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Posts posted by TNRabbit

  1. I have a Ht set-up with RF-63's, RC-64 anf RS-62. I have a RT-12D. I have the LFP off. I set the X-over for my mains at 60HZ, center 60 Hz and rears at 80Hz.

    I ran room correction. Phase at 0 degress.

    I was looking to get more slam.. I was thinking of adding a SVS 13PB ultra or HSU uls-15.

    Would this work? How do I set it up? I use an Integra DHC 9.9 preamp.

    I cannot believe you aren't getting enough slam from your setup. Somethign isn't right somewhere. Where is the sub located? What size/dimensions are the room? Got any pics? 95% of issues with "it doesn't sound like I thought it would" are due to improper speaker setup. We need more info to give you informed opinions.

  2. Hello Mallette -

    Thanks for posting this - very interesting... here's what I heard on my system...

    #1 - Closer recording and natural sounding.

    #2 - Phasey. Maybe more distant than #1. Not bad at reduced volume.

    As far as the engineering goes, I'd say #1 is a far better recording than #2.


    I agree completely with this assessment. In addition, I thought the second recording was a little bright, possibly due to the apparent live nature of the room/hall....*SEE EDIT BELOW*

    Of course, that version of "Claire de Lune" is one of my all-time favs for piano, so maybe I'm a little biased... [:D]

    EDIT: I've had another listen, and I don't think it's fair to use these two different performances to compare recording techniques; they are too dissimilar. #1 was recorded under the piano top while #2 sounds like it was recorded for 30 feet away. There are a lot of unnerving room reflections in #2. I noticed in one of the particularly rambunctious sections of #1 that there was overmodulation; was this the original recording or the re-recording (this sounds like an old 50s or 60s performance)? There are too many questions here to make an informed, unbiased evaluation....

    2nd EDIT: Armed with the further information stated about these recordings, I went back & listened on a pair of headphones (AKG-K701), I find the File 1 recording much more enjoyable to listen to, with the exception of a GRANDLY irritating distortion/buzz (overmodulation?) in the right channel which may or may not be part of the process of copying to mp3. I find it hard to believe that could be on the original recording...

    I just wasn't as happy with the File 2 recording. The imaging/phase shifts were very disconcerting.

  3. Interesting Q&A from the auction:

    Hi Bob... glad to see the latest set of amps here on the BAY! I wish
    that I could run a set of these for even a week! Are they able to be
    strapped together so they can run a set of speakers that need a common
    ground design amplifier? And have you thougt about a stereo tube
    design? Mar-12-09

    A: Hi 'john1, Hope you like these red ones on
    the Bay! Yes they can be strapped, and yes I have thought about a
    stereo tube design for about thirty micro-seconds. The problem is they
    would be too heavy for me to easily lift if I designed them the way my
    inner voice says. Thanks for your enthusiasm... means a lot to me, Bob

    Q: dear bob....I know what voltage you have to use on the
    output plates.....but what are you using for the screens?? Just curious
    cordially neal Mar-12-09

    A: Hi Neal, I love questions about
    screen voltage because it gives me the opportunity to talk about
    screens. What I did regarding the screen voltage was to perform a
    series of converging experiments at the time I designed these
    amplifiers. The experiments were quite involved, but here are my
    conclusions: Ultra-Linear screens reduce the maximum output current too
    much for me, and hence the ultimate performance of the amp.
    Ultra-Linear screens also saddle the output tubes with dangerously high
    voltage essentially equal to the plate voltage, often causing
    catastrophic and unexpected arc-over failures. I don't like that. I
    concluded, for better or for worse, that Ultra-Linear was scant more
    than a money saving method simply because it eliminated a second power
    supply. As far as the triode-like output impedance that it yields,
    KT-88's with a DC restorer and screens fed from a separate power supply
    can easily yield performance superior to the best Ultra-Linear
    configuration. Stu, Tim, and my own experiments taught me that. I
    operate the screens at exactly one half the plate voltage, or 330 volts
    DC. Good question; thanks for asking, Bob Carver

