Blue Circle Audio BC21.1 Tube Preamp with Stepped Attenuator
Super rare and unique tube preamp from Canadian maker Blue Circle.
Features a unique and highly regarded stepped attenuator for volume control which many swear is the best and cleanest approach to volume control.
This unit has been fully tested in our lab and listening room, and it is working to spec and sounding wonderfully warm and accurate.
Cosmetically it's near perfect with no signs of use or abuse. The brushed stainless faceplate is intact, and the wooden knobs are free from fingerprint or wear marks.
Includes just the preamp, nothing else. See below for product description.
DESCRIPTION COURTESY OF Hometheaterhifi.com:
The BC21.1 is Blue Circle's entry level tube preamp. It is a simple two-channel design with top notch sonics that could be the center of an audiophile's two-channel system. The design uses a pair of 6922 tubes, which are one of my favorite preamp tubes. The chassis is consistent with the Blue Circle signature designs (thank goodness no red shoes here) and is heavy for its size. The front is polished stainless steel, and the rest of the chassis is made of heavy gauge metal.
The BC21.1's wooden knobs control volume, balance, and selection of three inputs, while the small toggle switches control the tape loop and power. To keep with the wood theme, instead of rubber feet, the BC21.1 sits on top of three wooden feet, which means you will never end up with the matchbook under the table leg scenario even if Gilbert's feet are not cut to perfect tolerance. The single ended RCA inputs are gold plated and of high-quality.
The BC21.1 uses a standard IEC detachable power cord, which will make it easy to upgrade for those of you who believe in that sort of thing. Input labeling is silk screened both right-side up and upside down. This can be particularly useful when looking over the top of the unit. The large control knobs of the BC21.1 give a sense of very fine adjustment, somewhat similar to a large knob on an old tuner.
For volume control, the 21.1 has three options. The base option is a standard pot which can be upgraded to an RF based remote control pot or a Shallco 31 point stepped attenuator. For those of you not familiar with stepped attenuators, they control volume by using a single resistor for each volume setting. This eliminates using a carbon or conductive plastic pot which may have less then desirable sonic properties. It also allows for almost perfect left and right channel tracking if high tolerance resistors are used. Both the standard pot and the Shallco version were tested during the review period.
Sonically, the standard pot was adequate, but had two issues in my setup. It was much too sensitive with amplifiers with both of my solid state amplifiers. Secondly, it did not track the left and right channels together at very low volume. Using my Sonic Frontiers Power 1, a tube amp, with a much lower power rating than the solid state amps I had no problems with the stock volume pot. However, using solid state amplifiers such as my B&K or Anthem, the pot was far too sensitive and usually in a location which exhibited poor linear tracking. The problem is cause by the overall gain of the amp and preamp combo being substantially higher with the solid state amps. This problem is easily resolved by adding a resistor to Blue Circle's point-to-point wired equipment. If a customer experiences this problem, Blue Circle will make the necessary circuit change.
The Shallco pot on the other hand worked perfectly with both solid state and tube amplification. Gilbert claims to have taken years to figure out the perfect resistor values to work optimally with all types of amplifiers. The Shallco is set up using a non-linear ramp such that the attenuation points near the bottom are more sensitive than the ones at the top. This works perfect in my situation where I need small adjustments for late night listening, but stretching a couple of dB in either direction will not make much difference at loud volumes.
Although there was a 2-3 week gap while the Shallco was installed, I do feel there was a sonic improvement. My personal recommendation is to buy the Shallco up front, you will not be disappointed. However, if you do purchase the stock pot it can be upgraded at a later date.
Blue Circle also offers a remote control option with the BC 21.1. This involves using a motorized conductive plastic pot, which has similar sonics and issues as the stock pot, but is controlled via an RF based remote control. Yes, I said RF based, so you can control the volume from another room. Blue Circle does not necessarily recommend this option as they believe the Shallco provides the best sonic performance, but they do realize some users, such as my wife, would rather have the remote than ultimate sonics.