Marantz's Legendary Audio Classics
In this area of the site you will find reviews of gear that is of
particular interest to you, as a lover of classic Marantz gear.
Magnum Dynalabs model MD-205 "Signal Sleuth"
GeneralThe Magnum Dynalabs model MD-205 Signal Sleuth is a radio-frequency preamplifier designed to be inserted in the FM Antenna chain before the tuner or receiver antenna inputs, and after the FM antenna and antenna feedline. It provides one 75-ohm coaxial input and one 75-ohm coaxial output. The front panel provides a simple set of controls. These include switches for power on/off and amplifier bypass/in-line, and high-quality rotary controls for amplifier gain and tuning. There are also two LED indicators, one for power and one to indicate that the amplifier is presently in-line. The image above shows green LEDs; my unit came with red LEDs.
Although billed as a "rack-mount" device, at 16.0"W x 1.75"H x 5.5"D the unit I received is slightly narrower than the 19-inch standard rack requires, and in addition does not provide any mounting holes whatsoever, so rack mounting is problematical at best. You would have to purchase a rack shelf in order to mount the unit in this manner. The MD-205 utilizes a "wall-wart" style power supply, and so requires considerable room where you plug it in. The unit consumes 25 watts. It weighs about eight pounds.
Like most modern audio gear, the MD-205 is, unfortunately, black. The control legends are gold, and not all that difficult to read. They are definitely easier to read than white legends. I do wish they made a silver-faced version, and have contemplated going to our local metalworking shop to have them create a custom front panel that would cosmetically match the rest of my gear. I cannot find it in my heart to blame the manufacturer; black matches the current marketplace, and you just can't argue with the business issues.
Unit PlacementIdeally, such a preamplifier would be placed as close to the antenna as possible to reduce losses in the antenna cable before the signal enters the preamplifier, but as the MD-205 is strictly an indoor unit, and further, requires placement adjacent to the receiver or tuner, this is generally difficult to accomplish unless your FM gear is in a room in your home directly underneath the antenna itself.
The reason that the unit must be placed near your FM gear is that the MD-205's tuning requires re-adjustment when you change the tuning of your FM gear. Unless you listen only to one station, the unit will have to be right next to your tuning dial - its ability to bring out one station is a complement to its ability to reduce your ability to receive stations it is not tuned to.
Due to the placement requirement, you should use only the absolute highest quality coaxial cable to make the run from the antenna to the preamplifier; signal losses prior to the MD-205 cannot be recovered.
Installation consists of hooking your 75-ohm antenna feed to the MD-205, connecting the MD-205 to your receiver using the supplied high-quality 75 ohm cable, plugging in the "wall-wart" and then simply turning the MD-205 on.
PerformanceThe MD-205 has but one purpose; it is designed to enhance the performance of your FM tuner or receiver. Typically, when one adds a signal amplifier to an FM antenna system, broadband or tunable, you actually obtain a reduction in signal quality. Though signals may indeed be stronger, they almost always, in my experience, contain more noise, noise that was added by the preamplifier itself. This is not the case with the MD-205.
The design of the tunable RF stages in the MD-205 uses inherently quiet semiconductors and a remarkably low-noise design. Under no condition could I determine that the MD-205 was doing anything but amplifying noise it was being fed. With a 75-ohm shielded resistive source as the input instead of my APS-14 antenna, tuning the unit and adjusting the gain produced almost no signal detected on any of my most sensitive tuners. This is most unusual, and is a clear indication of the MD-205's inherent low-noise character.
The claimed noise figure according to the MD-205's designers is 4 dB; I will have to take them at their word, as my equipment isn't able to measure that low... a good sign in itself. The observed performance certainly shows that the MD-205's noise figure is below the 9 dB of my 2130.
That low-noise character is the reason why adding the MD-205 to the FM signal produced no measurable change in the THD or IMD of strong received signals; and it is the reason why one real-world very low-level signal that was considerably below my Marantz 2130's measured sensitivity (1.4 uV for 30 dB quieting) leapt from 18 dB quieting to 38 dB quieting, both in mono. You may be sure that got my attention!
