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    On the use of a preamp to improve sound quality with VTA70

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    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Sat Aug 11, 2018 12:44 pm

    audiobill wrote:If you're interested in high fidelity, you would not want to use the internal dac OR the analog output stage of an i-device.

    Actually, the quality of the analog audio output from the iPhone 5s/6s is excellent. The measurement results here show this:
    https://kenrockwell.com/apple/iphone-6-plus.htm#thd
    https://kenrockwell.com/apple/iphone-6s-plus-audio-quality.htm

    0.0012% THD,
    106.7 dB SNR (A-weighted),
    Freq Response +0, -0.08 dB, from 10 to 20KHz,
    Output Impedance 3.18Ohms,
    Channel balance within 0.0002 dB,  

    These numbers look really good. Better than other DACs I've seen specs for, but then I haven't look at the high end stuff.

    The ankaudiokit DAC you've got does look amazing, and I'd love to have one, but it's also $3100. I would expect that at this level we for sure are getting into the realm of performance that is better than an iPhone, but I'm afraid the rest of my system is no where near the level of audio perfection necessary to appreciate it. I am only using a lowly VTA70, a PAS 3X or SP12 preamp, and a pair Klipsch Heresy III speakers here. My iPhone if far from the weakest link. I've already explored that avenue.

    Are there any published performance specs for the ankaudiokits DAC? Not that numbers tell the whole story, but it would be nice to see what such high end stuff is capable of.


    Last edited by rjpjnk on Sat Aug 11, 2018 1:07 pm; edited 2 times in total

    audiobill

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by audiobill on Sat Aug 11, 2018 12:49 pm

    I've moved well beyond using numerical data to judge audio performance, sorry.

    I've come to trust my ears....

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Sat Aug 11, 2018 1:33 pm

    Understood. Appraising audio quality by numbers alone certainly has it limits, but so does subjective listening. Neither should be discarded. A balanced approach is probably best.

    There is the quantitative, and there is the qualitative. Both are valid, but the latter is harder to write down.

    But I appreciate you point. I would not buy a piano based on its frequency response, I would listen to it.







    audiobill

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by audiobill on Sat Aug 11, 2018 1:47 pm

    Sorry to have sounded pedantic, but this thing sounds amazing!
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    corndog71

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by corndog71 on Sat Aug 11, 2018 4:41 pm

    I wouldn’t call the VTA70 and SP12 “lowly”.  My SP13 is hands down the best preamp I’ve owned.  Both my VTA120 and M125’s also sound amazing.

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Sat Aug 11, 2018 11:04 pm

    Well maybe lowly only in cost. I was speaking relative to audiobill's DAC which costs more than my VTA70, SP12 and Klipsch speakers combined. I can't run with that league.

    I haven't built the SP12 yet. It is sitting on my workbench waiting for me to return from vacation. Should be a lot of fun.

    Can you tell me more about what you like about your SP13? What makes it the best preamp you've owned? What are you comparing it with? The only reference I have so far is my PAS 3X, which doesn't seem to add anything in terms of sound quality compared to direct connection, but I am enjoying the tone, volume, balance, and blend controls. It's fun to have knobs for a change. And it looks cool. Hard to believe this thing is likely 50 years old.
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    CletusB

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by CletusB on Sun Aug 12, 2018 10:35 am

    audiobill wrote:I've moved well beyond using numerical data to judge audio performance, sorry.

    I've come to trust my ears....
    ABSOLUTELY! cheers

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Sun Aug 12, 2018 9:01 pm

    CletusB wrote:
    audiobill wrote:I've moved well beyond using numerical data to judge audio performance, sorry.

    I've come to trust my ears....
    ABSOLUTELY! cheers

    Agreed. So far my ears and theory are in agreement that active preamps make no difference with line level signals. I was hoping to find some magic, but the ears could not be fooled. It would have been really difficult to determine this without a blind A/B switch in the circuit.

    Note: Only 1 preamp tested so far. Dynaco PAS 3X. So this is the only preamp I can comment on with experience.
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    Kentley

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by Kentley on Sun Aug 12, 2018 9:19 pm

    One comment: SP14. It will turn your head around. Guaranteed. But only when properly tubed.
    I'd be glad to elaborate.
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    solderblob

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by solderblob on Sun Aug 12, 2018 9:44 pm

    Kentley wrote:One comment: SP14. It will turn your head around. Guaranteed. But only when properly tubed.
    I'd be glad to elaborate.

