Vintage Alembic F-1X All-Tube Rack-mountable Bass (or Keyboards) Pre-amp

This 1 rack-space (1u) pre-amp is an amazing piece of sonic history. The premium rich, warm bass guitar sound from these units set the standard when it was introduced and is one of the Holy Grails of vintage tube pre-amps.

I am selling this mainly because I no longer use rack gear live. It has the usual dings and scratches you would expect from a piece of this age. I just had it gone-though and tested by my tech.

Below I've included some great info I found on the web; the manufacturer's description, and a subjective review on RexBass dot com. I hope they are helpful!

Description from Alembic:

The F-1X gives you a unity-gain impedance matching amplifier to feed guitar-level effects units. The effects return goes thru the tube gain stage and then to the tone controls. The signal from the tone controls is amplified and sent to the full-range output jack on the rear panel. This same signal is also fed to the crossover network. A transformer-isolated output feeds a 3-pin Cannon jack.

Circuit detail:

Two input jacks provide the same functionality as found on the F-2B preamplifier. The input is buffered by a cathode follower tube circuit, which is a unity-gain impedance matching amplifier to feed the guitar level effects loop. This gives minimum loading on the output signal from the guitar while driving the effects loop gear with the same signal voltage level as the guitar but at a lower impedance, to isolate cable and other loading effects from the guitar pickups.

The other half of the 12AX7 tube provides the preamp's gain. This gain comes before the volume control and the 300 volt supply assures that even large transients are handled without overload or distortion. The tone controls are the interacting Fender circuit. The bright switch shunts high frequencies around the volume control. The deep switch changes a capacitor value in the bass control to change the frequency response (and a second section on the deep switch changes the gain of the following amplifier to compensate for the resulting change in signal level).

A solid state circuit restores the signal level after the volume control and provides impedance matching to drive the full range output jack on the rear panel. Additionally, it drives the crossover network. The active crossover network provides 12 dB/Oct slopes to divide the output for bi-amping. The crossover points occurr at 6 dB down so that the acoustic signals from the loudspeakers add seamlessly. A front panel control trims the high-frequency signal component to match the level of the low frequency output.

A transformer-isolated balanced output to an XLR type connector provides auxiliary Recording or PA feed. A switch selects the source to be the effects return (Pre) or the full range output (Post). The transformer is large enough to handle the low-frequencies without distortion to give good clear lows and a resistive pad isolates the transformer from loading effects of long cables to give clear highs.

The heater of the 12AX7 tube is supplied by a regulated direct current supply to assure low hum. The AC Line (Mains) connection is an IEC (computer-type) detachable cord. The supply voltage can be changed by moving jumpers inside the unit to operate from 100, 120, 220, and 240 volts for operation anywhere in the world. The F-1X is housed in a sturdy, road worthy, steel enclosure.

Web Review:

The F-1X is not a stand-alone unit, and you will need to use it with a power amplifier, and probably some sort of quality equalizer (more on the EQ in a bit). This pre-amp fits into a single standard-sized rack space and just oozes handmade quality. The case is made out of heavy gauge powder coated steel, and it has an impressive heft. All of the pots, jacks and switches are quality components and they are easily serviceable. The power cable socket is the heavy-duty removable IEC C-14 type, so different types of power cables can be used. It is switchable for the different voltages that are used overseas and a jumper lead inside the chassis will need to be moved to accomplish this.

It is not terribly complicated to use. On the front you will find two input jacks, a volume knob, three tone controls (bass, middle and treble), bright and deep switches, a direct out socket, direct out pre/post and ground switches, and crossover frequency and level controls. Alembic put the power switch, a full-range out, high and low crossover outs and effects loop jacks on the back. That’s it!

Using the F-1X is straightforward once you know what everything does. The two inputs are not the same, as input 1 is a regular input and input 2 is padded by 6dB. It would be nice if Alembic labeled these inputs to indicate this. The volume knob controls the level of the full range and crossover outs.

The tone controls can be a little confusing, as they a passive interactive type, so it is important to know how they are wired. When one knobs is moved, the other two will not remain the same. So, if you want more treble, you can accomplish this by turning treble up, or by reducing the bass and mids. There really is no “flat” setting, but Alembic says that setting the knobs to 2:00 (bass), 10:00 (middle) and 2:00 (treble) will get you the closest. Many users are unable to get as much EQ adjustment as they want, so they usually add a quality EQ to their rack system.

The bright switch boosts the extreme treble range, and is progressively less effective as volume is increased. The deep switch cuts the lower midrange and leaves the lower frequencies untouched. The deep switch really tightens up my tone, and I find that I rarely use the bright switch.

It is nice to have two output choices, you can have the option of running a bi-amped or running a simpler single amplifier system. I only have one power amp, so I have only used the full range out, but the crossover system seems simple enough. There are high pass and low pass outputs that are controlled by a crossover frequency knob that might not work like you think it would. It allows you to select a frequency at which: above the frequency, low pass output decreases 12dB per octave and below the frequency, high pass output decreases 12dB per octave. The high level knob can change high pass output by a range of +/- 10dB to obtain more equal speaker cabinets volumes.

All of these neat features don’t mean much if the unit does not sound good, but there is nothing to worry about in that department. I did not mention that this is a tube-driven unit, did I? The F-1X is loaded up with a 12AX7 tube to provide the pre-amplifier’s gain. This is situated before the volume control and is powered at 300 volts to allow plenty of headroom for large transients without distorting.

This preamp sounds incredibly warm, and goes a long ways towards attaining my perfect bass tone. The low end is very round, and very punchy mids can be dialed in. This kind of warmth and natural sound is hard to come by, but Alembic has put together a very good package. Don’t mistake the Alembic F-1X with the cheaper amps you have head with tube pre-amp stages. This is the real deal, and provides real tube tone and characteristics.

I have also had good luck using the F-1X as a DI box, and having the XLR out, ground lift and pre/post switch on the front are a godsend, particularly with a rack-mounted piece of equipment. On the other hand, having the power switch on the back of a rack mount unit is a pain in the butt, and I do not buy Alembic’s rationale that everybody uses power conditioners. I still want to be able to get to the power switch easily.

The Alembic F-1X pre-amplifier is built to last forever and sounds wonderful, and of course it is not cheap. The list price on these is $1375, and the cheapest price I found online for them was $1099. Not many retailers carry them, and they do not show up very often on the used market. But, if you crave a wonderful tube pre-amp there is no substitute.

Review from RexBass dot com