Balanced Audio inputs for HB
I am considering building a HT Badger, but the pre-amp I'm considering using has balanced XLR line outputs (Marantz AV8802).
Would the input stage as currently designed work with balanced audio input if pin 1 of the XLR input is grounded to the chassis star ground, with XLR 2 and XLR 3 pins applied across R1?
One note about Ostripper's schematic - it looks like R1 is shorted out of the circuit. There is no clear Input+ / Input- on the schematic, only an implied one across R1. I would consider the 'input' on the wire only as a net name.
I am considering building a HT Badger, but the pre-amp I'm considering using has balanced XLR line outputs (Marantz AV8802).
Would the input stage as currently designed work with balanced audio input if pin 1 of the XLR input is grounded to the chassis star ground, with XLR 2 and XLR 3 pins applied across R1?
One note about Ostripper's schematic - it looks like R1 is shorted out of the circuit. There is no clear Input+ / Input- on the schematic, only an implied one across R1. I would consider the 'input' on the wire only as a net name.
Pin 1 of the XLR goes to Chassis.
Pin 2 of the XLR goes to +IN of the amp.
Pin 3 of the XLR cannot go to Signal Ground of the amp.
Check how your balanced Source works.
Some will automatically change the Source to suit the loading conditions.
Others will require you to change. You may have to load Pin3 with a resistor to signal ground, or you may be allowed to simply ground Pin3.
Pin 2 of the XLR goes to +IN of the amp.
Pin 3 of the XLR cannot go to Signal Ground of the amp.
Check how your balanced Source works.
Some will automatically change the Source to suit the loading conditions.
Others will require you to change. You may have to load Pin3 with a resistor to signal ground, or you may be allowed to simply ground Pin3.
That could just be an emitter resistor that is out of tolerance. If it bothers you, you could try replacing that resistor.
I'm interested in knowing how hot some of you have been biasing the outputs. I mistakenly biased mine mjl21193/4 at 180-200 ma each (82mv TP1-TP2). It ran stable for hours that way in a 90 deg shop. I was playing music through it to a EPOS esl 3 and it was sounding very good. I put the other board/channel in and had it biased to 40mv(TP1-2) it was not as sweet sounding and noticebly different. Can those outputs handle that kind of bias as long as the heatsink is adaquate?
))
bjt's biased hard are known to have lower distortions, but then their life is also short, perhaps forced air cooling or water cooling can help keep things cool can help...try biasing them at 125mA and see how it sounds...
ClassAB has an "optimum bias" current.
The output when lower than twice the "optimum bias" current is always in ClassA. It is very clean because there is NO crossover distortion.
The output when higher than twice "optimum bias" current has the least crossover distortion for that ClassAB amplifier.
If the output stage is biased to less than optimum then the output at all levels has more crossover distortion. At typical domestic listening levels the crossover distortion will be gross, because at ½W to 2W the % crossover distortion content is VERY HIGH !
If the output stage is biased to more than optimum, then the output at low levels stays in ClassA. The output at higher levels will have more crossover distortion than "optimum bias". Listening at normal domestic levels may result in most of the output being ClassA.
Only the transient peaks may stray into higher distortion ClassAB.
This could be quite pleasant to listen to. Especially with higher efficiency speakers and in quiet surrounds.
The next stage above that last (higher than optimum bias) is full ClassA, but the heatsinking requirement usually results in much lower maximum output. This too can sound very good and yet again this works very well with higher efficiency speakers.
The decision on whether to bias to "optimum", or higher than optimum, depends very much on the your own listening habits and your typical output currents delivered to the speakers.
The output when lower than twice the "optimum bias" current is always in ClassA. It is very clean because there is NO crossover distortion.
The output when higher than twice "optimum bias" current has the least crossover distortion for that ClassAB amplifier.
If the output stage is biased to less than optimum then the output at all levels has more crossover distortion. At typical domestic listening levels the crossover distortion will be gross, because at ½W to 2W the % crossover distortion content is VERY HIGH !
If the output stage is biased to more than optimum, then the output at low levels stays in ClassA. The output at higher levels will have more crossover distortion than "optimum bias". Listening at normal domestic levels may result in most of the output being ClassA.
Only the transient peaks may stray into higher distortion ClassAB.
This could be quite pleasant to listen to. Especially with higher efficiency speakers and in quiet surrounds.
The next stage above that last (higher than optimum bias) is full ClassA, but the heatsinking requirement usually results in much lower maximum output. This too can sound very good and yet again this works very well with higher efficiency speakers.
The decision on whether to bias to "optimum", or higher than optimum, depends very much on the your own listening habits and your typical output currents delivered to the speakers.
Last edited:
This statement is misleading.
It omits the limited conditions for which it holds true.
In general the limiting conditions are not met and the opposite is the case.
BJTs biased hard are known to have higher crossover distortions, than an optimally biased ClassAB, when the output current exceeds twice the bias current.