This is a review and detailed measurements of the Schiit Saga passive/tube pre-amplifier. It is on kind loan from a member who has waiting literally months for his review! The Saga costs USD $349 from Schiit direct with stock tube plus shipping. The tube supplied with this unit was the Russian 68HC which is their clone of 6N8S (dural triode).
The industrial design is typical of Schiit product but as usual, with a different switch mechanism and looks:
For reasons too embarrassing to explain, I had to open the unit and there, I noticed the analog volume control (which gets converted to digital), had a nice notch on it. I was happy they were using such as that would avoid the volume control becoming loose, only to realize the set screw goes on the round part of the shaft, not flat!
Anyway, back to the switches, the are microprocessor controlled and feel nice. Click the input one on the left and you rotate between five different RCA inputs. The switch on the right decides whether the Saga is a simple pass-through with volume control, or through an active hybrid tube+solid state output stage pre-amplifier. The gain in both cases is zero meaning whatever voltage you put in, is what you get out.
The volume control is a stepped attenuator using a handful of relays and resistors. Similar set of relays are used to select the right input.
Let's get into measurements and see how each mode performs.
Measurements
This being a tube amplifier, I thought I measure I measure its performance in active mode as it powered on to see how it changes:
As you see, performance is very stable. There is a very slight improvement in one channel up to about a minute but after that, there is no difference even at this magnification. This is a good thing as you don't want to age the tubes any more than you have to.
I am usually full of complaints about myths audiophiles believe it. In this case, the above busted one of my own myths that tube products require significant warm up to get to stable performance. @SIY had told me otherwise but of course, I did not listen.
With that out of the way, let's look at our usual dashboard. To really judge the performance of the Schiit Saga in passive mode, I thought I show the native performance of the Audio Precision APx555 by itself before routing the output through the Saga:
We see the tiniest amount of distortion at 2 kHz (level at -150 dB) and mains noise (level at -145 dB). There is some noise around our main signal skirt. I can get rid of that by using the digital (DAC) mode of the APx555 generator but then distortion increases. Anyway, we have a SINAD of 122 dB at this 2 volt output.
Routing the signal through Schiit Saga at max volume in passive mode we get:
There is some mains leakage that may be due to ground loop or leakage of the power supply for the active stage in Saga. Either way, this is exemplary performance with just 2 to 3 dB of loss compared to APx555.
I was holding on to my chair expect massive drop in performance when I switched on the tube:
Wow, this is very respectable! I have measured Schiit DACs with far lower performance. The offending distortion is the second harmonic at nearly -98 dB which sets the SINAD/THD+N. There are also power supply related spikes but they are at -108 dB and lower so don't come into play.
Overall, this is one good showing so far!
Let's measure frequency response at max volume:
The pass-through mode (in blue) is ruler flat, reflecting the superlative performance of the APx555.
I ran the active stage two ways: 1) with standard 100k Ohm input impedance of the analyzer (green) and 2) 600 Ohm load of the analyzer. We see that there is some droop with 100k Ohm load starting at 50 Hz and increasing to 2 dB at 10 Hz. This indicates a capacitor output stage which would naturally have increasingly higher impedance as frequencies decrease. Switching to 600 Ohm load emphasizes this and magnifies the problem substantially and artificially, giving us 16 dB of droop by 20 Hz.
The 600 Ohm impedance is essentially the inverted shape of our output impedance curve but let's run the full measurement to get the specific values:
Looking all the way to the right, the minimum impedance is 183 ohm. At the lower end of 20 Hz, impedance climbs to 3,130 ohm. Using the typical 10:1 rule, your power amplifier input impedance should be at least 30k Ohm to avoid frequency dependent/EQ changes. Put more simply, if you use lower input impedance power amplifier after Saga in active mode, your low frequencies below 500 Hz or so will attenuate. This may accentuate the rest of the spectrum you may like, or not.
The passive mode has its own issues here. Until now on purpose I have kept the volume at max as to keep the attenuator resistors out of the way. The moment you turn down the volume, you will be putting varying amount of resistance in the output path and thereby, increase impedance. Here is the output impedance curve in passive mode with volume around 20%:
The cursor is at 144 Hz showing an impedance of 2,760 ohm. This is in contrast to just 21 ohm impedance at max volume reflecting the 20 ohm output impedance of the APx555 analyzer.
Plotting a few points on the volume control gets us this:
So essentially, any volume level less than 50% is going to increase the impedance substantially. Fortunately the attenuation is not frequency dependent so the impact is not there as there is with tube stage. However if the input impedance of the power amp changes with frequency and is less than 30k Ohm, then turning down the volume may change the frequency response. Perfection in distortion and noise has this price.
Conclusions
I must say, I developed a fondness for this little pre-amp. I have no idea why as I would never use it myself. It just seems like a neat combination of features in a pretty low cost package. If you are looking for its features and are mindful of drawbacks with respect to its varying output impedance, then I don't see a reason to not get and play with it. You could use it as a nicely implemented audio switcher for example with the volume control for fine tuning of max level.
So, good job Schiit.
