Product Review - Audio
Electronic Supply AE-2 Preamplifier and SET-II Power Amplifier - February, 1996
By John E. Johnson, Jr.
Audio Electronic Supply Solid State Preamplifier AE-2; T-MOSFET, pure class A, single-ended; gain 15 dB line stage/40 dB phono stage; three separate regulated power supplies; output 10V; input impedance 100 kOhms line stage/47 kOhms phono stage; output impedance 620 Ohms; inputs: phono, CD, Aux1, Aux2 (RCA); outputs: one set of tape-out-RCA, one set of line-out-RCA; size 3.25"H x 15"W x 12"D; weight 9 pounds; black metal chassis; $599; Audio Electronic Supply, 111-A Woodwinds Industrial Court, Cary, North Carolina 27511; Phone (919)-460-6461; Fax (919)-460-3828.
Audio Electronic Supply Solid State Power Amplifier SET-II; T-MOSFET, pure class A, single-ended; power output 20 watts/channel into 8 Ohms; input sensitivity 2.5V; noise and hum -89 dB; frequency response 15 Hz - 45 kHz plus or minus 1 dB; total power supply capacitance 92,000 mfd; size 6.75"H x 16"W x 10"D; weight 23 pounds; black metal chassis; $899; Audio Electronic Supply, 111-A Woodwinds Industrial Court, Cary, North Carolina 27511; Phone (919)-460-6461; Fax (919)-460-3828.
Audio Electronic Supply introduced their class A single-ended tube preamp (AE-1) and power amp (SE-1) about a year ago, with great acclaim. Now, they have a new line of solid state equipment, still class A and still single-ended. The AE-2 is the solid state brother to the AE-1, and the SET-II to the SE-1.
We reviewed the AE-2 and SET-II as a pair (assembled at the factory, rather than in kit form), since they are designed as such. In fact, the instruction manual for the AE-2 states that the direct coupled (DC) output, bypassing a 10 mfd capacitor, should only be used with the SET-II which will accept the 20VDC offset that is output from the AE-2 with these jacks. However, other power amps that are capable of handling DC offset can be used as well (they have an input coupling capacitor). The direct coupled output of the AE-2 is from the drain of a single N-channel T-MOSFET for each side (the SET-II uses two MOSFETS per side, one each for two gain stages). In any case, there are also AC output jacks on the AE-2, which have the capacitor in series with the output jacks for those power amps that cannot handle preamp input with DC offset. Obviously, we connected the AE-2 to the SET-II using the DC outputs. (If this paragraph is confusing, to summarize, just make sure that either the preamp has a coupling capacitor at its output, or the power amp has a coupling capacitor at its input, to prevent DC from being fed through the system.)
There are several drawbacks to class A single-ended tube amps, one being the output impedance, which is high if no negative feedback is employed. A second drawback (tube) is that the frequency response often shows a rolloff at the high end and sometimes a poor bass response (in a real world situation - with cables and speakers - rather than on the oscilloscope). The use of an output transformer in the tube amplifier can exacerbate the problem of frequency response. The third problem is that single-ended tube amps, if they are triodes, have low power output (the AE-1 outputs 7 watts/channel). Solid state amplifiers can have some of these problems, but don't suffer all of them (typical solid state amps don't use output transformers). In listening to the SET-II (which has no negative feedback), we found that there was still a bit of a high end rolloff, but the bass was really quite deep. It is as though the designers were trying to achieve that velvety smooth upper end that the triode counterpart has. The mid-range, while glorious on a triode such as the SE-1, was more laid back on the SET-II. In other words, the sound was more neutral in the mid-frequencies, so singing voices were not as "in your face" as they are with the triodes. Orchestral numbers had more zing to the brass than triodes, yet they were not abrasive (there is no crossover distortion with single ended designs, whether they be tube or solid state). We connected an AE-1 tube triode preamp to the SET-II power amp, and we found that we actually preferred the AE-2/SET-II combination. These two components were really made for each other. We measured 90 dB SPL before the sound began to get mushy, using speakers with 89 dB/w/m sensitivity (Monitor Audio Studio 20 SE) and a CD with a music spectrum of 40 Hz - 6 kHz (small amounts of energy on either side of this range). However, even when the amplifier was obviously clipping, it was not grating on the ears, a testimony to the design of the this power amp. It is apparent that odd-order harmonic distortion is quite low.
On the front of the AE-2, there is an on/off rotary knob, selector knob, and volume control. There are no tone controls or balance control. This is in keeping with the high-end philosophy of having as little in the signal path as possible. The SET-II has an on/off toggle switch on the front and that's it, except for a cool blue SET-II back-lit logo. A blue LED indicates power-on for the AE-2 as well. The connection jacks on the back of the AE-2 and SET-II are all top notch. Gold plated speaker cable binding posts (on the SET-II) are a rarity on power amps at less than $1,000. Kudos. The AE-2 has a 1 amp fuse, while the SET-II has a 3 amp fuse. The SET-II has a noticeable power-on thump. I hate power-on thumps.
The SET-II output is 20 watts/channel, pure class A. This means that it runs hot, dissipating about 80 watts/channel in heat at idle. There is a large heat sink on either side of the amp, but after playing the amp for about an hour, the chassis still reached 134 degrees F. In fact, the back was hot, the front panel was hot, and even the metal handles were hot. This amp must be placed in a very well ventilated area, or trouble will come your way. The AE-2 preamp barely got warm, however. Even though it is also running in pure class A, it has to handle only about 12 watts.
The power supplies of both components utilize toroidal transformers, and in general, both are built with high quality parts: 1% film resistors, polypropylene and styrene capacitors. At your discretion, you can order the amps with oil-filled capacitors, Kimber Kable RCA jacks, and other goodies. Call or Fax them for the details before you order the components, so that options can be installed at the point of original purchase. Our units were shipped basic, with no optional upgrade parts. The toroidal transformer for the SET II was very noisy (mechanical hum), depending on the time of day (load on the AC lines in our area). A power line conditioner might be in order.
Good cables are always a plus, and we decided that Nordost Flatline Red Dawn Interconnects, AudioQuest Diamond Interconnects, and Red Dawn speaker cables gave us the sound we liked best. However, if this is too steep for the budget, AudioQuest Jade Interconnects and Type 4 speaker cables work quite well too.
In summary, the AE-2 and SET-II, while no match for a class A tube triode, have their own distinctive sound personality, and it is a very agreeable one. They work nicely together, and if you should decide to buy, get them both. Class A sound is vogue, and $1,500 for a class A single-ended preamp AND power amp is music to the wallet.
John E. Johnson, Jr.
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