Channel D Seta L20 Phono Pre-Amp – First Look

Image Credit: Channel D.

Let me first say that this top of the line Seta L20 MK2 has an MSRP of $63,000.00 and is manufactured right here in NJ, USA. Compare that with the $60,000.00 VITUS Audio MP-201, the CH Precision P1 with PSU at $50,350.00 or the Boulder 2008/2108 at $29,000.00, these are some of the worlds most expensive and respected phono pre-amps. Probably matching the “got to have it” value of the TechDAS Air Force Zero turntable. These pre-amps are in another financial stratosphere, where I couldn’t even take a breath. However, fear not, Channel D also manufactures several more affordable pre-amps, so read on. They also offer a hefty discount for factory direct purchase of the L20.

So what’s so special about these phono pre-amps? Like the Air Force Zero, it’s all about the extreme technical design & techniques, component quality, hand build and individual testing and calibration. Also the Seta range of phono amplifiers feature a fully balanced (from input to output), low-noise, direct coupled differential circuit design. Plus all these phono amps have very fast slew rates and exceptionally wide and stable bandwidths; up to 20MHz in the case of the L20 MK2. So how do they sound? I have no idea, but many of the reviewers of Channel D products consider them “laboratory class” and appear to be impressed with their sound quality, and of course their technical measurements.

Channel D manufactures several Seta phono amplifier models that provide excellent state of the art technical performance to include:

• Seta L20 Mk2
• Seta Models L/H
• Seta Lino C2.2
• Seta Piccola mk2

The recent technical upgrade to the L series now provides support for transimpedance amplifiers which may also be retrofitted to earlier L series models. Now I hear you say what are those amplifiers? In simple terms, phono amplifiers maybe split into two different categories:

1. Voltage amplifiers – by far the most common where the cartridge output is fed into some form of fixed resistive load and the output voltage across it is amplified.
2. Current amplifiers – or transimpedance amplifiers, where the output current from the cartridge is converted into a voltage.

Voltage amplifiers can be used for all types of cartridges, either moving magnet or moving coil, high or low output. Current amplifiers only work well with very low impedance sources so they only perform optimally with low output moving coil cartridges. The lower the cartridge impedance the higher the voltage gain of this type of amplifier, up to +85dB (>17,780). Furthermore, as they are ONLY amplifying the cartridge current output there is no requirement to load the moving coil cartridge with any resistor. So there is no requirement to select an optimal load value.

Phono voltage amplifiers require the cartridge current (I) to be provided with a restive load (R) so that it can generate a voltage (V) across it according to ohms law, V=IxR.

The value of this load resistor (R) will change the audible characteristic of the cartridge whether it is MM or MC. In the case of moving magnet and some high output MC cartridges, they are optimized to work best with a load value of typically 47K ohms. These cartridges may be further optimized by adjusting their load capacitance, typically between 47pf and 470pf. Generally speaking the input capacitance values found in either voltage or current amplifiers have little audible effect on a low output MC cartridges’ performance.

Most (low output) moving coil cartridges when driving phono voltage amplifiers work with load values (R) of between 10 ohms and 500 ohms. This much lower value of load for moving coil cartridges helps to reduce or damp the increase in output voltage at higher frequencies. Selecting this load value is often a compromise between top end ‘brightness’, bottom end extension and dynamics. Some MC phono amplifiers provide a continually variable load resistance (R) allowing the user to tailor the sound to their liking.

With current amplifiers (transimpedance amplifiers) life is simpler in terms of optimal loading. This is because the amplifier input resistance is usually very low, as low as 1 ohm, and takes the cartridge output current converting it to a directly proportional voltage. The lower the impedance (resistance) of the cartridge the more current it can supply. This translates to higher voltage gains (>80dB) (>10,000) and larger output voltages with less impact from gain related noise issues.

The above resistance and capacitance loading adjustments are available on appropriate Channel D Seta models.

