rjd2 wrote:2 things:
1- just had my OBXA open, and i'm 99% sure the only tants are in the PSU.
Take another look on the processor boards.
Welcome to the mess that is the schematics for the OBXa processor boards and calibration procedures.Skiroy wrote:2 questions
1. Where is C1? The manual says C0 is the very first C but it some parts of the tuning procedure it says to push the "transpose down" button so does the reference to C5 it describes in the procedure change? In other words where is C1?
The second C on the keyboard regardless if the transpose button is engaged?
The The second C with Transpose down engaged?
Or the First C on the keyboard when Transpose down is engaged?
And what is the frequency of C1 and C5 the manual refers to in the procedure?
2. Second question. The service manual under the upper and lower control board calibration procedure on page 11,3rd addition, refers to "Pin 7 on IC #64" for the DAC OFFSET ADJUSTMENT. Is this a typo because I cannot find this IC #64 anywhere on my board or in the manuals "Upper and Lower Control Boards" diagram. I only see a #164 and I see a C64 which I assume is a cap.
Thank You so much.scottrod wrote:The later OB-Xa serial numbers had an upper control board that was changed. I've never seen a schematic for it but yes, IC #64 was removed. Its functions were replaced with IC #166.
To confuse things further, the original manual had a typo for the DAC Full Scale Adjustment procedure where it calls out Pin 9 of IC #64 . It should have been Pin 7 like the other two procedures.
The correct DAC adjustment setup procedure for the late model OB-Xa should be performed with measurements taken at Pin 7 of IC #166.
"[C1 is] The second C on the keyboard regardless if the transpose button is engaged?
Yes. Per RJD2, note assignment is the physical key for non-midi instruments.
It seems I am getting conflicting info. Are you saying C0 is the first C on the keyboard no matter if the transpose button is in the up,middle or down position,according to the service manual?rjd2 wrote:AFAIK, C0-C5 typically refers to the actual, physical key.
So when it says in the service manual to play C5 with the transpose down button on and tune the initial frequency I am confused still. It explains this on pages 13-14 in the manual attached.madtheory wrote:I googled the frequencies for you:Skiroy wrote:Does that mean you dont know or you do know and wont tell me?
Yes, that is true.Skiroy wrote:It seems I am getting conflicting info. Are you saying C0 is the first C on the keyboard no matter if the transpose button is in the up,middle or down position,according to the service manual?rjd2 wrote:AFAIK, C0-C5 typically refers to the actual, physical key.
It is not playable enough to justify $2700.00. Really at this point I have nothing to lose to try and tune it because I will not use it sounding like this. If I make it worse I will get it done by a pro anyways.rjd2 wrote:are you calibrating scale because it sounds out of scale to you, or because you think this is something you should do? its a question worth asking. i am going to tell you right now that if you are planning on tuning the voice cards, and you dont have experience tuning synths, i will bet you $100 that you wont be able to navigate it. the OBXA is the most confusing synth i've ever tuned. if you cant scale it by ear using a 440 tone or a tuner, i strongly encourage you not to do it, as its very easy to throw it even further out of calibration. nothing personal. is the synth at all playable to you right now? or is the output just such an utter cacophony that its completely worthless, as a playable instrument?