I have serious problem with my mcintosh MC2105 power amp. With both left and right volumes at the same level the left output from the power amp has a significantly less amount of gain as the right output. I would say about 20 to 30 dB difference. The decibel meter for the left shows this gain difference between the 2 outputs. I try to crank up the left to compensate but then it distorts (noticeably) without that much gain. BTW the speakers I'm using with this are the ESS amt-1a (electro-static). I've tested the amp on diff speakers with the same result and different inputs. For awhile this setup worked well in the living room but then I put the amp in the basement for about 3 years when I got my surround sound and recently I tried getting this same setup to work again. I would really like to get this to work again.
Any ideas on what the problem is?
Should I try to get it repaired or should I try looking for a diff mcintosh amp (newer)?
I really miss listening to this amp (well more like the ESS speakers). Maybe I should try to look for a slightly used newer model.
Any ideas on what the problem is?
Should I try to get it repaired or should I try looking for a diff mcintosh amp (newer)?
I really miss listening to this amp (well more like the ESS speakers). Maybe I should try to look for a slightly used newer model.
Ok, after alot of logical thinking 
I've concluded that the small preamp circuit board in the MC2105 is broke. Here's my logic behind this deduction. The noticable decrease of gain is shown my the decibel meters and the headphone output and speaker output have little left gain. It has to be this little board because the decibel meter uses the output from this board and the headphones work off this board. So, I first tested the transistors to see if they all had the .67volts across base/emitter/collector and all of them turned out ok. Then I looked at the capacitors and there was a .0047 uf ceramic cap that was dead so I replaced it. After the replacement I tried the amp again and there was no improvement. So, now I'm thinking I shoud replace the blue electrolytic caps as well and go through each resistor. Here are some pics that show my amp
I also measured the input POTS and both are same resistance values on the meter, can I trust my meter or should I replace them anyway?
Does anyone have some ideas of what else might be wrong?
Does mcintosh sell these small boards seperately or does anyone knwo where I can get a used board that works?
I've concluded that the small preamp circuit board in the MC2105 is broke. Here's my logic behind this deduction. The noticable decrease of gain is shown my the decibel meters and the headphone output and speaker output have little left gain. It has to be this little board because the decibel meter uses the output from this board and the headphones work off this board. So, I first tested the transistors to see if they all had the .67volts across base/emitter/collector and all of them turned out ok. Then I looked at the capacitors and there was a .0047 uf ceramic cap that was dead so I replaced it. After the replacement I tried the amp again and there was no improvement. So, now I'm thinking I shoud replace the blue electrolytic caps as well and go through each resistor. Here are some pics that show my ampAn externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I also measured the input POTS and both are same resistance values on the meter, can I trust my meter or should I replace them anyway?
Does anyone have some ideas of what else might be wrong?
Does mcintosh sell these small boards seperately or does anyone knwo where I can get a used board that works?
another easy thing to do
also try swapping the driver (??) boards on the top of the amp between left and right channels to see if the problem follows the boards.
these slide in and out like PCI cards on a computer. might do well with cleaning the copper contacts too.
my mc2100 had a cap that needed replacing on one of these cards
also try swapping the driver (??) boards on the top of the amp between left and right channels to see if the problem follows the boards.
these slide in and out like PCI cards on a computer. might do well with cleaning the copper contacts too.
my mc2100 had a cap that needed replacing on one of these cards
I was incorrect about the decibel meters and headphones working off that little board. I switched the two output boards and guess what... the bad channel switch from left to right. Here are the two boards.
These boards have different components on them. I asked my dad if this amp was ever repaired and he said yes. Apparently when this amp was bought he moved into a brand new apartment and the builders mistakenly put 220volts for his appliance lines. This blew up the amp
So, the amp was then repaired but with different components (equivalents really). I checked all the resistors and the caps and the little transistors and all of them seem to be in working order. Then I flipped the board over to look at the solderings. Whoever repaired this board must have been an intern for mcintosh. There's a few coroded connections, one is barely connected to the board and there's a few cold solder spots. I hope I can repaired these connections without making a new PCB board for it. Heres a pic of the solder side...it doesnt do it justice but it's not a good soldering job.
