Help me understand matching a DAC with amp input sensitivity

[Swoof]

I have a DAC with pre-amp functionality, the SMSL M200. In DAC mode it outputs the typical 2V via RCA and 4.1V via XLR, but in pre-mode it outputs up to around 2.7V via RCA and 5.5 vs XLR. Now the input sensitivity of most amps I've looked at are much lower than 5.5 V, but many still have XLR inputs. Wouldn't this pretty much always exceed the ideal input sensitivity of most amps? I'm going to be using a nc252mp to 6ohm speakers, which means I think I'll definitely want to use the RCA out of my DAC so I'm not sending way too many volts on the line in to the amp.

Am I thinking about this correctly? What is the point of XLR out with higher voltage if most amps seem to have a sensitivity asking for a lower voltage?

 

[sq225917]

It makes no sense at all. For the longest time 26db was pretty much the standard gain on power amps. So a dac putting out 5v needs to be run at around -20 -30db if you're using 89dbwm speakers in your average room.

Dac manufacturers are chasing higher output because it let's them win the snr wars. That's fine if you're running 10-14db gain power amps, or an analogue pre amp, but otherwise you just end up throwing away 30db or more of level with the dac's digital volume control and end up chucking away bits.

Realistically we listen in a range of maybe 20db, at least that's the range between my late night listening and blasting out music when I have the house to myself.

I'd happily settle for less output from my dac. I have to use a pre amp (unity gain, no actual amplification) to attenuate level between my turntable and dac. I'd like to run the dac direct, but at the levels I most often listen at I'd be at -35db on the volume control. I may as well just use a run of the mill dac at that point as I'd be throwing away loads of snr.


I don't understand the reasoning. Cd was 2v, most phono out is circa 2v, why not just make dacs to fit that gain structure?

 

[Swoof]

So then is all DAC/pre output voltage exceeding the input sensitivity of the amp wasted? Does it just cause clipping? Is there any benefit to having headroom, can some amps handle voltage over the input sensitivity?

 

[mdsimon2]

So then is all DAC/pre output voltage exceeding the input sensitivity of the amp wasted? Does it just cause clipping? Is there any benefit to having headroom, can some amps handle voltage over the input sensitivity?

I personally like a little bit of extra output from the DAC. I use NC252MPs which have an input sensitivity of ~1.7V and a DAC with 4V output. It is important to remember that you will only see full output voltage from the DAC if you have an input signal at 0 dB (which for most well recorded music is unlikely) and the DAC volume is at maximum. To me the extra output from the DAC helps compensate for source material which may be at a lower level. With my setup it is possible to clip the amplifiers at volume levels greater than -8 dB but I only exceed this volume when listening to material with a lower than typical level.

Michael

 

[wjc]

I have a DAC with pre-amp functionality, the SMSL M200. In DAC mode it outputs the typical 2V via RCA and 4.1V via XLR, but in pre-mode it outputs up to around 2.7V via RCA and 5.5 vs XLR. Now the input sensitivity of most amps I've looked at are much lower than 5.5 V, but many still have XLR inputs. Wouldn't this pretty much always exceed the ideal input sensitivity of most amps? I'm going to be using a nc252mp to 6ohm speakers, which means I think I'll definitely want to use the RCA out of my DAC so I'm not sending way too many volts on the line in to the amp.

Am I thinking about this correctly? What is the point of XLR out with higher voltage if most amps seem to have a sensitivity asking for a lower voltage?

Don't worry too much about the output voltage levels (RCA 2.7V, XLR 5.5V). It's more important that your amplifier has a high input impedance to get good amplification. You may also want to lower the gain of you amp if it starts to clip.

 

[Harmonie]

I personally like a little bit of extra output from the DAC. I use NC252MPs which have an input sensitivity of ~1.7V and a DAC with 4V output. It is important to remember that you will only see full output voltage from the DAC if you have an input signal at 0 dB (which for most well recorded music is unlikely) and the DAC volume is at maximum. To me the extra output from the DAC helps compensate for source material which may be at a lower level. With my setup it is possible to clip the amplifiers at volume levels greater than -8 dB but I only exceed this volume when listening to material with a lower than typical level.

Michael

+1
It really depends on the recordings.
My amps have a low 0,775v input sensitivity, no issue to drive with some selected CD's even at -0db dac output.

 

[March Audio]

So then is all DAC/pre output voltage exceeding the input sensitivity of the amp wasted? Does it just cause clipping? Is there any benefit to having headroom, can some amps handle voltage over the input sensitivity?

Bottom line is just dont worry about it.

As mentioned you do need some headroom for quieter recordings. It won't cause clipping unless you turn the volume up too high. It's not outputting 5 volts all the time, you are in control of that with the volume control.

This is no different to how it's always been. A CD player might output 2 volts max and then the volume control on the pre amp reduces that voltage so that the power amp outputs the volume you want.

 

[sq225917]

It becomes an issue when you have to run a digital volume control at say -30db to get a sensible output level. One may be better positioned with a lower output dac that doesn't measure quite as well but can be run at 0db, giving a better relative snr.

 

[Swoof]

I think this is making a lot more sense now. The extra voltage from the DAC is nice, particularly for the occasional track or TV show that seems like the volume is really low.

