Tomba

670 with solid-state side-chain?
« on: July 09, 2005, 06:32:37 AM »
Hi everyone.

Has anyone ever done a Fairchild 670 with solid-state side-chain? It would be so much cheaper because you will need only half of the transformers and only four 6386's as you all know. I think few high voltage op-amps could do the job. And you don't have to charge the caps on high voltage if you place the voltage gain amp after caps.

What could be the benefits of the tube side-chain with i/o trafos? Have anyone calculated the voltage gain of the side-chain amp?


Rob Flinn

670 with solid-state side-chain?
« Reply #1 on: July 09, 2005, 08:28:26 AM »
Fairchild themselves did a sort of 670 with a solid state side chain called the 666

If you were making this stereo it would still need 8 6386
regards Rob

clintrubber

670 with solid-state side-chain?
« Reply #2 on: July 09, 2005, 09:21:14 AM »
That's interesting, a 670-version with some solid state thrown in being called 666... How ironic  :twisted:  :wink:   :twisted:  :wink:  :twisted:

Uhh, how many times will this remark have been made before ?


http://home.earthlink.net/~djahnsen/other.html

670 with solid-state side-chain?
« Reply #3 on: July 10, 2005, 10:34:33 AM »
kubi ...
nice info at your website ..
thqanks for posting it ....
i had searched for this 670 info before too....
i finallly found a studio owner who had one and was willing to send me the schematic ... i hve it in storage somewhere ..an actual copy of an original .... :grin:

but this is more convenient to have it on the computer too ....

one for the wall ... one for the computer .... that will work ... hehe :grin:

BTW:kubi ..underground log/pass request :wink:

i have also been considering the fred forsell DIY sidechain .. using some existing vintage RCA stuff i have ...

anyway thanks for the info
later
ts
I need help with  RCA BA-43/ BA-45. RCA BA-25a, RCA BC3 mic pre's, Gates Level Devil, Federal AM-864u, DIY la2a stuff, Altec 436b

670 with solid-state side-chain?
« Reply #4 on: July 10, 2005, 10:54:18 AM »
ALSO:fred forsell sent this reply concerning converting one of these magnacords i have to a compressor ... this is a general rule of thumb that can be applied ..

i had previously posted a thread about getting a "quasi" ba6a from a RCA line amp i have
i had discounted the idea thinking it would be too destructive of a mod for this vitage "tube snack"... but after the info from fred ... i think this is and easy mod and not very destructive at all ... the mod can be easily un-done and the unit returned to it's original vintage state if desired with no effect on the units value..

think i'm gonn try it ... here is freds reply to my inquiry ....

Quote
Jeff,

Yes, every compressor needs a way to make gain lost by the gain reduction
process.  If the preamp in the Magnacord is a line-level preamp then it
would be well suited for such a task. However if the preamp is a mic preamp,
then there is too much gain and you'd have to deal with that somehow.

That said, my opto compressor side-chain would work well for this.  Think of
the opto cell as an attenuator placed prior to the preamp. The preamp makes
up the gain lost by the cell and/or a master output level control, and it
also drives the outside world.

I hope that helps.

Fred Forssell


hope this helps
later
ts
I need help with  RCA BA-43/ BA-45. RCA BA-25a, RCA BC3 mic pre's, Gates Level Devil, Federal AM-864u, DIY la2a stuff, Altec 436b

CJ

670 with solid-state side-chain?
« Reply #5 on: July 11, 2005, 03:00:36 PM »
I think PRR has done something like this.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Re: 670 with solid-state side-chain?
« Reply #6 on: July 11, 2005, 06:04:03 PM »
...

strangeandbouncy

670 with solid-state side-chain?
« Reply #7 on: July 11, 2005, 06:39:10 PM »
Rob Flynn,

  I hate to be a stickler for details, but the Fairchild 666 i used to use was an OPTICAL compressor. True, the signal path was all tube, and there were some transistors in the side chain, but there were no 6386's at all. this particular unit belonged to Mark Thompson, and had been restored by Sean Davies. It was a truly wonderful compressor. i loved it on vocals and bass gtr. It had a much faster recovery than the La2a(with T4a not b!) next to it. This could have been down to the luminescent panel that Sean Davies had replaced (i believe), the original having failed. It had a strong characteristic sound, solid, creamy, and much "larger" than the La2a. Didn't suit everything,
tho'. Louis Austen used to have one too, but I never tried it.

       ANdyP
. . . . RUH ROH . . . . .

Larrchild

670 with solid-state side-chain?
« Reply #8 on: July 18, 2005, 06:02:30 PM »
I love how Rein Narma designed the best limiter ever with the 670, and in an effort to "go solid state" they made a turd with the 666.

"No Distortion introduced by Compression..No change in Tube Bias" they chimed in the sales brochure.

