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.

Eisenson's Revenge Chapter 99

Eisenson was the audio salesman and tinkerer who my friend George will never forgive for having an out-of-phase speaker system.

I myself have made so many major mistakes, often for weeks or months at a time, that you really do have to wonder.  Of course I believe that you can get an intoxicating effect, not to mention appreciation of music, or just plain old enjoyment out of a seriously out-of-whack sytem (as long as it doesn't sound extra harsh or annoying).  To deny that is to be a bit smug, I have always felt.  Also, one can't always be deploying one's inner audio engineer to ensure that all aspects of reproduction are technically correct.  Most of the time, one simply wants to enjoy.  I know Eisenson got great pleasure from the far reaches of the high frequency response, and perhaps when paying most attention to that he ignored the reduction in bass (or it was even helpful...).  It has always been my view that no one 'reproduction' is perfect, and many are good enough in one way or another to reveal some facet of the music with greater clarity.

Well in my latest mistake, I apparently had the subwoofers totally turned off since some experiment, perhaps written about here, from weeks ago.

I first noticed that when I selected the "movie" mode (which reduces bass in the periphery to make it less peaky there) it had little effect.  Then a week later I figured the exact cause of this discrepancy.  First I noticed one sub turned off (I remembered thinking "I'll notice this right away") and also the DAC muted (I had to do that for the other channel).  I was doing some kind of impulse test, perhaps before the first recent LP recording a few weeks ago).

My crossover is at 125 Hz, so a sub loss cuts out quite a bit of real bass.  But it all sounded fine.  (I wasn't doing much if any serious listening, the room has mostly been set up for showing movies and I've been to lazy to move the listening chair into the center.  But I might have listened to an LP or two, thinking it sounded a bit dry.  And then I wondered why recordings sometimes sounded better on my kitchen system when I was mastering them than in my living room system where I was recording them.  All clues I ignored, until I didn't.

Re-testing the antiskating force

 I've picked up some used records (from deceased or moving audiophiles) and started recording them (while often inspires me to record some of my own--which are usually better).

Occasionally I've noticed some groove chatter in mostly one channel which made me think antiskating was wrong.

I always run my Dynavector D17 version 3 (Diamond Cantilever) moving coil cartridge at maximum tracking force, 2.25g, but for awhile around 2022 I was running the antiskate near the maximum setting of 3.5g on the Ittok LVII.  That had two benefits.  For one it seemed to track better on some high velocity test I used, and it seemed to provide useful additional horizontal damping.

At some point I changed the antiskating back to 2.6...I now can't remember if that was just "temporary" (because it passed the silent groove) or part of a series of tests (perhaps reported here).

So the present mistracking was bugging me, perhaps 2.6 was too low and I needed to go back to 3.5.

I first tried the silent area (not a "groove" as such) test on my Orion test record (the one I bought most recently as "unused").  2.6g antiskating force nails it.

But it always occurs to me that silent area tests don't simulate the additional skating force that occurs in heavy modulation.  So I ran the 5 band tracking force test on the same Orion record.

That's a killer test because, contrary to what the announcer says, there are probably few if any cartridges that can play all 5 bands.  It starts at the maximum nominal level and goes up from there.  It's harder than the tests on Shure test records.

With 3.5g antiskating, I couldn't play band 4 without serious distortion.  With 2.6g antiskating, I could play band 4 with only minor distortion.

I also compared needle drops and didn't see any improvement with 3.5g antiskating.  In any case, the tiny resonances around 10 Hz are now looking to be rumble related rather than horizontal arm resonances as such.  Other turntables produce that too, though it often reaches higher in frequency with bearing noise.  The Linn keeps all it's motor and bearing noise below 10 Hz, so even though it's sizeable there it produces less coloration overall.

So it looks like 2.6g is indeed the correct antiskating adjustment, and some used records may just have asymmetrical record wear (possibly from misadjusted antiskate).

I still think an arm with much more horizontal damping would be desirable for the Dynavector cartridge.  The ultimate arm for the cartridge is the Dynavector arm with magnetic adjustable damping.

Antenna Grounds Tested

 My kitchen is now connected to 3 external antennas, two with FM whip antennas, and one shortwave antenna.  Shortly I will get foundation repair and some leveling which could potentially disrupt the integrity of their grounding (to underground rods which are "bonded" to the main panel ground through a long underground wire).

All 3 wires have coax cables coming into the house.  The shield of the coax cable of each is connected to ground in external grounding boxes.

