Roon DSP volume control vs dedicated preamp

(Philip Gibson) #1

By way of introduction, my setup looks like this:

iMac/Roon => ethernet => microRendu => Chord Qutest => Quad 66 =>Quad 606 => Quad ESL 63s.

I’m thinking of replacing the Quad 66 preamp – having talked to various people, it’s been identified as the weakest link.

I’m auditioning a number of possible replacements but someone has suggested doing away entirely with the preamp, connecting the Qutest directly to the 606, and using Roon’s DSP volume control to control volume.

Now, I’ve read that using software to control volume degrades the signal by reducing the number of bits being streamed. Is that how Roon’s volume control works and what would you advise – use Roon for volume control or stick with a preamp?

I’d love to hear your views.

Philip

DSP Volume control
(Henry) #2

That isn’t the way Roon works. It should convert to 64 bits floating then do the volume control before converting back so you don’t lose your original bit count. That said a good preamp is better than none. It isn’t intuitive but the business of matching source to power amplification makes a world of difference. I would suggest looking at a TVC or transformer volume control. I find these to be utterly transparent while doing a good job matching sources to the power amp.

(Philip Gibson) #3

Thank you, Henry, for your insight.

As I’m sure you can tell, I’m not an audio engineer or anything close so I wonder if you can help me to understand what a transformer volume control is. I’ve read a lot of good things about the Tisbury Mini Passive Preamplifier II. According to the website:

SMD Stepped Attenuator
Key to the excellent sound quality is the stepped attenuator, which utilises an array of thin film SMD resistors to provide precise, stepped volume control and excellent channel balance at all levels.

Alternatively, the Schiit Saga has a relay stepped attenuator volume control. What, if anything, is the difference between the two and, more importantly, do they qualify as transformer volume controls?

(Andrew Cox) #4

Neither of those is a TVC. Attenuators use resistors, stepped attenuators use fixed value resistors. A TVC uses a transformer with multiple taps to reduce voltages and consequently volume. The disadvantage of a TVC is that all transformers exhibit hysteresis effects which vary with the frequency of the input, meaning phase issues. The result can be a compressed narrower sound stage than with an active preamp.

I’ve tried various passive volume controls, but in the end I think active pre-amps sound better.

(Philip Gibson) #5

Thanks, Andrew. So a couple of questions, if I may:

  • In what order would you rank the three options that have emerged from this conversation: Roon volume control, TVC stepped attenuator? Is there likely to be a significant difference between the three in practice?
  • Can you recommend any preamps that incorporate a TVC stepped attenuator?
(Andrew Cox) #6

I would rank things as follows (as always YMMV):

First, a decent active preamp to replace your Quad. I’ve been very happy with the Doge 8. Mine is a few years older than that model.

Second a good TVC. I liked the Django but prefer an active preamp.

Third an attenuator.

Lastly direct connection between DAC and power amps. I’d rank this last not because Roon’s volume control is bad but because of impedance matching issues mentioned by Henry above.

The good news is that you can test a direct DAC to power amp connection without buying anything. Don’t play any music until you’ve adjusted the safety parameters on the Roon volume control. You don’t want to accidentally send full volume into your speakers.

See if you can audition some passive amps at home along with actives.

(Henry) #7

I differ in that my preference is a TVC. I can hear an active pre in the sort of price bracket I can afford. A TVC is less intrusive and my soundstage is lacking in nothing.
https://goo.gl/images/auX3RF
This is what I use. It compares favourably with items by Music First but can be had cheaper if you can find one. There is also a single ended version but I have never seen one of those in the wild.

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(Peter Lie) #8

In case you want to try the direct to amp configuration (without needing to buy anything), try setting your Chord to 1V RMS output (so that you lose the fewest number of bits), and turn the Roon volume way down before playing. In the unlikely event you find the output volume to be too low even with Roon at full volume, then set the Chord to 2V RMS output.

My observation is that most people like active preamp, but in suitable setups other carefully matched options might also work. Ultimately this is system dependent and depends on subjective audio preference as well.

For a digital vs analog volume introduction, google “ESS digital vs analog volume” for the ESS whitepaper.

For active preamp vs source direct to amp, this is affected by impedance matching between the DAC and the amplifier, the hardware design of the DAC, etc. in addition to the volume issue.

