The Arthur Loesch 1.1 Control Preamplifier is back!
Considered by many to be classics of the high-end tube revival, Loesch Preamplifiers have occasionally been produced on a one-off basis. Over the past 20 years, the original circuit was the inspiration for many variations by builders like J.C. Morrison, Herb Reichert, and Allen Wright. For a while, they were produced by John Wiesner under the Loesch & Wiesner name. Well-known audio aficionado Thorsten Loesch (no relation) has written, "The sound of the Preamplifier in Phono-mode is natural and lucid, with excellent sound staging and definition. Although the line stage is more an afterthought than a specific circuit exclusively intended for this purpose, it nevertheless is exceptional." In fact, the line stage is no longer an "afterthought," but enjoys it's own completely separate signal path and is as carefully thought out as the phono.
For this ultimate edition, Dr. Loesch revisited the RIAA Phono spec and recalculated all of the restoration parameters. Using a wide range of passive parts, many of which were unavailable in earlier versions, the end result is a complete reworking of the Loesch RIAA circuit, representing the last word in Phono reproduction.
In voicing the 1.1 Phono Stage, Dr. Loesch used unamplified music in an acoustic environment as his reference standard. The result is a natural, well-balanced sound, with nothing added or subtracted. If it's in the grooves and the rest of your system is up to it, you will easily hear details that were previously lost, including those unique, low-level cues which distinguish individual recording spaces. When properly integrated with equipment of equal quality, your system will disappear, leaving you alone with vocalists and musicians performing just for you.
About the Circuit:
Amplifying the audio signal in three gain stages, the Loesch Phono circuit is suitable for use with any moving coil cartridge, even those with outputs below 0.1mV. The only restriction is that due to reduced volume, cartridges whose output is both lower than 0.5mV and whose loading resistor is less than 100 Ohms should be paired with the built-in step-up transformers. Because of its exceptionally high gain, we do not recommend pairing it with cartridges whose output is higher than 1.5mV.
In this updated circuit, the slight roll-off at 2000Hz, for which the original Loesch circuit was occasionally criticized, has been restored to the correct value of 2122Hz, and a 4th time constant was added at 50KHz, so that the highest frequencies are no longer rolled off. This is known as the enhanced RIAA (or eRIAA) curve and was originally developed by Allan Wright and Jim Hagerman, among other experimenters.
The net result is that instead of letting the curve continue to steadily roll off from 20KHz, we now add a little gain causing it to flatten out. Even though this is out of range of normal human hearing, there is still an audible psycho-acoustic effect in the form of additional air and ambiance in the sound stage that was previously lost.
Features include:
- Battery regulated, fixed bias RIAA Phono Stage with +72dB of gain
- Optional built-in step-up transformers for up to an additional +30dB of gain
- 1 Active and 2 Passive Line Inputs, plus Mute
- Dual-Mono Ladder Volume + Balance Controls
- Optional upgrade of the Active Line capacitors from REL AudioCap Polystyrene to VCap TFTF Teflon®
- Infinite cartridge loading via plug-in resistors, shown here:
 A choice of tubes to tailor the sound to individual taste
- Solo or Dual-Mono tube-regulated power supplies, adjustable for 120V or 240V worldwide operation (pictured below)
 "Cost no object" parts including V-Cap TFTF, REL PCU Copper foil, and REL RT Polypropylene film capacitors, plus "Naked" Vishay, Caddock, and Audio Note resistors.
- WBT-0144 Topline sockets are standard on all inputs and outputs; WBT-0210 Ag NextGen Fine Silver Sockets are optional upgrades
 Teflon® insulated, extra-soft temper, fine silver wire throughout the signal path.
- 0.125" (1/8" or 3mm) rigid PC Board featuring 1 oz. thick copper traces.
Unique to this design, is the location of the 6.3V filament supply path on top of the board for maximum isolation. With few exceptions, all of the signal path components reside under the board for further shielding.
- Internally isolated audio circuit (shown below).
The dual mono PC boards are suspended from 1/2" (12mm) square aluminum rails that run between the sides of the chassis. Between the rails and the boards is a layer of damping material that acts like a shock absorber and completely isolates the circuit boards. Stand-offs or other direct metallic paths to the chassis, which run the risk of transmitting vibrations or mechanical feedback, have been completely eliminated.
- Soundcare® SuperSpikeTM feet for increased external isolation from airborne and mechanical feedback
The Active Line Stage provides the necessary gain for tape and other low level sources, while the optional passive inputs and controls provide an integrated control center for high level components, such as an FM tuner or a CD player. As illustrated below, the Active Line section runs parallel to the Phono Stage, amplified by the otherwise unused half of the dual-triode in the 3rd Gain Stage.
Each stage is built with its own optimal blend of parts. The 1st Stage uses a V-Cap TFTF Teflon® film and foil coupling capacitor plus Texas Components TX2352 ("Naked" Vishay) resistors; the 2nd Stage uses a REL PCU Copper foil capacitor and Audio Note UK Tantalum resistors; the 3rd Stage uses a REL Polystyrene output capacitor. Likewise, the B+ is filtered through a combination of HEI (Mills) and Caddock power resistors in alternating sections. By building each stage with a different mix, the sonic signature of any one component is effectively cancelled out, a fabrication technique pioneered by Dr. Loesch.