------------
As always, questions, comments, recommendations, etc. are welcome.
They say you should save money for a rainy day. It rains for about 6 months here so I need plenty of money!!! Please consider donating funds using:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
The industrial design is typical of Schiit product but as usual, with a different switch mechanism and looks:
For reasons too embarrassing to explain, I had to open the unit and there, I noticed the analog volume control (which gets converted to digital), had a nice notch on it. I was happy they were using such as that would avoid the volume control becoming loose, only to realize the set screw goes on the round part of the shaft, not flat!
Anyway, back to the switches, the are microprocessor controlled and feel nice. Click the input one on the left and you rotate between five different RCA inputs. The switch on the right decides whether the Saga is a simple pass-through with volume control, or through an active hybrid tube+solid state output stage pre-amplifier. The gain in both cases is zero meaning whatever voltage you put in, is what you get out.
The volume control is a stepped attenuator using a handful of relays and resistors. Similar set of relays are used to select the right input.
Let's get into measurements and see how each mode performs.
Measurements
This being a tube amplifier, I thought I measure I measure its performance in active mode as it powered on to see how it changes:
As you see, performance is very stable. There is a very slight improvement in one channel up to about a minute but after that, there is no difference even at this magnification. This is a good thing as you don't want to age the tubes any more than you have to.
I am usually full of complaints about myths audiophiles believe it. In this case, the above busted one of my own myths that tube products require significant warm up to get to stable performance. @SIY had told me otherwise but of course, I did not listen.
With that out of the way, let's look at our usual dashboard. To really judge the performance of the Schiit Saga in passive mode, I thought I show the native performance of the Audio Precision APx555 by itself before routing the output through the Saga:
We see the tiniest amount of distortion at 2 kHz (level at -150 dB) and mains noise (level at -145 dB). There is some noise around our main signal skirt. I can get rid of that by using the digital (DAC) mode of the APx555 generator but then distortion increases. Anyway, we have a SINAD of 122 dB at this 2 volt output.
Routing the signal through Schiit Saga at max volume in passive mode we get:
There is some mains leakage that may be due to ground loop or leakage of the power supply for the active stage in Saga. Either way, this is exemplary performance with just 2 to 3 dB of loss compared to APx555.
I was holding on to my chair expect massive drop in performance when I switched on the tube:
Wow, this is very respectable! I have measured Schiit DACs with far lower performance. The offending distortion is the second harmonic at nearly -98 dB which sets the SINAD/THD+N. There are also power supply related spikes but they are at -108 dB and lower so don't come into play.
Overall, this is one good showing so far!
Let's measure frequency response at max volume:
The pass-through mode (in blue) is ruler flat, reflecting the superlative performance of the APx555.
I ran the active stage two ways: 1) with standard 100k Ohm input impedance of the analyzer (green) and 2) 600 Ohm load of the analyzer. We see that there is some droop with 100k Ohm load starting at 50 Hz and increasing to 2 dB at 10 Hz. This indicates a capacitor output stage which would naturally have increasingly higher impedance as frequencies decrease. Switching to 600 Ohm load emphasizes this and magnifies the problem substantially and artificially, giving us 16 dB of droop by 20 Hz.
The 600 Ohm impedance is essentially the inverted shape of our output impedance curve but let's run the full measurement to get the specific values:
Looking all the way to the right, the minimum impedance is 183 ohm. At the lower end of 20 Hz, impedance climbs to 3,130 ohm. Using the typical 10:1 rule, your power amplifier input impedance should be at least 30k Ohm to avoid frequency dependent/EQ changes. Put more simply, if you use lower input impedance power amplifier after Saga in active mode, your low frequencies below 500 Hz or so will attenuate. This may accentuate the rest of the spectrum you may like, or not.
The passive mode has its own issues here. Until now on purpose I have kept the volume at max as to keep the attenuator resistors out of the way. The moment you turn down the volume, you will be putting varying amount of resistance in the output path and thereby, increase impedance. Here is the output impedance curve in passive mode with volume around 20%:
The cursor is at 144 Hz showing an impedance of 2,760 ohm. This is in contrast to just 21 ohm impedance at max volume reflecting the 20 ohm output impedance of the APx555 analyzer.
Plotting a few points on the volume control gets us this:
So essentially, any volume level less than 50% is going to increase the impedance substantially. Fortunately the attenuation is not frequency dependent so the impact is not there as there is with tube stage. However if the input impedance of the power amp changes with frequency and is less than 30k Ohm, then turning down the volume may change the frequency response. Perfection in distortion and noise has this price.
Conclusions
I must say, I developed a fondness for this little pre-amp. I have no idea why as I would never use it myself.
It just seems like a neat combination of features in a pretty low cost package. If you are looking for its features and are mindful of drawbacks with respect to its varying output impedance, then I don't see a reason to not get and play with it. You could use it as a nicely implemented audio switcher for example with the volume control for fine tuning of max level.So, good job Schiit.
------------
As always, questions, comments, recommendations, etc. are welcome.
They say you should save money for a rainy day. It rains for about 6 months here so I need plenty of money!!! Please consider donating funds using:
Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