So like, what's  the point in compressing then? lol

ps  i think the Pendulum limiters are remote-cutoff tubes w/ solid state sidechain.

soundguy

670 with solid-state side-chain?
« Reply #9 on: July 18, 2005, 06:14:44 PM »
the pendulum with the 6386 uses a chip output stage.

their optical limiter is crazy good, I believe that unit to be all tube.

dave

chips are good with dip...


chrissugar

670 with solid-state side-chain?
« Reply #10 on: July 19, 2005, 04:05:35 AM »
Quote from: "soundguy"

their optical limiter is crazy good, I believe that unit to be all tube.


I'm extremely curious about what trick they use to make the optocoupler behave fast.

chrissugar
Christian Mike Sugar
        CMS-LAB

gyraf

670 with solid-state side-chain?
« Reply #11 on: July 19, 2005, 05:07:03 AM »
Some of the new optos are inherently very fast..
..note to self: don't let Harman run your company..

chrissugar

670 with solid-state side-chain?
« Reply #12 on: July 19, 2005, 09:27:45 AM »
From what I read the VTL5c1 is the fastest opto suitable for quality audio. I also read that they use some special trick to make them respond faster (probably some similar trick like is the PWM in FET comps to make them faster)

chrissugar
Christian Mike Sugar
        CMS-LAB

670 with solid-state side-chain?
« Reply #13 on: July 19, 2005, 01:24:05 PM »
Yes the 666 is a turd, and not the simple 6386+SS Sidechain one would expect. I've used one and repaired a different one and wouldn't bother with either again.
I have done 6386 + SS Side chain, but not on a production level. It works fine, I have a customer using one for the last 8 years. Naturally, it doesn't sound like a Fairchild 660/670, however cool it is.
As for the EAR 660, there are too many different elements to call it a 660 in the Fairchild sense (besides that they sound and respond completely differently):
EAR                                             Fairchild
SS Shunt PSU...............................Toob Series Regulation
(this difference would make a fixed gain amp sound different)
SS Single ended comp pair out
Contol Amp...................................Differential toob Control Amp
(Response times and bandwidths are different, although EAR does properly separate AC and DC thresholds)
Cascode signal amp.......................triode signal amp
(there will almost always be bandwith differences here)
Wider bandwith Xfmrs....................UTC/Triad vintage-nice but not as wideband
(the EAR xfmrs cutoff @5Hz instaed of 20Hz, and it makes a difference because it's not even 1/10th of a dB down @ 100hZ)
To summarize, the EAR is way more wideband, though it's not color-free, it's less immediatyely obvious than a Fairchild. It also doesn't lop off bass as you compress, like a Fairchild. Both really do have thier time and place of use, and I wouldn't want to be without either in a studio.
regards,
D.Bock
Soundelux Microphones
Hollywood, CA

CJ

670 with solid-state side-chain?
« Reply #14 on: July 19, 2005, 04:39:10 PM »
Cool, David!
Come back more often,
No postage fee here.

 :thumb:
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

670 with solid-state side-chain?
« Reply #15 on: July 22, 2005, 12:53:08 PM »
Thanks, CJ!
Paul, of course I wasn't talking about your666!  While I don't doubt that you were able to use it effectively, it's definitely not a unit I would feel comfortable about pay any significant cash for.
So, I heard you sold Third Stone, true?
-DB

Rob Flinn

670 with solid-state side-chain?
« Reply #16 on: July 29, 2005, 03:30:24 PM »
Quote
Rob Flynn,

I hate to be a stickler for details, but the Fairchild 666 i used to use was an OPTICAL compressor. True, the signal path was all tube, and there were some transistors in the side chain, but there were no 6386's at all. this particular unit belonged to Mark Thompson, and had been restored by Sean Davies. It was a truly wonderful compressor. i loved it on vocals and bass gtr. It had a much faster recovery than the La2a(with T4a not b!) next to it. This could have been down to the luminescent panel that Sean Davies had replaced (i believe), the original having failed. It had a strong characteristic sound, solid, creamy, and much "larger" than the La2a. Didn't suit everything,
tho'. Louis Austen used to have one too, but I never tried it.

ANdyP
_________________


Andy, I bow to your superior real world knowledge of this product, & stand corrected, with a mouth full of humble pie.

However, in return I would be obliged if you could spell my surname correctly in future posts!! :wink:  :wink:
regards Rob

670 with solid-state side-chain?
« Reply #17 on: May 22, 2006, 12:47:38 AM »
I dont know if this question was answered at all. Can the Fairchild 670 sidechain circuit be easily implemented with a solid state sidechain?
This would cut down costs and it might be a good diy project. Once people have these sidechain circuits then they can experiment with different combos of vari mu tubes.
6386, 6BC8, 6ES8 etc etc.
Is anyone interested in chasing this idea. Is there something out there that can be modified to fit the criteria?

670 with solid-state side-chain?
« Reply #18 on: May 22, 2006, 05:14:39 AM »
bump

gyraf

670 with solid-state side-chain?
« Reply #19 on: May 22, 2006, 07:03:08 AM »
but then it won't be a 670. the sidechain is actually some of the relatively simple, cheap and easy about the circuit...
..note to self: don't let Harman run your company..


 

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