UTC y-6431 trafo info

pucho812 · Feb 1, 2005

Went through the meta's and couldn't find any info. I was hoping someone had info on this. Appears to be a input trafo on a fairchild unit I picked up. but no drawings on it suggestions?

CJ · Feb 1, 2005

Fairchild unit? What Fairchild unit!

Those OEM catalogs for UTC are really rare.

I think it's similar to a UTC A-10. 1:10 ratio.

pucho812 · Feb 1, 2005

Fairchild unit? What Fairchild unit!

like a kid in a candy store. :green:

It would be the one I am going to post pics of later today. I asked about it b4 not knowing what it was when I got it for 100.00. It's a fairchild conax model #602. It was used in vinal mastering. IT's a stereo tube high frequency compressor used to keep high freq in check when cutting discs. My idea is to remove the low pass filter(I think it's a low lass) well anyway the inductors that makes it a high frequency comp and turn it into a full bandwidth comp and use as a buss comp. I have started to map out a schemo/block digram as I have yet to find one. when my buddy comes over today I will start a new thread with pics.

CJ · Feb 1, 2005

This is all I have on the UTC:

"All I have here is the UTC Y-6431 number . I did go down and sweep it after the last transmission and it checks out to be a 1: about 9.7 or 600:55,300 ohms at 1000 cps with an open circuit rise at 10 DB at 40,000 cps. They sure are beautiful looking coils. UTC has not returned my calls. Okay, the A-10's are a 1:10 step-up so these could be used for inputs instead of the more expensive 6431's. You could use a HA-100X or LS-10X also. Almost any 1:10 will work. I think the 6431 was a special order although Fairchild liked to use available parts all the time because it is good sound business practice"

NewYorkDave · Feb 1, 2005

I don't have a Conax schematic, but I did find a fairly detailed description of its principles of operation from a person calling himself "8-H Haggis."

It was an audio-processing device that was
ubiquitous in all FM stations, recording studios,
and disk-cutting labs in the late 50s through the
60s...a hybrid valve/diode device that was used to
prevent overload on recording or FM/TV
broadcasting.

The Conax (for 'constant accelerator') was a
unity-gain balanced amplifier, which utilized a
shunt clipper circuit consisting of crystal
diodes. Since the topology wasn't really
patentable, Fairchild locked up the actual
clippers in an epoxied shell...I know what was in
there, because a friend of mine sacrificed one to
a hammer in order to investigate it!

The input stage had a variable equalizer circuit
(LC, I think) with several pre-emphasis curves
that could be selected by a 5-position rotary
switch. One of the curves was a close replica of
the 75-microsecond preemphasis of FM broadcasting;
others were more gentle or steeper.

The idea was to feed your audio through the Conax
and "pre-distort" it by clipping the highs, so
that their output amplitude would be below the
tape saturation level (or under the modulation
ceiling of FM.)

However, the crude diode clipping introduced an
incredible amount of harmonic and intermodulation
distortion; in addition, it sliced transients off
and caused a sonic rebalancing that had a tendency
to effectively increase midrange content, while
preserving a smeared, low-amplitude replica (with
lots of added distortion components) of the
original highs; so the overall "sound" was much
brighter than just "turning down the treble."

This gadget -- and later all-solid-state devices
like the CBS Recording Volumax -- would have this
kind of an effect on, say, a cymbal crash (an
instrument that I used to wield with enthusiasm in
student orchestras about 150 years ago):

The original cymbal sound on the mixer line goes
"CRASSsshhh..."

The output of the Conax sounds like
"tssssss..."

(Silly thing to try to explain this with words,
but recording engineers will immediately hear in
their heads what I am trying to convey!)

If you turned the unit to 'No. 5' or fed in a
line-level that was a bit too hot, the clipping
action was moved down into the midrange and low
frequencies. Then the output sounded like an FM
receiver tuned off-channel!

Even the earliest non-oversampled CDs did not
inflict this kind of damage to the sound. I found
the aural signature so distressing that I devoted
nearly 10 years of my life and career to helping
develop and market the next generation of audio
processing equipment that would not desecrate the
sound of classical instruments in full cry!

Yours,
8-H Haggis

Robert Orban writes:

In the Region 2 countries, 75µs pre-emphasis is used in FM and television sound transmission. This pre-emphasis is up 17dB at 15kHz and can cause severe over-modulation if its effects are not controlled. The obvious solution - placing a wide-band peak limiter after the pre-emphasis filter - proved unsatisfactory because high-frequency overloads would cause severe spectral gain intermodulation: cymbal crashes would cause the sound to literally collapse. The Fairchild "Conax" (originally designed for disk cutting) was often used to ameliorate the problem. This device divided the audio into two bands with a 1kHz crossover and applied pre-emphasis, clipping, and high-pass filtering to the upper band. The high-pass filter reduced the difference-frequency intermodulation caused by the clipper, yielding reasonably acceptable sound.

So it's a clipper, dog, not a compressor. I don't think you're gonna wanna use this as a buss comp. :wink: It would be less work to put your mix through a Rat pedal.

pucho812 · Feb 1, 2005

you guys rock. so smart and knowledgeable. I hope to be like that one day.

The input stage had a variable equalizer circuit
(LC, I think) with several pre-emphasis curves
that could be selected by a 5-position rotary
switch.

That would be the 5 position threshold switch.
I was missled by the threshold switch and left,right gain pots. :evil:

correct me if I am wrong if it's a clipper wouldn't that mean it is more close to a brickwall limiter and if I did remove the crossover,it would be acting more like a stereo limiter?