I disconnected all 3 coax cables from their receivers and measured their voltages and resistances to one another.  There were trivially small millivolt voltages I didn't write down.  The resistances were consistently around 0.5 ohms, 0.56 was my first measurement from the front to the back coax.

But this only proves they are bonded together, not that they are bonded to house ground.  So I got a 3 light AC wiring tester, for which one line lights up if the ground is good.  I plugged that tester into a 3 to 2 wire adapter to bleed off the ground test current.  I then plugged the 3 to 2 wire adapter into a bottom ac outlet so it did not contact the plate screw (which would ground it).  I connected a wire to that to the ground tab and now I can test anything for being an "acceptable" ground to this simple tester.

I tried the sink faucet and the dishwasher panel, they are not acceptable grounds.  The "grounded" light did not light up.  (The dishwasher is perhaps "multiple insulated" and the "stainless steel" is really coated in non-conductive coating.  The sink faucet is connected via PVC pipes.)

But the Grounded light did light up when I connected the wire to the shields of each of the 3 coax cables coming from outside.

I connected an ammeter in line with the wire going to the ground adapter, and measured 1.336 mA current with each of the 3 antenna coaxes.  This was actually better than the 1.333 mA I measured going back to the ground on the same wall socket.  (By contrast, there was only 0.05mA current measured to the kitchen sink faucet, though that was noticeably higher than not being connected at all, or me just holding the wire.)

Now I have some measurements I can repeat after the house leveling.

House ground resistance is supposed to be below 5 ohms.  I'm not really measuring that, but it appears my antennas and AC outlet grounds are no more than about 0.5 ohms apart, which represents the resistance of the ground wires and coax grounds, and indicates they are all bonded to house ground.

*****

After the foundation piering, I retested 2 of the grounds.  The third ground is temporarily disconnected and needs to be moved but is probably ok.

I first measured the ground to the roof peak antenna, the Magnum Dynalab ST-2.  At first it read 1.3150 ma, or about 2% lower than before.  But testing the actual house ground, it was also reading about 2% lower at 1.313.  Then when I tested the ground to the Godar 1000 antenna, it measured 1.32ma.  Retesting the other antenna again, it was now reading 1.32ma also.  So it looks like 1-2% fluctuation is normal and comparing antenna ground current with house ground current at the same moment works.  (It could be the "hot" line that is varying slightly, because what I am measuring is current flow from electrical hot to test-ground through a resistance built-in to the ground tester.)

Before the foundation work was done, I unscrewed all ground wires from their ground blocks outside but left them touching for protection.  I also loosened the plastic shields around the ground wires from being attached to the house.  Before doing the re-test, I screwed the two ground wires being tested back in to their grounding blocks outside.

Hum Bug Fixed

Noise at left speaker terminal (1V scale)

My kitchen system has had an increasingly awful "hum" (mostly 60 Hz AC line frequency and harmonics) for the last 3 years or so.  I finally had to do something about this, ironically, on Christmas Day 2024.

I used to pay very close attention to ground loops and other hum causing issues in the kitchen audio system ever since it first started coming together around 2005.  It's always been a very complicated system including VCR, digital video recorder, multiple monitors, inside and outside antennas, Tivo, big network switch, computer with loads of peripherals, etc.  I took great care when adding each new device to ensure a ground loop was not being added, and if it was, I found some way to eliminate it.

But what happened around 2022 is that the DEQ 2496 that was handling my subwoofer EQ, and which I was also using as an RTA to verify that the hum at 60 Hz was near zero (typically -110dB), summarily died after about 10 years of use as they have tended to do.

I then struggled to get the subwoofer working just as it had been before, but using the EQ built into my HTR receiver (a Yamaha HTR-5790).  But unlike the Behringer, the receiver lacked the balanced outputs to drive the small chifi preamp which gives me a subwoofer level control.  So my carefully constructed grounding scheme, reliant on a balanced connection in the middle, was no more.

And lots more stuff happened too, I just wasn't keeping track of things anymore because I didn't have a handy RTA to keep checking that things met the same hum free standard.  So I didn't much bother, and as might have been predicted, it just kept getting worse and worse as I added new features and/or devices.

Then last week I discovered to my horror that I had been connecting the Hafler 9300 power amp to the preamp output of the HTR-5790 using a 2000's vintage 12 foot Radio Shack standard interconnect.  Betting that was a problem, I ordered a new 13 foot Blue Jeans LC-2.  These are RCA terminated flexible coaxial cables with the best shield coverage you can get, along with the lowest capacitance, and they are as robust as it gets.

