Hey wise persons...-Question: -(Resolved)

I have VTA Mk IIIs and  SP14, which I really enjoy.  

I have a low hum in the right channel, just audible from 6 feet which doesn't follow volume control.
With shorting jack on that monoblock...-no hum, so it doesn't appear to be the amp.

With the amp connected to the SP14, even with the pre switched off, the hum is present.
When I switch the interconnects at the pre-amp or the monoblocks, the hum stays on the right channel (!!!)

Very confusing!!

I haven't changed any tubes in the pre yet, because the hum exists even with the pre off.  
Do the smart guys see anything obvious here?

Other suggestions for diagnostics?

Thanks a million,

K

Did you try swapping out the entire cable by disconnecting both ends and making the right cable now the left cable and vise-versa for the other cable?

Two-prong or three-prong mains plugs on the SP-14 and MkIII? Are your interconnects directional?

Three prongs on both amps and pre. Interconnects non-directional....
2 prong "cheaters" result in loud buzzing.

With interconnects switched entirely, hum stays put.

Thanks,

K

Ground loops are no fun. It's hard to have a single ground reference when you have multiple components with three prong plugs and bi-directional interconnects. This creates a distributed ground network rather than a single ground reference. My MkIIIs run with two-prong plugs to avoid hum. This represents a safety compromise given the MkIII's exposed chassis. Maybe one of our European friends can describe how they defeat ground loops with each component grounded via three prong mains plugs.

is that the other channel, (wired the same) is d-e-a-d silent...
Go figure.

K

Is everything plugged into the same AC outlet?

Process of elimination to narrow cause....

As suggested are all components using the same AC outlet?
Swap left and right preamp outputs. Is hum the same or move to opposite channel?
Swap monoblocks. Did the hum move or stay?

May be internal ground connection in one of the components as you stated hum is present with the preamp switched off.

.

FIRST!! Do Not Pass GO, Do Not Collect $200!! Go directly to your VOM or DMM. Identify a good ground and test in both AC and DC from your chassis to ground with each component *individually* (no interconnects). If you get more than a few millivolts, you have a problem within the system. Report back if this is the case, as the overall approach is quite different than ground-loop hum.

You have not mentioned the age of these devices, nor if you are running a turntable. I am assuming from your post that the hum is present irrespective of the component in play - tuner/CD/TT/Tape/whatever. You have not designated whether it is 60hz or 120hz, but for discussion purposes, I will assume 120hz, suggesting that your rectifier (at least) is OK. I am also assuming that this hum is a recent development, and that nothing otherwise has changed. You have not recently introduced a new component, reconfigured the system, changed a phono cartridge, changed tubes, or similar.

a) Check all interconnects. Make sure that they are tight both the shell and the prong. *MAKE SURE*. Most users stop with the shell and ignore the prong.
b) Use the shortest possible interconnects that you have.
c) Check the inside of the components for any poor connections. These can happen from thermal stress, simple age, or an initial cold-solder finally working loose.
d) Back to your DMM, and the components *entirely* disconnected both from each other and the wall: Measure the resistance at the input(s) and output(s) of each component, each channel. Is there _ANY_ difference?

And, absolutely make sure that all components are on one (1) dedicated circuit.

Please report back with results.

Great suggestions...
I will take some time to work through these.
They are all new (ish) VTA units. I built the Mk IIIs a couple of years back. I let Roy build the SP-14. I believe the hum is not a new phenomenon, as I have been aware of it, just kind of ignoring it, since it's not evident on playback.

I will let you all know what turns up.

Thanks again to all for your ideas / time.

Kevin

Yeah, what Peter W said. Definitely check for voltage potential between the amps first.
Have you tube-swapped in the pre-amp as well? Sometimes a hinky tube there can cause 120-cycle hum regardless of your gain-control setting. At least it's happened to me.

Being of rather lazy temperament, decided to focus on interconnects first, and voila, come to find out, one of my set is dodgy , as, after hooking up some good shielded connects hum is defeated . It was not the amp.

I know, I should have done the swap-out earlier, but was tricked by inability to switch the noise between channels by switching the old interconnects.

Live and learn...  REALLY glad this is apparently not an issue with the build.

Thanks to all for the diagnostic teach.  Maybe this should be a troubleshooting "sticky"??  
I know I'm going to archive it.

Mille grazie,

K.

Dingojazz wrote:Being of rather lazy temperament, decided to focus on interconnects first, and voila, come to find out, one of my set is dodgy:affraid: , as, after hooking up some good shielded connects hum is defeated:king: .

I know, I should have done the swap-out earlier, but was tricked by inability to switch the noise between channels by switching the old interconnects.

Live and learn...  REALLY glad this is apparently not an issue with the build.

