Annoyng problems with Subwoofer and Superuniti

Huge posted:

Salient points, please correct me if I'm wrong ...

When connecting to the low level input of the sub via the sub our RCA or the Preamp out DIN:

1  The noise is coming from the main speakers, not the sub
2  The amount of noise is related to the volume setting of the sub not the volume setting of the SU
3  When connecting the sub to the terminals of the speakers, there's no noise problem
4  It's noise not 50/60Hz hum

If the above are true, then I suspect one of the following:
A)  there's a fault on the low level input of the sub
B)  your low level cables to the sub are running very close to a mains cable carrying a noisy mains signal (e.g. from PLAs)
C)  your low level cables to the sub are running very close to the speaker cables
and this issue is injecting noise into the signal path of the SU, just before the power amp.

1 yes

2 yes when I lower the volume control of the sub noise it disappears even if the SU volume is on the higher levels:  add one thing: If the sub-level is relatively high while listening the SU at low volumes, when when increasing the  SU volume, noise occurs

3 I don't know exactly; I should use this connection for many days to verify, I hear the noise sometimes, not constantly

4 Not hum: it seems the radio FM noise , I would not know how to explain it in English but small electric shocks when the Radio Fm signal is not good

A) I hope so, I would not be happy if my new SU had some circuit problems

B) - C)  No, I do not confirm.

thank you Huge for your support

p.s. I keep  using low connection cause I want to find out the reason of the problem. My SU is under warrenty, in Italy is a lot more expansive than in UK ; 5800,00 euro more than a Devialet 120 or even a McIntosh MA5200

Item A)  If the SU works OK (no noise) when the sub isn't connected to the sub out or pre-out din, then the fault is more likely to be with the sub (and not in the SU).

That is the sub has a fault, where it's putting a noise signal out through the low level input connection and that's affecting the SU.

How long are the interconnect cables from the SU to the sub?

Huge posted:

Item A)  If the SU works OK (no noise) when the sub isn't connected to the sub out or pre-out din, then the fault is more likely to be with the sub (and not in the SU).

but if the problem is in the SU pre-out circuits,  without the sub I should not notice the noise... or not?

The cable (Naim 4Din) is 2m

I also had the same problem with a simple RCA cable from SU sub out phono.

If the problem was in the SU pre-amp output it would affect the SU's power amp even without the sub connected.
I don't believe the pre out or sub out connections in the SU are separately buffered; they are the same connection used, internally, to drive the SU's power-amps.

2m cable is no problem for the SU (if you were using 10m cables, they could be putting too much capacitance load on the pre-amp).

Huge posted:

If the problem was in the SU pre-amp output it would affect the SU's power amp even without the sub connected.

I am happy to learn this

Best

If you connect the cable to the SuperUniti but don't connect it the sub, do you still get the interference?

And does your mains power supply have an earth connection? Is the sub connected to earth?

best

David

Not to hijack the topic but I think an even bigger problem with connecting a sub to the SU is the lack of speakers setup (cutoff filter: sub+small spk / sub+big spk) as opposed to UnitiLite or NaimUniti1/2. Do you think a later firmware update will add this tiny but crucial feature?

Huge posted:

B)  your low level cables to the sub are running very close to a mains cable carrying a noisy mains signal (e.g. from PLAs)

I would like to thank everyone for the support, but a special thanks for Mr Huge : I don't know what mean " from PLAs" but  you are right when you wrote what I quoted. The noise has disappeared since I've isolated the low level cable from SU main power cable.

Naim signal cables are shielded or not? 

I am glad you have it now working. However if the SU pre out for the sub is not buffered seperately from the main pre out I do wonder if this is the most reliable way of wiring up to gain optimum sound quality? It might be you have no choice, but it intrinsically feels unstable to me.

Simon-in-Suffolk posted:

? It might be you have no choice, but it intrinsically feels unstable to me.

