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Cassette deck audio limiter, how does it work?
Cassette deck audio limiter, how does it work?
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Old 18th September 2019, 06:54 AM   #31
Mooly is offline Mooly  United Kingdom
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Cassette deck audio limiter, how does it work?
FET's can work well but the control voltages needed wouldn't fit in with this circuit as far as I can see.
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Old 18th September 2019, 11:35 PM   #32
PRR is offline PRR  United States
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Quote:
Originally Posted by lcsaszar View Post
What about using a jFET as a variable resistor instead of BJT?
There have been *hundreds* of limiters made since the 1930s. Many-many of these have been published and are easily found.

The BJT limiter is notable mostly because it is CHEAP. But even in the world of cheap guitar pedals, the JFET was more often used.

I posted a list of links above. Skimming that and following where it goes will give you far more background than would fit in any Forum.

An iconic FET limiter is the UREI 1176:
1176 Peak Limiter - Wikipedia
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Old 21st September 2019, 04:35 PM   #33
RJM1 is online now RJM1  United States
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Then there is always THAT corporation products that produced IC versions of the dbx VCA's and RMS detectors.


http://www.thatcorp.com/datashts/dn125.pdf


"The one knob squeezer"


Schematic page 9


The That 300 series are nice matched quad transistor arrays 36V 30ma.
2 NPN 2 PNP not cheap, about $7.00 USD.

.

Last edited by RJM1; 21st September 2019 at 04:52 PM.
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Old 21st September 2019, 06:54 PM   #34
franzm is offline franzm
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Quote:
Originally Posted by lcsaszar View Post
What about using a jFET as a variable resistor instead of BJT?
https://americanradiohistory.com/Arc...ld-1975-12.pdf page 587 (83).
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Old 22nd September 2019, 01:46 AM   #35
PRR is offline PRR  United States
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A competent design, with some period flavor.

I wonder what happened to this guy D. R. G. Self, B.A.?
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Old 22nd September 2019, 01:28 PM   #36
MarcelvdG is offline MarcelvdG  Netherlands
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He's on this forum with user name DouglasSelf, so you can send him a PM to ask him.
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Old 22nd September 2019, 03:12 PM   #37
JMFahey is offline JMFahey  Argentina
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I think PRRīs question was asked tongue in cheek
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Old 30th September 2019, 04:50 PM   #38
PRR is offline PRR  United States
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Originally Posted by PRR View Post
....I wonder what happened to this guy D. R. G. Self, B.A.?
Hey! He wrote a book!

And expands greatly on the subject of limiters. (It seems to be a special interest of his.) And notes "I produced a compressor/limiter design for Wireless World when the application of FETs in this way was relatively new; it was published some years after I designed it."

I STRONGLY suggest anybody interested in the topic get his Small Signal Audio book and digest the chapter "Level Control and Special Circuits".
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Old 30th September 2019, 06:00 PM   #39
lcsaszar is offline lcsaszar  Hungary
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Another solution it to use a light dependent resistor (CdS) and a LED. The photoresistor is used as a gain control element in a NFB loop. The LED is controlled by fast rise, slow decay DC voltage derived from the output signal. This arrangement has pretty low distortion in steady state.
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Old 30th September 2019, 06:53 PM   #40
PRR is offline PRR  United States
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> use a light dependent resistor (CdS)

Done that a LOT. Some advantages. Increasing disadvantages.

The compelling issue today is that CdS is now a Controlled Substance in Europe, and use is dubious. For this and other reasons, all the Old-Time CdS cell makers quit the business some years ago. You can get them from China. Uniformity is reportedly fair to awful.

Note that when CdS was a big deal, 99% of uses were dusk-dawn light switches and flame-detect in burners. These had no requirement on response speed, and loose requirement on R/light, only in a narrow range (dusk, or good-flame). An audio LDR for limiting must work over a wide range, either "fast" or with a controlled "tail", and we like to have two alike for stereo.

Still perhaps the cheapest way. At an extreme you run a rectifier on your power amp output to run an LED to shine on the LDR in an L-pad at the amp input. That works, though the THD at power-amp input level can be audible.
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