Circuit Review

ADVENT 300 FM STEREO RECEIVER   Revisited In the review below I observed that the strongest asset of the Advent 300 receiver is its tuner. While I have not revised my opinion of the tuner's ability to pull in stations well, it was a direct comparison to a Scott 330C/335 duo that opened my ears to its deficiencies. An occasional observation that the sound of the Advent tuner was a bit thin and acerbic was borne out when a DX test with the 330C/335 revealed that the latter had a top end that was vastly more musical and midbass hump notwithstanding, was the tuner to listen to, even in noisier stereo. My option, elected frequently, is to turn the treble down to about 10 o'clock while listening to FM, something that I am loath to do, but have been doing of late when I listen to the radio. The preamplifier and tone stage went unnoticed in my review below, and I am happy to note that the circuits still warrant little attention, and it is perhaps for this reason that I am unenthusiastic about inserting two more components into my electronic mess (a suitable tuner and, while I'm at it, a preamplifier that should sound better). As I am using the 300's power amplifier to drive the Gradient SW57 subwoofers, the upshot would be two additional components with the 300 still in use as an amplifier only. Since the preamplifier has some merit (surprise!), I have elected to retain the 300 as a tuner-preamp and power amplifier. My only other option would be to replace the 300 with my Scott R74S which I modified to permit separate operation as a tuner-preamp/amp. I may do so, but since I feel no great desire to pull it out of storage, things will be status-quo for a while. I should note that the 300 performed well with the Wharfedale W3's with (as noted below) some judicious treble adjustment, and even attempted to kick at the can of worms that the Quad ELS sometimes presents to solid state amplifiers. The original review... 03288 The Flexi-Boy of Audio that you can use in any way, but at this point in thyme, as an FM radio, mostly. The Advent 300's most distinctive attribute is that it looks like a miniature 311 series Scott tuner, or perhaps it is what a Scott 310F might have looked like, had Scott retained a vernier tuning dial on its designs beyond 1963. Similar to most, but not all vernier dial units, it offers FM only. For a person who wants to listen to all of the CBC broadcasts in Toronto, an AM radio is essential. The Radio-Canada service that remains on the AM band is an indispensable source of music, and yes, with a high resolution tuner, the AM band can be a thrill for reasons best explained in a separate article. Okay, here's a bit: With notch filters, the useful audio bandwidth can be extended beyond 11KHz, plus, and this is a biggie: the band self mutes, since minus a signal, there is only static and natural phenomena that, with notch filters, are inaudible. My description of the Advent 300 as a flexible receiver is no exaggeration: It has the one important option that only a handful of receivers and integrated amplifiers will make available to you and that is the point at which pre and amp join up in a system. With its inclusion, you have four ways of using the receiver in a basic sense: 1. as designed, by amplifying loudspeakers 2. as designed, by amplifying headsets or a line 3. as designed, by supplying an unamplified signal to a line or, 4. As available by supplying an equalized and a gain adjustable signal to a line, or, to an amplifier. Most of the unit's charm stems from its usefulness as a stepping stone to something better, which in most instances would be a power amplifier capable of demonstrating the capabilities of the receiver's tuner, and to a lesser extent, its phono stage. Allow me to say at the outset that I treated the Advent 300 as an integrated receiver, and I compared it to a Scott component that had a similarly sized power transformer with the same stack density and dissipation, etc. This turned out to be the 2502, a model that Scott built for their least expensive combination systems - you know, the kind of things with a Dual rim drive turntable slapped on the top. The 2502 is a good comparison unit in this instance in a rough sense. It is superior in that it offers an AM tuner, has a phono stage that is truly exceptional, and has an amplifier that sounds better. The FM tuner in the 2502 is compromised by Scott's least involving multiplex adapter, and even with close attention, the 2502 won't get near the Advent, despite having an alignable front end and i.f.   