Sounds like its doing what it should.
This is a critical adjustment and its safer to have it on the low side and to also recheck it when the amp is warm.
The manual says 40 millivolts (0.04 volts) across the two resistors. Set it no higher than that.
Then can you measure the DC voltage across the speaker output again.
This is a critical adjustment and its safer to have it on the low side and to also recheck it when the amp is warm.
The manual says 40 millivolts (0.04 volts) across the two resistors. Set it no higher than that.
Then can you measure the DC voltage across the speaker output again.
well, it's that time again. SWMBO has arisen, all the stars and planets have lined up, and her....errr, i mean my, bathroom reno beckons.
i think some progress has been made here today. good thing too. i'm off to toronto thursday morning, hopefully to deliver my son his amp.
i'm shutting down the variac, and doing a bit of a reassemble, and resisting the urge to "crank her up", until that is, i get your go-ahead. if you're available, i will be on here early tomorrow morning, say around 7:00 your time. in the meantime, have a wonderful day mooly and sakis, and thank you both so much for the walkthrough of the repair of this amp. a repair which was due to my own darn fault. oh well, if it works i will have gained a wealth of experience, and if it doesn't work i'll be gaing an even larger wealth of knowledge.
ok, have a great day guys.
aidan
i think some progress has been made here today. good thing too. i'm off to toronto thursday morning, hopefully to deliver my son his amp.
i'm shutting down the variac, and doing a bit of a reassemble, and resisting the urge to "crank her up", until that is, i get your go-ahead. if you're available, i will be on here early tomorrow morning, say around 7:00 your time. in the meantime, have a wonderful day mooly and sakis, and thank you both so much for the walkthrough of the repair of this amp. a repair which was due to my own darn fault. oh well, if it works i will have gained a wealth of experience, and if it doesn't work i'll be gaing an even larger wealth of knowledge.
ok, have a great day guys.
aidan
OK 
All being well I should be around then.
Important check points are that the DC offset (voltage across the speaker) is low. 0.2 volts was a bit on the high side but we can re-check and look at that later. And the bias should be 40 millivolts or a bit below.
Final check of the bias to be done on full mains voltage and when the amp has warmed a little because it will wander and change... that's normal.
Feeding time here
All being well I should be around then.Important check points are that the DC offset (voltage across the speaker) is low. 0.2 volts was a bit on the high side but we can re-check and look at that later. And the bias should be 40 millivolts or a bit below.
Final check of the bias to be done on full mains voltage and when the amp has warmed a little because it will wander and change... that's normal.
Feeding time here
Something different.
Don't feel obliged you have to try have this, its just here if you want to.
Here is the simulation file for the amp. The zipped folder has two files that need to be kept together for it to run. One is the simulation file and the other the models for some of the transistors. So just extract the contents and keep them in the same folder.
If you do install LTSpice then I recommend you set these options which will delete temporary simulation files automatically every time you close the program.
To run the Kenwood file you can either browse for it (click file and then open at top left) or just click the .asc file which will open LTSpice with that file.
Fifth symbol in from the left on LTSpice is a little running man. Click that and the program will run. You'll hopefully get a small window open with lots of voltages and info... close that and then just move your cursor over component leads, resistors, transistor leads etc and you'll get instant voltage and current readings together with power dissipation in all the parts. The info appears at the bottom of the screen and changes with your cursor position.
Get that far and your doing well
Don't feel obliged you have to try have this, its just here if you want to.
Here is the simulation file for the amp. The zipped folder has two files that need to be kept together for it to run. One is the simulation file and the other the models for some of the transistors. So just extract the contents and keep them in the same folder.
If you do install LTSpice then I recommend you set these options which will delete temporary simulation files automatically every time you close the program.
To run the Kenwood file you can either browse for it (click file and then open at top left) or just click the .asc file which will open LTSpice with that file.
Fifth symbol in from the left on LTSpice is a little running man. Click that and the program will run. You'll hopefully get a small window open with lots of voltages and info... close that
and then just move your cursor over component leads, resistors, transistor leads etc and you'll get instant voltage and current readings together with power dissipation in all the parts. The info appears at the bottom of the screen and changes with your cursor position.Get that far and your doing well
Attachments
good morning all! well, progress, i think, has been made. bias on both sides (L and R) is now set at .040 volts. however, DC offset is .008 on R, and a whopping .232 on L (GAK!). will placing a cap across Qe7 (from E to C i believe) block some of this DC voltage from reaching the speakers? what value should the cap be? also, would a cap in series with the speaker lead, lower the DC offset voltage reading?
aidan (el noobo supremo)
aidan (el noobo supremo)
Morning
Whether the cap across Qe 7 affects the offset is what I want to see.
When you have fitted the cap bring the voltage up slowly again monitoring the bias.
Caps in series with the speaker would kill any DC but you would need a non polarised one and its not the answer to the problem anyway.
Whether the cap across Qe 7 affects the offset is what I want to see.
When you have fitted the cap bring the voltage up slowly again monitoring the bias.
Caps in series with the speaker would kill any DC but you would need a non polarised one and its not the answer to the problem anyway.
That's not bad at all... I wondered if there was any instability and if so then the offset would have altered.
OK, let me have a think. Must admit I'm slightly puzzled as to why that is so.
In the meantime have you tried this AT LOW VOLUME) with speakers ? If you do then connect the speakers after powering the amp up. Just see if you have clean undistorted audio.
OK, let me have a think. Must admit I'm slightly puzzled as to why that is so.
In the meantime have you tried this AT LOW VOLUME) with speakers ? If you do then connect the speakers after powering the amp up. Just see if you have clean undistorted audio.
well offset might mean a small leak in some of the semis that cannot be traceable with a DVM
Often you have semis that measure properly outside the circuit but behave wrong while under voltage ...
The best way to see what is wrong is to carefully measure voltage drop across resistors and somewhere you will find difference next to the ""working"" ch. that will point out to you that there something wrong in the specific area .
I wonder now if there is any way to trace oscillation if any without a scope .....
I will have to presume that you don't have one ....
Here is a funny one
Oldtimers in the 70's when they had to check an amplifier for oscillation without instruments used a small battery AM transistor hoover it over the amplifier actually trying to "listen " the oscillation
( Requires fluorescent lights f your bench or other noisy equipment on your bench to be turned off )
Kind regards
Sakis
Often you have semis that measure properly outside the circuit but behave wrong while under voltage ...
The best way to see what is wrong is to carefully measure voltage drop across resistors and somewhere you will find difference next to the ""working"" ch. that will point out to you that there something wrong in the specific area .
I wonder now if there is any way to trace oscillation if any without a scope .....
I will have to presume that you don't have one ....
Here is a funny one
Oldtimers in the 70's when they had to check an amplifier for oscillation without instruments used a small battery AM transistor hoover it over the amplifier actually trying to "listen " the oscillation
( Requires fluorescent lights f your bench or other noisy equipment on your bench to be turned off )
Kind regards
Sakis
Morning Sakis. I'm wondering if one of the limiters is leaky and the amp is "fighting" that. Qe9 and 11 have a direct low impedance path to the rails when those original drivers failed.
Yes, its difficult without a scope to see low level instability. 200mv offset is high in real terms but low if it is a "hard" component failure.
No problem. I might disappear for a little while too.
Just remember to always bring the voltage up slowly to begin with after any work on the amp.
Did you solder or alter any parts around Ce7, a small electrolytic. No solder blob or short across the cap. Same for Ce1. It would be a chance in a million but worth mentioning.
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