An OTL (output transformer less) amplifier

[Deleted User]
[Deleted User] Posts: 7,658
edited February 2014 in 2 Channel Audio
Hello,
Here's something you might not have seen before, this is a single channel vacuum tube amplifier that uses 30 12B4A tubes as the output devices.
Enjoy, Ken
Post edited by [Deleted User] on
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  • tonyb
    tonyb Posts: 32,953
    edited February 2014
    Nope, haven't seen that before. Betcha the owner doesn't tube roll much.
    HT SYSTEM-
    Sony 850c 4k
    Pioneer elite vhx 21
    Sony 4k BRP
    SVS SB-2000
    Polk Sig. 20's
    Polk FX500 surrounds

    Cables-
    Acoustic zen Satori speaker cables
    Acoustic zen Matrix 2 IC's
    Wireworld eclipse 7 ic's
    Audio metallurgy ga-o digital cable

    Kitchen

    Sonos zp90
    Grant Fidelity tube dac
    B&k 1420
    lsi 9's
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  • pitdogg2
    pitdogg2 Posts: 25,383
    edited February 2014
    tonyb wrote: »
    Nope, haven't seen that before. Betcha the owner doesn't tube roll much.

    well I was thinking the same thing, but back in the day those tubes were like a dollar a piece....NOT NOW:smile:
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited February 2014
    The amp uses a 6AU6 as the input tube, a 6S4 as the phase splitter tube then all of the parallel 12B4A output tubes. The owner prefers them to several very expensive solid state and tube amps he also owns.
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  • woofiepaws
    woofiepaws Posts: 215
    edited February 2014
    Who made it?
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  • heartystatue
    heartystatue Posts: 329
    edited February 2014
    I'd have to say from the looks of it he did.:biggrin:
    HT: LSI15, LSIC, LSIFX, Emo XPA-3:biggrin: Onkyo TXNR809, Sony BDP-S500, PannyDMP-BDT320, MIT S1 SC. Mit 73842dlp
    2ch: SDA-SRS 2.3 Fully modded. BAT VK500 w/batpak, BAT VK5I, Essence HDACC.
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  • tonyb
    tonyb Posts: 32,953
    edited February 2014
    Kenneth Swauger wrote: »
    The owner prefers them to several very expensive solid state and tube amps he also owns.

    Of course he does Ken. Can't imagine going threw the time and expense building that thing and going " Eh, I don't like it".

    Sure worth a listen though.
    HT SYSTEM-
    Sony 850c 4k
    Pioneer elite vhx 21
    Sony 4k BRP
    SVS SB-2000
    Polk Sig. 20's
    Polk FX500 surrounds

    Cables-
    Acoustic zen Satori speaker cables
    Acoustic zen Matrix 2 IC's
    Wireworld eclipse 7 ic's
    Audio metallurgy ga-o digital cable

    Kitchen

    Sonos zp90
    Grant Fidelity tube dac
    B&k 1420
    lsi 9's
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  • Glen B
    Glen B Posts: 269
    edited February 2014
    OTL amps were introduced to home audio since the '50s, thanks to Julius Futterman. Atma-Sphere Music Systems currently makes balanced differential OTL amps.

    http://www.atma-sphere.com/Products/#MA-3

    http://www.atma-sphere.com/Products/#MA-2
    Main System: Denon DP-59L | Audio-Technica AT33EV | Marantz SA-11S2 | Classe DR-10 | Classe CA-300 | Classe RC-1 | PSB Stratus Gold i's | DIY Balanced AC Power Conditioner | Acoustic Zen and NeoTech cables | Oyaide and Furutech power connectors | Dedicated 20A isolated ground line.

    Home Theater: Toshiba D-VR5SU | Laptop #1 |Outlaw Audio OAW3 wireless audio system | Marantz SR-19 | Phase Linear 400 Series 2, modified | AudioSource 10.1 EQ (for subs) | Axiom M3 v3’s | Axiom VP150 | Optimus PRO-X55AVs | Dayton 12” powered subs (x2) | Belkin PureAV PF-60 line conditioner.

