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Author Topic: For those with passive monitor attenuators..  (Read 15974 times)

Viitalahde

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For those with passive monitor attenuators..
« on: March 07, 2009, 09:04:46 am »

What are you using?

There will be a 3rd and final console I'm about to build. I want to improve the mechanical quality by going from Elma switches to the great, sturdy Russian switches I've been using lately.

But most of all I want a bridged-T attenuator. Right now I have a 5k L-pad attenuator, 23x 2dB steps + dim. The new one will be built on a Shallco. I reckon something like 2k5 would be a place to start with Z values.

Since this is going get into general console discussion anyway, let me ask one more thing:

How many of you are using something more extended as a "console" than a monitor volume controller?

I switched to the current console about two years ago, and I personally love having all the bypasses at one single place. The amount of cable is for sure larger with all these sends & returns, but it's not often I have everything patched-in.
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Jaakko Viitalähde
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mastertone

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Re: For those with passive monitor attenuators..
« Reply #1 on: March 07, 2009, 11:39:46 am »

Hi Jaakko, does shallco offer ready made attenuators or just the switches?

Im pretty much in the same situation, but ive been lookin at the goldpoint att.
And my monitor section will have more functions than now.
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Jonas Ekstrom
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Andrew Hamilton

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Re: For those with passive monitor attenuators..
« Reply #2 on: March 07, 2009, 12:48:45 pm »

Shallco offers both ready-made attenuators at custom Z values, as well as the naked switches.  I'm using a Shallco-made 5k Ohm bridged H-pad (which is a differential path T pad).  According to Nelson Pass, the Pass Labs amps with SuperSymmetry actually sound better with differential sources, rather than single-ended ones, and he confessed to me that he has never been in a mastering studio that wasn't entirely wired differntially.

The use of bridged-T or -H pad lets you minimize the number of resistors in series to 2 (per leg), at all steps of the switch.  So, very quiet settings will not have more Johnson noise (; than higher loudness settings, as is the case with series-types. Also, the impedance seen by both the source and the destination does not change when switching steps with this type of circuit, so one can focus on the sound of the loudness differences without much interference from other voodoo.

The Lavry M•DA-824 can drive a 600 Ohm load, and Dan told me that 2k Ohms would be the theoretically ideal loading for that DAC.  So, I had a 2k Ohm balanced passive attenuator made by GoldPoint Audio which worked nicely for a while.  I preferred the sound of the CraneSong Avocet to that.  But after DC insisted that passive, when loaded properly, is "essentially blameless," I splurged for the $600 Shallco bridged H.  Of course DC was correct - at least according to my listening tests.  The Shallco 5k H pad is sonically invisible!  Loving the lack of color.

After I sold the Avocet, I had over $1500 left over to buy other things with.  I did implement a source switch, as well as an independent mute switch for left and right channels.  5k is what DC recommended as a good compromise between performance and flexibility,  and it is not much worse than 2k for human hearing requirements, as long as the cable is ultra~low capacitance and the leads are as short as necessary to reach the amps, and 5k does provide a little extra resistance for wimpy sources one might wish to audition on the same setup.  (Fwiw, I'm all Mogami 3080 right now, which is 14 pF/foot).  





Andrew




P. S., I'd like to know if anyone has modified their differential inputs and outputs on mastering gear to be single-ended and what was entailed as well as any gotchas.... I was once instructed to bypass the balancing stage (as well as anti-RFI components) of the inputs of a Dominator II by one of our resident electronics gurus, fwiw.  This was only to improve the purity of the sound, which I think it did.  But, it was on a multiband clipping limiter, so sound quality is a relative thing, right?  

Since mastering studios are usually quiet and specialized environments, why is so much mastering equipment differential?  There are a few notable exceptions for off-the-shelf gear, such as that made by Pendulum, which is deliberately single-ended.


 
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cass anawaty

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Re: For those with passive monitor attenuators..
« Reply #3 on: March 07, 2009, 03:53:58 pm »

I use the Goldpoint SA1X.  Very happy with it.
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Cass Anawaty, Chief Engineer
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Gold

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Re: For those with passive monitor attenuators..
« Reply #4 on: March 07, 2009, 03:58:45 pm »

I recently had a 10k:5k (full) H pad made by Shallco. I asked for a bridged H and they quoted me on that. Then they realized they only knew how to do an unequal impedance as a full H. So that is what I got. Apparently I was the only one who ever asked for that. A 12 deck switch for stereo. I got 30 position with 1.5dB per step. It's very impressive looking. I have a big knob for it.

I don't have it installed yet. I have meters on the way. They are all custom order Sifams. VU, PPM and correlation meter. All white background with black scales. The correlation meter is a vertical orientation edge meter. I got gray masks for the Clarity series VU and PPM and extra bezels for the edge meter which I will attempt to paint gray. It should be very pretty.

For bypass the grand plan is to have relays in the gear but control centrally located.
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Paul Gold
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dcollins

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Re: For those with passive monitor attenuators..
« Reply #5 on: March 07, 2009, 04:32:37 pm »

Viitalahde wrote on Sat, 07 March 2009 06:04

What are you using?



Shallco 2k5 bridged T.

Quote:


Since this is going get into general console discussion anyway, let me ask one more thing:

How many of you are using something more extended as a "console" than a monitor volume controller?



3 monitor inputs and 3 insert points.  Of which I use one of each on a normal basis.


DC

bblackwood

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Re: For those with passive monitor attenuators..
« Reply #6 on: March 07, 2009, 10:01:02 pm »

dcollins wrote on Sat, 07 March 2009 15:32

Viitalahde wrote on Sat, 07 March 2009 06:04

What are you using?



Shallco 2k5 bridged T.

Ditto (go figure).

