905 general questions
905 general questions
Hello everyone,
I have several questions on the module 905. I am just comparing pictures from both sides of the PCB with the schematics, the corrected schematics. And I am confused about some points and need your help for understanding.
First, the resistor which connects the emitter from Q2 with the connector of Q3 is 220K on the pictures I have. In the schematics it has a value of 100K. Is that correct?
Second, the Resistor from Q3 Connector to the +12V rail has no value in the schematics. Unfortunately I have 2 pictures of an 905. In one picture, the value is 4K7. In the other picture there is an additional resistor on the left side of the PCB with a value of 220K. When I am right in calculation both values (4K7 parallel to 220K) whould give nearly 4,7K.
So I am wondering why this 220K is used...
And the last point. When the corrected schematic is correct, then the following components should be linked to -6V: one side of the output of the Spring, one side of 82K, 100R, 10u, 2K2 and 75u. Can anyone please confirm this?
Now I compared the traces... beginning from the -6V line coming from the spring. Next stop is 82K, then 10u, 100R. Up to here everything is fine. Then the trace ends at a hole. This could be for a strip . But at the other end I find a 100K resistor which I do not find in the schematics. And the trace goes to 2K2 and 75u, which is correct regarding the schematics.
But now both pictures I have are a bit unclear. I think I see a connection to the 100K resistor (which is not in the schematics) and from there the trace connect the emitter of Q1 and Q4. But these line should be connected to ground (according the schematics).
So, the simple question is: what is right?
Can anyone help me?
Thanks a lot in advance
Bernhard
I have several questions on the module 905. I am just comparing pictures from both sides of the PCB with the schematics, the corrected schematics. And I am confused about some points and need your help for understanding.
First, the resistor which connects the emitter from Q2 with the connector of Q3 is 220K on the pictures I have. In the schematics it has a value of 100K. Is that correct?
Second, the Resistor from Q3 Connector to the +12V rail has no value in the schematics. Unfortunately I have 2 pictures of an 905. In one picture, the value is 4K7. In the other picture there is an additional resistor on the left side of the PCB with a value of 220K. When I am right in calculation both values (4K7 parallel to 220K) whould give nearly 4,7K.
So I am wondering why this 220K is used...
And the last point. When the corrected schematic is correct, then the following components should be linked to -6V: one side of the output of the Spring, one side of 82K, 100R, 10u, 2K2 and 75u. Can anyone please confirm this?
Now I compared the traces... beginning from the -6V line coming from the spring. Next stop is 82K, then 10u, 100R. Up to here everything is fine. Then the trace ends at a hole. This could be for a strip . But at the other end I find a 100K resistor which I do not find in the schematics. And the trace goes to 2K2 and 75u, which is correct regarding the schematics.
But now both pictures I have are a bit unclear. I think I see a connection to the 100K resistor (which is not in the schematics) and from there the trace connect the emitter of Q1 and Q4. But these line should be connected to ground (according the schematics).
So, the simple question is: what is right?
Can anyone help me?
Thanks a lot in advance
Bernhard
Re: 905 general questions
Great Questions!
I've been planning to add a spring reverb to my 55, and also wanted to know about the Q3 collector resistor and any other errors in the published schematics.
Hopefully Tom and others in possesion of functioning units can help clear things up?
I've already got the springs....
I've been planning to add a spring reverb to my 55, and also wanted to know about the Q3 collector resistor and any other errors in the published schematics.
Hopefully Tom and others in possesion of functioning units can help clear things up?
I've already got the springs....

