of the amps, Bryston and Bel Canto are top notch; add Benchmark amp to your quest
McC is a super value...
a high quality Class D is just fine with Maggies
Congrats on getting them. I love my 3.7i
Specs taken from HiFi Classic test: "The GFA-555 required an input of 0.13 volt for a 1-watt!! reference output" (Very very low gain)
The old war horse 555 is very low gain at only 130mV for a 1volt output. Which is: with a 2v source and a passive at full level, the 555, can only reach 16v!!! to the speakers
You either need a very high gain preamp, or seeing the Adcom is very old now you may want to get another amp, which most will have much higher gain than this old 555 more like 1.5v for full output (not 1v) and your source and passive will be fine then.
How about throw a Hail Mary pass and get a Parasound Halo Integrated amp? 160 wpc into 8 ohms and 240 wpc into 4 ohms, which is Magnepan's native mode.
Plus, it's a Class A Stereophile-rated component. Its phono stage accepts both MM and MC cartridges, it has a built-in DAC, AND it has analog bass management. Add a subwoofer to your MMGs, use the bass management to route the high pass signal to the MMGs, and they will sound twice as big and dynamic.
True, $2495 is a bit of money, but it's by far the least expensive Class A component in Stereophile's list of recommended integrated amps. Plus, you will get much better sound and way more gain than you can get from your present setup. The Adcom 555 was a good value for its time, but this Parasound will redefine *your* sound, and your passive line stage is *literally* not helping.
Also, to save some money, get AA's sale-priced demo.
george, may be you’re talking about something different but all things being equal, an amplifier with a 0.130 volt input sensitivity- not gain, will play much louder than an amplifier with a 1.5 volt input sensitivity. A line level input of 2 volts is "spent" more quickly on the amplifier that has higher input sensitivity.
P.S. GFA 555 is rated at 325wpc into 4 ohms so it has plenty of power to drive MMGs. You need an active line stage preamp. I have run MMGs with one paired to an Adcom preamp and you can barely push the volume past half before it gets way too loud (for me).
No Kalali read a bit closer, the specs on the MkI I got from the net (if right) said with .130v (130mV) input and it gave out only 1v from it’s outputs, that's a voltage gain of 7.6 times.
Don't mean to belabor the point but here's from Stereophile:
'Description: Output Power: 200W into 8 ohms (23dBW); 325W into 4 ohms (22.1dBW), all continuous power, 20Hz-20kHz, with 0.09% THD. Input impedance: 22k ohms. Sensitivity: 130mV'
The Sensitivity is normally rated at full volume output. Voltage gain is not shown but a 2 volt source will be 'louder' with 0.130V than 1.0V input voltage sensitivity.
Kalali & George, I looked at the specifications provided in the service manual for the GFA-555 II, which can be found at HiFiEngine.com. While as Kalali said it is usual for sensitivity to be defined as the input voltage required to drive an amp to its maximum power capability, that is not always the case. And my perception has been that it was especially common for it not to be the case a few decades ago, such as when the 555 was designed.
In this case the 130 mv input corresponds to an output of 1 watt, as stated earlier in the quote George provided and as also stated in the service manual I referred to. But George, note that it says 1 watt, not 1 volt. 1 watt into 8 ohms corresponds to about 2.83 volts, as I’m sure you realize.
Also, the service manual states that an input of 1.75 volts is required for the amp to provide its rated maximum output of 200 watts into 8 ohms. Which can be expected to also mean that an input of 1.75 volts would produce the amp’s rated output of 325 watts into 4 ohms
These numbers correspond to a gain of 27 db, which is about average for a power amp.
Also, I note that the manual for the Magnepan MMG recommends amplification having 8 ohm power ratings of 40 to 150 watts, less than the GFA-555 II is capable of.
So a digital source having a reasonable maximum output of 2 volts should be able to drive the amp to full power in conjunction with a zero gain preamp, on the peaks of recordings that have been engineered such that peaks reach levels that are close to "full scale." But having looked at actual signal waveforms of various recordings I can say that will sometimes not be the case. And in addition perhaps the OP is listening to LPs, it being very common of course for cartridge/phono stage combinations to provide much less than 2 volts on high volume peaks.
So my bottom line suspicion is that an active preamp is needed, or perhaps an integrated amp such as the Parasound Halo that was suggested (which provides a total gain of 38 db, 10 db in its preamp section and 28 db in its power amp section). But before recommending a course of action I would want to know what the source component(s) are.
Finally, regarding the flickering lights on the amp, the user manual states that is an indication that distortion is exceeding 1%, and will occur "occasionally" under high volume conditions. But if "they glow brightly or are on most of the time" ... "you are overdriving your equipment and should turn down your volume control."
Al, thanks as always for your input. As can experiment, I took my Schiit Sys out of the closet and replaced my Adcom GFP-750 driving my GFA-555 in my upstairs (analog only) system. I also dragged out my old DVD player and plugged it into the Sys. In my small room, I can go just over half way on the volume knob before it gets too loud for me. I was tempted to try hooking up my turntable but wasn't sure how to ground it. I suspect I would have had issues getting the volume high enough using the turntable. I do have very efficient speakers in this room @ 94dB.
I think in the OP's case, as Al mentioned, it would be important to know what source component is being used to cause the symptoms observed. A turntable could most definitely result in the low volume condition.
I second the Maggie ,Parasound Integrated recommendations . I used one with 1.7i for a year and just took a step up to the 3.7i the sound is fast and musical with plenty of power. You can always go the used route for $1500 - $1800. The phono section is a great plus as it takes mm and mc carttidges. Don’t think you’ll find better sound or quality for the $$.
You have a mismatch there, the Maggie’s have low sensitivity so require a coup,e of extra points on the volume knob, couple that with using a passive that also adds a coup,e of points and you’re maxed out. I have this with my setup. I use an active preamp with ss for big, loud, pieces and when I want quieter songs, like solo voice I switch tompassive and tubes. I would suggest a tube pre to take some of the edge off the Maggie’s.
I own the Schiit Saga Preamp and the Adcom GFA-5800 amp.
There is either something wrong with your GFA-555 amp or maybe the source. The GFA-555 is plenty powerful to drive the MMGs to a loud level.
You did not mention your source of music. If you are using a turntable, the Schiit Saga preamp does not have a phono input. It is all line level. You need to use a phono preamplifier between the turntable and preamp.
If you have a CD player, you should connect that to your preamp to see if anything has changed.
Depending on your definition of loud, the only way to get more out of a Maggie is to get a bigger Maggie. You might check out their bass panel with the smaller Maggie. I had 1.6 then 20.1 and the bigger ones can play loud. I never considered the 1.6 to get loud. Another suggestion is that your old adcom if it’s not been recapped is probably not as strong as it was bac in the 90s.