Radio Frequencies

After reading this blog, I decided a Tektronix 496 was a reasonable spectrum analyzer for me to look at RF's for my tuners and antennas, FM MPX signals, digital SPDIF signals, and audio frequencies when I want to see up to 100kHz or higher (the 496 goes from 1kHz up to 1800 Mhz, my old HP 3580 only goes to 50kHz).  The lowest center frequency is 1kHz, and the highest frequency is 1800 Mhz.  Obviously it's no good for wifi or things like that, and I would have liked to view wifi signals, BUT even the boat anchor pricing goes up another $1000 or more for spectrum analyzers with 2Ghz and above response--those microwave analyzers are still in heavy demand by professionals.  There's much less professional concern nowadays with mere VHF and UHF, so analyzers limited to that range are comparatively cheap.

While I'm slowly (very slowly) making progress debugging my Acoustat speakers (each new test requires 1-2 weeks "to be sure" because the problem is intermittant), I've decided to indulge my long running desire to get involved with...radios of all kinds.

I was blown away by the capabilities of the 1-30Mhz Icom IC-7300 and have one of those on order (due to recent rebate promotion, they were sold out so I'm still waiting for mine...but will have the assurance of a fully updated unit and still get the rebate--I hope).  I'm also planning to get CB radio (always wanted one of those) and a scanner.  I've started buying and setting up antennas for each, and will get them all professionally grounded with ground rods and bonded ground back to the main house ground rod.  Also finally I'll put up a rooftop antenna for FM, but it won't be my APS-13 which has been waiting in it's box for more than 10 years.  Sadly that's still to complicated because I refuse to have any antenna actually on the roof, so I need side mounted mast or tower, which I continue to think about how to do.  Professional antenna installers aren't interested in such things...they'll attach tiny HDTV antennas to your chimney or roof, and those are the only options they're interested in anymore.  I may get some hams to help me with my big antennas someday.  But first, I'm planning to become ham myself, with some smaller simpler antennas.  For FM I'll be using either a Godar FMDX 100 or Magnum Dynalab ST-2, which I can simply tack on to fascia board on the side of the roof at the peak (no massive tower or mast required).

One of the essential things for installing and comparing antennas is an antenna analyzer.  I could have used my Spectrum Analyzer if it had the tracking generator, but it does not.  So, instead, I got a Sark-110, which is a tiny miracle, which gets great reviews.

Here is a tutorial and video on the Smith Chart often used for understanding antennas.

Here is Paul's Antenna Attic about FM antennas.  I have an APS-9 and Radio Shack 15-2163 still in their factory boxes.  Sadly those will have to wait until I get some help installing them.  Whips are a comparative snap to put up, except for correctly handling the grounding which should be done by an electrician.

Measuring a trap using Sark 110.

List of Pirate Radio Stations on HF Underground.

Sherwood Engineering's tests of HF receivers.

Hardcore DX on HF (aka Shortwave) stations.

Factory brochure on Tektronix 496.

"Super Antenna."

Dave's Shortwave Receiver List.

Roger Russell's McIntosh Loudspeaker History, Part 2.

The Audio Expert (Ethan Winer).

Audio Myths workshop at Audio Nirvana Resources.

The JBL SA-1600 complementary symmetry amplifier reviewed by Julian Hirsch in 1966.

Best Antenna Analyzer for the money.

Poltergeist

Sunday night I played KPAC for 6 hours without shutdown.  Then, sometime after I let the cat back in, and was getting ready to take a shower, I went out to turn the amplifier off.  The amplifier was already off.  The cat was not far away in the living room.

Perhaps the cat rubbed or pressed the relatively soft touch button in front of the Krell.

I think a cat could learn to do this.  I know my cat loves to rub against the front of the Krell, though also has learned that I don't like it.  But, the fact that I don't like it makes it something the cat might do to get back at me when I'm not paying enough attention.

I know now this hasn't caused all of the shutdowns.  Because several have occurred when I was right in front of the amplifier listening to music.  (That hadn't been the case until a few weeks ago.  Until then, all of the shutdowns occurred while the amp was playing for background music, which is how I listen to music 95% of the time.)

This did not fit the now familiar pattern of shutdown within 60-120 minutes, that happens about 50% of the time.  It "might" be a different mechanism.

It certainly didn't explain the two shutdowns this weekend (1) with the Krell playing F-26 through Lavry as source, and (2) with the Krell playing F-26 through Sonos, both which involved playing in both channels, since in both cases, the cat was out.

The 3rd and final test was playing right channel through the now-right (formerly left) unmodified speaker with the NOS interface.  That didn't cause a shutdown for 6 hours, and by then I was strongly believing this speaker and channel were OK, it was the other one (that seemed to have groove in the variable resistor, and has the upgraded capacitor outside) that had issues.

I'm not taking that guess as disproven yet, it *could* be the cat or some other "3rd" mechanism this time.  But from now on I'll need to control for the cat possibility.  I've figured out I can leave a polycarbonate DVD-Audio case leaning in front of the amplifier, hiding the button, and meaning that in order to press the button the cat would need to knock over the plastic case, so it would also show that it had been done.

