My take on a Single Ended amp

Discussion in 'Tube Audio' started by kward, Jul 7, 2018.

  1. Tubeglowpio

    Tubeglowpio Active Member

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    "


    What you need is amps that play dynamically. This means NO chokes 50 Ohms or more, to the Finals, and ideally, 20 Ohms or less. It also means attention paid to lay out, wiring types, wire lengths, and wire AWGs, so as to maximize transfer efficiency in the SE amp, below deck. The good battle.

    As you go to higher current amps, you run into SE design problems, assuming you are seeking best sonics and performance.

    Dowto1000[/QUOTE]
    I don't mind my serious listening amps to be low powered because it is easier to find better parts but I would like to try a higher powered se amp that could rock my 96 db speakers.
     

     

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  2. dowto1000

    dowto1000 Active Member

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    I don't mind my serious listening amps to be low powered because it is easier to find better parts but I would like to try a higher powered se amp that could rock my 96 db speakers.[/QUOTE]

    Can you tell us what you use, as speaker leads, to the crossovers and crossovers to the drivers? Is that optimized? Maybe we need to try for better transfer efficiency, amp to drivers !! Care to share wire specifics??

    Dowto1000
     
  3. Tubeglowpio

    Tubeglowpio Active Member

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    Can you tell us what you use, as speaker leads, to the crossovers and crossovers to the drivers? Is that optimized? Maybe we need to try for better transfer efficiency, amp to drivers !! Care to share wire specifics??

    Dowto1000[/QUOTE]
    I am currently just using my Klipsch rp 160m speakers with about 4 feet of 14 awg copper speaker wire for each speaker, nothing fancy.
     
  4. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    I think i might have some high quality 5K multiturn pots, i.e., not made in China, if you want to try them. I got a bunch for cheap from Ivan in Oregon.
    Regarding pentode power supply; a cheap and easy solution that involves no circuitry is to add a choke to the G2 supply something around 20 to 30 ma about 20H. This is a fairly small and inexpensive. I find that it makes an audible improvement vs just a RC supply.
     
  5. dowto1000

    dowto1000 Active Member

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    Hello,

    I will contact you privately and help you with some speaker wire to try out.

    It will be a 57 1/8th inch ( a Bob Fulton determined basic length in "about" 1977 ) run of three paralleled wires, 12AWG + 12AWG + 14 AWG, m22759/11, to each speaker. You need to hear that first !!!!

    Then, we need to assess all the wiring in your Klipsch crossover, and from the crossover to the drivers, as a final item to deal with !!

    This is COST EFFECTIVE and gains transfer efficiency, and bandwidth. Lets get back to KT-88s and SE designing.

    Dowto1000
     
    Last edited: Jul 10, 2018
  6. kward

    kward AK Subscriber Subscriber

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    First of all thank you for your thoughtful reply though many of your ideas are outside the scope of this project. I expect I'll have many iterations as I learn and tweak my designs to optimize for a sound that works for me. I expect this will take years. I'm finally very happy with the sound of my KT 120 push pull amp that's on its third iteration now, and I've already got some ideas for iteration number four. I expect a similar arduous journey into the SE world as I pursue a design and sound that work for me.

    • The 12BZ7 won't work for me. Must be a current production tube.
    • I'll experiment with the power supply but likely won't change from CLC for this iteration.
    • Upgrading or obtaining different speakers not an option at this time.
    • 12AX7 directly driving KT88--dunno, probably not on the short list to experiment with this iteration.
    • Stereo chassis is a must
    • Cathode bias--not this time. Don't want the heat under the hood.
    • Need 10 ish watts. Must idle at 80% to get it but I might consider the KT120 although that limits choices to one vendor.
     

     

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  7. dowto1000

    dowto1000 Active Member

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    Understand !!

    Roger Sanders' great sounding SE KT-88 amp at RMAF that year, it was a cap couple, a REL teflon cap I was told.

    A small uF coupling cap will sound best, like 0.1 to 0.01uF.

    You will have a lot of work, time, and money tied up in this, and the main difficulty is that your speakers are not efficient enough. Those Seismic Coaxials I suggest are only about $240 a pair, shipped, 15 inch coaxials, 98 dB.

    Dowto1000
     
  8. kward

    kward AK Subscriber Subscriber

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    And also a lot of first hand experience, wisdom, and intuition gained along the way which for me is equally as important as the eventual final result. So I've got to forge my own path here. It's no fun for me at all just implementing others designs/ideas. There's no creativity or passion in that (for me).

    Concerning speakers, the WAF friendly Seismic's I looked at are 89 dB sensitive (they look like bookshelfers). Can you point to an exact model number for the speakers you are suggesting? Any other WAF acceptable speaker suggestions on a budget? (say under $500)
     
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  9. 6DZ7

    6DZ7 Super Member

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    Some vintage Sansui SP-2500. Beautiful grills @98dB. Could be had for @$250. 80W. Sound great driven with my little old SE Maggie.
     
  10. dowto1000

    dowto1000 Active Member

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    188

    I understand, I LOVE designing my own DC amps, SET.

