Digital Volume Control & Alternatives

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by direstraitsfan98, Jun 20, 2018.

  1. direstraitsfan98

    direstraitsfan98 D2Girls v2.0

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    If you were sticking with single ended I'd say a schiit saga would do the trick. Freya maybe? I think pass labs makes transparent preamps too but they are pretty expensive. I realy want to purchase one of those TVC thingies but I can't I just spent so much on new speakers... it would be great to compare 3-4 preamps.
     
  2. Kernel Kurtz

    Kernel Kurtz Almost "Made"

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    Try a Freya. If you don't like it, you can send it back, but I'll bet you won't.
     
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  3. Armaegis

    Armaegis Friend

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    I've played around with a few different options, and overall I liked the TVC the most. However, mine is collecting dust at the moment because of the convenience of digital/onboard volume control (and one less component on my cramped desk).
     
  4. NekoAudio

    NekoAudio Acquaintance

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    Goldpoint sells basic passive resister-based preamps in balanced and single-ended configurations.

    Channel Islands Audio has some potentiometer-based passive preamps with a few more bells and whistles (like toggle switches or a remote control) but only single-ended, but I think their VRX•1 balanced cable is designed to provide balanced operation with their passive preamps. You'd probably have to ask them how to use it.
     
  5. mitochondrium

    mitochondrium Almost "Made"

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    @Reggy

    if you want absolute certainty about which is the best category of anything I would suggest to join a religion.

    I do not think there are absolute truths in audio. We are all trying to solve the same differential equation, a long time ago I learned that the solution of such an equation depends on the boundary conditions. So depending on the individual conditions there will be different optimum solutions.
    So far I have gathered that you have an Ares sitting around but you lack a preamp, are you listening with speakers or with headphones?
    @Torq said that listening with headphones he found SE output superiour to balanced output, this may be an indication that you do not need a balanced preamp if you have no other source.
    Using to the Ares with speakers I could not make out a sonic difference between the different outputs.
    The Ares is quite hot it will output 2.3 V SE and 4.5 V balanced if I remember well. The one or other might be better for your transducers.
    If you decide for a TVC as a preamp the whole point is mute because the TVC will transform SE to balanced if you use the preamps balanced output. In that case using the Ares’ SE output you would get max. 2.3 V balanced out of your preamp.
    With a TVC the more you attenuate the lower the output impedance will get, given the Ares’ quite high output impedance that might be interesting, because then 4.5 V will give you the possibility of more attenuation. Again whether you need that depends on the input impedance of your transducers. As someone pointed out the inductance of the transformer also plays a role.

    Now I have just scratched the surface of all things that might matter.
    No one will be able to present you a ready made solution on a platter and if someone did I would not trust them.

    Experiencing music is something joyous and passionate at least for me. So delving too much in theory instead of listening is probably not the best way to do it.

    If you have the feeling that TVC is a valid preamp option and the Promitheus is within your budget why not go for it?
     
    Last edited: Jul 15, 2018
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  6. ultrabike

    ultrabike Measurbator - Admin

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    Regarding digital, active and passive volume control, as far as I known all approaches will reduce SNR and ENOB as things get dialed down. How much better one approach is than the other is likely a function of the overall architecture of the system. Remember, in general noise floor remains somewhat constant as volume is dialed down no matter what approach one takes (note I said in general and somewhat).

    As far as digital control, the RME ADI-2 PRO dedicates an entire section on their manual about the awesomeness of their solution (which "objectively" kicks NwAvGuy claims against sound card "Gain Matching" in the ass - yeah I know some folks like NwAvGuy and I do appreciate many of his contributions, but I don't think he was 100% right about that one).

    Not all digital control approaches may work equally well. Direct control from the Windows console or audio player may provide convenience at the expense of performance. One should be careful about generalizations.

    Active volume control can come in many shapes and forms. It is another wall wart to worry about. But it can reduce noise and help decouple devices when compared to a passive approach (or direct approach depending on what's before and after the pre-amp).

    A passive approach is just much more convenient and can perform better than some active and digital approaches. Again, one should be careful about generalizations.

    On a personal note, I use a Monoprice FiiO rip off as an active pre-amp for my bedroom TV. It is not the awesomest of solutions. But it works well. The active speaker's internal amps I have probably generate way more noise and degrade ENOB shit loads more than my low-fi pre-amp there.

    Since the Pass Labs XP-10 was brought up, my comment about it is that I would not buy it. I would probably not buy any pre-amp in that $5k range. Hell, I would just buy an RME TOTL deal for way less than that. That dude even offers an XP-30 for like $16k. Whatever floats one's boat. For that kind money I get 2 dScopes. So my recommendation about it is "Fuck That".

    But YMMV.
     
