NAD T778 Audio/Video Receiver (AVR) Review

[Naks]

I made a short video of the heatsink removal:

 

[pogo]

I think we are slowly getting closer to the matter of the failures. A change on the modules is not only recognizable on the coils. Maybe vibrations or local heat at the capacitors lead to a failure after a certain time.

 

[pogo]

Without changing the PCB layout, a way has probably been found to circumvent some problem. Without reason, one would not make such an additional modification to the modules:

 

[Naks]

And as a reward for my efforts, the sub pre-out seems to be timing out after a few minutes: I'm watching The Expanse, and even massive explosions are not triggering the sub.
On previous nights the sub would almost never go into standby when watching it.

Something is definitely funky with the subwoofer output without the amp modules present: I've boosted the sub levels to +17dB in my Dirac filter, and still it's not triggering during loud explosions...

Any ideas/suggestions on how to resolve this?

 

[pogo]

Try to use the trigger input on the sub.

 

[Naks]

Try to use the trigger input on the sub.

Unfortunately I can't as the sub is too far away & across a hallway from the T778.

I've been using the SVS wireless transmitter, I've resynched these as well, no change.

 

[pogo]

To rule out other sources of interference, I would move the sub closer and connect a trigger cable for test purposes. I would also connect the sub signal directly.

 

[Naks]

To rule out other sources of interference, I would move the sub closer and connect a trigger cable. I would also connect the sub signal directly for test purposes.

Ok, will try that.

I think this is the problem:

Sorry for my english.

Found a problem by accident in the NAD 778 receiver (which many may not know):
After turning on the receiver, the SubW preamp after 10 minutes lowers the volume by 10 dB. That is, 10 minutes after switching on, the subwoofer plays 10 dB quieter than it was configured. All other channels are normal in volume!
If you turn off the receiver from the remote control, and then turn it on again, the volume is restored, but after 10 minutes the volume again becomes quieter at the SUB output.

I tested with another subwoofer, the same situation.
The problem is in the receiver.
Another bug in NAD and their software?

I found only one way out, after turning it on I waited 10 minutes, then set up the system in Dirac Live already with the volume of the preamp output below 10db.

Everything works fine, the main thing is not to turn off the receiver, otherwise you will have to wait 10 minutes if you want to watch a movie with multi-channel sound, since the subwoofer volume will be +10 dB for 10 minutes after turning on the receiver

 

[Naks]

A few closeups of the new amp module

 

[Naks]

To rule out other sources of interference, I would move the sub closer and connect a trigger cable for test purposes. I would also connect the sub signal directly.

I've removed the SVS Wireless transmitter and connected the sub directly to the T778, and switched off my power amp so that the only speaker being driven is the sub.

I have my Oppo 203 looping one massive explosion from Sicario, and after about 7 min, the sub level drops dramatically.

Once I switch the T778 OFF and back on, the scene causes the windows to rattle, even my wife was commenting how much louder that sounded.

Switching Dirac on/off does not affect this, so not sure where to go from here.

 

[Naks]

Ok, not a very accurate measurement, since I don't have a sensitive multimeter nor the equipment to do so, but using a Sound Meter app on my phone at my usual listening position, and the same explosion on a loop:

65-67 dB when the unit has been switched on
50-53 dB after +-7 minutes of operation

 

[ban25]

Ok, not a very accurate measurement, since I don't have a sensitive multimeter nor the equipment to do so, but using a Sound Meter app on my phone at my usual listening position, and the same explosion on a loop:

65-67 dB when the unit has been switched on
50-53 dB after +-7 minutes of operation

Are you sure the sub is not limiting to protect itself? Does the plate amp feel hot to the touch?

 

[Naks]

Are you sure the sub is not limiting to protect itself? Does the plate amp feel hot to the touch?

It feels the same as the the room temperature, so I doubt it.

Tomorrow I will run the sub out to my power amp, and then to one of my front speakers. That should rule out the sub.

 

[Naks]

Ok, I connected the sub to the power amp to just the Front Right speaker, and at almost no volume on the T778, with the same test scene:
- 59-61 dB just after powering on
- 45-47 dB after +-7 minutes of operation

Same behaviour on both sub preouts.

I'm now noticing that the drop is not linear: initially by about +-5dB, then gradually until it settles.

And worse, a couple of times during my tests, there wasn't even any output after a while...

With the sub connected directly to the Oppo 203:
- a steady 69-70dB, no drop after 5, 10, or 30 minutes.

 

[Naks]

We just had my unit on a friend's test bench where we fed it a 50Hz, 0dB signal, and from the attached photos, you can clearly see the distortion in the signal after a while.

We then tested his unit, and discovered the exact same issue, so this may be a common issue with the units of the 2020/2021 batches.

 

[Naks]

A short video to show how the subwoofer pre-out signal changes

 

[Naks]

from AVSforum:

"You might want to ask NAD if they can send you the latest revision of the AM 230 module.

The DSP, DACs, and volume controls are on the AM230 module. I know it has been revised at least once (if not a few times) since the T778 started shipping.

The main preout board only houses the output buffers. The fact we’ve had more than one report of this manifesting on the sub outputs and not the other channels (yet) implies an upstream issue may be the culprit. I’d start there - on the AM230."

 

[Naks]

Finally heard back from NAD Support: they could not replicate the issue, which I was expecting, unless they also had the same hardware fault.

So I've taken it to the service centre, they'll have a look while I'm away in the bush.

But funny story: the serial number I sent them via a recent screenshot (K21YT77807755) does not match the one on the chassis (K215T77805671).

I thought that was very odd, so I went back through the various diagnostic logs I sent them over the years, and it looks like at some point the serial number changed.

I wonder how...

 

[Naks]

Unit has been sent to the agents for assessment.

While putting the amp modules bank in, I noticed this on the Amp Connection Board:

 

[Naks]

Finally heard back from the Service Centre: blown caps on the supply section of the MCU and on the VM310 MDC module input section of the MCU board.

They can't test anything else, because it's going into protection mode.

Looking at the cost of replacing these boards, I think it's time to set fire to that p.o.s