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MC2500/MC2300 Advice

Solder but they're easy ... I have on one occasion seen a bad bulb on the LIMIT side, but this usually indicates a problem elsewhere.

If the price is right, you may wanna jump.
 
damacman said:
Solder but they're easy ... I have on one occasion seen a bad bulb on the LIMIT side, but this usually indicates a problem elsewhere.

If the price is right, you may wanna jump.
Click to expand...

Well given the unkown it was priced right if there were no problems. So for the deal to go I'll have to see if he is flexible. There is a couple of techs local who service Mcintosh. Given what they charged on My Ebay Yamaha pro amp I got seller to cover with PayPal they probably will charge 200 ato 300 if issues are minor. If only lamps I will tackle that. I was hoping for turnkey but I have yet to buy vintage that is turn key.
 
The MC2500 is sufficiently advanced over the 2300 that it makes it the preferred amp.

I have two of them so I am a little prejudiced. Having said that, the specs are better on the MC2500.

Be sure to to eat your Wheaties. The 2500 is quite heavy.

The limit lamps will glow momentarily at power on provided the amp has been off for several hours. If the amp has been turned on anytime within the last few hours, the limit lamps will not turn on when power is applied. This is due to a combination of the extremely high impedance and the relatively large capacitance in the circuit.

There is an inherent design flaw that will permit some 60 hz leakage into the input side of the amp. Whether or not you experience it is dependent on several factors including humidity, aging of the wire insulation, etc. The fix for it is to redress the fan power wiring inside the amplifier. If you don't hear any residual hum, then I would just leave it alone. Since the fix, I can't tell if the amp is on or off by putting my ear next to the speaker.

For all the gory details, see this link.
http://rich.homeunix.com/mc2500/mc2500mod.html

The original lamps are always a problem on those amps. They just don't last as long as they should. Just plan on changing them every 7 years or so.
 
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So, what'd you end up doing? Be sure and check out the info Rich linked you to as well . . . good stuff.
 
damacman said:
So, what'd you end up doing? Be sure and check out the info Rich linked you to as well . . . good stuff.
Click to expand...

Well I did what I have been itching for...............and Seller took a price reduction that should cover me if there is a limit issue beyond the lamps.

right now I Have a MC2500 driving sweet Melodies out of those XRT20s and XR19s with some streaming Pandora.

The dynamic range is fabulous. It is different from the Yamaha PC2602 vintage Pro amp. Highs and mids are softer on the edge a different sparkle. They float great with the Yamaha but even better with the MC2500. Vocal harmonies are better on the Mc even more separate voice distinction. Bass is different. The Yamaha has a higher dampening ratio so it is a different slam maybe. Spent most of the night watching football hearing game from Mcintosh amp I was second guessing.

Once I kicked on the music a whole different story. Have not had a chance to push it to 500 WPC but for a brief bit, since it is late and don't want a police visit on Monday. But I am sure the SPL seems much louder. Even the music at low volume has great depth and clarity.

The 60 Hz buzz is not here with my system cables maybe real slight. Also noise floor seems less than the Yamaha which was quiet and had better specs on paper.

Now I need to source some lamps by part number and see if a DIY will get me back in business on lamps that are out. Would appreciate help on the part number and source. Will have to remove side grab handles to get it in my cabinet and tackle the dust bunnies internal first. Also size up reroute of wire harness per Rich Andrews link. Trying to figure out what to elevate it with once side handles are off so i still get air flow in the bottom. Amp sure runs cool with all of this mass so far.

After I listen to it and get accustomed to the sound I will toy with using the Yamaha to drive XR19s or sell it with some other receivers to cover a good chunk of the MC2500 cost.
 
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Nice! I'll bet it sounds pretty sweet. One of these days, I'd like to try another MC2500. I recommend that you keep the side rails on it unless you intend to rack mount it, otherwise there are about a dozen AKers that would love to buy those from you!