    I'm definitely interested in what you mean by properly tubed. My system is analog. I occasionally see a need to re-cartridge but usually no reason to re-tube. I'm interested in the SP-14 -- please elaborate!

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Sun Aug 12, 2018 9:44 pm

    Kentley wrote:One comment: SP14. It will turn your head around. Guaranteed. But only when properly tubed.

    Aw man, I already bought an SP12. I was hoping that would be good enough to test the waters. If it does improve the sound in any way, even a little, compared to direct I will get an SP14 next. Which 6SN7s do you think bring the magic?
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    Peter W.

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by Peter W. on Mon Aug 13, 2018 9:00 am

    Transducers (microphones, guitar pickups, phono cartridges) need preamps. Line level signals need attenuation, unless you like full volume all the time.

    False Premise #1.

    a) A properly engineered recording will have its peaks at the maximum output (voltage) of the playback device. Unless the source is highly compressed and/or with a very low P/A, these peaks will be seldom.

    b) Whereas having attenuation to achieve lower-than-flat volumes is useful for quiet listening, a properly engineered recording will provide a 'near-realistic' volume when played flat into normal speakers with an amplifier capable of making the peaks within its RMS output. On an amplifier not so-capable, the peaks will either disappear, or the amplifier will be driven to clipping.

    c) Such an amplifier will require over-voltage so as the peaks will be delivered (presumably) within its capacity for transient response. Not just "Louder" but more information will be available.

    He seems to understand that technically speaking, the preamp can only degrade the sound quality from any measurable point of view, i.e., SNR, dynamic range, frequency response, time/phase delay, etc. Yet, still the end result comes out sounding better somehow.

    False Premise #2

    Technically speaking, an active preamp reveals information previously below the noise floor. That it is an additional "processor" within the music chain does not require that it "only degrade sound quality" - when one's ears hear the difference so readily. The only difficulty that one may have in wrapping one's thoughts around this is that the information revealed is not audible otherwise under normal conditions. An amp that cannot make a transient within its RMS range cannot reveal all information on a well-engineered orchestral recording.
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    j beede

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by j beede on Mon Aug 13, 2018 11:23 am

    If you enjoy the music without a preamplifier, then consider yourself fortunate and enjoy the music without a preamplifier. If you cannot hear a difference between "straight in" and a pre-amplified signal, I think it is unlikely that the "missing magic" is due to your choice of preamp. Why not enjoy the music without a preamplifier and save yourself the cost and complexity of the additional stage and cabling? If you enjoy music sourced via cellphone, then be happy... you have been spared the inconvenience of owning a record player or 15 IPS tape machine.
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    corndog71

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by corndog71 on Mon Aug 13, 2018 12:49 pm

    rjpjnk wrote:Can you tell me more about what you like about your SP13? What makes it the best preamp you've owned? What are you comparing it with? The only reference I have so far is my PAS 3X, which doesn't seem to add anything in terms of sound quality compared to direct connection, but I am enjoying the tone, volume, balance, and blend controls. It's fun to have knobs for a change. And it looks cool. Hard to believe this thing is likely 50 years old.

    For 10 years or so I've built, tweaked, and used Bottlehead tube preamps.  Foreplay 2, Quickie, and finally Smash.  The first 2 kits were very cheap but with the right tubes gave pretty good performance.  The Smash, which is a single end triode based design improved what many refer to as "prat" (pace, rhythm and timing) yet I still felt like I wasn't get all of the music.  So I took a chance with the SP13.  

    I prefer the smaller 6FQ7 tubes in the SP13  because they're not as popular as the 6SN7s used in the SP14. (The circuit is essentially the same for the 13 and 14.)  I immediately heard improvements over the Smash.  Wider soundstage was the most noticeable.  Separation of vocals and instruments in space was also noticeably better.  Good recordings sounded less like a recording and more like a performance.  I could pick apart more details in complex recordings.  With better speakers the effect became even more noticeable.  As if the the sound wasn't even coming from the speakers.  It just filled the room.  

    For what it's worth I've also tweaked mine a little bit.  I've long known tube preamp output caps can change the sound slightly and I've experimented with several before finding ones that seemed to get out of the way of the music better than others.  Prices can be a bit daunting but aren't always the best indicator of preference.  I started with the supplied Audyn caps.  Which were ok but not great.  I happened to have a pair of .22uF teflon V-Caps from previous projects so I tried those.  Compared to the V-Caps the Audyns sounded more closed in and less resolving.

