Some work to be done...

The S300 is sick...

The left channel is hissing loudly (can be heard across the room) when the amp is warmed up. So, I phoned up lenbrook service department and he said "Oh yes, it's a couple of transistors that go noisy".

So I said that I could do the work myself if he told me which ones I was looking for. Gave me the circuit IDs, but warned that he had trouble getting hold of the parts. Asked what model transistors, and assured him that I would have no trouble at all in obtaining them...

ZTX453 and ZTX553. I will be having a word with the guy who designed them to check that the problem is understood.

 

Sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss

Regards

 

Hmm, some of your own then Isaac?

 

Yes.

I spoke to the designer, and he reckons it's an implementation issue and is going to have a look at the circuit diagram. As it is, I just need to obtain some of the devices from stores.

 

Right, got the new devices in. Bit of a pig of a job, and moving that amp around to get at top side, bottom side, top side, etc is a pain with the weight. That, and the 17 screws that have to be removed to get the bottom panel off (an interesting mix of 3mm allen, pozi #1 and a small torx...). Anyway, done now, and will know once the amp has warmed up if the problem is solved. It still works at least

 

Hi Isaac,

I'm a S300 owner too. I did read the thread on the subject elsewhere. I do not have the hum problem but I have the power lamp blinking at power on. Nad said it's no problem.

As a matter of interest, did you take pictures of the innards of the beast ?

Regards

:NADowner:

 

No, but I can do as I've not screwed the lid back on yet.

When I power on my amp, the power LED blinks for 30 seconds or so until the output relays click, and the power LED goes off. I too asked NAD about this and they said it is normal.

 

If you would be so kind. I'd hate to have to remove 17 screws if not absolutely necessary.

And I wouldn't be able to replace devices anyway ...

Name is Renaud (pronounced like Renault)

Cheers

 

Well, I already put the 17 for the bottom panel back in. Top panel has only 3 screws (torx). I'll get some pics done at some point...

 

Thanks, no hurry. I only hope you won't have to remove those screws again too soon ...

Cheers

 

I've heard about this. Mine behaves a little differently - the power LED comes on steady for 20 seconds or so until the relays click. stumblin on here (the previous owner) had it serviced by Lenbrook at some point, who apparently replaced the output stages with their updated design (or something - ask him if you want to know the details), so I don't know if it used to do the flashing business before that.

 

Here's what Nad replied to my query :

"Thank you for your recent request via the NAD Electronics web-site.

The S300 LED flashes for a good 15 seconds or more before the unit comes on. Your unit should be fine.

Best regards,

Karen Pritchard"

But they did not comment on the fact that the Manual says otherwise ...

 

And some pics of the inside:



These are the problematic transistors, Q315 and Q317.



The left channel of the amp, from inputs on the right, through the input selection relays into the early gain stages. Power supply (obviously) on the left with the transformer and big caps, meeting the early gain stages in the middle and jumping to the power output stage on the side of the amp (top of pic).



Showing both channels.

 

Good pictures Isaac. No wonder the beast is nose-heavy.

I take it you don't need to remove the boards to work on them from the bottom.

Cheers

 

No, just the bottom panel.

 

Hmmm, the led shouldn't flash, the person at NAD is being a moron. The led flashing is speaker protection mode.

When you first turn the amp you should get no output for about 10 seconds, and the led should be steady. This is normal operation.

 

Stumblin,

I bought my amp. new. As I had read the thread on the S300, I new something was wrong when I first switched it on. That's why I immediately mailed Nad UK (after checking my speaker cables). Apparently I'm not the only one with the "problem" and to get the same reassuring answer from them. The unit however works fine. Don't know what to do.

 

Stumblin - so far it only seems to be yours that doesn't flash. I've asked two different people from NAD on two separate occasions, and they've both immediately said that the behaviour is normal. Since one of these people was immediately able to diagnose the transistor problem in the S300, I'm prepared to take his word for it.

 

And yet the Manual says the opposite. The people at Nad should definitely get their act together.

 

Well, NAD didn't design the S300, and it's a low-volume model.