QUDOS - the brilliant new amplifier boards from Avondale

[misterc6]

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?

CORRECTION - it now appears that some at least BD237s need insulating pads - see post #305

No, it’s not. It worried me on my build but the metal back of the BD237 is not connected to any of its terminals. You can easily check this with a meter on a low resistance range.

http://www.farnell.com/datasheets/1...0.1560492544.1511900518-1648290522.1454516074

 

[laverda]

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.

I already have amps (NCC220) running at 150ma bias and they sound very nice, I'll wind the bias up after a day or so on soak...

 

[chiily]

First QDOS board transplant into my DIY Voyagers

Offset at 37mV, bias at 100mA (less as the front end is being supplied by a VBE board)

 

[chiily]

Number two warming up

 

[Marra]

Nice work chilly. That didn't take you long.

 

[laverda]

A pair of entry level monos...fresh off the bench and sounding great even new. Bias 100ma (at present) offset 22mv ish.

 

[chiily]

A pair of entry level monos...fresh off the bench and sounding great even new. Bias 100ma (at present) offset 22mv wish.

Oh, they look sweet.

Have you any idea what the feedback cap is under that sheath? Mine's a 100uf wet tant, supplied by Les.

 

[laverda]

Oh, they look sweet.

Have you any idea what the feedback cap is under that sheath? Mine's a 100uf wet tant, supplied by Les.

Sorry I don't know, not sure what it is under the cover ...Les said 'their a bit special' but their very very light for a wet tant? compared to the others I have in my bits box. I measured 109, 110, 110 & 111uf for the 4 Les sent me. They sound OK, much like a mil spec wet tant.

 

[chiily]

Nice work chilly. That didn't take you long.

They are pretty simple to put together. The PCB is top quality making soldering an easy task and everything is well laid out. Great work from Les as usual.

No release of magic smoke either, always a bonus.

Amps are plugged into the main system now. Hopefully I'll get some time for listening this week.

 

[chiily]

I've noticed that at idle that the amp cases become quite warm. The boards are running at +/- 44Vdc and with a bias current of 120mA that's about 10W. Previous NCC200s were about 3W at idle.

 

[Marra]

How are you liking the sound?

 

[337alant]

They are pretty simple to put together. The PCB is top quality making soldering an easy task and everything is well laid out. Great work from Les as usual.

I Have to say that LesW boards are superb quality, there is nothing available commercially they comes close IMO and they are a breeze to solder in the parts and the layout is very well thought out

alan

 

[laverda]

A pair of entry level monos...fresh off the bench and sounding great even new. Bias 100ma (at present) offset 22mv wish.

If you look close you'll see that the amp on the left (above) is using the 2N5551 in its usual on board location TR5. The amp on the right is using the DB237 (TO126) The experiment was to ascertain just how well it all holds together by bolting TR5 to the output sinks.

2N5551 ..after about 55ma it becomes very difficult to maintain a current at a steady state. I did wind it up to 80ma but within a short period of time it was running way on its own as it warmed up 100, 110, 120, 130, 150ma.....at which point I returned it to the norm 38ma.

On removing the 2N5551 and installing the BD237 a steady state 100ma was easaly achieved which with the chassis sled I'm using as a heat sink bolted to the 8mm thick case works well over an 8 hour period. Just warm +

I have to fit the facias at some point....

 

[chiily]

If you look close you'll see that the amp on the left (above) is using the 2N5551 in its usual on board location TR5. The amp on the right is using the DB237 (TO126) The experiment was to ascertain just how well it all holds together by bolting TR5 to the output sinks.

2N5551 ..after about 55ma it becomes very difficult to maintain a current at a steady state. I did wind it up to 80ma but within a short period of time it was running way on its own as it warmed up 100, 110, 120, 130, 150ma.....at which point I returned it to the norm 38ma.

On removing the 2N5551 and installing the BD237 a steady state 100ma was easaly achieved which with the chassis sled I'm using as a heat sink bolted to the 8mm thick case works well over an 8 hour period. Just warm +

I have to fit the facias at some point....

That's interesting about the 2N5551. With the additional bias current it must be crucial to have TR5 heatsinked and thermally coupled to the output devices.

I'm glad someone else is finding the cases warming up, obivious really based on the higher bias current.

I did a little probing around with my osciloscope last night, to to see if there was an oscollation generating the heat. But I couldn't find anything other than mains hum and the ripple on the supply caps.

Soundwise, they are a step up from the NCC200s. If someone had told me before hand that they would sound better than the NCC200 I would have laughed, 'cos the QDOS sound so clear, full of sparkle. I now understand what the Naim 'rip' is...

Anyway, anyone want to buy a set of working NCC200 boards?

 

[laverda]

But I couldn't find anything other than mains hum and the ripple on the supply caps.

I'm finding a low level hum 'at the speakers', I had it on the first NCC220 amps I built into one case...and resolved the issue by strapping the screen to mains earth but not so with the latest two amps....I'm scratching my head to find this loop...

 

[chiily]

I'm finding a low level hum 'at the speakers', I had it on the first NCC220 amps I built into one case...and resolved the issue by strapping the screen to mains earth but not so with the latest two amps....I'm scratching my head to find this loop...

Could it be that the -ive speaker post is shorted to the case?

With the speakers, mains and inputs disconnected, is there possibily a short between the PSU 0v (middle of the PSU caps) and the incoming main earth?

 

[laverda]

Could it be that the -ive speaker post is shorted to the case?

With the speakers, mains and inputs disconnected, is there possibily a short between the PSU 0v (middle of the PSU caps) and the incoming main earth?

Thanks for the input...I'll be having a good look/check over the next few days...

 

[Marra]

Just had a delivery from Farnell who unfortunately are out of stock of the MJ15003's. I have three left from a previous buy but they have low hfe; 5;7 and 70 whereas the MJ15004 are 170-200 hfe.

Does anyone by any chance have 2 or 3 with a higher hfe that I could buy from them? tia.

 

[laverda]

Just had a delivery from Farnell who unfortunately are out of stock of the MJ15003's. I have three left from a previous buy but they have low hfe; 5;7 and 70 whereas the MJ15004 are 170-200 hfe.

Does anyone by any chance have 2 or 3 with a higher hfe that I could buy from them? tia.

Don't concern yourself, they'll work just fine. I have 15003's of between 60 & 72 HFE in all 4 amps partnered with 15004's of 150HFE.

 

[venton]

How much do the Qudos boards cost in kit form? I searched Les's site but couldn't find them.