"Trumpet" Vacuum Tube Phono Preamp (discontinued)
The Trumpet phono preamp is a reference quality unit for the most demanding of audiophiles. It's main features are fully balanced operation and switchable polarity. Housed in a single chassis, the power supply is mounted well below the amplifier (about the same height as separate stacked boxes). Eight hand-matched Russian vacuum tubes complement the nearly dual-mono construction of the amplifiers.
The Trumpet implements a number of unusual circuit topologies and tricks to improve performance (way too many to list here). The highlights are: bipolar high voltage power supplies that are fully choke regulated (continuous current), choke regulated dc heater supply, class A differential long-tailed gain pairs, current source loaded cathode follower outputs, passive shunt power supply regulation, split RC equalization, and no feedback anywhere. Frequency response is tremendous, flat from 5Hz out past 250kHz. Distortion is exceptionally low at 0.03%.
Premium components are used throughout. Gold-plated connectors, sockets, and switches, audiophile-grade polypropylene coupling capacitors, metal-film resistors, soft-recovery diodes, film bypass capacitors, high-grade 0.063" thick aluminum sheet metal, cork/rubber damping, and the option of computer-engraved gold-anodized aluminum faceplates or hard maple wood panels (the original).
The chassis is a marvel of anti-vibration architecture. Circuit boards are freely hung like suspension bridges from solid support towers. Acoustic cork rubber is attached to the inside of the chassis cover. Sorbothane feet provide isolation from the mounting surface. Even the vacuum tubes are dipped in special high-temperature paint to reduce microphonics. And that's just the obvious. Look closer and you will find all transformers and chokes on nylon mounts, modified tube sockets that are actually bolted to the circuit board, and o-rings under large capacitors. In addition, the chassis benefits from an inherent chimney effect for enhanced convection cooling and increased airflow past the tubes. The sheet metal chassis forms a complete electric field shield around the electronics (with the exception of the exposed tube plates) with careful attention paid to internal shielding and grounding.
For more information, read my personal review, Michael Fremer's Stereophile review, Scot Markwell's (TAS) online web review, Dave Clark's Positive Feedback review, George Valley's Positive Feedback review, or these posts on audioasylum #1, #2, #3, #4, and audiocircle #5. Also some actual customer testimonials.
|Input Impedance||47k ohm plus 36pF|
|Output Impedance||750 ohm|
|RIAA Response||+/-0.5dB from 20Hz to 20kHz|
|Bandwidth (-3dB)||5Hz to 250kHz|
|SNR||74dB ref 5mV A-weighted|
|Overload||250mV @ 1kHz, 1% distortion|
|Power Consumption||70W (120Vac only)|
|Size||7" wide x 12" high x 12" deep|
|Tubes||12AX7 (ECC83) x 4, 12AU7 (ECC82) x 4|
"The Trumpet proved competitive in direct comparisons with the Lamm Deluxe, with an open, airy, detailed, and thoroughly intoxicating sound ... bass was very well-controlled, texturally coherent, and exceptionally nimble ... pacing and rhythmic flow were stellar ... In short, the Trumpet sounded stunning, and was a total pleasure to listen to - which is what I did for hours." - Michael Fremer
"I was particularly impressed with the overall lack of noise. Given that it is a pure tube unit, I expected more hiss and hum. But Hagerman's balanced circuit design and his meticulous attention to all details of noise isolation and tube heating have paid off in a superbly low noise floor and ravishing low-level detail retrieval ... best dynamic authority I have heard on anything short of my Plinius M-14 ... a really beautiful liquidity and utter lack of grain in the midband ... just correct harmonic integrity, excellent background silence, realistic dynamic contrasts, and a remarkable freedom from coloration ... the Trumpet is exceptionally quiet, and an outright bargain of the finest kind at the asking price." - Scot Markwell
"The Trumpet ... was big and dynamic, with a well controlled and powerful bottom end, along with a speed and clarity across the midband that was truly captivating ... The Trumpet had that 'solid state' sound with respect to soundstaging, dynamics, slam, etc., but none of the tradeoffs. It was a smooth and palpable performer that offered an extended and airy treble without a hint of grain, grit, or transistor hardness." - Dave Clark
Not only does this amplifier sound good, it measures good too! Careful attention to circuit design and phase linearity resulted in extremely good equalization characteristics. The recovered audio signal (from an LP) boasts a very flat frequency response with excellent time-domain performance. The following oscilloscope photos show the square wave recovery (this is the acid test, folks! - something a loudspeaker manufacturer will never show you) is near perfect. The bandwidth limiting is due to a special 32kHz low pass filter I used on the input signal. The actual -3dB bandwidth of the Trumpet measures out to several hundred kHz.
Distortion is vanishingly low: 0.03% at 1kHz. Such performance is suprising considering there is no feedback used in this amplifier. The photos show the distortion spectra for 50Hz and 1kHz signals. On the 50Hz test there is just a hint of 2nd order distortion, maybe some 60Hz hum in the skirt, and then a trace of 120Hz hum. But pretty darn clean. At 100Hz the total distortion measured 0.3%, and 0.2% at 10kHz. Note the 1kHz spectrum is perfect, all harmonics are lower than the noise floor of the instrumentation.
However, these are continuous test tones. How does it fare with real music? For this test I used the output from a CD player (Stereophile's "Intermezzo") into my inverse RIAA filter and through the Trumpet. I compared the raw CD signal with the recovered signal from the Trumpet. They are spaced apart vertically for clarity. There are no discernable differences in phase or amplitude. Second photo shows the two traces on top of each other. Yes, that is two separate traces! Perfect performance, at least with test equipment. But hey, if it doesn't measure good first, it's flawed.
StepUp Transformer (discontinued)
This phono step-up transformer accommodates use of low output moving coil cartidges with the Trumpet. It is based on the superb Stevens & Billington TX103. The chassis design copies the Trumpet in both appearance and anti-microphonic qualities. Output cables are hardwired to chassis not only for convenience, but to optimize reflected capacitive loading seen by the cartridge. Keep in mind here, that at 10:1 gain, every foot of output cable is equivalent to 100 feet of input cable. You wouldn't want 100 feet of cable loading your cartridge! That's why output cables are cut as short as possible. Now if you prefer your own cables, you can send me one and I will personally hardwire it into the unit, or I can build the chassis using female RCA jacks (no cables). Gain can be factory set to 14dB, 20dB, or 26dB.
When used with a Trumpet, I recommend using 26dB gain for cartridges of 0.05mV to 0.25mV, 20dB for 0.25mV to 0.75mV, and 14dB for 0.75mV to 1.5mV. Cartridges with higher outputs do not require a transformer.
|Gain||+14dB, +20dB, +26dB|
|Input Impedance||1900, 470, 120 ohms|
|Bandwidth (-3dB)||5Hz to 150kHz|
|Size||7" wide x 4.5" high x 5" deep|
Below is the EQ response of new step-up prototype and Trumpet (system gain 64dB). Top trace is input, bottom trace output. This is near-perfect EQ.
But that doesn't show the true wideband story. Below is the unfiltered input. Bandwidth into my trusty HP-333A was an astounding 4Hz up to 150kHz! There is a resonant 4dB peak at 130kHz caused by transformer loading and ringing.