2v or 6v into a tube pre-amp? what would you do (and why?)

[992Sam]

Ok, I've asked this question to the manufacturer of both pieces of equipment involved and gotten 4 different answers..  no lie.  Anyway...  I want to understand the why of something and maybe Ic an make up my own mind..

 

so the dCS Rossini has the ability to output (XLR Balanced) either .2v, .6v, 2.0v, or 6.0v... the later two being the recommended outputs unless using something like Apple Airplay etc..

 

I'm currently using the Rossini with just an Amp, as the pre-amp isn't due to arrive for a week or so...  the pre-amp (as listed in my signature) is a McIntosh C1100, which is a 100% tube pre-amp..   I don't know what type of volume control the Mc has (assuming digital), but the dCS is a digital volume control and so I assume I will want it set to the maximum (0.0db) once it's connected to the pre-amp... and then use the pre-amp volume knob, right?   But the bigger question is what voltage AND WHY?  2 or 6?  someone mentored more dynamic range in the 6v output, while someone else mentioned distortion possibly and over load?

 

Someone who knows more than me, and / or maybe owns a similar setup chime in and tell me what you would do?

[sandyk]

McIntosh Laboratory MC462 power amplifier Specifications ...

www.stereophile.com › content › mcintosh-laboratory-...

Voltage gain: 29dB, 8 ohms. Input sensitivity: 4.2V balanced, 2.1V unbalanced.

 

You will need to greatly attenuate the output unless you use 2.0V out from the DAC, otherwise you will substantially degrade the Signal to Noise ratio. You will most likely already need to use way too much attenuation with an amplifier with 29dB gain.  What is the typical volume control setting on your valve preamp at present ? Is it well left of the middle of it's range ? Valve Preamps do not normally like higher input voltages , and were often designed for more like 1V RMS input signals.

To get most benefit from a higher voltage source signal, you need a Power Amplifier with much lower gain, or having switchable Input voltage settings. 

[992Sam]

5 minutes ago, sandyk said:

McIntosh Laboratory MC462 power amplifier Specifications ...

www.stereophile.com › content › mcintosh-laboratory-...

Voltage gain: 29dB, 8 ohms. Input sensitivity: 4.2V balanced, 2.1V unbalanced.

 

You will need to greatly attenuate the output unless you use 2.0V out, otherwise you will

substantially degrade the Signal to Noise ratio. You will most likely already need to use way too much attenuation with an amplifier with 29dB gain.  What is the typical volume control setting on your valve preamp at present ? Is it well left of the middle of it's range ? Valve Preamps do not normally like higher input voltages , and were often designed for more like 1V RMS input signals.

To get most benefit from a higher voltage source signal, you need a Power Amplifier with much lower gain, or having switchable Input voltage settings. 

Thanks but I’m not going directly into the MC462... I’m going into a C1100 preamp ... can’t find anything about the input  other than its limited to 20v balanced.   But if I read you correctly.. sounds like the 2v is a good choice. 

[sandyk]

12 minutes ago, 992Sam said:

Thanks but I’m not going directly into the MC462... I’m going into a C1100 preamp ... can’t find anything about the input  other than its limited to 20v balanced.   Can you see if you’ve got better luck?

 I was going by this "I'm currently using the Rossini with just an Amp"2

 

C1100

• Total Harmonic Distortion

  High Level: 0.005%
  Phono: 0.05%

• Frequency Response

  +0, -0.5dB from 20Hz to 20kHz
  +0, -3dB from 10Hz to 100kHz

• Maximum Volts Out (Balanced / Unbalanced)

  20V RMS / 10V RMS

• Sensitivity High Level (Balanced / Unbalanced)

  900mV / 450mV

• Sensitivity Phono (Moving Coil)

  0.45mV

• Sensitivity Phono (Moving Magnet)

  4.5mV

• Signal To Noise Ratio (High Level)

  107dB

• Signal To Noise Ratio (Moving Coil)

  79dB

• Signal To Noise Ratio (Moving Magnet)

  77dB

• Voltage Gain (High Level)

  15dB

• Voltage Gain (Moving Coil)

  60db

• Voltage Gain (Moving Magnet)

  40dB

• Input Impedance (Balanced / Unbalanced)

  50K ohms, 25K ohms

 

[992Sam]

Well.. that’s interesting... so should I in fact use the 0.6v and not the 2v??  Wow... had no idea.  Got an email response form McIntosh just now where the guy said to use the 2v. 