    Another change I made was to the plate caps on the first tube the signal sees. I compared the stock 47uF electrolytic to the 45uF Clarity Cap TC film cap. I find the TC caps remove a slight haze to the sound that I hear from electrolytics. So I replaced those as well.

    I lived with this arrangement for a while and was satisfied until Clarity updated their MR series to the new CMR series. Out of curiosity I compared them to the V-caps and found them nearly identical in sound quality. They're also much cheaper than the V-Caps!

    So, hopefully this answered your question.


    Last edited by corndog71 on Mon Aug 13, 2018 1:19 pm; edited 1 time in total

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Mon Aug 13, 2018 1:18 pm

    j beede wrote:If you enjoy the music without a preamplifier, then consider yourself fortunate and enjoy the music without a preamplifier. If you cannot hear a difference between "straight in" and a pre-amplified signal, I think it is unlikely that the "missing magic" is due to your choice of preamp. Why not enjoy the music without a preamplifier and save yourself the cost and complexity of the additional stage and cabling? If you enjoy music sourced via cellphone, then be happy... you have been spared the inconvenience of owning a record player or 15 IPS tape machine.

    True, but then I'd be done. Part of the fun is the journey. To be honest, the most interesting thing about this hobby to me is the gear. The music is secondary.

    I enjoy listening to the equipment. I've heard it said that music lovers listen to music, audiophiles listen to equipment. Maybe there's some truth to that.

    I love everything about playing with these tube circuits, old and new, and learning about what makes one sound different than another, and most of all, tweaking stuff. As for the music, I mostly want to play whatever makes the equipment sound best.

    I love music too, and am a musician myself, but that is a different dimension not directly served by HiFi.
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    CletusB

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by CletusB on Mon Aug 13, 2018 1:54 pm

    I'm pretty much messed-up really, being a musician, music-lover, audiophile and electronics engineer  .....man, I'm really screwed! affraid

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Tue Aug 14, 2018 1:13 am

    I've been reading everything I can get my hands on for the past few weeks, including many other online forums, regarding this active preamp issue and almost everyone seems to be saying passive (i.e., simple resistive voltage divider) is better than an active preamp if you've already got line level signals. I must admit I am really at a loss to explain why anyone is using an active preamp with line level inputs anymore. The best arguments I've heard go something line this. If you've already got a line level signal (1-2 vrms) an active preamp first cuts this down to the millivolt range using a voltage divider, and then amplifies it back up to nearly the same volume you started with, so why not just use a stepped attenuator in the first place? All these active boxes are doing is making a smaller version of the input signal, and this can be done just as well by a simple voltage divider with two resistors (Stepped attenuator).

    For example. If you have a 1 VRMS source and you want to listen to it at a lower volume (say 6dB lower) you need to reduce the voltage by half. What you ideally want is an exact scaled copy of the input signal that is exactly have the value at every point. You could use an active preamp to accomplish this, but a simple voltage divider consisting of two resistors will do the exact same thing with less added noise. So why use the active approach?

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    peterh

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by peterh on Tue Aug 14, 2018 3:29 am

    A good use for an active preamp is to centralize control of sources, enabling the poweramp
    to move away from listening position. In addition it may be used to adjust the sound
    properties ( stereo blending, remove rumble or hiss , or plain adjust tine balance. It may also
    contain and power exotic converters ( RIAA, DAC bluetooth etc) for the sources. In
    addition might a preamp act as an impedance buffer, separating the sourc(es) from the
    poweramp and cabling, and maybe also drive a typically low-impedance soundcard.
    Some preamps also has the possibility to use a remote for volume control.
    All of the above is of null value for a person listening to same music from the same source.


    A good preamp will, if configured so, sound like a wire.

    rjpjnk

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by rjpjnk on Tue Aug 14, 2018 10:10 am

    Yes, this is the general consensus I am finding in my research as well. However, there are also several very convincing accounts I've found of people claiming their active preamps sound so much better than wires. For example, the video posted earlier, and some contributors in this thread.

    rjpjnk

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    SPICE and the art of preamplifier design

    Post by rjpjnk on Tue Aug 14, 2018 6:46 pm

    I wanted to share a link to this very interesting article I found by Norman L. Koren from 2001. I don't know much about the guy, but at the time he was attempting to use SPICE modeling correlated with listening to gain some insight into the "less measurable" amplifier qualities we have been discussing here. And his test subject was none other than a PAS preamp.

