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QUDOS - the brilliant new amplifier boards from Avondale

Joe Hart said:
I wonder how easy these are to fit for those lower down on the diy audio amp side
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Its not particularly dificult but a basic understanding of a Multimeter is required to check bias and DC offset after fitting. It goes without saying AC mains/electricity can kill. In short if you don't know, get some one else to do it who does or can show you.
 
chiily said:
I'm going to have to buy a set of boards aren't I....
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Fraid so have a pair singing in my Voyagers ,no contest that forced naim quality that even inflicts the NC to an extent is gone,female vocals never sounded so good in my system and only running normal bias.
 
"I wonder how easy these are to fit for those lower down on the diy audio amp side"

These are a drop-in, pin for pin replacement for the NAPA boards in most Naim amps
 
Les, could I also trouble you for a pair of Qudos boards (+heatsinks and bits)? I’ve dropped you a PM a while ago, but you must have missed it...
 
Bit of an update..now a week in and day by day sounding better. I did have a little issue, a hum. Pesky blighter that 50Hz, which turned out to be the need for the sig in 'screen' to be strapped to the mains earth (just one amp board) took a bit of detective work with a trusty bit of wire with crock clips each end but sorted it. Have never come across this before but the hum has completely gone and the amp/s sounding quite superb. It does take some time for things to settle and get up to speed as it where but as one actor once said "worth waiting for"

Les is going to ship me a couple of his HCR200 regs and transformers then I'll be able to maximise the potential lurking within the NCC220.

Graham
 
Graham
It should not need that earth to screen in the power amp but there should be one in your pre amp?, or is it a dodgy interconnecting lead?

Alan
 
Yes I know...I have a checked the leads and the pre amp. All good. The hum is there with or without the pre hooked up..?? I have checked and re-cheaked all leads and connections, probably 10 times!!! as you do.

I'm a pit puzzled by it. I don't get/have the issue on other amps I have built of late. Pass F5t stereo's and monos. All be it a different animal.

I will get to the bottom of it...but just now enjoying the sounds it makes as is.

Gra
 
Strange ?
Anyway glad its sounding great :)
You could however :rolleyes: try swapping the amp boards over an see if the hum follows the board ?, that would tell you if there is a fault in the amp board or the power supply.

Alan
 
337alant said:
Thought that the idea of the HCR200 was a high power reg that can regulate the full amp as in the NAP250/135, anyone compared it both ways, full amp vs front end only ?

Alan
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Yes it is Alan a full board reg... I'm looking forward too tying either or, or what about a HCR reg at both ends of a NCC2xx ???

Gra
 
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Les also sent me a pack of boards and some parts. The boards were completed last week and have had 2 days soak testing in an old NAP 110 'test bed'. Bias current adjusted to 135 mA and I'm getting about 30mV offset voltage at the speaker connections, so all looking good on the technical side. A few brief tests on an old TV speaker showed all OK, so they've had a few days to run in and I've tried them on the Quad 2805s with excellent results. These are a clear step up from the NCC 200s, even on the end of a small transformer giving 35V at the rails. They have a firm grip on the speakers combined with very flowing musical presentation and some new detail on familiar tracks. An iron fist inside a velvet glove.

The boards are up to Les's usual excellent standard of design and manufacture; and building is not really a challenge even for a DIY beginner should anyone be concerned. If you can solder well then all should be OK.

Next step is to build the VBE supply boards that have been in my projects box for a while and give the Qudos boards a 48V output supply and a separate R Core/VBE 54V front end supply...should be good.

So far a firm recommendation...more to follow.
 
My boards and bits have arrived. I beginning to get everything together for the build. I have a couple of questions..

Do the TO220 transistor need electrically insulating from their heatsink?

Does the BD237 need electrically insulating from the main heatsink?

I'm a little confused by the bias setting resistors. I'm guessing the the pot is 2k2, 10turn and the associated resistor is 1k2, yet the board has 2k2 as the associated resistor.

Any help appreciated.

Looking forward to getting these finished and my NCC200s sold on.

3jc6qmW.jpg
 
CORRECTION - It now appears that some, if not all, BD237s need an isolating pad - see post #305 and fit one anyway to be sure.

Neither the driver transistors (TO220s) nor the BD237 need isolating from their heat sinks. If you have the first issue boards as I did there are a number of differences between the legends on the boards and the circuit diagram (schematic) - if in doubt go with the circuit diagram. I took a scan of the board legends before I started construction, printed it out and updated the legends.

HTH
 
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Just finishing the third amp...bias 50ma and offset 35mv.

One to go..as I'm building an active setup.

I did have a little problem with this build!! At 30v on the bench supply during the testing phase with no output devises all measured ok. On finishing the whole board with the output devices fitted I was getting 8vdc as an offset. As I knew the rest of the board was OK from my previous testing 'at full voltage' it must be a problem with the output devices. It turned out to be either MJ15003 or 4, both new. Out of circuit they measured/tested OK by the Altas tester. I changed both 15003 and 15004 just in case, all is well now. It could of been a sil pad? so I replaced those too. But the old ones look fine..and I did check continuaty after fitting, no shorts were found.

38649604766_25078f6dc6_b.jpg
 
Don’t be afraid to wind the bias up, the QUDOS is designed for 120mA into the positive terminal and Les told he had run them at 150mA.
 
misterc6 said:
Neither the driver transistors (TO220s) nor the BD237 need isolating from their heat sinks. If you have the first issue boards as I did there are a number of differences between the legends on the boards and the circuit diagram (schematic) - if in doubt go with the circuit diagram. I took a scan of the board legends before I started construction, printed it out and updated the legends.

HTH
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Isn't the metal back of the BD237 its collector? Wouldn't that possibly cause a problem with the board's heatsink bolted directly to the amp's earthed case?

Yes, I marked up a scan on the QDOS PCB with the values from the cct diagram.
 
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