ECP Audio T4 technical measurements

Discussion in 'Headphone Amplifier Measurements' started by atomicbob, Feb 5, 2020.

  1. atomicbob

    atomicbob dScope Yoda

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    ECP T4 technical measurements

    Standard Prologue
    If you are unfamiliar with audio measurements please use a search engine with the query:
    "audio measurements" or "audio measurement handbook"
    Look for publications by Richard C. Cabot and also by Bob Metzler, both from Audio Precision. There are other useful publications as well. These will provide basic knowledge.
    Interpretation of the following measurements is beyond the scope of technical measurements posts.

    The data presented were collected as follows:

    1. PrismSound dScope III, picoscope 5243B, Keysight 34465A, Cal Test CT2593-2 balanced probe
    2. Balanced XLR cables Belden 1800F with Neutrik 110R AES connectors (if used)
    3. Single Ended cables Audioblast HQ-1 1.5 ft with Rean RCA connectors
    4. 32 and 300 ohm loads used for measurements
    5. dScope analyzer sample rate 48 KHz unless otherwise noted
    6. 0dBu level used for testing unless otherwise noted
    7. Amplifier input to output gain set for 0 dB unless otherwise noted
    8. Audioquest Forest and Schiit Pyst USB cables used with measurement equipment
    9. Vaunix Lab Brick USB hub
    10. Shielded 14AWG and 16AWG power cables
    11. ESD, EMI/RFI controlled lab bench and workspace

    Measurements are made in accordance with AES17:2015

    Sensitivity data for two headphones to keep in mind while viewing these measurements:
    HD 650 impedance 300R, sensitivity 98 dB/mW
    HE-500 impedance 38R, sensitivity 89 dB/mW

    SPL levels for above headphones for reference:
    0 dBu 300R 2.00 mW - 101 dBSPL @ 98dB/mW
    0 dBu 30R 20.00 mW - 102 dBSPL @ 89dB/mW

    All testing performed at 0 dBu unless otherwise noted.
    This level is consistent with listening to headphones (referenced above) at 90 dBSPL average with peaks to 100 dBSPL, if the music has 10 dB Peak to Avg ratio. That is LOUD for long listening sessions.

    ECP T4
    Measurements commenced after 168 hours of burn-in.
    Measurements each session began after 2 hrs warm-up.
    Measurements were performed over a period of several days.

    Index
    Post 1 - measurement setup description, highlights
    Post 2 - 300 ohm load SE input SE output part A JJ ECC81 tubes
    Post 3 - 32 ohm load SE input SE output part B JJ ECC81 tubes
    Post 4 - 300 ohm load SE input SE output part A Mullard CV4024 tubes
    Post 5 - 32 ohm load SE input SE output part B Mullard CV4024 tubes
    Post 6 - corrections or additional data if necessary
    Post 7 - backstory

    Notable highlights:
    Noise floor and residual mains noise are lower than -100 dBu which provides excellent blackground.
    Dynamic Range is approximately 108 dB.
    Bandwidth is > 300 KHz for 300R headphones which will result in excellent transient response.
    Distortion is 2nd harmonic dominant, with 3rd harmonic 20 dB lower and higher order harmonics lower than residual mains noise. This tends towards a very clean yet euphonic sounding presentation.

    Measurements of the T4 in my lab are long and storied, which will appear in another post. The greatest difficulty measuring the T4 was caused by my tendency to listen to amps while they warm up. In the case of the T4, good intentions ran afoul of lengthy listening periods. Total time allotted per session was spent listening to whole albums rather than measuring.

    Setup picture (measurements):
    DSC_0218_small.jpg

    Typical setup picture (listening):
    DSC_0239_small.jpg

    Output Impedance
    HiZ 26Ω
    LoZ 6.3Ω

    LoZ was used for both 300Ω and 32Ω measurements posted. 300Ω on HiZ is substantially similar to 32Ω on LoZ.
     
    Last edited: Feb 6, 2020
  2. atomicbob

    atomicbob dScope Yoda

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    300 ohm load SE input SE output part A - JJ ECC81 tubes

    ECP T4 A04 THD+N THD nth-HD FFT 300 ohm load SE input SE output
    20200205 ECP T4 Mullard CV4024 A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu.png

    ECP T4 50 + 7000 Hz 300 ohm load SE input SE output
    FFT_2_L1T13_1_A.png

    ECP T4 Gain Linearity 300 ohm load SE input SE output
    G2_L1T3_1_A.png

    ECP T4 THD+N vs Frequency 300 ohm load SE input SE output
    G2_L1T5_1_A.png

    ECP T4 Residual Noise 300 ohm load SE input SE output
    FFT_2_L1T16_1_A.png

    ECP T4 Square Wave 2000mV 10mS/div SE input SE output
    20200205 SigGen ECP T4 Mullard CV4024 20 Hz square 2000mVpp 10mS div 5MHz filter 300R.png