Radio There is bound to be some similarity between the 300's best feature (its radio) and other vernier dial units from Advent. Certainly the tuning capacitors are bound to be the same, and since front ends are critical, I expect that the Advent 400 (its contemporary, a table model) is as good as the 300. Considering the puny parts cost, I would be surprised otherwise. That aside, it is a very pretty little tuner with a four fet front end with a classic layout that passes off to a three i.c. intermediate frequency stage that employs ceramic filters. The detector appears to be a peculiar feature of the tuner (that may be a theme of the design...), using two filter-sized traps that are cross-connected to permit each trap to impinge the other, just as they would in a more conventional, full size detector can. The multiplex adapter appears to be on a chip, and it offers no 38KHz adjustment point for time switching, or oscillation between channels, nor for the 67KHz trap.. The 19KHz pilot can be adjusted. The i.c. offers no information about the method employed to place the time-switched signals upon the detected signal. There is no threshold adjustment, and the separation control is a bandwidth limiter which suggests that the tuner may be teased into performance levels that permit the separation threshold to be raised. The 300's squelch point is a tolerable compromise between overreach (which I prefer) and a light touch which tends to let noise through as the muting declutches. Since I tend to listen to a small number of stations, including some that come from a distance of about 100 miles, (my Buffalo coterie), I tend to tune with interstation muting off and I for the most part prefer to avoid muting circuits that cannot distinguish between a legitimate signal and a multipath, or other FM noise on the band. One of the nicest compliments that can be bestowed upon what is just a thing in a box is that it does some things well that are important. Stereo radios had better sound good in stereo and the Advent 300 manages to do just that. Distant stations hang in nicely with a smooth crossover into mono which suggests some sort of automatic stereo circuit. Distant signals hold stereo well, once tuned in. The 300 holds onto a weak multipath signal and it provides freedom from noise and physical disturbances (this might be something as simple as moving in front of the antenna) with no less success than any of the tuners that I have aligned recently, and considering how unadjustable the Advent 300's tuner is, perhaps this is a good thing. Gramophone The Advent 300 did not provide sufficient isolation to permit me to spend any time listening to the phono preamp. What I heard suggests that it works best with a high output moving coil cartridge, is sweet and certainly more pleasant, say, over your average cascade amplifier. More filtering, please. Holman obviously had an immediate urge to throw in some mumbo circuitry to weird out people in perpetuity, but my guess is the humpback transistor is a semiconductor mu-follower. A Hunchback of Notre Dame transistor. As I noted; a lack of power supply capacity prevented the Holman preamp from being evaluated with a medium to high output M.C. Regrettably, when I used the phono with a typical high impedance magnetic cartridge with an output of 2 mv, the sound lost all of the allure that it had demonstrated further into its noise floor. I always blind-date magnetic phono preamps with an average output moving coil cartridge because it is a litmus of performance close to the noise floor, where amplification is effortless and with low threshold noise (the Holman design does well here) the result can be near-stupefying. The Advent was in this instance, a classic tragic pairing of an upper-mid-fi-but-somewhat-mystical phono stage (but no more so than, say, Scott's i.c. phono preamplifier). That's where the similarity ends, since the Scott phono circuit employs a basic complementary circuit (and is very quiet) and the Advent follower is complementary with a more complex geometry. All noise floor notwithstanding: The a/c. spikes were terrifying. It was like listening to Sunshine On My Shoulder at 3 a.m., while in the bathtub in a room with tenement lighting. Amplifier Since the amplifier is all that remains to be discussed, it is obvious that it is the one portion of the circuit that I found to be the least satisfying. I can point to the obvious and say that the power supply is small, but the unit swings 44 volts and that is low for its rated output of 15 watts. While it is more than the withering 5 watts per side to twenty cycles that Flingpoo made it out to be, it is a class b sweetie that was designed to shake its bootie into a 1970's style stuffy acoustic-suspension loudspeaker. It draws itself out as far as far goes, toward its optimal class b range, ultimately giving out in a disintegrated class b wheeze and