I realize that age can have an affect on this but the other board is older than the one thats broke and still works perfectly.
An externally hosted image should be here but it was not working when we last tested it.
These boards have different components on them. I asked my dad if this amp was ever repaired and he said yes. Apparently when this amp was bought he moved into a brand new apartment and the builders mistakenly put 220volts for his appliance lines. This blew up the amp
So, the amp was then repaired but with different components (equivalents really). I checked all the resistors and the caps and the little transistors and all of them seem to be in working order. Then I flipped the board over to look at the solderings. Whoever repaired this board must have been an intern for mcintosh. There's a few coroded connections, one is barely connected to the board and there's a few cold solder spots. I hope I can repaired these connections without making a new PCB board for it. Heres a pic of the solder side...it doesnt do it justice but it's not a good soldering job.
An externally hosted image should be here but it was not working when we last tested it.
I realize that age can have an affect on this but the other board is older than the one thats broke and still works perfectly.
http://www.diyaudio.com/forums/showthread/t-1310.html
The drivers, no longer available from McIntosh, are available from Magic Parts for $11 each, or see above post for sub.
also read:
http://www.audioasylum.com/forums/amp/messages/49299.html
The drivers, no longer available from McIntosh, are available from Magic Parts for $11 each, or see above post for sub.
also read:
http://www.audioasylum.com/forums/amp/messages/49299.html
Do you have a product number for magic parts?
Is their website magicparts.com?
I think that is the best course of action for this amp and for myself. I'm probably going to buy 2 brand new boards for this amp and then use the old ones for spare parts. Of course if magic parts doesnt have these boards anymore then I'll have to replace components .
This is so great that this amp is going to work again. I miss it's...perfection
Is their website magicparts.com?
I think that is the best course of action for this amp and for myself. I'm probably going to buy 2 brand new boards for this amp and then use the old ones for spare parts. Of course if magic parts doesnt have these boards anymore then I'll have to replace components
.This is so great that this amp is going to work again. I miss it's...perfection
From the post you didn't read:
PNP
RCA 40409 .7(Ic)/90(V) TO-39
Driver Transistor w/heat sink
RCA 40410 .7(Ic)/90(V) TO-39
Send us an email to dealers@magicparts.com and include your zip code in your subject line. We will promptly reply with the dealers in your area.
"I'm probably going to buy 2 brand new boards "
Tell me another one.
McIntosh quit making that amplifier over 25 years ago.
PNP
RCA 40409 .7(Ic)/90(V) TO-39
Driver Transistor w/heat sink
RCA 40410 .7(Ic)/90(V) TO-39
Send us an email to dealers@magicparts.com and include your zip code in your subject line. We will promptly reply with the dealers in your area.
"I'm probably going to buy 2 brand new boards "
Tell me another one.
McIntosh quit making that amplifier over 25 years ago.
Was McIntosh warranty
Hi TheDude1884,
In servicing these amps, I have found that some of the electrolytics go open with time. Just replace them with new. There is also an optocoupler that may go defective. Order a manual from those fine folks at McIntosh, they may give you some suggestions.
Clean up the poor workmanship and replace any ECG / NTE parts with the real thing. There is no reason the replace the boards. I really hate crappy parts and sloppy work! I do have a list of McIntosh semiconductor numbers to real life.
-Chris
Hi TheDude1884,
In servicing these amps, I have found that some of the electrolytics go open with time. Just replace them with new. There is also an optocoupler that may go defective. Order a manual from those fine folks at McIntosh, they may give you some suggestions.
