ampvoice

Linn Sneaky DSM: hiss problem with external power amps

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Posted (edited)

Hello everybody,

I am quite enjoying the Sneaky DSM but, unfortunately, I can't plug my LK140 power amps in the unit (and go bi-amp) without listening a very loud and annoying "hiss" from DSM's analog outputs.

That happens only with the Sneaky amp (I have a Classik Music that works flawlessly with the bi-amplification). And yes, everytime I try to bi-amp, I turn off the internal amplifier and that loud hiss comes from every sources (hdmi, spdif, etc). 

Again, while I'm using the internal amp without my external power amps, everything is perfect. And I have a great Isotek conditioner to filter all potential noises.

My power amps are working flawlessly. They work very well with the Classik Music and also an old Arcam preamp.
 

Also tried to reduce the signal sensitivity from the power amps at their minimum level but the hiss persists. Connections are also correct (I have a phono preamp connected to audio in). 

Finally, I sent an email to Linn Customer Service and their prompt reply was:


"Thank you for your e-mail.
The Sneaky DSM is designed to be used with the internal amplifier of the unit.
There will be a level of hiss/buzz from the pre-outputs of the DSM, if using an external amplifier.
If you use the inbuilt amplifier of the unit, Do you hear the hiss?
If you feel these levels are excessive, I would suggest contacting your local Linn retailer"

Anyone had this issue before?

Thanks for your comments and replies!!
 

Edited by ampvoice

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Posted (edited)

Linn seems to indicate that this is a recognized issue, and purposely designed the Sneaky DSM to not be compatible with external amps.

It would appear that the external amp would be receiving an output voltage from the Sneaky that is too high, and the external amp  would be amplifying additional audible hiss?

It does not appear to be a viable option to run external amps with the Sneaky

Edited by Paulssurround

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I have the same issue with a Sneaky DSM. With the internal amp everything is fine.

With an external amp there is a hiss. For me it was not ok to use it as a destop system. The hiss is too obvious directly infront of the speakers.

Now I use it in an activ kaber setup. A few meters away from the speakers the hiss is acceptable to my ears.

My Sneaky DS with external amp in comparison was not completely silent but OK.

I'm with Paul (Hi Paul!) the Sneaky DSM is not the best choice with external amps.

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16 hours ago, Paulssurround said:

and purposely designed the Sneaky DSM to not be compatible with external amps.

I’d very much doubt that this was made on purpose since LinnDocs states:

ANALOGUE OUTPUT (RCA, variable/fixed level) - To connect to subwoofer or external power amplifier (or pre amplifier when internal volume control is disabled, this will also disable the internal Power amplifier/speaker outputs) with unbalanced (RCA) analogue inputs.
16 hours ago, Paulssurround said:

It would appear that the external amp would be receiving an output voltage from the Sneaky that is too high, and the external amp  would be amplifying additional audible hiss?

I’d guess that the analogue output voltage of the Sneaky DSM is the same as for all current DSMs (i.e. 2 Vrms @ 0 dB FS). What’s actually too high is the introduced noise from the Sneaky. This isn’t a design goal made on purpose, but a major hardware design flaw.

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I have a customer with a Sneaky DSM into Klouts driving Keltiks. No reports of hiss but will check with him. 

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Posted (edited)

Hello folks, thanks for all your comments.

I'll try once again this weekend to be extremely careful while turning the signal detector sensitivity control on the back panel of my Lk140 towards the minimum possible position to see if anything changes (just did a couple of times without success).

Anyway, it seems quite bizarre a company like Linn to build such refined streaming solution with a rudimentary analog output that simply doesn't work??? Engineering flaw? Material defect?? 

Edited by ampvoice

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2 hours ago, ampvoice said:

I'll try once again this weekend to be extremely careful while turning the signal detector sensitivity control on the back panel of my Lk140 towards the minimum possible position to see if anything changes (just did a couple of times without success).

Save your time and don’t do this, as it is pointless. The setting of the signal detector sensitivity determines at what input voltage level the amp powers up (i.e. leaves standby). It doesn’t change anything with respect to what you’re hearing if the amp is powered on.

Improving the signal-to-noise ratio would require to lower the gain of the power amp, which isn’t possible with LK140s. You might ask now why lowering the gain can (slightly) improve the signal-to-noise ratio. Usually output noise is rather constant and doesn’t change much with output voltage. If e.g. the gain of the LK140 would be 10 dB lower, the noise you’re hearing would be about half as loud (and for the same volume of the music you’d have to raise the volume setting on the DSM from e.g. 50 to 60). Majik and Akurate amps allow lowering the gain, but only by 3 dB…

2 hours ago, ampvoice said:

Anyway, it seems quite bizarre a company like Linn to build such refined streaming solution with a rudimentary analog output that simply doesn't work??? Engineering flaw? Material defect?? 

I’d vote for engineering flaw. In Linn’s hierarchy the Sneaky DSM was its low-end streamer, but given the absolute price tag it should provide a much better signal-to-noise ratio on its analogue output than it actually does.