But as I've been rather busy with parties and preparations prior to Christmas Day, I didn't get around to installing the cables which had arrived last Friday until after my big Christmas Day dinner (a buffet with friends).

I wanted to make sure I had good before and after measurements, so I got out my Meguro MN-455B noise meter, which is a very useful thing to have (and I needed to have a real electronic "noise" meter since the 1970's, there has been hardly any other way to get "A" weighted electronic noise measurements, but I only got this wonderful Meguro in the 2000's on ebay).

Because the Revel M20 speakers have widely spaced connectors, I couldn't just plug in my coax-to-double-banana adapter into the 5 way binding posts.  I had to rig up an extended connection for the minus terminal using two more double bananas and a short wire.

When it was all together, I was shocked to discover, that with the Yamaha actually turned off, but the Hafler on, I was getting 0.88V "A" weighted hum and noise at the speaker terminals.  No wonder it was beginning to get annoying.  It made no difference whether I had the Yamaha powered on or off.

I removed the input connections to the Hafler, and the audible hum vanished.  I could not hear anything from the normal listening position, and there was just a trace of hum at the speakers themselves.  But the A weighted noise level had only gone down to 0.4V.  That was because the Hafler 9300 has a fairly high 47k ohm input impedance, and a 500 kHz bandwidth, and the "A" weighting isn't even defined above 20kHz (but is often just extrapolated, not brick-wall filtered at 20kHz because it's inaudible).  I'm not exactly sure what the Meguro meter does on the "JIS A" setting.

But open inputs, a high input impedance, and high bandwidth ensures there's going to be a lot of high frequency noise, even if there weren't much anyway.  That's what I think is going on...the hum went away but the HF noise was even greater because of the now open inputs.

I could have measured with shorted inputs, as John Curl himself told me I must do in a message after I complained about the noise level in my HCA-1000A varying with input level position.  But I didn't bother this time, because I know the amplifier is near perfect anyway.  I didn't need to test the amplifier hum, what I wanted to do is find a way to have it hooked up without hum.

So I rolled out the new 13 foot cables, only to discover that 13 feet was actually way more than needed.  It left me with an extra 3 feet curled up on top of the amplifier (until I found a better idea).  What this revealed was that the original 12 foot cable, and I pulled it out to be sure it was a 12 foot cable, was twisted around so much stuff that it was only barely long enough, even though it should have had 3 feet to spare.

Even with the excess cable piled on top of the amplifier, but plugged into it, the audible hum was gone and the noise level was now 0.19V.

New cable with excess piled on amp, first time

But finding the Blue Jeans cable was too long left me in a quandry.  Do I send the cable back, and get one made to the correct length?  I wondered if Blue Jeans had cut the cable too long, so I removed it.  Only to discover that they had just barely cut the cable by an inch or so longer than the 13 feet, not including the jacks.  Radio Shack cables barely meet the advertised length WITH the jacks.  Now it was clear how much the Radio Shack cable had been wrapped around lots of stuff, probably mostly AC line cords on the floor.

I still couldn't make up my mind, so I reconnected the LC-2 cables just to have something working.  But now the hum level had gone up, to 0.6V.

WTF!!!

I quickly discovered that even with the best-in-class shielding of the LC-2, it makes a hell of a difference how the cable is laid with respect to AC line cords and other stuff.  Particularly bad, it seems, is the back panel of the UPS that powers most of my system.  If I run the cable next to that back panel, and it tends to fall that way if I am not careful to avoid it, hum goes way up.

Hum came back when cables ran this way

Rather than experimenting with each possible variation, I decided to just do-it-right from the start, by arranging the cable to be as as far away from everything, and especially AC power cords and the UPS, as possible.  I used my AV stapler to staple the LC-2 cables to the wall (the staples are just barely big enough, and a lot of them failed to attach properly and had to be removed, but it seems to be holding now) way above everything, then over to the table leg where they are held on with velcro ties, then down to the amplifier.

This got me to my lowest measured level, but not actually much better than my lucky first hookup, at 0.18V.

Noise after re-routing new cables

It sounds hum and noise free even ear to speaker.

I used to ignore hum and noise.  I started taking it seriously around 2002 when I found my incredibly well built 1978 Pioneer Series 20 D23 4 way electronic crossover had developed a ripple-hum (around 120 or 180 Hz).  That was what ultimately led to my using digital crossovers, and finally DSP based crossovers.

The kitchen Hum had become very irritating when there was no music playing.  But I never noticed it when music was playing, and even with it present I still felt I could make very fine audio judgements.

