851N noise help

[bvbellomo]

I bought a used 851N in December 2022. I was very happy with it until recently, and know it was a favorite of Jon and some of the others more experienced on this board, so hopefully I can get some help.

I noticed slight noise from the left speaker a few days ago, which is not usual, this time it sounded like intermittent FM radio static. I have 2 mischievous cats and have yet to build final cabinets with crossovers inside, so it wouldn't be the first time I've had to reconnect a wire nut. I am happy with the sound and very busy, so good carpentry hasn't happened yet. If I am listening to a great song or movie, I fix everything right away. If I am dead tired and throw on a sitcom rerun and hear an issue, I usually procrastinate. Yesterday I noticed the problem was worse, with the static getting louder and happening almost constantly. I rechecked the connections - still noise. I finally swapped the speaker for a commercial one, and had the same noise, so it isn't my speaker. Switching the left and right outputs from the 851N and I get the static on whichever speaker is attached to the left 851N output (regardless of swapping channels on the amp). I was using balanced connectors out of the 851N. Switched to the RCA connection, and I have no static, but I do have a low hum. This would be fine for a non-audiophile set up, but I am not happy with it. I didn't used the RCA connectors before, so I have no idea if the hum was there before. Any suggestions to fix or troubleshoot this further? I have to throw out this device after only 1 year, but I knew that risk buying used.

I did buy a new TV in December, which also involved disconnecting and reconnecting all equipment. This is probably unrelated as everything worked well for 3 weeks.

[JonMarsh]

Sorry to hear you've having troubles- static sounds like an internal variable breakdown of some kind- could be something as simple as a leaking blocking cap, or could be an issue with the D/A.

That you get output on single ended RCA that is clean except for slight hum is only diagnostic to the extent that it indicates a possible ground loop in the overall system configuration- a judicious use of ground lifts on 3 conductor power cords might address it. Or might not. This often indicates a potential difference in the ground connection on your grounding plugs. None of this is easy to diagnosis without some test gear, I'll grant. But it's also a possibility that an issue exists only in the system setup. For example, I might test your unit on the bench and not find anything amiss. Or, maybe I would- it's just a guess without doing it. Given the cost of shipping, you're probably better off working with Cambridge Audio direct.

Have you looked into the possibility of factory service, contacting Cambridge Audio?

I note there are manufacturer refurb units available on eBay for $899 typical. Both black and silver. New is $2200.

[bvbellomo]

I am outside my comfort zone taking this apart, and uncomfortable whenever capacitors are involved. I know most home audio is well below the voltage and amperage to kill a healthy adult. Is the 851N relatively safe to take apart? I like the idea of bad capacitor, it explains the sudden failure, and is easy and cheap for me to fix. Do you think if this is the issue I will be able to find it visually?

I did find a few 3-2 prong adapters I can use the cut the ground and ran some tests.

I get a hum with:

• 851N plugged in and grounded and connected to the 651W with unbalanced connectors. Turning the 851N on or off does not change the hum.
• 851N plugged in and ungrounded and connected to the 651W with unbalanced connector connected and the 851N turned on

There is no hum with:

• The 651W turned off
• 851N plugged in and grounded and connected to the 651W without either unbalanced connector connected
• 851N plugged in and ungrounded and connected to the 651W with unbalanced connector connected and the 851N turned off

The 651W without a ground still hums in all the same scenarios, but possibly hums less. I'd have to measure the db of the hum to be certain.

Are more expensive RCA cables likely to solve this? I used a cheap cord I had lying around. I don't typically use RCA cables, so I'd have to buy a better cord to try this.

My understanding is all the grounds and neutrals in the entire house are connected in the main breaker box. If this is true, moving things to different outlets or circuits is unlikely to change anything. But unplugging something far away on a different circuit, such as the refrigerator, potentially fixes it.

I doubt Cambridge wants to hear from someone who bought these well under $899 on ebay. It doesn't hurt to reach out, although if they want me to pay shipping both ways to England and parts and labor, that may not make financial sense.

As always, thanks for your help.

[JonMarsh]

It does sound to me like there are two problems here- the static bit, which is internal to the 851W(in all likelihood) and the ground loop issues.

Now, just to explain, when you have single ended connectors, the shield connection goes to the component system ground. For safety reasons, if you have a 3 prong power cord, the system ground is connected in some fashion to the ground plug. The ground loop issue can arise because other items connected to your house AC power system can have currents flowing through the ground pin which create voltage drops (AC) (small, in the mV range) but these drops can manifest between different outlets and connections, usually between circuits on different breakers. And they are added in series across the ground path between two connected components. This can also be a problem that becomes exacerbated due to age of the home and oxidation of copper in wire nut connectors.

