I finished assembling kx2 purchased from jim's audio but I'm having difficulty with the standard power supply pcb. I have a 19+19ac toroidal and when i connect it to pcb i get 40vdc. The connections are those indicated in the kx2 pdf. I read that bonsai used the same transformer but with the ripple eater pcb. I tried with a variac and I can get a correct dc value with the same connections. Should I just use a 12+12V ac trafo or try 19-0-19 (which I should buy)?
Resolved ! I connected the secondaries in series. Truly a great amp, I really enjoyed it. Thank you bonsai
Silkscreen for q7 in PCB is bc560 (PNP) , on schematic is a picture of NPN transistor but bc560 is written, on BOM also state bc560. I suppose it is bc550 but could you clear this to avoid confusion later.
Thank
Chatchai
Thank
Chatchai
Thank you for spotting that! it should be BC550 and NOT BC560. I will update the schematic and republish the slide deck later today.
You can use any of these transistors in that position provided they meet the hFE guidelines discussed in the slides.
https://www.onsemi.com/pdf/datasheet/bc550-d.pdf
You can use any of these transistors in that position provided they meet the hFE guidelines discussed in the slides.
https://www.onsemi.com/pdf/datasheet/bc550-d.pdf
Just checked - the BOM is ok - it calls up BC546 or BC547 - both NPN. however, I will put a further note on the BOM saying that the silk screen calls up the wrong part.
🙂
🙂
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Under the Label-Value column, item #27, the 1st BJT listed states BC560C which is what I was referring to 😉.
Best,
Anand.
I tested both channels and bias seem to be lower than suggested.
In class AB, no jumper, I have v across emitter of both output transistors to be 40mv which is around 60mA of bias current.
In class AAB jumper connect pin 2and 3, I have 80mv current around 120mA.
Hfe of q7 is around 510. Supply is +/-25vac which is +/-35vdc.
In class AB, no jumper, I have v across emitter of both output transistors to be 40mv which is around 60mA of bias current.
In class AAB jumper connect pin 2and 3, I have 80mv current around 120mA.
Hfe of q7 is around 510. Supply is +/-25vac which is +/-35vdc.
Bias seem to rise up a bit after 30-40min, it can reach up to 100mv. I hooked up to my main system and seem to be ok.
Sound is polite smooth and refine with details. This is excellent amplifier. Thank Bonsai.
Sound is polite smooth and refine with details. This is excellent amplifier. Thank Bonsai.
Chat72,
apologies for not getting back sooner. Those figures are indeed lower than expected. Please can you carefully check the values around the bias controller - if R18 nor R8 were incorrect (rg R8 lower than 4.7k) it would lead to the problem you have. Seems strange that both channels are behaving like this which is why I think one of the resistor values is perhaps not correct. (Thanks for you feedback BTW - glad you like the sound 🙂 )
apologies for not getting back sooner. Those figures are indeed lower than expected. Please can you carefully check the values around the bias controller - if R18 nor R8 were incorrect (rg R8 lower than 4.7k) it would lead to the problem you have. Seems strange that both channels are behaving like this which is why I think one of the resistor values is perhaps not correct. (Thanks for you feedback BTW - glad you like the sound 🙂 )
Color code for R8 is yellow violet green brown brown which is 4k75 but I measure it in the circuit to be 4k65.
For r18, color code gives 220k. I usually check every resistor before using it. I am quite sure that it is correct.
One thing that I change is r1, I did not want to run it in class A, so I change it to 100k.
I also measure v across r16 and r17 and it reads 460mv. V across d1 is 0.42v.
For r18, color code gives 220k. I usually check every resistor before using it. I am quite sure that it is correct.
One thing that I change is r1, I did not want to run it in class A, so I change it to 100k.
I also measure v across r16 and r17 and it reads 460mv. V across d1 is 0.42v.
The resistor values other than R1 all look ok. Can you measure the base emitter voltage of Q7 (and tell me what transistor you are using) and then the base emitter voltages of Q11 and Q6.