    Party System: Laptop #2 | Audioquest Dragonfly USB DAC | Technics SU-A6 | Acurus A-250 | Radio Shack 15-band EQ | Pioneer SR-9 reverb | Cerwin Vega DX9's | Dayton 100° x 60° horns with titanium HF/MF compression drivers.
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  • SCompRacer
    SCompRacer Posts: 8,485
    edited February 2014
    Nice design! Several years ago McAlister had offered me OTL tube amps using horizontal output tubes. They were made to drive ESL's.

    attachment.php?attachmentid=10901&stc=1&d=1126270768
    Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ * Signature Series Sonore Music Server w/Deux PS * Roon * Gustard R26 DAC / Singxer SU-6 DDC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *
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  • megasat16
    megasat16 Posts: 3,521
    edited February 2014
    Technics made a very cool OTL amps way back then. If you want an absolute transparency of a Tube sound, OTL is the way to go but then, you'll be buying a lot of tubes for every retubes.
    Trying out Different Audio Cables is a Religious Affair. You don't discuss it with anyone. :redface::biggrin:
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  • mhardy6647
    mhardy6647 Posts: 33,731
    edited February 2014
    The 12B4 is a remarkable tube for hifi - but don't tell anyone; it's still a semi-secret out there in the big ol' unwashed tube world.

    On topic: OTL vacuum tube amplifiers make me... nervous. I just feel better having something (i.e., the inductive coupling 'twixt the primary and secondary windings of an OPT) between my loudspeakers and that mean ol' B+ high voltage.

    That said, given the ready availability of high-sensitivity loudspeakers at my house, I do periodically get the urge to slap together one of these...
    http://www.transcendentsound.com/Transcendent/Mini_Beast.html
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  • disneyjoe7
    disneyjoe7 Posts: 11,435
    edited February 2014
    I remember Matt Polk talking about that amp or another amp which didn't use an output transformer once during a PolkFest.

    Speakers
    Carver Amazing Fronts
    CS400i Center
    RT800i's Rears
    Sub Paradigm Servo 15

    Electronics
    Conrad Johnson PV-5 pre-amp
    Parasound Halo A23
    Pioneer 84TXSi AVR
    Pioneer 79Avi DVD
    Sony CX400 CD changer
    Panasonic 42-PX60U Plasma
    WMC Win7 32bit HD DVR


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  • mhardy6647
    mhardy6647 Posts: 33,731
    edited February 2014
    Nothing new about OTLs - in the modern era, I think that Julius Futterman (Futterman Labs) kind of re-introduced them as commercial products, and Atma-Spere has kept the topology commercially viable for decades. More recently, Bruce Rozenblit (Transcendent Sound) has offered OTLs (assembled and kits) at pretty reasonable prices. He used to have a 1 wpc, very inexpensive OTL kit, which (as I mentioned earlier) has been supplanted by a 4 watt OTL (albeit more expensively).

    Another, somewhat more practical approach to OTLs was taken in the 1950s. Philips had a line of high-impedance (500 ohm, IIRC) speakers and companion OTLs to go with them. In the early 1950s, Stephens sold a 500 ohm version of one of their nice coax drivers and a companion amplifier:

    trusonic5.jpg

    http://www.hifilit.com/Stephens/trusonic5.jpg
    source: http://www.hifilit.com/Stephens/Stephens.htm
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited February 2014
    The amps were built by the MP Engineering Company, Fairfield, CT and the schematic has a date of January 1962.
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited February 2014
    Here's a link to a thread by Roger A. Modjeski (RAM Labs) about building an OTL series of amps:

    http://www.audiocircle.com/index.php?topic=121659.0

    Cheers, Ken
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  • Face
    Face Posts: 14,340
    edited February 2014
    The mid and high frequency section of my current speaker is 118db efficient. Only issue is that they're 16ohm, halving the amp output to 1.5w, but it should still be enough for some good dynamics.
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • zingo
    zingo Posts: 11,258
    edited February 2014
    A buddy has a pair of OTL amps and they are a pain in the butt. Last time he tried to demo them for me, we turned them on (as the lights in the house dimmed) and then one kicked into protection. He thinks one of the output tubes went bad, but wouldn't know until he removed and tested each one; followed by reinstalling and rebiasing each one. Obviously we did other listening and never got to hearing the amp that day. They are a great concept, but if you thought regular tube amps were maintenance...
    Jake
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  • Kasanay
    Kasanay Posts: 5
    KennethSwauger wrote: »
    The amps were built by the MP Engineering Company, Fairfield, CT and the schematic has a date of January 1962.