I agree that it is an unstable option but I have two more other options that I think are most optimal: 

1) the sub output phono sockets 

2) In Hi level to the back of the speakers that will be my final choice: the amp does not suffer from sub stress and, most important thing, better quality bass.

further advice are welcome

I've tried both the DIN preamp-out, and the RCA sub-out to run an N-Sub from my Superuniti using a rather expensive 10m interconnect. The pre out was slightly better, but the difference wasn't huge. (The only reason I changed is that I needed the pre out when I added an external power amp.) I will eventually get round to using a high level connection from the speakers, but haven't tried it yet.

The biggest advantage I have found from using the low level connection is that it allowed me to use a miniDSP 2x4 to accurately control the sub.  The result was a considerable improvement over using the sub's own controls.

Hungryhalibut posted:

I take the point, but it's really very easy. Once you've split the first inch of so of the outer insulation you can usually just pull on the separate wires with one hand and the insulation with the other, and it will simply peel off. 

 

Dear Hungryhalibut

unfortunately I can not confirm what you say; probably you have good skills in these operations, but it is not a job for me. The REL cable jacket  is very hard and it is not so easy to dissect: last night I spent a long time to isolate the yellow cable and it was a tiring and unnecessary work because I have caused small lesions on bare wire and now I'm afraid to connect it. I had to cut 3 meters with small scissors but I assure you it was not as easy as you say. 

Anyway at moment I gave up the hi-level connection, I'm using the phono sub output socket instead of pre-out output ( I reserve it for future upgrades as did Chrissu)

I'm using a cheap RCA cable, but soon I'll buy one better

Best 

p.s.

my Naim  4Din/2 Rca cable is now available for purchase on eBay

Hallo everybody

The problem has not been finally resolved, the noise occurs occasionally also isolating the analog cable.To avoid that damn annoying noise (which, however, it is not constant but intermittent It occurs only during the lower frequencies) I must definitely turn off the sub. For many years the subwoofer has been an important value of my listening and now that is in off I  miss it, the sound of the SU still great but seems more slender, lacks soul and warmth It is more transparent and pure but I love the bass

 Now the question is resolved with 2 options : 

I have to accustom my ear to this kind of polite sound.....

Or should I buy a new sub...and then if the problem occurs again? 

Anto68 posted:

Hallo everybody

The problem has not been finally resolved, the noise occurs occasionally also isolating the analog cable.To avoid that damn annoying noise (which, however, it is not constant but intermittent It occurs only during the lower frequencies) I must definitely turn off the sub. For many years the subwoofer has been an important value of my listening and now that is in off I  miss it, the sound of the SU still great but seems more slender, lacks soul and warmth It is more transparent and pure but I love the bass

 Now the question is resolved with 2 options : 

I have to accustom my ear to this kind of polite sound.....

Or should I buy a new sub...and then if the problem occurs again? 

Hi Anto,

There is another thing you can try.  I use a miniDSP 2x4 to control my sub.  This is a DSP filter device that sits between the sub out on my Nait XS and the low level input of my sub.  There's a pair of RCA cables from the sub out to the miniDSP unit then a single mono RCA cable from the miniDSP to the sub low level input (I've programmed the miniDSP to convert the stereo signal to mono).  I use it to control the integration of my sub with the room acoustics and with my main speakers.

However for you, it will also block the interference from the sub getting into the SU.

To check if this will work for you, turn your sub volume down to minimum, but leave it connected to the SU and powered up.  If you don't then hear the noise issue, then fitting a miniDSP unit will almost certainly stop the noise being fed back down the cable to the SU.

As a miniDSP 2x4 is $105 (USD) then it's probably a lot cheaper than changing your sub.  If you follow my guide lines you can also use this solution as digital room correction to handle bass resonances in your room without impacting the sound quality of your main speakers.

Huge posted:

 There's a pair of RCA cables from the sub out to the miniDSP unit then a single mono RCA cable from the miniDSP to the sub low level input (I've programmed the miniDSP to convert the stereo signal to mono). 