And while the grounds are all connected to the same breaker box, the resistances on those connections vary, and hence the voltage drop and relative voltage.

However, your report in detail (much appreciated) points possibly to internal power supply or other circuits issues in the 851N.

I get a hum with:

• 851N plugged in and grounded and connected to the 651W with unbalanced connectors. Turning the 851N on or off does not change the hum.
• 851N plugged in and ungrounded and connected to the 651W with unbalanced connector connected and the 851N turned on

There is no hum with:

• The 651W turned off
• 851N plugged in and grounded and connected to the 651W without either unbalanced connector connected
• 851N plugged in and ungrounded and connected to the 651W with unbalanced connector connected and the 851N turned off

The 651W without a ground still hums in all the same scenarios, but possibly hums less. I'd have to measure the db of the hum to be certain.

If the issue was due to a classic system ground loop, I would not expect that turning the 851N on or off to change the hum- unless the OFF mode completely disconnects the signal output, to- such as a relay controlled output that connects only after powered up and DC offset is not present (how most power amps work, many preamps). Even powered off, there is a finite impedance connecting to the 851 system ground. See, what I would do if this were my system would be to insert a current meter (DVM) between the ground connections on power and on the signal cable, and looking for any current flow- that would induce a voltage drop to appear. We're talking mA range stuff, mind you. Easier to use a scope on the hot lead of the RCA.

Now, a really high end RCA connector with heavy braid and low impedance all around might reduce the hum. IF it is the voltage drop across the RCA cable creating the AC hum voltage reflected to the input. Easy to tell using a scope, but most people don't have a lab like mine- the last 5-6 years at work, due to budget issues (near zero CapEx expenditures due to VP who wanted to optimize profitability on paper) I ended up supply nearly all my test equipment for work, as I'd brought in a customer colleague in the Minneapolis area to work on the AE team, and we needed to ship all the "normal" test equipment from my bench in Milpitas national headquarters to Minneapolis.

Questions for you - do you have access to something like a conventional CD player? Single ended outputs find- you can test your system with that in place of the 851N. If the hum goes away, this further points to the 851N, of course.

The other thing to try to generate another data point- plug the 851N and 651W into the same outlet, and disconnect anything else from these, other than speakers. Is this how you tested, or are they on different outlets? If on different outlets, possibility for relative voltage difference on ground exists.

Try this check, and also try with a different source component if you have or can borrow one from a friend. Ex, I have a Marantz SA-1151 SACD player with balanced and unbalanced outputs- I could check it out, make sure it's up to snuff, and pay to ship it to you, for your system checks, if you pay to ship back. I'll have to put together a new box and packing for it.



One of the things I've found effective for friends using unbalanced connections is a master power center for modest to moderate size audio setups (less than 1500W total draw)- something like this Monster Power HT control center, which I actually use on my semi-budget roll around audio test cart (has Audirvanna music server, Alpha USB, Soekris R2R ladder DAC, and Cambridge Edge W power amp on a stainless steel cart with bamboo top from Costco)





Lots of control, lots of EMI filtering, and only one connection to the household power.

OTOH, I still use balanced everywhere, unless I'm having to check out a component that doesn't balanced outputs. Rarely encounter those these days, but that's partly due to my self selection process. There's lots out there still.

[bvbellomo]

I feel incredibly stupid. My TV is not close to an outlet, so all my testing has been with the same surge protector. Just plugging in the 851N and 651W directly to a wall outlet and connecting unbalanced input does not hum! All that testing unplugging/plugging in of different devices with and without grounds connected, and it seems almost certain the surge protector itself is the problem.

I know they make high end audio surge protectors and "power centers" but these seem like snakeoil. What do you plug your equipment into?

I'd still appreciate advice troubleshooting why my balanced left channel has static, even if the hum is gone and I can use unbalanced connectors.

I did take your suggestion and connected a cheap SMSL DO100 preamp with balanced connectors to the 651W and do not have static.

[JonMarsh]

Well, this sounds like some good progress at your end, at least on the troubleshooting and info gathering side!

The TV being connected to the same system could also be a factor.

What I have found is that for me there is a reasonable point on the power center/EMI filter stuff that works well, but isn't ludicrously expensive (AKA "snake oil"). Note, I have one of those Monster Power control units, no issues with it, and I also have in the living room a somewhat more modestly priced Tripplite.



Now, I realize that what I call "not ludicrously expensive" may not align with everyone's definition of the term, but a well designed system like these should give some further control and assure low AC noise and freedom from ground point issues. (famous last words, right?)

I think the static thing is an issue with an internal stage in the 851W- but which one and how difficult to repair depends on the degree of integration in the chip set. You might investigate factory service. I like that part so much I've thought about buying another one, but I think a Schiit Kara will be up for consideration first.