OTLs and ESLs

by lewm on Ever Evolving

Description

I have been using OTL amplifiers with ESLs for 3 decades. But I am always looking to improve my OTLs and ESLs, so it is ever evolving. Just getting into vinyl in a bigger way than ever before. I never before had more than one tonearm/tt/cartridge combo.
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Room Details

Dimensions: 23’ × 15’  Large
Ceiling: 9’

Components Toggle details

    • Lenco L75
    Lenco L75 w/mods mounted in custom slate plinth using PTP3 top plate and Jeremy's Super Bearing (see Lenco Heaven). Tonearm Dynavector DV505. The Lenco is now featured in my basement system, based on Beveridge 2SW speakers.  Performance upgraded by the Phoenix drive amplifier in conjunction with the Roadrunner tachometer, controlling platter speed very accurately.
    • Kenwood L07D
    Direct-drive turntable with built-on tonearm, uses coreless, slotless motor, factory plinth brings total wt past 65 lbs. The quietest turntable I ever heard in my life. Seemingly antiquated tonearm sounds fab. I love this thing.
    • Technics SP-10 mkIII
    I found this Mk3 NOS in Florida. I made a slate and wood plinth for it, and Bill Thalmann went through the electronics. Bill also performed the Richard Krebs mod, and JP Jones added his chip made of discrete parts, which is a replacement for the OEM chip, MN6042 (I think). The slate is 2.5-inches thick, and the base is made of solid cherry and baltic birch. Imbedded in the bottom of the wood base is a large threaded brass block. A threaded brass rod traverses the block and contacts the underside of the bearing housing, a la Albert Porter's idea, to drain energy. A 10.5-inch Reed tonearm is mounted on a slate armboard. I also have some aluminum armboards and other tonearms to try.  Lately using the Boston Audio Mat2.
    • Atma-Sphere MP-1
    highly tweaked by moi. A wonderful unit to begin with.
    • Silvaweld SWH550
    All-tube phono stage, now discontinued. I use it for MM and MI cartridges and with the MC2000 via the outboard current-driven gain stage. Its output runs thru my 3160 phonolinepreamp linestage section.
    • Atma-Sphere MA240
    Many, many power supply and circuit upgrades since original. Originally used six 6C33C output tubes in circlotron OTL. Now modified to use four type 7241 triodes in output stage.  Output tubes are driven by four discrete Super Linear Cathode Followers, a la the late Allen Wright. This facilitates very accurate matching of output tubes for bias current, so no single tube is either hogging current nor not carrying its fair share. Uses solid state cascode constant current sources throughout. Now using type 7199 triodes as input dual differential cascode voltage gain section.
    • Sound Lab 845PX
    modified audio step-up transformer and crossover, to present a high impedance for my OTLs. All resistors and capacitors were removed from the passive crossover in the backplate. The OEM Sound Lab treble toroidal transformer was replaced by a full range EI type transformer with a 1:90 step up ratio. This full range transformer is in parallel with the OEM Sound Lab bass step up transformer. Photo shows old M1s in my listening/living room. Picture the same black monoliths only taller and wider, if you want to envision the 845PX.
    • Ortofon MC-7500 and MC2000
    The MC2000 is my current favorite LOMC cartridge.  Neither of my two high gain phono stages (MP1 or 3160) by themselves have enough gain for the 0.05mV output of the MC2000. I run it either through an outboard current-driven phono booster (think head amp or pre-preamp) built for me by Dave Slagle, into the MM section of my Silvaweld phono stage OR into the BMC MCCI ULN Signature current-driven phono stage, and then in either case to the linestage section of the 3160.
    • Koetsu, Stanton, Grace, Acutex, Ortofon, Dynavector, etc Phono cartridges
    I listen to a lot of different vintage phono cartridges. I have a small collection, many of which I have not yet heard. To date my favorites are the Stanton 980LZS, the Grace Ruby, the Acutex LPM320STRIII, and the B&O MMC1 and MC20CL . In many ways I prefer these cartridges to higher end LOMCs that I have heard, but the jury is out and probably always will be out.  Best MC types I own are the Orto MC2000, Koetsu Urushi (now at home in the Fidelity Research FR64S on my Victor TT101, to be found in my basement system), and the Dynavector 17D3.
    • 3160 Phonolinepreamplifier Full function preamplifier
    Fully balanced, dual mono, solid state preamplifier with two completely discrete high gain phono stages plus linestage. I have been using this unit for a few years along with the MP1.  It's by far the best solid state phono stage(s) I have heard in my system, and it rivals any tube unit as well. Built by R&J in Mexico.
    • Denon DP80 turntable
    Found this 100V unit in California.  Bill Thalmann replaced the single chip and upgraded all the discrete transistors and then calibrated it.  I use an inexpensive 120V to 100V step down at the wall socket. I had a 60-lb slate plinth made and mounted my Triplanar on the slate surface.  The Denon replaced the Lenco in my "upstairs" system, when I moved the Lenco to the basement Beveridge system.  Using a Boston Audio Mat2 here.

Comments 60

Showing all comments by dgarretson.

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Thekong, Sp38s on eBay makes a high-quality stainless steel platter for SP-10 MkII. Alternatively, I find that the 15 lb. 1.5" tall lead/delrin/cork platter from my early VPI TNT drops right inside the lip of the stock SP-10 platter. A layer of ERS cloth could be sandwiched between the two platters as a shield, with the possible added advantage of dampening at the interface. A spindle extension could be easily fabricated.

Jim Howard at Applied Fidelity does the sapphire bearing modification. This also entails enlarging the spindle diameter.

Have you opened up the motor housing as yet to inspect the thrust cap? Of the two MkII motors that I have, one thrust cap is worn through entirely. The other evidences minimal wear. My guess is that durability of the trust pad was a function of proper re-lubrication through decades of use. Does Richard Krebs provide a fresh thrust cap?

Lew, apologies for hijacking your virtual system page.

dgarretson

Thekong, I'm in the process of refurbishing and modifying an SP-10 MKII. This will eventually include a 20 lb. stainless steel platter, ruby thrust bearing, and an Albert Porter-style bearing well. FWIW I started by replacing all 31 electrolytic caps in both PS and plinth circuit boards-- tedious but relatively simple work. The strobe is now rock-solid, though I have yet to hear the TT in action. I've spoken with an "insider" modifier who believes that a heavily modified MkII can surpass a MkIII. This was at least sufficient encouragement to attempt what can be done to evolve the MkII for comparison to my L-07D.

dgarretson

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