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?     


Re: fairchild 660 type compressor with solid state side chain amp
« Reply #1 on: May 25, 2020, 07:48:30 PM »

     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

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #2 on: May 26, 2020, 02:02:56 AM »
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.
« Last Edit: June 03, 2020, 04:17:14 AM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #3 on: May 30, 2020, 09:05:40 AM »
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.
Jeffrey Toobin: "This is the most embarrassing week ever."

Rudy Giuliani: "Hold my pants..."

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #4 on: June 02, 2020, 11:44:13 PM »
Pendulum Audio also uses a solid state sidechain on their ES-8 remote cutoff tube limiter.

Rob Flinn

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #5 on: June 03, 2020, 05:41:56 AM »
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.
regards Rob

analag

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #6 on: June 10, 2020, 10:26:22 PM »
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.
Audio engineering suffers from misinformation, disinformation, and downright lying more than most fields of endeavour.

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #7 on: June 11, 2020, 01:05:31 AM »
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.   
Jeffrey Toobin: "This is the most embarrassing week ever."

Rudy Giuliani: "Hold my pants..."

analag

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #8 on: June 12, 2020, 03:50:02 AM »
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
Audio engineering suffers from misinformation, disinformation, and downright lying more than most fields of endeavour.

Re: fairchild 660 type compressor with solid state side chain amp
« Reply #9 on: June 14, 2020, 07:15:02 PM »
I have the schematic somewhere

Cool.  If you come across it and it's OK, I'd like to take a peek  :)
Jeffrey Toobin: "This is the most embarrassing week ever."

Rudy Giuliani: "Hold my pants..."


 

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