yeah , "ZM's criteria " .........
Stop being humble about this.
You taught him everything he knows. 😀
recently found Pa's reply to my very first e-mail to him :
as you can see , I started teaching him approx. 14 years ago .......
as you can see , I started teaching him approx. 14 years ago .......
Mr. Pass
Does it means that "power amp" part at INT-30 is different than in XA.30.5??
Hello, my XA30.5 (second hand from 2010) needle started to move a bit to early for my liking. I hooked up my oscilloscope at the output and with music playing at about 4V to 5V max peak-to-peak the needle starts to move for about 1mm to 3mm. The heat sinks are about 48C to 49C at room temperature (21C).
I opened up the amplifier and measured the bias-A and bias-B point and when fully warmed with lit on top they are about 122mV left and 127mV right. It looks low about the amount of a X100.5 instead of a XA30.5. How can this have happened or am I wrong? The pots are about in the same positions as pictures I have found on the internet. The meter needle is around 12 o'clock.
Does any one have a thought about this?
I opened up the amplifier and measured the bias-A and bias-B point and when fully warmed with lit on top they are about 122mV left and 127mV right. It looks low about the amount of a X100.5 instead of a XA30.5. How can this have happened or am I wrong? The pots are about in the same positions as pictures I have found on the internet. The meter needle is around 12 o'clock.
Does any one have a thought about this?
pot's position is hardly any reference
set reference voltages (for Iq) to preferred for XA30.5 , taking care primarily of said 30C difference between ambient and heatsinks
after that , set needle position in 12'o'clock , just for convenience (that's sole pot near central ribbon cable on motherboard)
set reference voltages (for Iq) to preferred for XA30.5 , taking care primarily of said 30C difference between ambient and heatsinks
after that , set needle position in 12'o'clock , just for convenience (that's sole pot near central ribbon cable on motherboard)
Thank you very much for your reaction, I am bit apprehensive, because my heatsinks (measured with infrared gun) are almost 30C above ambient (49 - 21 = 28). Still my ref voltages are around 123mV instead around 190-200mV....
I have no clue of how to calculate the maximum output power W in class A from this reference value..
Any ideas are welcome!
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Given that the temperature is good, you are probably measuring the bias
sensed across only one Source resistor to output instead of the usual two
Source to Source in series, so it would read 1/2 the sense voltage.
I checked, and an early version of the board was set up that way.
That being the case, you would be seeing Class A into 8 ohms to about 60W peak.
😎
Thanks you all... however one thing is still nagging me, why does the needle move with only about 4V to 5V peak-to-peak output on my oscilloscope?
Hope this can help somebody in the future,
I did some background research and re-measured the output of the amp. With two probes, one in inverse, grounds of probes to signal ground and scope on 'add' I measured indeed a lot more! With music it is a bit hard to see but at 24V peak to peak I definitively saw a little movement. Calculation; 24 / 8 ohm = 3A * (24V / 2) = 36W. So everything seems fine!
I measured about 123mV at my reference bias points, Nelson and Kent contacted me by email and confirmed there are some versions of the board which only sense one of the bias resistors. My XA30.5 had a factory reference of 125mV when it left the factory.
@Nelson / Kent; thanks a lot for the great after sales even for a secondhand amplifier. Much appreciated! This is not something you experience very often.
I love my XA30.5, great sound, much more detail and involvement in comparison with my previous Bryston 4BSST.
I did some background research and re-measured the output of the amp. With two probes, one in inverse, grounds of probes to signal ground and scope on 'add' I measured indeed a lot more! With music it is a bit hard to see but at 24V peak to peak I definitively saw a little movement. Calculation; 24 / 8 ohm = 3A * (24V / 2) = 36W. So everything seems fine!
I measured about 123mV at my reference bias points, Nelson and Kent contacted me by email and confirmed there are some versions of the board which only sense one of the bias resistors. My XA30.5 had a factory reference of 125mV when it left the factory.
@Nelson / Kent; thanks a lot for the great after sales even for a secondhand amplifier. Much appreciated! This is not something you experience very often.
I love my XA30.5, great sound, much more detail and involvement in comparison with my previous Bryston 4BSST.
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