This is the right channel of the Accurain Receiver sold by Radio Shack.
If someone could please take a look and describe the circuit? The amp has
about 15dB of gain without the pre section. It looks like some sort of double LTP.
Thread located here
http://www.diyaudio.com/forums/showthread.php?s=&postid=1802165#post1802165
If someone could please take a look and describe the circuit? The amp has
about 15dB of gain without the pre section. It looks like some sort of double LTP.
Thread located here
http://www.diyaudio.com/forums/showthread.php?s=&postid=1802165#post1802165
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The schematic is drawn very oddly but don't let it confuse you... This looks like a very typical amplifier topology with dual differentials feeding a dual VAS. I think you have just drawn the drivers incorrectly and mixed the base and emitter connections. The VBE multiplier should feed the bases and the emitters should feed the resistors of the output transistors. Those capacitors in the drivers are likely also drawn into a wrong place. I suggest you recheck the circuit for drawing errors.
I expect you have, because if you swap them around you pretty much get the circuit that teemuk posted.gni said:
It's a Vbe multiplier, so it's on the heatsink to keep it the same temperature as the output devices, for thermal compensation.gni said:
Q212 is part of the current limiting circuitry. It measures the current through one of the output transistors via the voltage across its emitter resistor.gni said:
Yes... i think the same.... dead...they have just forgot to buried this one
Inspired into Marshall Leach amplifiers from 1970.
And worse..seems this one has the output stage operating in class B.... tragedy!
I love those old technologies...but not Marshal leach amplifiers..and i hate, in special, double differential.
regards,
Carlos
Inspired into Marshall Leach amplifiers from 1970.
And worse..seems this one has the output stage operating in class B.... tragedy!
I love those old technologies...but not Marshal leach amplifiers..and i hate, in special, double differential.
regards,
Carlos
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Class B!
Is that why the amp is cold during idle and sounds harsh?
Remember -- this amp is the Accurain Receiver from RS.
But really the ST&S Corp Rx iSonic 84
"the receiver/amplifier receives the AC Line Audio Transmitter’s signal (4.3MHz to 20.9MHz) through AC power line and converts back to audio signal. The built-in 50-watt audio amplifier enhances sound quality"
http://www.stt.com.tw/product/rx84.html
Do you think it is possible to re-bias the amp to Class AB via the Vbe (Q211)?
Is that why the amp is cold during idle and sounds harsh?
Remember -- this amp is the Accurain Receiver from RS.
But really the ST&S Corp Rx iSonic 84
"the receiver/amplifier receives the AC Line Audio Transmitter’s signal (4.3MHz to 20.9MHz) through AC power line and converts back to audio signal. The built-in 50-watt audio amplifier enhances sound quality"
http://www.stt.com.tw/product/rx84.html
Do you think it is possible to re-bias the amp to Class AB via the Vbe (Q211)?
Milivolts readed into the power transistors emitter leads
means the ouput is conducting... this show the amplifier is operating in class AB...
No voltage (milivolts DC) measured over the emitter resistances seems the ouput is cutted...this will produce some distortions into low volume levels.... when cutted is operating class B.
One milivolt or less into the emitter resistances is enougth to avoid switching noises...will be less good if you do not find some milivolts there.
Previous stages, for sure..all them... are conducting, and this is made this way to avoid switching noises when amplifier goes from cutted to conduction as the effect of audio entering and producing the conduction.... you know...audio turns the transistor on.
Cutted output transistors can be used into Radio Frequency...because carrier will force them to conduct....but even into radio frequencies they use Class A...well..needs some constant signal above 500 milivolts to force transistor to conduct... audio can do that..but sometimes, into low volume moments, the audio is not enougth to force transistor to be "on"..so..it will be switching between on and off when level is near the threshold of conduction and cut.
Carlos
means the ouput is conducting... this show the amplifier is operating in class AB...
No voltage (milivolts DC) measured over the emitter resistances seems the ouput is cutted...this will produce some distortions into low volume levels.... when cutted is operating class B.
One milivolt or less into the emitter resistances is enougth to avoid switching noises...will be less good if you do not find some milivolts there.
Previous stages, for sure..all them... are conducting, and this is made this way to avoid switching noises when amplifier goes from cutted to conduction as the effect of audio entering and producing the conduction.... you know...audio turns the transistor on.
Cutted output transistors can be used into Radio Frequency...because carrier will force them to conduct....but even into radio frequencies they use Class A...well..needs some constant signal above 500 milivolts to force transistor to conduct... audio can do that..but sometimes, into low volume moments, the audio is not enougth to force transistor to be "on"..so..it will be switching between on and off when level is near the threshold of conduction and cut.
Carlos
And here are the measurements:
Andrew -- My meter will measure 0.1mV resolution. RS $70 unit. . . always bben good.
Destroyer X is correct -- the unit is class B . . . there just isn't so much as
a 0.1mV across those emitter resistors. Looks like the rest are 'on' and open
to conducting.
Andrew -- My meter will measure 0.1mV resolution. RS $70 unit. . . always bben good.
Destroyer X is correct -- the unit is class B . . . there just isn't so much as
a 0.1mV across those emitter resistors. Looks like the rest are 'on' and open
to conducting.
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