[Zachik]

Enjoying some EL34 rolls tonight in a Blue Halo via adapters.

I sure hope you're enjoying this amp, while building the next!
(and I am not even on the queue... )

 

[A2029]

This is quite interesting: EL34 tubes (Svetlana in this case) run in the BH have over 10X the 2nd harmonic distortion than a 6SN7 (Rogers branded Sylvania). This was at ~80dB into HD650's. The spikes at 8Khz and 16Khz can be ignored as they are from the switching power supply hooked up to the DAC feeding into the amp.

Edit: These results are to be expected as EL34 run in a BH are run near the "knee" of their plate curves, so more distortion is normal and predicted from simulations of these tubes.

EL34 - 2nd harmonic at 0.035%

6SN7 - 2nd harmonic at 0.0031%

 

[Zachik]

This is quite interesting: EL34 tubes (Svetlana in this case) run in the BH have over 10X the 2nd harmonic distortion than a 6SN7 (Rogers branded Sylvania). This was at ~80dB into HD650's. The spikes at 8Khz and 16Khz can be ignored as they are from the switching power supply hooked up to the DAC feeding into the amp.

EL34 - 2nd harmonic at 0.035%



6SN7 - 2nd harmonic at 0.0031%

I am curious: how did you generate those graphs? Can you please share with us the setup and measurement tools used?
Thanks!

 

[A2029]

I am curious: how did you generate those graphs? Can you please share with us the setup and measurement tools used?
Thanks!

Quite simple setup: Schiit Modius DAC fed from a laptop, going into a Blue Halo amp. Output from the BH going into a Motu M4. REW running on laptop to capture the distortion plots. After tubes were in place, amp was turned on and given 20 mins warmup and volume set to produce 80dB volume (sinewave of 1 Khz) into HD650s. Headphones unplugged prior to measurements.

 

[Zachik]

Quite simple setup: Schiit Modius DAC fed from a laptop, going into a Blue Halo amp. Output from the BH going into a Motu M4. REW running on laptop to capture the distortion plots. After tubes were in place, amp was turned on and given 20 mins warmup and volume set to produce 80dB volume (sinewave of 1 Khz) into HD650s. Headphones unplugged prior to measurements.

Interesting. What is the connection from the Motu M4 to the laptop? USB? (so Motu acts as an ADC?)

 

[A2029]

Interesting. What is the connection from the Motu M4 to the laptop? USB? (so Motu acts as an ADC?)

That's correct, USB with the Motu M4 acting as the ADC.

 

[leftside]

I was able to find triode curves for the EL6 and EL51, but not for the others, maybe they are out in the interwebs somewhere.

Do you still think you might get an etracer @leftside ? Could then trace curves for all of these old tubes, would be interesting to see their linearity relative to the EL34, EL3, etc.

Definitely will get the etracer. Just did a few mountain bike upgrades, so etracer will be Spring time.

 

[Zachik]

That's correct, USB with the Motu M4 acting as the ADC.

Cool. Maybe I should get one of those...
@L0rdGwyn - I know you use a different gadget for lowering from headphone out to line level (2V) and then feed it to sound card. Why not use the Motu M4 as well, fed straight from headphone out of your amp? or are you using the M4 but still need to lower the signal amplitude to 2V swing?

 

[L0rdGwyn]

That's correct, USB with the Motu M4 acting as the ADC.

Hey I have the same ADC in my measurements rig! Whatdoyaknow. Think I posted some loopback measurements over at Audio Science Review when the thing had just come out, pretty impressive for the price.

Cool. Maybe I should get one of those...
@L0rdGwyn - I know you use a different gadget for lowering from headphone out to line level (2V) and then feed it to sound card. Why not use the Motu M4 as well, fed straight from headphone out of your amp? or are you using the M4 but still need to lower the signal amplitude to 2V swing?

This works fine for headphone voltages, but not for speaker amplifier voltages. You can run a headphone out into the line input of a typical ADC without issue, but the signal needs to be attenuated for speaker level amplification, assuming the output swing it is greater than line level. For that, I use the Linear Audio Autoranger.

 

[Zachik]

This works fine for headphone voltages, but not for speaker amplifier voltages. You can run a headphone out into the line input of a typical ADC without issue, but the signal needs to be attenuated for speaker level amplification, assuming the output swing it is greater than line level. For that, I use the Linear Audio Autoranger.

Yeah, the Autoranger... forgot its name from when you mentioned it before
Cool - will get myself an M2 or M4. Should be fun being able to take basic measurements to compare headphone amps, or compare different tubes in the same amp
Any relevant difference between the M2 vs. M4 for that ADC application?

 

[A2029]

Yeah, the Autoranger... forgot its name from when you mentioned it before
Cool - will get myself an M2 or M4. Should be fun being able to take basic measurements to compare headphone amps, or compare different tubes in the same amp
Any relevant difference between the M2 vs. M4 for that ADC application?

M2 doesn't have line level inputs on the back, so has to go through the pre input on the front which I believe slightly reduces accuracy of the input and increases noise very slightly, but not a big deal unless you are doing sensitive measurements.

 

[Zachik]

M2 doesn't have line level inputs on the back, so has to go through the pre input on the front which I believe slightly reduces accuracy of the input and increases noise very slightly, but not a big deal unless you are doing sensitive measurements.

I guess for extra $50 - I may as well splurge and get the M4 then...

 

[Jaeger18]

I cant help but to post this

 

[Zachik]

I cant help but to post this

Beautiful amp!
I am jealous - none of my amps (and I have quite a few) have VU meter...

 

[leftside]

I cant help but to post this

I found those meters We had a bit of "trial and error" getting them to work properly, but I'm glad Mischa did as they do look nice. You are teasing us tho..... by only showing one...