Yes the NCC is a derivative of the NAP and that part is the same.yes, the 22 K is near TR1 (like in the Avondale NCC200) on the NAP schematic.
Can i say the mod is the same on NAP Board ? ... and change the resistor value with 1K (in place of 22K)
I think about the parallel output transistors, but i want a clear schematic to do this...
And for the resistor value? what is the sweet spot, 1K or another value like 3K3 or 5K or another?
Is there any feedback from people who made the mod.
What is you musical feeling with 1K instead of 22K from Avondale NCC 200 or Naim nap Board?
Is there a lack of body?
Hi,
I just read the proposed change which is the resistor based current mirror for the input stage. By changing the resistor, you are in effect increasing 2nd order distortion - which is pleasing to the ear.
It seems from the description of lean, clearer etc., then these are just examples of interpretation of distortion in the system.
Regards,
Shadders.
Hi,I assume higher value is higher distortion?
Having recently gone from NCC200 (with 22k) to Qudos with 1k, the Qudos board is audibly less coloured and lower in distortion than the former. How much of this is due to the output stage change versus the LTP resistor I can't say.
I'm quite tempted to change the old NCC200's to 1k and pop them back in to compare, and then maybe find if there's "sweet spot" with a view to updating the Qudos to that value as well.
Tonally the Qudos is a bit leaner than the NCC200 with 22k but also less forward in the mids, which is better. My speakers tend towards the leaner side of things anyway so the Qudos is probably just highlighting that at present.
Hi,
Yes, the difference in the LTP collector currents will increase 2nd harmonic distortion, and the greater the difference then the greater the distortion.
Doug Self's book Power Amplifier Design details this (6th edition page 131).
Regards,
Shadders.
Hi,The resistor change doesn't change the balance of the currents in the LTP (I have measured this). It changes the voltage and the voltage swing on the collector of the "feedback" transistor, which with higher resistor values increases the Early effect on that transistor.