    Q: Hi Bob - You
    are my hero!!!!, you and Nelson. I had an off the wall inquiry, can Joe
    work on old Western Electric gear? I'm a recording engineer and I need
    a WE mic pre spec'd out, recapped etc. can you get me his email? Thanks
    so much. Mar-12-09

    A: Hi '265, I felt like a hero yesterday, but
    today I cannot find my red cape and flying goggles, so I'll have to be
    a hero without them. You are making my day! Thank you '265. Joe can
    literally work on anything, especially old Western Electric gear. I'll
    forward this to him, and you are very welcome. Hero...Hmmm...Bob Carver
    Do I need a pre-amp to run these? Can you recommend one if so? Do you
    have one? do you have recommended speakers for these amps? Can I call
    you with more dumb questions? I am new to the tube amp world anf have a
    few more questions. Mar-12-09

    A: Hi 'comm, Yes you need a
    preamp. A vintage Citation I, Carver C-1, or Audio research SP-3.
    Others as well. I have lots of preamps. Their ARE no dumb questions
    except those that are never asked, so call anytime! Enjoy the tube amp
    world...it's lots of fun and very musically rewarding. Hope this helps,
    Bob Carver.

    Q: WOW, Bob Carver himself. It's great to see you
    back into tube equipment. I have a question about these amps, if you
    won't mind explaining. Sweet amps! Gorgeous! How do they get more power
    out at six ohms since they have output transformers that match loads?
    Thanks for your time, Chris Thomas - Texas Mar-11-09

    A: Hi.... Hey, I just answered that question! Warmest and best, Bob Carver

    WOW, Bob Carver himself. It's great to see you back into tube
    equipment. I have a question about these amps, if you won't mind
    explaining. Sweet amps! Gorgeous! How do they get more power out at six
    ohms since they have output transformers that match loads? Mar-11-09

    Hi '33, Here's how: a pair of KT-88's are rated for 100 watts of audio.
    Since I'm using three sets for 180 watts, or 60 watts per pair, they
    are operating conservately and are substantially underloaded. Now
    suppose the amp is delivering 180 watts into eight ohms using the eight
    ohm transformer tap, and suddenly the load changes to six or even four
    ohms (as can easily occur in a complex speaker load) as the frequency
    changes. Now the amp is more heavily loaded, and the power output can
    increase to almost three hundred watts ON THE EIGHT OHM TAP! The irony
    is that if the speaker were then connected to the four ohm tap, the
    power would drop back to 180 watts. This tube amp is really surprising
    that way (in that the power goes up as the impedance goes down) as
    those six mighty KT-88's continue to deliver ever more current and
    hammer on unfazed. They can do that in large part because of the
    separate power supply for the screen grids. Great question, thanks for
    asking. Bob Carver
    More Q&A for the record. I don't understand this stuff but I'm sure it's pure gold to the tube guys:

    Question & Answer

    Bob back again...so the solution was back to the sliding bias scheme to
    shrink the cathode resister as the tubes draw more current.. this time
    I use an led driver firing off 3 optocouplers which gradually turned on
    a transistor in parallel with the cathode resister.. a few extra
    resistore and trim pots and I got the same results lively dynamic sound
    ,efficient cool operation. This time around I abandond the big output
    tubes in favor of the russion military version of the 6bq5...I think
    they are fabulous. I just keep paralleling tubes to match what every
    Dyna OPT I choose, from the little bitty ones to the MK6 They are
    really tough.. I am using near 500 on the plates and 250 to 300 on the
    screens.. reading your description of you biasing scheme you MUST be
    using a sliding bias if you are idling at 25% normal...What is your
    method for shifting bias..just the general concept..your amps are the
    first I have ever seen in 20 years of looking over the world that got
    it right..... Mar-16-09