I don't have a service manual for the MC2500 but I'd bet the bulbs are 7381s or 7382s. Maybe Rich knows. So any pics to share?
 
damacman said:
Nice! I'll bet it sounds pretty sweet. One of these days, I'd like to try another MC2500. I recommend that you keep the side rails on it unless you intend to rack mount it, otherwise there are about a dozen AKers that would love to buy those from you!

I don't have a service manual for the MC2500 but I'd bet the bulbs are 7381s or 7382s. Maybe Rich knows. So any pics to share?
Click to expand...

The side rails will have to come off or it will not fit in the cabinet that is 19 inch rack width but with shelves. But I plan to keep if I ever have to transport for service. The side rails have had some use. Since one off the low ohm Terminal screws are gone suspect it saw a bit of PA or sound reinforcement duty miles. The knobs are great though.

I found on another DIY site that the limit light driver circuit on MC2500 often have a transistor failure that cause lamp to stay lit. So if it is not bulb then their is another possible easy fix

If I can't clean up the front rack handles. I may hit you up on NOS. I will snap some Pics when I crack her open. I am going to search out a good black touch paint for top where there are a few srcatches. It is flat but not totally flat black. Anybody know a color code or a source for the paint? I also have some bottom corner edges with worn off paint that was not visible when unit was on carpet Nothing some detailing can't fix.

The fuller sound with the detail there too is going to take some retraining of my ears. It is a lot more natural. The dog took notice right away. He kept standing on his back legs and barking cruising through the dog door trying to find source of sounds that the line array tweeters were throwing off into the room with increased 3D type placement. They even surprised me a few times walking through the listening area causing a double take of a voice singing suddenly behind me but not pinpointed to the speakers.

As for the bass I need to listen to more musical percussion off many sources to see if it gives the sharp initial whack. It maybe just another octave of rich bass throwing me off or not listening to a familair source I heard lately. .

But so far, yes I am a firm believer that a McIntosh Amp is a pleasant gratifying experience. Now only if I had 1000 WPC instead of just 500 how much better could it be?.......... ;)
 
3dB better! All you need is another MC2500 and they can be run mono ... In the meantime you'll have to get by on "just 500" wpc - lol!

As for the leaky transistor, I had an MC2205 that did exactly that. I replaced the transistor and all was good.
 
damacman said:
3dB better! All you need is another MC2500 and they can be run mono ... In the meantime you'll have to get by on "just 500" wpc - lol!

As for the leaky transistor, I had an MC2205 that did exactly that. I replaced the transistor and all was good.
Click to expand...

That was my thinking too bad my checking account was not supporting that 3dB balance yet.

I thought of an interesting amp comparison Run right channel off MC3500 with 1000 watts mono and Left Channel with Yamaha in Mono that is good for 800 WPC and evaluate how they compare with balance knob on pre. Someone at AK must have tried this? Seems like a good way to judge amp coloration and sound. Sort of a Frankenstereo Dastrapoff audition. If you can't tell a difference that solves all amps sound same argument.
 
I spent some more time restoring and playing the MC2500 yesterday. The handle rack rash and top and sides of front panel were addressed perfectly using a flat diamond stone. Which is stainless steel impregnated with diamond dust. It worked perfectly leaving the brushed look and square edges removing scratches abrasions and light gouges present after thirty plus years.

Paint touch up is going to be a bit tougher finding perfect match between the flat black or semigloss look.

Any worries about the amp having enough umph to push the XRT20s and XR19 under a 4 ohm load were vanquished. The 72 tweeters are laid back highs until the power kicks them. Normal dynamics are well handled and it is surprising what was missing. Even my wife said we have been depriving ourselves. I did find more evidence of the bass feed back affecting my turntable compared to the Yamaha amp. I gues it is the more power.

