Power Amplifier - Pioneer GM-1200
Agostinho Silva
GM-1200 Power amplifier (70W + 70 W).
I lost the original manuals. Any help on this will be very well apreciated.
Trevor Wilson
Bratislav,
I lost your email address in a recent crash, but in the last few weeks I
have had the opportunity to examine two Aragon products. I thought you may
interested in my thoughts and observations WRT you comments about Dan
D'Agostino and his design prowess.
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8008:
Things I like:
Reasonable size power transformer relative to output capacity.
1,500 Watt transformer for 258 Watts @ 4 Ohms and 441 Watts @ 4 Ohms (@
rated mains Voltage of 230VAC)
Design is clean with apparently symmetrical circuitry. Probably reasonably
low loop NFB. Stability was excellent.
Probable matched output devices. (Not enough of them, though.)
No output inductor (another indicator of low loop NFB).
Circuit layout is excellent and very well executed. Very tidy construction.
Attractive looking.
*****
Things I don't like. (Some of these comments are clearly not directed at the
designer/s, per se, but also to the manufacturer)
Not enough SOA for output devices, considering power output. (4 * 2SC3281 +
complements)
Bias current is not high enough for my liking.
Power supply has only 4 large filter caps. (4 * 18,000uF. One per rail per
channel.)
Rail fuses (yuk).
Heatsinks are adjacent to each other and thus will tend to heat each other.
(Dumb design decision, but it looks pretty)
Power supply wiring for RHC totals 66cm per rail + ground.
Power supply wiring for LHC totals 33cm per rail + ground.
Input wiring channels totals 56cm for each channel.
Output connectors are utterly hopeless and difficult to actually use in real
life. (They look nice and tidy, though)
Overall, this amplifier has allowed form to take precedence over function
IMHO.
How does it sound?
Not bad. Quite powerful. A little lean in the bass and a little coloured in
the top end, though. Imaging is OK. I found image height to be a little
lacking. Slightly flat and 2 dimensional for my liking.
--------------------------------
28k preamp.
Things I like:
Alps motorised pots.
Silver plated switch contacts (I think).
Good construction.
Probably good design (No circuit available). Looks to be nice and
symmetrical.
******
Things I don't like:
Very ordinary power supply. Zener regulation to TIP31 & TIP32.
Horrible power switch.
Too big, considering the amount of circuitry inside (in keeping with most
manufacturers in this part of the market).
Servicing this puppy is a nightmare. Everything must be removed to gain
access to the underside of the main (only) PCB. All switches, pots, rear
panel sockets, etc, must be removed.
No servo loop for DC stability.
How does it sound?
Very coloured. Bass is flabby. Imaging is poor and wanders. I could not
listen to this thing for very long at all.
--------------------
All in all, I have to say that this is not much of an advertisement for
D'Agostino's design prowess as discussed in our last communication. The
power amp is competent, but the preamp is a big let down. Perhaps the
manufacturer has cut some corners, perhaps not. I can't help but think that
that package has been designed more for style than substance. For an
expensive product, this is not a happy thought. The power amp is OK, but the
preamp is a huge let down. It will disappoint many.
bratislav
> have had the opportunity to examine two Aragon products. I thought you may
> interested in my thoughts and observations WRT you comments about Dan
> D'Agostino and his design prowess.
Thanks for the info, appreciated.
I'm not sure if Dan D was designer of the preamp as well. I only
heard it mentioned that he designed 4004 and 8008.
As far as bias goes, it is no suprise at heatsinking would not
allow higher A class bias.
Big transformer is (used to be ? as per your remark about KAV300)
Krell trademark. Smallish capacitors are again reflection of low
idle (A class) bias.
> Rail fuses (yuk)
Are they before or after caps ? If they are before, it doesn't
matter THAT much.
> How does it sound?
> Not bad. Quite powerful. A little lean in the bass and a little coloured in
> the top end, though. Imaging is OK. I found image height to be a little
> lacking. Slightly flat and 2 dimensional for my liking.
I guess not surprising, considering modest aspirations (it was mid price
product in USA). But I do agree it would have (has ?) pretty tough competition
in Oz with all local products in the same price bracket.
Bratislav