    A: Wow! I truly admire your thinking and
    your tenacity regarding the age old bias problem. Your transistor idea
    across the bias resistor is nothing short of inspired. Do you sense
    current or do you sense voltage to turn the transistor on? I like your
    scheme because the delay that will naturally occur is rendered
    irrelevant by the energy contained in the the cathode bypass capacitor,
    as it MUST deliver the required current during the time it takes for
    the control circuits to respond and turn the transistor on. My DC
    restorer is not a sliding bias approach, rather its purpose is to keep
    the DC value on the control grid at design center even in the presence
    of signals that have a DC component. Thank you '541 for sharing your
    thinking with me and with all of us. Was a real treat. Best wishes and
    warmest regards, Bob Carver

    Q: Bob about the magnetic lag at the
    polarity flip...the solution was to use TWO transformers one for push
    one for pull each one never leaving one polarity...Did it make a
    fifference? yes it did and quite noticable (But not as much as the
    dynamic bias...) not very cost effective but worth it if you have the
    iron By the way ,when I say I hear an improvement I go thru eons of
    time setting up two identical amplifiers with just one change,in one of
    them ,making sure the levels are the same and blah blah blah the worst
    mistake to make is to THINK you hear a change based on MEMORY...Have to
    constantly make 'reality checks' and never assume anything. So at this
    point I quit audio and went 'underground' with life's necessities..
    Next chapter: I surfased again again 10 years later thinking I was now
    in love with cathode bias scheme what with self balancing and 'plug and
    play' feature..Didnt' take long to realize that a big resister for idle
    wasn't cutting for heavy use.(continued) Mar-16-09

    A: Continued next.

    Bob..back again. so I could set the idle for 12 t0 15 ma and the max to
    whatever level I wanted even Way BEYOND what would be considerd safe or
    acceptable. This is where I thought it sounded the most lively and
    dynamic. Since the tubes were always trying to revert to the trickle
    bias condition (the troughs between the peaks, it was very efficient
    operation...one set of tubes should equal a lifetime. the heat didn,t
    seem any more than filaments at idle,,,no melting plastic cords here,
    and under operating conditions never did the plates glow and just
    faitly in the dark under heavy use,,,this is high voltage mind you. so
    it was the best of all world..best sound high effeciency ,long life At
    this point I had to put audio away having more pressing needs to look
    after,,,but not before I looked into the possibility of eliminating the
    the magnetic lag in the OPT just at the point where the push becomes
    pull and vice versa ,,this is where the magnetic polarity flips
    (contined) Mar-16-09

    A: Continued next.

    Q: Bob..back
    again...so I could set the idle for 12 to 15 ma and the max on heavy
    peaks normalor safe even WAY BEYOND what would be considered acceptable
    or safe. This is where I thought things were really sounding good and
    dynamic....its as if the burst of bias current added to the signal
    induced flow of electrons...here the really interesting part..even
    under extreme conditions the plates never got to glowing,,in the dark
    just faint glow.as looong as it was music and apeech.. stedy sine waves
    was a different story...the thermal stree was just a fraction of normal
    run bias because the tubes were doing everything they could to revert
    to the idle trickle condition... this is going on every trough between
    peaks on the waveform...I could actually put my hand on a tube at idle,
    and although hot I didn't feel I was going to get burned most of the
    heat seemed to be filament this is really efficient operation and cool
    operation in my book.the best of all worlds ( to be continued) Mar-16-09

    A: Continued next.

    Bob...ok I'm back....as I mentioned pentode sounded the best and the
    strss on the screens was taken care of but with hi voltages 'normal
    bias' bias ran the tubes too hot....since I knew that the tubes sounded
    just fine with real low bias current when playing really soft (I mean
    each half still looked like class A on the scope) but quicly caved in
    when pushed. it seem obvious that what was needed was a sliding bias
    which would manipulate the bias depending on input...it needed to mimic
    the dynamic nature of speech and music... I couldn' find any
    information anywhere,,so I was on my own...the solution took the form
    of an led driver which sequentially lit up three leds coupled to three
    cadmium sulfide cell( I didn't know about optocouplers at the time) the
    changing resistance in parallel with one leg of a voltage divider in
    the fixed bias supply..I few resisters to trim things out and by gosh
    it worked perfectly...I could reduce idle to about 12 to 15 ma. ( to be
    continued) Mar-15-09