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- noddyspuncture
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Re: 905 general questions
I'm sure I can do that for you..! Those errors are corrected in the previously attached pdf link by the way.synthguy wrote:Great Questions!
I've been planning to add a spring reverb to my 55, and also wanted to know about the Q3 collector resistor and any other errors in the published schematics.
Hopefully Tom and others in possesion of functioning units can help clear things up?
I've already got the springs....
The ground orientation was wrong... in fact my unit was actually wired that way and I worked that one out myself.
The others were quite a major errors - in where the 330K resistor from the emitter of Q3 goes and the base of Q2 being clamped directly to the -6v rail...!
Cheers,
Tom
Re: 905 general questions
Hello all,
so for me the main question is: Are the 2 components, 2K2 and 75u, coming from the emitter from Q3, connected to the -6V rail or to GND?
Thanks a lot in advance !
Bernhard
so for me the main question is: Are the 2 components, 2K2 and 75u, coming from the emitter from Q3, connected to the -6V rail or to GND?
Thanks a lot in advance !
Bernhard
- noddyspuncture
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Re: 905 general questions
Bernhard, do you have the corrected schematic...?Omega56 wrote:Hello all,
so for me the main question is: Are the 2 components, 2K2 and 75u, coming from the emitter from Q3, connected to the -6V rail or to GND?
Thanks a lot in advance !
Bernhard
Cheers,
Tom
Re: 905 general questions
Hi Tom,
I have this version: http://modularsynthesis.com/moog/905/90 ... ted%29.pdf
Is this the right version?
Cheers
Bernhard
I have this version: http://modularsynthesis.com/moog/905/90 ... ted%29.pdf
Is this the right version?
Cheers
Bernhard
- noddyspuncture
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Re: 905 general questions
Yes it is and it also shows you the answer to your questions about the 2K2 and the 75uF...!Omega56 wrote:Hi Tom,
I have this version: http://modularsynthesis.com/moog/905/90 ... ted%29.pdf
Is this the right version?
Cheers
Bernhard
Re: 905 general questions
Hi Tom,
thank you for the reply. I think that's exactly the point. I think there is a discrepancy between the schematics and the picture of a real PCB. I try to attach a picture. I 've painted the components into the picture to illustrate what I mean.
So the 6V line is coming from the left top (output side of the spring). Then you can see the 82K, the 10u, and the 220K (at the component side there is a 4K7). So far, so good. Now you can see the the trace moves to the left and then downwards and ends in a hole which seems to me that there is nothing connected to. The 2 other components (2K2 and 100u) you can find at the right. And now, if you have a look at trace which ends in the other "hole" you see another trace downwards. But this trace belongs to GND. Do you see what I mean? So this picture tells me that the 2K2 and the 100u (or 75u in the schematics) are NOT connected to -6V but to GND...... And that's the reason why I asked if someone can check this on an existing 905.
Cheers
Bernhard
thank you for the reply. I think that's exactly the point. I think there is a discrepancy between the schematics and the picture of a real PCB. I try to attach a picture. I 've painted the components into the picture to illustrate what I mean.
So the 6V line is coming from the left top (output side of the spring). Then you can see the 82K, the 10u, and the 220K (at the component side there is a 4K7). So far, so good. Now you can see the the trace moves to the left and then downwards and ends in a hole which seems to me that there is nothing connected to. The 2 other components (2K2 and 100u) you can find at the right. And now, if you have a look at trace which ends in the other "hole" you see another trace downwards. But this trace belongs to GND. Do you see what I mean? So this picture tells me that the 2K2 and the 100u (or 75u in the schematics) are NOT connected to -6V but to GND...... And that's the reason why I asked if someone can check this on an existing 905.
Cheers
Bernhard
Re: 905 general questions
Hi Bernhard!
It looks like we're both following the same discrepancies noted when you start to really look closely at the published/corrected schematics online vs what appears to be happening in an actual unit.
From what I've noticed so far, I completely agree with you, and I've asked a series of questions in the other thread on this that I hope that Rezin might be able to answer for us to help clear this up.
It also seems that the series input resistor On Rezin's unit is 15k (not 33k), the feedback resistor as you previously noted between Q2 and Q3 is 220k (not 100k) and there appears to be an unlisted 100k resistor terminating the output to ground.
The biasing resistor for Q1 is hidden, so I'm hoping to get confirmation of it's value with some newer pictures of it with a more advantageous angle.
The ground vs -6v paths are still unclear to me as well. Better pictures and perhaps a bit of ohming out the various traces should clear this up.
There's still some mystery here, I think!
It looks like we're both following the same discrepancies noted when you start to really look closely at the published/corrected schematics online vs what appears to be happening in an actual unit.
From what I've noticed so far, I completely agree with you, and I've asked a series of questions in the other thread on this that I hope that Rezin might be able to answer for us to help clear this up.
It also seems that the series input resistor On Rezin's unit is 15k (not 33k), the feedback resistor as you previously noted between Q2 and Q3 is 220k (not 100k) and there appears to be an unlisted 100k resistor terminating the output to ground.
The biasing resistor for Q1 is hidden, so I'm hoping to get confirmation of it's value with some newer pictures of it with a more advantageous angle.
The ground vs -6v paths are still unclear to me as well. Better pictures and perhaps a bit of ohming out the various traces should clear this up.
There's still some mystery here, I think!
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- noddyspuncture
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Re: 905 general questions
There shouldn't be any mystery... if you look at the corrected schematic - the recovery amp - Q2 & Q3 and associated components - are between the +12 and -6 rails. This section only connects to ground via the anticlockwise end of the level potentiometer.synthguy wrote: The ground vs -6v paths are still unclear to me as well. Better pictures and perhaps a bit of ohming out the various traces should clear this up.
There's still some mystery here, I think!
The corrected schematic diagram is very clear here...!
Cheers,
Tom
- noddyspuncture
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Re: 905 general questions
You are identifying traces and saying "this is ground" and "this is -6v"... but what are you basing those assumptions on...? You could be mistaken and have them crossed...? Have you identified the +12 trace...?Omega56 wrote:Hi Tom,
thank you for the reply. I think that's exactly the point. I think there is a discrepancy between the schematics and the picture of a real PCB. I try to attach a picture. I 've painted the components into the picture to illustrate what I mean.
So the 6V line is coming from the left top (output side of the spring). Then you can see the 82K, the 10u, and the 220K (at the component side there is a 4K7). So far, so good. Now you can see the the trace moves to the left and then downwards and ends in a hole which seems to me that there is nothing connected to. The 2 other components (2K2 and 100u) you can find at the right. And now, if you have a look at trace which ends in the other "hole" you see another trace downwards. But this trace belongs to GND. Do you see what I mean? So this picture tells me that the 2K2 and the 100u (or 75u in the schematics) are NOT connected to -6V but to GND...... And that's the reason why I asked if someone can check this on an existing 905.
Cheers
Bernhard
I cannot help there as mine is on perf-board and has no traces...!
The easiest way would be to build what you see on the schematic and see if it works...?
Cheers,
Tom
Last edited by noddyspuncture on Mon Feb 08, 2016 4:26 pm, edited 1 time in total.
Re: 905 general questions
Hahaha, that's exactly what I plan to do !
Bernhard