[Bill Brown]

@sandyk is giving good advice.  Getting good gain structure/gainstaging (what you are working on) is very worthwhile.

 

One rule of thumb would be to minimize any gain that you subsequently attenuate.  This maintains S/N ratio.

 

Generally the least gain required to get the maximal speaker output that you want is best.

 

The above specification 900mv balanced/450mv unbalanced, means that those are the voltages at which the preamp will amplify it to its maximum output.  Anything sent to the preamp higher than that must be attenuated in the preamp (which it will do) or it will drive the preamp into clipping.  Tube preamps are traditionally high gain, though not always these days.

 

From the specs above, your gain on the high level inputs is 26.9 db:

 

gain = 20(logVo/Vin) db

 

Most amps will be driven to clipping with 2-4V (thought that, too, has changed some).  To get 4 V out of your preamp you need to put in only 181mv (0.18V)........

 

If you knew the line level input sensitivity of your amp you could calculate the whole gain structure with precision.

 

People don't realize how much gain we discard since the development of the CD with its 2V standard

 

Hopefully I didn't screw up any of the calculations!  :)

 

If I had your system I would decrease the output of the DAC as much as possible.  My goal would be to have my typical max volume settings for listening as close to 0.0 db on the digital side if using that for volume, or the knob on the preamp as close to wide open as possible (3 o'clock or greater with old analog pots).

 

Objectively, I believe the above will give you the best measured dynamic range.  Re. subjective "dynamics" I am not sure where the notion you described comes from (not that I don't believe in the concept of dynamics).  I wonder if it relates to our prior experiences with old high gain equipmentwhere by 9 o'clock on the knob it was blasting.

 

Bill

 

 

[992Sam]

@Bill Brown wow, Bill, thanks for that very well put explanation on what was said above..  So my choices are .2v and .6v also... wonder if the .6v is the wise choice based on what you told me since from what even dCS has to say, you want to run the volume (digital volume) at 0.0db or max...  My dealer (McIntosh dealer) also seems to think the Pre-amp will allow me to trim the input voltage via some kind of setting...   

 

But to understand you completely...  I essentially don't want any voltage above 900mv into my pre-amp, otherwise it has to attenuate that excess... so even at 2v, it's too high.. and I might end up needing to run the volume at higher than 0.0DB from the dCS, maybe closer to -10db?

 

I'm obsessed with a perfect match you see... and the other other source I'll be running is a McIntosh SA/CD player which will mostly play via SPDIF connection to the DAC anyway unless I'm actually playing an SA/CD, in which case I'll have no choice but to use the built in DAC for the MCD600 player.

 

[Bill Brown]

My pleasure.  I find these calculations sort of fun.

 

I looked for the input sensitivity on your amp.  It wasn't on the main web page, but I find it in the owner's manual:

 

4.2V in balanced will drive the amplifier to its rated output (half that for unbalanced), so that is the most your preamp will have to put out.

 

I was pretty close with my 4V calculation above :).

 

For 4.2V out your preamp needs 0.189779V :).

 

I like to use digital attenuation so as not to have to buy a preamp as I think small amounts of digital attenuation (possible with good gain staging) are transparent.  If I had that preamp though, I would use it.  I would set the DAC output at 0.2V and listen.  If I needed more volume than I could get with the knob all the way up I would go to 0.6V (though see below re. the autoformer taps), and then up again if needed.  The choices of voltage outputs on your DAC are great in this regard.  At 0.2 or 0.6V your gain arrangement will be fantastic and you will get the full S/N ratio out of your system.  The key is the lowest setting at which you get full power output with the least attenuation with your volume knob.

 

There is one more choice you are going to have to make....which autoformer tap you are going to hook your speakers to, and the gain of the amp depends on that.  With tube amps I like to use an output that is always at or below the speaker's impedance.  JA's measurements also suggested that with this amp setting lower rather than higher was better from a distortion perspective (though you get more power from higher ohm taps relative to the load).  You can't break anything by hooking to any of them.  Your speakers are rated at 8 ohms, but that is always nominal, there may be dips here or there.  I would probably use the 4 ohm outputs, there is still plenty of power from that tap.

