I have an autocorrelator in the garage. It gives about the same noise reduction as Dolby-B.
The I/O buffers were RC-4136 - essentially quad 741 opamps. The bandpass filters are LM-3900
Norton amplifiers. The 3900s are not in the signal path, just making control signals for the
correlator. The 4136s ARE in the signal path and are quite lame. A TL075 are the same opamps
as a TL074 but hase the same pinout as a 4136. There was a noticeable sonic improvement with
the TL075 amps.
I haven't used the Phase Linear in 30 years but it's still in the garage. There are several on eBay.
G²
I bought one for 100 bucks today. In the original box... pictures show it in very good shape. But as usual, the eBay seller just claims the light turns on but didn't run it.
You recommend replacing the 4136 for TL075? I suppose these are all DIP? Maybe I ought to put some sockets?
You're up in LA, I'm in The OC.
You recommend replacing the 4136 for TL075? I suppose these are all DIP? Maybe I ought to put some sockets?
You're up in LA, I'm in The OC.
The TFT monitor also used an integrator FM decoder. Dead straight transfer 'curve'.
They probably sounded great but the stations (analog TV and FM) generally used them
just to verify proper operation. I had one at the Madison Wis CBS TV affiliate in the
'80s.
G²
The panasonic STG7 frequency tripler really does the job, as it also triples the deviation. The 10.7Mhz was first tripled to 32.1Mhz and then downconverted resulting in a 800khz wide deviation signal. Linearity was perfect resulting in a 0.01% distortion figure, usually better than the transmitter ...
I definitely recommend replacing ANY 741 (or variants) opamps. There
are some small 'lytics in the signal path that would likely be good to
replace. You're right about DIP chips. I bought mine in 1975 and there
wasn't any SMD yet. The push switches will give you some grief but are
easily cleaned. Nearly all the processing is on plug in daughter boards but
the 4136 is on the mother board. I wouldn't bother with film cap
replacement as they almost never fail but at least check all the 'lytics.
The hardest thing will be locating the TL075s but if push comes to shove,
I believe there is room to make an adapter to use a TL074. I always try
to do mods that use no trace cuts hence the adapters if needed.
G²
I found in re-mastering old 1/4" master /copy master tapes to DAT, that one of the biggest problems
was masters encoded with DBX & Dolby A.
The simple reference level tone was not always enough for a good transfer. The worst cases I found were Dolby A.
After obviously determining IEC / NAB EQ , there were occasions where PRE-DECODING equalization was needed
to solve 'tonal balance pumping'. This is quite different to post decoding test-tone alignment.
After DBX entered the SEMI-PRO domain, it turned out that there was a total of 3 different decoders to pick from,
you just had to find the right one
( I think after hearing different pressings of some identical albums, remastering requires a passion plus 'golden ears' )
was masters encoded with DBX & Dolby A.
The simple reference level tone was not always enough for a good transfer. The worst cases I found were Dolby A.
After obviously determining IEC / NAB EQ , there were occasions where PRE-DECODING equalization was needed
to solve 'tonal balance pumping'. This is quite different to post decoding test-tone alignment.
After DBX entered the SEMI-PRO domain, it turned out that there was a total of 3 different decoders to pick from,
you just had to find the right one
( I think after hearing different pressings of some identical albums, remastering requires a passion plus 'golden ears' )
I would guess a stereo solution is preferred as dual mono will not keep the center stable
The Studer A726 uses a coaxial cable for frequency to phase difference conversion, followed by a multiplier-type phase detector. It should be nearly perfectly linear when used with square waves (and the limiter produces square waves).
It's off topic anyway, because I think this thread is about undoing the damage done by dynamic range compression on the studio or transmitter side.
The studio side compression like the popular orban processors allowed the transmitter to deviate more than regulations allowed to create the louder experience. This worked fine as long as the receiver had sufficient received signal strength, to allow proper limiting, and the actual IF bandwidth was increased due to the limiting effect. When this was not met, a good chance was that the strong deviation went outside the IF bandwidth resulting in distortion.
You never worked in a braodcast facility. You have 2 parameters that MUST be obeyed. Spectrum
and power. At least in the US you have to stay in those limits. The Orban processor does NOT
change the maximum modulation depth. Analog TV max modulation is +/- 25 KHz. Analog FM is
+/- 75 KHz. AM transmitters are equally difficult. If you go less than 0% power you station splatters
all over the place and you're outside the spectrum requirement. I was never an AM radio guy but I
believe the positive modulation can go to 125%
G²
In my area most FM transmitters are semi ligit, they pay VAT but there is no official spectrum allocation. As the link from studio and processors to the actual transmitters is mostly analog, the deviation is manually set, with the resulting possibilities of error. Some operators do not even have a deviation meter. The only thing they know to do well is RF output filtering with cavities as they combine more freqs on a single antenna. any possible mixup to the airtraffic band should be avoided at all cost, as that results in a direct action of the authorities. As long as the transmitter power stays below 1kW the operators are left free. A bit of a leftover of the franco dictator days, when illegal radio was the basis for the current political parties .
Looking at the output stage - I am not that convinced that the station is the main culprit. Seems like some "taming" is happening also in the tuner.
If it were my tuner then I would replace the lytics in signal path and test reducing Cg83 and increasing Cg85/87.
Adding local reservoir capacitors to the power rails near the opamp would probably not hurt either.
That translates to ca 5 kHz -3dB cutoff frequency?
12 Hz is really not worth mentioning (except - what is tits practical benefit?) but usually the capacitors in signal path are larger than these two in series.
Bottom line is - higher frequency content is cut off? What is the reason for that (especially when the "technical" signal filtering seems to be already done (Flg6 etc)?
Sorry for the ignorance but FM signal has not been my specialty
Edit:
As comparison Onkyo T-4090 has 25, 50 and 75usec switchable by user (and no further filtering):
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