"Non-optimal" only in a strict sense, in that if you turned up your volume to full, and played music where the peaks hit full amplitude, the peaks would be clipped. But how often do you play with volume at full?
hypex ncore
The conclusion we came to was the reason that some tracks were unable to drive the DAC's outputs to 3V was because the level they were recorded at. So you suggested using replaygain, to set the level of all tracks the same. Well how do you do this with a CD transport, or SD card transport?
For instance some of my DSD recordings are 7db lower at the same volume setting. Without the full 4.6v output my DAC has, I wouldn't be able to listen to them at the volume level I sometimes like to listen at.
Yes I agree, if all I listened to was white noise, that was at the level of exactly 2v output when the volume is set to max, then 2v should be perfect.
The conclusion we came to was the reason that some tracks were unable to drive the DAC's outputs to 3V was because the level they were recorded at. So you suggested using replaygain, to set the level of all tracks the same. Well how do you do this with a CD transport, or SD card transport?
For instance some of my DSD recordings are 7db lower at the same volume setting. Without the full 4.6v output my DAC has, I wouldn't be able to listen to them at the volume level I sometimes like to listen at.
Yes I agree, if all I listened to was white noise, that was at the level of exactly 2v output when the volume is set to max, then 2v should be perfect.
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Ah ok, I misunderstood. I never go to full volume on the MDAC... so I guess in this case it's not an issue. Thanks
Let's not confuse gain and voltage level. Sounds like you have a DAC that *can* output 4.6V, but you never use the full output amplitude. That is of course totally OK, as long as you don't play music that is normalized to 0dB at full volume. So you don't actually need 4.6V, but need enough gain that even your DSD music, at -7dBFS, gets up to 2V. The difference between 2V and 4.6V happens to be 7 dB...
hypex ncore
Yes so the 4.6v max output capabilities is great. However if I connect a DAC up that only can put out a max of 2v, I'd never be able to get the 2v out of the DAC with these tracks.
Even with my 3v output DAC, I could crank some songs to the max and they wouldn't be loud enough. So having the 4.6v on tap, allows me to listen to any track in my collection at the same max level I want to listen at.
Ever listen to the Sheffield drum and track disk at 115db? Won't happen with my 3v out DAC.
Yes so the 4.6v max output capabilities is great. However if I connect a DAC up that only can put out a max of 2v, I'd never be able to get the 2v out of the DAC with these tracks.
Even with my 3v output DAC, I could crank some songs to the max and they wouldn't be loud enough. So having the 4.6v on tap, allows me to listen to any track in my collection at the same max level I want to listen at.
Ever listen to the Sheffield drum and track disk at 115db? Won't happen with my 3v out DAC.
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I just realised that the output I quoted is wrong 2.0v is for RCA from the Audiolab balanced xlr it is 4.1v same as above MDAC.
My present power amp is 1.5v input so I guess should not have a problem except my gain will go up a bit.
True - but that is an issue with those tracks and your sources. if you were to listen to normalized PCM tracks at full volume, you would drive the amps to clipping.
Occamsrazor also asked about "optimal", and your setup is not "optimal" in the sense that by getting the gain structure exactly right would allow you to make some small improvements - but so small that it probably doesn't matter.
By lowering the gain of the nc400's (by replacing R141) by 7 dB, from 26 to 19, you would get a situation where full scale output from the DAC will just bring the amps to the clipping point (but not beyond). This might improve SNR (but that depends on the noise structure of your DAC - you will reduce the post-volume-control noise level by 7 dB, but it won't affect the pre-volume-control noise). According to Bruno, it should also improve the performance of the nc400 a bit due to increased feedback. Anyway, differences so small that they are insignificant compared to the noise and distortion in any source material.
The reason you can't do that in your particular situation is that some of your recordings are not normalized to 0dBFS - a problem with DSD, as unlike PCM, DSD doesn't have a fixed "full scale" point, and thus the SACD reference level is 6 dB down from PCM full scale in order to leave head room for "goes up to 11" situations - but if you would play those recordings at full volume, with your "7 dB too hot" gain structure, those situations would drive your amps into clipping.
