- but with only four voices available to each patch! Thank you for your insight.

I assume it is a very easy problem to fix (single IC replacement), but in order to know which, you have to determine what is the problematic ADSR element and on which of the boards.

The ADSRs are voltage controlled and their voltages come from the S&H after the DACs. These circuits are on a separate board from the voices boards. It is very likely there is a dirty connector contact between the voice board and the S&H board. Contacts get dirty as they age and you will lose critical control voltages across them. That is a big reason why Memorymoogs have a reputation of unreliability.

I found mismatches between how the upper and lower boards acted with ADSR and it appeared that two ICs where bad.

I have a similar problem with my T-8. One voice has a noticably longer releasetime than the rest of the voices. Now, the envelopes in te T8 is software generated......hmm....something for a rainy autumn perhaps ?

WT

This will probably be a support part to the 3372.

Yeah I was thinking along the same line. Thanks for the help, I