 

I am sure you have seen these:

 

https://www.stereophile.com/content/mcintosh-laboratory-mc462-power-amplifier-measurements

 

No matter where you try the voltage/which output tap, you won't break anything, so just try different settings and enjoy.  I have never lived with Mac components, but I strongly suspect you are in for quite a treat!

 

Bill

[Bill Brown]

I realized I may have implied your amp had a tube output stage, but I know it is SS.  The commonality it has with tube outputs is the transformer output (actually an autoformer with Mac, unique in that regard and a neat concept).

 

Bill

[992Sam]

@Bill Brown... thanks very much for that wealth of wisdom and calculations... its surprising that .2v might be the solution and a blessing that dCS even offers this.. .6 might even be ideal depending on how it sounds after I play around with it.  Even in their own owners manual they don't imply this is the normal voltage setting for using with a pre-amp, they mention something about Apple Airplay, but they imply that 2v is the normal with 6v for "some pre-amps".

 

I guess I will start with .2 and work up from there..   counter intuitively, It seems the lower the voltage in, the better ... I'd expected it to be totally the opposite.  Moreover, I've been using the setup without the pre-amp (As that's not due to arrive for a week) at 6v and occasionally 2v.. seems to sound good, but I can see how it would be easy to over drive the amp at full volume with the 6v setting based on how loud it gets even at -15db.. much less closer to 0.0.

 

Is the volume on the C1100 a digital volume control also?  My main concern is that I don't want to leave any signal behind in the chain... I want the most clarity and resolution. 

 

 

[lucretius]

On 10/26/2020 at 1:12 PM, 992Sam said:

I'm currently using the Rossini with just an Amp, as the pre-amp isn't due to arrive for a week or so...  the pre-amp (as listed in my signature) is a McIntosh C1100, which is a 100% tube pre-amp..   I don't know what type of volume control the Mc has (assuming digital), but the dCS is a digital volume control and so I assume I will want it set to the maximum (0.0db) once it's connected to the pre-amp... and then use the pre-amp volume knob, right?   But the bigger question is what voltage AND WHY?  2 or 6?  someone mentored more dynamic range in the 6v output, while someone else mentioned distortion possibly and over load?

 

Assuming your using the balanced connection, you can use an input anywhere from 900mV to 20V.  I'd say go with the 6V for the balanced connection.  Pro gear (which usually uses the balanced connection) is generally hotter -- up to 10V out.

 

OTOH, if you choose the unbalanced connection (450mV to 10V per C1100 manual), go with the .6V or the 2V (depending on the effect on the volume control).  Note that most consumer gear (which is what uses the unbalanced connection) would usually be somewhere between .7V to 1.3V where a CD player could be 2V output.) 

 

On 10/27/2020 at 8:00 PM, 992Sam said:

I guess I will start with .2

 

.2V is too low!

[lucretius]

Is that a volume control I see on the dCS Rossini?  If so, disable (bypass) it when the C1100 is inline.

[992Sam]

10 minutes ago, lucretius said:

Is that a volume control I see on the dCS Rossini?  If so, disable (bypass) it when the C1100 is inline.

Apparently there is no way to do that, so I will just leave it maxed ...

[sandyk]

On 10/28/2020 at 11:00 AM, 992Sam said:

I guess I will start with .2 and work up from there..

 0.2V suggests that they may have already digitally (most likely) attenuated it already.

[992Sam]

15 minutes ago, sandyk said:

 0.2V suggests that they may have already digitally (most likely) attenuated it already.

 

Which I would want to avoid, and frankly listening to the system as it stands now with the C1100 not in the mix (it comes next week), and with the Rossini directly into the Amp,  even at 2v it's not remotely loud... at 6v it comes to life..  

[sandyk]

1 hour ago, 992Sam said:

 

Which I would want to avoid, and frankly listening to the system as it stands now with the C1100 not in the mix (it comes next week), and with the Rossini directly into the Amp,  even at 2v it's not remotely loud... at 6v it comes to life..  

 Then unless you like (need?)  a little Tubey artificial warmth along with S/N degradation etc. along the way, why do you need the C1100 unless you have other sources to select ?

