# Opinion on Amps to keep from the Repair Experts



## BadSS (Feb 2, 2008)

I really need to let some amps go and was wondering from a design, durability, and ease of repair standpoint which of these would the repair experts choose to keep. 

Diamond D5 (Made in USA)









MB Quart RAA (Rockford Made in Korea)









Boston GT (Made in Italy)










I’ve compared them all - they all sound great so I have no real preference. I have run the MBs before and they deliver, the D5s are real lookers and there’s a certain amount of appeal for the versatility of the GTs and being associated with STEG/Mosconi. I probably won’t even use the one I keep as I have a number of HiFonics Gen X amps that are my “go to amps” and what I’m currently using. 

Any input would be appreciated.


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## KSakai (Jul 31, 2015)

I'm not really sure about their measurement frequency are the same or not (for THD measurement)

but let's say they measured on the same freq (either 1kHz or 20kHz), Diamond D5 has slightly lower THD than MB Quart.. the SNR on D5 also a bit better (100dB vs 92dB)..

so, if i can give an advice, i'd like to keep the D5 

i have no idea what series of boston GT is that.. I can't look for any data without knowing the exact series :blush:


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## BadSS (Feb 2, 2008)

I appreciate the reply but all three make rated power with plenty reserve, sound fine, and have acceptable noise levels. That’s my main criteria for a good amp. Fitment (size), features, and looks round things out (in that order). I’m more interested in getting some inside info from the repair guys on their thoughts on the internal layouts and the lack of,,, or the ease of repair factor regarding these three amps. 

The D5s (300.2s, 300.4, and 600.2), are power houses and feature rich, but to get an acceptable noise level from them (based on my standards) you have to bypass the front end (which kills all the features). You also have to defeat the front end on the MBs as well (RAA-4200, RAA-2400) to get a more than acceptable, near zero noise level (have to get right up on the tweeter to hear any noise). You can’t bypass the crossovers or defeat the front end on the Boston GTs (GT-20, GT-40, and GT42s), but as is, they’re almost as “clean” as the MB amps when “defeated” – meaning all the bells and whistles still work.

As an FYI, here’s some info and measurements on the Diamond D5 and the Boston GT amps. I couldn’t find any full test and distortion level info on the MB’s, but was able to find a few tests showing they bench over rated and like I said, I have no issue with how any of them sound. 

I just wanted to know which ones were “built” better. The old Hifonic IV amps I had were still going strong after 20+ years of daily use in 3 different cars and I pulled them only because I wanted to run the new-old-stock Gen X Hifonics I had. The Gen X are still kicking strong after 8 years of daily use and I expect to get at least another 12 years out of them – lol.

*Diamond D5 300.2*, 2-channel car amplifier, Rated Power 11V DC.
75W x 2 @ 4 Ohm Stereo, 150W x 2 @ 2 Ohm Stereo, 300W Bridged @ 4 Ohms

*Auto Sound Magazine 3/2003* 
Maximum power (14.4 V, THD = 1%, 4 Ohm / 2 Ohm), 
116w/214w (55% more than rated / 43% more than rated)
THD (1 kHz, P = 0,1 Pmax, 4 ohm / 2 ohm) 0.011% / 0.012 
Input sensitivity, 0.27 -> 12 
S / N ratio, 104 dBA 
Crosstalk, dB 59 
Frequency range, Hz (+ 0 / -1 dB) 4 - 33000 
The rate of rise of the output signal, V / ms 20 

RATING - Power 9, Specifications 8, Up-to-9, Filters 9, Ease of installation 8 - TOTAL 43


*Boston GT-50*, 5-channel car amplifier, Rated 14.4 volts:
at 4 ohms: 55 watts RMS x 4 at + 250 RMS watts x 1
at 2 ohms: 85 watts RMS x 4 + 350 watts x 1

*Auto Sound Magazine 4/2003* 
Maximum power (14.4 V, THD = 1%, 4 Ohm / 2 Ohm), 
bass channel 251w / not tested
the remaining 75.7w / 141w (38% more than rated / 65% more than rated)
THD (1 kHz, P = 0,1 Pmax, 4 ohm / 2 ohm) 0.008% / 0.013 
The input sensitivity of 0.21 - 6.0 
S / N ratio, 103 dBA 
Crosstalk (LR / FT) dB 62/68 
Frequency range, Hz (+ 0 / -1 dB) 13 - 60000
The rate of rise of the output signal, V / ms 20 

RATING - Power 8, Specifications 9, Up-to-9, Filters 9, Ease of installation 9 - TOTAL 44


*MB Quart RAA 2400 *(Rated 200x2 @ 4ohm / 800 bridged @ 4ohm)
(forum member bench test)
4ohm = 271.6 watts/channel w/14.07 volts (36% more than rated)
2ohm = 450.6 watts/channel w/13.83 volts (13% more than rated)
4ohm bridged= 829.4 watts w/13.84 volts 
2ohm bridged = 1176 ("not recommended but certainly capable")


(tested at AMP-Performance)
Power measured in accordance with DIN 45500-1% THD at 13.5V 
1 × 240 watts into 4 ohms Channel 1 
2 x 240 watt channel 1 + 2 at 4 ohms (20% more than rated)
Current consumption 49,5A Efficiency 71.9% 

1 × 829 watts channel 1 + 2 bridged into 4 ohms at 13.4V supply voltage 
Current consumption 91,2A Efficiency 67.9%


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## OldSchoolAddict (Sep 23, 2014)

Despite those God awful transistor clamps, I'd much rather work on the Boston than the Diamond or Quart


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## BadSS (Feb 2, 2008)

OldSchoolAddict said:


> Despite those God awful transistor clamps, I'd much rather work on the Boston than the Diamond or Quart


Thanks, I appreciate the response - that's exactly what I was looking for.


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