I've got couple of old decks with limiter. The limiters are interesting but the release is too slow to make it usefull in a studio. Is there a way to mod it for faster release, maybe adding a pot somewhere? I'm not really sure how these limiters work but with faster release I can see a potential for compressor use. Anything I can do? Thanks for advice
Hm, I believed a limiter is just a nonlinear gain block, where gain approaching zero at the instantenous amplitude peaks (soft clipping).
On the other hand, a compressor has a variable gain, controlled by the amplitude at its input, and it is not instantenous. It has a fast onset and longer decay.
I have a Sony cassette tape deck with a very nice peak limiter.
On the other hand, a compressor has a variable gain, controlled by the amplitude at its input, and it is not instantenous. It has a fast onset and longer decay.
I have a Sony cassette tape deck with a very nice peak limiter.
Limiter has various meanings. In an RF context, it is usually a hard clipping amplifier, in an audio context, a compressor with infinite compression above a certain threshold.
@6V6dude If you can find and post type numbers or preferably schematics, you have more chance of getting a sensible answer. Chances are that you can make the release faster at the expense of more low-frequency distortion while limiting, but I wouldn't know how to figure out how to do that without schematics.
@6V6dude If you can find and post type numbers or preferably schematics, you have more chance of getting a sensible answer. Chances are that you can make the release faster at the expense of more low-frequency distortion while limiting, but I wouldn't know how to figure out how to do that without schematics.
Old style ALC (automatic level control) were ubiquitous in all kinds of tape and cassette recorders, to try to improve the abysmal S/N ratio.
Low level was swamped by hiss, high level easily saturated tape, so if at all possible they tried to record at constant "acceptable" level, so a strong but slow compressor was mandatory.
Only 3 technical conditions needed to be met: cheap, cheap and cheap 😉 , so ubiquitous was a single transistor attenuator, controlled by rectified audio voltage, as simple and crude as possible, typically a diode from tape recorder speaker out .
So level detection chain was speaker out > diode > large electrolytic capacitor > large resistor > transistor base.
Since base and collector currents are not really separated (both pass through emitter which has not zero impedance), part of the control signal gets mixed with audio signal, creating pops and thumps.
Typical solution is to make it slooowwww meaning well below audio range, so normal circuit roll-off keeps it away.
But if you shorten timen constants, all kinds of problems appear.
Similar circuit, although way more modern than what you have there (Op Amps, Darlington attenuator, etc.)
IF you wish, disable the cheesy original one and build a new one using a FET (hint: NO Base current so audio/control independence) and improving the signal rectifier filtering.
Low level was swamped by hiss, high level easily saturated tape, so if at all possible they tried to record at constant "acceptable" level, so a strong but slow compressor was mandatory.
Only 3 technical conditions needed to be met: cheap, cheap and cheap 😉 , so ubiquitous was a single transistor attenuator, controlled by rectified audio voltage, as simple and crude as possible, typically a diode from tape recorder speaker out .
So level detection chain was speaker out > diode > large electrolytic capacitor > large resistor > transistor base.
Since base and collector currents are not really separated (both pass through emitter which has not zero impedance), part of the control signal gets mixed with audio signal, creating pops and thumps.
Typical solution is to make it slooowwww meaning well below audio range, so normal circuit roll-off keeps it away.
But if you shorten timen constants, all kinds of problems appear.
Similar circuit, although way more modern than what you have there (Op Amps, Darlington attenuator, etc.)
IF you wish, disable the cheesy original one and build a new one using a FET (hint: NO Base current so audio/control independence) and improving the signal rectifier filtering.
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Change the capacitor. Smaller for faster.
In most simple plans, this also changes the attack. In cheap AGC, a fast attack "distorts". That may be acceptable as "effect".
You really want to find out what is in these unnamed "old decks" and understand it.
Are we discussing limiters, like there used to be in professional and semiprofessional recorders for reporters, or ALCs, like there used to be in the very cheapest consumer gear? Both are compressors, but the requirements and designs are very different.
plus simple statistics makes me think of the cheesier ones.
If so, a significantly smaller capacitor will at least cause "pumping/breathing" but even worse, thumping or plain old motorboating.
Lift the "limiter" circuit and post it here, it might be the base for a better one, to control either a FET or turn a LED on, illuminating a CDS photocell.
Otherwise it will approach polishing a turd.
Unfortunately I don't have the schema and looking at the board I see nothing that would resemble limiter unless the large noise reduction chip does that as well. Just to make it clear, I wasn't thinking of converting it to nice compressor. But I thought it might be possible to turn it ion to a filthy distorting comp/limiter possibly well suitable for drums. Comps I have are just boring clean and no fun in studio.
But I will look for a capacitor, that actually makes sense that the release could be simple cap value dependent.
But I will look for a capacitor, that actually makes sense that the release could be simple cap value dependent.
DO you have a "large noise reduction IC" there?
Then it might do double duty as a signal peak limiter.
Of course receiving such data little bit by little bit will stretch this thread forever.
As of "looking for a capacitor" ... be my guest, there must be dozens there.
If that´s your only clue .....
Then it might do double duty as a signal peak limiter.
Of course receiving such data little bit by little bit will stretch this thread forever.
As of "looking for a capacitor" ... be my guest, there must be dozens there.
If that´s your only clue .....