Are they connected as they should be?
Where one pair?
Or across B speaker terminals the resistors as they are on the picture and A speakers outputs without any resistor in the path?
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Just for better understanding ..
The last test was done with those 8Ohm resistors across the B speakers terminals, B speakers engaged.
The A speakers output remained unchanged, those 8Ohms resistors overthere were there just for reducing the output level signal, which I would need to do anyway using the pot..
To me it seems that first measurement I did was actually without simulated speakers load through A terminals and second measurement with simulated load on B speakers terminals using both A+B speakers output.
Is that correct understanding?
Perhaps first measurement should be done also with additional resistors across A speakers terminals?
You are complicating things 😉
Just remove the first pair of resistors (on A-termnals), connect the soundcard to A-terminals, connect the 8R resistors to B-terminals and perform two measurements - one with B-speakers inactive (off) and the other one with B-speakers active (on).
Then we have a clean starting point.
Just remove the first pair of resistors (on A-termnals), connect the soundcard to A-terminals, connect the 8R resistors to B-terminals and perform two measurements - one with B-speakers inactive (off) and the other one with B-speakers active (on).
Then we have a clean starting point.
Ok, the first conclusion seems to be that both channels behave pretty much the same i.e. they are not "broken".
Change in crosstalk when connecting a load indicates internal wiring or grounding problems.
Also power supply noise is visible.
Next question is - what do you want to do with this amplifier?
Change in crosstalk when connecting a load indicates internal wiring or grounding problems.
Also power supply noise is visible.
Next question is - what do you want to do with this amplifier?
Thank you, seems good so far 👍
I am not in rush, but why not to do something, right?
1- I am curious how to sort out the imbalance of the channels.
2- That crosstalk, if there is some grounding problem, how can I find it?
3- How can I find the cold joints if there are some? (Maybe they contribute to noise etc)
4- If power supply shows noise, is there way to improve it?
Thank you
I am not in rush, but why not to do something, right?
1- I am curious how to sort out the imbalance of the channels.
2- That crosstalk, if there is some grounding problem, how can I find it?
3- How can I find the cold joints if there are some? (Maybe they contribute to noise etc)
4- If power supply shows noise, is there way to improve it?
Thank you
"right" - beauty lies in the eye of beholder 😉
In other words there is surely more than one way to proceed - perhaps some other forum members will also chime in...
1. "sort out imbalance" - easy way is to turn the balance knob, correct way would be to start feeding sine signal (e.g. 400 Hz or 1 kHz) and start measuring AC in both channels along the signal path according to the schematics on service manual. How good are your skills in reading such schematics?
2. Crosstalk - grounding problems do not jump to your eye, you have to be prepared to cut traces and wires and add alternative wires to different grounding points. May involve a lot of trial and error attempts.
3. Cold joints - take a good loupe or magnifying glass/headset and start looking under the print board for anything that looks like a crack in solder.
Some people resolder whole boards before attempting to improve anything else - takes an hour or two but sets your mind at ease.
4. Power supply noise is probably (hopefully) not caused by the main (large) capacitors but the small ones. Although it seems to be 50 Hz and also tricky to trace and fix. So you may face the replacement of lytics. Good news is that the small ones are pretty cheap so your time invested will be the biggest effort.
Anyhow, if you want to continue renovation of this amplifier then one of the first things to do would is to replace capacitors in signal path. Just like surgeons wash their hands before surgery.
Whatever you do - if you want the forum members to follow your activities then take one step at a time...
In other words there is surely more than one way to proceed - perhaps some other forum members will also chime in...
1. "sort out imbalance" - easy way is to turn the balance knob, correct way would be to start feeding sine signal (e.g. 400 Hz or 1 kHz) and start measuring AC in both channels along the signal path according to the schematics on service manual. How good are your skills in reading such schematics?
2. Crosstalk - grounding problems do not jump to your eye, you have to be prepared to cut traces and wires and add alternative wires to different grounding points. May involve a lot of trial and error attempts.
3. Cold joints - take a good loupe or magnifying glass/headset and start looking under the print board for anything that looks like a crack in solder.
Some people resolder whole boards before attempting to improve anything else - takes an hour or two but sets your mind at ease.
4. Power supply noise is probably (hopefully) not caused by the main (large) capacitors but the small ones. Although it seems to be 50 Hz and also tricky to trace and fix. So you may face the replacement of lytics. Good news is that the small ones are pretty cheap so your time invested will be the biggest effort.
Anyhow, if you want to continue renovation of this amplifier then one of the first things to do would is to replace capacitors in signal path. Just like surgeons wash their hands before surgery.
Whatever you do - if you want the forum members to follow your activities then take one step at a time...
Thank you! 👍 Yes, I was thinking longer what next, and it seems good idea to start with schematics, as I am beginner touching that.. then to replace the electrolytics first. I am trying to understand what is the actual signal path now..
This is pretty confusing part - to find what capacitors or perhaps even transistors to update in signal path. I guess the resistors are not as critical.
I may ask plenty of basic questions, like:
Up to what extend do I need to understand flow of signal through various semiconductors?