Who on this planet doesn't have recordings that are at different levels? I have no concern of overdriving the amps to clipping. I haven't yet. You just simply don't turn it up as loud with higher gain recordings. My ears can tell me when it's loud enough.
My DAC has an S/N ratio of 130db. When I turn it to max and put my ear to the tweeter, there's absolute silence. Sounds like the amps are off. Besides if your DAC is capable of 4.6v and your only asking 2v out of it, the noise and distortion at 2v will most likely be less.
Fair enough as it applies to you, but maybe not the best advice to others, who might not be as good at manually applying dynamic gain control.
Distortion will probably be less, but noise will be at the same level, so the signal-to-noise ratio will be lower.
Again, gain is one thing, voltage another. If your DAC and preamp have a gain that makes them produce 2V at 0dBFS, then you have a nominally 2V output that happens to be able to produce 4.6V if needed - for example by playing DSD recordings so that they go (due to volume control settings) above 0dBFS.
And just to be sure - you do understand what 0dBFS means for a PCM recording?
hypex ncore
That would mean the point where the gain is as OdBFS. Which should drive your DAC to its rated output. And yes some recordings I have will do that at -12 on the volume setting. And some will at -5.
I really don't see it as a danger unless your using something like a slider volume control on a smartphone app for volume control or something where it's easy to slip up and crank to max.
. A person who knows his system, knows when it's it the maximum threshold of comfort. Unless your worried about your kids blowing your speakers when your out of town. Then it may be a concern.
That would mean the point where the gain is as OdBFS. Which should drive your DAC to its rated output. And yes some recordings I have will do that at -12 on the volume setting. And some will at -5.
I really don't see it as a danger unless your using something like a slider volume control on a smartphone app for volume control or something where it's easy to slip up and crank to max.
. A person who knows his system, knows when it's it the maximum threshold of comfort. Unless your worried about your kids blowing your speakers when your out of town. Then it may be a concern.
Again, that might be something you might be comfortable with, and it might possibly make sense with really insensitive speakers, but it goes against all normal professional practice.
hypex ncore
I guess I must be a rebel in the world of audio then, for wanting to listen to my DSD tracks at 115db on occasion.
I guess I must be a rebel in the world of audio then, for wanting to listen to my DSD tracks at 115db on occasion.
I guess I must be a rebel in the world of audio then, for wanting to listen to my DSD tracks at 115db on occasion.
I guess somebody has to...
The 4.5 is just the buffer stage gain. The total gain is 4.17 * (1 + 2 x Rf / Rg), so with the original values, 4.17 * (1 + 2 x 2.2k / 1.2k), or 19.5.
With Rg (R141) completely removed you only get the buffer stage gain, 4.5, so instead of 2V for full output without clipping, you can go to 8.7 V, but with the lower gain, a 2 V signal will of course cause an output level that is 13 dB quieter.
The optimal R141 for a 4.6V input signal would be 4.7k, resulting in a gain of 8.
Power Switching
My amplifier will be going in a cupboard so I will not be able to switch on if a switch is fitted on the back. So I want to fit a power switch in the front to switch on both SMPS600s. Has anyone got any idea of a power switch that would be suitable with a neon. I could of course fit two switches one for each power supply if it helps with amp rating.
Also I would prefer a round switch as it will be easier to fit to a 10mm thick aluminium front panel
My amplifier will be going in a cupboard so I will not be able to switch on if a switch is fitted on the back. So I want to fit a power switch in the front to switch on both SMPS600s. Has anyone got any idea of a power switch that would be suitable with a neon. I could of course fit two switches one for each power supply if it helps with amp rating.
Also I would prefer a round switch as it will be easier to fit to a 10mm thick aluminium front panel
Buy the nice machined stainless blue LED Bulgin push button off the Hypex webshop. But you'll need their soft start with it, or make your own supply. I used it with the soft start on my first build a couple years back and worked beautifully.
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