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Oppo HA-1 Impressions Thread

Discussion in 'Headphone Amps (full-size)' started by aamefford, May 7, 2014.
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  1. HasturTheYellow
    What you are describing is a digital, not analog, audio control mechanism. That is not what we wanted for the HA-1. We wanted a truly analog device from beginning to end, which means using a high precision, motorized analog potentiometer for volume control
    A potentiometer will have some amount of lag associated to it as you need to take the digital volume controls from the remote control or the HA-1 application for Android/iOS devices, convert this to analog, then move the motor. This is also why the volume control and the readout on the front panel are also not 1:1 as the HA-1 needs to convert the analog volume information to a data plot for display on the VFD.
    Digital volume controls, which pretty much all AVRs use, do not have this lag since it is digital in; digital out. These volume controls also have no beginning or end, which is why you can rotate the volume knobs indefinitely.
  2. x RELIC x Contributor

    This I understand, but what would explain the overshoot when the volume button is released on the remote, as in the volume continues to increase after the button is released. It doesn't bother me, and I'm happy to live with. Just curious if it's the servo controlling the potentiometer or simply input lag from the signal? Thanks.

    Edit: Never mind. Once again, I failed to read the post as you already answered the question. D'oh!
  3. Badas
    Yeah. I thought that might be the case. Analog rather than digital.

    Like I said to be honest it doesn't bother me and I think Oppo made the right choice. Quality first, powerful amp, pack in some cool features like volume control (not many have), awesome display etc.

    Now I know how it works I kinda got a so what attitude. I just look at the white marker and listen to the volume than what the display reads or does.

    On another note. I think the Oppo goes through a change as it breaks in. I swear mine is sounding so much warmer. Through the headphones and as a pre-amp to speakers. The bass and midrange seems bang on now when I thought it was weak at first. Could this be the case or a case of placebo?

