balanced attenuator

[baadc0de]

ok, so I know this forum isn't a generic helpdesk for all of my electronic woes, but maybe someone would please help me with this..

I bought a "balanced XLR" attenuator from HERE and the seller isn't really helpful in getting it wired up.

I'm looking to use it as a balanced line-level attenuator before an altec 436 compressor build of mine that has a Sowter 8346E input. The idea is to put this between the XLR input and the 8346.

The attenuator itself has 4 24 position tracks that seem to be identical. I haven't added up resistor values, but I assume they add up to 10k.

Cheers,
B.

 

[RuudNL]

Did you see this picture? I think this explains how they should be connected. If you really would like to have a balanced attenuator, you could use an attenuator in each 'leg', although in this case you would get a double logarithmic characteristic, no idea how that would work in real life...
I see the attenuator is constructed around those cheapo Chinese switches. I don't have very good experiences with them.
The switches I have used didn't switch both sections at the same time, this causing more attenuation in one channel than in the other.
I took them apart and glued the rotors (carefully!) to the shaft, this solved the problem.

 

[baadc0de]

Hi,

Mmkay, I understand now - I thought this was either a PI or T mono attenuator, but in reality it's just a double, um, double variable resistor (for "balanced") again doubled up for stereo. Silly me, reading too fast.. I think the "attenuator" wording got the best of me. Well, I guess I could do both legs but I'm not sure what the input transformer will say about this. I guess I could convert this to a T-pad arrangement anyway what with 4 tracks.

Sorry to hear about the chinese switches :/ I hope mine behave better.

EDIT:
Actually, wouldn't the tracking stay the same, i.e. logarithmic, when applied to both legs of the input signal? Also, I think this could be made into a balanced U-pad? http://www.uneeda-audio.com/pads/ in example1 from this site, there is a calculation that I don't pretend to understand through and through, but let's say Zout = Zin = 10k, k = 10000 (80dB)... but that gives a ridiculously small Rshunt?

 

[Kingston]

Don't you already have the dual 50k+50k attenuator right after the transformer in your build?

Set up like this: http://www.triodeel.com/al436c.gif

If not, you can just as well use those 10k logs in that position.

You would need something like a 600-ohm T-attenuator (not going to happen with those 10k rotaries), if you want to drop level before the input transformer. Anyway, Sowter 8346E should be able to handle line levels with ease so you don't really need to do that.

 

[baadc0de]

hmm, you got me thinking...

otherwise, no, I don't have it setup that way, these are drip's altec PCB builds and his build manual states that the 50k/50k are for the real sowter input trafo, not the version with the fairchild 660 input trafo (which is what I built). I need *some* level control and I need it stepped because I use these a lot for stereo material, especially overheads and pianos. Cool, I'll try to use these in the 50k spots, it's not like something weird could happen in that relatively low voltage area.

 

[ruffrecords]

I think what you bought is really a stereo attenuator. I suspect they used to term balanced to mean the two channels track each other better than a stereo pot. Rather misleading in my view.

Cheers

Ian

 

[Kingston]

it's not like something weird could happen in that relatively low voltage area.

20k (10k+10k) will load the input transformer a bit more than 100k (50k+50k). But it's likely most gear you have is low impedance out and will drive that with ease. Depends on the transformer a bit as well. Check frequency response after installing them.

 

[baadc0de]

I'll install it and measure the response. If it will suck too much, I'll just sell them on I guess. These are really colour boxes for me, but bass response is primo the way it is now. I was under the impression that they are O, T or H or whatever pads, balanced, mono, but it turns out that they are just 4 tracks of 10k log tapped resistance.. yeah, I didn't like being shafted by that, but most of the info was on the page if only I could be bothered to read all of it carefully.. lesson learned, I guess.