    Ken,
    Do you have the schematic of this amp?
    I happen to own a system that was built by MP Engineering but it mine missing the power amps. I have been searching high and low for any and all information on MP Engineering (also MP Audio Corp., MP Television and MP Concert Installations).
    Here are the preamps and power supplies:
    pp7h84lqwp6w.jpg
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    Hello,
    Yes, I have the complete schematics plus a parts list and test voltages. I can have them scanned and sent to you. I'll send you a PM with details.
    Ken
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  • Kasanay
    Kasanay Posts: 5
    KennethSwauger wrote: »
    Hello,
    Yes, I have the complete schematics plus a parts list and test voltages. I can have them scanned and sent to you. I'll send you a PM with details.
    Ken

    Ken,
    I just wanted to say thank you very much for the schematics - very interesting, indeed.
    I have been able to locate a gentleman in the northeast that claims to have an "extra set" of these amps and is willing to part with them. I hope to have them in my possession by this June.
    Thanks again,

    Joe Y

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  • [Deleted User]
    [Deleted User] Posts: 7,658
    That's great, Joe. Matt Polk is the owner of the amps I worked on and he continues to enjoy them, very much. In fact if you ever wanted to sell your preamps, please let him know.
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  • Kasanay
    Kasanay Posts: 5
    KennethSwauger wrote: »
    That's great, Joe. Matt Polk is the owner of the amps I worked on and he continues to enjoy them, very much. In fact if you ever wanted to sell your preamps, please let him know.

    I don't think I'll be giving up the preamps as I am now the proud owner of a pair of MP Engineering power amps!
    ozg7tj9xurku.jpg
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  • mhardy6647
    mhardy6647 Posts: 33,731
    heh -- real hifi needs a wheeled dolly under it ;)
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  • lightman1
    lightman1 Posts: 10,788
    Jimminy Crickets! Does that beast have a UL tag on it? I forsee an upgraded electrical service to your home.
    Where do you load the Plutonium rods?
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  • Kasanay
    Kasanay Posts: 5
    lightman1 wrote: »
    Jimminy Crickets! Does that beast have a UL tag on it? I forsee an upgraded electrical service to your home.
    Where do you load the Plutonium rods?

    Funny thing---- this was all plugged into a super lightweight extension cord!
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  • lightman1
    lightman1 Posts: 10,788
    edited October 2016
    Kasanay wrote: »
    lightman1 wrote: »
    Jimminy Crickets! Does that beast have a UL tag on it? I forsee an upgraded electrical service to your home.
    Where do you load the Plutonium rods?

    Funny thing---- this was all plugged into a super lightweight extension cord!

    :s Yep,,,, I see the the evil little coil of potential fire in the middle.
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  • Nightfall
    Nightfall Posts: 10,086
    Kasanay wrote: »
    lightman1 wrote: »
    Jimminy Crickets! Does that beast have a UL tag on it? I forsee an upgraded electrical service to your home.
    Where do you load the Plutonium rods?

    Funny thing---- this was all plugged into a super lightweight extension cord!

    https://www.youtube.com/watch?v=RTkEN_wB2A4
    afterburnt wrote: »
    They didn't speak a word of English, they were from South Carolina.

    Village Idiot of Club Polk
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  • [Deleted User]
    [Deleted User] Posts: 342
    edited October 2016
    This is the OTL I would buy if I were in the market right now...Einstein The Silver Bullet

    28zsfkf64tkm.jpg

    rsymdg70gbwq.jpg
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    Congratulations, Joe, I'm glad you were able to find them. They look to be in great shape! Enjoy!
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  • westmassguy
    westmassguy Posts: 6,850
    Holy Cannoli. Those need their own room. Congrats!
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
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  • Kasanay
    Kasanay Posts: 5
    westmassguy wrote: »
    Holy Cannoli. Those need their own room. Congrats!

    That is exactly how they were originally intended to be set up.
    These have a low voltage interface connected through a relay so that they could be powered up for the main listening area. These ugly beasts could then be hidden away in a back room or closet.
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