Re: Thanks
Why not go to this website and download the Service Manual for the MC2505?
http://www.berners.ch/McIntosh/en/Matrix.htm
MikeW said:
Why not go to this website and download the Service Manual for the MC2505?
http://www.berners.ch/McIntosh/en/Matrix.htm
.In reply to an earlier post asking about the inductor at the output--it's not an inductor, per se, it's an autoformer. Autoformers are sort of like one-coil transformers. McIntosh has used them for years. Their position is that you paid for a 100W amplifier, and they're going to give you 100W into any load that you might care to use--none of this doubling into 4 ohms nonsense...perish the thought.
Just think of it as a transformer output, even if the amp itself is solid state. How that relates to the sound quality I will leave to your imagination. I used to own some of their stuff back in the '70s. It was not what you'd call state of the art, even then. That said, I still think they have some of the sexiest looking gear that's ever been made.
I have my fingers crossed that their recent re-entrance into the tube market will lead to good things, even if I don't like the current cosmetics quite as much as the '70s & '80s product.
Grey
Just think of it as a transformer output, even if the amp itself is solid state. How that relates to the sound quality I will leave to your imagination. I used to own some of their stuff back in the '70s. It was not what you'd call state of the art, even then. That said, I still think they have some of the sexiest looking gear that's ever been made.
I have my fingers crossed that their recent re-entrance into the tube market will lead to good things, even if I don't like the current cosmetics quite as much as the '70s & '80s product.
Grey
"How that relates to the sound quality I will leave to your imagination. I used to own some of their stuff back in the '70s. It was not what you'd call state of the art, even then. "
The autoformer has less phase shift at high frequencies than the transistors do.
The problem with McIntosh amps are related to poor quality caps.
For a 70s vintage MC2120/2125:
"Which caps are they DJK? I'll try them in my 2125."
Add one 47µF across each ±42V rail at the main filter caps
Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)
Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)
Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)
Add a 0.1µF film in parallel with C219, 220 (feedback cap)
Add a 0.1µF film in parallel with Q215, 216 (bias transistor)
Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)
Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)
I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.
I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.
I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.
Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.
The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.
Even though this changes no measurable performance specification, it will change the sound more than you can believe.
Jackhammer bass from an amp with a DF of only 14?
For the MC250/2505, MC2100/2105:
The sound would benefit greatly from replacing a few dried out electrolytics, and adding a few film types here and there.
C301, 302 is the main input coupling cap. It is a Mylar type so it is likely to be OK, upgrading it to a Polypropylene type with give a smoother sound to the high end (0.47µF).
C307, 308 are emitter bypass caps, 100µF 15V. Replace with same type and add a 0.1µF film bypass.
C309, 310 are the output coupling caps for the pre-driver section, 10µF 25V. While a film type would be better, size is a problem. The DC bias across this cap also helps out with its being an electrolytic. Replace with same type and add a 0.1µF film bypass.
C303, 304 are the DC power supply caps for the front end, 470µF at 25V. Replace with same type and add a 0.1µF film bypass.
C1, 2 are the feedback loop caps, 330µF at 3V. The signal goes through these so replacing these with new ones and adding a 0.1µF film bypass really opens up the sound. Go with as high a voltage as what space permits.
C11, 12 are the DC supply caps for the voltage gain stage, 150µF at 50V. Replace with same type and add a 0.1µF film bypass.
C201, 202 are the main filter caps, 39,000µF at 40V. These may be quite expensive new, although I have seen them surplus for very low prices. I would use then unless signs of leakage or amplifier hum are there. Add a 47µF at 50V cap in parallel with each.
C203 is a multi-section cap that will be very hard to find a fresh date code. New caps are small enough that they may be wired to the terminals of the old one, leaving the old one in place. This cap is important as it provides the current for the diff pairs and the VAS. The sections go 80/80/150/50µF with the voltages being 200/200/150/150V. If you measure the voltages 100/95/90/80V are typical, so 200V caps are not really needed, but 100V is not enough.
The autoformer has less phase shift at high frequencies than the transistors do.
The problem with McIntosh amps are related to poor quality caps.
For a 70s vintage MC2120/2125:
"Which caps are they DJK? I'll try them in my 2125."
Add one 47µF across each ±42V rail at the main filter caps
Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)
Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)
Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)
Add a 0.1µF film in parallel with C219, 220 (feedback cap)
Add a 0.1µF film in parallel with Q215, 216 (bias transistor)
Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)
Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)
I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.
I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.
I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.
Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.
The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.
Even though this changes no measurable performance specification, it will change the sound more than you can believe.
Jackhammer bass from an amp with a DF of only 14?
For the MC250/2505, MC2100/2105:
The sound would benefit greatly from replacing a few dried out electrolytics, and adding a few film types here and there.
C301, 302 is the main input coupling cap. It is a Mylar type so it is likely to be OK, upgrading it to a Polypropylene type with give a smoother sound to the high end (0.47µF).
C307, 308 are emitter bypass caps, 100µF 15V. Replace with same type and add a 0.1µF film bypass.
C309, 310 are the output coupling caps for the pre-driver section, 10µF 25V. While a film type would be better, size is a problem. The DC bias across this cap also helps out with its being an electrolytic. Replace with same type and add a 0.1µF film bypass.
C303, 304 are the DC power supply caps for the front end, 470µF at 25V. Replace with same type and add a 0.1µF film bypass.
C1, 2 are the feedback loop caps, 330µF at 3V. The signal goes through these so replacing these with new ones and adding a 0.1µF film bypass really opens up the sound. Go with as high a voltage as what space permits.
C11, 12 are the DC supply caps for the voltage gain stage, 150µF at 50V. Replace with same type and add a 0.1µF film bypass.
C201, 202 are the main filter caps, 39,000µF at 40V. These may be quite expensive new, although I have seen them surplus for very low prices. I would use then unless signs of leakage or amplifier hum are there. Add a 47µF at 50V cap in parallel with each.
C203 is a multi-section cap that will be very hard to find a fresh date code. New caps are small enough that they may be wired to the terminals of the old one, leaving the old one in place. This cap is important as it provides the current for the diff pairs and the VAS. The sections go 80/80/150/50µF with the voltages being 200/200/150/150V. If you measure the voltages 100/95/90/80V are typical, so 200V caps are not really needed, but 100V is not enough.
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