    Last edited: Jul 30, 2018
  7. MrTeaRex

    MrTeaRex His head's not fat, he's my brother!

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  8. ultrabike

    ultrabike Measurbator - Admin

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    I think in that application (Pure amplifier w/o integrated DAC), they would need to add an AD/DA deal which may cause some degradation and headaches depending on implementation. It maybe hard to accommodate every single DAC output level among other things.

    As far as their write up against passive approaches, it seems to boil down to high resistors introduce noise. Low value resistors can current starve the DAC and cause distortion. Can happen.
     
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  9. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    Regardless of preamp tech approach, it's probably useful to remember that in any case, a good match of gain and attenuation is necessary. Ideally getting to almost max the preamp's output at the listening level, but the most advanced guys here already know that.

    @ultrabike as usual, devil's in the details, especially with digital attenuation. From what I gather, in some cases the noisefloor will actually go higher and not stay the same. Latest matrix dac reportedly does that, and unless i'm mistaken, the adi dac does some voodoo trick by actively changing the output level on the fly to adapt the gain to the most appropriate output level, which would greatly mitigate that kind of problem, but not eliminate it completely.
     
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  10. ultrabike

    ultrabike Measurbator - Admin

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    Maybe. Dunno.
     
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  11. ultrabike

    ultrabike Measurbator - Admin

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    Since I'm playing with the 2i2 here is what I got:

    44.1 kHz/24 bits balanced loobpack, volume knob all the way up @ -9 dBFS through digital level control using REW.

    (Note: I choose -9 dBFS since it's sort of a sweet spot. A few dB higher and one actually starts to clip. There was no calibration effort. Could adjust ADC to exactly 0 dBFS but it may not be as sweet of a spot. I think ARTA can be sort of level calibrated, but ARTA has it's demons too.)

    THD+N = 0.0027% (91.4dB which seems sort of in agreement with the published specs), THD = 0.00040% (-107.9 dB)

    THD_1kHz_balanced_1.png

    Now @ -69 dBFS using digital level control (60 dB down from the -9 dBFS reference point):

    THD+N = 2.48% (-32 dB), THD = 0.052% (-65 dB). This yields something like 92 dB of dynamic range (again, not necessarily too confident about the levels).

    THD_1kHz_balanced_2_69dBFS_digi.png

    Now @ -69 dBFS using the pot:

    THD+N = 2.35% (-32 dB), THD = 0.066% (-63.6 dB).

    THD_1kHz_balanced_2_69dBFS_pot.png

    I dunno man. At least w the 2i2 I don't see much of a difference when using ASIO and digital level control, and just the monitor pot. Yeah, there is some little bit more distortion, but the THD+N is kind of the same because it seems performance is dominated by noise floor. Who knows, getting the pot to hit 69.1 dB was hard too. Things maybe actually matching within "measurement noise".

    Maybe things are different in any given random interface.
     
    Last edited: Jul 31, 2018
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  12. Hrodulf

    Hrodulf MOT - Sonarworks

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    To properly measure digital volume control performance, one would need to take AD loading out of the equation by maintaining constant signal levels with a reasonably transparent analog gain stage. I suspect that THD gains from digital attenuation is due to lower signal current throughout active analog circuitry.

    As for noise floor, I don't think that it's an issue with most modern dacs.
     
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  13. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    I see your point, Ultra, but I would add two potential objections (i'm no EE and you know it) :

    - THD isn't the only culprit when it comes to distortion (both measured and heard).

    - What about gear that actually measures better ? Not gonna start yet another audibility debate, we've had those ad nauseam already. But we now have dac resolving down to 120dB or so, the difference heard might simply be within that range, and not further up.
     
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  14. mitochondrium

    mitochondrium Almost "Made"

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    Not much voodoo just number crunching:

    The ADI-2 DAC has two unbalanced analog outputs that can operate with levels up to +13 dBu.The short circuit protected, low impedance line outputs are available as RCA jacks on the back of the unit.To maintain an optimum level for devices connected to the analog outputs and to maximize the dynamic range, the ADI-2 DAC internally uses hi-quality electronic switches, which realize a hardware based Reference Level selection in steps of 6 dB overa range of 18 dB: -5 dBu, +1 dBu, +7 dBu and +13 dBu.
    To maintain an optimum level for devices connected to the analog outputs and to maximize the dynamic range, the ADI-2 DAC internally uses hi-quality electronic switches, which realize a hardware based Reference Level selection in steps of 6 dB over a range of 18 dB: +1 dBu, +7dBu, +13 dBu and +19 dBu.
    Example: Ref Lev is set to +19 dBu, Volume is turned down to -20 dB. The effective signal tonoise ratio at the XLR output is now 117 dB minus 20 dB = 97 dB (RMS unweighted). While it is unlikely that any noise will be audible, changing the Ref Level to +1 dBu would need only a Volume setting of -2 dB to achieve the same level or volume. The effective SNR then becomes 115.4 minus 2 = 113.4 dB (16.4 dB higher). Such settings are usually done manually by the user. Auto Ref Lev takes over this task, working in both directions when turning Volume up or down.

