Joined: Mar 14, 2011
|Posted: Sat Sep 03, 2011 11:23 am Post subject:
Moog 904a component value discrepancies
I wonder if anyone would be able to clear up a few issues I've been having with identifying the values of some components in the 904a.
Firstly I hope I've posted this in the right place, it seemed the most relevant forum but if not then I apologise.
There seem to be a few versions of the 904a schematic out there - the most likely to be correct seem to be the one from the 'Norlin' service manual, and this official Moog one - http://www.freeinfosociety.com/electronics/schemview.php?id=943
Confusingly both are labelled 1149, but there are discrepancies between the two for several component values, and the service manual is not dated. If anyone could shed some light on which schematic is considered the 'correct' one, or which values should be used for best results for the components in the list below, it would be much appreciated.
R6 - 2.7K or 2.7M?
R13 - doesn't seem to appear anywhere in either schematic - I assume it's a mistake.
R22 - do the arrow and 'c.w.' indicated turning the pot clockwise?
R41 - 3.3K or 33K?
R45 - .47 - does this mean 470 Ohms, or 47?
C1 - 0.003 or 0.005? What is the unit?
C2 - 100mmF - does this mean 100uF?
C3 - '10'. No unit given.
C4 - '10'. No unit given.
C5 - '80'. No unit given.
C6 - Is this electrolytic?
C7 - '2.5'. No unit given.
C8 - 2.5 or 25? What is the unit?
C9 - '10'. No unit given.
I'd be very grateful to anyone who can clarify the correct values or units in any way. Cheers!
Joined: May 25, 2008
Location: Suffolk, UK
|Posted: Mon Sep 19, 2011 7:57 am Post subject:
|Oh the joys of hand-drawn circuits, meant to confuse the industrial spies.
I do not know the Moog, nor am I familiar with the other circuit of which you speak, but we can make some observations from the circuit context.
R6 sources current through Q1 and Q2, and there won't be an awful lot of that using Megohms (especially splitting it two ways).
Since R12 appears three times (once on Q3 base [51k], twice at top-centre[330R] where somebody's annotated a 1 and a 2, do you think R13 was meant to be one of these? You do not specify a value for R13.
Similarly R44 appears twice R44-1 (10R) and R44-2 (330k) but I cannot see an R45 (0.47). Unless given reason to believe otherwise, this is half an ohm.
R22 Yes, clockwise, unless turning it whilst looking in a mirror.
C6 is drawn as an electrolytic (USA style) and is in-line with filtering current through low-value R46.
C2, on the other hand, is not drawn as an electrolytic and bypasses feedback resistor, presumably for high-frequency stability or noise reduction. 100MMF is an abomination and I can only guess that it is saying Micro-Micro which is 100pF ("Puffs")
C2, similarly, is not drawn as an electrolytic and would therefore be 0.003uF or in Euro-speak, 3.3nF or 3n3.
Good luck on your mission, should you choose to accept!