    Complete 300 ohm load SE input SE output analysis and square wave reports pdf attached
     

    Attached Files:

    Last edited: Feb 6, 2020
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  3. atomicbob

    atomicbob dScope Yoda

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    32 ohm load SE input SE output part B JJ ECC81 tubes

    ECP T4 A04 THD+N THD nth-HD FFT 32 ohm load SE input SE output
    20200205 ECP T4 Mullard CV4024 A04 THD+N  THD  nth-HD FFT 32R - 4+HD+N with 60Hz 0dBu.png

    ECP T4 50 + 7000 Hz 32 ohm load SE input SE output - Left Channel
    FFT_2_L1T13_1_A.png

    ECP T4 Gain Linearity 32 ohm load SE input SE output - Left Channel
    G2_L1T3_1_A.png

    ECP T4 THD+N vs Frequency 32 ohm load SE input SE output - Left Channel
    G2_L1T5_1_A.png

    ECP T4 Residual Noise 32 ohm load SE input SE output - Left Channel
    FFT_2_L1T16_1_A.png

    ECP T4 Square Wave 2000mV 10mS/div SE input SE output - Left Channel
    20200205 SigGen ECP T4 Mullard CV4024 20 Hz square 2000mVpp 10mS div 5MHz filter 32R.png

    Complete 32 ohm load SE input SE output analysis and square wave reports pdf attached
     

    Attached Files:

    Last edited: Feb 6, 2020
  4. atomicbob

    atomicbob dScope Yoda

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    300 ohm load SE input SE output part A Mullard CV4024 tubes

    ECP T4 A04 THD+N THD nth-HD FFT 300 ohm load SE input SE output
    20200206 ECP T4 Mullard CV4024 A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu.png

    ECP T4 50 + 7000 Hz 300 ohm load SE input SE output
    FFT_2_L1T13_1_A.png

    ECP T4 Gain Linearity 300 ohm load SE input SE output
    G2_L1T3_1_A.png

    ECP T4 THD+N vs Frequency 300 ohm load SE input SE output
    G2_L1T5_1_A.png

    ECP T4 Residual Noise 300 ohm load SE input SE output
    FFT_2_L1T16_1_A.png

    ECP T4 Square Wave 2000mV 10mS/div SE input SE output
    20200206 SigGen ECP T4 Mullard CV4024 20 Hz square 2000mVpp 10mS div 5MHz filter 300R.png

    Complete 300 ohm load SE input SE output analysis and square wave reports pdf attached
     
    Last edited: Feb 6, 2020
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  5. atomicbob

    atomicbob dScope Yoda

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    32 ohm load SE input SE output part B Mullard CV4024 tubes

    ECP T4 A04 THD+N THD nth-HD FFT 32 ohm load SE input SE output
    20200206 ECP T4 Mullard CV4024 A04 THD+N  THD  nth-HD FFT 32R - 4+HD+N with 60Hz 0dBu.png

    ECP T4 50 + 7000 Hz 32 ohm load SE input SE output - Left Channel

    FFT_2_L1T13_1_A.png

    ECP T4 Gain Linearity 32 ohm load SE input SE output - Left Channel

    G2_L1T3_1_A.png

    ECP T4 THD+N vs Frequency 32 ohm load SE input SE output - Left Channel

    G2_L1T5_1_A.png

    ECP T4 Residual Noise 32 ohm load SE input SE output - Left Channel

    FFT_2_L1T16_1_A.png

    ECP T4 Square Wave 2000mV 10mS/div SE input SE output - Left Channel
    20200206 SigGen ECP T4 Mullard CV4024 20 Hz square 2000mVpp 10mS div 5MHz filter 32R.png

    Complete 32 ohm load SE input SE output analysis and square wave reports pdf attached
     
    Last edited: Feb 6, 2020
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  6. atomicbob

    atomicbob dScope Yoda

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    20200206 Correction
    The data presented in posts 2 and 3 are for JJ ECC81 tubes, not Mullard CV4024 as originally labelled.
    If you downloaded the pdf reports, please download the correctly labelled reports.

    reserved.
     
    Last edited: Feb 6, 2020
  7. atomicbob

    atomicbob dScope Yoda

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    Backstory

    ECP Audio T4 arrived from Tom at Beezar early April of 2019 and was immediately setup in my lab for burn-in and initial listening evaluation. My first notes mention non-fatiguing clarity and single track auditions evolving into entire albums with time disappearing in the blink of an eye. This theme would repeat over the next 10 months and why T4 isn't a Flavor-Of-The-Month amp but a quality component destined for a permanent place in my lab inventory.

