I've just looked at the circuit and I can see how it works.
It passes a small DC current through the speaker when the speaker switch is OFF, and a comparator is used to detect whether the impedance is high or low.
That result then sets the rail voltage which is another unique feature and done by using a thyristor controlled bridge rectifier.
So up to you... if you are curious then by all means check, however unless there was a major pre existing fault (such as the rails being very low) then the impedance adjustment will have no effect on your perceived sound quality in normal use.
An incorrect bias setting (to low) can give higher distortion (more easily heard at very low levels), and if to high then the amp will run hotter than it should.
It passes a small DC current through the speaker when the speaker switch is OFF, and a comparator is used to detect whether the impedance is high or low.
That result then sets the rail voltage which is another unique feature and done by using a thyristor controlled bridge rectifier.
So up to you... if you are curious then by all means check, however unless there was a major pre existing fault (such as the rails being very low) then the impedance adjustment will have no effect on your perceived sound quality in normal use.
An incorrect bias setting (to low) can give higher distortion (more easily heard at very low levels), and if to high then the amp will run hotter than it should.
If you look at the transformer on the block diagram it also appears to use switched secondary voltages. Its an interesting design for sure.
Possible issues could be presets that haven't been turned since manufacture and its impossible to second guess whether they are OK or not. They might be fine and operate smoothly or they might be flaky and jumpy, possibly with the connections (rivets) to the carbon track becoming slack with time. Just something to be aware of.
If you replace the presets then its vitally important that the bias setting ones are turned initially to the position that gives minimum bias before you power on. Maximum bias could be destructive.
Have to leave it for now...... but its up to you whether you want to check it out
Possible issues could be presets that haven't been turned since manufacture and its impossible to second guess whether they are OK or not. They might be fine and operate smoothly or they might be flaky and jumpy, possibly with the connections (rivets) to the carbon track becoming slack with time. Just something to be aware of.
If you replace the presets then its vitally important that the bias setting ones are turned initially to the position that gives minimum bias before you power on. Maximum bias could be destructive.
Have to leave it for now...... but its up to you whether you want to check it out
I have found part of the problem I had the mid out of phase it is supposed to be in phase with the tweeter
If you look better, the midrange has the cables inverted; blue (+) goes to ground and white ( minus...err, standard phase ) goes to the amplifier +++/crossover +++.
So replace the original polarity as usually it's the norm to mount the mid reverse-phased with 2nd order crossover
Yes, replace it with original ( reversed ) polarity.Hi pici, I get confused easily
But...Are you making all this adjustements by screwing and unscrewing the drivers every time ? Because of the hidden crossover...that's why I suggested
to move it outside of the box- also because the box should ( well, that is primary ! ) work for mechanics only and not let electronics mix with it.
Also the L-pads...the lights are also a surplus ( I read that you already encountered some problems...) .
So, check if the driver's chassis ( rim ) is still attaching firmly to the baffle
Hi pico,
I have the polarity on the midrange and tweeter the same now, opposite to the bass.
The lights have me confused the most, they never ever flashed on my original speakers, the amp was the same model as well, only differences is about 38 years and now using PC as a source through a DAC, where before I had a nice SL-10 turntable with the moving coil pickup, ( much better sound ) so can not rule out the source signal perhaps not being as "pure" I guess.?
I agree the crossover should be outside might still do that. I have already bypassed the L pads, might bypass the overloads and lights latter if I can be sure there is nothing wrong. Don`t wont to burn out a speaker.
Thank You
I have the polarity on the midrange and tweeter the same now, opposite to the bass.
The lights have me confused the most, they never ever flashed on my original speakers, the amp was the same model as well, only differences is about 38 years and now using PC as a source through a DAC, where before I had a nice SL-10 turntable with the moving coil pickup, ( much better sound ) so can not rule out the source signal perhaps not being as "pure" I guess.?
I agree the crossover should be outside might still do that. I have already bypassed the L pads, might bypass the overloads and lights latter if I can be sure there is nothing wrong. Don`t wont to burn out a speaker.
Thank You
They are confusing me as well
You are referring to the LED on the speaker ?
When you say 'original speakers' do you mean another different pair you used to have years ago ?
If so, then as we have said before, the LED is purely a voltage indicator. The LED doesn't know whether the amp has a problem or is being overload or driven to hard.
The LED illuminates when sufficient voltage is present to overcome the zener diode voltage. That is all the LED does.
To test the amp involves you having a dummy resistive load. The speaker isn't really suitable because it would be far far to loud and also it could be damaged with prolonged testing.
Resistors are readily available in low values/high power ratings as here (quick example). Dangled in a bucket of cold water and they would allow decent power testing.
http://cpc.farnell.com/welwyn/wh50-4r7-ji/resistor-ww-50w-5-4r7/dp/RE03489?st=resistor
Memory of how things used to sound is notoriously unreliable and so I wouldn't like to say regarding the older speakers. Your perceptions could have changed over the years as well.
Resistors are readily available in low values/high power ratings as here (quick example). Dangled in a bucket of cold water and they would allow decent power testing.
http://cpc.farnell.com/welwyn/wh50-4r7-ji/resistor-ww-50w-5-4r7/dp/RE03489?st=resistor
Memory of how things used to sound is notoriously unreliable and so I wouldn't like to say regarding the older speakers. Your perceptions could have changed over the years as well.