Bernhard
Re: 905 general questions
Hi All!
I've been doing the same thing as Bernhard, and have noticed the same differences.
The Trace that The 2.2k and 75uf capacitor are connected to are the same trace that the emitters of Q1 and Q4 are connected to.
I think that this is the ground trace as there also seems to be a couple of shield wires connected to it, and the emitters of Q1 and Q4 are shown as connected to ground in the schematic.
Also, if you look at the ground wire connected to pin 22 on the corrected Version of the schematic, you'll notice a single unconnected wire stub. I think that this was supposed to show where the unlisted 100k resistor was connected (between the module output and ground) but was either missed during the schematic capture or accidentally erased and not properly restored during a subsequent cleanup.
I'm not sure how to attach a picture to my posts yet, but I'll try when I get home this evening.
I've also created a "stuffing guide" (not as nice as Bernhard's, though!) showing what's connected to the backside traces, which is where things began to create these questions.
Mine shows all known component values and locations, the +12V rail, and what are probably the -6V and ground rails, although I still don't have enough info to be completely sure about them.
It think it helps when you can see the big picture for yourself.
I've been doing the same thing as Bernhard, and have noticed the same differences.
The Trace that The 2.2k and 75uf capacitor are connected to are the same trace that the emitters of Q1 and Q4 are connected to.
I think that this is the ground trace as there also seems to be a couple of shield wires connected to it, and the emitters of Q1 and Q4 are shown as connected to ground in the schematic.
Also, if you look at the ground wire connected to pin 22 on the corrected Version of the schematic, you'll notice a single unconnected wire stub. I think that this was supposed to show where the unlisted 100k resistor was connected (between the module output and ground) but was either missed during the schematic capture or accidentally erased and not properly restored during a subsequent cleanup.
I'm not sure how to attach a picture to my posts yet, but I'll try when I get home this evening.
I've also created a "stuffing guide" (not as nice as Bernhard's, though!) showing what's connected to the backside traces, which is where things began to create these questions.
Mine shows all known component values and locations, the +12V rail, and what are probably the -6V and ground rails, although I still don't have enough info to be completely sure about them.
It think it helps when you can see the big picture for yourself.
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Re: 905 general questions
Hello Synthguy,
I am completely with you. I learned the last days how difficult it is only to describe the problem without having something visual, a picture or so. It's much more easier to explain things when you have a picture to which you can refer to.
So I hope we will get some more pictures from different angles to clear it up what are the right connections.
For me it was the question: What is my trusted source? Is it the schematics (with all known errors) or is it the real PCB which should work perfect, because it's almost out of a production process.... unless your name is Tom
But sometimes the pictures are not perfect and you cannot see exactly this detail which you are interested in.....
I could tell you stories with the 921B / 921.... It was an awful work because I guess it was the first time Moog was using doublesided PCBs. At the end I decided to make my own layout and ... it worked !!! Surprise, surprise

