Kitchen Hum was back and now fixed again

A lot of things relevant to the kitchen electronics have happened in the last year, and not surprisingly the hum is back.  It's an annoying hum I can hear when neither the refrigerator nor the dishwasher is running.

With just the power amp running, and the Yamaha receiver which provides the signals to it is off, the left channel noise measured 0.54 mv (measured at the left speaker terminals with my A-Weighted Meguro noise meter).

With the receiver turned on, the hum rises to 0.74 mv showing that some of the noise is being caused by the receiver.  But less than half.

With shorting plugs in the amplifier, the noise drops to 0.078 mv, nearly 20dB lower.

So hardly any noise is being caused by the power amplifier.

I tried removing several different connections (not all at once because I'd lose track and it would take days to get it all back together) from the receiver and none had much effect so far.

Before even doing these measurements, I moved or checked the routing of the power cord to the power amplifier, which *seemed* to have made a big difference last time.  Whatever moving I did made no difference audibly.

A very well shielded Blue Jeans LC-1 interconnect is being used.

So today I removed everything except the preamp outputs, and noise dropped to 0.1 mV with the Yamaha off, and 0.18 mV with the Yamaha on, and no audible hum.

So I started re-connecting, starting with the coax digital inputs which I thought I had individually tested the day before.  Now it was different.  Adding the Pioneer LX70 digital input was what created the audible hum with measured noise at around 0.4mV.

So, I disconnected everything from the LX70.  What ultimately made the difference was the HDMI output, which connects to my Wolfpack HDMI switch.

So I tried disconnecting HDMI sources which had been added this year: the Tivo and the new security cameras.  The Tivo was what made most of the difference.

I bought a special power cord for the Tivo to be sure it was plugged into the same AV rated UPS as everything else, including the power amplifier.  That wasn't enough.  The Tivo antennas are both indoor antennas but one is on the other side of the room and has a long coax.  That runs through a UHF/VHF joiner.

So I don't understand why the Tivo should be a problem, but I had a simple solution, use an ground isolation transformer on the LX70 audio output.

For some reason the LX70 does not have optical digital outputs, only coax.  I could use a digital coax to SPDIF converter, but all the ones I have are either in use or broken.  That's a very common trick I use to break ground loops.

So this time, I thought I would attempt to use a ground loop isolation transformer for component video, which has approximately the same bandwidth as coax digital, a Jensen Iso-max VB-1 RR.

Jensen Iso-Max VB-1 RR

It works great, noise with the Pioneer connected to the Yamaha and the Yamaha running is a 0.15mV and there is no audible hum.  The audio from the Pioneer works fine (and this is really only a "convenience" input anyway, when I'm making videos on the Pioneer which I hardly do anymore, and the audio output is for non-critical monitoring.  But I hear no problems, no underwatery garbled sound like you get from way too much jitter, and no dropouts.  I'm not going to bother to measure it with my jitter meter today.  The isolation transformer may have bandwidth equal or greater to the coax to optical converters, which lose a lot of bandwidth themselves.

I turned out that the coax from the Pioneer wasn't the only source of problems.  There was also the analog output from the Pioneer.  The analog output is needed if you are recording from an analog source, as the Pioneer will not output analog sources to its digital ouputs.  I decided to do without that feature except when needed by keeping the cables unplugged.

It figured that analog and digital cables from the Pioneer were infected with the ground loop.  AND, if I were disconnecting just one thing at a time, as I did the first night of these tests, I would NOT catch problems like this, which is why the correct approach is to do what I finally did: disconnect all the cables not needed and add them back in one at a time.  AND it helps to have an accurate noise meter, because relying on auditory memory is futile.

There was also a problem with the analog surround outputs which go to a chifi preamp for adjustment and routing.  That chifi preamp has (uncharacteristically for preamps) a grounded plug, AND there is not external ground lift switch.  Even though the things is made like a brick pool house, I decided to continue with the safety orientation and not lift the ground with a grounding "cheater" adapter.

So instead I pulled out another isolation transformer, a Jensen CI-2RR for stereo audio, and connected that between the Yamaha receiver and the Chifi preamp.  Problem solved.

Jensen Iso-max CI-2RR

Ultimately with everything plugged back in and running (except the Pioneer LX-70 analog connections) noise measured 0.18 mV.  Hum is just about inaudible with ear to speaker (this "just about inaudible" can seem louder sometimes when it's quieter, making it essential to have a meter, though it would be more helpful if my meter only measured hum, which it doesn't).

I could have used another Jensen CI-2RR for the Pioneer LX-70 analog outputs, but I don't have any more spares.

Tuning the "Movie" EQ

 Nowadays I'm keeping my room more and more in "movie" configuration, with no chair in the "hot spot."  The closest thing is the loveseat in back.  But along the back wall, the hot seat EQ is very boomy.  So I created a second EQ for the back, which is the Movie EQ.

Well it's becoming clear that the Movie EQ might well be better for most background listening, which is what I do most of the time.  So it looks really like the Movie EQ should be the default, and the Hot Seat EQ should be the 'Special.'  Well, that's exactly how I did things in my previous generation of less-well-tuned EQ's, when I had "Normal" (now Movie) and "Boost" (now Hot Seat).

