DS Jr. and Attenuator


#1

Between my XA30.5 power amp and DS Jr. I’ve noticed when no music is playing that I get a low-level of noise. It’s almost like subtle static rather than any buzzing. I use balanced connections however nothing changes when I use RCA connections - same noise, same amount of noise.

My new speakers are a bit more sensitive than before (90 vs. 87db) and during quiet passages it is audible for a couple feet away.

For whatever reason I decided to try the attenuator today, despite me not needing to decrease gain. Heard a hit ‘pop’ and the noise is essentially gone unless my ear is on the woofer! Microdetail is much more apparent than before!

I tried listening from the couch and turning the volume to hear the same music level with and without the attentuator in (my iPad measures about 80db on both settings). With the attenuator in, I don’t notice this noise like I do with the attenuator out.

What does the attentuator do inside the dac?


#2

The attenuator changes output levels by adding a shunt resistor to the signal ground via a relay. Engaging the 20dB attenuator is akin to turning the volume down by 40.

Engaging the analog attenuator also lowers the noise floor by 20dB as everything the DAC outputs is lowered by 20dB, including the noise. That is, you are using the attenuator for one of its intended purposes.


#3

The attenuator is just that - it attenuates the output by 20dB by putting a resistor to ground on the outputs.

By attenuating the signal by 20dB you also attenuate the noise by 20dB. So if you have an external preamp and use it to make up the volume difference (leaving the volume setting alone on the DS), the 20dB attenuator should make no difference what so ever.

But if the volume setting on the DS is used to make up the difference (assuming it can “reach” to the level you want to listen at) then using the 20dB attenuator will get you 20dB less noise.

So for those people who can get to the volume they want using the attenuator, the attenuator provides a 20dB cleaner signal. For those that have to make up the 20dB totally outside the DS the attenuator should do nothing.

Since nothing in this world is perfect one may prefer the sound with or without the attenuator, but that difference should be fairly subtle.

I guess one other possibility when you use exactly the same volume setting on the DS and make up the volume difference with a preamp is that preamp overloads with the louder signal or the interconnects used between the DS and the preamp react differently to a 20dB difference in level, but neither of those is very likely.

[Edit: Elk typed faster :slight_smile: ]


#4

Man. I have read similar threads on this subject but I believe now I get the picture. Many variables- attenuation in or out, pre or not, use volume on Dac or Pre, Lower noise floor vs bit depth?

Anyway, sounds like if you have a noise issue, then the attenuation may help you by adding it into the equation.

So- I am lucky and have zero noise. Nada. Therefore Attenuation out, DSD at 100, control volume w/ Pre = best configuration?

(Adding attenuation is just playing with a cool feature I don’t need.)

Pre gets to about 40 and many would consider leaving the room (lol) about 90 db or so. I don’t think I am over stressing anything.


#5

I’m beginning to understand how the attenuator works but I don’t think fully or I’m explaining myself poorly.

I don’t use an external preamp, instead I use the volume control in the DSJr directly to my XA30.5

Lets use the example of no music playing.

  1. Attenuator in, volume from 1-100 does not have any background noise

  2. Attenuator out, volume from 1-100 has background noise, and the noise level does not change regardless of the volume value chosen. That is, the loudness of the noise is the same at 1 as it is at 100.

**Shouldn’t the background noise that I hear with the attenuator out change as volume does? Why does the background noise basically go away regardless of volume with the attenuator in?


#6
Roninaudio said Lower noise floor vs bit depth?
No. The DSD never throws away bits to lower the volume. Also, the attenuator is analog and, thus, does not decrease bit depth.

Roninaudio, in your case, you may want to try lowering the volume on the DAC to perhaps 80 There is a tiny bit less THD at 80 on very loud passages, but slightly lower S/N. Experiment.


#7

Thanks Elk. Trying this now. I could of sworn I read something about bit depth being affected/not optimal at lower DAC settings so running at 100 or 106 was optimal depending on attenuation. I could be wrong, I frequently am when we get into this level of detail. I just want to be set up optimally. I’m at 80 now (lower than I have ever tried) and am adjusting pre accordingly. Thanks again and I’ll just read as I don’t want to hijack the OPs thread.


#8

For my system it would be perfect if the attenuation was about 6 to 10 dB less.
Would it be practical to change the shunt resistors to a higher value to accomplish this?


#9
st50maint said

For my system it would be perfect if the attenuation was about 6 to 10 dB less.
Would it be practical to change the shunt resistors to a higher value to accomplish this?