Cheers
Bernhard
I am completely with you. I learned the last days how difficult it is only to describe the problem without having something visual, a picture or so. It's much more easier to explain things when you have a picture to which you can refer to.

So I hope we will get some more pictures from different angles to clear it up what are the right connections.
For me it was the question: What is my trusted source? Is it the schematics (with all known errors) or is it the real PCB which should work perfect, because it's almost out of a production process.... unless your name is Tom

But sometimes the pictures are not perfect and you cannot see exactly this detail which you are interested in.....
I could tell you stories with the 921B / 921.... It was an awful work because I guess it was the first time Moog was using doublesided PCBs. At the end I decided to make my own layout and ... it worked !!! Surprise, surprise



Cheers
Bernhard
- noddyspuncture
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Re: 905 general questions
synthguy wrote:Hi All!
I've been doing the same thing as Bernhard, and have noticed the same differences.
The Trace that The 2.2k and 75uf capacitor are connected to are the same trace that the emitters of Q1 and Q4 are connected to.
I think that this is the ground trace as there also seems to be a couple of shield wires connected to it, and the emitters of Q1 and Q4 are shown as connected to ground in the schematic.
Also, if you look at the ground wire connected to pin 22 on the corrected Version of the schematic, you'll notice a single unconnected wire stub. I think that this was supposed to show where the unlisted 100k resistor was connected (between the module output and ground) but was either missed during the schematic capture or accidentally erased and not properly restored during a subsequent cleanup.
I'm not sure how to attach a picture to my posts yet, but I'll try when I get home this evening.
I've also created a "stuffing guide" (not as nice as Bernhard's, though!) showing what's connected to the backside traces, which is where things began to create these questions.
Mine shows all known component values and locations, the +12V rail, and what are probably the -6V and ground rails, although I still don't have enough info to be completely sure about them.
It think it helps when you can see the big picture for yourself.
The "unconnected wire stub" you are seeing would be representation for the shield connection of the jack socket. If you look at the input jack representation it also has a "stub" coming from the ground line... so that one is a red-herring I think...!
Also, if you study the complete schematic... the *only* place where the -6volts appears is that very rail you are disputing and calling possibly ground.
If this were the case... why would the unit even have -6volts routed to it..? There would be no point.
I still need to pull mine out and check these points with my meter... but I can't help feeling that you are all mistaken. I think one of you should bite the bullet and build it on vero-board and then report back...

By the way... as this is the "corrected" schematic, I think that the -6 would have also been *corrected* to show the ground symbol..!?
Cheers,
Tom