But the Movie EQ was a giant hack which I did, after months of tuning the hot seat EQ, I simply added a graphic EQ overlay to dampen the excess bass along the back wall.  I realized then I should re-do the Movie EQ from scratch, or at least so it isn't an EQ on top of an EQ, but the original EQ simply tailored for that position.

That was about the time I discovered the polarity problem with my DEQ, which made it complicated to do the in-position adjusting my method requires.  Then it turned out I could buy a brand new DEQ, and I did, and I now have that.  But then many other urgent situations arose: needed were new dishwasther, new computer, new phone, new security system, ceiling repair, foundation repair, under slab drain repair, and ultimately a new car, which I just drove home last week.  It's been a busy year, and that's just part of it.

But for a week, it seemed I had some time (which is now evaporating) and just did some measurements of the current state.  The adjustments are the same, but the hot seat has been moved to the side so the room is in movie viewing configuration but without the screen set up, which is pretty much the norm except when I'm doing Serious Listening, maybe once a week or so.

I'm using the iPhone 8 I used for previous measurements again.

First I measured the background noise:

Background Noise

Then, the response at the old "hot seat" location, but with the actual chair moved to the side:

Hot Seat Location Without Chair

There's a notable dip at 31 Hz, otherwise pretty smooth to 1k then rolled off as intended.  I don't remember that dip from the earlier measurements.  Anyway this is "invalid" without the chair at that position anyway, I just wanted to take a look.  Actually it looks like it may need some analyzing.  Perhaps something is wrong or changed.  It was nearly flat 20-1000 Hz.

And while I was doing this looking, I decided to try turning off the Bag End E-Trap, which is currently in the corner of the hallway connected to the living room, where there is normally a HUGE bass boom.  The trap clearly reduces the boom in the hallway and the first bedroom, but what effect does it have on the living room response???  It was supposed to help that by cancelling the boom which gets reflected back to the living room.

Above, but no E-Trap

Well, strangely enought, the no E-Trap version perhaps looks better, though the depression IS extended higher up, it doesn't go as deep.  Actually, it's not clear which is better, because the greater depression at 31 Hz probably isn't as audible as the broader depression going up to about 45 Hz with no E-Trap.  I decided to leave the E-Trap on for now, because at least it removes the boom in the hallway, and reflected bass from the hallway probably isn't great even if it does make the RTA response look better.

I repeated these measurements (made with my iPhone stand adapter, same as last year's adjustments) and got identical results.  It wasn't just random variation, the effect of the e-Trap on the RTA response is fully confirmed, it produces a deeper but less wide bass depression.

Either way, it looks like some fixing may already be required in the hot seat response, though it is still quite good.

Back at the loveseat, but using the hot seat EQ, things are much worse.

Back Wall, Hot Seat EQ

Let's see how well my Movie EQ fixes this:

Back Wall, Movie EQ

Well, it's not too bad below 125 Hz, which is about all the current setup which changes only the bass EQ can do.  It looks like I have to get another midi cable or something and control have two EQ's for the panels too.  In fact, fixing the irregular midrange response (which has may have something to do with hout it is 'flattened' at the hot seat) looks more important at this time, though the RTA is hiding the fact that the fairly smooth bass response is EQ on top of EQ, which intrudes some issues of it's own, so it is still workth re-doing the bass EQ for the Movie EQ so it's done simply with one set of EQ's.

******

I charged ahead and adjusted the new movie EQ by sweeping, cutting, and fine tuning with pink noise.  I was able to get both channels reasonably flat in the bass with just 4 PEQ's on the left and a remarkable 2 PEQ's on the right.  It's flatter than before on the pink noise.

I first used a -5dB "Gain Adjustment."  I'd never realized before testing it now that I could have a different gain adjustment in each EQ memory slot.  -5dB was still giving considerable rise in the bass overall measured at the back center seat.  So I went to -10dB on Sunday morning and that permitted adjustment to virtually flat, my new standard as of last year (I decided flat with no boosted bass "room curve" was the best of all).  (The other EQ, now called the Hot Seat EQ, effectively uses a higher bass level to permit filling the depression in the middle of the room without any EQ boosts as such, just lots of cuts.)

I whipped this up pretty quickly but I decided it was so good I'd better "ship it" as we used to say in the audio modification store backroom, as in ship it before we mess something else up.

I can now play Bass Erotica a full levels without it sounding just awful.  It's actually musical now, I can follow the bass lines in background positions all over the house, not just boom boom.

Left Channel, new Movie/Background Adjustment

Right Channel, new Movie/Background Adjustment

Right Channel PEQ's

Left Channel PEQ's

I was listening in background on the evening of September 14, and I decided it was too bass shy.  So I bumped the gain compensation from -10dB to -9dB, and reduced the 2-octave cut centered at 45.3 in the Left channel from -6.5dB to -5.5dB.   I allow myself to make small changes like these by ear when they also seem sensible too, even if possibly the measured result might "look" a bit worse.

It might not have needed this change in the center seat in back but elsewhere.