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Basic Balanced Volume Control
Old 24th November 2015
  #1
Gear Head
 
audiopc2000's Avatar
 
2 Reviews written
🎧 10 years
Basic Balanced Volume Control

Hi Gearslutz friends.

I am writing this message because I need suggestions and advices about to make a balanced monitor controller.

I am looking for an inexpensive but good enough potentiometer to control my balanced output from Prism Orpheus Line level for 0dBFS: +18dBu (+4dBu' setting Output impedance: 100R balanced to Emotiva XPA-2 amp Input Impedance:33 kohms (balanced)

Actually I am reducing some -20 db average using the digital attenuator inside of Orpheus for listen music but I like to avoid that because many people say that digital attenuator reduce the quality.

I have seen some inexpensive units as
-Monicon
PMONICON Palmer PRO MONICON - Passive Monitor Controller

-McONE McTwo
Products

In this forum I saw a picture inside of theMcONE unit
Palmer Monicon anyone?

It uses the Alps Blue velvet 10KAX2 pot and two additional 10K resistors.

I want build my own unit but I am a little confuse. In the DACT attenuators webpage Wiring a balanced stereo passive volume control
appears that I need a quad potentiometer for make a BALANCED stereo volume control.

But NOS McOne and Monicon have balanced inputs and outputs using only one dual pot from Alps.

I was thinking in a Alps RK27114 (40$)
ALPS Quad Potentiometer RK27114 blue velvet 10K Pots logarithmic 10KDx4 log | eBay

Please any help will be welcome.

Best regards

Edgar Puglisi

Last edited by audiopc2000; 1st December 2015 at 10:23 PM..
Old 24th November 2015
  #2
Lives for gear
 
mirochandler's Avatar
 
🎧 10 years
On their website you can read:

Balanced ¼'' TRS connections to sources and monitoring system (The McONE is Unbalanced internally)

So the McOne is unbalanced internally and therefore only 2 decks are required for Stereo. With balanced Stereo you need a 4 deck potentiometer.
Maybe it is to save costs, maybe it is because normal potentiometers are too much imprecise to build it for symmetrical. Note that nearly all hardware devices internally unbalanced.

Go with the DACT, it is a attenuator for your lifetime.
Old 24th November 2015
  #3
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by audiopc2000 ➡️
//Actually I am reducing some -20 db average using the digital attenuator inside of Orpheus for listen music but I like to avoid that because many people say that digital attenuator reduce the quality.//

//appears that I need a quad potentiometer for make a BALANCED stereo volume control.//
Digital level adjusment is perfectly fine if implemented to modern standards.

A balanced VC can be realized with one stereopot or stereo attenuator. One resistor in series with each balanced leg and the adjustable R bridging the circuit after these R.
Old 26th November 2015
  #4
Lives for gear
 
sdbmastering's Avatar
 
Verified Member
🎧 10 years
Get a goldpoint switch or already assembled box.

Goldpoint Level Controls
Old 26th November 2015
  #5
Lives for gear
 
🎧 10 years
Well, problem is, typical audio logarithmic pot has quite significant issues with channel imbalances.. Especially at low levels. Black velvet is one of best available pots, but still can't match precision of stepped attenuators.
If you wan't to solve it, you can either DIY a box with stepped attenuator or purchase completed one, like mentioned Goldpoint. If you would like to further save some money, you can get also Elma switch and solder matched resistors to it.. But it is quite labor intensive.
Another really nice solution is digitally controlled resistor network Volume control - two boards can be controlled from one remote for balanced connections.

Lately, I've stumbled upon company called Mammoth Cave Audio
Products |
They have very affordable boxes with stepped attenuators (basic one is under 100USD) and boxes looks like devices from M.A.S.H. tv series . I don't have any of their products, but there were some thread with owner on GS, maybe try to seek for it.

Michal

Last edited by msmucr; 26th November 2015 at 02:23 PM..
Old 26th November 2015
  #6
Gear Guru
 
Thomas W. Bethe's Avatar
 
Verified Member
1 Review written
🎧 15 years
It is funny that they are calling themselves Mammoth Cave Audio but they are in Denver and Mammoth Cave (the last time I was there) is in Kentucky..FWIW
Old 26th November 2015 | Show parent
  #7
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Thomas W. Bethe ➡️
It is funny that they are calling themselves Mammoth Cave Audio but they are in Denver and Mammoth Cave (the last time I was there) is in Kentucky..FWIW
Maybe designer has strong experience from the visit of Kentucky, that he decided to build his own cave in Denver..

