May 2002

Andy Bartha's Amanda Monoblocks

Review by Wayne Donnelly
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Photos by Leonard Norwitz

  Andy Bartha is a clever and resourceful independent engineer who lives in south Florida. His primary business is doing modifications, notably to inexpensive Pioneer DVD players. I have two of those players, and will be covering them in a future review. But Andy has also designed and built some interesting products: The amplifiers being reviewed here, and a silver-wired moving-coil step-up transformer (review also in progress). Martin G. DeWulf has reviewed these compact monoblocks in Bound for Sound under the name "m" -- understandable, as that is the only identification on the front panel. That letter is actually intended to signify the MUTE position of the front panel toggle switch. Andy advises me that he has now dubbed these the "Amanda" monoblocks, after his partner's daughter. Works for me.

Keep It Simple...

The Amanda is designed around a single National Semiconductor LM3886 Overture IC. This amplifier-on-a-chip handles all basic amplification functionality, input to output. Andy freely admits that his design was inspired by Sakura Systems' 47 Laboratories Gaincard amplifier. He feels that his choice of premium parts and beefier power supplies, resulting in a 50-watt output into 8 ohms, provides a more robust and cost-effective amplifier than the [quite excellent] 47 Labs.

The amplifiers are fully protected from over voltage, under voltage, shorts to the power supply, thermal runaway and instantaneous temperature peaks. The amplifiers are not protected, however, against ON/OF switching transients generated by some preamplifiers. The user should adopt a last-on/first-of procedure in powering up the Amandas. Alternatively, the amplifiers can be left ON and the MUTE switch used as a standby, to be disengaged only after the preamplifier has been turned on and has stabilized. I adopted this latter method, as the amplifiers sound noticeably better when fully warmed up, and warm-up from a cold start could take more than an hour.

I am indebted to MGD's BFS article for the following parts identification. (Our critical conclusions differ considerably.) Surrounding the amplifier chip are FK Blackgate capacitors, Holco resistors, Schottky diodes, separate power supply bridges for each rail, and a 230 VA toroidal transformer. Internal wiring is from Jena Labs. Simplicity rules outside as well. The front panel contains only the aforementioned MUTE toggle and two LED "ON" indicators. The back panel holds the IEC socket, a single RCA input jack, one set of Edison-Price binding posts, and a 3-position Power/Polarity switch. This ingenious switch is one of the best things about the Amanda. In its center position the amp is off. Flipping it up turns the amp ON with normal electrical polarity. Moving it down two clicks, through the OFF position, reverses electrical polarity (also called phase by some folks).

Polarity Matters, Dammit!

Those of you who are already hip to polarity can skip this paragraph. If you don't get it, here's a simple description: A wire carrying AC or audio signals must have two conductors (and a third for ground in balanced configuration, but we'll keep it simple here) -- like that lamp cord we used to use for speaker hookups before we all got religion. One conductor is positive (+), the other negative (-). Proper polarity means simply that the AC cords, interconnects and speaker wires are interfaced positive-to-positive and negative-to-negative to throughout the system. If the polarity is wrong, there's no disaster -- everything still works. Perhaps that's why some contractors and electricians are not overly concerned when wiring a new house. AC outlets wired in reverse polarity are very common. (There are simple tools to help you determine if your outlets are wired correctly or not.)

A lot has been written about how -- and occasionally, whether -- polarity affects audio reproduction. The most persistent apostle for polarity is Clark Johnsen, in his book on the subject, The Wood Effect, and countless articles in the audiophile press. The argument is that the wrong polarity adversely affects the sound of a system. This is not a glaring problem (except to keen-eared zealots like Clark!), and many listeners apparently hear no difference when polarity is changed. But lots of us do, and I think it is something you can learn to detect by listening attentively. Clark would argue that incorrect polarity accounts for much of the malaise that lots of people feel when listening to audio. I would add that the psychoacoustic effect is very like a difference between time-coherent and non-time-coherent loudspeakers -- to which, of course, many listeners are also apparently oblivious.

A CD player or DAC is a good place for a polarity reversal switch, especially because there is no consistency in the polarity of recordings, even sometimes from the same label. (Apparently, many recording engineers don't think it's important either.) A preamp is even better, since that location allows the listener to correct polarity on LPs as well. But a scandalous majority of manufacturers, of even extremely expensive hardware, blithely continue to omit this feature. Now, you can change polarity manually by reversing your speaker cables at one end, or by reversing the component's AC plug (which usually means using a cheater plug and lifting the ground -- not a great solution). But let's face it -- those methods are a giant pain, and nobody is going to do that when going from one CD to another through a listening session.

Andy's combination Power/Polarity switch neatly solves the problem. If you have the Amandas together (they generally run cool enough to stack) and oriented so that the back panel is accessible, it's duck soup to change polarity. Just be sure you pause for one quick beat in the middle, to avoid generating a transient pop. In my setup the amplifiers are located on either side of the central equipment rack, so I have to do one at a time -- but that is not a problem. Hats off to Andy for this valuable feature.

Amanda Improved

The monoblocks under discussion here, while they are the same boxes MGD reviewed, differ in more than just name. Before sending them on to me, Andy made two major modifications. First, he removed transformers that had made the input impedance 600 ohms. That value could be problematic with some preamplifiers, especially tubed designs. The input impedance is now 100K ohms, a common value. I experienced no interface problems with the Amandas.

Andy's other modification was to install eight Bybee Quantum Purifiers inside each monoblock. These little magic bullets have made wonderful improvements in my system, and I have put them into every component save the turntable motor (no room). The Bybee devices were also part of the Pioneer DVD upgrades Andy did for me. I did not have a chance to hear the Amandas in their pre-Bybee state, but given the improvements I have heard, not only in my own gear but also in numerous other components, I feel safe in saying that the purifiers are contributing significantly to the sound of these amplifiers.

