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QUDOS - the brilliant new amplifier boards from Avondale

@Stanney2001 You need to explain more fully what you are intending to do. You entered this thread saying you were populating a pair of Qudos boards and asking for advice on component choices and now you say you want to build a NAP135. The NAP135 and the NAP250 are different from the other Naim amplifiers of the 1970s, 80s and 90s as they have regulated power supplies. The NAP135 is a mono power amplifier so you would need two for stereo. You can fit Qudos boards to these amplifiers but need to make adjustments to the regulator boards which, from memory, has been discussed earlier in this thread. The Qudos boards can be easily fitted to most other NAP amplifiers from the period, but not the very early ones which have the output transistors attached directly to the case rather than to heatsinks attached to the amplifier boards.

If you have a NAP135, or two, you would probably be better following Jonathan's advice and take a look at the thread on Avondale's NCC300 project. If you have a NAP110, 140, 160 or 180 then, subject to what I said above, you can easily fit your Qudos boards to it.

If, on the other hand, you are building an amplifier from scratch there is plenty of advice to be had on this thread.
 
Well, this is interesting. I just discovered that the Nap 140 used the Sanken 2SC2922 (NPN) transistor.

Actually, it used two of them, despite the existence (and use in many amplifiers) of its complementary partner, the PNP 2SA1216.

BugBear
 
The Naim NAPA circuit was based upon a quasi-complementary RCA design. At that time PNP power transistors were rare, expensive and somewhat flaky compared to the equivalent NPN devices which explains why quasi-complementary circuits were the norm. Naim did use the 2SC2922 for some NAP140s but fitting one of these and a 2SA1216 would have required further changes to the circuitry and PCB layout to accommodate a fully complementary design.

The Avondale NCC200 circuit brought a number of important improvements to that basic design but it remained quasi-complementary with the need to add a diode into the lower half of the output circuit. The Qudos (NCC220) circuit, by contrast, is fully complementary with both NPN and PNP power devices in the output stage, this, together with other improvements including an improved version of the input LTP circuit are, IMHO, why the Qudos sounds so good.
 
The Naim NAPA circuit was based upon a quasi-complementary RCA design. At that time PNP power transistors were rare, expensive and somewhat flaky compared to the equivalent NPN devices which explains why quasi-complementary circuits were the norm. Naim did use the 2SC2922 for some NAP140s but fitting one of these and a 2SA1216 would have required further changes to the circuitry and PCB layout to accommodate a fully complementary design.

The Avondale NCC200 circuit brought a number of important improvements to that basic design but it remained quasi-complementary with the need to add a diode into the lower half of the output circuit. The Qudos (NCC220) circuit, by contrast, is fully complementary with both NPN and PNP power devices in the output stage, this, together with other improvements including an improved version of the input LTP circuit are, IMHO, why the Qudos sounds so good.

Ah - I hadn't noticed a detailed examination of the circuit changes NCC200 vs NCC220. Given that Les is selling some NCC200 altered to be more NCC220 like, I assumed they were very minor, with complementary output being the principle one.

BugBear
 
is it feasible to convert a NCC200 to a NCC220 Im at the stage where I've just finished the NCC200 board build and was wondering about modifying them to be NCC220.
Is the sound difference that great?
 
is it feasible to convert a NCC200 to a NCC220 Im at the stage where I've just finished the NCC200 board build and was wondering about modifying them to be NCC220.
Is the sound difference that great?

If you mean modifying the board itself then no, you need a new Qudos board.You can add some of the improvements by adopting the changes made in the VAS stage there is a circuit diagram earlier in this thread.The output stage is changed to a fully complimentary layout and the new board is needed for that.There are plenty of descriptions of how much better it is and I agree with them.
 
Would these be a straight swap for the NAPA boards in my power amps. It’s already a bit of a squeeze.

NAP110-Mono-amplifier.jpg


I’ve been planning something more exotic for my retirement system but the mscaler has just eaten a huge hole in my budget.
 
Would these be a straight swap for the NAPA boards in my power amps. It’s already a bit of a squeeze.

NAP110-Mono-amplifier.jpg


I’ve been planning something more exotic for my retirement system but the mscaler has just eaten a huge hole in my budget.
Yes its a drop in replacement.
 
is it feasible to convert a NCC200 to a NCC220 Im at the stage where I've just finished the NCC200 board build and was wondering about modifying them to be NCC220.
Is the sound difference that great?

I believe it is possible because i looked into what was needed. A bit of jiggery pokery required but can be done.
 


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