My MC2100 has developed a hiss on the left channel. I've also noticed that the board on the left side of the capacitors (if you consider the long branded side the front of the unit) put out far more heat than those on the right. Are these issues related? Are there any ideas of how I can fix the hissing? Thanks.
It's between 30~40 years old, it's worn out.
I would replace everything except the chassis, transformers, and heatsink.
The two driver transistors are no longer available from McIntosh, but they are still available (at a price). A set will cost about $40 for both channels. A set of 12 outputs and all the other transistors will run about the same (from an industrial distributor, not from McIntosh).
Most of the smaller caps I would buy from Digi-Key.
You may be able to find a surplus deal on the main filter caps (make sure they have fresh date codes).
I would buy the resistors from Digi-Key or Mouser.
After you freshen it up it will run another 30 years.
I might be able to arrange to have your driver boards rebuilt by a friend, I have an MC2100 to check them out in.
I would replace everything except the chassis, transformers, and heatsink.
The two driver transistors are no longer available from McIntosh, but they are still available (at a price). A set will cost about $40 for both channels. A set of 12 outputs and all the other transistors will run about the same (from an industrial distributor, not from McIntosh).
Most of the smaller caps I would buy from Digi-Key.
You may be able to find a surplus deal on the main filter caps (make sure they have fresh date codes).
I would buy the resistors from Digi-Key or Mouser.
After you freshen it up it will run another 30 years.
I might be able to arrange to have your driver boards rebuilt by a friend, I have an MC2100 to check them out in.
Hi djk,
Outputs worn out?
I'd be looking at caps and maybe small signal transistors first.
-Chris
Outputs worn out?
I'd be looking at caps and maybe small signal transistors first.
-Chris
"Outputs worn out?"
Maybe not, but being 30~40 years old and only about $2.50 each I would replace them while I've got it on the bench (I've seen a few in the last 10 years or so that were blown).
Drivers are RCA 40409/10.
Maybe not, but being 30~40 years old and only about $2.50 each I would replace them while I've got it on the bench (I've seen a few in the last 10 years or so that were blown).
Drivers are RCA 40409/10.
Hi djk,
My cost is a fair bit higher per piece. Then there is the labour of picking out matched sets along with the "waste" of transistors that do not match.
If we are going to do this, may as well do it right. I must say that On Semi's newer parts have a much higher yield though.
-Chris
My cost is a fair bit higher per piece. Then there is the labour of picking out matched sets along with the "waste" of transistors that do not match.
If we are going to do this, may as well do it right. I must say that On Semi's newer parts have a much higher yield though.
-Chris
Chris,
Even with the higher cost associated with replacing the outputs and drivers the end result is well worth it. Outputs never go to waste because they can sit on the shelf until they are used and the cost is naturally passed on to the consumer. I learned the hard way that DJK is correct. Years ago I was trying to repair a large power amplifier and I got it running but failed to listen to Mr. DJK's warnings to replace the driver and output stage and blew it up again. I repaired it the second time and replaced all the semiconductors per DJK's recommenfations and it is still running to this day and that was over 25 years ago.
Years ago Mr. DJK was the service manager of a large high end electronic store that was a major MacIntosh dealer and he knows his ****.
Are the RCA parts still available today or were these house part numbers? What can they be replaced with ?
Even with the higher cost associated with replacing the outputs and drivers the end result is well worth it. Outputs never go to waste because they can sit on the shelf until they are used and the cost is naturally passed on to the consumer. I learned the hard way that DJK is correct. Years ago I was trying to repair a large power amplifier and I got it running but failed to listen to Mr. DJK's warnings to replace the driver and output stage and blew it up again. I repaired it the second time and replaced all the semiconductors per DJK's recommenfations and it is still running to this day and that was over 25 years ago.
Years ago Mr. DJK was the service manager of a large high end electronic store that was a major MacIntosh dealer and he knows his ****.
Are the RCA parts still available today or were these house part numbers? What can they be replaced with ?
Digi-Key current cost for TO-3 devices is $2.45 each in 100 lot trays (most models). Probably higher in Canada.
The RCA 40409/10 are the original RCA part numbers and used in other designs (all the SWTPC amps). I buy mine from a distributor:
http://www.magicparts.com/
In Canada:
http://www.audionova.ca/
This list is for the MC2100, electrically it is the same as the MC2105, just without the meters.
Even though your old amp is still working, you have no idea how much of the music you are missing.
The parts are inexpensive.
Digi-Key is good, Mouser has no minimum order.