Amanda Works Out

Andy says that he designs these amplifiers principally for use with highly sensitive speakers, for which 50 watts is more than enough power. In the Paravicini 312 review in this issue, I mention that the Amandas saw some duty driving the Von Schweikert dB-100 speakers. They acquitted themselves quite honorably in that job, although ultimately the WAVAC EC-300B (at nearly six times the price of the Amandas) proved to be the optimum choice for the dB-100s. After completing my time with the dB-100s, the Meadowlark Blue Herons moved in. The bulk of my auditioning of the Amandas was done with the BHs, and with my Thor TA-1000 line stage replacing the Paravicini.

The BH is fairly sensitive at 90 dB. But as it is a full-range speaker -- whereas the dB-100 has an active bass system which greatly lightens the amplifier's burden -- with a four-ohm impedance, I wondered if the little Amandas would be up to driving the BHs, which love to play loud. Yes, the Amanda's output power rises to 70 watts into four ohms, but that isn't terribly significant in determining how loudly the amplifier will drive the speakers. So for a while I stuck to the gentler end of the dynamic spectrum.

With the excellent speed of both the Amanda and the time-coherent Blue Heron, some very good things happen. Anything with a strong rhythmic pulse takes off. Put on The Blasters [Slash/Warner Bros. BSK-3680 LP], and by the end of "Marie Marie" there's a party going on. The Dave Brubeck Quartet's virtuoso rhythm seminar Time Out [Columbia CS-8192, Classic Records reissue LP] sucks me in completely as the musicians' deft interplay unfolds from track to amazing track. Joni Mitchell's Blue [CZS-1132, DCC reissue CD] just sounds reborn -- that great acoustic guitar on "Carey" demands my seated boogie, with all body parts in motion.

Voices sound great too, at once nicely fleshed out and crisply rendered. From Emmylou Harris to Steve Earle to Rene Fleming to Bryn Terfel, any voice -- even Neil Young, b'gosh -- sounds right, drawing me into the music. (Just kidding, Neil.)

The Amandas handle all of this music with aplomb, even when The Blasters and Steve Earle get to pretty raucous levels. Now for the acid test. How would these little amplifiers do on big-scale symphonic music? I was in for a real surprise. Of all the things I listened to, I'll boil it down to the XRCD2 reissues of two great recordings by Fritz Reiner and the Chicago Symphony Orchestra.

Bartok's Music for Strings, Percussion and Celesta has a huge dynamic range. If you turn it up so the ppp percussion sounds more or less normal, the fff tuttis can get you -- and your amplifier if it's not up to the task. And in Dvorak's New World Symphony, the furious dramatic climaxes -- and especially the heroic brass and percussion -- are even more of a challenge in the power department. So I start at a gentlemanly level, well below my habitual practice, and gradually turn it up. And up. And up some more. But damned if the Amandas are clipping. Finally, I do make them clip, and I assure you it's not a sound you want to hear more than once. Later, inching up near the clipping point, I can hear clearly that the sound begins to show strain, indicated by a flat, glarey quality.

But the Amandas drive these speakers to pretty robust levels, and sound good doing it. The bass is a surprise, with more weight than I expect, and transient speed, less surprisingly, is superb. The midrange sound will not be mistaken for tubes, but neither is it beset by the dryness and excessive leanness of some lesser solid-state designs. The soundscape is decently wide, but somewhat shallower than with my big VTL amps. For the long haul, I would want more power with the Blue Herons, but the Amandas are no slouch, and I thoroughly enjoyed my listening sessions with them. I suspect that they will be dynamite with speakers of about 94 dB sensitivity and up.

Bottom Line?

This part is not easy. As you will have gathered, I really like these amplifiers. But the price as reviewed here (with Bybee upgrade) is $3,500. Without the Bybee mod they are $3,000. Since the $500 differential is less than just the retail price of the Bybee purifiers, the upgrade should be a no-brainer if you're interested in the amplifiers. Even without a comparison, I'll go out a little way on a limb for that assertion. There are lots of amplifiers around this price point, many of them with more power than the Amandas. But if your need is not principally for power, these refined and very musical amplifiers are definitely worth consideration.

You will want to try some good power cords. I found significant sonic changes from the four I used. I would also recommend some aftermarket support/isolation gadgets. The stainless steel craft-box-looking enclosure is quite sturdy, but the little square stick-on feet are just a placeholder for something better. I get very good results with both compliant feet (Navcom) and solid cones (Goldmund and Polycrystal), with attendant small sonic changes that amount to matters of taste.

These amps look a bit rough-hewn, but their performance is silky and subtle.

Specifications

Output power into 4 ohms: 70 watts
Output power into 8 ohms: 50 watts
Instantaneous peak power: 135 watts
Frequency response: 20-100K Hz, +/-1 dB
Input impedance: 100K ohms 
Total harmonic distortion at rated power: .03%, 20-20K Hz
intermodulation distortion: .004%, 20-20K Hz
Signal to noise ratio: 92 dB with typical noise floor of 2 mV
Dimensions: 16" x 13" x 2.5" (WxDxH)
Weight: 15 lbs. each 
Warranty: one year parts & labor; damage from misuse not covered 
Price with Bybee upgrade: $3500
Price without Bybee upgrade: $3000

Company Information

Andy Bartha Audio
4680 SW 74th Terrace
Davie, FL 33314

Voice: (954) 583-7866
E-mail: abad54@covad.net