You'll need to do 6 resistors/ channel (R709 ... R714). I need about 15 ohms to ground but the lowest available resistor that otherwise is of the quality I want there is 47 so I use three in parallel. You could remove all three and put one 62 ohm and you'd get about -10dB instead of -20dB.

FWIW I use thin film, 0.1% tolerance, 25 ppm/degree C, 1/8 watt, 0805 surface mount resistors here (and similar quality in the rest of the analog.)


#10
Roninaudio said

Thanks Elk. Trying this now. I could of sworn I read something about bit depth being affected/not optimal at lower DAC settings so running at 100 or 106 was optimal depending on attenuation. I could be wrong, I frequently am when we get into this level of detail. I just want to be set up optimally. I’m at 80 now (lower than I have ever tried) and am adjusting pre accordingly. Thanks again and I’ll just read as I don’t want to hijack the OPs thread.

In general the DS sounds best at around 100, too much higher and you're getting more THD, too much lower and the signal is getting closer to the analog noise floor (tho this doesn't matter if you aren't hearing noise at whatever setting you are using.)

There’s nothing special about 100 vs., say 99 or 101 - they all do the same amount of work and hence cause the same analog noise and or digital signal degradation (both of which are essentially zero.)

As Elk mentioned (and unlike most DACs) there’s no loss of digital accuracy with any particular volume setting. Starting with Huron I’d be comfortable listening to a volume below 10 (as long as any noise from the analog noise floor isn’t a problem.) (Before Huron, I’d rather that people were listening at around 50 or higher.)

The one catch is that Redcloud sounds a little more like Huron with a high signal level and high volume setting. (I hope to de-Huron-ize things in a furure release.) So listening to less dynamic music (say, music whose average level is with in 10dB of the max.) at levels above 80 may be more like Huron when the music is near the max.) This only lasts as long as the digital level of the samples (after applying the volume) are within about 10dB of the max, so you’ll never hear any difference with dynamic music since it spends very little time near the max. I only mention this because knowing what’s going on is important to some people.


#11
Roninaudio said I could of sworn I read something about bit depth being affected/not optimal at lower DAC settings . . .
This was true of many older PCM DACs which did control volume by throwing out bit depth. I bet this is what you recall. This is many years ago however and not the case with the Directstream.

I have not heard any meaningful difference between 80 and 100 volume settings on the Directstream running through a preamp. I think I hear a difference and then in a bit I am unsure. Part of this is likely because I rarely listen to music which is routinely at the top of the volume range so I probably do not experience the differences in THD.

Do not worry about mucking up the thread. We are very free form here as to topics and often questions/observations lead us to even more interesting discussions.


#12
Ted Smith said

You’ll need to do 6 resistors/ channel (R709 … R714). I need about 15 ohms to ground but the lowest available resistor that otherwise is of the quality I want there is 47 so I use three in parallel. You could remove all three and put one 62 ohm and you’d get about -10dB instead of -20dB.

FWIW I use thin film, 0.1% tolerance, 25 ppm/degree C, 1/8 watt, 0805 surface mount resistors here (and similar quality in the rest of the analog.)

Thanks Ted. I actually have a Directstream Senior. Are the details the same for that model?

I assume I could just remove two resistors per channel and get a sufficient increase in level for my needs?


#13

Both the Jr and Sr use the same scheme and same resistors there. The reference numbers I gave were for the DS Sr.

Yes just removing two per channel will make the attenuator do about -12dB instead of -20dB.


#14
Ted Smith said ... But if the volume setting on the DS is used to make up the difference (assuming it can "reach" to the level you want to listen at) then using the 20dB attenuator will get you 20dB less noise.

So for those people who can get to the volume they want using the attenuator, the attenuator provides a 20dB cleaner signal. For those that have to make up the 20dB totally outside the DS the attenuator should do nothing.


Hey gents. Haven’t been back on for while.

So Ted: Now that I have a BHK should I be running the attenuator on my DSJ?


#15

Thanks Ted and Elk. You guys are a big part of what makes this a killer forum to be in. With the addition of the pre I don’t get that razor sharp detail at volume I did with DAC direct to 700s. I probably listen 40, 40, 20 = Low, Med, high volume%. But at “loud” things sound really good for almost all files- hi res or not. (see setting below) However I need that “loud” fix.

