VAC Renaissance 30/70 - Manual (Page 9)

7
TIPS & ADVICE
A Word About Low Level Tubes
The Voltage Amplifier/Phase Splitter and driver tubes in the Renaissance Seventy/Seventy is the 6SN7 medium mu octal
twin triode. Your amplifier is fitted with the current production British/Chinese Golden Dragon, which we find superior
to the NOS types we have tried. There are dozens of versions of this tube available in new old stock (NOS) from a variety
of sources. It would be impossible to characterize them all. The usually are not terribly expensive, and may be worth
experimenting with. VAC welcomes your comments.
One NOS variant worth mentioning is the RCA "Special Red" industrial version 5692. These represent the pinnacle of
RCA's tube knowledge.
Other equivalent type numbers are 5692, 13D2, B65, ECC32, QA2408, QB65, and CV1988.
A Word About Impedance Matching
We strongly suggest that you experiment with the three available impedance connections for the best sonic match with
your system. Since no loudspeaker represents an unchanging impedance at all frequencies, it is impossible to assert with
certainty which output tap is appropriate to use. In many systems an amazing difference in sound will exist between the
various impedance taps.
Since the impedance of most loudspeakers vary over a wide range experimentation is essential. We often find that
matching a speaker's minimum impedance is more important than matching its nominal (average) impedance.
If you bi-wire your system (run separate speaker leads from the amplifier to the high and low frequency transducers)
you may discover that two different impedance taps work best. For example, with early production Martin Logan Sequel
II we find that the bass speaker is best matched with the 4 ohm tap, while the electrostatic panel is best controlled by the
2 ohm tap. On later production Sequels we use the 4 ohm connection to both drivers.
Contrary to popular misconception, no power is lost due to unused output taps. Also, the amount of negative loop
feedback in the amplifier does not change, being fixed at approximately 8 decibels for all output taps. For more
information consult VAC Technical Monograph 90-9.