[sdiy] Tone control questions

Terry daytona at verizon.net
Tue Mar 11 17:14:54 CET 2014

The Roget Luther site Moogarchives has a few of the earlier schematics.  
Not all of them though.
Just go to Instruments/Modules. Some of module descriptions have a box  
labled schematics. Click on those to see some that are different from  
those copied Norlin ones. Handy to compare to the later ones to identify  
errors. The 911A is correct on Moogarchives, but has an error on the  
Norlin copy. 2.7K is mislabled ar 27K on the Norlin one. Those originals  
always had R.A.Moog, Trumansburg,NY on the bottom right. Note: There were  
many revisions over the years. My summer 1969 system has certain revisions  
that are unique to that time period. My 902's are the third revision and  
do not have the bridge rectifier and a coulpe of other parts that appeared  
later that year and into the 70's. Moogs would usually include those  
blueprints for your particular unit when originally shipped. There should  
be plenty of early revision blueprints out there.

Could ask the BMF (Bob Moog Foundation). They claim to have all the  
unpublished schematics, but have not yet finnished scanning or posting.

> what is the best page to find the pre-norlin blueprints ?
> thnx
> Sent from my iPhone
>> On Mar 11, 2014, at 3:02 AM, "Terry" <daytona at verizon.net> wrote:
>> Quite a few mistakes in those Norlin issued Moog modular schematics.  
>> These seem to be just simple copy mistakes where whoever copied these  
>> over from the original blueprints, did not proofread very well. Bottom  
>> line, if you are using the Norlin schematics, you are going to find  
>> these silly mistakes like 4.7K when they should have copied over 47K.  
>> Best to use the originals or a combination of the two copies.
>> The Norlin issue 984 schematic has a few differences from 1967 the  
>> blueprint. You noticed the one pot labled 2.5K when they are all 25K  
>> pots. There is the bass circuit where the 4.7K is mislabled as 47K. The  
>> 80uF cap on the -6 rail is missing the +/- signs. And perhaps where you  
>> may be having a problem, the first resistor after the 22K mixer  
>> resistors is mislabled as 4.7K where it is 47K on the original  
>> blueprint. Could try subbing in 47K for that one?
>> Another observation, the old circa 66/67 Moog circuits mostly used  
>> 2N2926 for NPN's and 2N3702 for PNP's. These were found in the early  
>> 901's oscillators, 902 VCA, 904 filters. By 1969 Moog was using 2N3392  
>> for the same NPN's, and 2N4058 for the PNP's. Most schematics were  
>> updated with these, but that 984 schematic is the same revison from  
>> 1967. Wouldn't surprise me if those later 984's used the 2N3392's for  
>> the NPN's in that circuit. Guess you figured out those odd value filter  
>> caps are those Mallory tropical fish type. Would like to see a close up  
>> of an original board layout. The 984 had two circuit cards, each with  
>> two identical mixer circuits.
>>> Hello everyone,
>>> I'm building a Moog 984 4 channel mixer and I'm having problems with  
>>> the
>>> tone controls. I found and fixed two errors in the schematic already,  
>>> the
>>> resistance of an input attenuator pot was mismarked and one of the  
>>> resistors
>>> in the bass control was mismarked as 47k when it should have been 4.7k.
>>> Anyway, I simulated the circuit in Multisim and with the correct  
>>> resistor in
>>> the bass control, it simulates perfectly. When I assembled the PCB, the
>>> mixer part is fine, but the bass and treble controls don't work right.
>>> Instead of going from an attenuation at full counterclockwise to  
>>> neutral at
>>> mid-point, to boost at full clockwise, I get attenuation at both  
>>> clockwise
>>> and counterclockwise and either neutral or boost at midpoint for both
>>> controls.
>>> I think I get the general picture of what the tone controls are doing,  
>>> but I
>>> don't understand the details. Has anyone any thoughts why the  
>>> simulation
>>> would work but not the actual circuit?
>>> I've done the following:
>>> 1. Triple checked all the component values on the PCB 2. Quadruple  
>>> checked
>>> my schematic against the Moog schematic and the Multisim schematic.
>>> 3. Replaced the transistors
>>> 4. Replaced the tone control pots
>>> 5. Played around a lot with the Multisim simulation trying to get a  
>>> handle
>>> on what the various components do and what would happen with a wrong  
>>> value
>>> in the tone control circuit.
>>> 6. Tried to check the dumb things like power supply voltages, etc.
>>> If anyone wants to see my schematic capture, the moog schematic, or my
>>> multisim schematic/project I'm happy to send them along.
>>> Thanks everyone.
>>> David
>>> David M. Ingebretsen
>>> Collision Forensics & Engineering, Inc.
>>> 2469 E Ft Union Blvd, STE 114
>>> Salt Lake City, UT 84121
>>> dingebre at 3dphysics.net
>>> dingebre at CFandE.com
>>> _______________________________________________
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>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
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