Passive monitor control questions...

[CurtZHP]

I'm in the process of preparing for some major changes in my home studio.  Most notably, I'm kicking around unloading my digital console and associated interface (which are starting to show their age), and downsizing to a more streamlined setup.  I just don't do the kind of work I used to, and this stuff is mostly overkill.  Pretty much all my mixing and processing takes place "in the box" now, so the mixer has become nothing more than a glorified router and monitor control.  That's a lot of bells and whistles for what could be accomplished with a knob and a couple switches.

While I'm shopping around for what I will ultimately replace it with, I'm experimenting with a few options.

One is in the form of an eight channel sound card I inherited from the radio station where I work.  Eight analog and/or digital ins/outs, but no monitor control.  So, I'd have to build/buy one.  I was tinkering around with this design....

http://www.audiotechnology.com.au/wp/index.php/on-the-bench-diy-monitor-controller/

Is this a truly balanced signal path, or should I do something different to achieve that?  I was also thinking of something similar involving a good ol' Alps RK27 quad pot, putting each stage on both + and - of each channel, but they're not very easy to come by.  And would that even be an improvement worth that much extra cost?  Basically, I'm coming out of balanced outputs 1 and 2 of the sound card (using other outputs to feed the occasional headphone amp), and going into the balanced inputs of an amplifier.

Didn't want to shell out a lot of money, because I'd rather put that toward what I ultimately end up with.  But then, if this works out as far as workflow is concerned, I could see putting the funds into improvements on this setup.

 

[moamps]

...Is this a truly balanced signal path, or should I do something different to achieve that?

It is balanced, but the main problem is questionable tracking between the channels, especially at low levels. 

 

[CurtZHP]

It is balanced, but the main problem is questionable tracking between the channels, especially at low levels.

Would a better quality pot improve matters?  An Alps RK27 dual gang is certainly easier (and cheaper) to find.

 

[gyraf]

Low-level tracking is optimized with the use of "DIM"

RK27 is plenty fine here - and you do not need balanced unless you have a very long, noisy distance from pot to amplifiers.

Jakob E.

 

[CurtZHP]

Low-level tracking is optimized with the use of "DIM"

RK27 is plenty fine here - and you do not need balanced unless you have a very long, noisy distance from pot to amplifiers.

Jakob E.

"DIM?"

 

[gyraf]

-20dB switch

 

[CurtZHP]

-20dB switch

Ah!  Since you typed it in all caps, I assumed it was an acronym for something.  ;D

 

[mjrippe]

I built one of these for a client some years ago and they were very happy with the performance. 

 

[ruffrecords]

If you want accuracy and good tracking, even at low levels, then stepped pot is the way to go.

Cheers

Ian

 

[CurtZHP]

If you want accuracy and good tracking, even at low levels, then stepped pot is the way to go.

Cheers

Ian

That was going to be my next question.  If I wanted to go with a stepped attenuator, is it just a simple matter of substituting that for the pot in the above schematic?

 

[pucho812]

That was going to be my next question.  If I wanted to go with a stepped attenuator, is it just a simple matter of substituting that for the pot in the above schematic?

yes.

 

[CurtZHP]

Anyone here had any luck with the cheap Ebay knock-offs like this one?

https://www.ebay.com/itm/Stepped-attenuator-24-position-stereo-10k/152749600304?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Db2e1cc5552cc4ce4abad2b23f3631228%26pid%3D100675%26rk%3D2%26rkt%3D15%26sd%3D152541780899%26itm%3D152749600304&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3A86aeac7b-b1f8-11e8-95df-74dbd1803a5c%7Cparentrq%3Aafe22dc11650a9c943e2dc90fffffeb2%7Ciid%3A1

 

[scott2000]

Anyone here had any luck with the cheap Ebay knock-offs like this one?

https://www.ebay.com/itm/Stepped-attenuator-24-position-stereo-10k/152749600304?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Db2e1cc5552cc4ce4abad2b23f3631228%26pid%3D100675%26rk%3D2%26rkt%3D15%26sd%3D152541780899%26itm%3D152749600304&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3A86aeac7b-b1f8-11e8-95df-74dbd1803a5c%7Cparentrq%3Aafe22dc11650a9c943e2dc90fffffeb2%7Ciid%3A1

Never tried that but I had one of these in the past.....

https://www.ebay.com/itm/DACT-Type-21-Stepped-Attenuator-Volume-Control-Hi-Fi-Grade-for-Amp-Preamp/202242320352?hash=item2f1694e7e0%3Am%3AmzeTLWK9sN8OHriv9TouXHQ&var=502206917988


it was very accurate at low levels as well..

Something about the sound wasn't jiving with my set up... was too clean??? I'm not sure....it was still very good and I wouldn't hesitate recommending it.........but I like the ALPS RK.....


I remember Gold maybe recommending some other brand as being the best but I don't recall the name or thread..... it's here somewhere...

 

[Matt C]

I built a passive monitor controller using the basic guidelines in the link you posted.  It works great.  I used a Alps RK27 dual gang linear pot with slugging resistors, the top and bottom  of the pot connected to the (+) and (-) phase of each channel, the wiper being the output.  It works great and the tracking is very very good.  Maybe not good enough for super OCD mastering guys but I think I measured it once and the two channels were within 0.1dB through the entire rotation of the pot.  Good enough for me.

 

[benb]

yes.

Well, yes and no. It will "work" but you may not get the same dB volume drop for each step in that circuit as you would using the stepped attenuator in a "standard" volume control circuit.

 

[scott2000]

Low-level tracking is optimized with the use of "DIM"

Nice! Makes total sense....

Thanks!!!

 

[Gold]

TKD CP-2500 series.

 

[moamps]

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.

 

[CurtZHP]

I strongly suggest using a 24 or (better) 32 position switch based attenuator here.

I'm inclined to agree.  I think I'll spring for one of those Ebay cheapies, and if this whole thing works for me from a workflow standpoint, then I'll replace it with something of higher quality.

 

[ruffrecords]

If you driving interface can handle it, I would also be tempted to reduce the values of the the resistors from 4K7 to 1K each and reduce the total resistance of the stepped pot to 2K. This would give you a lower driving source impedance and reduce any potential HF losses  and phase errors due to cable capacitance.

Cheers

ian