Hi Huge,

my configuration is different, which is the opposite to your

my sub has only one RCA low level mono input while from the SU there are 2 stereo RCA phono  sub output. Could this work the same?

Anto68 posted:

Huge posted:

 There's a pair of RCA cables from the sub out to the miniDSP unit then a single mono RCA cable from the miniDSP to the sub low level input (I've programmed the miniDSP to convert the stereo signal to mono). 

Hi Huge,

my configuration is different, which is the opposite to your

my sub has only one RCA low level mono input while from the SU there are 2 stereo RCA phono  sub output. Could this work the same?

 

Hi Anto,

Yes, the miniDSP is ideal for that, in fact, that's just what I actually do: Although my sub has stereo inputs, I only use one of them and run the sub in mono mode, the miniDSP does the stereo to mono mixing, before sending the signal to the sub.

Driving a mono sub from a stereo sign in one of the jobs its specifically designed for.  There's a software programming plugin module for it specifically created to make this use easier to do it's called "miniDSP 2 Way Advanced 2.1".  Their website shows the programming screen used to set the crossover frequency for a sub - it may look a little complicated, but I posed a step by step guide to how I did it in another thread on this forum:
https://forums.naimaudio.com/to...on-using-a-subwoofer
This covers correction of room resonances as well as setting the sub crossover point and level.  If you're worried about the complexity I can send a guide to just the crossover point setting without the room correction parts.

Sorry to hear you still have the problem.  I would try using the high level connection first. You don't need to worry about expensive speaker cable just to try it out, so buy some 79 strand stuff from a DIY store and just run the cable from the back of the two speakers to the sub (this us assuming your sub will accept a high level input). If it works then you can worry about how to hide the cable.  You must take the feed from the loudspeakers and not from the speaker terminals on the amplifier.

i hope this helps.

best

David

Hi David

With the help of my son, who sees very well, we have secured the Rel's cable for the high level sealed with an insulating tape the micro cuts on bare wires I caused when I cut cable jacket and now it run from the back of the speakers : no more noise problem and better quality bass than before. I contacted a specialist shop that will provide me a new cable as well.

Thank you all for sharing with me these experiences, I wish you a peaceful weekend.

Very good! I'm glad you got it going.  Enjoy the music this weekend.

best

David

Today I spoke by phone with the specialist that will build me the new cable for the high-level access: he remained perplexed when I told him that I will use the cable to the speaker inputs, he says that the amplifier still suffers an impedance alteration anyway, therefore, connect the cable to the amp main speaker outputs or to input speaker inputs does not change anything: my speaker have impedance 4 ohms, the REL 100 ohms (in Hi level).

So why Naim recommends this configuration?

......I would like to hear opinions from both brands Rel and Naim

Can someone suggest me the e-mail address in order to contact technical support?

He's wrong.  The inductance in the speaker cable is in series with the speakers, so if you connect to the speaker end of the speaker cables, this inductance protects the SU from the additional capacitance of the extra cable.

As Huge says, Naim are very clear about this. It is essential that you connect at the loudspeaker end and not the amplifier end of the loudspeaker cables. It doesn't matter what REL say because the issue is about the load on the Naim amp, not the input seen by the REL. or to put it another way, REL won't mind where you get the signal from, it's the effect on your Naim you have to worry about.

if you want to talk to Naim, the contact details are in the sticky post in the top part of the forum, but they will say as above.

best

David

Huge posted:

He's wrong.  The inductance in the speaker cable is in series with the speakers, 

Exactly in series......while if I did run the cable from the amp main speaker outputs it would be in parallel.

And why Rel provides suitable cable to be connected to the amplifier and does not consider this feature? Anyway what you say is important to me, and I trust you (otherwise I would not come here)

Best

I guess your 'specialist' is not a Naim specialist, or else he would understand the different design of their power amps compared to other brands, and the importance of the speaker cable as an integral part of this design. I'm fairly sure Rel are aware of this issue, too. Naim support will be able to clarify this, give them a call or email them.