Mc2300 in the Hospital

quartersaw

Super Member
Something didn't come out quite right with the output board transistor upgrade that I executed some weeks ago. I was very meticulous with the removal/installation of the components, but the amp has a background hum that was not there before. The left channel output seems to be lower as well.
I upgraded the small + - caps on both my 2300's at the same time, but the transistor upgrade on Amp 'B' took a wrong turn somehow.
I don't have any test equipment other than a Multimeter, and a Variac, so I road tripped the amp down to Audio Classics. They tell me that it could possibly be ready by Friday. The meters were also out of calibration, so I figured I'd have the amp spec'd out and bench tested as well.
I'm going to finally give a shot at running them as Monoblocks when the amp comes back home.
 
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Well, at least you brought it to the right place. Things sometimes go wrong on old stuff no matter how careful you are. It's the nature of things, especially the 2300. Who knows? Your new output transistors could be bad, they could be fake (Chinese copies), or whatever. Luckily I had the luxury of someone curve-tracing and matching complete sets of original NOS 070s when I did mine.

What speakers are you using now?
 
Well that will be exciting!! Get those suckers cranked in mono mode!!
That's going to be some fun alright!!
 
Hello !

but the amp has a background hum that was not there before

I think your big capacitors are very old now and maybe starting going bad . When such trouble happen it is easy to know from where your problem is , if you move the left driver board to the right and the same with the other channel .

This way you know if the noise is following the driver board or not . Once the information analysed you know if power stage is gulty or not .

AC is the right place . Ryan or Georges will save it don't worried !

:thmbsp:
 
Hello !

but the amp has a background hum that was not there before

I think your big capacitors are very old now and maybe starting going bad . When such trouble happen it is easy to know from where your problem is , if you move the left driver board to the right and the same with the other channel .


:thmbsp:

Two key parts of 2300 trouble shooting. Move the cards around, and those power supply caps do not last 40 years. They are expensive, but make a huge difference. I know of one recording studio that has 2300s that do the four big caps every year.
 
Well, at least you brought it to the right place.
What speakers are you using now?

There was no noticeable hum before I did the upgrade. One channel did sound a bit 'tired'.
I accidentally mixed up the boards as I was doing the caps for both my 2300's at once.
I did have a hum in my original 2300 (Only with my iMac connected) that went away when I put the 'old gang' (boards) back together, so that's why I suspect something is amiss with my refurb of the transistors. My other 2300 is only 12 numbers apart (1Y987)(1Y975-new transistors) and it is playing at a tip-top level with the original caps underneath.
My speakers currently are Cerwin-Vega 15" cabinets with multiple Altec/JBL drivers/compression drivers installed
 
Well that will be exciting!! Get those suckers cranked in mono mode!!
That's going to be some fun alright!!

Should be interesting!
I've also got that 1200 watt Mackie amp that I am going to use for subs one of these days when I have some time. At this rate, I should have the system configured the way that I want it to be in about 10 years! :D
 
Two key parts of 2300 trouble shooting. Move the cards around, and those power supply caps do not last 40 years. They are expensive, but make a huge difference. I know of one recording studio that has 2300s that do the four big caps every year.

I was pricing those caps some time ago, but I was talked out of replacing them. There seems to be different schools of thought surrounding those caps. My feeling is that those oil filled GE caps just might have a very, very long service life. I'm sure Audio Classics will let me know if they are still in spec.
I'll report back with their findings.
 
All of that sounds fun. Strapped MC2300s is really tough to beat.
Keep us in the loop!

For sure I will. My wife has been after me to setup my 'sound studio'. Our Kitchen is 15'X30', and that's where I've had the single 2300 set up at the other end of it. I've been anchored there for 15 months now.
It might be time to relocate to the space where I can really move a serious amount of air. :D
 
Hello !

but the amp has a background hum that was not there before

I think your big capacitors are very old now and maybe starting going bad . When such trouble happen it is easy to know from where your problem is , if you move the left driver board to the right and the same with the other channel .
:thmbsp:

I should've tested the amp a bit more. When I heard the hum, I shut it down in disappointment, and the amp sat for several weeks before I drove it down to Audio Classics. (Two hours away)
 
Well, at least you brought it to the right place. Things sometimes go wrong on old stuff no matter how careful you are. It's the nature of things, especially the 2300. Who knows? Your new output transistors could be bad, they could be fake (Chinese copies), or whatever.

I bought the upgrade kits straight from Mcintosh. I also inquired about new driver boards, but they are no longer available.
 
Spoke to George Melnyk, @ Audio Classics today. (Very interesting individual!) He stated that there was a number of grounding problems with the Mc2300. The big caps had worked their way loose. The amp was not making anything close to full output due to the marginal grounding of the big caps. It was a matter of tightening the screws that secure the caps. George recommended that I check the cap screws on my other Mc2300 for tightness. He stated that the amp came up to full output when all of the grounding issues were corrected. All transistors are O.K.(They are all original) The (all original) big caps are well within spec for DSR, and capacitance (>30,000mf) Even the small can cap was well within spec. He said my speaker connectors are in bad shape, so they are going to be replaced. The meters will be brought back to spec as they will not adjust correctly.
The replacement diodes on the output boards were too close to the transistors, and the (few) radial capacitors that I installed were replaced with axials. The braided wire going from the potentiometers to the input board was brittle,( I had difficulty soldering those connections as they broke a few times) so he replaced that,and the pots as well.
He wants to 'burn in' the amp for a day, but it is essentially finished. - Back to original Mcintosh specs. :D
 
Very nice. I'd be curious to hear how much power per channel the old girl belts out once George is done with it.
 
Finally got the notification from Audio Classics that the amp is completed. Ryan tells me the amp is putting out 400WPC, and I'll have a bench test report, and a hand written note from George telling me exactly what was done. If all goes well, I should be able to pick the amp up on Saturday.
 
She is a beast & is doing 400 watts with both channels driven at 2Khz. AND when the unit is running at rated output of 300 watts with both channels driven, the distortion is less that .06%! So strong and silent!! If the neighbors complain, it will be because of too much GOOD CLEAN sound!
 
She is a beast & is doing 400 watts with both channels driven at 2Khz. AND when the unit is running at rated output of 300 watts with both channels driven, the distortion is less that .06%! So strong and silent!! If the neighbors complain, it will be because of too much GOOD CLEAN sound!

There you go. An amp that was only rated at 300 watts. I tell people this all the time and they think I am making this up.
 
I don't think most folks have any idea how much power 400 wpc really is. It was crazy talk when these amps were new and is still somewhat mental even today. [I just giggle when a dealer demos a system to me on a pair of 1.2kws with the meters hovering at 1.2 wpc. It's like, what's the point?]

Most high powered consumer power amps are good for a half an hour to an hour when cranked to party approved levels whereas the MC2300 will make that power all day long. Mc certainly has more refined designs. But, the MC2300 remains the power/dollar value in Mc's line after all these years and I can't even think of a close second. It'll also drive nearly anything you could conceivably connect to it. (16) pairs of 8 Ohm speakers? No problem. Bridged mono to (16) 4 Ohm woofers wired in parallel? No sweat.

I'll never sell mine.
 
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