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QUDOS - the brilliant new amplifier boards from Avondale

Nice work Malcolm looks great in the 110 case :) good to hear it sounds great as well
Like the idea of the bias transistor being directly attached to the heat sink ;)

Alan
 
LesW said:
I'm sure you're not suggesting that only the most complicated circuits have
any merit when it comes to sound quality.?

Have a listen to a Nelson Pass class A amp for instance - as simple as it gets.
Click to expand...

Are they emitter follower outputs or sziklai?
 
LesW said:
I don't care for Darlington pairs, very difficult to keep under control.....
Click to expand...


With a Sziklai output stage, if the bias transistor and the driver transistors are mounted on the same small heatsink away from the output transistors then you get excellent thermal stability and can bias it into class A up to the SOA limit of the transistors.
 
misterc6 said:
That's the bias transistor it can be fitted where the blank pads are or on the main heat sink, I chose the latter.
Click to expand...

If its a Sziklai stage and the emitters of the drive transistors are joined at the collector of the output transistors before passing through the emitter ballast resistor, then the bias transistor and driver transistors should share a small common heatsink, bias stabilty will be excellent and with reduced voltage you could run it in class A.
 
Loverly..... :) things of beauty - simple yet very elegant.

I suspect they epitomise the epithet that sometimes "less is more"

I'm currently using 2x mono 110's for my Revelation 2's and was going to build myself a 6 pack of "mono 110"s based on the NCC200, to convert my Revelation 2's from passive to active.

But (hope hope) if Les makes these boards available commercially, I'll be aiming for these instead.
 
A couple of answers to points raised:

The Qudos boards will be available as bare PCBs with a BOM or fully built modules

NCC300s are still being built and evaluated and when 'signed off' they will be
available as fully built modules for the time being as I suspect NAP135 owners
will be anxious to have their amps upgraded so supplies may be limited for a
while.
 
Great news looking forward to upgrading my Voyagers ,need a project for the winter ��
 
Does anyone have a rough idea of the price of these yet,I have an old Avondale ampVI that iam thinking of upgrading with these
Clive
 
Same price as the NCC200: £327.00 per pair incl shipping

PCBs with BOM: £28.00 per pair incl shipping
 
HI Les, how much does the BOM differ from the NCC200? I have everything here to build a pair (been sat here for 8 months or so) and am considering switching the build.
 
James Evans said:
HI Les, how much does the BOM differ from the NCC200? I have everything here to build a pair (been sat here for 8 months or so) and am considering switching the build.
Click to expand...

Having built both NCC200s (at least six pairs) and the new Qudos boards I would definitely recommend you go with the latter. The BOMs are very similar, there are six MFR5 resistors whose values are changed, you lose a 1N4148 and 100R resistor from the output stage and TR10 changes from an MJ15003 to an MJ15004. It is advisable to fit TR5 on the main heat sink which involves an extra tapped hole on the sink and a change from 2N5551 to BD237, you will need the new board for this as it has additional tracks on the upper surface to enable it. Alternatively you can stick with the 2N5551 as the original pads for this are still present but you lose the improved thermal tracking. The choice of feedback capacitor is a mystery as the ones I received were tightly sleeved. I also had an option of a BC128 or film capacitor for the input coupling and chose the latter.

Good luck,

Malcolm
 
misterc6 said:
Having built both NCC200s (at least six pairs) and the new Qudos boards I would definitely recommend you go with the latter. The BOMs are very similar, there are six MFR5 resistors whose values are changed, you lose a 1N4148 and 100R resistor from the output stage and TR10 changes from an MJ15003 to an MJ15004. It is advisable to fit TR5 on the main heat sink which involves an extra tapped hole on the sink and a change from 2N5551 to BD237, you will need the new board for this as it has additional tracks on the upper surface to enable it. Alternatively you can stick with the 2N5551 as the original pads for this are still present but you lose the improved thermal tracking. The choice of feedback capacitor is a mystery as the ones I received were tightly sleeved. I also had an option of a BC128 or film capacitor for the input coupling and chose the latter.

Good luck,

Malcolm
Click to expand...

I have already got MJ15003 's for TR10 for the NCC200 's I was planning to build. Can Les or Malcolm advise if I can use these instead of the MJ15004 's
for the QUDOS ? If so is there a downside ?

Thanks in advance for the advice
 
grahamdocman said:
I have already got MJ15003 's for TR10 for the NCC200 's I was planning to build. Can Les or Malcolm advise if I can use these instead of the MJ15004 's
for the QUDOS ? If so is there a downside ?

Thanks in advance for the advice
Click to expand...

I think you've missed the point that the Qudos has a fully complementary output stage compared to the quasi-complementary stage of the NCC200, Naim NAPA and many other amplifiers. The complementary stage is more elegant and, from my experience with the Qudos, better sounding. You need one NPN and one PNP output transistor for the fully complementary circuit, so you need the MJ15004 for the Qudos.

Historically in the early days of semiconductors when germanium was used to manufacture transistors it was easier to make PNP types rather than NPN transistors. This led to the development of the quasi-complementary stage using two PNP transistors with the Baxendall modification which adds a diode to the lower half of the output circuit in order for the two halves to appear balanced to the driver stage. With the development of silicon semiconductors it became easier to manufacture matched PNP and NPN devices. The quasi-complementary topology continued in use, usually with two NPN devices, but the fully complementary stage with one NPN and one PNP device is simpler and, in my view, better topology.
 
The late JV said of Naim's use of quasi-complimentary stages that PNP and NPN output transistors were like "a man and a woman pushing on opposite sides against the same wall" or something like that, i.e. they had different capabilities. It was decades ago, though, and things have moved on a lot since then, not least semiconductor technology and feminism.

He also said you couldn't reset the trip on the 250 power supply board. I wrote the board test program that did!
 
misterc6 said:
Having built both NCC200s (at least six pairs) and the new Qudos boards I would definitely recommend you go with the latter. The BOMs are very similar, there are six MFR5 resistors whose values are changed, you lose a 1N4148 and 100R resistor from the output stage and TR10 changes from an MJ15003 to an MJ15004. It is advisable to fit TR5 on the main heat sink which involves an extra tapped hole on the sink and a change from 2N5551 to BD237, you will need the new board for this as it has additional tracks on the upper surface to enable it. Alternatively you can stick with the 2N5551 as the original pads for this are still present but you lose the improved thermal tracking. The choice of feedback capacitor is a mystery as the ones I received were tightly sleeved. I also had an option of a BC128 or film capacitor for the input coupling and chose the latter.

Good luck,

Malcolm
Click to expand...

Thanks Malcolm.

Another question re drop in replacement suitability - are these new boards still happy with the vbe front end supply as used in voyager/clones?
 
MJS said:
The late JV said of Naim's use of quasi-complimentary stages that PNP and NPN output transistors were like "a man and a woman pushing on opposite sides against the same wall" or something like that, i.e. they had different capabilities. It was decades ago, though, and things have moved on a lot since then, not least semiconductor technology and feminism.

He also said you couldn't reset the trip on the 250 power supply board. I wrote the board test program that did!
Click to expand...

JV had some very peculiar ideas as I found when I visited Salisbury in the '80s

My take on Quasi-comp is like trying to dance using two left legs with one
of them 'arse-about-face'
 
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