balanced audio fader design

[jemduff]

Hi folks

I want to create a fader circuit that can fade balanced line level signals for riding vocal levels before they hit the compressor (think
Maximum level: +26dBu from Baby Animal pre and tla 5051's in the chain)

the problem is I have this beautiful Penny and giles fader but I don't want to spend 200 bucks on transformers balancing the thing.

Are there any passive designs using a single fader that can keep the signal balanced?

If this is not possble, are there any simple and clean unity gain balanced line/out driver circuits kicking around?

Ideas?

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[Svart]

buy another fader? Edcor? one of the many (de)balancing ICs?

 

[PRR]

Run it unbalanced. Keep the output cable under 10 feet. Nobody will know.

 

[NewYorkDave]

Examine your reasons for "needing" a balanced fader.

You can use an unbalanced fader between a balanced output and a balanced input; just don't connect the low side to ground. The line won't be truly balanced anymore (due to the asymmetric impedances) but it'll work fine in most cases. Give it a try.

 

[pstamler]

If you really need it to stay balanced, and are willing to accept some loss and variable load, a "U" pad will do fine.

From the balanced input jack, connect a pair of 5k resistors. Hang the fader across the ends that aren't connected to the input, rigged not as a potentiometer but as a variable resistor -- hook the slider to one of the fixed resistors, and the end that's normally grounded to the other fixed resistor. Now hook the two legs up to the output jack.

With the pot wide open, assuming a 10k fader and a 10k load on the output, your loss will be about 10dB; with lighter loads on the output the loss will be less and the fader's taper will be more accurate. The load on the preamp will be 15k with the fader wide open and 10k with the fader closed, probably not an issue.

Peace,
Paul

 

[jemduff]

Thanks folks...
Looks like I'm going to go the unbalanced route as it is the simplest and I'm only dealing with short distances ( essentially less than a few feet).

 

[jemduff]

oops .. peskky submit button...

but thanks for all of everbodys input.. this forum is the best!

BTW I built a small balanced in/out buffer using a tl074m on perf board that I'm yet to test.
Are tl074's evil?
Will I get seven years bad luck for going non-discrete?

 

[PRR]

> Are tl074's evil?

Many of the commercial recordings you enjoy have been through several 351 or 072 chips.

The worst fault is: they will NOT drive low impedances.

When working into loads much higher than 2K: they do add a little "zing" which shouldn't be there. Depending on the material, the circuit, the level, the loading, and the listener, this may be good, inoffensive, or irritating.

When in doubt, reach for 5532. They've been made in many factories on several masks on several processes over the years, and sharp ears can hear good and bad vintages. Newer chips have FAR better specs. Still the 5532 is a workhorse.

 

[Oliver Archut]

Hello there,

instead of using the low quality P&G try to get a hold of the Eckmiller or Danner passive faders from the 50 and 60s... They show up on e-bay sometimes for next to nothing, the W85 are the best but the W68 will work fine too.
There are also CLG and EMI faders that will work same as good but due to the EMI white magic they are way to expensive...

Another easy solutions are the active TAB/TELE/Siemens faders that you can pick up here and there for $15 to $50, the Telefunken discrete W690 either the mono or dual or stereo has a taped transformer input design that will work wonders regarding reflected load impedance etc. Be careful with the later Siemens or TAB ones they just suck, the ANT Telefunken that are readily available are junk, or better the electronic is...

Best regards,

Oliver