Active vs. Passive Faders

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flextone

Active member
Joined
Dec 3, 2011
Messages
34
Hi,

I'm slowly filling up my german broadcast modules lunchbox and I want to put some faders in there so I could have more control over levels. Basically I'd like to be able to hit each module harder or softer, according to the circumstances. I feel this will come in handy especially with micpre's. Thoughts on this?

Should I be looking at passive or active fader designs? I don't quite grasp the difference. Is it like in active vs passive DI boxes?
 
These active faders are capable of adding gain ...basically a self contained module with transformer in and outputs + DOA as gain element.
I don't know if passive faders even exist for these German broadcast desks....AFAIK, they're all active.
 
Passive faders do exist for this format, I already saw a few.

Thanks, I'm glad the answer was that simple. A lot more questions need to be answered before I could complete this project :) 
 
flextone said:
Passive faders do exist for this format, I already saw a few.

Thanks, I'm glad the answer was that simple. A lot more questions need to be answered before I could complete this project :)
Actually, active fader is a misnomer. By definition, a fader is passive, its' an attenuator.
The fader "cassettes" such as Danner, Neumann,... are the combination of a passive fader with an input and output stage. Originally, faders were constant-impedance designs, so they could be integrated in the then-current impedance-matching scheme.
Originally, they used switched precision resistors,  a very expensive method; the steps between resistors created zipper noise when doing a quick fade.
Then came faders using linear potentiometer technology, using straight resistive tracks with wipers.
The drawback of this design is that constant-impedance faders require at least two tracks that require extremely tight tolerances; as a result, that was also very costly.
Then, in the late 60's/early 70's, the cost of electronice became less and less, and the impedance-matching scheme was replaced by the impedance-bridging scheme that has become de facto standard today. As a result, the use of a non constant-impedance fader became a practical solution.
The big advantage of non-constant impedance faders is that they use only one resitive track, that can be laser-trimmed for extreme accuracy.
However, in the transition period, there was a combination of impedance-matching and impedance-bridging, so many manufacturers produced "active" faders, which could be used in conjunction with any type of equipment.
 
Do vintage German passive constant impedance faders (Eckmiller W85 discrete resistors)influence the sound in terms of dynamics and frequency response vs carbon track type faders?
 
Gyraf,

I hear brighter and more transparency in the 1-3khz region using discrete resistors fader. These faders are 200ohms input and output. The newer faders (carbon track type) are 600 ohms input and 200 ohms output sound flatter and uniform frequency response. Is the sound difference due to impedance of the 2 type of faders?
 
Gyraf,

I hear brighter and more transparency in the 1-3khz region using discrete resistors fader. These faders are 200ohms input and output. The newer faders (carbon track type) are 600 ohms input and 200 ohms output sound flatter and uniform frequency response. Is the sound difference due to impedance of the 2 type of faders?
What are the source and load impedances applied to the faders?
The faders themselves should not have frequency response issues, but the stages that drive and receive the fader signals may have frequency response quirks if the impedances are not what they have been designed for.
Most modern faders are supposed to receive from a very low Z source and send to a high Z stage.
Vintage faders were designed to operate from matching impedances, where the source and load are equal. Often 600 ohms, but not always. Mainly for getting the proper taper, not for frequency response reasons.
In your case, 200 ohms is a load that the driving stage may struggle with. It may result in harmonic distortion that would result a subjective perception of increased upper midrange.
 
Gyraf,
I have 3 sources with impedances below,

1. EMT tube phono output is 50 ohms for load of 600 ohms
2. Nagra recorder output is 30 ohms for min. load impedance of 200 ohms
3. Telefunken recorder output 45 ohms for min. load impedance of 150ohms (+18dBm) or 200 ohms (+24dBm)

These sources are connected to Eckmiller passive faders W85 (200 ohms input and output impedance)

Then the w85 fader output is connected to TAB tube V74 line stage amp. The V74 input impedance is either 600 ohms or 10kohms.

I think both recorders should be fine in terms of impedances matching with W85 fader. I suspect only problem is the EMT tube phono output expect to see 600ohms but it only see 200 ohms?
 
It sounds like we are mixing discussion about old legacy technology (like constant impedance attenuators) and modern console faders.

Typical modern mixer/console gain structure is to follow a passive fader with +10dB fixed active gain stage, this covers most mixing level trim needs.

JR
 

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