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In addition, the Control Preamplifier can be purchased as the stand-alone 1.1 Phono Stage, omitting the Line Stage and Volume/Balance controls.
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The standard tube complement is:
| 1st Stage |
2nd Stage |
3rd Stage |
Raytheon 5842
Western Electric 417A
|
RCA 6GK5 |
Tung Sol 5687
Amperex 7119
Bendix / MU 6900 |
NOS tubes in Bold Face are supplied. Tubes in Light Face can be substituted, enabling you to fine tune the sound to your personal taste, compensating for differences in music or source. Changes in overall gain can also be effected this way. For example, replacing the 5687 with a 7119 will increase the output by about +3dB, as well as change the sound more toward the 6DJ8 family.
| 1.1 Phono Stage | Specifications |
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| Gain | - 72dB RIAA via Direct Input (75dB with 7119 3rd Stage tube)
- Up to 30dB additional gain via optional, built-in Step-Up Transformers
- 18dB Active Line Stage (1.1 Full-Function Control Preamplifier only)
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| Frequency Response | 12Hz - 50KHz |
| Phono Input Impedance | Infinitely variable via plug-in resistors:- Direct Input Default = 47K Ohms (supplied)
- Step-Up Default = 640K Ohms in parallel with 100pF capacitor
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| Phono Output Impedance | 3K3 Ohms (typical) |
| Total Harmonic Distortion | No more than 0.1% |
| IM Distortion | No more than 0.1% |
| Signal-to-Noise Ratio | Better than 87dB |
| Phase | Non-Inverting |
| External Ground Connectors | Earth Ground (AC Earth)
Common Ground (AC Neutral) |
| Signal Ground | Switchable via locking toggle:- Signal to Earth (Default)
- Signal Float
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| Inputs | Unbalanced WBT RCA:- Phono In Direct
- Phono In Via Step-Up (optional)
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| Output | Unbalanced WBT RCA: |
| Dimensions | 16.75" Wide x 16.0" Deep x 4.5" High, including feet, excluding power supplies
(425mm Wide x 406mm Deep x 114mm High) |
| Net Weight | 15 lbs. (6.8 kg) |
All features, parts, and specifications are subject to change without notice.
The Arthur Loesch 1201B+ Power Supply
Based on a design originally developed for military and laboratory test equipment, the Arthur Loesch 1201B+ Power Supply is a separate tube regulated unit that has been completely updated and optimized for high-end audio.
Click here for complete Power Supply specs. |
| Prices | Plus shipping from Troy, NY 12180, USA |
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| 1.1 Control Preamplifier with Single Power Supply | $5,900
Includes Active Line Stage, 2 Passive Line Inputs, and Dual-Mono Volume/Balance Controls |
| 1.1 Phono Stage with Single Power Supply | $4,800 |
| Second Power Supply | +$1,800 for full Dual-Mono operation.
All audio stages are pre-wired for Dual-Mono power supplies and do not have to be returned for this upgrade. |
| Upgrade 1st Stage Tubes to WE417A | +$250/Matched Pair of extra quiet NOS Western Electric 417A tubes |
| Additional Phono Load Resistors | +$35/1% pair of TX2352 ("Naked" Vishay) resistors in any value up to 47K |
| Built-In Step-Up Transformers | +$750/Matched Pair
Including three pairs of TX2352 ("Naked" Vishay) resistors to adjust the gain
+10dB, +15dB, or +20dB |
| Upgrade Line Stage | +$380
Upgrade the 1.0uF REL RT Polystyrene Capacitors with VCap TFTF Teflon® Capacitors (1.1 Control Preamplifier only) |
| Upgrade RCA Jacks to WBT NextGen Ag | +$75/Pair
Upgrade the jacks from WBT Topline Gold-plated Brass to WBT NextGen Ag Fine Silver. There are two pair on the Phono Stage and seven pair on the Control Preamplifier. Installing the Step-Up Transformers adds another pair of jacks to either unit.
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| Upgrade Power Cord | Upgrade the standard 14 AWG shielded power cord to a 12 AWG double-Teflon® insulated and shielded power cord, featuring WattGate Audio Grade terminations.
+$250/6 feet, +$10 each additional foot, per power supply |
| Warranty |
- 10 Years (transferable) on all parts and labor, with the exception of
- 90 Days on tubes
Unauthorized parts substitution may void Warranty |
| Availability | Now ! All units are built to order by hand in our workshop in Troy, New York, USA.
Lead time is typically 2-4 weeks from order to shipment depending on the individual configuration. |
30 Day, Risk-Free Trial
Because we only sell directly to you, all Tempo Electric products come with a 30 day unconditional refund period. This allows you to make a full evaluation in your own home, at your own convenience, without the pressures of time or sales personnel. In fact, if you're not completely satisfied and live in the Lower 48 United States, we'll even cover the cost of shipping both ways. Listeners outside of the Lower 48, will receive a $100 credit toward shipping and return. Certain restrictions apply.
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