    Here we are.

    These are BRAND NEW speakers, not stuff that "you don't know what they have been through, signal-wise and loss-of-magnetism wise". They are only $129.99 each, .........with FREE SHIPPING.

    https://www.seismicaudiospeakers.com/products/15-inch-coaxial-speaker

    A highly-experienced friend of mine, ( owner of Serious Stereo ) has a pair, and normally uses GPA 604s in great MLTLS, and he tells me this Seismic Coaxial 15 is a steal for the money, and quite OK sound-wise. Just think, a single point source !! 98 dB rated.

    Dowto1000
     
    Last edited: Jul 10, 2018
  11. kward

    kward AK Subscriber Subscriber

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    Concerning the "extreme position" placed on the driver stage with the use of output stage plate feedback, the related issue I'm mulling around is the use of fixed bias on the output stage. Fixed bias requires strict attention to the output stage's grid leak resistor size. 6550 data sheet says 50K max for fixed bias, while KT88 says 100K max for fixed bias. This value can be raised quite a bit if using cathode bias, to 250K for the 6550, and 100K for the KT88. The driver tube working into a 250K or even 100K load would be much easier than working into a 50K load. But, as I mentioned, I am not interested in putting a hot cathode resistor under the chassis. So I'm going to have to live with the more difficult 50K load demanded by fixed bias as well as being compatible with either 6550 or KT88 types.

    What I really need is a driver tube with a bunch of gain like a 12AX7 but with a bunch of current capability like a 6SN7, and having that tube be a more common 8- or 9-pin type that ideally is available in new production. I don't think there is such a thing....

    I've been thinking then about relaxing this requirement, meaning using any tube I can find either new production or old stock that has a mu say of 50 and able to handle 10 mA current. This kills tube rolling choices though, but maybe it's the lesser of the evils.

    Another idea. Using a single triode, the flatter I can make the driver stage load line, the more gain I can realize, limited by mu of the tube. Maybe I should consider a CCS plate load. I could get nearly 70x gain with a 12AT7. That would allow the application of more feedback to get to my targeted 10 dB feedback range.

    Another idea. I could use a compound driver with a stacked triode topology. Something like a pseudo current source with another 12AT7 triode, or a SRPP, Mu follower, or even a cascode. Any of these approaches would also increase available gain. Don't really like any of these approaches because of the need for elevated heaters, but I'm not ruling them out yet, either.

    My very strong inclination is to keep things simple. So I'm guessing I will end up sticking with the common cathode topology, either 12AT7 (preference), or another old stock tube that meets the high mu, high current capability requirement. If I use a CCS, it will be discrete silicon based (thus avoiding the elevated heater issue). Probably not interested in the IXYS 10M45 current source. I've tried it before and I don't really care for it. Just personal preference on that.

    So It turns out, I'm finding that designing a decent SE amp may be a lot harder than designing a decent PP amp. Relatively speaking, PP amps are "easy" to design well, in my opinion, because they implicitly solve a lot of the most plaguing problems of SE amps--less expensive power supply, noise and distortion cancellation, higher efficiency, more power with less iron weight, inverter can act as a driver and can give you a crutch of a little extra gain. Affordances that are readily available in PP amps are non existent in SE amps.

    Back in the mid 90's I met Bill Conrad (of Conrad Johnson). He came to a brick and mortar re-seller store in Salt Lake City for a routine visit. I happened to be in the store at the time. So I asked him why CJ did not build SE amps. He gave me a long list of reasons that are mostly summarized in the above paragraph. Now that I build my own amps, I can see his point much clearer than I could back then.

    So anyway, enough musing. Back to figuring out how I should move forward here...
     
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  12. 6DZ7

    6DZ7 Super Member

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    My Genalex sheet says you can use 220K if the plate+G2 dissipation is under 35W.
     
  13. kward

    kward AK Subscriber Subscriber

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    I'd be at 34W. But it isn't compatible with the 6550, which wants max at 50K for fixed bias. :(
     
  14. dowto1000

    dowto1000 Active Member

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    Here is what "I" think:

    The best sound in a SE amp comes from as simple, but as well done design as possible. Schemes such as SRPPs, Cathode followers, three stage amps, and CCS should be AVOIDED like the plague, if you want the best possible sound quality. CCSes and SRPPs are only good for people who do not know how to build a good supply to start with !! A crutch, a band aid, that will sound "forced", compared to an optimized simple implementation.

    Heat under the hood from a cathode bias resistor is NOT as bad a choice as YOU , or 95% of the people in this world, would make by employing a fixed bias supply. I have never seen a great fixed bias supply !! Anyone who could design that, will chose self-bias instead.

    The fixed bias supply you build will be ON THE GRID of the KT-88 and it will NOT be good enough supply, in its design, and in its parts quality !!!

