Hifisonix kx-Amplifier

[andrikstormik]

I understand that replacement of transistors undesirable.... but as far as it maybe to apply 2SA2031 / 2SC5669 ?

 

[Bonsai]

Hello Andri, I will have take a look and come back to you.

 

[Bonsai]

I had a quick look. The fT is quoted at 10 MHz and output capacitance at 200 pF Vs. 30MHz and 600 pF for the devices specified.

You could try them, but you may need to change the compensation. The existing compensation has 80 dev phase margin and about 15 dB gain margin.

 

[andrikstormik]

to choose the capacity of indemnification(68пф) ? what criterion for the choice of capacity = absence of excitation ? rectangular impulse on an oscillograph ? how is it correct to pick up a capacity ? on what criterion ? will I be very thankful for an answer or where reading it is possible ?

 

[andrikstormik]

I used FJAF4210\FJAF4310 . works perfectly. distortions not more than 0.01%. excitation is not present. a parasite generation is not present

 

[Bonsai]

Sounds like it’s all ok! That’s great!

 

[oloppolo]

I bought NTE 373 and NTE 374 for Q10 and Q11. Do I have to match the gain?

NTE 373/374 for Q10 / Q11 in this amp is a very bad idea.
It is Better BD 139/140

 

[Wolfman1969]

Hello.
Can I use MJE15030,15031 in SIMPLE RIPPLE EATER PSU if i don't have 15032,15033

 

[Bonsai]

Yes, you can use MJE1530 and 1531

 

[daanve]

PCB's are out of stock?

 

[oloppolo]

Hi, I checked the voltages as in the diagram and everything is ok, but I hear the mid-high and high frequencies decreasing compared to my reference. I have tried with many sources and preamps. Can you help me? I have no oscilloscope to measure.

 

[Bonsai]

PCB's are out of stock?

The kx2-Amplifier is coming that wrinkles out some of the issues builders had with the original kx-Amp.

I am in the middle of build 2 and once this is measured and meets the same performance as build 1, the Gerbers will be released to Jim’s Audio - another 2-3 weeks at most.

 

[Bonsai]

Hi, I checked the voltages as in the diagram and everything is ok, but I hear the mid-high and high frequencies decreasing compared to my reference. I have tried with many sources and preamps. Can you help me? I have no oscilloscope to measure.

Olopolo,
I will make a list of things for you to check to try to solve your problem - not easy without a scope.

Do you have this problem on both channels?

How bad is it compared to your other amplifier?

 

[oloppolo]

The problem is quite evident in two channels. Light low and medium frequencies also a little analytical. High down. I used no matched transistors.

 

[oloppolo]

I measured with inexpensive oscilloscope, no problem. I tried to disconnect ZN and the sound changed, it is now more airy. !!! ???

 

[thimios]

What is ZN?
Do you mean the zobel network?

 

[oloppolo]

Yes, 10 ohm + 0.1 uF.

 

[oloppolo]

ZN connected, not twisted: change the sound again.

 

[Bonsai]

You cannot omit the Zobel network on any feedback amplifier where it is part of the design. Please make sure it is connected and the wires are tightly twisted to the PSU.

Check that R4 and R5 are 1 k Ohms and not 10 k

For you HF loss problem, can you check C15 (270 pF) and R31 (1k). If one/both of these are high, you may get excessive treble roll-off

 

[oloppolo]

R4, R5, C15 are ok. R31 is 1.8K.