Posted by djk (M) on July 11, 2004 at 04:29:36
In Reply to: Re: MC2105 @ $ 100 even @ 20 yrs old is a best buy for me. posted by julian4@telkomsa.net on July 06, 2004 at 14:58:04:
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 RCA 40409/10 are the original RCA part numbers and used in other designs (all the SWTPC amps). I buy mine from a distributor:
http://www.magicparts.com/
In Canada:
http://www.audionova.ca/
This list is for the MC2100, electrically it is the same as the MC2105, just without the meters.
Even though your old amp is still working, you have no idea how much of the music you are missing.
The parts are inexpensive.
Digi-Key is good, Mouser has no minimum order.
Posted by djk (M) on July 11, 2004 at 04:29:36
In Reply to: Re: MC2105 @ $ 100 even @ 20 yrs old is a best buy for me. posted by julian4@telkomsa.net on July 06, 2004 at 14:58:04:
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.
First, I apologize for the thread jack. While we are discussing Mac's,
I would like to seek some advise.
I have a MC2120. I believe it is very close to the MC2100, no meter
and 20 wpc more. It has a problem that the right channel produces no sound when power on, sometimes it comes back after a few mad on/off's. Then it will stay until the next power on/off. I sent this to a Mac authorized repair shop, and the problem came back after 90 days warranty expired and $450 lighter ..... So, I am going to try repairing it myself. Any advise where the problem might be? I do have the service manual.
Thanks,
I would like to seek some advise.
I have a MC2120. I believe it is very close to the MC2100, no meter
and 20 wpc more. It has a problem that the right channel produces no sound when power on, sometimes it comes back after a few mad on/off's. Then it will stay until the next power on/off. I sent this to a Mac authorized repair shop, and the problem came back after 90 days warranty expired and $450 lighter ..... So, I am going to try repairing it myself. Any advise where the problem might be? I do have the service manual.
Thanks,
Hi Fred,
I have seen some intermittent relay contacts and the odd bad solder. I've even had an intermittent capacitor kill the sound.
Hi Joe,
Just questioning to pick up some knowledge here. I will replace outputs when I see issues. Low gain is the most common, followed by leakage. I suspect in your case that you may have had some leaky transistors. Just guessing since I have not seen the amp and only you can know exactly what happened. After it blowing up again, I would have done the same thing. I do tend to measure gain and leakage in my normal cleanup.
Hi djk,
You are giving good advice for someone who doesn't test the output transistors. I normally test them all and rearrange them if needed to match gains between channels and push or pull ( 😉 ). I haven't had one come back yet, although a couple didn't pass the hot test. Never for a blow up though, always an intermittent.
Please don't take this as a criticism at all. I'm here to learn also.
-Chris
I have seen some intermittent relay contacts and the odd bad solder. I've even had an intermittent capacitor kill the sound.
Hi Joe,
Just questioning to pick up some knowledge here. I will replace outputs when I see issues. Low gain is the most common, followed by leakage. I suspect in your case that you may have had some leaky transistors. Just guessing since I have not seen the amp and only you can know exactly what happened. After it blowing up again, I would have done the same thing. I do tend to measure gain and leakage in my normal cleanup.
Hi djk,
For sure!
You are giving good advice for someone who doesn't test the output transistors. I normally test them all and rearrange them if needed to match gains between channels and push or pull ( 😉 ). I haven't had one come back yet, although a couple didn't pass the hot test. Never for a blow up though, always an intermittent.
Please don't take this as a criticism at all. I'm here to learn also.
-Chris
Chris,
I do own 3 Sencore transistor testers and I do always test the transistors. I do find however that age is an important fact here as I have had problems with transistors that showed no leakage and had gain within the normal parameters.
I still change out the old transistors with new matched ones because it makes life so much simpler in the long run.
I do own 3 Sencore transistor testers and I do always test the transistors. I do find however that age is an important fact here as I have had problems with transistors that showed no leakage and had gain within the normal parameters.
I still change out the old transistors with new matched ones because it makes life so much simpler in the long run.
Hi Joe,
I'm not familiar with your testers, so I can't say how effective they are. I have at least 5 different transistor testers plus a curve tracer (old Heathkit thing). The one I use the most measures beta and leakages (collector base and collector emitter). This tester almost never misses to catch iffy devices. That and my familiarity with it, Heathkit IT-18. The other testers came later as I searched for a better tester. That older simple one has not been beat yet. Guess how much $$ I wasted trying for a better tester? I am currently thinking about buying that USB transistor curve tracer and have built a few jigs that I find very useful.
Anyway, in no way was I trying to degrade your troubleshooting procedure. Sorry if it sounded that way.
