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  1. Old Comment
    rjm's Avatar

    Szekeres 2015

    The variation in supply voltage with load current depends on the power supply impedance. Properly bypassed, there is little impediment to the return of load currents from circuit common to the supply, nor are the load currents (headphones!) so large as to be a concern. Not enough that I'd toss away 10-20 dB of PSRR for at any rate.

    In the spirit of experiment however it's an interesting notion.
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    Posted Today at 03:01 AM by rjm rjm is online now
  2. Old Comment
    abraxalito's Avatar

    Szekeres 2015

    PSRR is only part of the equation - the other half of it is how much signal-correlated noise gets induced on the rails by the load current variations in the first place. PSRR is only needed to compensate for noisy rails. With the signal returned to the positive rail, no load-induced variation will occur on the rail other than imperfections in the current source, which can presumably be compensated for with additional devices.
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    Posted Today at 02:02 AM by abraxalito abraxalito is offline
  3. Old Comment
    abraxalito's Avatar

    Why might a diamond buffer sound better?

    I agree Charles' 'explanation' doesn't make sense but then he's maintaining the 'mystique' perhaps for marketing reasons. Likewise his 'argument' for why no feedback doesn't make sense to me either whereas I can quite see why he avoids it from my pov. As far as I know he's not using his in classA, must be AB.
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    Posted Today at 01:56 AM by abraxalito abraxalito is offline
  4. Old Comment
    rjm's Avatar

    Szekeres 2015

    With the circuit as presented above, returning the signal to the positive rail degrades the PSRR.

    I imagine with a bit of tweaking of the current source you might get it to work though equivalently though.
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    Posted Today at 12:43 AM by rjm rjm is online now
  5. Old Comment
    rjm's Avatar

    Why might a diamond buffer sound better?

    The economy of the diamond buffer is in the way the bias for the output pair is set by the Vbe of the input set. The driver and Vbe multiplier are one and the same functional unit.

    The downside is the bias current in the driver and output pairs must be equal unless different transistors are used or small resistors on the driver emitters are added. Both options are sub-optimal. Much as I like working with the Diamond Buffer circuit, I'm not convinced the design has any intrinsic merit sonically speaking. It is a relatively simple circuit element with high PSRR and low distortion. That's the sum total of the attraction as far as I am concerned.

    The rationale Charles Hansen gives for it sounding better, viz. having no Vbe multiplier to make the input signals "unequal" is bogus, due credit that he himself admits as much, and for the correct reason. In my opinion if you have to add a third pair of transistors in front of the buffer in order to drive it you've negated the advantage of using a diamond buffer in the first place. The diamond buffer is now nothing more than a compound transistor for current gain. You might as well capitulate and use a Sziklai arrangement.

    P.S. It's not clear whether his power Diamond buffers are intended for Class A or Class AB operation. The Diamond circuit works fine in class A, no feedback required. Class B is a different story!!
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    Posted Today at 12:22 AM by rjm rjm is online now
    Updated Today at 12:27 AM by rjm
  6. Old Comment
    abraxalito's Avatar

    Szekeres 2015

    It would be interesting to compare the sound between returning the headphone 'ground' side as shown and then to the +ve rail so the rail draw becomes constant and the FET is acting as a 'shunt' amp.
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    Posted Yesterday at 07:09 AM by abraxalito abraxalito is offline
  7. Old Comment
    rjm's Avatar

    Why do I need a preamp?

    A preamp makes more sense in an historical perspective: consider LPs and the need for a phono preamplifier. Yes you can do it all in one chassis, but do you really want your phono preamp circuit running off the same power supply as your power amp, in proximity to high currents and noise of that circuit?

    That and physically all the components for the phono stage, line stage, tone controls, and headphone amp found in a high end preamp literally required so much space that a separate chassis was needed.

    Today with microelectronics, remote volume controls, and most people choosing to have a phono preamp or headphone amplifier external to their preamp, the need is simply not the same. The remaining components: line stage, volume control, input selectors ... can easily be put in together with the power amplifier. Even the line stage isn't really needed, since its purpose was to buffer the output of the volume control and drive the interconnects ... just increase the gain in the amplifier stage to compensate.

    I think it was Wes Phillips at Stereophile who many years ago made the most eloquent case for why you would want to invest in a really nice preamp. Basically he said, look, this is the bit you physically interact with. It's also the bit that all your audio signals pass through. Get a really nice preamp and you get all the functionality (phono, headphone amp, mute or balance) in an elegant, uncluttered chassis with the transparency to be able to truly hear all the other components in the system.

    I never did get around to following his advice since I'm forever putzing around with phono stages and headphone amps, but I've always thought it was a wonderful goal.
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    Posted 16th May 2015 at 12:48 AM by rjm rjm is online now
    Updated 16th May 2015 at 12:51 AM by rjm
  8. Old Comment

    Schitt's flagship DAC uses a not-for-audio DAC chip.

