Hi.
This amp got a lower left channel or somewhat a bit "muffled" in the top region. Tried cleaning the volumepot, a 4 pin type with center tap. I took the pot apart and had a look at it, no obvious tracks or other fault. Adjusted the bias to specified 24mV on both channels, no change. Sanded the output relays, same result. Could it be a dry cap or something in the center tap circuit messing up? It´s a nice amplifier, mosfet driver and output stage. I would really like to get it sorted so I can use it for preamp paired with a couple of TA-N55ES. I have the servicemanual if anybody care to take a look at it. It´s not easy to find a new pot either since it´s a 120k type and have the center tap.. 🙁
This amp got a lower left channel or somewhat a bit "muffled" in the top region. Tried cleaning the volumepot, a 4 pin type with center tap. I took the pot apart and had a look at it, no obvious tracks or other fault. Adjusted the bias to specified 24mV on both channels, no change. Sanded the output relays, same result. Could it be a dry cap or something in the center tap circuit messing up? It´s a nice amplifier, mosfet driver and output stage. I would really like to get it sorted so I can use it for preamp paired with a couple of TA-N55ES. I have the servicemanual if anybody care to take a look at it. It´s not easy to find a new pot either since it´s a 120k type and have the center tap.. 🙁
A four pin type pot is used when in the preamp is loudness switch. It doesnt have to be a big problem to buy it. Try to take a look at circuit board from the bottom side, look carefully if all solder point are good soldered. Replace the input capacitors with same value ones, voltage and capacitance. I would change all capacitors. I dont know if you have the same problem on all inputs. Maybe some there are capacitors and resistors, check the soldering points.
if your Sony have separated preamp board try to connect the outputs to another amplifier or to headphones. If all is fine, then you have a problem with power amp. If oposite, your preamp is the reason of the bad sound. Also you can skip the vol. pot. buy adding a 2 ressistors one in serie with inut signal and the second one to the ground. To ground try 47K and you can use 470k for input in series.
The amp does not have a loudness button. I have a regular alps 100k 3 pin type, what happens to the circuit if I put it in for a test?
Maybe your speakers are damaged, change the left speaker to right chanell and listen if you still have the problem.
Its hard to say without service manual what will happen if you put the 3 pin pot. As i said, try to locate the point when preamp and power amp are connected. take inputs from pream and use headphones.
Have tried several pairs of speakers, sources etc. Tried headphones just now, same imbalance and does not change pressing the mono switch or source direct. I´ll happily send you the manual, just need your email adress.
Page 11, remove the original 4 pin pot. the first pin of your 100K alps to ground and to body of pot., the second pin to R351, on third pin you can solder the input signal from Cd or some other source, or to solder it to cd direct switch, in this way you will skip some filters, like subsonic and tone controls.
Havent proceeded with the test you advice, yet. I´m missing some suitable wire and test speakers. I´m looking at page 7 and the source direct switch, when it´s activated/on, does it cancel the loudness function from pin 4?
Yes, when source direct is at ON position it canceling all filters. In Your case i think that fourth pin is for subsonic filter. You can even try to solder the ALPS directly to resistors i mentioned above (pin 2), pin 1 to the ground, and solder the wires and female chinches for input signal on pin 3 of ALPS. For testing it will be the best if you tuch with fingers the wire soldered on pin 3 (input) in case the ALPS is in position to proceed to loud signal. Correct it, and connect the external source (CD player)
By the way using test speakers is good idea. If my suggestion doesnt help, we will go forward and look for problem in the circuit.
I dont know the level of your skills in electronic and soldering. But, yes You can use the variable output CD player, in that case unsolder the pin of your 120K potentiometer which is connected to R301 (for the other chanell to R351) and in that point solder the hot wires of coaxial audio cables (any type, the cheapest) with female chinches on the other end. (Dont forget to solder ground wires of coaxial cables to the ground point of circuit board and to ground points of chinches). Then you can use your variable output of your CD player. You can use the headphones to check the sound.
Also in the schematic I can see that you have a pre-out, if there is a main-in on the back of your Sony You can connect the variable output CD player directly to main-in inputs. (Pre-out and main-in should be connected between by peaces of short wire on the back of Your Sony). If that is the case disconnect them. And connect the variable output CD player to main-in. This will help to check if all is fine with your power amplifier.
(I would suggest this option to try before You start with soldering)
You can check the pre-out by connecting another amplifier or even a headphones. This will helps to check if all is fine with preamplifier and your 120K 4-pole potentiometer.
(I would suggest this option to try before You start with soldering)
I really hope that My bad english doesnt confusing You. If something is unclear for You in my suggestions, feel free to ask about before You start to do anything.
Tested the preout but it´s the cheap type, resistors on the speaker output terminal so it had same difference. On older Sony´s there are a out/input called adaptor and when I took the signal from the output to a JA20ES minidisc deck the channels were equal and sounded good..So I guess the EQ/INPUT board is ok. At least the section shown at page 6 top left corner.
Will try what you have suggested, just waiting for wires and testspeakers. Thanks for all help so far 🙂
Will try what you have suggested, just waiting for wires and testspeakers. Thanks for all help so far 🙂