Nice little compressor

[Mark Hammer]

Following up on a link to Spin Electronics over on the DSP subforum, I noticed they had some decent documents on a few analog modules.  This link is for what appears to be a quiet and decent compressor: http://www.spinsemi.com/appnotes/spn1001/AN-0003.pdf

It is supposedly based on David Blackmer's VCA design which is a decent pedigree.

[puretube]

now where`s that son-of-ota-thread again... ?

[Dragonfly]

cool !  thanks Mark !

AC

[markm]

Wonder how this thing would handle operating at +9V?
Probably not as clean huh?

[puretube]

now where`s that son-of-ota-thread again... ?

here

[jmusser]

I'm guessing Q7 would be another 4403? It looks like it would be worth while to go ahead and build with the 5534 in the front end, to keep this thing as noise free as possible, because it just gets amplified as you go through the circuit. It looks very promising. I would guess that the 12V- and + supply would really make this thing sing.

[StephenGiles]

Very interesting indeed, thanks Mark.

[brett]

Hi
I'm no expert, but I think it might work ok on 9V.
The first op-amp only provides 6x gain, so a moderately big guitar signal will only swing +/- 1.5V of 4.5V, which is ok by the 5534.  Likewise, the latter op-amps are all working within their limits for a 9V supply.  If the transistors in the VCA are ok, then it should all be cool.
cheers

[markm]

Hi
I'm no expert, but I think it might work ok on 9V.
The first op-amp only provides 6x gain, so a moderately big guitar signal will only swing +/- 1.5V of 4.5V, which is ok by the 5534.  Likewise, the latter op-amps are all working within their limits for a 9V supply.  If the transistors in the VCA are ok, then it should all be cool.
cheers

Cool, thanks brett!
Maybe I'll give her a whirl perhaps. 

[Transmogrifox]

At the expense of a somewhat diminished Signal-Noise ratio, it may be a worthy trade-off to put a voltage divider on the input to reduce the gain to about 1/3, then modify the output stages to boost it if necessary.  I think the part of the circuit that could suffer the most from the reduced power supply is the envelope detector.  I have a similar problem in an envelope filter I just built for a friend, where the 9V supply isn't enough to maintain an adequate response, thus I need to modify the envelope follower design to work with the lower supply voltage.

Thanks for the link, Mark.  I am always interested in seeing a VCA block that I have not yet seen  (VCF's, too, for that matter)