I’m really pleased with the sound. This is the best system I have ever owned and I’m positive the Jr and the 700s are playing a major role in that. My speaker upgrades have not hurt either as something with the nature of the electronics and the Dyns did not get along. So a change was needed.

I made an executive decision after a session and I’m running Attenuation out, Dac at 95 and Pre = volume control. All files+ streaming at everything from nite time quiet to tympanic membrane rupture warning sound great. I’m sticking with this as the variables are too many and I’ll go nuts otherwise.

(Thanks again)


#16

After some further searching, I came across a post that makes a bit more sense to me. Here it is if someone else was as confused as I was initially!!

The 2xDSD digital signal at the output stage of the DAC has a certain noise floor. For simplicity of explanation, imagine that it’s 100dB lower than the maximum signal level the DAC can create in the audio band below 20kHz, but it rises through the octaves above that to be a whole lot of ultrasonic noise. (The actual noise floor is lower than -100dB, this is just an easy figure for illustration.)

The passive, analog low-pass filter stage is designed to let all the content below 20kHz pass through (both the desired audio and the noise floor) and then as the frequency rises impose greater and greater limitation on the unwanted ultrasonic noise so that a minimum amount of it reaches your amplifier.

The shape and level of that filtered noise is fixed. It doesn’t alter when you adjust the volume setting of the DAC. Even if you are playing no audio, that noise floor is still leaving the DAC and heading to your amplifier.

Now let’s imagine you have a piece of music which peaks all the way to the maximum digital signal level. If you have the DAC volume set to 100 and the attenuator off, the peaks of the music will be stretching the output of the DAC to its maximum level. Since we have a noise floor roughly 100dB lower than that, your signal-to-noise ratio there is 100dB. Awesome.

But your amplifier and speakers might take a signal at that level and produce a sound that’s way louder than what you want to hear. So you turn down the DAC volume control, way down to 20. Each volume step on the DS DAC is half a dB, so -80 volume steps is -40dB in signal level. But the noise floor hasn’t changed. Your signal now peaks at 40dB below maximum, and your noise is still there at 100dB below maximum, so your signal-to-noise ratio has dropped to 60dB.

If your amp and speakers are very sensitive, this can happen and the noise becomes intrusive in your listening experience. So, here comes the attenuator.

The attenuator takes the analog output of the DAC and throws some of it away. 20dB worth of it. Doesn’t discriminate between audio signal and noise. Everything gets 20dB quieter, including the noise. Reaching the same listening level requires you to turn the volume control up to 60 (adding 40 half-dB steps for an extra 20dB of signal) but your noise doesn’t get any higher. So now you are listening to the same signal but with the noise 20dB lower. You now have a signal-to-noise ratio of 80dB instead of 60dB.

This increase in SNR at the same volume only applies if you normally listen with at least 20dB of unused headroom – ie with your volume set to 60 or lower, meaning you are able to increase to 100 after enabling the attenuator.

http://www.psaudio.com/forum/directstream-all-about-it/minimum-recommended-volume-setting-for-directstream/#p58161


#17
Ted Smith said

Yes just removing two per channel will make the attenuator do about -12dB instead of -20dB.


I decided to only remove 1 of the 3 resistors in parallel at first. That is 4 resistors altogether. Each channel has 2 shunts to ground since it is balanced.

So the shunt to ground is now 23.5 ohms instead of the 15. This has resulted in an increase in level of 3.2dB. I think this increase will be enough for me. It keeps my typical level in the low 90s instead of the high 90s. Which means I no longer hear those pops with SACDs that sometimes occur at a level about 98 and above.

Thanks to Ted for the information on how to do this.


#18

Well done! An excellent bit of problem solving.


#19

This was a great read, thank you everyone! I’m getting very close to aquiring a DSJ and I am currently planning to use the digital volume control of the DSJ without a separate preamp. The DSJ will be outputting to a pair of Stellar M700’s that feed a pair of JTR 212RT 101db/w sensitive speakers. With speakers this sensitive the noise floor of any product generally comes through so the 20db attenuator of the DSJ sounds like a perfect feature for my setup!

With all the information on the internet it can get confusing when trying to learn about the potential trade-offs of digital volume control. I’m very glad to see here that with Red Cloud even low digital volumes can be safely used. I predict that even with the 20db attenuator in the signal path I won’t be anywhere near 100 volume on the DSJ due to my speaker’s sensitivity, so this is a great relief!


#20

Would you use the attenuator if going from a DSJ to just powered speakers, direct?

I would love a second Junior (no pun intended) :slight_smile: