• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Stax Tube Amplifier Distortion vs Solid State

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
#1
A few weeks ago I compared the measurements of my Stax SRM-007t differential tube amplifier against the SRM-313 solid state amp. Results showed that the tube amplifier showed significantly more distortion as levels increased compared to solid state:



Objection was raised that the 100 kilo ohm input impedance of my audio analyzer was to low for the tube amp and hence stressed it more. I bought the parts to build a higher impedance load but by then I had also purchased my new GRAS 45C headphone measurement system. So I thought we cut to the chase and measure what the headphone itself produces when driven by the two different amps. Such acoustic measurements are tricky though as they are subject to noise so accuracy is not high at low amplitude. So I measured from medium to high output level. The volume control was set to 7 on both amps and I ran a sweep driving two channels but showing one. Here are the results:

Stax SRM-007t tube amplifier versus SRM-313 Solid State Distortion Measurements.png


The two follow each other within margin of error but then distortion takes off in the tube amp(SRM-007t) while it stays level in stolid state (SR-303). Other than low resolution of the acoustic measurements, the results correlate well with our electronics measurement.

Note that the distortion could have been increasing earlier in the tube amp but masked by the headphone distortion.

Conclusions
There is no question that the tube energizer has lower power capability before its distortion rises. To the extent you listen softly then you won't notice it. In my use I do and have been frustrated for a lot time about the tube amp becoming distorted before I run out of satisfaction with the volume. :)

And oh, this is evidence that electronic distortion can be worse than our transducers (speakers and headphones). Always get electronics that are far better than your transducers to avoid this. Definitely don't skimp on power capability.

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
Thread Starter #2
BTW frequency response was identical using both amps so any perceived tonality difference is imagined. :)
 

Francis Vaughan

Addicted to Fun and Learning
Forum Donor
Joined
Dec 6, 2018
Messages
908
Likes
4,330
Location
Adelaide Australia
#5
then distortion takes off in the tube amp(SRM-007t) while it stays level in stolid state (SR-303).
Hmm, trying to work out how to compare the different graphs. The gap between the 007t and the 303 starting to clip is only 2dB spl.
Yet the previous power distortion graphs has three decades of power difference between the two breakpoints. That is a big disparity.
Do we know the sensitivity of the phones, so we can align the two graphs?
2dB could easilly be accounted for by the higher voltage drop through the tube versus a transistor.
 

YSC

Major Contributor
Joined
Dec 31, 2019
Messages
1,252
Likes
849
#7
Conclusions
There is no question that the tube energizer has lower power capability before its distortion rises. To the extent you listen softly then you won't notice it. In my use I do and have been frustrated for a lot time about the tube amp becoming distorted before I run out of satisfaction with the volume. :)

And oh, this is evidence that electronic distortion can be worse than our transducers (speakers and headphones). Always get electronics that are far better than your transducers to avoid this. Definitely don't skimp on power capability.

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/[/QUOTE]

wait, before clipping was at 112 dB SPL, I think you won't want to listen to that level;) I do most of my listening at ~65dB SPL measured by phone dB meter, any louder may cause slightly discomfort.

BTW frequency response was identical using both amps so any perceived tonality difference is imagined. :)
So those harmonic distortions of some 40-50dB SINAD don't translate into the final output? find it difficult to get it this way
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
Thread Starter #8
Hmm, trying to work out how to compare the different graphs. The gap between the 007t and the 303 starting to clip is only 2dB spl.
Yet the previous power distortion graphs has three decades of power difference between the two breakpoints. That is a big disparity.
You don't know the lower bound of the second measurement because the distortion of the headphone itself dominates.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
Thread Starter #9
wait, before clipping was at 112 dB SPL, I think you won't want to listen to that level;) I do most of my listening at ~65dB SPL measured by phone dB meter, any louder may cause slightly discomfort.
You don't listen to continuous test tones. Momentary peaks especially in low frequencies are not loud at all. Threshold of hearing at 20 Hz is 70 dBSPL. If you are listening at 65 dB, you are not hearing anything at that frequency let alone it being loud!

Really folks, this whole dBSPL thing is so misunderstood it seems. What did you measure with it anyway? Noise? We are not talking about noise.
 

