HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

I would be tempted to add a blocking cap on the input, and possibly a RC low pass, it may be there are step voltages out of the DAC that the valve amp wont be seeing. Or there may be RF due to not having enough filtering on the output. A scope would help, but that’s not much help remotely.

I have 470pf / 47k on the input.

Dr Bunsen Honeydew wrote: ↑Mon Dec 03, 2018 1:20 am I have 470pf / 47k on the input.

Ok, may be worth trying a blocking cap then. DC is more likely I would have thought. BTW, the 470pf one its own will do nothing, the HF roll off will depend on what’s feeding it. If you add 100R in series it gives you a more defined roll off, but that’s probably neither here or there. RF on its own shouldn’t hurt the output stage (I would have thought).

It seems there is a fault on the Metrum.

"I have been in contact with Cees Ruijtenberg of Metrum and he has asked me to try a few things before the Dac is considered at fault and then subject to being returned. Looking at some initial test’s this morning with all inputs working and producing music Coax and Optical stage are faulty as the error light comes on for both of these and the music played stutters and faults badly. The USB stage is fine but it was the coaxial stage that would have been in use when the amps failed."

Interesting, Doc. Good to see that the cause of the problem has been found.

Well now where this now leaves us = for me confused again.

"More testing of the Metrum Onyx reveals the coax/optical issue's i had last test session have been fixed i had a combination of a bad feed from radio paradise volumio flac feed can be troublesome sometimes and a faulty rca coax connection on one of the R Pi units which was generating the stuttering and led error light more or less constantley on. Odd how it did it across 2 inputs playing 2 different radio feeds but it has been playing albums and various radio stations for 2 hours across all inputs and seems fine now no led error light on or flickering this will continue for a day or two until i'm happy it has no obvious faults then it's time to speak to Cees at metrum.


Next to test is the Rpi unit with allo Digione spdif card on top of it and it's associated linear power supply."

Dr Bunsen Honeydew wrote: ↑Wed Dec 05, 2018 10:13 pm .... and a faulty rca coax connection on one of the R Pi units which was generating the stuttering and led error light more or less constantley on. Odd how it did it across 2 inputs playing 2 different radio feeds

Maybe this was causing a grounding/feedback situation that got passed on to the power amps ?

No the RPI unit with the faulty rca coax that was making the error led flash was one not used before on this system i have pinched units from other places to populate all the inputs on the Onyx to try top make it fault but up to know it's behaving normally .

There are lots of maybes, all I know is *something* is sending something nasty to the power amps. *Nothing* should be sold that creates situations like this where things are so intermittent you can't even pin down the fault condition.

I had a similar situation with speaker cables where I had no control over what was being done to my amps, even finding unwound capacitors (Goertz and Litz) speaker cables being used. So what choice did I have, make my amps worse musically just so people could use stoooooooooooooopid badly designed loudspeaker cable, or insist on my own ones being used, even at the expense of most of the cables that work perfectly safely.

Do I now have to specify DACs that can't go wrong or create situations where I have to get back and repair FIVE different amplifiers, and can't send another until the problem has a solution, FFS how many amps do I have to repair, not to count a couple of replacement drive units for his Cubes.

Lazmo wrote: ↑Thu Dec 06, 2018 12:23 am No the RPI unit with the faulty rca coax that was making the error led flash was one not used before on this system i have pinched units from other places to populate all the inputs on the Onyx to try top make it fault but up to know it's behaving normally .

So now you confuse me again.

The point of this thread is to see if someone has any experience of anything similar with the Metrum or any information that can help.

I think we will leave it at that until you pin down IF there is a fault with the Metrum or not.