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Avondale NCC200 V1.3 Magic smoke !

E

eddie pugh

pfm Member
Really enjoying the music trying out the loaner Arkless's GTI MC Stage and my NCC200 based NAP250 decides to give up the ghost and produce some smelly smoke which appears to be limited to one channel. Happened just as the LP was coming to the end and the SL10 auto lift and return was negotiating the end bumpy track bit.

The Arkless GTI sounds really good by the way and I would have loved to hear some more on this my main system

Visible damage seems to be limited to the 100 ohm resistor located between the zobel copper coil and the heatsink to TR7. The resistor is mostly vaporised and the board is really black and burned where the resistor used to be. Damage seems to be limited to the fibreglass though and no visible copper tracks.

Thankfully my prized Yamaha 1000 speakers are fine but the amp generated a loud buzz through one channel while I was dashing for the off switch

What could have caused this? Trying to decide whether to just order a pair of NCC220's or do some fault finding Any suggestions/ Of course it would happen on a Bank Holiday Anyone have a single NCC200 going spare ?

eddie
 
Bumpy track contains many frequencies and it likely kicked the amp into oscillation.

Is it a recent aquisition or have you had it years?
 
David

I've had the Avondaled NCC200 NAP250 for over 10 years and never had any trouble with it I've also a pair of M130's in another system which have been 100% reliable

The SL10 I've had for about 40 years and it still sound really good. Still on its original Technics EPS310MC cartridge In truth it really has not had much use but I've been enjoying vinyl of late and thought I'd try out Arkless's GTI stage.

I've a sneaking feeling that the way the SL10's auto lift handled the end of side and the bumpy leadout combined with the super base performance of the stage might have had something to do with the NCC200's demise

The question is if it went into oscillation, has it blown anything else. I guess I could try just replacing the 100 ohm resistor and see if it blows again but that's not really a good way to go about things
or is it?

Thanks for answering

eddie
 
Id be tempted to check the output stage hasnt gone dc , certainly check the output dc offset before connecting anything up to it.
 
Maybe add in a Velleman K4700 DC blocker on the outputs to make sure this won't happen again and save the Yamahas. ~£20 well spent.
 
Hmm that's the second NCC200 to go DC on one channel for no apparent reason this week on pfm! I've got "djftw"'s coming in for repair later this week. It took out his woofers so you are mega lucky the Yams were not damaged. A speaker protection module would seem de rigueur for these...
 
What are the rail voltages out of interest? I seem to recall some folks using like +/- 55 or 60V which I said was kinda pushing things a little...
 
JimmyB said:
Thought 50v was the norm from a 35v traffo? Front end a bit higher if split & regulated.
Click to expand...

Indeed it is. I just had a recollection of discussion on here about using as much as maybe even 65V rails for Avondale modules, and that some folks were in fact doing just this and it had been OK so far.... it may have been a different product even... are there not two power amp designs at least?
For one pair of output devices this is really pushing it on the SOAR front! The original NAP250 was about +/- 40V IIRC
 
If its a 250 with Avondale boards it will be 40V, Les recommends up to 50V as maximum the NCC300 board's run higher but use parallel output transistors.It's probably an output transistor and associated 0.22R resister blown just remove them and check they are OK.When they are removed check the voltage across the biasing transistor it should be 1.7-2 volts if it is then the front end is OK.
 
My Avondaled Nap250 is dual mono running off a common Traffo
Rail voltages are +\- 50 volts DC

I'm going to replace the resistor tomorrow and see if I get more smoke
I'm certainly not connecting up the speakers until I check for DC on the outputs
Anyone any idea what else might have blown I have a transistor tester and some misc spares from builds that have not yet started

Eddie
Ps Martin. Thanks for the offer I'm still half way up Lansdown and may well get in touch
 
GWM said:
If its a 250 with Avondale boards it will be 40V, Les recommends up to 50V as maximum the NCC300 board's run higher but use parallel output transistors.It's probably an output transistor and associated 0.22R resister blown just remove them and check they are OK.When they are removed check the voltage across the biasing transistor it should be 1.7-2 volts if it is then the front end is OK.
Click to expand...

Could well have been the NCC300 yep... was some time ago... If it's all NAP250 except the amp boards and retains the Naim regulators then 40V indeed.
It's the 100R resistor between driver and output device from a quick look at the schematic but obviously the 0r22's and all transistors need checking.
 
eddie pugh said:
My Avondaled Nap250 is dual mono running off a common Traffo
Rail voltages are +\- 50 volts DC

I'm going to replace the resistor tomorrow and see if I get more smoke
I'm certainly not connecting up the speakers until I check for DC on the outputs
Anyone any idea what else might have blown I have a transistor tester and some misc spares from builds that have not yet started

Eddie
Ps Martin. Thanks for the offer I'm still half way up Lansdown and may well get in touch
Click to expand...

It WILL be more than the 100R resistor. Don't waste your time changing just that.... Almost certainly an output device has gone short circuit and may well have taken out the other output transistor and both drivers for starters....
 
david ellwood said:
I’d be interested in any other people who have had issues with Avondale amps going bang.
Click to expand...

An NCC200 fried a woofer here about 2 years ago. I can't remember the version, but it wasn't current. Not sure of age - at a guess what would now be 10, perhaps nearer 15 years old - I was the third(?) owner.
 
I just put a pair of NCC200 (v1.3 I think) into my Olive Holden and Fisher NAP250 this morning. The Naim reg boards were set at 40v. I increased this to 44v for the Avondale drop in NCC200s. Set at 35mA. 7 and 13mV DC offset. Sounds good and actually cooler than with the Naim boards. The Naim versions ran warmer than I liked. There is no room for a Velleman unit.
Does this sound OK to continue?
Reassurance would be appreciated.
Chris
 
chrisn said:
................................... There is no room for a Velleman unit.
Does this sound OK to continue?
Reassurance would be appreciated.
Chris
Click to expand...

Surely Naim kit will be fitted with speaker protection anyway??????? (That is logic, not experience or knowledge speaking.)
 
chrisn said:
I just put a pair of NCC200 (v1.3 I think) into my Olive Holden and Fisher NAP250 this morning. The Naim reg boards were set at 40v. I increased this to 44v for the Avondale drop in NCC200s. Set at 35mA. 7 and 13mV DC offset. Sounds good and actually cooler than with the Naim boards. The Naim versions ran warmer than I liked. There is no room for a Velleman unit.
Does this sound OK to continue?
Reassurance would be appreciated.
Chris
Click to expand...

There are a lot of NCC200 boards in use and just because two have failed in a week belonging to pfm members does not mean they are all about to blow up.... It's just one of those things that a "Friday afternoon" output transistor can work flawlessly for a few years and then go short circuit for no obvious reason whilst the other channel works reliably for 30 years...
It wouldn't hurt to add an external Velleman unit if it can't fit in the box though...
 
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