DIY Big Knob! (Pictures Included!)

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chrissugar

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Jun 4, 2004
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1,314
Location
Romania
Hey Marc

I would sugest you to build a stepped attenuator, something similar to the ones at www.dact.com ( http://www.dact.com/html/attenuators.html ) or www.goldpt.com
They are expensive so use those pages as inspiration. Buy some 24 steps ELMA switches and resistors, and make them yourself. You will never look back to pots for monitoring. Pots have very bad stereo tracking (10%-20% tolerance) while with attenuators you can achive by measuring the resistors 0.05dB error.

Here are my attenuators routers based on ELMA rotary switches (built them four years ago):
http://img.photobucket.com/albums/v292/chrissugar/CMS-LAB-AT1/AT1-FRONT.jpg
http://img.photobucket.com/albums/v292/chrissugar/CMS-LAB-AT1/AT1-BACK.jpg

chrissugar
 

sleepingtiger

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Joined
Mar 29, 2005
Messages
98
Location
NC
Hey,

I just got one of these after seeing it suggested in another thread (by New York Dave, I believe. Pardon me if I'm wrong...) They don't have the accompanying pcb's so they're inexpensive. I haven't soldered the resistors on yet but it looks like it will work fine. 23 steps instead of 24 but that's no big deal to me...

Good luck!

woops! :oops: I left out the link

http://www.triodeelectronics.com/4pol24posals.html
 

Vince@Speck

Active member
Joined
Jun 10, 2004
Messages
40
Location
San Diego
[quote author="Marc Girard"]Frankly, I'm not 100% sure it's a log pot... I couldn't find a pot with 4 decks easily so I ordered the pot from the local Presonus service center. The Central Station is a passive unit so I figured out that I would be all right using their pot, since there's not a hundred ways to do this... I might be completely wrong! The markings on the pot says: (A) C10Kx4 (A) for the Taiwan Alpha Logo.

Tried so research on Taiwan Alpha's web site, no luck really.[/quote]

C10K is a reverse-audio taper.

Vince Poulos
Speck Electronics
 

Minguta

Well-known member
Joined
Jun 5, 2004
Messages
172
Location
Thailand
[quote author="chrissugar"]Here are my attenuators routers based on ELMA rotary switches (built them four years ago):
http://img.photobucket.com/albums/v292/chrissugar/CMS-LAB-AT1/AT1-FRONT.jpg
http://img.photobucket.com/albums/v292/chrissugar/CMS-LAB-AT1/AT1-BACK.jpg

chrissugar[/quote]
Look so coolllllllllll :shock:
did you built something differrence like Select output?
2 channels input( left and right ) -> selecter 6 Channels out ( for 3 pair monitors ) :grin:
 

Marc Girard

Well-known member
Joined
May 15, 2005
Messages
113
Location
Montreal, Canada
[quote author="chrissugar"]I would sugest you to build a stepped attenuator, something similar to the ones at www.dact.com ( http://www.dact.com/html/attenuators.html ) or www.goldpt.com
They are expensive so use those pages as inspiration. Buy some 24 steps ELMA switches and resistors, and make them yourself. You will never look back to pots for monitoring. Pots have very bad stereo tracking (10%-20% tolerance) while with attenuators you can achive by measuring the resistors 0.05dB error.[/quote]

That was the initial plan! I salvaged an old ELMA 24 position rotary switch from a legacy WBS deck. I got to clean it out and resolder all the resistors but that's gonna be my plan-B. What's the best way of building the resistor network? Like, One on each pin of the swtich and one commun that ties'em all up? Thanks again!
 

chrissugar

Well-known member
Joined
Jun 4, 2004
Messages
1,314
Location
Romania
Hi Marc

It would be a good idea to build a series attenuator. Here is a picture:
http://www.goldpt.com/schm_ser.html
And here is a table with resistor values for various total impedance values:
http://www.goldpt.com/r_series.html
If you want it balanced think about everything double, 2 waffers per channel, 4 waffers for balanced stereo.
I would sugest to do it unbalanced, easyer and cheaper to build. You will have to connect only the + side (pin2 XLR) of the source signal to the attenuator. Also the attenuated signal only to the + side (pin2 XLR) of the balanced amplifier input (pin3 XLR input to ground). And of course don't forget ground connections (pin1 XLR in, to pin1 XLR out, to attenuator GND).

chrissugar
 
G

Guest

Guest
Alternatively, you may want to consider employing resistors for controlling volume. MCS has a few attenuator kits, which are probably cheaper than an ELMA switch and resistor kit.

And in addition, you'll get more attenuation steps too: 64 if you're choosing the RelVol attenuators.
 

Marc Girard

Well-known member
Joined
May 15, 2005
Messages
113
Location
Montreal, Canada
Here's the latest development on the DIY knob saga.  It works perfectly now!  Meanwhile, I got a copy of the Pres0nus Centr4l St4ti0n Schematics and I studied them.  I added 100k ohm (1% Xircons) to the mute switches, converting them in DIM switches instead.  Works great and sounds good.

Final pics:

4.jpg
 

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