Simple way to do audio dynamic range compression

[TheTigerEye]

I have been looking at several ICs, including the SA572/1/0 but I can't seem to find a decent schematic. Does anyone know of a simple way to do this?

[DrGeoff]

There should be plenty of app notes for the old NE571/NE572 devices around.
Like this one: http://www.onsemi.com/pub_link/Collateral/AND8159-D.PDF
It depends on what exactly you want to do with it.

If you are looking for better audio quality, there's a circuits and details for an 1176LN clone here: http://www.axtsystems.com/index.php?option=com_content&view=category&id=34:1176ln&Itemid=62&layout=default
I use several of these in audio production work.

[TheTigerEye]

I'm using it for amateur radio, so high quality is not of essence. Do you happen to have a PCB layout for the NE750/751 compressor schematic ?

[DrGeoff]

I remember ETI published on back in the 1970's. It was project ETI484.
Compression and expansion, ratio up to 2:1 with fixed attack and slow/fast release. Fairly simple and made to help with noise reduction on cassettes.
There are probably other projects around, it was quite popular back then.

There are also opto compressors, VCA compressors and FET compressors used in pro audio. There are quite a few circuits around for these.
It sounds like you only want compression, and only one channel, so it should be fairly simple to build.

[kripton2035]

some archives I have in my hard drive :

[kripton2035]

a circuit from siliconchip

[kripton2035]

some old poptronix ...

[kripton2035]

and some specialized circuits from analog devices, some may still be available as samples ?
look also SSM2164 or SSM2165

[kripton2035]

also this link with an avr compressor
http://www.nlvocables.com/blog/?p=803

[krivx]

and some specialized circuits from analog devices, some may still be available as samples ?
look also SSM2164 or SSM2165

They are not available new, and they tend to be pretty pricey on eBay. I think the high prices is because they were used in synths and users want spares.

[DrGeoff]

Yes, I have a 4-channel VCA compressor I built using the SSM2120. Great device and quite versatile. But unfortunately unobtainable.
I had to salvage the SSM devices from some old broadcast VCA modules, and that would have been back around 2001/2.

The 1176LN is simple though, and all the parts are obtainable. For the OP's use the transformers can be excluded, as a balanced output is probably not required. Saves quite a bit on cost, as the Lundahls can be very expensive.

[TheTigerEye]

Wow. Thanks for all of this. I'm thinking of going for the SSM2166 one - I can find the IC for just under £5 on Farnell and it seems well documented. What kind of sound quality should I expect from this (roughly)?
I'm not ruling out the 1176LN either, but it might be slightly overkill and too pricey for this application.

[Circlotron]

I'm using it for amateur radio,

If it is for a base station, would a pc-based audio processing setup using only the sound card be okay? Someone must know of one out there.

[kripton2035]

SSM2166 is still in production @ analog.com, and is still available as sample...
http://www.analog.com/en/products/audio-video/audio-amplifiers/ssm2166.html#product-samplebuy

[kripton2035]

simple ssm2166 application :
http://www.muzique.com/tech/2166.htm

[PeterZ]

There is also a whole range of chips dedicated for audio dynamics processing made by THAT Corp:
http://www.thatcorp.com/THAT_Dynamics_Processing_ICs.shtml
Especially a single chip solutions like the THAT4301 (more advanced compressor) or simpler THAT4315 might be interesting.