Fairchild 660 from scratch

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remsouille

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Truly amazing. That wiring :eek:
Say you'd want to keep the same attack on position 4 (0,8ms), but have the release time of position 1. How would you do it?
 

DaveP

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Say you'd want to keep the same attack on position 4 (0,8ms), but have the release time of position 1. How would you do it?
Referring back to the timing circuit on the previous page:
The attack times are not decided by series resistors as in other compressors, the attack times are decided by the output resistance of the control amp (100 ohms) and the time it takes to fill the capacitors as they are added or subtracted.

The release time of position 1 is the parallel value of 220k//68k which is 50k in combination with 2uF , which is 2x 0.05M=0.1.

If you add the capacitors of position 4 , that is another 6uF making 8uF in total.

So the resistance must be changed to 0.1/8=.0125M or 12.5k

You could do this by connecting a 27k resistor across each of the capacitors on position 4.

So the parallel combination would be 27k//27k//220k = 12.5k

DaveP
 

IBart

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Well after being in possession of this great 660 for two days. I have managed to play electric guitars & Bass guitars through it, I've recorded acoustics and recorded two singers , one who is newly signed to Warners UK  ( as they were over on separate days to write or record their songs).

I have only used one vintage 660 once in my life and it sounded classy for sure.  Not overly coloured. And i remember the compression sounding very smooth indeed.
I find / found Fairchilds to roll of the transients as well without any compression in a musical and pleasing way.  And watching a few youtube clips of Fairchilds online it also has this earthy sound as well.  My Vintage Gates 39b also has this earthy vibe going on, but a different EQ curve of the tone of the box.

And this 660 that Dave has built has a similar sound vibe. Its got that smooth sound, the slight rolled transient and that lush middle-y buttery sound and with that the earthy-ness and this great compression for vocals (at the setting 1 or 2) And it carries on being smooth right over 10db of compression!

I am SO pleased it and its being used on records each day.

Here are few pictures i took on the first morning.
Just after i carefully uncapped this black beauty verrrry carefully !
 

IBart

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Here are some pictures of this great 660.

Dave you are a genius !

http://s1262.photobucket.com/user/ianbarterbarter/library/660%20compressor?sort=3&page=1
 

skal1

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Hi Davep,

where did you connect the feedback resistors  for the  driver tube  in the control amp, can not see were you connected them , are they  on the base or on the tag stripe.

cheers

Skal

 

DaveP

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where did you connect the feedback resistors  for the  driver tube  in the control amp, can not see were you connected them , are they  on the base or on the tag strip.
They are difficult to see because they are hidden under those two black mic cables.
The two feedback wires from the OPT go to the tag strip.  Soldered in with each one is a 3k going to the earth busbar and a 120 ohm going to the cathode of the driver tube.  the cathode also has a the 1k soldered in going to earth.

DaveP
 

skal1

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ok  yeah ,can kind of work it out now, while am here were's did you put the  ratio pot..

you  have gave me some vibes to finish mine , just  soldering up the tag stripes to the tube base's hope look's as good as yours.

cheers

skal
 

DaveP

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while am here were's did you put the  ratio pot..

It's between the transformers at the back of the amp, (the front in this pic) there is a nut to lock it at the correct setting, in this case 5V.

DaveP
 

skal1

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Hi Davep,

thanks for all the help, i must be doing your head in ;D cheer , by the way  did you cope the 8346E or did you flip the out tx, can not afford that right now , but i still need  an alterative to put their , have you got any suggestions

regards

Denis
 

DaveP

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I used the Sowter 9062, with a slightly different ratio, the frequency response is flat to 48kHz.

If you are happy with the normal 20 -20Khz, then you could use a pair of OEP 187B's from RS at about £38 each.
http://uk.rs-online.com/web/p/audio-transformers/2106352/

DaveP
 

skal1

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ok  Davep , but does that extended  frequency response of the input tx  translate  through the out tx  ?


regards

DEnis
 

skal1

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Thanks again Davep for your insight's into this whole project . i think  i might go for one of those inputs you used and  try runing the output tx backwards as an input ..

regards

Skal
 

skal1

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Hey, Davep how did you determine what particular filter device to  provide the correct isolation  for the unit, is their a calculation need.

Regards

Denis
 

DaveP

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how did you determine what particular filter device to  provide the correct isolation  for the unit, is their a calculation need.
I don't really understand what you're asking?  Are you talking about capacitors or transformers?

DaveP
 

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