    A: Hi Neal '541, Good to have you back!
    Your solution to the high voltage and bias problem is extremely
    creative, and provided you listened to it deeply, carefully, and found
    it to have just the right dynamics for music, speech and our human
    hearing mechanism, a tip of my hat to you Neal! Well done. Well earned.
    Bob Carver

    Q: Greetings again. I have another quick question for
    you about these amplifiers. I am currently running a pair of Carver
    Platimun speakers. Would I better off using these amps on my speakers
    using the original passive crossovers that are built into them, or
    would I be better off finaly bi-amping my speaker, and using these amps
    on just the ribbon drivers and using my existing amp for the bass
    drivers? Thank you for any advice you can offer. Mar-15-09

    A: Hi
    'io, Either way will work, but here's what I would do. Separate the
    woofers from the ribbons while retaining the passive crossover, drive
    the ribbon part of the crossover with these tube amps, and the woofer
    part of the crossover with your existing amp (probably a solid state
    amplifier). You would then be able to independently adjust the level of
    ribbon-to-woofer for the balance you like the best. Or you could bi-amp
    them and build an external EQ circuit. The EQ is necessary for the
    ribbons in order to voice them properly, and to blend them seamlessly
    into the woofers. This headache is avoided if you use the built-in
    crossovers (The work has already been done.) with just a small loss in
    drive voltage due to the passive nature of the crossover. And these
    amps have lots of power and current, so not a problem. Great question,
    Bob Carver

    Q: I have searched around on the net trying to find
    contact info for "Tubular Joe" to no avail. As a very pleased owner of
    one of your earlier brown sets I'd like to ask Joe some questions about
    their construction. Could you pass on my contact info, please? Mar-15-09
    Hi 'rama, I haven't heard from you lately; it's good to hear from you,
    and yes I will tell Tubular Joe this afternoon. I'm sure he would love
    to answer any questions about the amp he so lovingly built. He is the
    best! Hope this helps, Bob Carver

    Q: hello Bob....near as I can
    tell , you put together an amplifier using the concepts I came up with
    about 15 years ago. I wanted to see what would happen with jacked up
    plate voltages on the outputs and soon ran into distressibg
    observations ....the plates were starting to glow even at idle and the
    screens glowing on and off like light bulb filaments under dynamic
    conditions...there had to be another way....then I found out thar el34s
    are perfectly happy with 800 volts on the anode and 400 on the
    screen...its right in the tube manual...I was surprized at how low the
    screen voltage could be reduced and the tube stll function
    fine.....Pentode mode allows this and I always thought pentode sounded
    more lively and musucal than UL or triode...I never could understand
    the infatuation with triode mode......both triode and ultralinear have
    a severe internal feed back mechanism working wihin the tube...pentode
    mode eliminates most of it to my understanding..(to be continued)......

    A: Hi '541, Your love of amplifiers shows in your
    passion for trying different ideas, and you are absolutely on the right
    track! It took me awhile to notice that ALL the tube amps I really
    liked for sweetness, detail, envelopment and just full blossom power
    output always turned out to possess pentode output stages in their
    purest form. Pure classical!

    Q: oops i fell asleep during last message hope i didnt bungle it up Mar-15-09

    Hi Randy, Yes you did, and I could not make sense of your message. The
    beauty of it all is we have all the time in the world, so try again
    friend Randy, and I promise to get out my Captain Marvel decoder ring
    and properly respond. Bob

    Q: Bob, One more question if you don't mind.... These are transformer coupled right ? What about OTL designs ? Mar-15-09

    Hi'52, I love questions, the more the better! Yes, these are
    transformer coupled. OTL designs are great too, but Bob's my name and
    powerful amps are my game. OTL designs just don't have much current
    output capability, and therefore cannot easily drive difficult reactive
    speakers to satisfying levels. But that's just me, still, they can
    easily drive vintage horn speakers (and some others too) when we want
    to reproduce the sound of wind-chimes at realistic play-back levels.
    Feel free to ask more question, please don't be shy. Anybody! Bob

