Which 2270 production lines can handle 4 ohm speaker loads?

[luddite]

Recently I picked up a 2270 to run AR3a speakers but soon read that this was not what the early 2270 could do without risk to the receiver itself. Later, Marantz apparently upgraded the 2270 to deal with the 4 ohm speakers coming on the market. Question is, how do I determine if my unit was an early production model or one of those later ones?
Anybody know? Is it a matter of checking the serial number against production line records?

 

[quadklipsh]

id also like to add to the question whether a 2230 is even capable of handling that kinda load of speakers too!
I own this one and donot want to burn it ......

 

[ZombyWoof]

Recently I picked up a 2270 to run AR3a speakers but soon read that this was not what the early 2270 could do without risk to the receiver itself. Later, Marantz apparently upgraded the 2270 to deal with the 4 ohm speakers coming on the market. Question is, how do I determine if my unit was an early production model or one of those later ones?
Anybody know? Is it a matter of checking the serial number against production line records?

Where did you read this? I've never heard anything like this.
The 2270 came out in 1971. It has clearly been rated for loads of 4 to 16 ohms since the beginning. In my experience the pre 80's Marantz gear was conservatively designed and somewhat overbuilt, some more than others. Through the years I have bench tested many and never had any reservations of doing power outpet testing at 4 ohms. My 2270's have no problem driving a pair of stacked Advent speakers, to high levels.
As for the 2230 same story.

 

[ChrisMarantz]

The 2270 service manual shows 70 WPC into either 4 or 8 ohms.

The 2230 service manual shows 30 WPC into either 4 or 8 ohms.

 

[onemug]

There are nice 4 ohm loads and some nasty ones. The AR3a is a somewhat nasty one and if you play your music long and loud "with that speaker" you may damage the 2270.

I have a couple of the real early 2270's (gold/engraved) and have used each of them on my Magnepans, which are 4 ohms but an easy load, and I never had a problem.

Amps may be rated to put out x# of watts into 8 and 4 ohms but thats hooked up to a resistor, speakers are not resistors. My Maggies approximate a resistor, the AR3a's are far from it with dips to or below 2 ohms and a phase angle that wants a LOT of current at the lower frequencies making it even harder.

I believe the later production ones did add some protection circuitry to keep them from self destruction when taken out of the "safe operating area".

Give the serial # and maybe someone will know.

If it were me, I'd use what you have and just not play it hard.