    Rks, heat : My upcoming 6AQ5 DC stereo amp will have 177.5 VDC on each cathode ( elevated due to DCing ) at 35.5 mA., so that is two resistors in a stereo amp, each dissipating 6.30 Watts, , or 12.6 Watts total.. So what ?? I have ALL the advantages of cathode bias in reliability and in sonics !!! Each Rk is 5K, 1%, wirewound, a single 50 Watt chassis mount, with thermal grease, so it is operating at 12.6 % of the R's rated power. Far better than adding a complex, and mis-designed fixed bias supply to the grid !! See Rks below, with three dimensional layout and short signal paths employed, not yet fully evident.

    I chuckled when you dismissed my driver tube suggestion, because it is no longer in production. You are an amateur DIY builder, like me, and you are likely older, like me, and NOT going into production. WHY is current production tubes a requirement. You could buy four 12BZ7s ( I like Raytheons) over a few months, and your GRANDKIDS will still be able to use the amp with those four tubes you buy in 2018 !! How about, the BEST tube compromise, as a choice ?

    The 12BZ7 IS a compromise., in that it does not have great, linear tube curves, when you look at large signal swing. A typical EE will poo poo it, dismiss it. A good DIYer, on the ball, will not dismiss the tube. Its a great mu of 100 driver, sounds GOOD, robust sounding, nice large plate and cathode !! I like it around 2.2 mA and 190 Ea by ear. I have the cajones to use it, others won't bother. LOL.

    Recall, the Roger Sander's QuickSilver KT-88 amp that was SO GOOD at the Azzolina room at RMAF years ago, was 1/2 a 12AX7, cap coupled with a small uF REL Teflon coupler, to the grids of a KT-88 !! You should talk to him, not amateur DIYer me.

    All of this is in my opinion, I am sure you realize that, and that we can discuss this on Forum.

    Dowto1000

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    Last edited: Jul 12, 2018
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  15. kward

    kward AK Subscriber Subscriber

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    Hi Primo, Yes, I remember. How has the fixed bias worked out? Is the amp quiet? I'd appreciate your insight as one the few I know who have tried fixed bias on an SE amp.
     
  16. vrusso123

    vrusso123 Well-Known Member

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    following...
     

     

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  17. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    Oh yeah, i appreciated your help on that . Your recommendations worked out perfectly. I have 3 SE amps with fixed bias. To me the extra circuitry is worth the effort. I always use Schottky diodes and for my amps i also use film caps if there is enough room, instead of electrolytics. The flexibility wiht adjustable fixed bias is hard to beat if you want to use different power tubes. For instance original Tung Sol black plate 6550 can burn up quickly if you run them hard. I adjust the bias for around 70ma. which sounds sweet. KT88 and KT90 i run at 90 ma, and KT120 i am running at 110 ma.
    I used a reversed wired 6.3v filament trans on an extra tap from my power trans in 1 amp and in another amp that had plenty of spare current on the filament, i used the trans off of that. If you run the trans off the already used filament circuit, you need to remove any existing grounds from that circuit or you will create a short when you ground your negative voltage circuit. Although i am sure you are aware of that eventuality.
    I used high quality Allen Bradley pots and i am not really worried about problems. Both amps are dead quiet and that is with Altec 19 which are over 100db sensitivity. I think i mentioned that all my PS have 2 chokes in either CLCLC or LCLC. The first cap should be a film cap and the second or final cap if you are using an electrolytic there , i always bypass with a film cap. Most recommend 1% of the capacitance of the last cap, but i like to use about 10% if there is enough room. Since SE is mostly current requirements, it makes sense to me that 2 chokes are better than 1. My first SE amps were rebuilds using just a single choke, and after experimenting with a 2 choke PS which sounded better, i built all the other amps that way. It would be fairly easy to try an additional LC section with some test leads, if you don't want to commit to the extra expense, chassis space and installation effort. If you can make a 2 chassis amp would be the best way to make your amp dead quiet and give you room to play with transformer and component layout.
     
  18. prelius

    prelius AK Subscriber Subscriber

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    Kevin,
    I apologize if I divert the discussion a tiny bit, but I would like to ask Dowto to expand on his statement about PSU.

    Dowto100, you've stated on several occasions (in this and other threads) that PSU is critical for SE amp, and I fully agree with you on that. But what does it mean (for you) to build a "high-quality" PSU? Can you list a "full" set of specifications? And how do you determine/measure the performance of your PSU as it relates to the amp performance? Are these measurement objective and quantitative (i.e. done with the scope/analyzer and can be plugged in to Excel for analysis or graphing), or are they subjective and based on the listening tests? BTW, I either way is fine with me, please don't take my questions as insult or challenge, but rather as a learning/sharing inquiry.

    Sincerely, Paul.
     
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  19. Selmerdave

    Selmerdave Well-Known Member

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    Do an internet search for LSES power supply, you'll find extensive commentary about it (particularly at the Asylum) addressing all of the above.
     
  20. prelius

    prelius AK Subscriber Subscriber

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    Sure, I've read through a few of these discussions, not only on Asylum, but here on AK, diyaudio and other places, but I am interested in understanding Dowto100 specs.

    Or, did I miss his reference to the LSES design in this or another thread? )This could have happened for sure... :)

    Thanks, Paul
     
    Last edited: Jul 12, 2018

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