    Some additional measurements have surfaced here: Yggdrasil Measurements

    What surprises me is the zero cross-over distortion - I can't understand how this can occur with the +/- 1 LSB INL distortion figures quoted in the AD data sheet... any explanations? Or is this actually within spec? I can't tell that either based on the scale of the measurements...

    Edit: Nothing in the DS referencing signed magnitude implementation.... but again, the INL plots don't suggest there is an issue with crossover distortion.
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    Posted 15th May 2015 at 07:11 PM by aive aive is offline
    Updated 15th May 2015 at 07:37 PM by aive
  9. Old Comment

    Building a vacuum tube amp vs a solid state amp

    Quote:
    Originally Posted by rjm View Comment
    Transistor power amps are fun if you really get into it, do the design and testing yourself, but that's a step above doing the same kind of thing with tube amps in terms of complexity and investment.
    I totally agree. The simplicity of tube circuits and point to point wiring make it much easier to get into. The only real barrier for me is the cost of output transformers. Which is basically why I want to start with an OTL headphone amp.

    I am starting to realize that it might not be that much cheaper to DIY as I get deeper in this hobby. Though I will still retain the fantasy that I am saving money building circuits and price/performance ratio remains near the top of the things I value in a DIY project.
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    Posted 14th May 2015 at 06:13 AM by cspirou cspirou is offline
  10. Old Comment
    fas42's Avatar

    Exploring laptop sound

    Since foobar player is mentioned often, especially in reference to the ABX comparator, I thought it would be a good idea to install the latest version - wasn't there prior - and see how it went. Oh dear!! Immediate reaction to the default installation, absolutely nothing done to optimise anything, first playback - it's awful!!! Dead as a doornail, boring as hell, lifeless as ... I will need to go some number of rounds, to see if I can bring it to life, if this program can be made to behave ...

    Edit: OK, probably was too harsh with poor littl' foobar, but all the ridiculous, constant updating of display data was killing the quality, totally - switched off everything, the display is now completely static while playing a track, and the sound is starting to get somewhere ...
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    Posted 13th May 2015 at 11:32 PM by fas42 fas42 is offline
    Updated 13th May 2015 at 11:55 PM by fas42
  11. Old Comment
    fas42's Avatar

    Exploring laptop sound

    Just to emphasise, yet again, what it means, as people say over and over again in comments about what they hear when they listen to a newly improved component, or refreshed area of the system, or new DIY effort, referring to "improvements in SQ". This is actually code for removing, temporarily or permanently, some handicap, impairment in the playback process - never is the actual source material, the music track, "improved", over and over again - but, an improvement in the integrity of the playback chain may very well have been achieved.

    So this is what I'm now doing in reversing some of the tweaks of the laptop - I'm losing a little bit of the integrity, "quality" of the processing of the audio data to produce sound, with each undoing. I've got the laptop to the point where it produces pleasurable sound for as long as I care to listen to it; and the typical result of each "untweaking" is that the sound becomes less pleasurable, there's an edge, uncomfortableness, dullness, lack of life, smallness which is immediately noticeable or which makes me lose interest relatively quickly in what's playing - I want to stop listening.
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    Posted 13th May 2015 at 12:15 AM by fas42 fas42 is offline
    Updated 13th May 2015 at 12:19 AM by fas42
  12. Old Comment
    abraxalito's Avatar

    New year, new DAC

    Low hanging fruit all gone now, have to climb higher and higher to get my paws on the rest....
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    Posted 11th May 2015 at 06:11 AM by abraxalito abraxalito is offline
  13. Old Comment
    fas42's Avatar

    Exploring laptop sound

    Some things to note about the track I just used to easily highlight the player software difference:

    * It was nominally a "poor" recording

    * I was looking for an instrument or sound element that was in the background, it was not primary in the mix

    * That sound element is one that one has a good acoustic memory of - say, real pianos are heard over and over again, and one tends to be able to say immediately whether the instrument sounds 'right'

    This is a simple, and very effective way of selecting a music track for evaluating system performance - I use variations of this all the time.
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    Posted 11th May 2015 at 04:50 AM by fas42 fas42 is offline
  14. Old Comment
    fas42's Avatar

    New year, new DAC

    Ol' Diminishing Returns could be kicking in - at a certain point key flaws will have been eradicated or sharply diminished, and the gains will be harder to come by ... this is when I start upping the room volume more, extra stress everywhere can bring further things to light ...
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    Posted 11th May 2015 at 03:46 AM by fas42 fas42 is offline
  15. Old Comment
    fas42's Avatar

    Exploring laptop sound

    Done quite a bit of fiddling with Blu-Tack, can never get it quite perfect, I have a rough Mario Lanza CD here which excites resonance like you wouldn't believe - this is much, much better now but still the metal grille goes into a merry dance, momentarily, while the disk plays. But, I don't want to lift the lid yet - so I'll leave it as a known fault, which can be fixed if I go the extra step ... .

