I've just checked my kx2 for Iq vs Vsupply. On +-25V I am getting 1.06A in class A, 0.67A in class AAB and 0.25A in AB.
These figures are for the whole amp, so OPS bias currents will be about 50mA less so for the above 1A, 620mA and 200mA.
So there is a reduction in standing current with supply voltage of 20% from 22V to 30V. Most amps will run between +=25V and +-30V in class A and this will result in about a 14% increase in standing current with the higher supply voltage.
Unless you have any glaring errors like incorrect resistor values, or you've used >1% resistors, I'd say your amp is good to go except for the swapped class A<>AAB thing - but this wont affect operation - just flip the switch round in its mounting hole.
Please note, my readings were done within 10 minutes of powering up - so they would go up after about 30 minutes by another 4-5%.
I'll add the Iq vs Vs data into the build document.
These figures are for the whole amp, so OPS bias currents will be about 50mA less so for the above 1A, 620mA and 200mA.
So there is a reduction in standing current with supply voltage of 20% from 22V to 30V. Most amps will run between +=25V and +-30V in class A and this will result in about a 14% increase in standing current with the higher supply voltage.
Unless you have any glaring errors like incorrect resistor values, or you've used >1% resistors, I'd say your amp is good to go except for the swapped class A<>AAB thing - but this wont affect operation - just flip the switch round in its mounting hole.
Please note, my readings were done within 10 minutes of powering up - so they would go up after about 30 minutes by another 4-5%.
I'll add the Iq vs Vs data into the build document.
Hi, I built the kx2. The new Kx ate some transistors from the old Kx. At the moment it is not easy to buy transistors. I compared in my memory kx and kx2, I thought they were no different. But then I opened J3 and the flower blossomed. I don't know why, I don't know electronics, but in my hi-fi system this compensation sounds better. Now I am listening in AB mode and I am very happy. Thanks Bonsai!
Last edited:
Davide,
quite a few people prefer the sound of standard Miller compensation (that's what you have with J3 Open) and its one of the reasons I offer both TPC (or TMC as in the case of the kx2) and standard Miller through jumper selection. So indeed you should listen carefully and then decide what you like.
I'm glad you are happy with the sound!
quite a few people prefer the sound of standard Miller compensation (that's what you have with J3 Open) and its one of the reasons I offer both TPC (or TMC as in the case of the kx2) and standard Miller through jumper selection. So indeed you should listen carefully and then decide what you like.
I'm glad you are happy with the sound!
Nice one Andrew, I like your specs and always respected your design and manufacturing work, it is impeccable!
Hi, I checked the connections thousands of times, but in my hifi system, kx2 lose the low frequencies and I get a fatiguing sound with the outputs correctly connected, instead the sound is better if I invert a channel. This only happens with kx2, no with other amplifier. This is possible?
Last edited:
Oloppolo please check
1. your wiring from the input connectors to the amplifier boards and make sure you have not crossed the wires.
2. Check the voltages across R40, 41 and R34 and R35 and let me know what your readings are
3. measure the output DC offset
4. Can you tell me what you are using for the source
1. your wiring from the input connectors to the amplifier boards and make sure you have not crossed the wires.
2. Check the voltages across R40, 41 and R34 and R35 and let me know what your readings are
3. measure the output DC offset
4. Can you tell me what you are using for the source
I misured:
A: R40 137,2 mV - R41 137,8 mV - R34 144,7 mV - R35 142,4 mV - DC offset 2,4 mV
B: R40 138,6 mV - R41 138,0 mV - R34 145,0 mV - R35 143,3 mV - DC offset 2,0 mV
+- 27,00 V in the rail
In class AB
Last edited:
Those figures all look ok - that means the front end is working ok. Can you measure the voltage across each of the 0.33 Ohm resistors - from this we can check that the OPS is working ok. Also, can you measure across R10 and R11 - this will tell us how the VAS is working.
What are your supply voltages?
What are your supply voltages?
I measured:
A: R12 10,0 mV - R14 8,6 mV - R13 27,8 mV - R15 29,4 mV ------ R10 0,456 mV - R11 0,455 mV
B: R12 7,9 mV - R14 7,4 mV - R13 26,4 mV - R15 23,8 mV ------ R10 0,454 mV - R11 0,456 mV
power supply AC 19 Volts DC +- 27
There is a lot of difference between emitter NJW 3281 and emitter NJW 1302 compared to 0 volt.
Last edited:
R10 and R11 do not look right. You should be measuring about 560mV (that's about half a volt), not 0.45 mV. If you are in fact measuring 456 and 455 mV then that's ok - but please recheck.
The voltages across R12-R14 and R13-R15 are all on the low side. You should be measuring about 40mV across each resistor in class AB mode and about 65mV across each transistor in class AAB mode.
Can you measure, wrt the output (ie the output side of L1) the voltage at the collector and the emitter of Q7. You should measure about 1.3V to the collector and then -1.3V to the emitter.
BTW, make sure for all your measurements that the inputs are shorted.
The voltages across R12-R14 and R13-R15 are all on the low side. You should be measuring about 40mV across each resistor in class AB mode and about 65mV across each transistor in class AAB mode.
Can you measure, wrt the output (ie the output side of L1) the voltage at the collector and the emitter of Q7. You should measure about 1.3V to the collector and then -1.3V to the emitter.
BTW, make sure for all your measurements that the inputs are shorted.
R10 and R11 are Ok, 450 mV more or less. Q7 collector / emitter 1,20 v -1,20 v more or less.
The sound is better with the my smartphone output (xiaomi) rather than with the preamplifiers. With the preamp the sound seems saturated. Have I impedance or level problems? Which preamp do you recommend?
The input impedance of the kx2 is 11k (you should measure it just to make sure). This is not a heavy load and the BA3 output stage can easily drive it. Do you have a scope and/or sound card that you can check both the amp and preamp with?
The kx2 is a very smooth open sounding amp, so I am perplexed as to why you have sound problems.
The kx2 is a very smooth open sounding amp, so I am perplexed as to why you have sound problems.
It seems to me that I have achieved a significant improvement with a channel in class AAB and another channel in class AB, playing at the same time. Is it possible that I have transitors matching problems?
Oloppolo, you would have to have gross mismatch problems for this to be an issue. Also, your voltages are all correct, so I doubt this is your issue. I'd check your load (speaker connections) and your source.
Have you tried swapping the speakers around to see if the problem moves to the other speaker and then same on the inputs?
Have you tried swapping the speakers around to see if the problem moves to the other speaker and then same on the inputs?
