original 670 poor version DIY

I was looking for here and I can not find anyone there who tried to clone the fchild670.
whether that is very difficult and it´s got esoteric parts but I just trying to do something.
I know that there is already a pm670.
Actually I already bought the pcb´s of a pm660.
sowter has got the transformers, JJ recreates 6386.
Also is not going to sound exactly the same but I hope  getting a very good compressor.
Someone is trying to do this ?, or did it ?.I`m trying, someone who advice me?

Greetings.

I went through the schematic the other day and added up the parts cost.  It came to about $3,000 for parts.  Could be less if you go with a solid state supply.  All of the parts are now available, as far as I can tell.

the power-suplay solid state is what I thought at first. I have doubts about the input and gain reduction atenuator pot.
3000 dollars seems a bit exaggerated.
I believe that while cost 3000 dollars in materials is still very interesting to build.

I have a part built 670. 

I'm waiting on a front panel to move the project on further.

rob that good news!.
I'm not the only crazy!
has some photos?
the power suply built with solid state or original?
to use all the original tubes?
I have several hesitations:
1) if using direct 6ba6 instead of 6386.
2) if 6V6 in place of 6973.(I saw that the sowter recreating this tube).
3) as a replacement would gain reduction pot?.
4) the input attenuator can be replaced with something like this? http://www.groupdiy.com/index.php?topic=2229.0

Magoo,

I don't have anywhere to host any pics at the moment, & also there isn't oo much to look at right now.

I'm using a valve PSU.

With regards to your points 1 -4

I'm not using any of these substitutions for my 670, so therefore I haven't really considered any of them.   Although I have used the 6BA6 sub for something else, where it worked ok, with no problems.

Oh & by the way you are crazy.  I started getting the parts together for this roughly 6 years ago.  I'm not even close to it being finished.  I'm not much further than having the valve bases & transformers mounted on the chassis, & it already very heavy to lift.

How long ago was it that I sold you those 6973, Rob  ;D

Rome wasn't built in a day.

Justin

thermionic said:

How long ago was it that I sold you those 6973, Rob  ;D

Rome wasn't built in a day.

Justin

Click to expand...

Precisely !

well ...
we do a brainstorming to see how to do an economic version of Fairchild?
it's a good idea to use the Transformer kit sowter?
someone knows the original transformers ratios?
anyone know a replacement transformer of edcor?

SUPERMAGOO said:

well ...
we do a brainstorming to see how to do an economic version of Fairchild?
it's a good idea to use the Transformer kit sowter?
someone knows the original transformers ratios?
anyone know a replacement transformer of edcor?

Click to expand...

My more economical, but still pricey version;
6BA6's in // but cascoded.  An appropriate ratio but outstanding quality signal output transformer.  Akin to the Hi-Nickel 9661 but 10:1

Similar outstanding transformer on the input. 

Tube rectifiers (damper?) for noise reasons but simpler regulation for the VCA (neon or squalid-state?)

Squalid-state side amplifier.  No transformer used on input but a relatively cheap jobbie to drive the bridge.

The only part I haven't proof built is my own solid-state side amp.  Used a -tve bench supply first and then a cheap and cheerful power amp!  No DC thresh on that last one but I'll put it on my own amp.  Someday...

I built a clone of a Fairchild 670 a few years ago.
It has 16 6BA6 tubes in it which I matched in 4 quads which were pretty damn close in tolerance to each other.
I got the original Fairchild transformers for the signal amp.

For the control amp I built a solid state chip amp about 10 watts.
The sound of the signal amp is awesome real smooth and the 6BA6 matching seems to have worked well.
But I think I have some issues with the unit.

The attack times of my limiter seem to be not as quick as the original Fairchild.
I think I made a mistake with the loading of the control amp. Or perhaps the amp needs to be a bigger rating - more like 20 watts.
On the output I used a standard speaker line transformer which was 8ohms to 10 watts. I loaded down the transformer in exactly the same way as the original Fairchild control amp output transformer and I built exactly the same time constant circuit. If I remember right it has a 2700 resistor strapped across the secondaries. (Do I need this with my amp/transformer combination or will this slow it down???)

The control voltages look good on a scope and measure -70 volts or more in deep gain reduction.
The gain reduction tubes do not thump and seem to be well matched and sounding good.

But the real point is that my limiter is not quite fast enough to squash those really fast transients on drums. On Pro Tools I can see tiny millisecond peaks before gain reduction kicks in.
Anyone got any ideas how I can improve things????

I am tempted to go ahead and build a tube control amp for the unit if I cannot solve these issues.

I thought trying to adjust 7es8. seems that the 6ba6 is the winner!
I think the power-amp control is strictly linked to
attack time of the compressor.
would have some mp3's drums via your 670?

offtopic: good fairchild link http://recforums.prosoundweb.com/index.php/m/0/27498/144/prevloaded/0/

control amp w/ hammond tx: http://www.groupdiy.com/index.php?PHPSESSID=3f38495d7290077c43b87bb981bfa0e2&topic=33160.0

http://www.youtube.com/watch?v=OkoVits-3sA

SUPERMAGOO said:

http://www.youtube.com/watch?v=OkoVits-3sA

Click to expand...

Ha!  I believe I built the mic amp that is being used there.  I also built the LA-2A that is compared in the complete Masterclass set.  I lent them one LA-2A while working at UA and then built the two they then ordered as a break from the design work grunt I should have been doing.

Thanks for posting.

wow curve tracer!  http://www.youtube.com/watch?v=LmoEAIUshAE&feature=related

my idea

Good idea!...so you can have powerfull sidechain with tone control or even with overdrive...how it's sound?

unfortunately not working well. :-\
when the audio pass through without the control-amp of the contributes something nice
in the sound.
when the control-amp works sounds bad ...
has oscillations.
not that I'm doing wrong ...
be wrong is the relation of the output transformer control-amp.
I do not know how to calculate that ratio.

I bet the output of your guitar amp is unbalanced, so it must create havoc with the negative bias.

I use a guitar amp instead of control-amp is just to see if it works.
The guitar amp is isolated from the ground of the compressor.
the bridge rectifier has a negative offset voltage.
should work. although it is bad ...