The Sneaky DSM has been discontinued, but the very similar Sekrit DSM is still available. It would be interesting to know if it shows the same issue. There are two variants of the Sekrit DSM (2012 and 2018)…

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Posted (edited)
17 hours ago, BB1 said:

Save your time and don’t do this, as it is pointless. The setting of the signal detector sensitivity determines at what input voltage level the amp powers up (i.e. leaves standby). It doesn’t change anything with respect to what you’re hearing if the amp is powered on.

Improving the signal-to-noise ratio would require to lower the gain of the power amp, which isn’t possible with LK140s. You might ask now why lowering the gain can (slightly) improve the signal-to-noise ratio. Usually output noise is rather constant and doesn’t change much with output voltage. If e.g. the gain of the LK140 would be 10 dB lower, the noise you’re hearing would be about half as loud (and for the same volume of the music you’d have to raise the volume setting on the DSM from e.g. 50 to 60). Majik and Akurate amps allow lowering the gain, but only by 3 dB…

I’d vote for engineering flaw. In Linn’s hierarchy the Sneaky DSM was its low-end streamer, but given the absolute price tag it should provide a much better signal-to-noise ratio on its analogue output than it actually does.

The Sneaky DSM has been discontinued, but the very similar Sekrit DSM is still available. It would be interesting to know if it shows the same issue. There are two variants of the Sekrit DSM (2012 and 2018)…

Thank you for great feedback, @BB1 

Such kind of problem coming from a simple analogue output stage still seems SO odd to me...

My question now would be (as I lent my preamps to some friends so I can't perform a test right now) if I connect the Sneaky to a preamp (therefore disabling the internal volume control, which will naturally also disable the internal Power amplifier/speaker outputs), I can use the DSM only as a digital source without the hiss...

Edited by ampvoice

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On 15/04/2020 at 07:54, CJ1045 said:

I have a customer with a Sneaky DSM into Klouts driving Keltiks. No reports of hiss but will check with him. 

Thanks for your feedback @CJ1045 that will surely help me and others readers to better understand this issue

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10 hours ago, ampvoice said:

My question now would be (as I lent my preamps to some friends so I can't perform a test right now) if I connect the Sneaky to a preamp (therefore disabling the internal volume control, which will naturally also disable the internal Power amplifier/speaker outputs), I can use the DSM only as a digital source without the hiss...

Disabling the internal volume control is the same as setting the DSM volume control to 80. If my assumption that the Sneaky’s analogue output noise doesn’t significantly increase with output volume is right, it would result in the best possible signal-to-noise ratio.

The signal-to noise ratio is only of value if music is playing (noise added to the music degrades sound quality). If „silence“ is needed (e.g. in between tracks), there is no signal and the gain of the external amp (amplifying the Sneaky’s output noise) determines the level of noise you hear.

Fortunately enough using a pre amp would drastically reduce the required gain of the external amp (i.e. gain of pre and power amp in total), especially at a modest volume. As an example for the same listening volume:

1. Sneaky DSM + LK 140
Volume setting: 50 (equals a voltage gain of -30 dB)
LK 140 gain: 28.6 dB
Total gain: -1.4 dB (-30 dB + 28.6 dB)
Total amplifier gain: 28.6 dB

2. Sneaky DSM + preamp + LK 140
Volume setting: 80 (equals a voltage gain of 0 dB)
LK 140 gain: 28.6 dB
Pre amp gain: -30 dB
Total gain: -1.4 dB (0 dB + 28.6 dB - 30 dB)
Total amplifier gain: -1.4 dB (28.6 dB - 30 dB)

As you can see, setup 1 would amplify the Sneaky’s output noise by 28.6 dB (a factor of 26.9) whereas setup 2 would attenuate it by 1.4 dB (a factor of 0.85). In other words. if the Sneaky’s output noise is 1 mV, setup 1 would feed 26.9 mV into the speakers, whereas setup 2 would only feed 0.85 mV into them.

10 hours ago, ampvoice said:

Such kind of problem coming from a simple analogue output stage still seems SO odd to me...

Actually it isn’t as simple as you might think. Even experienced engineers having designed a lot of analogue circuits before run into a lot of trouble if trying to design for the very first time any circuit requiring very low noise levels. Things are getting worse, if board space is restricted and other noisy circuits are in close proximity, as it it most likely the case for the Sneaky DSM.

I don’t think that using external amplification has been considered by Linn as a relevant use case. As stated earlier, I’d guess that the Sneaky DSM and the Sekrit DSM are quite similar and share the same analogue output stage. Interestingly enough the Sekrit DSM documentation states:

ANALOGUE OUTPUT (RCA, variable/fixed level) - To connect to subwoofer (note:when the internal volume control is disabled, this will also disable the internal Power amplifier/speaker outputs) with unbalanced (RCA) analogue inputs.

External power amps aren’t mentioned and using the analogue output for a sub seems to be the intended use case. Therefore I wonder what are the dominant frequencies of the hiss. Could it be the case that they are higher than any sub can reproduce? Hence I’d be interested in the spectrum of the hiss.

