Hi,
I am recapping my Philips Ag9018. I am actually trying to solve a channel imbalance problem. I've replaced the pots and still have the channel imbalance problem. It is an integrated amp and the imbalance occurs on all sources. My research tells me to start with coupling caps. I do not know how to identify coupling caps. I need help identifying the coupling caps. Attached is the schematic.
Ryan
I am recapping my Philips Ag9018. I am actually trying to solve a channel imbalance problem. I've replaced the pots and still have the channel imbalance problem. It is an integrated amp and the imbalance occurs on all sources. My research tells me to start with coupling caps. I do not know how to identify coupling caps. I need help identifying the coupling caps. Attached is the schematic.
Ryan
Connect A1 to A2 with the mono switch. Test.
If all is well, the output and driver stage is OK. There is a fault in the pre stages, using an audio oscillator (or CD player with pink noise will do), trace the circuit until you have found the problem, comparing channel for channel.
Keep a logical head and don't change stuff for the sake of it, you may damage it completely!
If all is well, the output and driver stage is OK. There is a fault in the pre stages, using an audio oscillator (or CD player with pink noise will do), trace the circuit until you have found the problem, comparing channel for channel.
Keep a logical head and don't change stuff for the sake of it, you may damage it completely!
Thank you guys for your response.
Jon, all I have is a multi meter. The unit plays really good in mono. When I switch to stereo the volume drops dramatically. I will Be able to play pink noise but what do you mean by "trace the circuit until you have found the problem, comparing channel for channel." Do you mean I should change components one by one?
Ryan
No, it means find the fault and then fix it.
He means you should follow the signal through the circuit until you find the point where it becomes unbalanced. My guess is that you don't have the equipment or knowledge to do that.
Coupling caps are unlikely to cause a channel imbalance. Two reasons for this:
- a coupling cap would have to significantly reduce in value to affect gain, and well before you noticed the change in gain you would notice a big change in tone (bass would go first)
- coupling caps are usually very reliable
Channel imbalance (what you said in post 1) and 'volume drops in stereo' (what you said in post 4) are two quite different symptoms with possibly two quite different causes. Which is actually happening?
In any case, the first thing to do is check DC voltages (when working) and resistor values (when switched off). Be very careful when working on live equipment - keep yourself and the equipment safe!
He means you should follow the signal through the circuit until you find the point where it becomes unbalanced. My guess is that you don't have the equipment or knowledge to do that.
Coupling caps are unlikely to cause a channel imbalance. Two reasons for this:
- a coupling cap would have to significantly reduce in value to affect gain, and well before you noticed the change in gain you would notice a big change in tone (bass would go first)
- coupling caps are usually very reliable
Channel imbalance (what you said in post 1) and 'volume drops in stereo' (what you said in post 4) are two quite different symptoms with possibly two quite different causes. Which is actually happening?
In any case, the first thing to do is check DC voltages (when working) and resistor values (when switched off). Be very careful when working on live equipment - keep yourself and the equipment safe!
If your research was what other people did when faced with this complaint, that is not real research. The internet is full of fruitless part changing.
Start with coupling caps? For reasons DF96 explained well, it likely is not a cap, but in any case, the proper repair approach is not to start changing parts, it is to isolate the problem, THEN make whatever changes that requires.
When you say it is OK in mono, but in stereo a channel drops, that tells me that the power amp is likely OK in both channels, and the mono signal you are hearing is probably mostly the strong channel. SO in all likelihood, one of your preamp channels is weak. it does it on all sources, so it is after the input selector.
Please don't pull all the parts out to measure them. You can measure them in place, but compare the strong channel to the weak. If for example a 47k resistor measures only 18k, if it measures 18k in the good channel also, then we can usually assume that is an OK reading. Besides, it is EXTREMELY rare that a resistor would go down in reading. On the other hand it is extremely common for in-circuit resistors to have parallel resistive paths that lower the reading. You are looking for differences between good and bad channel, not hoping to find one wacko resistor.
As was suggested above, play a steady signal into it. Pink noise is great if you have it, but even just music will work. Set your meter to AC volts and probe along the signal path. It will pick up the music signal as it flows through the stages. Start at the input, comparing left to right channels. Once you find some spot in the circuit where all of a sudden one channel has a lower voltage signal than the other side, you have isolated the problem.
You know what I used to use for test signals sometimes? A cheap little Yamaha keyboard, the kind about the size of your computer keyboard. It has a line out jack on the rear. I used that thing all the time. I could play music on it, or I could trigger the demo tune and it played itself. Also, I could select a steady patch, like ORGAN and set something on the keys to keep them pressed down, et voila, a steady tone out of the thing. I do have a selection of signal generators, function generators, and music feeds (Like CD players), but I liked that old thing. I don't remember what happened to it.
Start with coupling caps? For reasons DF96 explained well, it likely is not a cap, but in any case, the proper repair approach is not to start changing parts, it is to isolate the problem, THEN make whatever changes that requires.
When you say it is OK in mono, but in stereo a channel drops, that tells me that the power amp is likely OK in both channels, and the mono signal you are hearing is probably mostly the strong channel. SO in all likelihood, one of your preamp channels is weak. it does it on all sources, so it is after the input selector.
Please don't pull all the parts out to measure them. You can measure them in place, but compare the strong channel to the weak. If for example a 47k resistor measures only 18k, if it measures 18k in the good channel also, then we can usually assume that is an OK reading. Besides, it is EXTREMELY rare that a resistor would go down in reading. On the other hand it is extremely common for in-circuit resistors to have parallel resistive paths that lower the reading. You are looking for differences between good and bad channel, not hoping to find one wacko resistor.
As was suggested above, play a steady signal into it. Pink noise is great if you have it, but even just music will work. Set your meter to AC volts and probe along the signal path. It will pick up the music signal as it flows through the stages. Start at the input, comparing left to right channels. Once you find some spot in the circuit where all of a sudden one channel has a lower voltage signal than the other side, you have isolated the problem.
You know what I used to use for test signals sometimes? A cheap little Yamaha keyboard, the kind about the size of your computer keyboard. It has a line out jack on the rear. I used that thing all the time. I could play music on it, or I could trigger the demo tune and it played itself. Also, I could select a steady patch, like ORGAN and set something on the keys to keep them pressed down, et voila, a steady tone out of the thing. I do have a selection of signal generators, function generators, and music feeds (Like CD players), but I liked that old thing. I don't remember what happened to it.
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