I did get to push the amp and found out low and behold the left limit light does work. Thanks to a Don Felder guitar solo my wife wanted cranked, btw that was quite amazing. It just takes a whole lot more volume to engage the power guard on left channel. Is this normal one channel hitting the guard sooner? Both meters will not activate the PG until past 500 WPC. Since it Performed with the Sellers Pre and mine I doubt it is source coming in. I appreciate any assistance as to whether this is normal and what might cause disparity. I have seen channel clip light differences on other amps where right channel lights sooner always too that compare incoming signal to outgoing.

Next Questionis MC2500 fan performance are they coupled or does right and left work independtly? I finally got a fan yesterday on the right channel. The left side was not producing same flow and air flow was opposite direction like it might not have activated. Normal?
 
I spent some more time restoring and playing the MC2500 yesterday. The handle rack rash and top and sides of front panel were addressed perfectly using a flat diamond stone. Which is stainless steel impregnated with diamond dust. It worked perfectly leaving the brushed look and square edges removing scratches abrasions and light gouges present after thirty plus years.

Paint touch up is going to be a bit tougher finding perfect match between the flat black or semigloss look.

Any worries about the amp having enough umph to push the XRT20s and XR19 under a 4 ohm load were vanquished. The 72 tweeters are laid back highs until the power kicks them. Normal dynamics are well handled and it is surprising what was missing. Even my wife said we have been depriving ourselves. I did find more evidence of the bass feed back affecting my turntable compared to the Yamaha amp. I gues it is the more power.

I did get to push the amp and found out low and behold the left limit light does work. Thanks to a Don Felder guitar solo my wife wanted cranked, btw that was quite amazing. It just takes a whole lot more volume to engage the power guard on left channel. Is this normal one channel hitting the guard sooner? Both meters will not activate the PG until past 500 WPC. Since it Performed with the Sellers Pre and mine I doubt it is source coming in. I appreciate any assistance as to whether this is normal and what might cause disparity. I have seen channel clip light differences on other amps where right channel lights sooner always too that compare incoming signal to outgoing.

Next Questionis MC2500 fan performance are they coupled or does right and left work independtly? I finally got a fan yesterday on the right channel. The left side was not producing same flow and air flow was opposite direction like it might not have activated. Normal?
 
When using the amp in stereo playing music, its not uncommon for one channel to light the power guard lamp before the other at party approved levels. Obviously, this is a function of the recording. OTOH, you could have a slight imbalance in overall gain between channels.

To eliminate guesswork, I like to set gains with the assistance of some tools. At the bare minimum, you can use a DMM and a 1 kHz test tone to balance channels. You'd be surprised how much of a difference this makes in achieving the ideal balance between channels.

As far as the fans go, I believe they do indeed operate independently of each other. Thermo switches are mounted on each the left and right heat sinks. I don't have a service manual but anyone that does can verify via the schematic.
 
damacman said:
When using the amp in stereo playing music, its not uncommon for one channel to light the power guard lamp before the other at party approved levels. Obviously, this is a function of the recording. OTOH, you could have a slight imbalance in overall gain between channels.

To eliminate guesswork, I like to set gains with the assistance of some tools. At the bare minimum, you can use a DMM and a 1 kHz test tone to balance channels. You'd be surprised how much of a difference this makes in achieving the ideal balance between channels.

As far as the fans go, I believe they do indeed operate independently of each other. Thermo switches are mounted on each the left and right heat sinks. I don't have a service manual but anyone that does can verify via the schematic.
Click to expand...

Damacman,

That sounds to be a good solution. If the fans are independent and there is a gain difference it also explains why right channel lights quicker and kicked the fan sooner. I'll have to find a test tone online. It beats replacing all the transistors in the limit light circuit.

I was concerned I might have an output with issues in one circuit. I thought that would be audible like it was on my Yamaha.

Thanks!
 
It goes without saying that you'll be disconnecting speakers before doing any of this ... PM me if you need test tones ...
 
damacman said:
How'd you make out?
Click to expand...

