Passive Volume Control for DACs/Sources

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by Madaboutaudio, Dec 20, 2015.

  1. Merrick

    Merrick A lidless ear

    Pyrate
    Joined:
    Jan 6, 2016
    Likes Received:
    12,569
    Trophy Points:
    113
    Location:
    Portland, OR
    I’m honestly just trying to compensate for the insanely high gain on my Liquid Platinum. JRiver is my main audio player, are you saying their digital attenuation doesn’t throw away bits? Maybe I’m misunderstanding.
     
  2. bixby

    bixby Friend

    Pyrate
    Joined:
    Sep 26, 2015
    Likes Received:
    3,988
    Trophy Points:
    113
    Location:
    Northern Colorado

    I use Jriver as my main player and have tried their digital attenuation in the advanced volume settings. I think Bob Katz asked them for one variant cuz it sounded better. (I'll fire up jriver and let you know which it is). It did sound the better of the options available.

    With modern dithering I did not notice any apparent loss at moderate reductions. Worth some experimenting if you determine there is an audible benefit to changing your setup as described earlier. You may try to live with it for a while and hold off spending more cash.

    In my setup I used the rotary encoder on the Prism dac to control volume and it is just a tad better than controlling via JRiver, I may have to re-do that listening test but definitely the system opens up more with the passive and short cable. I am rearranging things and have the passive in a TV setup right now but may have to buy another. Cheap and cheerful for me since I only need single ended.
     
  3. Cspirou

    Cspirou They call me Sparky

    Pyrate
    Joined:
    Sep 27, 2015
    Likes Received:
    8,200
    Trophy Points:
    113
    Location:
    Northwest France
    Maybe @atomicbob can chime in but from what I understand the cable length really matters for high current applications such as speaker wire or headphone cables. Or for high frequency digital signals like SPDIF, USB, HDMI or ethernet.

    Low current and low frequency (<30khz) line level signals you won't really run into issues until it's 100 meters, even for RCA. Concerts have tons of mics with XLR cables 50 - 100 meters long.

    not quite sure there is an issue at 10ft of XLR or even RCA cable as long as it's shielded.
     
  4. bixby

    bixby Friend

    Pyrate
    Joined:
    Sep 26, 2015
    Likes Received:
    3,988
    Trophy Points:
    113
    Location:
    Northern Colorado
    @Merrick
    In Jriver, the advanced setting is TPDF dither and using application volume.
     
  5. bilboda

    bilboda Florida boomer

    Pyrate Banned
    Joined:
    Nov 20, 2016
    Likes Received:
    834
    Trophy Points:
    93
    Location:
    Miama
  6. GoodEnoughGear

    GoodEnoughGear Evil Dr. Shultz‎

    Pyrate
    Joined:
    Oct 25, 2015
    Likes Received:
    3,070
    Trophy Points:
    113
    Location:
    Cape Town, South Africa
    This may shed some light.

    http://www.dact.com/html/ac_calculator.html
     
  7. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

    Pyrate
    Joined:
    Apr 15, 2020
    Likes Received:
    12,239
    Trophy Points:
    113
    Location:
    Bay Area, CA
    Home Page:
    That’s a bit over my head at the moment especially running on no sleep.

    I would think this would be a more well known issue. Using powered monitors is very common these days as there are such good ones at such low prices. And everyone who uses a DAC will need a preamp. I’m not going to say who told me to just get a passive preamp back when I first setup these speakers but he’s prominent in the scene and well trusted.

    If using a passive preamp is a problem with powered monitors then a lot of people are setup incorrectly.

    I guess I’m saying this is such a common situation I’m surprised there is any question about it at all at this point.
     
  8. skem

    skem Friend

    Pyrate
    Joined:
    Nov 1, 2017
    Likes Received:
    1,911
    Trophy Points:
    93
    Location:
    Charles River
    I did
    With respect to the capacitive effects, that’s incorrect. It’s independent of current (unless you lose dimensional stability from Lorentz forces, which isn’t happening here)
     
  9. mitochondrium

    mitochondrium Friend

    Pyrate
    Joined:
    Sep 1, 2017
    Likes Received:
    1,115
    Trophy Points:
    93
    Location:
    A Cell
    I would recommend to stay calm and collected and to not get your knickers in a twist. I use a Passive TVC into powered monitors. In the past I used to run 25 ft xlr between pre and monitors, no probs. You should nevertheless pay attention to the capacitance of the cable. Mine was like 70 pF per meter.
    A lot of what is being said about passive pres is said by people having a vested interest in selling active pres.
    I have to admit that I have no experience with passives based on a resistor network.
     
  10. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

    Pyrate
    Joined:
    Apr 15, 2020
    Likes Received:
    12,239
    Trophy Points:
    113
    Location:
    Bay Area, CA
    Home Page:
    My knickers are already so twisted though! :p
     
  11. bilboda

    bilboda Florida boomer

    Pyrate Banned
    Joined:
    Nov 20, 2016
    Likes Received:
    834
    Trophy Points:
    93
    Location:
    Miama
  12. bixby

    bixby Friend

    Pyrate
    Joined:
    Sep 26, 2015
    Likes Received:
    3,988
    Trophy Points:
    113
    Location:
    Northern Colorado
    I just got off the phone with my friend who has built a variety of passives using fancy Japanese shunt resistor to Bent Autoformers. I brought up the whole passive thing with him again and he stated, even using the same cable wire and ends although one about 3 foot and one 10 inches the change was dramatic. He noted even Bent used to sell a super short (under a foot) cable so their passive could sit right on top of the amp.

