What's in a passive line attenuator?

[Harry Klippton]

Is it just resistors? anybody have experience with these?
I'm talking about this kind of device

Paging @PunchySunshine

 

[JTEX]

Just resistors. Something along these lines:

 

[Harry Klippton]

Thanks for confirmation @JTEX I'll just build a box and play around with the values

 

[pricklyrobot]

They need some better marketing. I’d be selling this as a “Discrete-Channeled Differencing Mixer”!

 

[Paradox916]

Thanks for confirmation @JTEX I'll just build a box and play around with the values

Dual gang pot with a 1k bridge?

 

[jwin615]

Dual gang pot with a 1k bridge?

Only if you can get pots with near matched wafers. Definitely want a quality 5% 9mm, not a 20% 16mm.
On the higher end, a dual rotary with matched resistors.

 

[Paradox916]

Only if you can get pots with near matched wafers. Definitely want a quality 5% 9mm, not a 20% 16mm.
On the higher end, a dual rotary with matched resistors.

Did think of tolerance, yeah it really wouldn’t be a balanced out if they weren’t matched, still working on my first cup of coffee

 

[Harry Klippton]

Lucky for me, I want them to be unbalanced anyway

 

[Erik S]

Lucky for me, I want them to be unbalanced anyway

What for?

 

[Harry Klippton]

What for?

The group outs on my mixer are +4 and all my tape machines are -10. I need to actually fuck around to see where I'm at so I'm just pondering in the meantime

 

[JTEX]

@Paradox916 : You'll need to match R1 and R2 to at least 1% tolerance to keep your balancing, but you can use a pot for R3 (wired as a variable resistor) if you want varable attenuation. If you're going to plug the attenuator into a mic pre, R3 might degrade your noise performance if it's higher than around 150 ohms or so.

 

[jwin615]

Dealing with unbalanced gear in the studio - Crookwood

Sigh. Dealing with unbalanced gear in the studio is a pain and always results in a compromise. Why? Well because: The tiny audio signal return goes down the same wire as the mains ground currents The levels are often lower than pro levels The output impedances are often stupidly large However...

crookwood.com

I suspect your mixer is hard balanced unless it has transformers on the group outs.
Do the group outs have inserts? Are they a single TRS for both send and return?

 

[Harry Klippton]

Dealing with unbalanced gear in the studio - Crookwood

Sigh. Dealing with unbalanced gear in the studio is a pain and always results in a compromise. Why? Well because: The tiny audio signal return goes down the same wire as the mains ground currents The levels are often lower than pro levels The output impedances are often stupidly large However...

crookwood.com

I suspect your mixer is hard balanced unless it has transformers on the group outs.
Do the group outs have inserts? Are they a single TRS for both send and return?

The group outs are 1/4 unbalanced+4db. They have TRS inserts

 

[jwin615]

Hmmm
You need a T pad
Assuming 600 ohm output on the groups, cause I have no idea

 

[jwin615]

If you're not using the inserts, build the pad on TRS plugs and stickem in the inserts.

 

[Harry Klippton]

@jwin615 yeah 600 ohms. I don't actually want them on plugs. I was just gonna chuck em in a BB or something