Noise Performance

The Seta L20 MK2 achieve its astonishing noise performance by basically paralleling sixteen Seta L input stages per channel. Please see here for a simple explanation as to how this improves noise.

Image Credit: Channel D. Each Orange rectangle is a Seta L head amp

A – Weighted SNR Comparisons (per Stereophile magazine):

• Channel D Seta Model L20 mk2 – 87dB
• Channel D Seta Model L – 71dB (updated figure by Channel D)
• Boulder 1008 – 64.75dB
• Vitus Audio MP-P201 Masterpiece – 62.8dB
• Boulder 2008 – 49dB

Clearly in terms of noise the L20 MK2 is right out at the front by 16dB or a factor of more than 6.

Equalization

For those of you who want to ‘tweak’ the EQ curve, set their own or modify it to suit their personnel taste these phono amplifiers may be purchased with no EQ or have a dedicated flat output that in the case of the L20 MK2 extends out to 20MHz. Channel D sells a software package called Pure Vinyl that when loaded onto a suitable MAC with a high end sound card or external USB ADC/DAC can be used to create the required EQ curve in the digital domain to process the phono amps line level flat output. Pure Vinyl is also an excellent vinyl recorder with a great range of features.

Power Supplies

All Seta models run off internally mounted, high capacity, float-charged, AGM (Absorbent Glass Technology) lead acid batteries that disconnect from the incoming power when an active signal is detected.

Brief Technical Specifications:

• Seta L20 Mk2
  • Frequency Response (-3dB): DC to 20 Megahertz Bandwidth
  • Equivalent Input Noise (EIN): -134dB
  • Gain:
    • > 85dB (MC), depends upon cartridge impedance
    • 60dB-73dB (MM)
  • Distortion 20Hz to 20KHz: <0.00007%
  • RIAA module EQ accuracy: ± 0.05 dB, 20Hz-20KHz

• Seta Models L/H
  • Frequency Response (-3dB). At all gain settings:
    • DC to 5MHz (Model L)
    • DC to 1MHz (Model H)
  • Gain:
    • 55dB-65dB (Model L)
    • 35dB-44dB (Model H)
  • Input resistance:
    • Model L: 2K, adjustable to: 25/50/100/150/200/500/1K ohms – supports custom pluggable values
    • Model H: 89K, pre-configured to 47K, supports pluggable values
  • Input Capacitance:
    • Model L : 12pF
    • Model H: 10pF to 220pF – supports custom pluggable values
  • Distortion 10 Hz to 40 kHz, with 600 Ohm or greater load:
    • < 0.001% (Model L/MC)
    • < 0.007% (Model H/MM)
  • Output Impedance: <40ohms balanced
  • RIAA module EQ accuracy: ± 0.1 dB, 20Hz-20KHz

• Seta Lino C2.2
  • Frequency Response (-3db) – DC to 200KHz. At all gain settings
  • Gain: > 80dB, depends upon cartridge impedance (typically 65dB-75dB)
  • Input resistance – <1 ohm
  • Distortion: < 0.005%, (20 Hz-20 kHz)
  • Channel Separation: >= 80dB (20Hz-20KHz)
  • Output Impedance : <100 ohms balanced
  • RIAA EQ accuracy: ± 0.1 dB, 20Hz-20KHz

USA MSRP – with RIAA EQ:

• Seta L20 Mk2 – $63,000.00. Factory Direct Pricing – $42,000.00
• Seta Models L/H – (L)current mode-MC(FET), (H)voltage mode-MM(bipolar) – $7,598.00
• Seta Lino C2.2 – current mode MC only – $2,699.00
• Seta Piccola mk2 – voltage mode for both MC and MM – $2,748.00

Channel D web site links:

• Seta L20 Mk2
• Seta Model L/Model H
• Seta Lino C2.2
• Seta Piccola mk2

Here is my original post on phono cartridge basics 101.