Majestic12 builds Drip Fairchild 670

[radiance]

Try to get these distressor knobs without the numbers...otherwise it's a mess, both number on knob AND panel...

 

[wave]

I am also interested in those knobs for a friend of mine who is building a Drip 670 ..... if it is something that we can buy in bulk then I would consider making them a stock part.

Colin
www.audiomaintenance.com

Colin,
Have you read this post on the GS forum?
http://www.gearslutz.com/board/q-dave-derr-designer-distressor-compressor/4170-dave-where-can-we-buy-distressor-knobs.html

Wave

 

[Majestic12]

I got the distressor knobs directly from Empirical Labs after asking Dave if he can buy some from him. But I don't really want to use them on the 670, it was just a joke
I don't know who's making those knobs, I think you will have to ask somebody from EL...

BTW: I recently started to put all the components on the main pcb. For personal satisfaction I try to lift up all components a few mm from the board, especially the 3W resistors for better heat dissolving...

 

[Stagefright13]

That's awesome thanks for the pics!! I been contemplating one of these myself for A long time. Things will pick up here in A couple months. But doubtfully enough to cover one of these. lol. Would love to build one tho. If someone is afraid to do it themselves let me know!!

Keep up the pics.

John

 

[Majestic12]

Today, I had the chance to take a look at an original Fairchild and examine some things that weren't clear for me until now, especially concerning the stereo link and the DC Threshold.

Beautiful unit, even when there's a lot of dust and dirt inside

 

[loopermc5]

Very Interested in what you found out with the stereo link been holding off on doing mine.

Thanks

 

[Majestic12]

The stereo link switch connects both time constant networks. Best place for it is right after the time constant bridge rectifiers. Unfortunately, you can't tell from the schematic if the (+) or (-) sides of the rectifierers have to be linked. In the original unit, it seem's that it's the (+) sides, but I'm not quite sure yet...

 

[hop.sing]

I always thought that the original Fairchild had no stereo link ability. but if I would connect the two sidechains, I would do it right after the rectification on the side of the timeconstant network. (I guess, that is the + side of the diodes)
You double the capacitance in the network this way, but at the same time, resistance is halved and that way all the time constants should stay the same.

 

[Majestic12]

I think the original unit definately has the stereo link. When you look at the picture, the switch is located on the right side between time constant L and the stereo/ms switch.

 

[hop.sing]

Ah, ok, but that might be a retrofit, at least, it looks like it. Does not really fit into that beautiful symetric front panel

 

[Majestic12]

Yeah..could be. Not all the 670 seem to have it.

 

[emrr]

Stereo link is standard, it's in the original manual.  This is old dead ground, long covered.  The real manual and schematic are available online for those willing to search and understand.  As implemented, the time constants are different for stereo versus mono.  We've also covered this in the pimp/mod the pm 660 thread. 

 

[loopermc5]

Stereo link is standard, it's in the original manual.  This is old dead ground, long covered.  The real manual and schematic are available online for those willing to search and understand.  As implemented, the time constants are different for stereo versus mono.  We've also covered this in the pimp/mod the pm 660 thread.

oh yeah duh! cool I used your suggested method in my pm ill do the same in the 670
http://www.groupdiy.com/index.php?topic=29056

 

[hop.sing]

Stereo link is standard, it's in the original manual.  This is old dead ground, long covered. The real manual and schematic are available online for those willing to search and understand.

M/S processing of course, but I did not know of simple stereo linking. That is my resource: http://audio.kubarth.com/fairchild/index.html
At a first and even at a second glance I cannot find any hint there. But nevermind, I might be blind... or am not willing to search and understand ;D

As implemented, the time constants are different for stereo versus mono.  We've also covered this in the pimp/mod the pm 660 thread. 

Of course you are right, Attack time should change, but release is essentially the same. I went through that thread (Never did before, because without schematics, it seemed pointless), it is an interesting read. Is suggests, that the attack time is primarly determined by the drive ability of the sc amplifier to load that capacitor. Which I found true on my experiments with a fairchild like topology.
And if I remember right I found out that simply tying the contol voltages together did not double the attack time, like it should.I think, I did not measure or hear any difference at all. But I have to verify again. Maybe it is because you double the drive ability the same time you double the capacitance, so the attack time roughly stays the same. Would be easy to test with a signal just on one channel, than it should really be slower.

 

[hop.sing]

As implemented, the time constants are different for stereo versus mono

Hi
I just want to share a little observation with my homemade compressor, that is made of 4 parallel gain reduction tubes per channel, biased as in a 660, and a Tip41/42 driven Sidechain, which is driving the time constant network trough a transformer. The time constants do not change, no matter if the channels are linked (The control voltages are simply connected, no diodes) or not, BUT only if I drive both channels simultanuosly. Driving just one channel into the linked network slows down the attack time considerably. Which illustrates the point, that the attack times in that compressor topology are really dependent of the drive ability from the side chain. Thinking about it, it seems a cool feature actually, centered signals get reduced fast and everything on the sides takes a little longer, which seems practical in real live (Even though I never really noted that behaviour on musical signals, just measured it on a 10k sine).

 

[emrr]

Very interesting, thanks.

 

[Majestic12]

Short update. Soldered in all the jumpers and a bunch of resistors. I just ordered all missing caps and parts for the main pcb. Now it's time to save money for the sowter transformer package...

 

[dagoose]

oeh... nice!

 

[danander11]

I'm watching closely...  I'll start mine sometime this year..  Need to finish a few other things first though.

Thanks for posting these.

 

[RATMNL]

Yeah man, make as many pictures as possible....
I am planning om making one as well!

Regards,

Mark