    He and his friend also build tube based powered preamps for their own use and agree, totally different animal than a passive. You can run 50 foot XLRs with no issues at all, sound great.

    I suppose the best thing for one who may be curious would be to try it. Short cable from the passive pre to amp vs long. What do you hear?
     
  13. batriq

    batriq Probably has made you smarter

    Pyrate
    Joined:
    Oct 31, 2015
    Likes Received:
    1,041
    Trophy Points:
    93
    From the Schiit Sys FAQ:

    Okay, let's be serious. This is one cheap little gadget. What's the downside?
    The downside to a passive preamp is exactly that—it's passive. That means there are no electronics in it. Which means it can't drive really long cable runs. If you're expecting to run 35' RCA cables to your power amp, Sys isn't going to be the best option. If you're running 6' cables to desktop speakers, that's not a problem. We'd be careful with anything longer than 15' on Sys, depending on the cable type.
     
  14. bixby

    bixby Friend

    Pyrate
    Joined:
    Sep 26, 2015
    Likes Received:
    3,988
    Trophy Points:
    113
    Location:
    Northern Colorado
    Okay, let's be serious.

    yea, we were all kidding

    EDIT: Obviously the post above with this quote was removed or deleted. Tried to help, but like much of the uncertainty in audio, points of view seem to create a religious like denial for some. I am just trying to promote the idea of try something and trust your ears, "is that so wrong" hahaha.

    Love that line was it SNL?

    EDIT2: Forgot posts disappear when you put someone on ignore, unignore restored sorry.
     
    Last edited: Apr 26, 2021
  15. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

    Pyrate
    Joined:
    Apr 15, 2020
    Likes Received:
    12,239
    Trophy Points:
    113
    Location:
    Bay Area, CA
    Home Page:
    Why is something so common this controversial
     
  16. batriq

    batriq Probably has made you smarter

    Pyrate
    Joined:
    Oct 31, 2015
    Likes Received:
    1,041
    Trophy Points:
    93
  17. batriq

    batriq Probably has made you smarter

    Pyrate
    Joined:
    Oct 31, 2015
    Likes Received:
    1,041
    Trophy Points:
    93
    It shouldn't be contraversial. The passive preamp creates a voltage divider with your amp's input impedance. The issue arises at low volumes where the output impedence of the preamp is high.

    The cutoff or corner frequency is then: f = (R1 + R2) / (2 * pie * R1 * R2 * C)
    Where:
    R1, R2 are the output impedance of the preamp and the input impedance of the amp.
    C is the cable capacitance.

    Let's say you're listening at 20 kOhm volume and your amp's input impedance is 100 kOhm. Let's also say your cable is 3m at 150pF per meter (e.g. you have a Canare quad cable). Then the corner frequency is:

    f = 120K / 2 * pie * 0.9 = 21 kHz

    OK, now let's say your cable is 10m, then:

    f = 120K / 2 * pie * 3 = 6.3 kHz

    So yeah, if I did this right, you really shouldn't have long cables, or if you want long cables, the volume should be set high.

    Finally, if you're using an active preamp with output impedance 75 ohm like the Freya. Then R1 is negligable, and there's nothing to worry about (because you get f ~= 100K / a very small number).
     
  18. Armaegis

    Armaegis Friend

    Pyrate BWC
    Joined:
    Sep 27, 2015
    Likes Received:
    7,469
    Trophy Points:
    113
    Location:
    Winnipeg
    That's how you improve the highs...
     
  19. mitochondrium

    mitochondrium Friend

    Pyrate
    Joined:
    Sep 1, 2017
    Likes Received:
    1,115
    Trophy Points:
    93
    Location:
    A Cell
    Hi,

    I like batriq’s posts because they expose the problem very well, yet I come to a different conclusion. The problem is not the length of the cable but the capacitance of the cable. A cable with a capacitance of 150 pF per meter is not fit for this purpose. It is horses for courses. There are cables available both balanced and unbalanced with a capacitance of 30 pF per meter. Get one of these cables and according to batriq’s calculation you can run 15 m and the corner frequency is still 21 kHz. In atomicbob’s post linked further above he gives numbers for Belden 1800F an example for a low capacitance cable. Here are other examples:

    http://www.funk-tonstudiotechnik.de/Audiokabel-analog.htm

    So yes if you combine a shitty passive with high output impedance with a cable with high capacitance then you cannot run long cables. Combine a good passive with a cable fit for the job and longer runs are no problem at all.

    @rhythmdevils

    what is the input impedance of your active monitors? Do they have both balanced and unbalanced inputs? I would redo batriq’s maths using the input impedance of your monitors and the capacitance of a cable fit for the job which is inside your budget price-wise. I would be very surprised if you were not able to find a viable solution.
     
    • Like Like x 5
    • Epic Epic x 2
    • List
  20. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

    Pyrate
    Joined:
    Apr 15, 2020
    Likes Received:
    12,239
    Trophy Points:
    113
    Location:
    Bay Area, CA
    Home Page:
    great post. This subject needs its own thread.

    I have Mackie HR624 mk1’s. I just found this wich says they have an input impedance of 20 K. They have balanced inputs. I’m running balanced JPS labs ultraconductor cable from the passive pre to the speakers in XLR 6-8ft or so. Should be better than the Belden cable. (I lucked out and a friend got a bunch of this cable somehow and made IC’s for me.)

    I can’t do the math but maybe I’m not loosing any magic bunnies.
     

Share This Page