Pioneer TX-9500 II

Pioneer TX-9500 MkII (top)

I bought this Pioneer about 8 years ago, and it finally went up into my Kitchen audio system today.

It's a fine sounding tuner, in the 3rd upper rank at least.  It's considerably more musical sounding than the Kenwood 600T and all the other silver Kenwoods from the 1970's.  Everything sounds sweet and lively.  Noise seems separated from the musical image (sadly, the Kenwood 600T does not do this).  But the noise is not as low as with the 600T.  The 600T is at least as sensitive and selective, if not slightly moreso.

I'm ranking it sonically just below the Kenwood L-1000T, and then the Pioneer F-26, in the 3rd rank of tuners which includes the Sony 730ES, Sansui D-99AMX, Yamaha TX-1000, and Marantz 20B.  The Pioneer is better sounding than a lower set includes the all the 70's Kenwoods (600T, KT917, KT7500, KT8300) I have listened to and the Onkyo 9090 MkII.  And then, most strangely of all, not sounding as good as the others mentioned, at the bottom sonically of all the super tuners I have, the McIntosh MR78.  (MR78 is plain ok sounding, but many tuners like the Pioneer TX-9500 MkII have a wider bandwidth and even lower distortion detector and MPX that give more lifelike detail without more brightness--with the MR78 already has plenty of but it doesn't help the apparent relatively dead and boring sound.)

Compared with the Pioneer TX-9500 MkII, the Kenwood 600T sounds cold, sterile, flat, uninvolving, much too bright and steely (unless high filter activated), but also slightly quieter.  In short, the noise and some of the life have been sucked out of the music with the 600T, but not with the 9500 MkII.

But I should continue to refrain that the 600T is a fine sounding tuner anyway.  If you had never heard anything else, you'd think it was fine.  Low noise and distortion, high performance.  But then fire up the 9500 MkII, and everything comes alive in a way you wouldn't have thought possible.  

(MR 78 is like the 600T in these regards, but differently.  If all you ever listened to was MR 78, you'd think it was fine.  But while the 600T adds a certain fuzziness to the sound because it has a resolution-losing but very wideband detector, the MR 78 adds a slight hardness to the sound because it's just trying too hard with a not-quite-wide-enough-wideband detector.) 

The Pioneer Signal Strength meter actually tells you nothing about the signal strength.  But it's a pretty good measure of signal quality, sort of like the inverse of "Multipath".  When you get to the top of the meter, no matter how strong the signal actually is, you're getting sound about as good as it gets.  Most stations vary from 4.5 to 5.  It's even more difficult than most to use as a precise tuning meter, so a scope hookup is recommended.

The TX-9500 MkII uses a very linear and wideband FM detector proprietary to Pioneer (P.L.B.) that works on the principle of being a phase compensated delay line.  This may have been Pioneer's all time best detectors, also used in the F-26 and F-28, all made in the late 1970's, which was a golden age for Japanese hifi because of the exchange rate.  Later, in the 1980's, the Pioneer F-91,2,3 series in the 1980's got progressively worse in terms of noise and distortion, something David Rich lamented in a classic Audio Critic tuner review in 1990 (while admitting that he himself had an F-93 because on some very weak channel he liked, the fake stereo it did was the best sound he could get).

In the wide mode, there are no ceramic filters in the IF path, only tuned filters (I used to think that was crucial) and a SAW (Surface Acoustic Wave filter, computer designed whizbang technology which became available in the late 1970's).  Ceramic filters are inherently noisy and "acoustic," so having all or mostly tuned filters could provide a "purer" sound.  But tuners using all or mostly tuned filters include MR 78, Marantz 10B and 20B, Sumo Charlie*, Kenwood 600T and KT917 in wide mode, and all classic tube tuners, a mixed bag sonically, and many ceramic-filtered tuners sound fine.

(*Inspired by the Marantz 10B, James Bongiorno used all tuned filters in the Charlie, except just one wide tuned ceramic, because, as he once told me when I asked him about this, "You need something to kill the crap way out there."  Well that's similar to Pioneer using one SAW in the TX-9500 II wide mode, except that a SAW is more sophisticated than a wide ceramic.)

The Pioneer front end is basically the best design you can do with a 5 ganged air capacitor, and more gangs are sometimes wasted in other super tuner models.  Being based on ganged air capacitors (turned by the tuning knob) rather than varactors has advantages in front end dynamic range, which is why many classic tuners are so good without being anywhere near as "sophisticated" as later tuners.