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TM-5 All-Pentode Vacuum-Tube Guitar Preamp (N.O.S.)


  • $ 84900

This Metasonix TM-5 is a N.O.S. (New Old Stock) item which was discontinued in 2009. The TM-5, like all Metasonix products, was lovingly handcrafted in Lakeport, California (by fairies).

The TM-5 uses an all-vacuum-tube circuit which is unlike any other. Because it is unique, its sound is thick and powerful--and its features are different from ANY other preamp meant for guitar, past OR present.

The TM-5 contains three tubes in the signal path:

1. First in the path are two pentode type tubes for gain--lots of gain! We use NOS pentodes only. Pentodes have a nice, strong sound, especially at clipping. They have lots of voltage gain. Their screen voltage may be varied to change the tube's gain. And pentodes don't need huge plate voltages to sound good. The pentodes in the TM-5 operate on a 70-volt DC supply--they don't need 250v or more, which most triode tubes need. We don't use 12AX7s because the tonal effect of a 12AX7 is very, very well known--and we HATE it. Soft, mushy, indistinct, weak. The only way to "improve" a 12AX7 preamp is to put costly NOS tubes in it, and even that is only an incremental improvement! Pentodes were used in the first generation of guitar amps and professional audio equipment, almost exclusively. 12AX7s replaced them in the 1950s, purely for economic reasons--NOT for better sound!

2. Then the signal passes through a special tube. The "BN6" was originally developed by Zenith in 1948, to act as an FM detector in table radios. It is a special "beam modulator" device, roughly similar to a pentode with a very weird structure. It gives asymmetrical clipping, which may be adjusted by varying the voltage on its screen grid. BN6es have NEVER been used in audio amplifiers before, so far as we can tell. The TM-5 can accept any of the usual three versions of this tube--it comes in different filament voltages, 3BN6, 4BN6 or 6BN6--without changing anything in the TM-5 circuit. (They all have the same behavior in this circuit, we merely provide this option to allow the use of any of the listed NOS types.) The result is a unique "buzzy" tone, which heavy rockers will find invaluable.

In case you are wondering, the TM-5 is DESIGNED to process guitar signals to properly drive our TM-1 waveshaper. So the TM-5 and TM-1 are made to work together.

3. Finally, the signal passes through a buffer to provide a low output impedance of 1k ohms. The BN6 tube output, which is very strong, is fed to a peak detector and filter to provide an envelope output (a DC voltage which tracks the output level of the preamp). This envelope voltage can be used to effect other analog-synthesizer circuits.

Sample sounds of TM-5 with guitar

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