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  1. Old Comment

    Szekeres 2015

    Great and nice stuff on this blog - many thanks for posting
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    Posted Yesterday at 07:12 AM by kasey197 kasey197 is offline
  2. Old Comment
    abraxalito's Avatar

    Szekeres 2015

    Sorry, yes I just realized I hadn't read the small print on your schematic. The BD136 data from Siemens looks quite decent for VAF - probably no advantage going to the 1381. There does though look to be a 'quasi saturation' region below 10V for VCE where the output impedance reduces. Above 10V all looks dandy for IC up to 200mA. I wonder how much variation there is between manufacturers in this though - NXP doesn't show any data like this in their DS.
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    Posted Yesterday at 01:59 AM by abraxalito abraxalito is offline
    Updated Yesterday at 02:03 AM by abraxalito
  3. Old Comment
    rjm's Avatar

    Szekeres 2015

    @kasey197 I uploaded my version a split second before you posted that! It matters not though: we arrive at the same point. Good.

    @abraxalito In a practical build it must be something bigger than the BC337/327 at any rate.
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    Posted Yesterday at 01:50 AM by rjm rjm is offline
  4. Old Comment
    abraxalito's Avatar

    Szekeres 2015

    In pursuit of even more PSRR you could also try changing Q1 to 2SA1381 - Bob Cordell has the model on his website. It has better VAF than the BC327-25 I seem to recall. Downside is its only good for 100mA so two would need paralleling for higher biasses which will negate some of the VAF advantage.
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    Posted Yesterday at 01:45 AM by abraxalito abraxalito is offline
  5. Old Comment
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    Posted Yesterday at 01:42 AM by kasey197 kasey197 is offline
  6. Old Comment
    rjm's Avatar

    Szekeres 2015

    The improvement was so dramatic I've replaced the schematic above with the modified CCS.
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    Posted Yesterday at 12:28 AM by rjm rjm is offline
  7. Old Comment
    abraxalito's Avatar

    Szekeres 2015

    The 'reverso's PSRR could probably be improved still further with Elvee's mod to the current source - adding a resistor to cancel out the supply voltage variation of the biassing current. I seem to recall Elvee said 20dB improvement was possible.
    I suspect you're getting much better PSRR with the P-channel FET because the source follower doesn't do too well on PSRR, a CCS has the potential to do much better.

    A listen to both side by side would be very interesting.
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    Posted 27th May 2015 at 01:57 PM by abraxalito abraxalito is offline
  8. Old Comment

    Szekeres 2015

    I recall there was one such follower in wireless world - very popular... The usp was its reference to the positive rail and the shunt action of the amp... Can't remember what it was called tho
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    Posted 27th May 2015 at 12:59 PM by kasey197 kasey197 is offline
  9. 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 26th May 2015 at 03:01 AM by rjm rjm is offline
  10. 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 26th May 2015 at 02:02 AM by abraxalito abraxalito is offline
  11. 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 26th May 2015 at 01:56 AM by abraxalito abraxalito is offline
  12. 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 26th May 2015 at 12:43 AM by rjm rjm is offline
  13. 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!!
    permalink
    Posted 26th May 2015 at 12:22 AM by rjm rjm is offline
    Updated 26th May 2015 at 12:27 AM by rjm
  14. 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 25th May 2015 at 07:09 AM by abraxalito abraxalito is offline
  15. 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 offline
    Updated 16th May 2015 at 12:51 AM by rjm
  16. 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
  17. 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
  18. 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 online now
    Updated 13th May 2015 at 11:55 PM by fas42
  19. 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.
    permalink
    Posted 13th May 2015 at 12:15 AM by fas42 fas42 is online now
    Updated 13th May 2015 at 12:19 AM by fas42
  20. 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
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