The unit's tuning is smooth and reasonably linear from 87 to 109 MHz. The 600 kHz design bandwidth means that it is easily placed "over" an FM signal, which is nominally only 200 kHz wide. Because this bandwidth is essentially three FM channels broad, the MD-205, predictably, does not provide any help with adjacent-channel selectivity. However, as the slope of the preamplifier's bandwidth is quite sharp after that, my 2130's alternate-channel selectivity increased by about 5 dB to a measured final value of 90 dB.
The MD-205 provides up to 30 dB gain; this is probably overkill for most installations, but not all. Certainly the MD-205 will not provide an additional depth of 30 dB (approximately 1000 times amplification) to any Marantz front end's sensitivity, and so from that standpoint, 30 dB is definitely overkill. However, if you use the MD-205 to drive more than one FM front end via one or more signal splitters, you'll be quite grateful for the additional gain; each split will (at the least) cut the signal level by 3 dB; adjusting the MD-205's gain upwards will entirely compensate for those losses.
The gain control is smooth, has a wide range and is delightfully easy to adjust to the precise level desired. I can attest to this personally, as my own office FM setup is presently driving five separate front ends flawlessly using the MD-205 reported on here.
The MD-205 can produce as much as one volt of output signal with a strong input signal; generally, the output is proportional to the input. It is worth noting that it can also suffice to provide up to 30 dB of signal reduction, something you might want to take advantage of if you have adjacent or alternate channel problems with an otherwise strong station.
Because in addition to amplifying the desired signal, the MD-205 reduces other signals proportionally to their distance from the adjacent channel (in other words, beginning one station away), a number of other improvements in overall tuner performance will be noted. Specifically, spurious response rejection will improve a great deal, image rejection will vastly improve to the point of being no longer an issue, and your tuner or receiver will consistently run closer to its ultimate quieting point with all stations. That last issue will be the most often (and very welcome) perceived benefit for most owners, in my estimation. Surely everyone appreciates a quieter signal.
SummaryThe MD-205 is a particularly appropriate accessory for owners of classic Marantz receivers and tuners, because these classic FM designs are lacking in only one area, and that is the FM front end - the exact area that the MD-205 applies its considerable effectiveness to. In many ways - ultimate quieting, THD, IMD, stereo separation, quieting slope, subcarrier rejection - classic high end Marantz tuners and receivers still have very few peers indeed. But in the area of front-end design, where signals are down literally near the thresholds of the inherent atomic noise of semiconductors, advances have indeed been made - and the MD-205 brings those advances immediately home to us without requiring any kind of refit or rework on our valuable classic audio gear.
The MD-205 is $295.00 from Magnum Dynalabs. You can reach them by phone toll-free (in North America) at (800) 551-4130, or at (905) 791-5888 if you are located elsewhere. You can reach them by FAX at (905) 791-5583, and by email at firstname.lastname@example.org
No matter your previous experience with FM preamplifiers, I urge you to try the MD-205. It is different. If you can possibly afford the MD-205, get it. That's my final word.
Antenna Specialties model APS-14/APS-13 FM Antenna
Look for a review of the APS-13 spring 2003.I have the antenna, I'm just waiting for some kind of reasonable weather so I can put it up. It's cold in Montana in the winter! In the meantime, check out the APS-14 review, below:
GeneralThe APS-14 is a high-performance antenna designed for FM broadcast band use between 88.1 and 107.9 MHz. It is a 75-ohm design, with a specified average gain of 10 dBd and a front to back ratio of 30 dB. It is physically somewhat large, 200 inches from end to end, and requiring a minimal guy wire installation to a mount several feet above the antenna mount point. It requires about 128 inches clear in all directions from the antenna mount if it is to be used with an antenna rotator, which is the most likely type of installation. Construction is superb as evidenced by the use of aircraft aluminum, self-locking ABS insulators, heat-tempered rivets and stainless steel accessory fittings.
AssemblyThe afternoon the APS-14 arrived by UPS, I wasted no time getting all the parts out of the box and spread out on the ground, ready to go together. The APS-14 was relatively easy to assemble; no problems of any note were encountered. I simply read the directions through once, then followed them step by step and was rewarded with a properly completed antenna in about one hour. There were no parts left over (always a good sign!) and everything fit together very well, no "fudging" required. None of the parts were bent or otherwise damaged during shipping, rather amazing considering the large size of the box. You'll definitely want to insure this item when you order it. It appears to me that the odds of shipping damage are very high, despite the fact that my unit arrived undamaged.