Clean up the poor workmanship and replace any ECG / NTE parts with the real thing. There is no reason the replace the boards. I really hate crappy parts and sloppy work! I do have a list of McIntosh semiconductor numbers to real life.
-Chris
the service manual for the 2100/2105 are available for free at http://www.berners.ch/McIntosh/en/Frame_McIntosh.htm
I found the problem!!!
it's the 330uf capacitor on the board thats causing problems. I switched the caps from bad board to good board and the channels switched again. Instead of just replacing that cap im going to replace all the electrolytic caps on the 2 boards (4 caps). I do have 2 brand new rca transistors coming in the mail as well.
Thanks to everyone for the suggestions. Without you it'd be another week before I figured out what the problem was. This is the best audio electronics forum on the web and don't let anyone tell you different.
it's the 330uf capacitor on the board thats causing problems. I switched the caps from bad board to good board and the channels switched again. Instead of just replacing that cap im going to replace all the electrolytic caps on the 2 boards (4 caps). I do have 2 brand new rca transistors coming in the mail as well.
Thanks to everyone for the suggestions. Without you it'd be another week before I figured out what the problem was. This is the best audio electronics forum on the web and don't let anyone tell you different.
"I have found that some of the electrolytics go open with time. "
Gee, I already said that, and gave the values and schematic reference numbers, and a brief description of what each cap does and how to improve the sound.
"There is also an optocoupler that may go defective."
Not in this model.
"There is no reason the replace the boards."
I agree.
"Clean up the poor workmanship and replace any ECG / NTE parts with the real thing. "
I agree.
Gee, I already said that, and gave the values and schematic reference numbers, and a brief description of what each cap does and how to improve the sound.
"There is also an optocoupler that may go defective."
Not in this model.
"There is no reason the replace the boards."
I agree.
"Clean up the poor workmanship and replace any ECG / NTE parts with the real thing. "
I agree.
Hey djk,
I don't see your post where you gave part #'s for caps. Going from memory, I know that the optocouplers can be problematic in some of these models. I am mistaken here, but I just look for them if the amp is in front of me.
Anyhow, unwind & relax. We are all bound to miss a post & repeat some information.
-Chris
I don't see your post where you gave part #'s for caps. Going from memory, I know that the optocouplers can be problematic in some of these models. I am mistaken here, but I just look for them if the amp is in front of me.
Anyhow, unwind & relax. We are all bound to miss a post & repeat some information.
-Chris
"I don't see your post where you gave part #'s for caps."
From post #6:
http://www.audioasylum.com/forums/amp/messages/49299.html
"I used bypass 47uF bypass cap across the big electrolytics as you suggested on your from your AA post , .. seemed to clear up some fuzz in the sound.
someday, i hope to go through the other mods on the (t)rusty old mc 2100 to make it a little more special"
The biggest bang for the buck in addition to adding the 47µF bypass caps in parallel with the main filter caps are tacking a 0.1µF film acrosss C309, 310 the 10µF output coupling caps for the pre-driver section, and tacking a 0.1µF film type across C1, 2 the feedback loop caps, 330µF at 3V. Adding the 0.1µF film bypass really opens up the sound.
I call it "the $4 mod", and virtually every amp I touch gets it.
From post #6:
http://www.audioasylum.com/forums/amp/messages/49299.html
"I used bypass 47uF bypass cap across the big electrolytics as you suggested on your from your AA post , .. seemed to clear up some fuzz in the sound.
someday, i hope to go through the other mods on the (t)rusty old mc 2100 to make it a little more special"
The biggest bang for the buck in addition to adding the 47µF bypass caps in parallel with the main filter caps are tacking a 0.1µF film acrosss C309, 310 the 10µF output coupling caps for the pre-driver section, and tacking a 0.1µF film type across C1, 2 the feedback loop caps, 330µF at 3V. Adding the 0.1µF film bypass really opens up the sound.
I call it "the $4 mod", and virtually every amp I touch gets it.
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