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(Philip Gibson) #9

Thank you all for your helpful explanations and suggestions. I’ve spent the whole day listening to different preamplifiers and I’ve also had a go at plugging my DAC directly into my power amp. Unfortunately the Doje 8 isn’t in my price bracket and I didn’t have the Django to try out, though it sounded an interesting option.

The preamps I tried come from Icon Audio (valve), Schiit (switchable between valve and passive) and Tisbury Audio (passive). They all sound pretty fantastic and if money were no object I might have gone for the Icon. But the Tisbury runs it pretty close (in my system and to my ears) so that’s what I’m veering towards.

No preamp sounded very similar to the Tisbury, I guess not surprisingly) but the Tisbury seemed to place the instruments just a shade more precisely (no idea why – doesn’t seem very logical) plus it would make it less likely that I blow up my speakers by forgetting to reduce the volume in Roon.

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(Adam Goodfellow) #10

It depends on how Roon works with a specific DAC and the capabilities of the DAC.

The 64bit float calculation performed within Roon are basically the same as the processing done in a professional DAW in modern mastering, so don’t worry about that at all. The degredation that can occur depends upon what happens between the internal 64 float pipeline in Roon and the I/O to the DAC. Ideally, when using DSP (for EQ or even volume control), Roon should switch the DAC to its maximum bit depth which would be ideally 32bit (maybe it always does this - I have no idea).

With a 32bit DAC, that would basically mean that Roon can apply up to 96dB of cut and still yield CD quality, assuming also that the dithering algorithm was a professional standard shaped noise algorithm.

With a 24bit DAC, then after about 48dB of cut you will be loosing resolution. If the DAC is left in 16bit mode, than any processing will degrade the signal by raising the noise floor (relative to signal).

Also of course it depends on the gain of your amp. It you have a massively over powered amp, with multiple internal gain stages so that it can output several hundred watts and thus has to always apply a lot of gain reduction before the amp for normal listening, then of course issues may be become apparent far sooner than say with a low power valve power amp for eg. While a pre-amp faces the same problem with an under utilized amp, noise due to insufficient bit depth can be more unpleasant than analog noise depending on how it is shaped.

Best ask the Roon folks how Roon actually behaves. Personally, unless I know how a specific digital end to end pipeline works, I prefer analog control so I can just ignore it.

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(Andrew J Shepherd) #11

Watch out, everyone, resolution is on the “loose.”

In all seriousness, getting the amplifier, loudspeaker, media, and listener gain/sensitivity combination optimized can be a challenge with only a digital volume control at your disposal. But if you can swing it, removing the analog preamp attenuation/amplification stage out of the signal path is the way forward.

And remember, if you are using volume leveling, then you already are applying the Roon 64 bit volume control all of the time, regardless of what level controls you may have downstream.

AJ

#12

I have a Berkeley Alpha Series 2 DAC and a Hegel integrated amp so I can control the volume from either. I’ve tried both and can’t hear the difference. BTW the Berkeley’s volume control is digital.

(Peter Lie) #13

This means that in your system, to your ears (highlighted so that people don’t treat the following as a universal statement and start arguing), analog volume (as done by the resistors in the passive preamp) is better than digital volume. One possible explanation is lowered noise floor.

I’m not surprised that a passive preamp sounds better than a direct to amp configuration, otherwise there would be no customer for those GBP9000+ passive preamp.

(Gautam Ramnath) #14

The truest way to see if you need a new preamp at all is to simply implement roon volume control into the Chord DAC and if it sounds better then live with it for a while

That becomes your new baseline for comparison so there is no distraction by the excitement of the new, of simply the different, without being truly superior.

Very much a system dependant process

My sons system with digital volume control lovely sound and perfect. My big rig is much better with dedicated preamp. Happy to listen to Either

(Chris Brown) #15

Hi Philip

I am in a very similar situation as you. Which pre amp (if any :wink: did you go with in the end. I’m leaning toward something that has a remote, so interested in any plus’s/minus’s you may have noticed with the Schiit?

Kind regards

Chris

(Philip Gibson) #16

I bought the Tisbury and I’m really enjoying it. I had set aside a budget and could have afforded to buy either of the other other two options, but in the context of my system I actually liked the Tisbury at least as much overall and it was a whole lot cheaper. I haven’t regretted the decision for a minute.

