This 35 ohm reading drops to about 20 ohms then stalls around there going up and down. Probably because caps can play tricks on meters, and this one is particularly cheap tends to use a lot of sense current and gives some wonky readings. I suppose an appropriate resistor should be chosen to set the feedback current, this will effect gain and stability, no?
Judging by the looks of the board, these center pins on the J18 connector are signal ground. I think they may be carrying this ground to the front panel, or receiving it from there. I will have to look and find out.
EDIT: These pins are bringing signal ground from the volume pot to the front panel controls. Interestingly, in this design signal ground is the same as chassis which makes testing a breeze but I am surprised it is not a virtual or floating ground. I will connect the feedback loop back together with 39 ohm resistors. The resistance between pins 1-2 and 4-6 starts at about 35 ohms and drops indefinitely if the meter is left long enough. This is the effect of a capacitor I am sure now.
How can this design be considered serious? To run ground from volume pot RIGHT NEXT TO TONE CONTROLS to this board and then back TO TONE CONTROLS??? What were they thinking??? Maybe all grounds in one spot, but there must be better ways to do this I think.
EDIT2: Hate to keep making a new post every time I discover something, but I understand the more information I can provide the better the help I can get. My meter reads all dead shorts as .5-.6 ohms no matter what, when source direct switch is on between pins 1-2 and 4-6 I get open circuit reading like there is no contact between these pins. The diagram shows these pins to be connected shorted, and the parallel resistor can make no difference right? What the heck is going on?
EDIT: These pins are bringing signal ground from the volume pot to the front panel controls. Interestingly, in this design signal ground is the same as chassis which makes testing a breeze but I am surprised it is not a virtual or floating ground. I will connect the feedback loop back together with 39 ohm resistors. The resistance between pins 1-2 and 4-6 starts at about 35 ohms and drops indefinitely if the meter is left long enough. This is the effect of a capacitor I am sure now.
How can this design be considered serious? To run ground from volume pot RIGHT NEXT TO TONE CONTROLS to this board and then back TO TONE CONTROLS??? What were they thinking??? Maybe all grounds in one spot, but there must be better ways to do this I think.
EDIT2: Hate to keep making a new post every time I discover something, but I understand the more information I can provide the better the help I can get. My meter reads all dead shorts as .5-.6 ohms no matter what, when source direct switch is on between pins 1-2 and 4-6 I get open circuit reading like there is no contact between these pins. The diagram shows these pins to be connected shorted, and the parallel resistor can make no difference right? What the heck is going on?
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OK on 200k ohm setting meter reads the 47k resistors only tone controls on, weird varying resistance with source direct ON tone controls (supposedly) off.
EDIT: This varying resistance has been driving me nuts. I was thinking a capacitor was causing this but it goes down steadily, not up. I was playing with the switch and it is the darned switch contacts. I can tame resistance down to 1 ohm when holding it right, and up to about 35 ohms that I was seeing with minimal contact pushing it the opposite direction. I think I may have found the source of my channel imbalance and answered a good many questions all in one go. With this connector floated and jumpers across connections 1-2, 4-6 this amp will (should) go from noisy and finicky to simple and clean. The buttons on the front panel are worthless, and there is little hope of salvaging any of its functionality without replacing them. This would be too labor intensive and I don't plan to sell this amp since it was free anyway. I will just turn it into a plain old power amp with an on/off switch. If only my cable arrived today like it was supposed to, I could perform these modifications and test it.
EDIT: This varying resistance has been driving me nuts. I was thinking a capacitor was causing this but it goes down steadily, not up. I was playing with the switch and it is the darned switch contacts. I can tame resistance down to 1 ohm when holding it right, and up to about 35 ohms that I was seeing with minimal contact pushing it the opposite direction. I think I may have found the source of my channel imbalance and answered a good many questions all in one go. With this connector floated and jumpers across connections 1-2, 4-6 this amp will (should) go from noisy and finicky to simple and clean. The buttons on the front panel are worthless, and there is little hope of salvaging any of its functionality without replacing them. This would be too labor intensive and I don't plan to sell this amp since it was free anyway. I will just turn it into a plain old power amp with an on/off switch. If only my cable arrived today like it was supposed to, I could perform these modifications and test it.
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Your problems with the switches are one reason I abandoned using any mechanical switches or relays in the audio path a long time ago. They are just to unreliable long term. Same goes for speaker relay contacts too. Its a recognised problem and one I though affected other people and not me 😀 I was wrong. So its solid state all the way now.
Those 47 k's The switch diagram clearly shows pins 1 and 2 and 5 and 6 as being shorted which is the same as linking directly on the main amp PCB as I showed earlier.
Those 47 k's The switch diagram clearly shows pins 1 and 2 and 5 and 6 as being shorted which is the same as linking directly on the main amp PCB as I showed earlier.
Yep, now that I have fought the switch I can get the meter to read "its idea" of a dead short, .5-.6 ohms. If this thing reads .7 ohms however, it means it! A Fluke will read .7! Below .7 it could be anything... I hate this meter. I need a job. My new ribbon cable should be coming today, I will attempt to get my soldering iron back from my friends house and try these mods. Unfortunately I have company on the way, I'll have to hide out and work on audio when I can for the next week...
This amp is now a plain old power amplifier, no more volume control, no more input selection. Nothing, nada. Sounding super clean and powerful and the channels are very well matched.
All signal grounds separate to star ground
Soldered those darned ribbon cables directly, forget the sockets
Soldered those darned ribbon cables directly, forget the sockets
Absolutely not going back to an integrated without a complete overhaul. Don't see that happening to this amp, I'll probably keep it forever as a backup. It has tremendous drive and really has big creamy bass, smooth and plentiful. I just feel that it lacks the midrange clarity and detail that my Sony 55ES has. Definitely a powerful sounding amp but not my cup of tea. Still a lovely piece of early digital gear for my little collection.
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