I found a 1 KHz test tone on you tube. I decide to try aligning gain levels with the MC2500 meters for a first cut. The right channel had more gain. So I balanced using the Db scale on meters. Swapped over to music and slammed the volume. Sure enough nearly synched powerguard lights given the different music levels in stereo. Right channel lights still a bit ahead a little more often but could have been music. Could also be meters cal is different right to left . Any knowledge how to calibrate those?

I also found an interesting set of sine wave tones going from 20 Hz to 20 KHz on you tube that displays the frequencies. That proved a good hearing test and also gets the dog excited and let's one hear how well balanced your hearing is or perhaps it is crossovers speakers and amp performance and room nodes show up.

Either system reproduction performance drops off quickly over 18.5 KHz or my hearing does. Lol. Most likely the latter. Interesting to hear some right to left stereo drops between ears as the spectrum changes. Could be hearing, crossovers, or speaker reproduction limitations or variations. At no time did I hear total silence both ears just variations in the stereo effect some frequencies. Too bad it moves so fast through the demo.

Thanks for the tip. I already like the balance better. Did finf the gain pots are scratchy with a 1KHz signal. I finished paint touch upon flat back top schematic just have a few letters to make a bit more readble with exacto. . Time to open her up and clean interior and deoxit and tke off side rails stuff in the cabinet.
 
Rich Andrews said:
The MC2500 is sufficiently advanced over the 2300 that it makes it the preferred amp.

I have two of them so I am a little prejudiced. Having said that, the specs are better on the MC2500.

Be sure to to eat your Wheaties. The 2500 is quite heavy.

The limit lamps will glow momentarily at power on provided the amp has been off for several hours. If the amp has been turned on anytime within the last few hours, the limit lamps will not turn on when power is applied. This is due to a combination of the extremely high impedance and the relatively large capacitance in the circuit.

There is an inherent design flaw that will permit some 60 hz leakage into the input side of the amp. Whether or not you experience it is dependent on several factors including humidity, aging of the wire insulation, etc. The fix for it is to redress the fan power wiring inside the amplifier. If you don't hear any residual hum, then I would just leave it alone. Since the fix, I can't tell if the amp is on or off by putting my ear next to the speaker.

For all the gory details, see this link.
http://rich.homeunix.com/mc2500/mc2500mod.html

The original lamps are always a problem on those amps. They just don't last as long as they should. Just plan on changing them every 7 years or so.
Click to expand...

Hey Rich,

Thanks for the rewire tips. I moved the fan control wiring and overheat thermocouple this weekend. Yes it really made a noise difference an at idle with full gain. I spent a while trying different fan thermocouple wire routngs. I found. A route over the. Bottom of heat sinks to be quietest maybe not as pretty as your pics. . Keeping away from outputs and away from filter caps gave the optimum result. I chose SQ over wire loom beauty and since she will not see road hours chafing is of little worry.

I doubt I'll execute your circuit filter cap improvements pilfered from from MC2600 circuits until their is need for revitalization rework. It is about time to stuff this monster in the cabinet. Removed side rails and finished paint and AL touchups. All she needs now is a strappin sister.

Just heard some Steely Dan, Nineteen a song to appreciate low noise floor and clear highs! Wow a Jackson BrowneRunning on Empty. Live version just startled me with backup vocals I had never heard. Jumped out and grabbed me. Got to love the Mcintosh goose bumps!

Thanks for sharing your expertise with an AK newbie!
 
That was the first thing I noticed about the MC2600 after I connected it - how dead quiet it was. Makes me wonder just how much better the new amps are in regard.

VB - I'm sure quartersaw would love to have those side rails ...
 
damacman said:
That was the first thing I noticed about the MC2600 after I connected it - how dead quiet it was. Makes me wonder just how much better the new amps are in regard.

VB - I'm sure quartersaw would love to have those side rails ...
Click to expand...

Damacman,

I would bet MC2300 uses same fan control wiring routed by inputs as MC2500. You should check it out and try it when you unpack your amps . The MC2500 is significantly quieter and I only had to snip two zip ties. It is easy gratification moving around wires. Almost as much fun as rabbit ears and old TVs.
 
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