Marantz 2270 vs 2275 and 2285

[shurev15]

What is the difference regarding behavior at 4 Ohms? Do anyone know the different in poweramp circuits? Are there changes in 2270s long run, I own a serialnumber 511xxx . Can You alter the conservative layout of the protection circuit to manage 4Ohm load better?
herbert

[Nakdoc]

You answered your own question. Both have output current limiting. The newer 2275 has a slightly more generous Safe Operating Area because the output transistors are better, so 4 ohm performance is better.
If I had a stock 2270, I would not modify it. After it blows, I suppose with better outputs you could remove the two current limit transistors on each driver board.

[ruesselschorf]

Hello,
my benchmarks:
Conditions: Mainsvoltage 230Volt/50Hz 400Hz sinewave (it's easier to my ears than 1kHz) both channel driven into 8 and 4 Ohms resistive load at no more than 0,5% distortion:

Marantz 2270: 85/8 or 125/4 Ohm
Marantz 2275: 85/8 or 130/4 Ohm
Marantz 2285: 100/8 or 140/4 Ohm
Marantz 2285B: 95/8 or 130/4 Ohm
Since all receivers are set to 220Volt at the selector, they get a little more powerful.
the 2270 does not show signs of early current limiting into a 4 Ohm RESISTOR but maybe a reactive 4Ohm speaker is another story.
You could put in new MJ21193/4 outputs and alter or remove the current limiter, but how would this alter the sonic character of this classic receiver?
Since the 2285 and 2285B have 4 power transistors per channel, maybe they are better into low load resistance. But i get a lot more 2285B/2285 with a literally burned out poweramp than broken 2270/2275 poweramp stages

Helmut

[alexkerhead]

ruesselschorf,

Thanks for the info, I was curious of this myself.
Have you benched a 2265B by any chance?

[shurev15]

Hi, Helmut!
Your infos about the poweroutput is correct. But in the 2270 IM-Distorsion is at 40-50 W at 4Ohm extremely increased. You find the datas in a test by CBS-labs, You find the information in Yahoo/marantz talk/files/ tec.review. In discussion I`ve read, the reason is the current limiting. What is Your opinion?
Are there differences in the long run of the 2270, my one has the serialnumber 511xxx?
Herbert

By the way, my set will be in Your clinic soon and I want to clear this, because maybe You can do some changes. Most speakers have low impedances today, but I want to stay with my loved 2270.

[shurev15]

Helmut, another Question,
My 2270 is set to 240V in Germany, is that wrong or worse?
Herbert

[bully]

The 2270 is known for a weak power supply and doesn't do well with lower impedances. The 2275 corrected the problem. The 2285 is minimally more powerful.

[ruesselschorf]

...got a 2265B in my inventory, I'll bench it over the weekend.

No knobs = No Good I agree! But on the other hand: If it's got knobs, buttons, wheels or tits - it's gonna make trouble sooner or later!

Helmut

[ruesselschorf]

Hello Herbert,

setting the 2270 to 240Volt won't hurt, but reduce the output power by 15% or so compared to the 220Volt setting.
Don't have the equipment to measure IM-Distortion. But my audio analyzer should have showed some reaction to very high IM into 4 Ohms.
The Marantz 2270 had a long production span, early units had Motorola outputs, later Fairchild (same as the2275) still later Hitachi. The circuit design did not change much. But maybe they adjusted the current limiter with the newer and better transistors for better operation into 4 Ohms?
Looking forward for your 2270 to arrive to take a closer look at the current limiter...

Helmut

[ruesselschorf]

Hello, promised to benchtest the Marantz 2265B:

conditions as above, Marantz 2265B serial: E101108 from 25/1978 (label on tuner)
Power 8 Ohms, 25Vrms: 78 Watt. 4 Ohms, 20,5 Vrms: 105 Watt, both channel driven

Helmut