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

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

    Post by Bob Latino on Thu Jul 26, 2018 6:34 pm

    corndog71 wrote:

    I almost when down the PAS road.  I looked at all of the various upgrade boards out there because I didn't want a stock PAS, I wanted great performance.  Ultimately I was able to build Roy's SP13 for around the same cost.  

    Within seconds of playing music through the SP13 I heard way more detail with a bigger soundstage and knew I made the right choice.  Changing the output caps the Clarity CMR and a couple of the power supply caps to Clarity TC upped the resolution a few more notches.  I saved a little money building it into a relatively cheap aluminum Hammond box.


    What Corndog has said is so true .. I played around with PAS preamps for 40+ years. No matter what you do with them > bypass the tone controls, beef up the power supply, alter the RIAA curve etc., etc., they will never sound as good a one of Roy's SP preamps.

    Those who read this board know that I love older Dynaco tube gear. The PAS preamps are nice to have if you are a collector of vintage tube gear but in stock form or even if modded, they are not the best sounding preamps to use with any amp. The Dynaco PAS preamps always held back the Dynaco tube amps from performing their best.

    Here is a true story .. In the late 1970's I was still cruising along with my Dynaco PAS-3 preamp and ST-70 amp. A friend (Paul H.) lived diagonally across the street from me and had just bought a solid state preamp from a company in Oregon called Audionics. He asked me if I would like to try it out with my ST-70. The next day he brought it over, I hooked it up and we listened. From the first minute, I could tell that this preamp had much more "jump factor" on transients then the PAS preamp that I had. Things like bass drums, cymbals etc. really jumped out at you. The PAS3 sounded "muted" on the same music on every transient spike.

    Just my opinion but if you are looking for the best sound from your music system, you shouldn't really consider any of the PAS preamps as your front end ..

    Bob

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

    Post by rjpjnk on Thu Jul 26, 2018 7:13 pm

    Glad to hear you like it corn dog. As I mentioned, this is a starter preamp. If it improves the sound as many say it does, I may step up to a VTA pre next. Good idea building in your own box to save money. Where did you get the transformer?

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

    Post by rjpjnk on Fri Jul 27, 2018 1:07 am


    That picture is so pretty. If I were an electron I would love going into one of those big white caps. Smile

    I have decided to build an SP12 as well, so I'll have both the PAS 3X and the SP12 to evaluate soon.
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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 Jul 30, 2018 10:01 pm

    rjpjnk wrote:

    That picture is so pretty. If I were an electron I would love going into one of those big white caps. Smile

    I have decided to build an SP12 as well, so I'll have both the PAS 3X and the SP12 to evaluate soon.
      "If I were an electron I would love going into one of those big white caps"  Totally agree! Laughing

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    On the use of a preamp to improve sound quality with VTA70 (Early listening results)

    Post by rjpjnk on Thu Aug 02, 2018 1:03 pm

    Well the PAS 3X arrived yesterday and it appears to be in excellent condition. I gave it a thorough inspection, checked all DC voltages, tested tubes, and cleaned all pots and switches. Only one capacitor was in need of replacement. Still using the original can at this point. Seems to be doing the job, so left it alone for now.

    As for listening experience. It seems very quiet. No added noise that I can hear. The tone controls are some of the most effective I have every heard. Huge and well contoured increases in either bass or treble are produced effortlessly, and the tone bypass seems to be working well too. However, at this point I do not hear any obvious improvement in sound quality compared to just plugging into the VTA70 with attenuator directly. Not saying this preamp doesn't help, just that whatever it is adding is subtle enough that closer listening will be required to appreciate it. Probably using an A/B setup.

    This thread was created precisely to explore this issue. It is no secret that I began this experiment of the opinion that there is no sound technical reason why an active preamp should improve the sound of my VTA70 + iPhone compared to a direct connection using only a passive volume control. I still stand by this point technically, as I could find no evidence to the contrary. But thanks to the many comments and insights from others I now appreciate more fully that there is an artistic dimension to sound as well, and this dimension may not be understood in terms of numbers or circuit theory.

    I am aware of the need to remain mindful of my initial bias and not let it influence my perceptions. Since that time I have read so many accounts of how much better systems sound with preamps, that I may have gone too far in the other direction in anticipation. I was hoping to be blown away by the enhanced dynamics I've been hearing so much about from others' accounts. I am a little disappointed, but it is still early in the testing phase. I wonder, does the PAS need any work to sound as good as it should? Perhaps some new capacitors would help? Or maybe this as good as it gets.
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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 Thu Aug 02, 2018 1:13 pm

    Where an active pre-amp does best is with highly dynamic sources run at moderate-to-loud volumes such that the power-amp will be required to respond to transients above its RMS rating. Below those levels, it will be largely indistinguishable from a passive attenuator but for the various controls and filters.

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

    Post by audiobill on Thu Aug 02, 2018 1:39 pm

    I would submit that an ancient PAS is no comparison for the improvement that one of Roy's preamps can make, just as Bob suggested above....

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

    Post by rjpjnk on Thu Aug 02, 2018 3:11 pm

    Perhaps. But this thread is not about whether Roy's amps are better than PAS (I believe everyone agrees they are). It is about whether or not an active preamp brings any improvement at all in my particular home setup -- which at this point consists of a recent VTA70 build, Klipsch Heresey III speakers, and a variety of modern line level input sources such as iPhone 6S, macbook pro with Tidal lossless, and CD player.

    I am building one of Roys SP12 preamps as well, but it won't be completed for a few weeks due to vacation plans. I figure the only way to know for sure what benefit a preamp can bring is to go out and buy some and test them myself.

    My working assumption has been that if preamps have merit (for me), then the PAS 3X should show some improvement over direct, and an extremely good modern unit like a VTA SP12 or SP14 should show even more.

    I am betting the SP12 will sound great, but I am okay with the possibility I will hear no difference as well.
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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 Thu Aug 02, 2018 3:23 pm

    My working assumption has been that if preamps have merit (for me), then the PAS 3X should show some improvement over direct, and an extremely good modern unit like a VTA SP12 or SP14 should show even more.

    I am betting the SP12 will sound great, but I am okay with the possibility I will hear no difference as well.[/quote]

    All true - but you will have to use the pre-amp as an active device - that is, one that pushes the output beyond source line-level for the transients. Otherwise it serves no function other than as a switch-box, control center and filter. And you will realize no benefits from its use.

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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 Thu Aug 02, 2018 3:48 pm

    rjpjnk wrote:However, at this point I do not hear any obvious improvement in sound quality compared to just plugging into the VTA70 with attenuator directly. Not saying this preamp doesn't help, just that whatever it is adding is subtle enough that closer listening will be required to appreciate it. Probably using an A/B setup.

    Might there also be the possibility it doesn't sound as good?  Maybe not in terms of dynamics and transient response but loss of transparency, imaging, soundstage depth and the experience of listening to real instruments and performers.  Other than the transient response, we can wonder how additional circuitry, switches, etc. in the PAS preamp can do anything but degrade the sound.  Not saying it does, but your ears will decide.

    When I first went preampless, I was amazed.  It was like washing my windows (which I need to do Crying or Very sad ).  The fog cleared.  I'll not go back unless I can determine that the windows will stay clean.  I should also re-state that I don't believe my preamps were state of the art in the area of transparency.

    dave

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

    Post by zx on Thu Aug 02, 2018 4:20 pm

    I have Been in this Audio hobby/Bizz/Sales for more than 40 years....Never owned a St70 or a Pas...well no pas that was not moded …..But got a Pas3 an St70 All stock-little rust added.... in a trade....
    Vary shocket….I have owned minny pr of MK3...an have 3pr here now....had Eico,Marantz,Heath kit,Audio Research,Vac,VTL,Jadis CJ.....Tube amps an preamps…Sand preams Krell,Classe, CJ,Sunfire, Bells,Pass labs,
    I can say as far as Better sounding Than passive…
    Not....just different!...
    The Sound of a passive...Just a pot in a box....has a great sound...But I thnk most Know that...well if thay heard one....

    The Pas 3.....All stock ….But with a 250k blue alps $14. pot from Parts Express....add diff tone...
    I like the tone controls Also...there in the feedback loop...You can add some Warmth Cant do that with Passive..Vary helpful...With the Non forgiving  Speaker I use.... Martin logan CLS ESL speakers most of the time...But it always for me come back to the two 12AX7s you put in the preamp....I have two tube I pull out of a old Fisher....No name can be found on them....But I have never found any other12Ax7s that sound like thay do....
    I must have 30 other pr....I like the sound of the selenium rectifier.....put new Sand Diodes in...pull them out ASAP
    I know the tube heaters went up a volt...not good to my ears...By pass the tone...NO...back in...the two DC blocking 1mf caps off the tone controls output too the board...put minny poly,oil, NOT...back to the chep medle BP caps...Pull the rectifier tube......Not  back in....Vary Good sound..
    Cant stop Using the Pas...

    Is a preamp Needed....Why Not..It all good fun....
    But the passive well drive any of my Amps to full output....Yes,they all sound different......The Bigest  Sound differents is in Speakers...Get the Right speaker for your ear...Thats the key.

    All just one mans finding....


    Thanks for the Site Roy...……..
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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by corndog71 on Thu Aug 02, 2018 4:26 pm

    Not to knock your speakers but they could also be a limiting factor. Have you considered upgrading the crossovers in them? Even just swapping the caps in line with the tweeters can improve resolution.

    I had a pair of Heresey IIs years ago and while upgrading the tweeters and the crossovers improved their sound quality some, they could still be bested by more modern designs in overall resolution.

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

    Post by zx on Thu Aug 02, 2018 4:56 pm

    I had a Odd Experience with a Guy I had sold Some Speaker  ….About 5 years ago I befriended a guy  we had some Audio things in common....Panels speaks an tube sound....One night he was over an I had my passive box setup on a pr of my MK3s Amps...An Acoustat ESL speaker ...Same type speakers as he owened....he had never heard or seen a passive preamp.
    Well....The sound to his ear was to diff.....it made him uneasy...I had to put in a Active stage in so he get his brain Back rapet around the sound…..Thin I put the passive back in....It made him vary uncomfterble ….He did not like it at All.....Hehe...Live long a nuf you get to see it all I gess…

    By the way.....Looking at the tube preamps SP12-14....So simple...Thay have to sound great....But in your setup....with your speakers...who knows....



    Thanks for the Site Bob......
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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by peterh on Thu Aug 02, 2018 5:25 pm

    If one cannot detect any differences when signal goes direct or when signal passes a PAS3/x , then the PAS3 should be a very accurate amplifier by definition. ( sounding like a straight wire )

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

    Post by rjpjnk on Thu Aug 02, 2018 6:19 pm

    [quote="solderblob"]
    rjpjnk wrote:

    Might there also be the possibility it doesn't sound as good?  Maybe not in terms of dynamics and transient response but loss of transparency, imaging, soundstage depth and the experience of listening to real instruments and performers.  Other than the transient response, we can wonder how additional circuitry, switches, etc. in the PAS preamp can do anything but degrade the sound.  

    dave

    Dave, If you read my earlier posts, this is indeed my understanding as well. Technically speaking, there seems to be no reason to expect an active preamp to "add quality" to a signal. It should, as you point out, only degrade the sound (SNR/Bandwidth), or at best leave it completely unaffected. That's why I started this thread. To investigate this topology of serial amplifiers and get a better understanding as to why it is so popular among audiophiles.

    I noticed that lots of people a lot more experienced than me are spending a lot of money on preamps, and I have read countless accounts on this forum and elsewhere describing how the sound is "just more right" with the pre, or more dynamic. That sounds very attractive to me and I want it If I can get it.

    It may be that in the end I am right back where I started, just running my iPhone straight into my VTA70. And that's not a bad thing at all. But if I didn't at least give the active pre a try I'd always be wondering if I was missing something every time I heard some reviewer gushing over them.

    Anyway, I only have about 30 minutes' listening experience in yet, and only on the PAS. It is WAY to early to make any conclusion other than the one I made above -- that if there is a difference it is subtle.  I still remain optimistic that the less tangible sonic properties an active preamp can add will outweigh the losses described above, which are a nonnegotiable property of physics, I agree.

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    I want a preamp MUCH better than wire.

    Post by rjpjnk on Thu Aug 02, 2018 6:28 pm

    peterh wrote:If one cannot detect any differences when signal goes direct or when signal passes a PAS3/x , then the PAS3 should be a very accurate amplifier by definition. ( sounding like a straight wire )

    Well, I already have plenty of wire. Smile

    The idea here is to buy or build a box that is MUCH better than wire. Isn't that the whole idea?

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

    Post by audiobill on Thu Aug 02, 2018 6:41 pm

    Simply put, my SP14 says "Who's your Daddy" to my M125s.......then on to my Magnepan 3.6/R or PBN Montana speakers.
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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by peterh on Thu Aug 02, 2018 7:09 pm

    rjpjnk wrote:
    peterh wrote:If one cannot detect any differences when signal goes direct or when signal passes a PAS3/x , then the PAS3 should be a very accurate amplifier by definition. ( sounding like a straight wire )

    Well, I already have plenty of wire. :)

    The idea here is to buy or build a box that is MUCH better than wire.  Isn't that the whole idea?
    This implies changing the signal, this has nothing to do with accuracy and high fidelity, it's more an act of sampling and changing sounds to make them more appealing to your ears.

    Hifi is the sport to reproduce a musical event as natural as possible. ( in my ipinion).

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

    Post by rjpjnk on Thu Aug 02, 2018 8:55 pm

    peterh wrote:
    rjpjnk wrote:
    peterh wrote:If one cannot detect any differences when signal goes direct or when signal passes a PAS3/x , then the PAS3 should be a very accurate amplifier by definition. ( sounding like a straight wire )

    Well, I already have plenty of wire. Smile

    The idea here is to buy or build a box that is MUCH better than wire.  Isn't that the whole idea?
    This implies changing the signal, this has nothing to do with accuracy and high fidelity, it's more an act of sampling and changing sounds to make them more appealing to your ears.

    Hifi is the sport to reproduce a musical event as natural as possible. ( in my ipinion).

    Correct.

    It seems there are many different opinions. Some value preserving the original signal as much as possible as the ultimate goal (This can be measured), others value less tangible qualities I often hear referred to as musicality, dynamics, or richness. I think only the former is actually "HiFi", since high fidelity literal means a faithful reproduction of the source. So yes, I agree with this point.

    However, if we put the race for fidelity aside, there seems to be a wide range of opinions as to what sounds best, and "best" is not always pure. For example, I have heard many accounts of listeners that eschew tone controls but still love rolling tubes. How can this be one might ask? It is widely known that each tube presents its sound a little differently: warmer, cooler, more analytical, more detailed, greater soundstage, smoother, wonderful mids, heavenly vocals, etc. Each tube, in essence, is its own "tone control". So why discriminate?

    In short, I can definitely appreciate the goal of being pure, but I also like the sound of tube gear. So I am trying to keep an open mind in terms of sonic alterations.

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

    Post by audiobill on Fri Aug 03, 2018 7:18 am

    It's kind of like using your ears or test instruments to evaluate sound. Your ears are a more direct interface to your brain for sound than your eyes.......but to each their own I guess.
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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 Fri Aug 03, 2018 8:12 am

    In short, I can definitely appreciate the goal of being pure, but I also like the sound of tube gear. So I am trying to keep an open mind in terms of sonic alterations.[/quote]

    Once again, an active pre-amp will "make a difference" only when it actually *goes active*. Putting tone-controls, filters and contour functions aside:

    a) For a good pre, there will no sonic alterations whatsoever, nor should that be under discussion as a concept.
    b) Signal already present may become audible as with a passive attenuator, it may have previously been below the noise floor. But,
    c) That is not adding anything, just revealing what is already there.

    The key issue here is that for, probably, 60% of users here, and for about 80% of what those individuals use as signal (48% of the time, overall), there is no need for an active pre-amp. But for those who are stretching their amplification to its limits, and often sourcing highly dynamic signal, good results would simply not be possible without an active pre-amp. This group requires access to the full transient capacity of their amps.

    So, to test an active pre-amp, let it go active.

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

    Post by rjpjnk on Fri Aug 03, 2018 9:53 am

    I think we've already exhausted that line of reasoning Peter. Cascading two amps simply to make the output louder is not specifically a preamp benefit. The same can be achieved with a single larger power amp. I have never felt my VTA70 to be lacking volume for my listening levels. I rarely ever run it on full as is.
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    Re: On the use of a preamp to improve sound quality with VTA70

    Post by corndog71 on Fri Aug 03, 2018 10:19 am

    It's not about making it louder.  There's a different component to what the preamp's active stage does to the signal.  It fleshes it out.  It exposes the dynamics of the music.  I know there's a better explanation for it but it eludes me.  My observations were consistent with various active vs passive preamps.  There's a trade off either way.  Ultimately, active preamps offer more control as well additional gain at the line level.  They're helpful too if you have multiple amps to drive.  For instance in my rig I'm not just running the signal to my M125s, but also a pair of subwoofer amplifiers.


    Last edited by corndog71 on Fri Aug 03, 2018 12:15 pm; edited 1 time in total
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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 Fri Aug 03, 2018 10:38 am

    rjpjnk wrote:I think we've already exhausted that line of reasoning Peter. Cascading two amps simply to make the output louder is not specifically a preamp benefit. The same can be achieved with a single larger power amp. I have never felt my VTA70 to be lacking volume for my listening levels. I rarely ever run it on full as is.

    Transients - not RMS.

    A snare-drum rim-shot will typically be around 125 dB in free air at the drummer's ears. Down about 4 dB at 20 feet. Attack to decay (below 80 dB) is less than one (1) second.

    If, using reasonably efficient speakers, 1 watt = 96 dB, 106 dB will require 10 watts, 116 dB will require 100 watts and 125 dB will require ~900 watts. A more reasonable 120 dB will need ~300 watts (all numbers approximate and rounded to lower whole number). Most well-designed power-amps are entirely able to make such transients, if allowed (driven to) do so. Remember, transient capacity is a function of peak-power capacity over time. Not RMS power continuously.

    And that is the point-of-departure. A source that will not drive your amp to reproduce said transient will not provide the full dynamic range of the original source. Full Stop.

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

    Post by rjpjnk on Fri Aug 03, 2018 4:10 pm

    Peter W, Let's just agree to disagree on this one and move on.


    Last edited by rjpjnk on Fri Aug 03, 2018 9:54 pm; edited 1 time in total

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