-Chris
I'm not familiar with your testers, so I can't say how effective they are. I have at least 5 different transistor testers plus a curve tracer (old Heathkit thing). The one I use the most measures beta and leakages (collector base and collector emitter). This tester almost never misses to catch iffy devices. That and my familiarity with it, Heathkit IT-18. The other testers came later as I searched for a better tester. That older simple one has not been beat yet. Guess how much $$ I wasted trying for a better tester? I am currently thinking about buying that USB transistor curve tracer and have built a few jigs that I find very useful.
Anyway, in no way was I trying to degrade your troubleshooting procedure. Sorry if it sounded that way.
Well, of course! That's as long as the customer is willing to pay for them when they know the amp was not suffering from output failure. That can be a hard sell my friend. 😉 Only when I can justify the reason for changing the outputs do I suggest that course of action.
-Chris
I would have made the same assumption. There are still a few of us that do take the time and trouble to try to do a good job.
Never had a problem selling the repair to a customer. When the age is brought up the answer is always the same.... do what it takes to make it run properly.... and I do.
Hi Joe,
That I do know about you.
Many of my customers will allow me a free hand to replace what is required. Replacing "good" outputs is tough to do up here.
-Chris
That I do know about you.
Many of my customers will allow me a free hand to replace what is required. Replacing "good" outputs is tough to do up here.
-Chris
My customers usually brought it to me last. I was usually the third or fourth tech to work on it. If they didn't want it fixed properly I wouldn't work on it.
I took to buying blown amps and re-furbishing them. I would fix what was blown in the one channel and replace all the outputs and drivers in the other channel. I would then re-sell the amp with a warranty, usually a year (same as a new amp from Peavey).
A few leading questions were usually all it took to get them around to my way of thinking:
How long did it run after your last repair job at (dealer name)?
How bad were your speakers damaged?
Were you able to finish the gig and get paid?
What kind of a 'bargain' was that 'band-aid' repair?
Are you you going to keep the amp after it's fixed, or are you going to dump it?
I took to buying blown amps and re-furbishing them. I would fix what was blown in the one channel and replace all the outputs and drivers in the other channel. I would then re-sell the amp with a warranty, usually a year (same as a new amp from Peavey).
A few leading questions were usually all it took to get them around to my way of thinking:
How long did it run after your last repair job at (dealer name)?
How bad were your speakers damaged?
Were you able to finish the gig and get paid?
What kind of a 'bargain' was that 'band-aid' repair?
Are you you going to keep the amp after it's fixed, or are you going to dump it?
Hi djk,
You and I are in the same position exactly. It was always a string of morons technicians before it came in to us. Then it was a write off or repaired. As a result, many customers send the stuff in first. The pro guys included. The problem is that they normally have road techs to get stuff running (good enough for rock and roll). There is internal conflict when they want to send amps out. We also did the same thing. Complete rebuild.
The standard repair is replace the transistor or couple that actually failed. Normally without new grease.
Our high end customers have been burned so badly in the Toronto area that referrals from other customers is required. Still, the dollars are tight. At least all my customers are reasonable to deal with and don't argue if the work done is required or preventative in nature.
-Chris
You and I are in the same position exactly. It was always a string of morons technicians before it came in to us. Then it was a write off or repaired. As a result, many customers send the stuff in first. The pro guys included. The problem is that they normally have road techs to get stuff running (good enough for rock and roll). There is internal conflict when they want to send amps out. We also did the same thing. Complete rebuild.
The standard repair is replace the transistor or couple that actually failed. Normally without new grease.
Our high end customers have been burned so badly in the Toronto area that referrals from other customers is required. Still, the dollars are tight. At least all my customers are reasonable to deal with and don't argue if the work done is required or preventative in nature.
-Chris
Duh
Talk about stupid. Half a year ago purchased aworking mc2100. I could tell it was used countless hours over the years compared to the ohther SS mac I have tonal/clearity wise.
Overhaul time no rush:
1st was cap replacement guide found in this forum. TNX
2nd ,gain pots,1/4inch l n r input jacks,brass banana jacks on com,8,16ohms. Th e other ohms and circular output jack disabled.
Next transistors and the retarded move I made was not labelling the driver card's slots wire colours to the approp. transistor pins on heat sink.
Any help would be gratefully appreciated.
Thanks,
hawk
Talk about stupid. Half a year ago purchased aworking mc2100. I could tell it was used countless hours over the years compared to the ohther SS mac I have tonal/clearity wise.
Overhaul time no rush:
1st was cap replacement guide found in this forum. TNX
2nd ,gain pots,1/4inch l n r input jacks,brass banana jacks on com,8,16ohms. Th e other ohms and circular output jack disabled.
Next transistors and the retarded move I made was not labelling the driver card's slots wire colours to the approp. transistor pins on heat sink.
Any help would be gratefully appreciated.
Thanks,
hawk
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