Anyway Mammoth Cave Audio company looks very sympathetic to me..
https://www.facebook.com/mammothcaveaudio/
Tim Gerak of Mammoth Cave Studios is debuting a line of hand-made audio gear | Westword

Michal
Old 26th November 2015
  #8
Lives for gear
 
TheBrightSide's Avatar
 
🎧 5 years
I recently bought this controller. It's fully balanced throughout .It seems to work well though I don't have anything else to compare it to.

Solid State Discrete Balanced Monitor Volume Controller AND 4 WAY Switcher NEW | eBay
Old 30th November 2015
  #9
Gear Head
 
audiopc2000's Avatar
 
2 Reviews written
🎧 10 years
-20 pad line level balanced attenuator

I friends..

Thanks for your all answers and suggestions.

Now I am thinking in something more simple but I have some doubts to make a -20 dB pad for my balanced equipment.

Here the graphs that I made from some info that I collected on-line but not sure if they are correct.

https://gearspace.com/board/attachme...1&d=1448908822

https://gearspace.com/board/attachme...1&d=1448908822
Attached Thumbnails
Basic Balanced Volume Control-pad-balanced-20db-rev2-.jpg   Basic Balanced Volume Control-pad-balanced-20db-rev1-.jpg  
Old 30th November 2015 | Show parent
  #10
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SmoothTone's Avatar
 
Verified Member
🎧 5 years
Quote:
Originally Posted by msmucr ➡️
Maybe designer has strong experience from the visit of Kentucky, that he decided to build his own cave in Denver..

Anyway Mammoth Cave Audio company looks very sympathetic to me..
https://www.facebook.com/mammothcaveaudio/
Tim Gerak of Mammoth Cave Studios is debuting a line of hand-made audio gear | Westword

Michal
I recently ordered a Mammoth Cave controller. Tim is very passionate about musicality, quality and functionality. A pleasure to deal with too: quick to respond, provided lots of info and answered all of my questions.
Old 1st December 2015 | Show parent
  #11
Gear Nut
 
wooly mammoth's Avatar
 
🎧 10 years
Quote:
Originally Posted by Thomas W. Bethe ➡️
It is funny that they are calling themselves Mammoth Cave Audio but they are in Denver and Mammoth Cave (the last time I was there) is in Kentucky..FWIW
Ha! It's long story. The Mammoth name has been around for a long time but changed over the years. My old studio was called "Wooly Mammoth Studios" and I operated under that for a while. Then about ten years ago, I was informed that there was another nice studio (in Boston if memory serves) with the Wooly Mammoth moniker and they had also been operating for a bit. (albeit without the bastardized american spelling of Wooly with one L). I had just built out my new space in Akron and decided to change it to Mammoth Cave studio to keep Mammoth in the title somehwere but differentiate myself for album credit and google reasons. It fit because the space was kind of cavernous and cave like. And then when I started making gear on the side, I just extended the name over. I'm an Ohioan at heart which isn't far from Kentucky... but that didn't have much to do with it. The old cave drawing of a mammoth that I turned into one of my logos actually comes from a cave in France. Those buggers roamed all over the place. But I love that bands always send me pictures of the exit sign when they drive through Kentucky on tour. And I've had a few bring me back souvenirs.
Old 1st December 2015 | Show parent
  #12
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by audiopc2000 ➡️
I friends..

Thanks for your all answers and suggestions.

Now I am thinking in something more simple but I have some doubts to make a -20 dB pad for my balanced equipment.