InstallationThe APS-14 comes with fittings for mounting on a standard TV antenna mast with a diameter of 1.25 inches. My tower carries a Hy-Gain antenna rotor that has a much more substantial mast, and so I ended up mounting a short length of lighter mast offside of my main mast to support the APS-14. In my region of the country (the high plains of Montana), it is not advisable to use light antenna masts in the general case; we see winds in excess of 90 MPH more than once a year. I attached the short length of light mast at two places, so it is an exceedingly sturdy mount for the APS-14.
No problems were encountered during installation other than the above mast diameter issue. The APS-14 utilizes a pair of DacronTM guy ropes that mount several feet above the antenna to support the 200 inch boom length. When I first installed the antenna, I was a little concerned about this, but in the months following which included one full winter season and almost one complete summer season, these supports have not stretched or otherwise shown any tendency to not hold up to the rigors of the installation. This is important, as without these ropes, the antenna would sag and its performance would suffer greatly. I think I would have preferred that the antenna itself had a more substantial boom design and the guys, but in retrospect it has held up perfectly thus far and perhaps I'm just being a little too nervous about our weather.
One unusual step that is performed during installation is to add a ferrite choke at the antenna end of the coaxial feedline. This is something that I have never seen before in a commercial design, and it is a most welcome one. What this does is essentially removes effects that the feedline can have on the antenna's gain and directional characteristics. Ham radio operators (such as myself) have known about this trick for years, but this is the first time I have seen such attention to detail in a commercial antenna design. Antenna Performance Specialties gets serious brownie points for this one!
PerformanceCommercial FM antennas are, by and large, a highly varied lot. Some issues that are typically encountered are gain peaks at some frequencies that are not actually at the front of the antenna. This can lead to pointing the antenna one way for one station, and pointing it yet another for a different station that is actually in the exact same direction. The above mentioned ferrite choke helps to work against this exact problem, and in fact the APS-14 exhibits excellent directivity. I am in the perfect situation to test this against real-world signals, as I am about 200 air miles from Billings, Montana, and Billings has stations scattered all across the dial. All of them show up in the exact same place on the antenna rotor, and that tells you that the APS-14 has it's most sensitive peak in a single direction, a highly desirable characteristic for an FM antenna.
In terms of gain, the APS-14 outperforms every FM antenna I have previously owned. I've had a Channel Master CM 3025 up there, the high end Radio Shack antenna (which is not a bad antenna at all, but can't compare to the APS-14). The peak sensitivity of the antenna is surprisingly broad, in that the rotor has to turn about ten degrees before a weak station drops out. It may be that a higher gain yet could be achieved by an antenna with an even tighter pattern, but I find I like the moderately broad pointing character of this antenna a great deal. It makes it easy to find weak stations at great distances. Another benefit in my area is that in situations where the wind is kicking up, although the antenna does wave back and forth quite a bit due to the considerable amount of leverage the wind applies to all that aluminum, the signals vary less than one might expect with such a high gain design.
I regularly listen to KMHK in Hardin, Montana. KMHK is 179 air miles away, and that is a huge distance to try and cover, even situated on the plains as we are here. I have the antenna mounted about 30 feet above the ground and pointed slightly above the horizon to catch low angle incident reflections. KMHK is a high powered station, and has a very impressive tower itself. All of these factors work together, and for the first time since I have moved to Montana, over tens years ago now, I have FM radio I can listen to continually and enjoy. Our local FM station is, how shall I put this... "not well handled."
There are some stations closer, at distances between 50 and 100 miles, and these stations are receivable quite easily using the APS-14, while they were definitely just "fringe" for the radio shack antenna and only reasonably listenable using the Channel Master CM 3025. Unfortunately, these stations don't broadcast anything I want to listen to. Still, they provide a number of real world benchmarks that I trust more than any set of measurements.
