fairchild 660 type compressor with solid state side chain amp

[lewilson]

Hello, its been some time since ive posted here.
    I have been busy and have built a few 660/ 670 type compressors from scratch.
Id like to build one with some power transisters in place of the power tubes in the side chain.  This means no output transformer.
The whole amp will need a redesign .The impedance will be lower also?  not the usuall 600 ohm out . Any ideas how i can aproach this?   

 

[gridcurrent]

    I have been busy and have built a few 660/ 670 type compressors from scratch.
Id like to build one with some power transisters in place of the power tubes in the side chain.  This means no output transformer.
The whole amp will need a redesign .The impedance will be lower also?  not the usuall 600 ohm out . Any ideas how i can aproach this? 

essentially copy the Tim P.  (EAR) sidechain.  TL084 sections with a complementary output pair.

 

[abbey road d enfer]

Hello, its been some time since ive posted here.
    I have been busy and have built a few 660/ 670 type compressors from scratch.
Id like to build one with some power transisters in place of the power tubes in the side chain.  This means no output transformer.
The whole amp will need a redesign .The impedance will be lower also?  not the usuall 600 ohm out . Any ideas how i can aproach this? 

You want to build an amp that's capable of delivering about 80V peak with 100mA of current. That means a bipolar rail voltage of about 100V. You would use high-voltage MOSFET's. The amp would be under heavy NFB, so, yes, it's output impedance would be very low.
Ther is also the possibility of building a low power amp that delivers symmetrical outputs, which would be directed to MOSFET's. Some thinking must be put in making them reasonably linear. You could think of it as some kind of push-pull class C.

 

[Winston OBoogie]

The E.A.R. gets away with using a lower voltage amplifier with regular op-amps and buffer because Tim used 7ES8 valves for gain control which don't require more than 15V or so for full limiting.


Otherwise, what Abbey said.

 

[AusTex64]

Pendulum Audio also uses a solid state sidechain on their ES-8 remote cutoff tube limiter.

 

[Rob Flinn]

I just made a gain cell using four 6bc8's in parallel with some edcors for i/o duties.  I was controlling it with a bench PSU for test purposes & it worked very well & sounded nice.    My intention was to use a generic amplifier i.c as a side chain amp, because, as previously stated the 6bc8 & 6es8 don't need such a big control signal.  I got as far as ordering some ampi.c's but have got swamped with some other jobs.

 

[analag]

The sound of the CV amp influences the compression curve. My big mu compressor with 6L6GC powered CV amp sounds very different from the PM660 I have here.  It's swinging a lot of voltage into those 10 grids per channel.

 

[Winston OBoogie]

The sound of the CV amp influences the compression curve. My big mu compressor with 6L6GC powered CV amp sounds very different from the PM660 I have here.  It's swinging a lot of voltage into those 10 grids per channel.

Didn't ever get to see the schematics of your units (hint ) but I don't doubt what you say.  I've heard such a difference too. 

 

[analag]

Didn't ever get to see the schematics of your units (hint ) but I don't doubt what you say.  I've heard such a difference too.

I have the schematic somewhere

 

[Winston OBoogie]

I have the schematic somewhere

Cool.  If you come across it and it's OK, I'd like to take a peek