What it did was free up budget to spend elsewhere and I ended up buying second hand on eBay a pair of Quad ESL 2905 speakers. My impression is that once a system is of a certain quality (vague, I know), then the component that makes the biggest difference is the speakers. The 2905s are just incredible and, I’d add, haven’t to my ears revealed any weaknesses in the Tisbury.

You asked specifically about the Schiit. I’m not sure I have a whole lot to add to what I wrote in a previous post. It sounded very nice and I would have been very happy with it but it didn’t offer enough (to my ears and in the context of my system) to justify the additional expenditure. I also spent some time looking around the Internet for reviews and experiences and came across Audio Science Review. They hadn’t reviewed the preamp but had been very critical of a number of Schiit products and I found that a bit off-putting.

If you can possibly do so, audition candidates at home with the set-up you’ll be using and the music you’ll be listening to. I found the results surprising and the surprise was a nice one. And once you’ve made a decision, stop looking at audiophile magazines and websites and just enjoy your music. After all, that’s the whole point – and Roon makes it such an enjoyable experience. Oh, and let us know how you get on and what you decide.

(Ali Fatemi) #17

I have connected my Chord Qutest directly to EAR 869 SET integrated amplifier by bypassing its pre section, 15watt power driving my Wilson Sasha2. Volume is controlled by Roon DSP. This way I have better resolution and transparency and detect no inferiority compare to using EAR own pre. Every bit of sound is better than with pre. I also had Audio Research ref 6 preamp, 15000$. I still preferred direct to amp set up by far! I sold ref 6 and very happy with qutest-EAR-Wison directly controlled by Roon. My next step is to get dCS new Bartok although Qutest is very good indeed. I put Qutest output to 3 volt since my amp is not powerful. Cables are Audio quest diamond usb, Furotech Flux interconnect and Transparent Ref XL speaker cable. IMHO, Instead of investing on pre to degrade your sound, get better DAC, say, Chord own Hugo TT2. Good luck.

(Chris Brown) #18

Yes, I have tried the direct connection approach and it worked well. The issue I have though, is that Roon still does not seem to have any ‘line in’ capability for me to connect my turntable through. There is an existing, very old thread on the line in topic, which has been ‘bumped’ a few times, however it seems that the Roon development team has stopped doing any work on it :frowning:

So I ended up buying the Tisbury, which, up until yesterday has been great and to my and other peoples ears, is transparent sound wise. The only issue now is that the Tisbury source selector switch has become ‘noisy’, so the unit is going back to Tisbury for repair/replacement.

if Roon could only implement ‘line in’ then I would probably give DSP volume control a go again.

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(Nils Tikkanen) #19

Piling onto this thread:

I am currently using Roon to stream to a Devialet powering some Dynaudio Confidence speakers, which is a pretty simple setup and sounds pretty good.

However, I am considering a set of speakers that are biamped and employ a digital crossover. I’m guessing that it’s preferable to avoid converting to analog for a preamp just to convert back to digital for the crossover.

(Also, I used to have a Bent Audio TAP-X autoformer volume control preamp and it was transparent like nothing else!)

– Nils

(Chris) #20

I have a RPi with HifiBerry DAC + Pro XLR going directly into Hypex NC400 monoblocks. It has device-level digital volume in the DAC, controlled via Roon directly, so no DSP volume. This works extremely well.

I have an iFi micro iDAC 2 connected via USB to the PC which I use as a headphone DAC and amp. Now, it has a physical analog volume control for the headphone amp. To use that, I set Roon to fixed volume (ie. 100%).

However, I now have a Teenage Engineering Ortho Remote - a bluetooth controller, to have a physical control surface for adjusting volume, play/pause, skip tracks. I can use the controller to control Roon and hence any of the endpoints (the Hypex system, the iFi, etc.).

In order to control the iFi with the Ortho remote, I had to switch the iFi DAC/amp to use DSP volume in Roon. According to the signal path display in Roon, it uses 32bit DSP volume way at the end of the chain.

I can’t do ABX testing, so my subjective impression is that I can’t hear a difference between the analog volume on the iFi and DSP volume in Roon.