NDX analogue O/P drive capability

Posted by: Kemills1 on 12 February 2015

Hi

My brother has an NDX and XPS2 power supply connected to a MF nuvista amp. Everything is fine until he connects a Sennheiser hdvd800 headphone amp to the line out of the nuvista. With hdvd switched off, the sound is distorted and quite low in volume. With the hdvd switched on, things are better but still not right. We believe the MF amp is simply routing the source to the line out so the NDX is "seeing" the input impedance of the hdvd.

The input impedance of the hdvd is quoted as 10k ohms and the minimum load impedance of the NDX o/p is quoted at 10k ohms.  Although the o/p impedance of the NDX is quoted at 10 ohms it seems to stuggle with a 10k i/p impedance presented by the HDVD.

Has anyone had a similar experience with the NDX?

Sincerely

Kev.

Posted on: 13 February 2015 by sjbabbey
Originally Posted by Kemills1:

Hi

My brother has an NDX and XPS2 power supply connected to a MF nuvista amp. Everything is fine until he connects a Sennheiser hdvd800 headphone amp to the line out of the nuvista. With hdvd switched off, the sound is distorted and quite low in volume. With the hdvd switched on, things are better but still not right. We believe the MF amp is simply routing the source to the line out so the NDX is "seeing" the input impedance of the hdvd.

The input impedance of the hdvd is quoted as 10k ohms and the minimum load impedance of the NDX o/p is quoted at 10k ohms.  Although the o/p impedance of the NDX is quoted at 10 ohms it seems to stuggle with a 10k i/p impedance presented by the HDVD.

Has anyone had a similar experience with the NDX?

Sincerely

Kev.

Sorry I don't have any experience with the amp/headphone amp setup you mention. Indeed, you don't say which model the Nu-Vista is. The 800 perhaps?

 

If so, the 800 has both line level and preamp RCA outputs. Has your brother tried both sets of outputs and, if so, is the distortion (through the speakers or headphones?) the same in both cases?

 

Is there a reason your brother is not connecting the Sennheiser h/p amp direct to the NDX either by the second analogue output (DIN or RCA to RCA depending on the connection from NDX to the Nu-Vista) or via the NDX's digital output given that the Sennheiser has its own DAC?

 

The direct analogue connection would shorten the signal path and should therefore theoretically at least improve the sound. Of course the digital connection would entail missing out on the sound of the NDX's own DAC.

Posted on: 13 February 2015 by Kemills1

Hi, 

thanks for the response.  The amp is the nuvista 800 and he has tried the pre out and that was okay. Distortion is through both the speakers and the headphones.

He is using the RCA outs from the NDX to the amp and I don't know if he has a suitable DIN/RCA lead to wire directly from the NDX to the HDVD800.  

He doesn't use a digital connection as he prefers the sound of the Naim DAC over the Sennheiser DAC.

As it stands, MF have requested the amp back for investigation so we'll see what happens.

Posted on: 13 February 2015 by sjbabbey

Hi Kev,

 

Glad to see that MF are investigating.

 

It might still be worthwhile for your brother to invest in a DIN to RCA lead and try out the direct analogue route from the NDX to the Sennheiser h/p amp. I guess he'll be doing this anyway using the RCA/RCA while his Nu-Vista amp is away being checked out.

 

ATB

 

Steve

Posted on: 21 February 2015 by Kemills1

Well, the amp has been with MF a week now and they've not been able to reproduce the condition.  The dealer, Unilet, have now sent their demo amp, their HDVD800 and a creek amp to MF in order to reproduce the condition.  Not sure of the logic there but apparently that is what has happened as Unilet's demo amp does not exhibit the same symptom.

Something else which my bother has told me, and why Unilet have sent a creek amp to MF, is if he connects the line out of the MF to a line in on a Creek Destiny 2, the speakers go completely dead if, on the creek, he selects an input other that that to which the MF is connected.  It kind of suggests that un-selected inputs on the creek are grounded.  By playing a test tone of 1kHz on the NDX, he has measured the input voltage to the MF and has observed that the voltage does not change even when the speakers go silent.

We'll see what develops at MF....

Posted on: 05 March 2015 by Millzee60

I've tried both the DIN and the RCA connections, one each to the NuVista and the HDVD800. No matter which way round, one affects the other when I turn off the HDVD800.

 

Curiously, the same happens when I tried the MF MX-HPA. And Unilet's demo NuVista 800 has the same issue.

 

Unilet and MF are all over this so there may yet be a solution. Fingers crossed.


Colin.