Here the graphs that I made from some info that I collected on-line but not sure if they are correct.

https://gearspace.com/board/attachme...1&d=1448908822

https://gearspace.com/board/attachme...1&d=1448908822
Yep, those will work for roughly 20dB attenuation, I would go with schematics at second picture with three resistors without connection to ground pin.
Topology there is called U-Pad and it is most commonly used for that purpose today.
Your interface will have low output impedance, so I would probably adjust resistor values to 470ohm and 100ohm.. ratio will stay the same.
Ideal value for series resistors that 1:10 ratio (-20dB) will be 450ohm, but 470 is readily available at standard component series and will be fine for that.
Pick some 1% metal film resistors (Vishay is most common vendor here for example), watt rating doesn't matter there, you'll likely find 0.25 or 0.5W ones.
Most practical to me is to built all that directly into XLR connector and make special attenuator XLR cable pair.. I'm using similar thing with my personal Zoom H4 recorder, which doesn't have pad and it is very easy to clip it with standard line level signal.

EDIT: this site offers great explanation about pads
http://www.uneeda-audio.com/pads/

Michal

Last edited by msmucr; 1st December 2015 at 01:51 AM.. Reason: add link
Old 1st December 2015
  #13
Gear Head
 
audiopc2000's Avatar
 
2 Reviews written
🎧 10 years
Thanks for the ideas

Hi for all.

With respect to the Michal suggestion

I am not absolute sure if your values for the two series resistor (450 Ohms) and shunt (100 Ohms) are good because the input impedance of the pad (the sum of all resistors) is 450+450+100= 1000 Ohms

When a passive preamplifier or pad is placed between an audio source and an amplifier, the source now “sees” not only the amp’s impedance (Ramp), but the combined impedance of the Passive Preamp (Rpre) plus the amp, let’s call that Rt. It’s an unfortunate consequence of physics and math that the combined effective impedance of R2 and R3 is always lower than either alone.

Rt = (Rpre x Ramp)/(Rpre + Ramp) where Rt is the total combined impedance of the preamp and amp.

Combining your values for the pad 1K and my Emotiva Amplifier 33K we'd have:

Rt = (1k x 33k) / (1k + 33k)
Rt = 33000K / 34K
Rt = 970 Omhs

The ratio will be 970/100 = 9.7 (a little low)


The actual Impedance Bridging Ratio (ratio) between my orpheus DAC 100 Ohms (balanced output) and Emotiva Amp (balanced input) 33k is
33000/100= 330 which is outstanding

I am thinking to make the pad with a input impedance of 10K

In this case

Rt = (10k x 33k) / (10k + 33k)
Rt = 330000K / 43K
Rt = 7.6K

The ratio will be 7.7K/100 = 77 (excelent)

--------------------

I got more info here:

Passive Preamps With Adjustable Impedance

Mini-V Resistor Lists

https://gearspace.com/board/attachme...1&d=1449004781

https://gearspace.com/board/attachme...1&d=1449004828
Attached Thumbnails
Basic Balanced Volume Control-attenuation.gif   Basic Balanced Volume Control-list-resistor.jpg  
Old 2nd December 2015
  #14
Lives for gear
 
🎧 10 years
Hi, sorry for the my bad advice, you're true of course.. resistor values 4k7 (or 4.5k) and 1k are fine, exactly for the impedance bridging reason and driving of combined input impedance, which you correctly wrote.
I had probably my head already in standby mode at yesterday night, when I replied to your posts.. next time, I will think more about my post before sending.

Anyway, good luck with your attenuator.

Michal
Old 7th June 2016
  #15
Here for the gear
 
🎧 5 years
Hey did you came with some result with attenuator? i'm building a passive xlr mixer with this principle and i'm not sure about wich type of design and values proceed. i'd logically go for this simple schematic:

Wiring a balanced stereo passive volume control

and then sum three channels via 10k resistors and a 100k resistor to ground.


But i saw the variabile pad U shaped design that use a resistor that bridges the two xlr's 2 - 3 pins after the dual gang potentiometer.

Which are the best option in order to mix three xlrs? and which the pot/res values? I'd go for 1k log dual pot and a 150 ohm for shunt, then 10k summing resistor and 100k from out pins to ground.

Second option it would be 10k dual pot and 1k for shunt.

i have only 1k and 100k dual pot... eventually i can raise 1k pot soldering a resistor across pin 1-3 to obtain a 10k pot?

thank you and sorry for my confusion resulting in many questions...

Old 7th June 2016
  #16
Gear Nut
 
🎧 10 years
Ive got an McOne on my monitor outs. Its nice and basic and feels well made. Sound is fairly uncoloured to my ears too.
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