To get a clue about the dominant frequencies you could use almost any free audio spectrum analyser app available for your phone or tablet (e.g. "Audio Spektrum Analysator" for iOS).

Disclaimer:
Don’t trust any absolute value measured by this kind of apps. Nevertheless they would give a good approximation for the dominant frequencies of the hiss.

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Posted (edited)
On 15/04/2020 at 07:54, CJ1045 said:

I have a customer with a Sneaky DSM into Klouts driving Keltiks. No reports of hiss but will check with him. 

IMO a seriously unbalanced system. Sell him an ADSM…

Edited by BB1

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I had a Sneaky DS running as a fixed line level source through a Majik-IL230 (in Wakonda mode) into LK140s/Katans for a good long while and never experienced hiss, well that's a little lie, when I fitted 2nd hand Aktiv cards I got hiss but removing them sorted that out. To me a pre-amp is the way to go. You may loose your volume control through Kazoo so choose something with a remote.

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19 hours ago, BB1 said:

Disabling the internal volume control is the same as setting the DSM volume control to 80. If my assumption that the Sneaky’s analogue output noise doesn’t significantly increase with output volume is right, it would result in the best possible signal-to-noise ratio.

The signal-to noise ratio is only of value if music is playing (noise added to the music degrades sound quality). If „silence“ is needed (e.g. in between tracks), there is no signal and the gain of the external amp (amplifying the Sneaky’s output noise) determines the level of noise you hear.

Fortunately enough using a pre amp would drastically reduce the required gain of the external amp (i.e. gain of pre and power amp in total), especially at a modest volume. As an example for the same listening volume:

1. Sneaky DSM + LK 140
Volume setting: 50 (equals a voltage gain of -30 dB)
LK 140 gain: 28.6 dB
Total gain: -1.4 dB (-30 dB + 28.6 dB)
Total amplifier gain: 28.6 dB

2. Sneaky DSM + preamp + LK 140
Volume setting: 80 (equals a voltage gain of 0 dB)
LK 140 gain: 28.6 dB
Pre amp gain: -30 dB
Total gain: -1.4 dB (0 dB + 28.6 dB - 30 dB)
Total amplifier gain: -1.4 dB (28.6 dB - 30 dB)

As you can see, setup 1 would amplify the Sneaky’s output noise by 28.6 dB (a factor of 26.9) whereas setup 2 would attenuate it by 1.4 dB (a factor of 0.85). In other words. if the Sneaky’s output noise is 1 mV, setup 1 would feed 26.9 mV into the speakers, whereas setup 2 would only feed 0.85 mV into them.

Actually it isn’t as simple as you might think. Even experienced engineers having designed a lot of analogue circuits before run into a lot of trouble if trying to design for the very first time any circuit requiring very low noise levels. Things are getting worse, if board space is restricted and other noisy circuits are in close proximity, as it it most likely the case for the Sneaky DSM.

I don’t think that using external amplification has been considered by Linn as a relevant use case. As stated earlier, I’d guess that the Sneaky DSM and the Sekrit DSM are quite similar and share the same analogue output stage. Interestingly enough the Sekrit DSM documentation states:

External power amps aren’t mentioned and using the analogue output for a sub seems to be the intended use case. Therefore I wonder what are the dominant frequencies of the hiss. Could it be the case that they are higher than any sub can reproduce? Hence I’d be interested in the spectrum of the hiss.

To get a clue about the dominant frequencies you could use almost any free audio spectrum analyser app available for your phone or tablet (e.g. "Audio Spektrum Analysator" for iOS).

Disclaimer:
Don’t trust any absolute value measured by this kind of apps. Nevertheless they would give a good approximation for the dominant frequencies of the hiss.

 

Hello @BB1 thank you so much for your sage advice! I really appreciate it that you took the time to voice your opinion.  

I have come to a conclusion that leads me in a certain direction: acquiring a great old school, high-current, low-output-impedance Linn's analogue preamp to guarantee the best sound dynamics possible (thinking about maybe an Exotik, Kairn). Do you think this is the best way to go?

Regarding what Sekrit manual states, it's a little bit different from Sneaky's (maybe they realised the issue in between):

ANALOGUE OUTPUT (RCA, variable/fixed level) - To connect to subwoofer or external power amplifier (or pre amplifier when internal volume control is disabled, this will also disable the internal Power amplifier/speaker outputs) with unbalanced (RCA) analogue inputs.

And yes, I'll try to plug a power amp tomorrow and check the signal amplitude.

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Posted (edited)
8 hours ago, silkie said:

I had a Sneaky DS running as a fixed line level source through a Majik-IL230 (in Wakonda mode) into LK140s/Katans for a good long while and never experienced hiss, well that's a little lie, when I fitted 2nd hand Aktiv cards I got hiss but removing them sorted that out. To me a pre-amp is the way to go. You may loose your volume control through Kazoo so choose something with a remote.

Thanks for your reply. I think that too. Although your problem regarding going aktiv is something to consider... 

Edited by ampvoice

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