Francis Vaughan

Addicted to Fun and Learning
Forum Donor
Joined
Dec 6, 2018
Messages
908
Likes
4,330
Location
Adelaide Australia
#10
You don't know the lower bound of the second measurement because the distortion of the headphone itself dominates.
Quite. But we can none the less align the graphs in the area where the power amps are dominating.
Clearly the 007t has got into trouble earlier. However the parts of the comparison where we see the amps dominating could usefully be overlain onto the amp distortion graphs knowing the sensitivity. That would tell us quite a bit.
 

Degru

Active Member
Joined
Feb 19, 2019
Messages
230
Likes
223
Location
Beaverton, OR
#12
Would be interesting to see this with something like 35 or 40hz. I am pretty sure it would clip far earlier on both amps because I was easily able to get energizers to clip on bassy songs such as


(12:20 ish cannon blasts)

Just make sure the headphones are fully sealed onto something (bass extension should measure flat) because extremely loud bass into unsealed estats is not healthy for the diaphragm and can potentially damage it, as well as vastly inflating the harmonic distortion of the driver itself.
 
Last edited:

Francis Vaughan

Addicted to Fun and Learning
Forum Donor
Joined
Dec 6, 2018
Messages
908
Likes
4,330
Location
Adelaide Australia
#13
Would be interesting to see this with something like 35hz. I am pretty sure it would clip far earlier on both amps.
The headphones may run out of movement, but the amps should behave identically to how they behave at 1kHz. Would be nice to know what headphones were used for the test as well. There is a such a mish-mash of units it is hard to discern what is going on.
 

Degru

Active Member
Joined
Feb 19, 2019
Messages
230
Likes
223
Location
Beaverton, OR
#14
The headphones may run out of movement, but the amps should behave identically to how they behave at 1kHz. Would be nice to know what headphones were used for the test as well. There is a such a mish-mash of units it is hard to discern what is going on.
I had an SRM-3 and a 212. Both could do earsplitting levels in mids but gave up trying to push bass to loud volumes, especially transients. My current speaker amp and SRD-7 setup has no problems on such tracks with the same 404LE headphones so it's not the driver.

Providing adequate current to estats is a challenge for direct drive amplifiers, and the power demands for bass are quite a bit harsher than mids.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
Thread Starter #15
Me thinks that 112dBSPL vs. 114dbSPL difference is inconsequential, and below that the headphone distortion clearly dominates any differences between amps there are.
Except that I have listened to both and the limits of the tube amp is quite audible and earlier. You can see in the response of the solid state amp that the headphone distortion is well below that of the tube amp.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
Thread Starter #16
I should note that even the solid state amp is underdelivering relative to the distortion of the drivers themselves:



If the amp had not clipped, it would have kept going.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,645
Likes
117,741
Location
Seattle Area
Thread Starter #17
Would be nice to know what headphones were used for the test as well. There is a such a mish-mash of units it is hard to discern what is going on.
What do you mean mish-mash? It says right on the graph that I used Stax SR-303 headphone.
 

trl

Major Contributor
King of Mods
Joined
Feb 28, 2018
Messages
1,512
Likes
1,583
Location
Iasi, RO
#18
How loud is +112 dBSPL?
It is very loud if you're willing to listen to 1 kHz sinewaves, but if 112 dB SPL only represents peaks of a song then, depending on song's dynamic, this could mean anything between 85-95 average SPL, which is a moderate to high listening level for a regular person.

My opinion is that every headphones amplifier I own should have enough power to drive any of my headphones to 120 dB SPL. This should ensure a lower THD with "domestic" power levels and also ensure that any distortions I might hear are not cauesd by the amp itself, but by the headset I'm using or by the song I'm listening to.
 

gvl

Major Contributor
Joined
Mar 16, 2018
Messages
2,582
Likes
2,604
Location
SoCal
#20
Except that I have listened to both and the limits of the tube amp is quite audible and earlier. You can see in the response of the solid state amp that the headphone distortion is well below that of the tube amp.
Perhaps 1kHz is not the best frequency to see it on the graph then, with headphones in the loop.
 

Similar threads

Top Bottom