Tuesday, September 20, 2011

A Visit with the B&K Pro-5 preamplifier

The interest in my hobbies wax and wane depending on what else I am doing with my busy schedule. Lately I have been writing, publishing, weightlifting and enjoying time at the beach. With the end of summer, I suddenly had the urge to mess with some audio gear. Since I needed a ‘backup’ to use in case my vintage Threshold FET-10/HL or Audio Research SP-7 preamplifier went down for repairs, I opted to buy a full-function unit. With a B&K ST-140 already in the stable, why not try a matching preamplifier? So I went and bought a B&K PRO-5 for $195 via Audiogon.

Upon arrival, I opened the box and was greeted by a nice looking unit. The gold lettering, handles, and black faceplate are conservative in an 80s kind of way. The back has a number of RCA jacks that appear to be of questionable quality – they look nickel-plated and are soldered directly to a rear-mounted PCB board. The selector switch has a nice solidity, but the other controls feel on the low-rent side.

Cracking open the case, I found the parts quality to be rather pedestrian. For example, the volume, balance, treble and bass pots are small carbon units that look like something you would find on a 1970s receiver. The power-supply is a joke with a tiny transformer, a pair of 1000uf capacitors, and a pair of 15V regulators. The phono stage uses a few capacitors, FETs or transistors, and some op-amps involved. The same is true of the linestage and tone-controls. There really is nothing here that screams AUDIOPHILE with big bold letters, but let’s see how the B&K PRO-5 sounds.

Removing the ARC SP-7 from my second system was easy enough. I then hooked up the turntable to the new preamp phono input and then connected the line outs to the ARC D-52B amplifier. I switched on the preamplifier and the front rocker light turned on with a pleasant glow. With my first record, I was greeted with sound alright, but the left channel was missing. I wiggled the back RCAs and *pop* I started getting sound out of both channels. Obviously these RCA jacks are going to be troublesome for long-term use.

As far as sound in active mode with the tone-controls bypassed, the B&K PRO-5 has a pleasant, slightly warm sound. Some treble detail is a little glossed over, but the bass is good and punchy. Overall depth and soundstage width is a little squashed, but this is certainly a better overall-sound than many other budget preamplifiers I have heard – which is quite surprising considering the lack-luster parts quality. But if there is anything that I have learned from this zany hobby - it’s that you have to trust your ears and not your eyes.

I mentioned the ‘active mode’. You see, the PRO-5 allows you to bypass the active linestage with a push of the button. In this passive mode, the gain understandably drops and you have to crank up the volume control to get the same output as before. But the sound, though less punchy, becomes more neutral. It’s almost like having two preamplifiers in one box. As far as what sounds better – that’s entirely up to your system and musical tastes. Perhaps it is the psychological effect of having to turn up the volume control so much, but I preferred the active linestage for most of my pop/rock music. With classical music CDs, the passive section was given the nod.

In overall quality - both sound and mechanical - the Audio Research SP-7 still wins. It is a little brighter and brasher in comparison, but the overall sound is more neutral. Of more importance - especially in a system that is heavily used by my family - the ARC has much more solid connectors plus a positive volume and selector-switch action.

Note - during my listening sessions with the B&K Pro-5, I found the RCA connections to be very problematic. Later versions apparently used better parts, but for owners of the older model, you are stuck with some very poor connectors. Replacing the RCA jacks with something sturdier looks like a difficult task, but I’m going to give it a try. So stay tuned for a future update.

Second System:
Preamplifier: Audio Research SP-7
Amplifier: Audio Research D-52B
Analog: Dual CS-5000 turntable - Audio-Technica AT95E cartridge
Digital: Pioneer DVD-V7400
Speakers: KEF iQ30
Speaker Cable: Canare 4S11 Quadlink
Interconnects: Cardas Crosslink