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Tubes Asylum: REVIEW: Electronic Tonalities Foreplay Preamplifier (Tube) by Tom S.

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REVIEW: Electronic Tonalities Foreplay Preamplifier (Tube) Review by Tom S. at Audio Asylum

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Macrodescription:
This kit costs $99 for parts and pre-punched aluminum chassis plate. You can make your own base or buy a precut,unfinished wood base kit from ET for $29. The kit uses two 12AU7's, one for each channel. There are three inputs and one output.

Parts Description:
The kit uses two mono-volume control pots, one for each channel. I didn't want to constantly balance each pot every time I wanted more or less volume so I put in an Alps potentiometer from Angela Instruments (not the only thing from them that I put in the kit). The kit uses 1% metal film resistors, Nichicon power supply capacitors, metallized polyester coupling capacitors, and (in my kit) RCA clear top 12AU7's. The power trannie
is a custom job. The builder has to supply solder (2% silver reccomended) and hookup wire. I used some solid core silver coated copper that was readily available.

Circuit Description:
This is a very simple point to point wired circuit. The input voltage is attenuated by the potentiometer onto the control grid of the voltage gain stage section of the tube. The output of voltage gain stage is wire(!) coupled to a cathode follower stage. A capacitor couples the cathode to the output. The FWBR power supply filter is a psuedo double pi-type: cap-resistor-cap-resistor-cap (all caps are to ground with resistors coupling the caps together). The heaters are AC powered direct from the power trannie.

The Build:
I had more difficulty getting the hardware together than wiring the circuitry. For awhile, I couldn't figure out how the ceremic tube sockets stay in place until I tightened the the fastening nuts which bent the tube retainer ring in place (I'm not mechanically gifted). I really appreciated the pre-puched chassis plate. There are times at my own job when I have to come up with a filter circuit in a project box and it is a bitch getting the holes drilled in the right spot for a perfect fit. The wiring was a different story. Getting point to point wiring done correctly is easy but tedious. I did learn a few pointers like running signal wiring perpindicular to the AC heater wiring to reduce hum.

Subjective Analysis:
Every peice of music that I ran through the preamp to the sony receiver sounded smoother and refined. While the receiver/foreplay combo does not sound as good as the modified Jolida 302B I have been using, the music does become less listenable (harsh, in-your-face) w/o the Foreplay hooked up to the receiver. The sonic character of the combo did change with tube brands. The included RCA clear tops sounded very smooth and laid back when compared to other tubes used. The E.German AU7 offered more detail and crisper vocals without sacrificing tube warmth. The Holland Amperexes brought a sweet balance of detail and smoothness.

Mods To Original Kit:
I already explained the reasoning behind the potentiometer mod. The other mod I did was replace the cheapo green coupling capacitors with copper foil in oil caps from Angela Instruments (they really look nice when you peak under the cover). The copper foil caps brought even more smoothness to the midrange but made the low bass info less punchy. The cause of the bass problem could be attributed to the fact that I used a 1µF cap in place of the 2µF coupling caps. Doing some calculations, this does increase the -3dB high pass crossover freq of the output stage. It's no fault of the Foreplay's manufacturer/designer (Doc B.)



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Topic - REVIEW: Electronic Tonalities Foreplay Preamplifier (Tube) Review by Tom S. at Audio Asylum - Tom S. 08:45:57 05/14/99 ( 6)