Regarding SNR - What is going on with a DAC pre-amp? My m200 goes from 40-0dB, I'm not sure how well this will work with the nc252mp. I may end up having to run -20, would I be better off running a 10dB XLR pad or keeping volume low on DAC? Or simply just running RCA cables with lower output?

 

[mdsimon2]

You are probably over thinking this. If you pad the DAC output by 10 dB you will effectively reduce the maximum output voltage from 5.5V to 1.7V which is the input sensitivity of the NC252MP and will have lost the ability to compensate for lower level recordings.

Although it is true that digital volume control will "throw away bits" because the AK4497EQ is 32 bit (and your source material will be 16/24 bit) you can afford to do this.

Some good but simple resources on DAC volume control:

http://www.esstech.com/files/3014/4095/4308/digital-vs-analog-volume-control.pdf

Michael

 

[Swoof]

You are probably over thinking this. If you pad the DAC output by 10 dB you will effectively reduce the maximum output voltage from 5.5V to 1.7V which is the input sensitivity of the NC252MP and will have lost the ability to compensate for lower level recordings.

Although it is true that digital volume control will "throw away bits" because the AK4497EQ is 32 bit (and your source material will be 16/24 bit) you can afford to do this.

Some good but simple resources on DAC volume control:

http://www.esstech.com/files/3014/4095/4308/digital-vs-analog-volume-control.pdf

Michael

Thanks, this was super helpful. Can we assume all modern DAC's with digital volume control have access to the DACs internal data path? Is that baked into the chip itself, or on the manufacturer to implement correctly?

 

[mdsimon2]

Thanks, this was super helpful. Can we assume all modern DAC's with digital volume control have access to the DACs internal data path? Is that baked into the chip itself, or on the manufacturer to implement correctly?

Modern ESS and AKM DAC chips are 32 bit and have volume control on chip.

That being said it would be possible for a DAC manufacturer to implement another form of volume control (for example analog volume control downstream of the DAC chip) but I imagine you would only see this in more esoteric/expensive designs.

At the end of the day there is no free lunch. If you want the ability to compensate for lower level recordings you need some way to get more voltage to your amplifiers. Again, just my opinion but I think using a sufficiently high performance DAC with 32 bit digital volume control and maximum output voltage that is 5-10 dB above the input sensitivity of your amplifier is a good compromise. If you want absolutely the highest performance possible you would use a low noise analog volume control downstream of your DAC but I would strongly question whether this would provide any benefit in a real world scenario.

For example in my current system I use a miniDSP SHD Studio for volume control which is a 32 bit floating point processor. With this processor it is very easy to measure the performance impact of digital volume control in REW as it has bi-directional USB audio so it can be used as both an input and output device (all digital, no analog). Here is what SINAD looks like vs volume control level (my typical listening level is between -12 and -24 dB).

0 dB: 130 dB
-3 dB: 129 dB
-6 dB: 127 dB
-12 dB: 122 dB
-24 dB: 110 dB
-36 dB: 98 dB
-48 dB: 86 dB

Considering the NC252MP amplifiers I use have a SINAD of ~94 I think this is an acceptable compromise.

Michael

 

[sq225917]

Regarding volume and ess chips, mytek have both analogue and digital attenuation options. I couldn't tell any difference when I owned a Brookland until I got to around-40db. Even then it just sounded a touch more coarse, a little rougher.

 

[bh69]

My old Marantz PM44se has input sensitivity 0.15V (new PM6007 0.2V).
Audiolab M-DAC RCA output has 2.25V RMS.

Can this cause problems with clipping (amplifier input overdrive) ? I don't think because of the high volume of reproduction, I listen quietly, but because of the input signal too high - is it a problem or is it okay? Why input sensitivity of amps is so low compared to output from DAC od CD player ?

 

[sq225917]

Yes it can likely cause clipping at full volume. Just turn the vol pot down and run the dac at -20db

 

[AnalogSteph]

My old Marantz PM44se has input sensitivity 0.15V (new PM6007 0.2V).
Audiolab M-DAC RCA output has 2.25V RMS.

Can this cause problems with clipping (amplifier input overdrive) ?

No. Input sensitivity != input clipping level.

Input sensitivity is the input level that will produce full rated amplifier output with the volume turned all the way up. Integrated amplifiers have traditionally been designed to hit nominal consumer line level of 300 mVrms plus 4-6 dB worth of gain to spare. This is roughly in line with the 250-500 mV of nominal output from the phono stage over a typical range of MM cartridges at nominal output. With a 2 Vrms source, you should never need to turn up the amplifier beyond about 12 o'clock.

Input clipping level, on the other hand, is the maximum level the input can accept without distorting when amplifier volume is turned down. It is rarely less than 2-3 Vrms in hi-fi gear, and may be up to >10 Vrms depending on amplifier construction (how input selection and volume control is implemented). Working back from specified phono max input level in the PM-6007, we may be looking at around 9 Vrms.

It is still a good idea to keep very hot recordings a few dB away from 0 dBFS to avoid digital filter overload... the use of playback volume normalization (e.g. ReplayGain; streaming services also tend to use some system) tends to accomplish this along the way.