    A quote from his introduction :
    "A central mystery of high-end audio amplifier design is the poor correlation between subjective sound quality and conventional measurements (frequency response, harmonic distortion, etc.). For this reason, many of the choices involved in amplifier design-- the selection of the overall circuit topology, the use of negative feedback (NFB) and the often-overlooked tradeoff between frequency response extension and radio frequency (RF) interference-- have remained an art."

    I'm not sure if his amplifier designs turned out well or not, but I admire his approach. Anyone know what became of this work?

    Here is the full text
    http://www.normankoren.com/Audio/Spice_preamp.html
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    pedrocols

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by pedrocols on Tue Aug 14, 2018 7:35 pm

    I sold my BAT active tube preamp after I listened to a passive one.  Yes the BAT was somewhat more dimensional and fuller but for the price difference you would expect that the BAT would mop the floor with the passive preamp. Needless to say that was not the case.
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    solderblob

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by solderblob on Tue Aug 14, 2018 10:07 pm

    OK, I did a test.  Not a good test but a test nonetheless.

    Normally my setup is phono to step-up transformer to phono preamp to stepped attenuator to amps.  Normally it sounds amazing but I have reservations about some stridency in the sound of massed strings in some of my classical records...

    So I substituted the stepped attenuator with my old Adcom preamp.  Aux input with "lab output" bypassing tone controls.  Acting as a line-only preamp.

    I listened to two records.  I only tried two records so I'd have a better chance of remembering what I heard...

    First was a Beethoven RCA LSC piano concerto #4 Van Cliburn.  With the Adcom, there was more bass but the piano sounded somewhat dry, less organic.  Seemed to lack the power of the piano.

    Then I went on to try a Chesky Records Riimsky-Korsokov Scheherazade to hear some massed strings.  I think I noticed less distortion with the strings.  Loud strings/horns are something I have problems with normally.  With the Adcom, I think the loud strings were less strident.  Solo stings, horns, etc sounded OK.  Good ambience.

    Then I removed the Adcom.  

    The Scheherazade was similar, hard to tell.  Massed strings maybe more strident.  Solo instruments more clear.

    Returning to the Beethoven.  There was no comparison.  The piano was alive -- like it was right there.  Amazing.  No going back!

    What I was hoping to hear was the Adcom supporting transients in massed strings and I think that might be the case.  

    So this is a lame test/comparison.  It was hard to match the volume; that can make a big difference.  Also, warm up was not equal as I had to shut everything down to switch interconnects.

    But I'm sure I noticed a loss of clarity/transparency with the Adcom in the signal path.  Granted the Adcom is a mid-fi preamp; I think I paid $300 for it in 1988.  Conclusion?  I think it's worth looking into a line preamp to improve some situations of the massed instruments, but it really needs to be an absolutely transparent device.

    dave
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    Kentley

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by Kentley on Tue Aug 14, 2018 10:34 pm

    Massed strings, along with complex vocal choruses, are the hardest things in sound to reproduce, due, i believe, to their complexity.
    We have a tendency to increase the volume when the music sounds good. We also increase the volume to make amemic sound sound nicer. Both are sidestepping reality.
    Peter W. is really onto something re: adjusting peak levels.
    There is an optimum listening level. It is whatever level was used in the mastering room. Right or wrong, there's no way around it.
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    corndog71

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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by corndog71 on Tue Aug 14, 2018 11:39 pm

    I also own a Bryston B60 integrated amp.  It has dual mono power supplies and separate preamp and amp sections.  Bryson’s are pretty well engineered as I’m on my 18th year of its 20 year warranty.  I’ll probably never sell it as it’s practically bullet-proof.  Yet as great as it is it comes with limitations.  

    I’ve used the preamp section with my first ST70 and it worked well.  But when I built the Bottlehead Foreplay 2 kit with 12AU7 tubes there was something present that even the Bryston couldn’t capture.  A liveliness.  With more experiments with different tubes, caps, and even volume pots I heard variations both good and not so much.  

    It was during this time when I found PEC pots.  I was shocked at how much better they sounded over the cheap alpha pots that came with the kit.  Later I built a stepped attenuator and that was even better sounding.  I tried those alone in a passive arrangement to see if I even needed the preamp.  It sounded really good at first but eventually I started noticing the dynamics just weren’t the same.  I went back to active because it just drove the music better.  Gave it life.  That’s the best way I can describe it. I can hear how much the pot alone can get in the way of the music.

    I know this misses the technical reasoning but I gave them all fair chances.  Lived with them to get used to them.  I know when my system sounds good and when it fails.

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