xm26 tube electronic crossover network kit

#Xm26 tube electronic crossover network kit full#
#Xm26 tube electronic crossover network kit Pc#

R16 and C16 provide the 50Hz (3180µs) RIAA rolloff pole. R14 is needed to stop a 40MHz oscillation involving U2 and/or U3. U2 provides selectable gains (7.2dB for MM, 27.2dB for MC, at 1kHz) and has a flat response to audio it’s -3dB at 2MHz in MC mode, from C12, which ensures HF stability.ĦL6G 6SL7 6SN7GTB 6V6GT 12AX7 12AX7/ECC803S 5881 6550 KT66ĪudioXpress September 2007 colin2774-2.indd 7 Together, they’re down 3dB at 4.7Hz, in addition to eliminating DC offset accumulation. Close enough for vinyl record-setting!Ĭ10 and R8 form a 3.0Hz high-pass rolloff, as does the C15/R13 combination at the output of U2. (Who am I to argue with a record-setting astronaut?) This rolloff is -0.64dB at 20kHz, hence the above (doubtfully audible) 0.65dB boost. I say “normal,” because, as Norm Thagard1 points out, record cutter heads use a 50kHz rolloff pole to protect the modern kilowatt liquid helium-cooled mechanics from RIAA pre-emphasized ultrasonic transients. The net result is that at 20kHz the response is +0.65dB with regard to the normal RIAA curve. Pensated for by the R9/C11 rolloff before the second stage U2. However, R7 (and the non-inverting configuration with R3) cause the -20dB/decade slope to flatten with a transmission zero at 35.6kHz, where Xcg = (R3//R6) + R7 2:10 PM = 44.7Ω. R6, R7, C9 form the 2122Hz RIAA rolloff (where the reactance of C9 equals R6 + R7 = 750Ω). R5, C6 form a 10kHz pole, but the high loop gain through Q1 extends this to well above 100kHz. R5 gives U1 DC stability, while R4, C5, and C6 provide HF stability (the AD797 is capable of 110MHz oscillation, so you must closely ground C7 and C8). But the connection through R6, R7, C9 to the JFET source (and R3) is overall inverting, providing negative feedback (NFB). The paralleled JFETs (Q1) are ACcoupled into the inverting input of U1, whose output is non-inverting with reference to the input signal. Output) divided by 9.13µV RMS (“A” weighted output noise), which is 118dB, in MM mode (98dB in MC mode). Overall, the preamp’s own dynamic range (apart frompage cartridge noise Classic Tubes_half 5/10/07 limitations) is 7.2V RMS (maximum Thus, the MM/MC gain switching can be done in the second stage, allowing the all-important input stage to be optimized as a “fixed gain cell” of very high dynamic range. The input stage (and the entire preamp) can accommodate this, while the input gain (35.7dB at 1kHz) is high enough to amplify MC outputs (0.5mV at 5cm/sec typical) well above the noise level of the following circuitry. Norm Thagard1 reports that Shure Labs found velocity peaks of 25cm/sec at 1kHz and 50cm/sec at higher frequencies. This minimizes the gain range (over frequency) required, allowing enough gain at 20kHz to maintain a good overall noise figure (NF). Note that the input stage provides only the 2122Hz (75µs) rolloff portion of the RIAA de-emphasis. As is, the 1kHz gains are 43.8dB (MM) and 63.8dB (MC). If desired, you can easily change the MM and/or MC gains. Stage this is because of the comfortably lower required closed-loop gains. Additional benefits are independence between MM/MC gain switching and the RIAA equalization, and lower distortion than a two-įIGURE 1: Block diagram overall 1kHz gain = 43.8dB (MM), 63.8dB (MC). 1) is configured to avoid noise degradation by circuitry following the input stage, particularly at high frequencies where the RIAA rolloff results in the lowest gain. The three-stage design (see gain partitioning in Fig. Passes the sonic “intrinsic fidelity” test (described later).įor those interested in obtaining the naturalness and resolution that LPs are capable of, this phono preamp provides excellent reproduction and resolution over a very wide dynamic range. Typical headroom re 5cm/sec is 19dB at 1kHz, 36dB at 20kHz. Preamp dynamic range is 118dB (MM), 98dB (MC). Instant MM/MC switching, no “tweaky” circuitry, no adjustments.

#Xm26 tube electronic crossover network kit full#

0.002% THD, mostly 2nd harmonic, full spectrum. Low noise over the full spectrum, not just averaged. MM, 75dB with MC, and 89dB with high-output (2.5mV ) MC, re 5cm/ sec. Omeone writing to Stereophile complained that vinyl can’t provide sonic fidelity, because this “primitive system uses physical contact.” Apparently this writer isn’t aware that vibrating strings, and so on, physically contact the air, which physically contacts your eardrums! Sound quality is extremely natural, transparent, and dynamic. The LP 797 Ultra-Low Distortion Phono Preamp A JFET input and ultra-low distortion AD797 op amps provide excellent full-spectrum noise figure, headroom, and RIAA precision.

#Xm26 tube electronic crossover network kit Pc#

PLUS DIY PHONO PREAMP WITH ULTRA-LOW DISTORTION ALL ABOUT BENDIX TUBES PC BOARD WORK MADE EASIER Cover-907.indd 1 Tube, Solid State, Loudspeaker Technology EASY WAY TO PLOT ANODE CHARACTERISTICS S E P T E M B E R