    I have even tried other Dacs and now the Oppo sounds lively. If others don't like the neutral sterile sound when first installed. Wait. I swear it changes.
  4. SharpEars
    For the rest of my response, let's remove the possibility of a digital volume control out of the equation. For better or worse, the HA-1 has an analog volume control that is rotated by a servo motor and that is the topic of my discussion.
    Given the information in your quoted response, I still do not understand why there is such a long latency between when the following two points:
    1) The remote receiver on the HA-1 stops processing a volume +/- signal from the remote
    2) The square wave signal that is being fed to the servo motor controlling the potentiometer responsible for volume control stabilizes to a fixed pulse width (causing the servo motor to stop).
    I ask this especially in light of the fact that the servo motor seems to react almost instantaneously to remote instructions to increase/decrease volume - instructions which should follow the same signal path within the unit.
    The transitions and propagation delays of these signals take (perhaps hundreds of) nanoseconds (but, let's say it is even microseconds due to processing overhead in some micro-controller or CPU). None of this accounts for the extremely large amount of latency we are witnessing. I would like to know the facts of why this is, given that the digital silicon in the unit works at MHz if not GHz frequencies, so the delays are not a function of the hardware per se.
    Given my personal experience with such circuits (from using servo motors for robotics applications) the slowest part in the equation is the servo motor that controls the volume potentiometer. However, it is clear from observation of actual behavior that this motor reacts very fast, since it starts spinning the potentiometer very rapidly and once it actually begins to slow it down to a stop, it stops almost instantaneously. That is a function of any good servo motor (i.e., to start when it is signaled to start and to stop when it is signaled to stop).
    Therefore at a low level, the problem seems to be based on the fact that the pulse width sent to the servo motor keeps on increasing or decreasing long after it should have stabilized. This implies that the instructions that cause the pulse width to keep increasing/decreasing are continuing to be fed to the circuit that controls the servo motor long after the remote volume button is released.
    Since we have many electrical engineers on this forum including myself, I would be very grateful if you could get a response from one of the (senior) engineers familiar with the HA-1's internals as to why the unit is so slow to respond to a "volume control stop" signal from the remote. Given the remarkable design and excellent performance of the rest of the unit, I am certain that there is a logical explanation for the behavior. It is just not obvious and I would like to hear it from the proverbial "horse's mouth" rather than continue speculating.
  5. SharpEars
    What you have witnessed has less to do with unit burn in and more to do with your acclimation to its characteristic sound signature. I can assure you that had you measured the frequency response of the unit when it was brand new and its current response there would be little if any change. What has happened and I noticed it as well is that our brains have gotten used to the higher amount of perceived treble energy that is characteristic of ESS Sabre DACs. If I was a guessing man, I would speculate that this has to do with overshoot (and perhaps subsequent ringing) which can be seen on an oscilloscope plot of the output signal created when a square wave is fed digitally into the unit.
    Unfortunately, until we get to see some objective third party measurements/reviews of the electrical characteristics of the unit's output as a function of its input this is all speculation. I am hopeful that a quality magazine such as Stereophile gets to review the unit in the near future and presents substantive electrical measurements by no less than John Atkinson. So far, all I've seen are reviews of the HA-1 written by hacks with a blog, not withstanding the several decent reviews that for the most part seemed to favor subjective listening impressions followed by emotional descriptions to any objective measurements of characteristics significant to the (audible) performance of the unit presented as graphs. I would expect these sorts of subjective impressions as posts in response to this thread, not as (the sole content of) quality reviews made by professional audio equipment reviewers. That is, if a "quality" review cannot show measurements that back subjective impressions than it is a work of (convincing) well written fiction.
  6. HasturTheYellow
    The HA-1 uses a pure analog audio path after its DAC and the volume is adjusted by rotating a potentiometer either by hand or through the motor mechanism (IR, Bluetooth).
    The numeric volume display is created by taking samples of a voltage divided by the potentiometer and is described in the manual in great depth Page 15
    “The HA-1 implements its volume control with a pure analog signal path. The numeric dB value displayed on the screen is based on the measurement of the Volume Knob position. It indicates the approximate gain or attenuation level of the Pre-amplifier Output relative to the input signal. It is normal for the display value to vary a few dB when the Volume Knob moves in the very low range due to the logarithmic nature of the volume control curve.”
    When a user tries to hold down the remote control button to reach a certain numeric dB value as indicated on the front panel of the HA-1, the following delays are involved:
    • The time it takes to measure the potentiometer position and averaging multiple measurements to get a reliable reading.
    • The human reaction time from seeing the desired dB number to releasing the remote control button.
    • The “de-bouncing” time for processing the “button up” event, so the HA-1 knows that the button is indeed released and it is not a signal interference or a button contact glitch.
    Keep in mind when all these happens, the knob is still rotating. As a result, if you see a desired number and release the button, it will be overshot by 2dB.
    This is markedly different from a device that uses a purely digital volume control. A digital volume control on a receiver, for example, may look something like this:
    • The remote button is pressed down.
    • The controller adjusts the volume number display according to the remote command. The volume knob does not rotate in this case.
    • Once the remote button is released, the controller programs the DSP (digital signal processor) to the desired volume level, usually with a “soft ramp” to avoid sudden volume change.
    As the loop for rapid volume adjustment is purely between displaying a number and releasing the button, the total delay is shorter. This is a benefit of digital volume adjustment. It is also much simpler in software and cheaper in hardware implementation, but the quality of sound is can be affected depending on the digital components and algorithm used by the digital volume device.
    The purpose of the HA-1 is audio quality beyond all else. So we decided to go analog, not digital, for our volume controls.
    The “press and hold” function or the HA-1's remote or the Bluetooth remote application is meant to be a convenience feature for rotating the volume knob rapidly. It is not designed to reach a certain dB number in a single shot. It is always best to use the knob by hand, or use the volume buttons repeatedly as single clicks, if you want precise adjustments of the volume.
    As for adjusting the behavior of the remote volume experience, this can be looked into, but likely not something that we pursue as we would need to significantly slow down the motor mechanism which will really defeat the purpose of having the "press and hold" functionality in the remote.
    Currawong likes this.
  7. SharpEars
    Hastur, thank you as always for the wonderful detailed reply. Just to be specific, the item I am having an issue seems to be reduced to item #3 and the possible speed of the potentiometer:
    Item numbers 1 and 2 can be ignored, since I am only considering the time from the point the button is actually released (i.e., the button is already down and the reaction time to release is not at issue, since the issue is the latency from the point of actual button release until the time the potentiometer stops spinning).
    So, this gets narrowed down to two possible requests for improvement via firmware if possible, either (or both) of which would help mitigate the issue:
    1. Decrease the de-bounce time for the button up event to something reasonable (i.e., 50-100 milliseconds is very generous for a remote control button). In fact you can be more liberal with a button up event (i.e., stop spinning) than with a button down event (i.e., start spinning, possibly against the user's intention).
    2. Reduce the angular momentum of spin of the servo motor driving the volume control. It is currently very fast and most volume adjustments do not need the speed, since they are around a central "commonly acceptable" volume level. Speaking from personal experience, the three o'clock setting is my comfort zone and I make volume adjustments right around that neighborhood.
    Just my two cents worth in terms of user feedback. Perhaps others can chime in as well if they find the behavior annoying...
  8. MattTCG
    Seriously? [​IMG]  I don't ever want to demean anyone's point of view or opinion. It's yours and you're certainly entitled to it. The answer has been given regarding this matter. Your position is duly noted. Can we please move on now? 
  9. Badas

    I agree. I find it a non-issue. I'm just glad it has a remote. [​IMG]
  10. rambotan
    Non-issue for me.
  11. Badas
    Is this a bad idea or okay?
    I was thinking of throwing my Ordered WA22 on top of the Oppo. Just wondering about heat from the tubes pushing hot air down that Oppo heat grate.
  12. x RELIC x Contributor

    Terrible idea. Tubes on top of Class A. Something's going to melt.
    Badas likes this.
  13. Badas

    I thought so. I will throw that idea out. [​IMG]
  14. Smarty-pants
    ^Agreed... very bad idea.
    You want to give as much space as possible above the HA-1.
    Keeping that vent wide open with cooler air above it is imperative, or else more than likely, eventually it will fail.

    For example I have an amp in my theater room that gets quite hot.
    I have about 10 inches of space above the amp and then there is a shelf with another component on it.
    After the amp is on for a significant amount of time, and even with the component above not even turned on,
    the bottom of that shelf above is significantly warm.
    So it doesn't take much to trap heat above an amp that has the potential to get hot.
    Badas likes this.
  15. SharpEars
    It's only a bad idea if there is no active air flow. Put a fan behind the arrangement blowing forward between the units and it's not a bad idea (looks be damned!).
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