    It is a little like an automatic clutch which automatically chooses the apropiate gear to have optimum torque. Compared to most other DACs with volume control the ADI-2 (PRO and DAC) have four times more choices for the output level at zero attenuation, therefore being able to reduce the amount of attenuation (and maintain high effective SNR).
     
    Last edited: Jul 31, 2018
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  15. ultrabike

    ultrabike Measurbator - Admin

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    I think different solutions may fair differently with any given volume level control approach.

    +++

    Shit. I still can get over the XP-30 sticker price. $16K for an active pre-amp?

    I'm reading Stereophile about this money burning device:
    https://www.stereophile.com/content/pass-laboratories-xp-30-line-preamplifier

    "At $18,500, the Ayre KX-R was way too expensive for my budget, but since then I have reviewed more affordable preamplifiers: the Simaudio Moon Evolution P-8 ($16,000, September 2009), the Ayre K-5xeMP ($3500, June 2011), and, most recently, the Classé CP-800 ($5000, September 2012), which includes an excellent D/A section."

    $18,500 is too expensive. Bend over and pick up the soap with the "more affordable" XP-30 or Evolution P-8.
     
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  16. ultrabike

    ultrabike Measurbator - Admin

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    Man, that review is hilarious:

    "I was comparing Ayre Acoustics' then-new KX-R line preamplifier with no preamplifier at all... I wanted to determine by how much the Ayre preamp fell short of that standard."

    "And as well as Nelson Pass, Wayne Colburn is responsible for creative engineering." (ROFLOL "creative engineering")

    "Pass is fond of saying, "The shark must go forward": the business must always advance."

    "The volume control, also carried on a small daughterboard, is based on a Muses NJU72320 integrated circuit."

    Data Sheet:
    https://www.mouser.com/datasheet/2/294/MUSES72320_E-218542.pdf

    Availability and price ($25 for one):
    https://www.mouser.com/ProductDetail/NJR/MUSES72320V-TE2?qs=sGAEpiMZZMutXGli8Ay4kGGAzD%2bGvKCK61ZbF0J5SXg=

    "I was alarmed when I first set up the XP-30: I could get no sound out of it...I put the problem down to my usual bad kable karma and sat down to some critical listening."

    "As I listened to these files, the XP-30–centered system became a time machine!" - Reads: I was smoking dope.

    "Our canaries—sopranos Julie Adams and Carin Gilfry, tenors Daniel Montenegro and Daniel Favela, bass Rod Gilfry—materialized in my room." - Reads: Then I moved to the hard stuff.

    "...the Pass uses negative feedback both in its audio circuit and in its many three-pin voltage-regulator chips, and has an integrated-circuit volume control." (Wait. What? Negative feedback even in the freaking voltage-regulator?)

    Little concern:

    "The frequency bandwidth was independent of the volume-control setting, but into the very low 600 ohms impedance the low frequencies rolled off prematurely."

    So use about > 10K ohm input impedance amps for this one. LOL! or add a passive pre-amp with at least 10K ohms (such as the $50 Schiit SYS pot) for the Pass $16K active pre-amp.

    EDIT: BTW, There are many things that are interesting to me about that JA review. But bare in mind that the Pass pre-amp might be indeed the crazy sex. And for some it may indeed be worth $16K or be a bargain at that. That is not for me or anyone to decide for someone else. I can only say, it is likely not for me.
     
    Last edited: Jul 31, 2018
  17. Cspirou

    Cspirou They call me Sparky

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    Isn't there relay based switching for TVC?
     
  18. Armaegis

    Armaegis Friend

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    My TVC just has a hefty 4-pole rotary switch, but there are certainly variants with relays.

    A year or two ago Sowter had partnered with someone to offer kits, but I can't seem to find it anymore.
     
  19. trung225

    trung225 Almost "Made"

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    Pass Labs operates in a consumer share of the market, which means nearly all amplifiers have high input impedance (10K Ohms or higher), so their preamp is fine, as the roll-off will be negligible with 120 Ohm output impedance of Pass's preamp
     
    Last edited: Jul 31, 2018
  20. Riotvan

    Riotvan Got lost for three weeks at Delft City Hall

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    There are some cheap kits here, it says UK made transformers but it doesn't look like Sowter: https://www.hificollective.co.uk/kits/glasshouse-kits/glasshouse-tvc.html
     

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