fry. Within a more typical listening range, the amplifier continued to unimpress me, but at no time did it offend me. I cannot account for the amplifier and I won't try. Why should I? I'm not Holman, eh? The Advent 300 delivered a constrained, pinched, near fatally bright sound that was an immediate and substantive move away from the sound of the high impedance, high efficiency speakers with the Scott 2502. My Comparison is far less flattering when a Scott with a rated capacity of twelve watts is used, such as the FM-only, quasi-complementary TYPE 341. With a treble adjustment while listening to the Wharfedale W3's, I was able to derive some enjoyment from the circuit. Jay Bee, a staffer who spent some time with the Advent 300 believes that a treble adjustment that corrects a deficiency in the component is unacceptable. Correcting the treble problem is easily accomplished due to the design of the unit. Since a second loop (preamp out to amp in) is supplied, it is easy to strip in a resistor of a value that will provide simple resistance sufficient to tame the treble. If I had to guess, I would start at 270k. While I am talking about tone deficiencies, I should mention that the bass has problems that can't be solved. There is neither weight nor detail to the bottom frequencies. Of course, the champ amp fared better up to its power limit. What's with the topology? The amplifier looks like a fireman's ladder, and of all the circuits, it looks the most simple. It is the first balanced circuit in an amplifier that jumps all over the place between unbalanced, floated, and truly complementary. Admittedly I prefer single rails and I may be getting annoyed about an utterly symmetrical design for a symmetrical, ugh amplifier. On the other hand, I have yet to listen to a symmetrical amplifier that matches my view of what is the Audion sound of solid state: Quasi-complementary. I wish that I could point to some redeeming factor of the design, or at least an interesting one, but the obvious factor isn't there. Each circuit stage is terminated with a decoupling capacitor. It's not even direct-coupled. What a disappointment. I have chosen to eschew what some call 'mods.', (but are only substitutions) and have evaluated the amplifier without any adjustments or tests. The Advent 300 was not designed to be adjusted, and it never should need to be. Perhaps it would benefit from service. There are an abundant number of 300 fans who would have you believe this to be so. As I have heard other complementary amplifiers that leave me cold, I know that it is a -circuit-affair-   Look at the wires The Advent 300 serves as a good example of what happens when a bunch of designers get together and throw stuff at a box, and then throw the power supply in, after that. Indeed, the only circuit with an elegant implementation with respect to power supply. is the tuner. This is no surprise as the supply crowds the tuner. It is easy to use the 300 as a standalone tuner. Lifting the tuner signal off the record output will bypass all other affected circuits, since the tuner's detected stereo outputs are amplified separately. This is surprising in one sense, since it makes sense to use the pre amplifier to amplify the high impedance, low voltage signal from the tuner. On the other hand, it speaks to the parts bin approach to the design. There's no way for the tuner to use Holman's phono stage because there was no dialogue between Holman and the tuner designer who as rumor has it, is also a chap named Holman. Perhaps he designed one while he was in the bahamas, the other while he was sitting on it. Or... Leave the power supply stuff in and carefully consider what it is about the 300 that motivates me to comment on its tuner alone. It could be that I don't like the sound of any of the other amplified stages, or that all is great but the tuner is exceptional. In answer, I did find the 300's tuner to be worthy, and as hardly any tuners extant present themselves as worthy or even listenable, this is a commendation enough. Considering how expensive a capacitively tuned radio has become, the 300 is a reasonably close glance at adequate tuner performance. If it included an AM section of commensurate quality (and here I would gladly enjoy the AM section of the Scott 2502), the 300's tuner would be complete. On the other hand, an FM only receiver has a lot of cachet, especially in those cases where the tuner is of exceptional quality, which for its price point, the 300 squeaks, 'flexy boy... I look like a TYPE 310F,' and so on. Flexy adaptability helps too. The Advent 300 can be had for below $50.00 for a wreck to close to $200.00 for one with the original factory carton and Henry Kloss' personal okey dokey. ed.