Passive monitor control questions...

[Gold]

The additional source of mistracking in this type of attenuator (balanced L-pad) can be also the total resistance tolerance of pot's gangs which is +/-20% for Alps and TKD.
I strongly suggest using a 24 or (better) 32 position switch based attenuator here.

The TKD are much much better than 20%. Have you ever tested one? Every one I have has been less than 0.2dB difference between channels for the whole throw.

 

[moamps]

The TKD are much much better than 20%. Have you ever tested one? Every one I have has been less than 0.2dB difference between channels for the whole throw.

I mentioned the total resistance tolerance of channels. I worked with TKD faders, 10klog for consoles. The total resistance was never 10k. The P&G was the same.

 

[Gold]

But total resistance doesn’t matter in this context. It’s channel matching that does.

 

[ruffrecords]

But total resistance doesn’t matter in this context. It’s channel matching that does.

It does matter in an L pad.

Cheers

Ian

 

[Gold]

It does matter in an L pad.

Cheers

Ian

The TKD is not an L pad.  It’s a ladder attenuator. But why does it matter in an L pad for a monitor attenuator?

I just checked the data sheet and it says a potentiometer circuit. I do remember reading it’s not a straight resistive track but I don’t see that on the data sheet.

 

[ruffrecords]

The TKD is not an L pad.  It’s a ladder attenuator. But why does it matter in an L pad for a monitor attenuator?

I just checked the data sheet and it says a potentiometer circuit. I do remember reading it’s not a straight resistive track but I don’t see that on the data sheet.

In the schematic the OP posted there are two fixed 4K7 resistors with the pot (wired as a variable resistor not a ladder attenuator) across it. The minimum attenuation depends on the ratio of the 4K7 resistors to the pot overall resistance. if the latter has a 20% tolerance then there will be an difference between channels.

Cheers

Ian

 

[Gold]

In the schematic the OP posted there are two fixed 4K7 resistors with the pot (wired as a variable resistor not a ladder attenuator) across it.

Ah, I didn’t look at the schematic. I was thinking more generally. As long as the two tracks on a stereo pot are matched, the exact resistance overall doesn’t matter too much unless you need a specific amount of attenuation.

 

[ruffrecords]

Ah, I didn’t look at the schematic. I was thinking more generally. As long as the two tracks on a stereo pot are matched, the exact resistance overall doesn’t matter too much unless you need a specific amount of attenuation.

Correct and that is also why pro users tend to use linear pots rather than log ones. Linear pots tend to track much better than log ones due to their simpler construction. It is normal to slug a linear pot to obtain a kind of log law. At Neve it was common to slug a linear pot with half its value. The gives a -10dB mid point which is very handy for gain trims or  AUX sends.

Cheers

Ian

 

[CurtZHP]

"...to slug a linear pot to obtain a kind of log law."

Can you explain this further?

 

[ruffrecords]

Can you explain this further?

A linear pot on its own will  give a 6dB loss at the centre position. If you connect half a linear pot's total resistance from wiper to ground then at the mid point the resistance to ground is one quarter the pot value (half in parallel with half). The resistance from wiper to the top of the pot is half the pot value so the loss is one third which is close to 10dB. By altering the value of the slugging resistor from wiper to ground you can get different values of attenuation at the mid point and hence different laws.

You can also connect the resistor from wiper to the top of the pot so the mid point attenuation is less than 6dB. This is typically done in pan pots where you want about 3 to 4dB  attenuation at the mid-point.

Cheers

Ian

 

[CurtZHP]

For now, I'll likely go with a stepped attenuator.  Just need to decide which one.

This?
https://www.ebay.com/itm/Valab-23-Step-Attenuator-Potentiometer-10K-Log-Stereo/113234175382?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D0ca99ef65b524675b4406e766fb5d4dc%26pid%3D100675%26rk%3D2%26rkt%3D15%26sd%3D302838078107%26itm%3D113234175382&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3A5496d59c-b4ed-11e8-9597-74dbd1803b3f%7Cparentrq%3Ac341f8d61650aad0aa762fdcfffc2dd7%7Ciid%3A1


...or this?
https://www.ebay.com/itm/Valab-23-Step-Ladder-Type-Attenuator-Potentiometer-10K-Log-Stereo/113234175363?hash=item1a5d486583:gDkAAOSwkNZUqwuK

The latter appears to be a "ladder" attenuator.  (See what I did there?  ;-)  )
Would that replace a standard pot as easily as the other one?

 

[moamps]

Both will work but most probably not in the optimal increments, IMO.