[992Sam]

3 minutes ago, sandyk said:

 Then unless you like (need?)  a little Tubey artificial warmth along with S/N degradation etc. along the way, why do you need the C1100 ?

the short answer is, especially when listening to classical music, I prefer that warm sound (albeit not when it's too in your face, and the C1100 was less so than the other pre-amps I tried)..  The other part is the logistics of running an SACD player (I have a decent collation of SACDs)  and eventual plans to add a Phonograph and getting good headphones makes that a bit more convenient (possible). 

[Bill Brown]

14 hours ago, sandyk said:

 0.2V suggests that they may have already digitally (most likely) attenuated it already.

 

I would be very surprised if that is the case.  I would make a huge bet it is in the analog stages.  An interesting question to me would be the raw voltage coming off the DAC chips as to whether they are voltage or current output.  If the latter it would require a I/V stage and gain.  Hard to know whether the gain stage/output driving stage is optimized at 0.2, 0.6, 2, etc. volts.

 

I am sure it is implemented very well regardless making the latter consideration moot, and the S/N issues described above remain.  The DAC is certainly not operating in isolation.

 

With wide dynamic range material (very soft sections not boosted by compression) the need for more gain might be seen (heard).  That is where I would start- a wide dynamic range classical recording, setting the V out so those were at the max level I needed.

 

Bill

[Bill Brown]

Truthfully, though, this is all sort of "how many angels can dance on the head of a pin" kind of stuff anyway.  It is a beautiful system that will sound great no matter what you do.  I would just play with it, pick a setting, and forget it/listen to music.

 

Bill

[992Sam]

26 minutes ago, Bill Brown said:

Truthfully, though, this is all sort of "how many angels can dance on the head of a pin" kind of stuff anyway.  It is a beautiful system that will sound great no matter what you do.  I would just play with it, pick a setting, and forget it/listen to music.

 

Bill

True ... sort of a first world problem among first world problems.... but much like a video game I used to play years ago called world of warcraft, where you could either be a "casual" and play it that way, or hard core, and min/max your player to the highest possible level.... this hobby is the same, and I'm in that min/max mode these days... but I'm sure it will wear off. 

[Bill Brown]

No worries. :)

 

Most of us have been there (I know I have)!

 

Bill

[Summit]

If the amplifier can receive 6v without overload, I would definitely choose it. I have tried different voltage from my DAC and 6v sounds, I am not kidding, much better than 2v. The sound becomes more dynamic, effortless, and believe it or not, much clearer. I would contact the amplifier supplier and hear which voltage exactly your amplifier can take at the XLR input. If it's a power amp, I would be very surprised if it could not handle 6v.

 

That there should be a sound difference is not peculiar from a scientific perspective either, as S/N is always better on/with a stronger signal. The reason to this is that the audio signal becomes less sensitive to external noise. A weak signal is (everything else held equal) more sensitive to EMI/RFI compared to a stronger signal, and 3 times as strong is no minor feature we are talking about.

[Summit]

16 hours ago, Bill Brown said:

Truthfully, though, this is all sort of "how many angels can dance on the head of a pin" kind of stuff anyway.  It is a beautiful system that will sound great no matter what you do.  I would just play with it, pick a setting, and forget it/listen to music.

 

Bill

 

Truthfully, why this type of comment to a serious question? I do not believe it’s stupid to try to get the best SQ out of one’s system and discuss which “things” and implementations that does.  

[Bill Brown]

5 hours ago, Summit said:

 

Truthfully, why this type of comment to a serious question? I do not believe it’s stupid to try to get the best SQ out of one’s system and discuss which “things” and implementations that does.  

 

"Stupid" isn't a word I used.  I would ask you to not put words into my mouth.  Also, why would I write so much above about a subject that I think is "stupid?"  Did you read near the top where I emphasized the importance of gain staging in some detail?

 

My point above is not that it isn't worth thinking about and that it wouldn't be fun to experiment, but that in the end, his equipment is so well-engineered that any combination of settings will work fantastically (a point I have repeatedly emphasized).

