Fairchild 661tl Gate... convert to Compressor?

[dustbro]

I have a few Fairchild 661tl gate modules laying around the shop. A friend of mine suggested that they may be able to be converted to compressors. Does anyone have a schematic for this unit? Or even better, an idea on what this mod might be?
thank!
Dan

 

[dustbro]

I actually found someone who had a schematic! Now I need some help from you electronic masters

 

[dustbro]

Ok.. here's the Fairchild 663 schematic. Boy does it look similar

 

[rafafredd]

you probably could try some modern LDRs in place of the originals, but do not expect exact same sound.

 

[Joechris]

Looks like all you have to do is rewire the input/output arrangement?? :shock: Since there is only a LDR in the signal chain, I think you need a external makeup amp to make this thing work right.
jo

 

[dustbro]

[quote author="rafafredd"]you probably could try some modern LDRs in place of the originals, but do not expect exact same sound.[/quote]
NOT Sounding exactly like the original is fine with me. I'm trying to find a practical use for something just sitting around.
Could you elaborate on your idea? Im still pretty new at all of this.

 

[dustbro]

[quote author="Joechris"]I think you need a external makeup amp to make this thing work right.
jo[/quote]
Is that what is at the top right portion of the 663 schematic?
and now I'll show just how new I am at this... on the 661 schematic, what is the dotted line going from the 5k threshold pot to the break in the circuit?

 

[Joechris]

what is the dotted line going from the 5k threshold pot to the break

Thats to show that the pot and the switch is linked.

Is that what is at the top right portion of the 663 schematic?

No, the entire schematic is just a sidechain to drive a lamp. You have to make a 25db amp to follow the LDR.

 

[maxheadroom]

hi dan, i have also two of the 661tl laying around here.
did you mod yours?

 

[dustbro]

Its so funny that this thread got dug up. Havent done the mods yet, but got inspired by the diyLA-4 the other day and decided to knock this out sometime this week.
Maybe I'll design a little PCB that you can just drop in for the mod???

Would the Silonex NSL32 work in this situation?

 

[rhardman]

Hi...newb to this forum. I just stole one of these off ebay last night. I am intrigued with the makeup gain amp idea.

I have a RDL stick-on line amp laying around that would need to be recalibrated. And maybe add a stepped ladder attenuator on the output side as there is no easy way to adjust the gain on the stick-on (trim pot only)

Any thoughts???
Thanks!

Rawl

 

[strangeandbouncy]

Hi,


  just as easy to replace trimpot with a pot as to add a ladder innit?


    ANdyP

 

[rhardman]

Not on this one...the trim pot is part of the unit. A really tiny stick on (literally) From Radio Design Labs. It would not be accessible when racked. The ladder idea was to get repeatable make up gain settings. I will probably just use a pot across the out to keep it simple.

 

[rhardman]

Anybody know which terminals are the hot and neutral on the 661????

I would like to get this bad boy flying.

 

[klett]

as noted above the circuitry is all just for detecting signal envelope and controlling the light bulbs.  The LDR's are supposed to SHUNT to ground so you have to control both the source and load impedances to make these work right...

comments re fairchild

http://www.technicalaudio.com/pdf/Fairchild/Fairchild_Junk_and_Jems_post_edit.pdf

and here's another schematic for the 663

http://www.technicalaudio.com/pdf/Fairchild/Fairchild_663_mono_compressor_schem.jpg

I have more on 663 and 661 in the files but not scanned...  the gate had two LDR's so you could make two "T" pads with LDR's being shunts and either do two in series to get more cut or do them as balanced "T"

the 663 schematic does not show it but I'm pretty sure I've seen a 663 with two LDR's on it...

 

[pinebox]

I actually found someone who had a schematic! Now I need some help from you electronic masters

Anyone have this schematic? Thanks.

 

[gridcurrent]

Anyone have this schematic? Thanks.

you are welcome.

 

[mjrippe]

I just added that schematic to the 661 Technical Bulletin PDF and uploaded it to the Tech Docs section of GDIY.  However when I click on the Fairchild heading it only shows the first 6 posts  :-\  So I'll attach it here as well.

 

[RSRecords]

From the GRAVE...
Anyone ever try to convert one to a compressor? I just picked a 661TL up pretty cheap. You know, drinking' and ebaying...

 

[gridcurrent]

Anyone ever try to convert one to a compressor?

very similar to the 663.  shouldn't take you more than 15 minutes to convert.