Thanks to all for the diagnostic teach.  Maybe this should be a troubleshooting "sticky"??  
I know I'm going to archive it.

Mille grazie,

K.

You want good interconnects, go to Blue Jeans Cable in Seattle. All Belden shielded wire, sturdy ends, a steal at 4x the price. Speaker lines, I'd recommend Paul Laudati at Clear Day.

If you prefer the DIY route, I've had excellent results with CanareGS-6 cable with Canare F10 connectors. I make them to 10 feet each.

https://www.markertek.com/product/gs-6-bk/canare-gs-6-guitar-cable-per-foot-black?gclid=Cj0KCQiA6enQBRDUARIsAGs1YQi17IG33ODN_I0U56DUSTVh8qhmmEXkZL0p9uTLaSMZyZl_vtfSfwEaAufnEALw_wcB

https://www.redco.com/Canare-GS-6.html

https://www.redco.com/Canare-F10.html

I have used these as well...very nice https://www.parts-express.com/neutrik-nf2c-b-2-profi-professional-rca-plug-pair--092-114

I've been tempted to try building some interconnects... this may be the incentive to try it out.

Cheers,

K.

Since Blue Jeans offers the Belden 1505F , you may want to try it over the Japanese Canare.

https://www.markertek.com/product/bl-1505f/belden-1505f-rg59-21-sdi-coaxial-cable-ft

I made a few with microphone cable just to see how they sound (Canare L-4E6S Star-Quad Microphone Cable). I like them, still using them.

I always mention Signal Cable. They were recommended here by Bob Latino. I just got my last cable from them last week (turntable cables) and they seem to be fine quality for a very reasonable price. Quick and friendly service. No connection, just a customer...

http://signalcable.com/analogone.html

Brute fact of the matter is that after some (pretty basic) minimal quality standards, there is not much to choose between interconnects whether rolled on the thighs of Virgins on Walpurgisnacht, or from some sweatshop in China. Nor do electrons understand the concept of 'directionality' very well.

However, a well-made cable using decent parts and high-quality materials is a joy and a pleasure to use, will remain reliable over time, and not fail under difficult conditions. It does not have to be a AMG Mercedes SL-series, but neither should it be a Trabant.

Always use the shorts cables that do the job without strain or stretch.

Every so often, remake the connections - did I ever tell the story of "BREAKER, BREAKER" coming across a Bach harpsichord concerto one Saturday afternoon? Apparently just enough corrosion salts had formed on the turntable input on my amp to rectify in the CB range. The truck was on the street outside and clearly had linear amps on board.

Another reason not to use rivets when assembling amps, especially to anchor ground points. They also corrode and may create some interesting effects. KEP-nuts or knurled lock-washers are the better means to assure a tight connection.

Once again, PeterW is correct. Electrons are ignorant of direction. There are variations in interconnects that play out on 100 km runs but are utter gibberish for our purposes. The terminations should be of high quality, but that's about it. Keep yer contacts clean is the other thing. They do tend to crud up over time.

I'll plug my hometown source for bulk cable, terminations and custom made stuff.
https://www.performanceaudio.com/

They are primarily focused on Pro audio and live performance equipment for people who make a living making sound and thus gold plated predatory pricing for clinched sphincter audio types is not  present.  Lots of bulk wire by the foot and various connectors.  Bulk multiple conductor (16 channel soundboard snake cable anybody??) cable that can be handy for some situations too.

it's amazing to me that the few times that people have hum and think it's the preamp, many times it turns out to be a flakey interconnect.
They look OK, and sometimes even work OK because you're swapping things around and maybe the bad connection goes good.
BUT, don't always assume it's the equipment . . . this is the 3rd or 4th time this year I've heard of customers with flakey interconnects causing hum !

Intermittent problems/connections....fun! I recently had a hum on a pre-amp....it was the amp. Disconnected everything going into the amp (CD, Tuner, Phono...etc), then connected to a dedicated AC line I had wired to the breaker box some years ago. Shut off all the breakers to the rest of the house except the one I was on, connected a set of headphones using an RCA to mini connector/adapter....and there it was, very faint due to the lack of headphone amp, but it proved to me the amp had an issue.

cci1492 wrote:Intermittent problems/connections....fun! I recently had a hum on a pre-amp....it was the amp. Disconnected everything going into the amp (CD, Tuner, Phono...etc), then connected to a dedicated AC line I had wired to the breaker box some years ago. Shut off all the breakers to the rest of the house except the one I was on, connected a set of headphones using an RCA to mini connector/adapter....and there it was, very faint due to the lack of headphone amp, but it proved to me the amp had an issue.

Not sure that's proof, unless you shorted the inputs. An open input jack will pick up all sorts of crap.