Here's a short list of remaining open hypotheses:
1) Damaged variable resistor in one or both speakers.  (Could explain some, or all shutdowns if both.)
2) Damaged big capacitor attached to case of modified speaker.
3) Damaged factory capacitor in NOS interface speaker.
4) Amplifier changes during last two repairs.  (This would now be the biggest bitch, since the amplifier has already been checked out for this problem by the factory, I'd have to have a specific shutdown causing protocol for them to find problem, or chances are they never would.)
5) Now running on two AC circuits (a change made earlier to prevent shutdowns, but possibly causing some too).
6) Teflon speaker wire (another change made to prevent shutdowns, seemed to work for one day).
7) Change to F-26 causing some inaudible spurious output that causes shutdown even over Sonos (most shutdowns recently caused by FM, since it's too hard to keep music playing without using FM).
8) Cat pressing power button somehow, to play with me (could explain some, but not all).
9) Burst of RF energy from something.  (I had turned off buglight on Sunday night, so that didn't cause Sunday night shutdown, but it could have caused many previous shutdowns.)  This could explain shutdowns with no other explanation.
10) Deteriorating AC power contacts.

Another unexpected result

I'm playing KPAC-FM, the classical music station, and it is delightful.

The F-26 tuner is hooked to a Sonos Connect input, then the digital output of that very same Sonos feeds a Belden cable (terminated by Blue Jeans Cable with Canare "true 75 ohm" RCA's) carrying SPDIF digital to my Tact RCS 2.0 Preamp.  Thus is an "analog source" converted to digital for processing by my DSP's for crossover and EQ and time delay.

Actually, for high class sources, I prefer to digitize through my Lavry AD10 digitizer at 24/96.  The Lavry feeds a Geistnote AES cable to the Tact RCS.

However, a long time ago, back when I had all the equipment in front and was playing the Krell, long before the Capacitor Service in March 2017, I was playing a Pipe Dreams show on KPBS, using the Lavry instead of Sonos to digitize the output of the tuner.  And the Krell shut down.  That is the very first time I remember such an incident.  I figured right then that there was a motorboating DC or high frequency burst that is not nice.  And digitizing through the lowly Sonos somehow suppresses it.

Perhaps it's just a matter of 96kHz vs 44.1kHz sampling.  Or it could be transparency to DC, quite likely the consumer friendly Sonos has a steep high pass keeping DC out of the system, whereas perhaps the Lavry goes deeper in the low Hz.

I resumed the Lavry connection, praising it as far superior, in May 2017.  And that was actually the first time a shutdown occurred since I got the Krell back from Capacitor Service.  It was a few days before the high power incident that blew speaker fuses and which I still believe was responsible for a fundamental bit of destruction that has been causing many, if not all, of the shutdowns.

Right then, I figured the problem playing the F-26 through the Lavry was AC power limitation, with the subs demanding current at the same time as the amplifier to meet some demand caused by a presumed low frequency burst (which I've never heard...since the amp just shuts down).  The Krell must be allowed to scale up it's AC power consumption fast to meet any higher bias plateau level the computer with in it demands.  If there is any glitch in scaling up the power consumption, it will shut down for "inadequate AC power."  Actually, this happens when the rail voltage regulators, which are rare in any power amplifier (but there are a few other very high end amplifiers, such as the Mark Levinson ML2, which have this feature), run out of regulator margin...which is precisely because the AC hasn't kept up.

Anyway, it is quite possible that the problem tracking down the problem with amplifier shutdowns is that there is more than one process involved that causes the shutdowns.  One might be that running the F-26 through the Lavry simply creates a problematic signal.  The other one, which I believe must have been caused by the high power accident, has yet to be determined, but as of the beginning of this weekend was hoped and believed to be the LF transformers inside the Acoustats.

Well, so I was thinking Sunday morning as I started playing KPAC through Sonos, with the LF transformers in the Acoustats disconnected.  This was surely the issue, more than one cause of the shutdowns, and by avoiding the F-26/Lavry input, and disconnecting the bass transformers, I had isolated both of them.

And I was so sure of this, I started writing this blog post after it had been playing for 90 minutes.

And then, there was a shutdown, a shutdown that could not be explained by either theory.

I have noticed that sometimes, also, that Sonos blanks out for about 1-2 seconds, or maybe it's the tuner blanking out.  Perhaps that happens when Sonos is suppressing some DC from the input or something.

Anyway, this result doesn't disprove the idea that I should avoid the F-26/Lavry input.  That was known to be problematic in the distant past.

But for years and years I played the F-26 through Sonos without shutdowns.  So that is most likely the "new" problem I am trying to find.

At this point, sadly, I'm out of good theories.  Back to there being a malfunction in the Acoustat attenuators???

I concede it could also be a problem with the Amplifier, though the amplifier was just checked out at the factory.  But I won't make any headway with that until I have a consistent explanation of the problem.  I may need to measure voltages in and out.  Which would be another major challenge...I'd have to build a custom attenuator to protect my measuring recorder inputs.