Help me level match my DSD and Stellar GCD

dac

#1

@Paul @tedsmith

To start with, everything is connect via balanced XLR cables.

Ok, from my understanding the DSD’s volume levels are in 0.5 dB increments. Let’s say I want to match a volume setting of 30 on the DSD. That’s 70 steps down from 100 corresponding to 35 dB of attenuation.

Going into the Stellar GCD, it has has 80 dB of range, some 0.5 dB increments, some 1 dB increments (as per the spec page). A setting of 76 is unity gain, so going up to a volume of 100 (24 steps) gets you +12dB, so 0.5 dB/step. Assuming the 0.5 dB increments are adjacent to a volume of 76, (this is my fundamental point of uncertainty) 16 steps down from 76 will yield 8 dB of attenuation at a volume setting of 60, so the remaining steps from 60 to 0 will give you an additional 60 dB of attenuation in 1 dB increments so that the total range is 80 dB. Ok, but I only need 35 dB of attenuation total, so I need 35 - 8 = 27 more 1 dB steps down from 60…

So, a setting of 33 on the Stellar GCD should give me 35 dB of attenuation, no?

Though from listening, this is clearly not right. A 100 setting on the DSD and 33 on the GCD is way louder than a setting of 30 on the DSD going straight into my amps.

Are there any little details I’m missing or false assumptions that I’m making?


#2

The digital volume controls are relative to 0dBFS, i.e. relative to what the device puts out for a full scale wave. The full scale output of the DS is 1.414VRMS, the most common output level for CD players and SACD players is 2VRMS. So the DS is 3dB quieter that a typical CD player. I don’t know the output levels on the Stellar line.


#3

So for the DSD, a setting of 30 does indeed give you an attenuation of 35 dBV, correct?


#4

Yes…


#5

Ok, then I guess the mystery does lie with the GCD. I’m not sure why my calculations are so off wrt the actual output of the GCD. Guess I’ll have to wait for someone at PSA to chime in.

Thanks.


#6

What are you trying to do? Do you want to play the same source through both DACs and compare, like an A/B test?

If so you could probably only do it at a specified volume, I doubt the two volume controls will track the same.

Choose a level on one, and using a test one and a SPL meter set the other component to match. Each time you move the volume on the first component, you would have to run the test tone again.


#7

Not comparing the DACs, comparing preamp vs no preamp.
I’m comparing the DSD directly into the M700s vs going throught the GCD first.

I don’t have an SPL meter, so I wanted at least a first order approximation to level match the two outputs. I will eventually get an SPL meter once I move to a place with a better room.

Of course I get get a volt meter too and match the outputs that way, but I was trying to avoid that for now.


#8

Download a sound meter on your phone.

AudioTools is good.


#9

Oh, I forgot. I actually do have a couple of sound meter apps! But honestly, I’m lazy and I just want someone to tell me the theoretical matched output settings, haha!


#10

In the time it took me to post this topic, I went ahead and opened up my spl app (thanks for reminding me) and tested the outputs at 100 Hz. It seems as though a setting of 20 on the GCD with full volume on the DSD is pretty close to a volume of 30 on the DSD.

I’d be cool to have an engineer confirm this based on hardware design parameters, for my edification.


#11

Ted - why was it choosen to set the DS 0dBFS out to 3dB below the established / common 2VRMS for this kind of equipment ?


#12

When we first designed the DS we wanted existing PWD owners to be able to upgrade - I was fine with the original back panels, they had a reasonable set of inputs and outputs. The display and the display/control processor were fine as well - my main purpose was to make a better sounding DAC, not add features. The power supply seemed close enough, I could add power supply filtering on the boards. But that meant that I had to live with the voltages available, I used 5V for digital and 12V for analog. The power supply filtering eats multiple volts, the passive output filtering eats half of the final output voltage… We ended up with a signal that was about 3dB lower than we liked, but that meant people could upgrade two boards at a reasonable price point.

At the end (when we were listening to and measuring the first production run) Paul decided to pay for a more expensive transformer on the power supply. With 20/20 hindsight we could have considered going back and redoing the primary power supply card and voltages and then redoing the analog card to have a higher output, but this would also have affected the final price of the unit.


#13

I upgraded from the PWD and am thankful that route was provided. My PWD was pretty new when the DSD was introduced. Wasn’t happy about spending for the upgrade. It sure has worked out!! Greatest piece of stereo gear I’ve purchased.


#14

Thank you Ted, interesting as always :slightly_smiling_face: