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    Gain and Buffer positions

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    litefootdan

    Posts : 16
    Join date : 2014-03-21

    Gain and Buffer positions

    Post by litefootdan on Sun Jun 28, 2015 2:05 am

    Hello Everyone,

    In a previous thread titled "Three months of SP-14 Bliss" Kentley discusses using RCA tubes in the Buffer stage and Sylvania tubes in the Gain stage of his SP14 preamplifier.  I am curious as to how rolling different pairs of tubes will affect my SP14 as well.  Can someone please tell me specifically which tubes positions relate to the gain stage of both right and left channel as well as which tube positions relate to the buffer stage of both the right and left channel.

    Do Gain and Buffer stages in an audio circuit affect the sound in different manners?  

    Any and all information about experience or theory is highly appreciated.  

    Bravo to en excellent Preamplifier, it is a superb product.

    Kentley

    Posts : 335
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: Gain and Buffer positions

    Post by Kentley on Mon Jun 29, 2015 5:01 pm

    OK Dan. Since no one who really knows the theory has stepped up, let me give you, from my layman's perspective, the rationale here.
    The two tubes to the left of the amp, looking from the front, are the crucial ones for sound, as they are the ones which actually amplify. Top is left, bottom is right. The two to their right are not as critical, so any good pair of fuctioning 6SN7s will suffice if they are reasonably well-matched.
    The tube to the right side of the chassis is the rectifier, once again not a critical part of the signal path.
    So the idea is to use your best matched pair in the first two holes on the left. Jim McShane supplied me with excellent new TungSols in all four positions. I decided to try some NOS and used US-made tubes to reserve the new ones, and read somewhere about prioritizing in the manner described. The new TungSols are fine, bright and solid choices. The old RCAs are a bit on the dark side. The Sylvanias are right in the middle, as are some NOS TungSols I lucked out on from EwBay.
    What will satisfy you is going to depend on the rest of your equipment and your taste.
    Someone who really knows what they are talking about can take it from here. BTW I got 8 RCA 6SN7s from the aforementioned auction site, and they were dirt-cheap - about $4 apiece, and tho I don't care for them in the gain position, I will never run out. Can't remember what the other old US tubes ran, but it was no more than $25 each. So you won't need a second mortgage on your home to start the tube rolling. It's addictive. And it forces you to really learn to listen for subtleties in sound which you may have taken for granted.
    Enjoy!

    litefootdan

    Posts : 16
    Join date : 2014-03-21

    Re: Gain and Buffer positions

    Post by litefootdan on Mon Jun 29, 2015 9:51 pm

    Kentley, Thanks so much for clearing my questions up.  I had guessed oppositely, considering where the gain and buffer stages were located.....  But I'm new to this stuff and I suppose there are no hard rules to anything.  I've experimented with the current production Electro-harmonix tubes and in my estimation, they are do not exemplify the capabilities of the SP14.  I have tried an unknown quad of Baldwin's which were better and have found my best result to be with brown based Sylvania's.  I did not know that I did not really need both pairs of a certain tube to get the most of the circuit.  But I suppose I will have lots of careful listening to do when my old production CBS, RCA, GE and Tung Sol's tubes arrive.  Again, thanks for helping me with your knowledge and sharing your experience.  I'll report back when I've had a bit of time to roll through some of those tubes.....  But I have a feeling I'll be leaning toward the softer/darker sounding tubes as I'm running a pair of Holton A's for speakers.  They are not so dynamic, but they can get a tad bright for me.  Thanks again Kentley.

    Kentley

    Posts : 335
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    Re: Gain and Buffer positions

    Post by Kentley on Mon Jun 29, 2015 10:14 pm

    You're welcome. Always glad to share my ignorance, as I have no shame.
    I must concur re: the EH's. All four of mine were horribly microphonic, and muffled and dusky to boot.
    The most foolproof source of both old and new tubes is Jim McShane, IMHO. He not only knows tubes inside and out, but he also has much more sophisticated testing equipment than anyone out there.

    litefootdan

    Posts : 16
    Join date : 2014-03-21

    Re: Gain and Buffer positions

    Post by litefootdan on Tue Jul 07, 2015 11:41 pm

    Well the only pair or 6SN7's that I've received as of yet are a pair of CBS's.  I ran them in the Gain positions and thought that I like them better than the brown based Sylvanias, ones with green print.  After quite a while I switched the Sylvanias back to the gain position and quickly realized I preferred their richness and tonal qualities over the CBS's.  Just for fun I put the Electro-harmonics in the buffer stage in place of the CBS's and again, they left a lot to be desired.  The CBS's gave an obvious presence to the music.  What is it with NOS tubes?  For further experimentation I sourced an Amperex rectifier.  I could not tell directly whether I liked it better than the General Electric rectifier that Roy provided with the tube compliment, six in one and half dozen in the other.  This is curious because when I've experimented with rectifiers in my amplifier, the results have been dramatic at times.  But I wonder if this is the case because the amplifier does not have any diodes.    

    This leads me to my next question.  For anyone in the know, is the PH16 circuit similar to the circuit of the SP14?  If there are gain and buffer positions, which are which please?  I could just shoot in the dark, but I'd rather go into it with some advice.  I'll soon have some some nice Amperex 7308's and a pair of 6922 Telefunken's.  If anyone can offer their knowledge, I'd sure appreciate it.  Thank you.

    Kentley

    Posts : 335
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: Gain and Buffer positions

    Post by Kentley on Wed Jul 08, 2015 12:42 am

    We are getting into the mysterious world of Subjective Soundscaping. Some people "hear" great differences in sound where there technically should be none. Other times the opposite is true.
    It has been wisely stated that there are some differences which can be measured objectively which cannot be perceived. And that there are differences which can be heard but not measured.
    Add to this complex equation the infinite combinations of equipment, and one realises that there are only general rules. Technically, the choice of rectification should never dramatically alter sound, given that it supplies adequate voltages. But I've heard quite obvious changes in sound between the Weber SS recti and the Mullard GZ-37 in my ST-120.
    To me, science has barely begun to understand the perception of music, or the way the brain compensates for any number of factors in perception as a whole.
    To make matters more confusing, we have obviously trained our brains in an individual manner. I'm less likely, for example, to be impressed with Pink Floyd than by Bach on the same equipment. There are such fundamental differences in our perceptual mechanisms that have been formed by nature and nurture that any consensus on what "sounds good" is unlikely.
    So bottom line - take any advice with a grain of salt. Ultimately, unfortunately, experimentation is the only path to fulfillment. Our ears - and brains - are fickle creatures.

    My brother-in-law has a theory which he's attempting to test - that atmospheric pressure influences sound. It could have validity in that the relative density of the air must somehow influence soundwave propagation. It's these unaccountable phemomena which might be what we do not take into account when we jump to easy conclusions about our precious systems. I think we've all had the experience of listening to the same piece of music at different times and thinking "This sounds terrible today. Why did it sound so good yesterday?" We tend to want to find an objective or technical solution, such as "my amp was warmed up longer yesterday" or "Probably a tube going south". When in fact the real reason may be simply that you were in a better mood yesterday.
    There are times when my well-oiled and tuned system just doesn't satisfy me. And there are times when the neighbor's Bose radio sounds perfect. Go figure.


    Last edited by Kentley on Wed Jul 08, 2015 1:02 am; edited 1 time in total (Reason for editing : additions)

    audiobill

    Posts : 270
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Gain and Buffer positions

    Post by audiobill on Wed Jul 08, 2015 5:27 am

    Kentley, could the brand of Scotch in your tumbler have any effect?

    Kentley

    Posts : 335
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: Gain and Buffer positions

    Post by Kentley on Wed Jul 08, 2015 11:18 am

    audiobill wrote:Kentley, could the brand of Scotch in your tumbler have any effect?

    Not only the brand, but the temperature, the shape of the glass, and Gandhi's last meal have a profound influence. Just ask him.

    audiobill

    Posts : 270
    Join date : 2014-03-13
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    Re: Gain and Buffer positions

    Post by audiobill on Wed Jul 08, 2015 12:26 pm

    Gandhi......wasn't he the drummer in The Grateful Dead?

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Gain and Buffer positions

    Post by deepee99 on Wed Jul 08, 2015 12:39 pm

    Kentley wrote:
    audiobill wrote:Kentley, could the brand of Scotch in your tumbler have any effect?

    Not only the brand, but the temperature, the shape of the glass, and Gandhi's last meal have a profound influence. Just ask him.

    Kentley: Don't forget the shape of the ice cubes, if you're one who likes to dilute his single-malt. Hard edges bruise the beverage.
    Litefootdan, while I fully endorse Jim McShane you might also check in with Andy Bowman, or at least visit his website, on vintage tubes. Lot of good info there. Many of the older tubes were re-branded. GE and Tung-Sol made the original 6550s, but the Tung-Sols came out with a lot of different names.


    audiobill

    Posts : 270
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Gain and Buffer positions

    Post by audiobill on Wed Jul 08, 2015 6:43 pm

    David, Lisa concures on cube shape.

    litefootdan

    Posts : 16
    Join date : 2014-03-21

    Re: Gain and Buffer positions

    Post by litefootdan on Wed Jul 08, 2015 8:29 pm

    Was that water reverse osmosis, distilled, or charcoal filtered before it was frozen into a cube?  Smile  But truthfully guys, does the PH16 have gain and buffer stages; and if so, which are which?

    deepee99

    Posts : 1333
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Gain and Buffer positions

    Post by deepee99 on Thu Jul 09, 2015 11:02 am

    litefootdan wrote:Was that water reverse osmosis, distilled, or charcoal filtered before it was frozen into a cube?  Smile  But truthfully guys, does the PH16 have gain and buffer stages; and if so, which are which?

    Yes, I believe it do. Best to ask Roy Mottram at tubes4hifi or tmadden here on this board. If I can find my PH-16 schematic I'll PM you, but I think some circuit changes have been made over the years so best to check with the experts. Roy designed the PH-16 but Troy mainly builds them. It is a superb phono preamp in any iteration, dead quiet. IIRC, the earlier versions used 6CG7s for the gain section and 6922s for the buffers, but don't hold me to that.

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: Gain and Buffer positions

    Post by tubes4hifi on Tue Jul 14, 2015 12:38 pm

    first two tubes in the PH16 (on the input end) are gain stages, the final two tubes are buffers

    litefootdan

    Posts : 16
    Join date : 2014-03-21

    Re: Gain and Buffer positions

    Post by litefootdan on Tue Jul 14, 2015 8:31 pm

    Smile Thanks!

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