Quote:


Since this is going get into general console discussion anyway, let me ask one more thing:

How many of you are using something more extended as a "console" than a monitor volume controller?


Six sources, seven monitor positions, six inserts.
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Brad Blackwood
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Andrew Hamilton

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Re: For those with passive monitor attenuators..
« Reply #7 on: March 08, 2009, 01:43:30 am »

2.5k? Oh, DC...  My 5k system craps out at 227 kHz. );  

(Or, do I add the amp's input Z to that of the attenuator?  If so, I'm actually down at 42 kHz before I enter the cross overs)

You know, 1/2πRC...    My feeling is that I would not add the amp's 22k Ohm input Z to the 5k Ohms of the attenuator, because the resistive part of the amp's impedance is _after_ the capacitative part of the network (i.e., there's no more cable once it hits the amp).    However, I have read people to write that one must factor in all the Z's in each circuit...  





Andrew
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Viitalahde

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Re: For those with passive monitor attenuators..
« Reply #8 on: March 16, 2009, 06:16:39 pm »

Been thinking about this.

2k5 or 5k bridged-T sounds like a good route. I just bought some naked Shallcos off eBay, but we'll see if I get around designing my own attenuator or ordering one from Marchand.

I was looking at Dangerous Master earlier, and the three insert points got me curious. Makes sense to me. I could group pieces that usually go together behind one insert, and still use each piece's own bypass. Not all of my tools have a bypass (since it's in the console), but some do.

It's easy to go nuts with console design, when all I need is a simple one. The current one has pre-process attenuators, which I never use. The first one had a fancy L mono/mono/R mono switch, which could be handy but not really necessary.

Restrictions have always made me tick better.  
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Jaakko Viitalähde
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jdg

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Re: For those with passive monitor attenuators..
« Reply #9 on: March 16, 2009, 07:00:53 pm »

i am on rev 5 of mine. and i really simplified it.
6 source, 1 insert, 3 outputs. 5k attenuator

the one insert is now really just a global bypass for the whole process chain
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john mcCaig
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Andrew Hamilton

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Re: For those with passive monitor attenuators..
« Reply #10 on: June 28, 2009, 09:07:39 pm »

After re-reading the Pass Labs X-350 manual, I think Nelson was trying to say that _he_ prefers balanced (i.e., balanced Z legs of differential pairs, as the) signals rather than single-ended, and that, _if_ one is using his amps and _not_ using a balanced source, then s/he is _not_ benefitting at all from his patented SuperSymmetry feature, which requires a balanced signal as source.  The distortions of each leg will not be appreciably reduced (though somewhat, yes), but the differential distortions will tend to cancel by over a factor of 10, when SuperSymmetry is "enabled."

Furthermore, if, as DC has often said, one's mastering studio is capable of dealing with single-ended signals without noise or RF, then there's no reason (or tends to be little reason?) to employ balancing receiver/driver circuits, which, in the absence of other maladies, can _only_ negatively impact the sound (if there is any impact at all).  Who needs SuperSymmetry in these rooms, after all?  And I think I can agree that the Pass amps sound more like a very clean tube amp, in terms of open-ness, when operated single-ended, as compared with differential-sourced.  

Even Nelson's manual states that simpler is always better, with an allusion to Occam's razor...   But he clearly intended the Pass X series to be operated in balanced installations and barely mentions the RCA inputs.   Interesting polyphase logic?

It is also curious that he was saying that he was unaware of any  single-ended implementations in mastering studios.  Maybe he thought I meant mixing studios?  

Fortunately (for me), a bridged H-pad can be used as a bridged T-pad.  If I wanna go balanced again for some reason, the extra decks are in place.  

Also, by using the M•DA-824 in unbalanced output mode, one gets another 6.02 dB attenuation free of charge.  (hehe)  



Andrew
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bruno putzeys

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Re: For those with passive monitor attenuators..
« Reply #11 on: June 29, 2009, 03:24:35 am »

The best compromise is to keep differential inputs but remove any circuitry explicitly designed to make a symmetrical output, as it is unnecessary. Don't remove differential input circuitry, you really need it.

There's no reason for an output to have voltage symmetry. As soon as the hot and cold wires are driven by the same impedance, you have a balanced output, meaning that a differential input will be able to ignore any ground differential that may exist between boxes. The cold wire may simply be tied to signal ground with a build-out impedance equal to that of the driver. Voil
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Viitalahde

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Re: For those with passive monitor attenuators..
« Reply #12 on: July 16, 2009, 02:03:27 pm »

Bruno has many fine points that anyone needs to read!

But I got an on-topic question since I'm designing a new console right now.

How are you people doing level-matched comparisons between the source and the processed, post-A/D audio? In my current console, I have no way of doing this, and I've simply been turning the monitor volume up & down.

This needs to be changed.

What I have in mind is that my "monitor source" switch in the new, passive console could have a "compare" -position, in which a variable, stepped attenuator is inserted to the DAW feed. The attenuator would be out in any other position.

Since my monitor attenuator is going to be bridged-T (2k5, most likely), I suppose I'll have to make the comparison attenuator of bridged-T type, too.
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Jaakko Viitalähde
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bblackwood

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Re: For those with passive monitor attenuators..
« Reply #13 on: July 16, 2009, 02:24:16 pm »

I turn the ceiling output down on the L2 to match.
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Brad Blackwood
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Re: For those with passive monitor attenuators..
« Reply #14 on: July 16, 2009, 02:25:29 pm »

Viitalahde wrote on Thu, 16 July 2009 14:03

 I've simply been turning the monitor volume up & down.

This needs to be changed.




That's what I do. I think it works well enough. To my mind it's mostly a Go/No Go test. An exact level match is impossible once more than a tiny amount of processing has been applied.
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Paul Gold
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