In general, there is an input signal and there is power supply to amplify and to correct the signal to keep its characteristics. That I can assume.
Seeing some youtube videos about how transistor works is helping a little, not much though.
Capacitors polarities in circuit are also not very clear to me..
It is just not straightforward, but complexity of flow. Despite of that, I have tried to figure out a bit within preamp section..
Here is the first identification attempt of simplified signal path marked by green line..
In this start above, I assume pin 2 to be input and pin 6 signal output.
Here is first question:
Why + polarity of C403 is on its output side and then + polarity of C417 on its input side?
And basic one, I assume
25V4.7 means 4.7uF rated up to 25V electrolytic capacitor, correct?
Here the signals passes through various selectors somehow 🙈🙂 but output should be through R503. By the way I did just left channel ..
Here it goes through loudness (don’t know how exactly if applied) and muting (that’s quite clear).
Then balance (I considered it off, if on, there are just small values mylar capacitors)
Then cascaded transistors Q501 and Q503.
Here I have question, whether C515 coming from Q501 emitter should be also part of the signal path?
Then Low and High filters with some strange high resistance (R535 33k?)..
And after Q505 there is strange joined output from both collectors of Q505 (left channel) and Q506 (right channel), which suggests that some part of the signal should go also through their emitters through C529 (C530). That is confusing too, is that normal?
It shows that C529 should be in the signal path as there are 2 low noise caps C707 and C711, I hope that’s correct..
Then we finally get pre out through C715..
Thank you for all suggestions whether I got it right up to some extend 🙂, then power amp..
I may ask plenty of basic questions, like:
Up to what extend do I need to understand flow of signal through various semiconductors?
In general, there is an input signal and there is power supply to amplify and to correct the signal to keep its characteristics. That I can assume.
Seeing some youtube videos about how transistor works is helping a little, not much though.
Capacitors polarities in circuit are also not very clear to me..
It is just not straightforward, but complexity of flow. Despite of that, I have tried to figure out a bit within preamp section..
Here is the first identification attempt of simplified signal path marked by green line..
In this start above, I assume pin 2 to be input and pin 6 signal output.
Here is first question:
Why + polarity of C403 is on its output side and then + polarity of C417 on its input side?
And basic one, I assume
25V4.7 means 4.7uF rated up to 25V electrolytic capacitor, correct?
Here the signals passes through various selectors somehow 🙈🙂 but output should be through R503. By the way I did just left channel ..
Here it goes through loudness (don’t know how exactly if applied) and muting (that’s quite clear).
Then balance (I considered it off, if on, there are just small values mylar capacitors)
Then cascaded transistors Q501 and Q503.
Here I have question, whether C515 coming from Q501 emitter should be also part of the signal path?
Then Low and High filters with some strange high resistance (R535 33k?)..
And after Q505 there is strange joined output from both collectors of Q505 (left channel) and Q506 (right channel), which suggests that some part of the signal should go also through their emitters through C529 (C530). That is confusing too, is that normal?
It shows that C529 should be in the signal path as there are 2 low noise caps C707 and C711, I hope that’s correct..
Then we finally get pre out through C715..
Thank you for all suggestions whether I got it right up to some extend 🙂, then power amp..
Nice to see your progress ;-)
I do not have too much time today, perhaps a longer reply (if no-one else chimes in) in the evening.
Two quick coments:
I do not have too much time today, perhaps a longer reply (if no-one else chimes in) in the evening.
Two quick coments:
- probably you do not need to replace any semiconductors - if any of these would be malfunctioning then your channel output measurements would differ from each other substantially.
- at Q505 output you make a mistake - B1 power line, signal proceeds via C529.
Thank you!
Yes, I am confused with Q505 transistor orientation/ flow through.. means the signal goes through emitter? I expected it to go through collector as it is the same type of transistor - 2SC1327 like previous Q501 and Q503..
The current (creating/forming the output signal) flows through emitter to collector.
The output signal can be taken from both of these pins - current is converted to voltage by the load resistor in that path - R547 here, U = I*R.
When signal is taken from emitter then this kind of circuit is called emitter follower - it does not amplify the signal voltage but provides "more powerful" output to steer the following stage.
The output signal can be taken from both of these pins - current is converted to voltage by the load resistor in that path - R547 here, U = I*R.
When signal is taken from emitter then this kind of circuit is called emitter follower - it does not amplify the signal voltage but provides "more powerful" output to steer the following stage.
You are correct about the pins.
About polarity - electrolytic capacitors need the DC voltage to be applied to its leads in the correct way to build and maintain the internal isolation layer (electrochemical process). If you apply it vice versa then the insulation layer will break (or not build) and the capacitor will blow.
The + sides of C403 and 417 are connected to the IC chip and you can read the positive DC voltages there from the schematics. The other leads of those capacitors are grounded via resistors i.e. their DC is 0V. So the + terminals of the capacitors are connected to the schematics part with higher DC voltage (correctly).
Yes, 25V4.7 means what you write.
This depends on how orthodox you are about schematic grammar 😉
It is not in direct signal path but it does affect the signal - it is in the feedback path so you do not want a capacitor in bad condition there.