    OK, let's start going backwards, as I mentioned earlier. Just change one thing, undo one tweak, and see what that gives me ...

    First up, the playing software: using MediaMonkey (MM) for best performance, so now the m/c is going nicely, just stop MM and swap to Windows Media Player.

    To test, using a rough blues recording CD, a no-name compilation that's as dirty as one could want. Track is Crying, by Jimmy Witherspoon, and there is a piano accompanying in the background, a nice tinkly element to the sound.

    No contest: Windows player gives me a flat, dead tone to the piano, no sparkle, a transistor radio tone, the life is sucked out of the track. Restore MM, and the piano comes to life, becomes a real instrument, and has a "space" about it.

    Windows player does all the wrong things: chews up lots of CPU time, and constantly accesses the CD-ROM drive, and HD. This was an easy one, but serves to give one an instant taste of the type of losses one hears when playback is not optimised.

    Edit: Just in case someone immediately runs to this, there is no equalisation going on in any of the software I'm using - this stuff slugs the quality so severely, and I keep right away from the nonsense ...
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    Posted 11th May 2015 at 02:00 AM by fas42 fas42 is offline
    Updated 11th May 2015 at 02:10 AM by fas42
  16. Old Comment

    Schitt's flagship DAC uses a not-for-audio DAC chip.

    the yggy is shipping, lots of ballyhoo about the days of warm up/burn in required for best sound

    some measurements: yggdrasil technical measurements

    not stellar but not obviously over audible thresholds

    would be nice to know if its the 5791 limiting the #

    or "audiophile" "good sounding" supporting circuitry - of course it could be just the limitations of the measurement too
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    Posted 10th May 2015 at 08:57 AM by jcx jcx is offline
  17. Old Comment
    fas42's Avatar

    Exploring laptop sound

    Blu-Tack to the rescue! So thoughtful of HP to "engineer" a cover plate for the speaker area of the laptop, such that it resonated unpleasantly with certain types of musical material, perhaps to encourage the buying of, hopefully HP, external monitors, etc, . Yes, this is a type of metal grill, which "sings" quite offensively, especially since it is not tightly bonded to the plastic surround it's mounted in - so, I'm getting a fair distance with careful inserting of gooey muck around the visible perimeter - no dismantling yet - killing a lot of the ringing! It's still trying hard to make noises, so I may have to subtlely bend some of the metal, or place strongish pressure at certain points, to fully deaden it.
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    Posted 9th May 2015 at 01:05 AM by fas42 fas42 is offline
  18. Old Comment

    What's the PSRR of an emitter follower?

    I have a rather old book by E.F.Wolfendale entitled "The Transistor" an Introduction to It's Applications, published by Heywood & Co Ltd in 1963. It discusses transistor behavior in terms of transmission lines, T circuits and hybrid pi equivalents.

    In Wolfendale's model representation of the collector, the collector depletion layer looks like a parallel plate capacitor known as depletion capacitance (Cc,dep) that appears in parallel with the current that reaches the end of an RC transmission line and an open circuit.

    I had never thought in terms of collector impedances - the power supply constituting a load which might alter the voltage according to the collector current being drawn. The collector depletion layer width is a function of the voltage applied to the collector and the greater the voltage the greater the width of the collector depletion layer. As a consequence of the width of the base narrows, which corresponds to a reduced length of the transmission line and reduced input impedance.

    My initial thought was that MJE15032 might one of those devices that are less susceptible to base width modulation effects, as used in a Vas stage.
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    Posted 8th May 2015 at 07:34 AM by mjona mjona is offline
  19. Old Comment
    fas42's Avatar

    Exploring laptop sound

    This is a nuisance ... I did an exercise to track down where the resonance issues are, and unfortunately it's the bits of plastic, etc, that make up the case of the laptop. Created a sine wave sweep through the suspect frequencies, round 600-800Hz. A bad one was at 750Hz, so did a pure 750Hz sine waveform and started pressing on bits of the case while playing continuously - this nicely made the noises come and go! Meaning, I will have to dismantle and try damping various areas of the body of the laptop to get this irritation to go away - is it worth it ??

    Unfortunately, big male and female vocals, and very old recordings have lots of these frequencies at high levels, and that makes listening to this material less than brilliant with this added bzzz'ng ...

    Will I do something about it? Not sure, will need a bit more motivation to go this extra step ... let it sit for the moment ...
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    Posted 7th May 2015 at 11:57 PM by fas42 fas42 is offline
  20. Old Comment
    fas42's Avatar

    Exploring laptop sound

    Might just note that I've reached the target that I placed up in the first post here - that "What I'm aiming for is to get the sound to be pleasurable to listen to". If every tweak is in place then I have no trouble just leaning back and soaking up whatever track is playing - all the right things are coming through, and minimal bad things are happening ... this everyday laptop is getting the job done of delivering the sound that's on the recording without intruding any more than minimally - quite remarkable, really ...
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    Posted 3rd May 2015 at 01:27 PM by fas42 fas42 is offline
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