 

I would also encourage you to read a bit on the effect of S/N measurements after gain and subsequent attenuation:

 

"But if we look back at the system, we see that for most situations, we have more gain than we need. Maybe 15 to 20dB (10X) more gain than we really need. And that can lead to noise. Why? Because any noise that occurs after the volume control does not get attenuated. In fact it gets amplified. You've cut down the signal from the CD player by 17dB, so now it's 17dB closer to the noise in every circuit that follows. Any noise from the preamp, the cables, bad connections, etc. will be also be amplified 30X by the power amp. You took a medium level signal of 320mV (0.32 volts) and divided it down to 44mV so its now much closer in level to all the noise living in the bottom of the system."

https://www.diyaudio.com/archive/articles/160464-de-lite-amplifier-next-thread.html

 

"One consequence of this is that the more you attenuate the signal the more you reduce the SNR (since the noise is fixed). So gain management consists of adjusting and/or selecting a chain of components that will amplify the signal enough to listen to and not much more."  @Kal Rubinson in Stereophile

 

"The maximum gain for both balanced and unbalanced inputs to balanced outputs was just 0.2dB. This is lower than the norm, but it's something I welcome because preamplifiers in general are used to attenuate, not amplify, the levels of source signals" JA in Stereophile measuring an integrated amp

 

• Low Gain – The AHB2 has a low gain setting that optimizes the gain structure of professional monitoring systems. Maximum rated output is reached at an input signal level of 22 dBu. This places the upstream equipment in an ideal operating range to maximize the SNR of the monitoring chain. Most power amplifiers have far too much gain, and this degrades noise performance of the overall system. The AHB2 has an ultra low-noise input amplifier with two gain boost settings that can be enabled to allow direct interfacing with Hi-Fi components that usually operate at significantly lower signal output levels.

https://benchmarkmedia.com/blogs/application_notes/14680625-the-ahb2-a-radical-approach-to-audio-power-amplification

 

"The DAC1, DAC2 and DAC3 all have internal pads on the XLR outputs that should be used to set the output levels to the range that is required by the downstream device. This will allow direct interfacing to virtually any pro or consumer product.

Turning down the volume control is not a substitute for selecting the proper pad setting!

Excessive use of the volume control skews the measurements by adding excessive noise. This in turn impacts the linearity measurements, which at their low end are really SNR measurements. The tests should be run at or near maximum volume (or the calibrated switch on the back of the DAC1 should be enabled)."

 

Jon Siau, Benchmark designer

 

"The wideband S/N ratio, measured in the high-gain, stereo condition with the input shorted to ground and ref. 1W into 8 ohms, was very high, at 89.3dB. Reducing the measurement bandwidth to 22Hz–22kHz increased the ratio to 106dB, while switching an A-weighting filter into circuit increased it further, to 108.5dB. Referenced to the AHB2's clipping power of 100W, this is equivalent to a dynamic range of 128.5dB, which is close to the specified 132dB. The S/N ratio did increase by around 3dB in the lowest-gain condition, implying that the specified ratio was measured in that mode."

 

https://www.stereophile.com/content/benchmark-media-systems-ahb2-power-amplifier-measurements#HkauPY4Q0eXu8lOd.99

 

"To maintain the full dynamic range within the best operating level, RME's ADI-2 FS includes electronic switches, which give control over input and output level via two keys from the front plate, for a perfect adaptation to the levels +4 dBu, +13 dBu and +19 dBu. Two compact level meters provide 6 LEDs each. Multiple brightness stages and peak hold functionality make read- ing and adjusting input levels easy and convenient."

 

0. Mode ANA (Analog In to Analog Out)

   •  Signal to Noise ratio (SNR) @ +19 dBu: 123 dB RMS unweighted, 126 dBA

   •  Signal to Noise ratio (SNR) @ +13 dBu: 119 dB RMS unweighted, 122 dBA

   •  Signal to Noise ratio (SNR) @ +4 dBu: 112 dB RMS unweighted, 115 dBA

https://www.rme-audio.de/downloads/adi2fs_e.pdf

 

The last shows the best dynamic range with the least attenuation (the closest to wide open, i.e.the least attenuation of preceding gain).

 

I'll quit.  The Liverpool game is about to start. :)

 

My implication throughout this thread is that there are things worth considering, but should be approached as fun.

 

Bill

 

[Kal Rubinson]

Well done, Bill.

 

I have progressively removed the preamplifier from my main system, lowered the gain on the power amp and now use very little signal attenuation (less than 10dB in normal playing conditions) in the DAC or player.  The silence is golden.