First i'm no guru. This was a a listening and observation that created this thread.
I’m presenting this as a service to anyone opening up an Accuphase C-200 preamp.
I purchased this about 6 months ago but hadn’t dug into it until about 2 months ago. It came to working though I thought it lacked something sonically. I had hoped it just had tired caps and it would sing nicer after the elytics were replaced. As a side note the power board had a couple of disintegrating resistors and I replaced them all (precautionary, they did all tend to meet spec.) After replacing the electrolytics, I still didn’t think it sounded quite right.
Thinking perhaps a tone section issue (which admittedly is more complicated than I understand) I started checking components against schematics and found an error. On the switch assembly there are 2 resistors that are part of the tone bypass circuit R7, and R8 which should be 560 ohms. In my unit they were 39 ohms. Luckily I had a pair on hand (I figured I could change them back if it turned out that didn’t help). The change in fact improved the presentation immensely.
I spent some time listening and felt it still wasn’t quite right so I embarked on a search through each board looking for similar discrepancies. (Not actually believing I’d be so lucky, but I figured what do I have to lose?).
Low and behold I found several
On the tone control assembly board (712-0001-00)
I found 3 issues
R1 and R2 should be 390 ohms. Mine were in fact 3.3k
R19,20,21,22 were 3k, where they should have been 2.4k
R23,24 should have been 100 ohms when they were 180 ohms
On the headphone amp assembly (715-0001-00)
I found R17,18,19,20 which should have been 47 ohms were actually 4.7 ohms
On the equalizer amp (711-0001-00)
R19,20 were 390 ohms rather than 330
R17,18 were 3.3k rather than 2.2k
For the record, I suspect this is an oddball unit. I suspect the large majority of these are correct from the factory. Also for what it’s worth , I found all the resistors I tested were well within spec of their markings usually close to 1% or better. I used 1% for all the replacements.
I used 2 versions of S/M schematics, the original parts list and the service bulletins as the reference for my conclusions. I am aware there are frequent on the fly changes made during production and there are often errors in the S/Ms, schematics and parts lists (I was prepared to go back and I did them one change at a time).
I’m not saying this is a good method or a cure all. I merely wanted to make this information available to someone dealing with one.
It has in fact improved the sound of this unit greatly. I hope it helps someone along the way
I’m presenting this as a service to anyone opening up an Accuphase C-200 preamp.
I purchased this about 6 months ago but hadn’t dug into it until about 2 months ago. It came to working though I thought it lacked something sonically. I had hoped it just had tired caps and it would sing nicer after the elytics were replaced. As a side note the power board had a couple of disintegrating resistors and I replaced them all (precautionary, they did all tend to meet spec.) After replacing the electrolytics, I still didn’t think it sounded quite right.
Thinking perhaps a tone section issue (which admittedly is more complicated than I understand) I started checking components against schematics and found an error. On the switch assembly there are 2 resistors that are part of the tone bypass circuit R7, and R8 which should be 560 ohms. In my unit they were 39 ohms. Luckily I had a pair on hand (I figured I could change them back if it turned out that didn’t help). The change in fact improved the presentation immensely.
I spent some time listening and felt it still wasn’t quite right so I embarked on a search through each board looking for similar discrepancies. (Not actually believing I’d be so lucky, but I figured what do I have to lose?).
Low and behold I found several
On the tone control assembly board (712-0001-00)
I found 3 issues
R1 and R2 should be 390 ohms. Mine were in fact 3.3k
R19,20,21,22 were 3k, where they should have been 2.4k
R23,24 should have been 100 ohms when they were 180 ohms
On the headphone amp assembly (715-0001-00)
I found R17,18,19,20 which should have been 47 ohms were actually 4.7 ohms
On the equalizer amp (711-0001-00)
R19,20 were 390 ohms rather than 330
R17,18 were 3.3k rather than 2.2k
For the record, I suspect this is an oddball unit. I suspect the large majority of these are correct from the factory. Also for what it’s worth , I found all the resistors I tested were well within spec of their markings usually close to 1% or better. I used 1% for all the replacements.
I used 2 versions of S/M schematics, the original parts list and the service bulletins as the reference for my conclusions. I am aware there are frequent on the fly changes made during production and there are often errors in the S/Ms, schematics and parts lists (I was prepared to go back and I did them one change at a time).
I’m not saying this is a good method or a cure all. I merely wanted to make this information available to someone dealing with one.
It has in fact improved the sound of this unit greatly. I hope it helps someone along the way