SummaryI could not possibly recommend this antenna too highly. It is the perfect size in that it is not too heavy for even a modest antenna support, yet it is probably the best FM antenna on the market. The APS-14 qualifies for an unreserved "Get It"! You'll need an antenna rotor as well, unless you plan to listen to stations that are located only in one direction forever. Remember that new FM stations appear from time to time, and old ones go off the air or change formats. I recommend you get a rotor no matter what.
Terk "AM Advantage"
GeneralThe "AM Advantage" is a loop antenna intended to provide enhanced reception on the US AM broadcast band from 535 KHz to 1.700 MHz. It is a very attractive design, slate grey with a pleasing combination of squared off edges and rounded surfaces, actually very reminiscent of classic Marantz gear, other than the color. It has only one actual control, and this is a smoothly knurled knob located at the base of the loop, facing up. There is a graduated, easily read dial scale designed to serve as a coarse aid in tuning. The unit is fully assembled out of the box, and a small booklet is supplied which answers most common questions in a simple, easily understood format. No power is required for operation of the antenna, so there are no batteries or power cords to be concerned with. There is a 1-year warranty during which Terk will repair or replace the product if it is found to be defective.
Installation & PlacementThe "AM Advantage" is designed to be used in one of two ways. It may be connected directly to the AM antenna inputs of the AM tuner using a supplied jack and simple feedline, or it may be placed near the existing AM ferrite antenna bar, where enhanced reception occurs as a result of inductive coupling between the "AM Advantage" and the receiver's ferrite bar.
If the intent is to couple the "AM Advantage" to the existing ferrite antenna, then placement must be quite near the receiver. The nearer, in general, the better. However, you can't make any assumptions here, as the character of AM signals is such that there will be better locations, and worse locations, all within a few feet, or even inches, of each other. This is even more so when a building has metallic construction such as steel framing members or inside a trailer home, for instance.
If the intent is to use the supplied jack and feedline, then the antenna doesn't have to be near the receiver, but it still will have to be carefully positioned in order to obtain the best possible reception of the desired signal.
In either case, the "AM Advantage" will often require readjustment of it's operating position on a station by station basis, which means that when you set it up, you need to be sure that you have at least a little bit of room to allow you to turn the loop to any angle. So it does take up a fair bit of space, and you can't assume that any one orientation will be "it".
The antenna itself has a broad base with a soft mat attached which serves as a very stable platform for the loop; all you need is a flat surface and it is very unlikely indeed that you would have any difficulty with stability.
PerformanceIn a word, outstanding. This antenna provides a huge performance gain operating in either the wired configuration or coupled inductively (simply placed near the ferrite antenna on the receiver.) The antenna is highly directional (normal for any loop antenna) and it is very sharply tunable. The end result is that it helps a lot. I saw signal increases from "barely there" to full-signal strength readings. Signals went from noisy and basically unlistenable to almost completely quiet. This antenna does much more for AM than any comparable amplifier I've seen does for FM. The reason for this is partly because AM receivers aren't all that great overall in the first place, and partly because AM antennas aren't all that great either. The bottom line is this is a killer add-on.
SummaryOur classic Marantz gear, for the most part, does not offer outstanding AM reception. There are a few exceptions, notably the very high end tuners and some of the earlier receivers that were designed when AM was much more popular than it is today. So most Marantz gear can use some help in this area, and the Terk "AM Advantage" is definitely one of the best ways to go about getting it, especially for a stereo receiver.
I am delighted with the appearance of the unit, even more so with the results obtained with otherwise poorly received AM signals, and what I would have to describe as nothing less than the resurrection of the AM sections of my various Marantz tuners and receivers. The antenna is quite portable even when wired directly, because Terk used a standard jack and the feedline can be pretty much any insulated wire pair. As a result, I set things up so that I can use it on any of my classic systems, and it gets moved around quite a bit.
You know, I actually do listen to AM regularly... I am vastly amused by talk show host Art Bell's "Coast to Coast" show wherein aliens, ghosts, and vast legions of deluded callers get equal time. Until the Terk "AM Advantage" arrived, I was using a Panasonic RF-2200 to listen to Mr. Bell's antics, and I am delighted to report that with the addition of the "AM Advantage", I can now use my Marantz instead, and the RF-2200 will now be used only for trips.