21 February 2013

hot rod amplifier

Last weeks adventure with all that McIntosh gear
gave me the not-needed distraction to pull out
my own MC2300 that I grabbed a couple months back.
It has been quietly waiting,
stashed behind a speaker in the living room.
A great place for a 130+ pound amplifier.
McIntosh MC2300

Here's a refresher...
perich brothers (and sister): basking in the blue glow

Oldies Month #12
Otis Redding - Hard To Handle


Like most deals I get,
this one needed some fixings.

The needle was broken on the left meter.
A NOS replacement was found on ebay,
but never the time to swap it out.
The light so-cal rains were a perfect excuse.
McIntosh MC-2300 Amplifier

After seeing Sean rip his amp apart,
I figured how bad could it be.
Unlike stereo receivers
which are very delicate in there intricate layers - tuner/amp/preamp,
the MC-2300 is built to repair.
It's really the hot rod of vintage solid state amplifiers.
Everything is held together by screws or machine screws,
no fragile glass or plastic - all aluminum or sheetmetal.
Other than remembering where the wires go,
the layout is very accessible.
MC 2300 minor repair

The front plate could be partially removed without taking knobs off.
There had been some definite hack work done in the past.
The light fixture had some custom hacketry added,
which had perplexed me earlier.
I figured out that the light mounting bolts on the meters had broken off,
and so the tech had rigged it up.
mc2300 meters

The meter swap could have been a quick fix,
while also solving the light mounting problem.
Out of curiosity I took apart the old meter.
busted McIntosh 124-018 meter

Lo and behold the needle was laying inside the housing.
Better yet the needle wasn't broken,
and wasn't a needle but actually a straw or tube.
It easily slid back over the actual gauge pin.
Guess I'll save the NOS meter for later!
Still need to get that light assembly solidly mounted.
fixed McIntosh 124-018 meter

The next issue was the driver cards.
Something wasn't quite right with the sound,
and the heat sinks wouldn't heat up evenly.
At first I thought it was some toasted transistors,
but when the cards switched sides,
the unevenness would follow.

Basically if you look at those 8 heat sinks,
the 2nd and 3rd would be hot but not the 1st and 4th,
then the 5th and 8th would be hot,
but not the 6th and 7th.
mc2300 guts

The driver cards belong in those 2 empty slots,
there between the autoformers and heat sinks.
Like I said this thing is built to repair.

Late last year I had sent them to the McIntosh guru Terry DeWick,
but he's so back logged they're still there.
Fortunately Sean let me borrow a couple in the meantime.
1Y McIntosh MC2300 driver cards

After a quick install,
the old amp was back in business.
I'm no electrical technician,
but it seemed like it needed some juice to burn the cobwebs out.
I swapped the cards back and forth,
to do that heat sink test again,
and after a couple hours just idling and some mid-level playback
the amp has really come back to life.
Like all 300 watts per channel have been unlocked.
What can I expect from 40 year old capacitors and transistors!
I'll need to do some research on upgrading those later on.
test system - sansui 9090 + MC2300 + 4-JBL 4311

Now it is hooked up to the computer using the sansui 9090 as a preamp.
I also hooked up all 4 speakers to draw more power out of the amp,
and it seems to like it.
There is a row of ohm connectors ( 0.5/1/2/4/8/16) in the back,
with the wires hooked up parallel on the 4 ohm post.

Resistance = (Speaker A x Speaker B) / (Speaker A + Speaker B)

and 8x8ohm/8+8ohm = 4ohm
However some say these JBL 4311's are closer to 5 ohm,
so that would be 5x5ohm/5+5ohm = 2.5.
MC 2300 backside

Yeah this stuff gets a little technical!
One thing I gotta say is when this thing is semi-cranked,
the heat builds up in there,
and those 2 fans kick in.
Sure there's no sound difference,
it's just plain cool!
inside MC-2300

I will say this thing has a really sweet sound.
Most say there's a warm tone and that would be a good term.
While it's not necessarily louder than the 110 watt 9090,
there is a bigger or fuller sound, like getting hit by a good size wave.
Also I bet this could handle another pair of speakers without a sweat.

 Anyway let's see how long this thing can last in the middle of the walkway!



  1. Given that Phil Lesh powered two 40 foot stacks of JBL D140s (36 drivers) with four of them in the Wall of Sound, you know that they can put out a lot of power at a low impedance for extended periods of time.

    The whole PA was powered by them except the high end of the vocals, which were MC3500s, mono tube amps.


    1. Thanks for the info.
      I've since gotten one that actually works!