    Q: if you had your preferance would you run these with a
    set of brysyon 7b or the beautiful jewwls you hold. as the magnapan
    tympani 1 B are quite power hungry and i believe 10 watts at 96 db's
    could be off here a bit but it isn't much would these develop the lows
    needed to warm things up. i also realize that magnapan developed the
    tympani 3a's four panels of woofer material to off set the lack of lows
    in the ones i have. i would love your advice here. of course i have
    bi-amping questions i would hate to bore you with but i can run thre
    top end with either two bridged a-760's or two pm900s or run them
    ftraight with these or the brystons. i love ur stuff and genuis. randy
    hart Mar-14-09

    A: Hi 'hart420, I'd hook these amps straight into
    the Maggies...the lows would warm up a lot because their impedance
    rises nicely on the low-end. The extra coherence and warmth you would
    get by running the amps full range into the Maggies would more than
    offset the extra volume level you could get by bi-amping. Bi-wiring
    (some units had bi-wiring capability, some did not) or straight in is
    my recommendation! Glad you love my stuff... hearing that helps make my
    day. Thanks for writing, Bob Carver.

    Q: Hello Bob, Nice amps. I
    have recently read that to control a speaker you need lots of amps
    (current). Like 100 A. What do these provide ? What is your opinion ?
    Thanks Mar-14-09

    A: Hi '52, Controlling a loudspeaker is a
    complex, deep and non-trivial issue. Still, and just the same, the
    notion that 100 amps is needed is a false belief. The damping current
    required for total speaker control is never more than the peak input
    current at any given instant in time....micro-second to micro-second.
    That's why both two watt and 200 watt amplifiers work, and work very
    well. The maximum output current these amps provide is three times the
    maximum plate current of each KT88 (Three pair) times the turns ratio
    of the output transformer = approximately 26 amps p/p. Thanks for
    writing and for the illuminating question, Bob Carver

    Q: Hello
    Mr Carver, Thanks for the straight on shot (picture), You didn't forgst
    did you? It will certainly be of help to me. I will ever be greatful to
    you Bob. Best Regards, "jay" Mar-14-09

    A: Hi Jay, I'm pretty
    sure I sent you a "straight shot". The chassis shot in this auction is
    the only one I have, and close inspection should reveal all. I now have
    an assistant to help me keep track of my promises, and if I promise to
    send you something she will make sure I don't forget. I hope I didn't
    already forget; if I have, let me know. Bob Carver

    Q: WOW, just
    like I want to build! I still own my Phase 400 from 1974 with warrantee
    cards. Anyway, Bogen used voltage regulation for the screens on the
    KO100 (2 EL34) and the DO-70 (2 EL34s). The DO70 uses the grid voltage
    sent to a 12B4A regulator tube to derive the screen current and the
    KO100 uses a winding designed into the power Transformer to an EZ81
    rectifier tube to derive screen voltage. It seems that the design using
    the grid voltage (regulated via 12B4A) to supply the screen voltage is
    more stable. Since you have vintage iron, my question is: does your
    power transformer have a winding dedicated to the voltage regulator (DC
    restorer) OR did you just use the grid voltages regulated down to
    supply the screens (easier to do). The design I am looking at also uses
    a 6C4 also, which monitors the EL34 current. Did you accomplish the
    same job with a 6AL5 or am I off track. Thank You, Mar-14-09

    Hi 'frank, I don't know who designed the Bogen amps, but I wish I did.
    He or she got it right: separate power supplies for the screen
    grids(often regulated), a very modern hi-tech output tube, British
    style stability compensation for the output transformer, nice high
    plate voltage,I could go on and on. These amps of mine have a separate
    power supply for the screens, which operate at approximately 330 volts.
    The 6AL5 has nothing to do with the screen voltage, rather it's purpose
    is to maintain the correct DC signal component on the control grids
    through the entire audio signal swing, allowing each tube to idle at
    about 11 watts instead of 32 watts, for any given distortion level and
    at the same time eliminating DC shifts and bounces. Hope this helps,
    thanks for writing, Bob Carver
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