    Middle of Apr 2019 I began measurements only to find the second section of the right channel JJ ECC81 had 14 dB more noise than expected. This in turn would produce higher distortion and residual noise measurements than representative of the true amplifier capability. At this point I acquired a MaxiPreamp II to facilitate tube qualification. See E5 in the chart below:

    20190811 T4 12AT7  tube measurements - v2.png

    Another set of JJ ECC81 was acquired and qualified, as shown in the chart above. Tom had also kindly sent a matched pair of Mullard CV4024, which were qualified along with an additional pair acquired from another source for backup.

    Now set to dig in on the T4 during after-hours from corporate acoustic work, an unfortunate event occurs. Water pipes in the wall leak, flooding a portion of the house causing extensive damage. For the next several months my residence, including personal lab, would be highly disrupted while restoration occurred. Drying fans and de-humidifiers, though necessary, are LOUD. Constant agitation for several weeks. Another side effect was the need to box and store many items to make room for all the displaced furniture, etc. moved out of the way. Quickly packed items have a habit of becoming temporarily lost to on-demand retrieval. T4 tubes were among those items.

    In July a restart was attempted for T4 measurements. Data was acquired, looked good, but during data vetting I discovered a generator setting had somehow changed from a ratio to an offset for the IMD measurement with the second of two tones, 20 KHz set 18 dB higher than the 19 KHz sine. IMD indicated approximately 0.002% higher than it would with correct generator measurements. Another set of tests necessary to properly reflect accurate T4 performance.

    But ... as long as the place was torn apart it was decided that we should also have the hardwood floors refinished. This requires everything to be sealed off that one doesn't want contaminated with dust from sanding. Also we have to move out for a few days. Another couple of weeks disruption. Lab completely dismantled and packed.

    Meanwhile, corporate project experiences an acoustic derailment with the rather unfortunate combination of a cooling fan and a microphone for recording located inside the same, sealed enclosure. Countless hours attempting to mitigate (polite word for defy) laws of physics with only result of some rather good documentation on why that wasn't a good idea. I'm oversimplifying this, the details of which could make a multi-day presentation.

    While lab was dismantled I decided to bring in an EMI/RFI and ESD controlled laboratory technical bench. More effort to install, reorganize power distribution, network infrastructure, signal routing, even lighting position and color temperature. Ultimately better for workflow while maintaining highly consistent measurement conditions. However components keep arriving into measurement queue; the backlog continues to grow.

    Now add to the mix a 99.5 yo mother injuring her head after falling and spending the next several months in and out of ER, rehab, assisted care, not to mention the scare she gave us and we have an emotional roller coaster. She is doing better now.

    From the foregoing it is easy to see why when I managed to carve out some time for T4 measurements, warm-up listening often evolved from single tracks to albums. Transported temporarily away from reality with an immersive, engaging musical experience made it difficult to buckle down for a task requiring care in methods, precision of execution, mentally demanding to avoid errors, etc. While I do employ scripts to assist, there are many steps where manual adjustment, intervention, screenshots, and more are required to execute a complete suite using multiple instruments, not just a single analyzer. Even the reports have manual steps involved.

    So today the T4 measurements are finally published. Perseverance because the T4 well deserves the attention. Now driven by a KTE May for more evaluation / enjoyment for a limited period. Time for a good glass of red and more albums, many new, thanks to all of you who post in the Jazz Nuts and What are you listening to right now threads.
     
    Last edited: Feb 6, 2020
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  8. TomB

    TomB MOT: Beezar

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    Many, many thanks, atomicbob!!
     
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  9. Lyander

    Lyander Too sensitive for SBAF

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    The amount of work you went through to publish meaningful measurements is very nearly as high a feat as the crafting of an amplifier this well-made and beloved is. Holy poop I wanna hear this one on my Senns.
     
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  10. yotacowboy

    yotacowboy McRibs Kind of Guy

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    This is the real good news.
     
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  11. purr1n

    purr1n Finding his inner redneck

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    For the [ECP T4 THD+N vs Frequency 32 ohm load SE input SE output - Left Channel], I assume you limited bandwidth to 20kHz? Hence the dropoff in distortion past near 10kHz?

    This is a good measuring tube amp. Very good measuring.
     
  12. atomicbob

    atomicbob dScope Yoda

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    Yes, the drop off is due to 2nd harmonic distortion and above being 20 KHz and above. The graph should terminate at 10 KHz but that isn’t how the built-in plotter works.

    It is a good sounding amp in addition to having a measurement profile having a high match to my personal preference profile.
     
    Last edited: Feb 7, 2020
  13. dsavitsk

    dsavitsk Friend

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    I'm glad to hear your mother is doing better.

    Thank you for the detailed analysis. It's nice to see how the amp holds up under a stress test.
     
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  14. Hi-Fi-Anatomia

    Hi-Fi-Anatomia Rando

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    That distortion is really low for a tube amp. How are the tubes used in the circuit I wonder? Are they used as only voltage gain devices or something? Nonetheless very impressive results for a tube amplifier and the price looks to not be egregious!

    I also love the look, touch of modern in the tube world (;
     

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