Monday, December 5, 2011

Bi-Amping the Magnepan 1.6QR speakers

When I bought the Yaqin amplifier, I was impressed by the fidelity.  But since it didn't have enough power to drive the Magnepans 1.6QRs, I considered selling it.  Instead, a friend of mine suggested that I bi-amp.  Since then this has been on my to-do list for the past couple of weeks, but I've been busy with some other pursuits. But I recently had some free time and finally gave this a spin. First of all, my Threshold FET-10/HL preamp only has one set of outputs. Since I wanted to roll off the bass for the treble amplifier, I took one of the tape outputs, added in an in-line capacitor (calculated at .02uf for the 20k input impedance of the treble amplifier), and essentially made another set of outputs by paralleling it with the standard line out.

The bass amplifier was a Threshold S/500 - a powerhouse that has long been one of my favorite amplifiers. This amplifier will run full-range into the bass panel, where the stock crossover is still doing its thing.

The treble amplifier is the ultra-budget 50WPC Yaqin MC-10T with a coupling capacitor upgrade, 1950s-era Tungsol 12AT7s for the input tubes, Mullard CV4024s for the phase-splitter, and real Mullard XF2 EL34s.   The volume pot allowed me to match levels (by ear) with the Threshold amp. Extra speaker and interconnect cabling for this was a mish-mash of wire from my junk drawer.

I was immediately struck by the increase in fidelity - since the bass is rolled-off for the tube amplifier, it never seemed to run out of power. The sound with the stock setup (Threshold amp) has always been very good, but now the combination is 'the best of both worlds' - the bass definition and control of a big SS amp with the extended/clean treble of tubes. The soundstaging also had a more 3-D effect.  There is also less grain and less apparent distortion, the music sounding less forced and breathing with a graceful easiness.

One of my good audiophile friend came over and we took the chance to do listen to several records - Donald Fagen - The Nightfly, Fleetwood Mac's s/t, Pink Floyd - Animals, some Creedence, etc etc - and bi-amping has been a major, almost mind-altering improvement. The amount of detail, depth and sheer musicality has been greatly expanded. I really didn't expect this level of fidelity from the change, but I can't imagine going back to a single amplifier. With the big SS power driving the bass panel and the (bass-limited) tube amp driving the tweeter, a very good system suddenly became great.

I'll have to do some more listening, cable swapping, and tweaking - but so far I like what I'm hearing, making me afraid to do any radical changes. In the future I would like to remove the passive crossovers of the Magnepan and use an active one instead.

preamp: Threshold FET-10/HL modified for bi-amping
phono preamp: Audio Sector Phono Stage
amplifier: Threshold S/500 (bass) and Yaqin MC-10T (treble)
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - modified Denon DL-103R
speakers: Magnepan 1.6/QR with Sound Anchor Stands
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C

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