I have a Mcintosh mc2205 that I inherited from my dad and besides minor problems like the speakers knob occasionally blocking the signal to the right channel so I have to turn it off and on and that fixes that. Also the meters are slightly off, for example increasing the signal by 10 db doesn't neccesarily move the meters by exactly 10db, and I measured this with a volt meter on the output. But the meters are approximately accurate within probably 3-5 db. Also the gain knobs are no longer matched so for equal output they are at different settings for the left gain and the right gain, and the left gain when taken to the max will cause some static.
But despite these, the amp still sings and none of those really bother me. But as for the reliability of the amp, I don't want to avoid doing maintenance on it at the risk of harming the amp. If the amp still sounds great and I don't really push it past 20wpc anyways, am I at any risk of causing harm to the amp?
But despite these, the amp still sings and none of those really bother me. But as for the reliability of the amp, I don't want to avoid doing maintenance on it at the risk of harming the amp. If the amp still sounds great and I don't really push it past 20wpc anyways, am I at any risk of causing harm to the amp?
Well, i gave my son my dad's Dual CV40 amp, made in 1978.
We disassembled it to the last bolt, to clean, de-oxydize and recap. I measured all caps in the amp, they were spot on their nominal values ; even the bias pots needed no adjustment at all... All in all, we vacuumed a ton of dust, changed the speaker plugs which were oxydized black beyond cleaning, waxed the wood case, and the amp looks and sounds like new without deoldering any cap...
So it might make sense to start mezsuring those caps before making more harm than good...
We disassembled it to the last bolt, to clean, de-oxydize and recap. I measured all caps in the amp, they were spot on their nominal values ; even the bias pots needed no adjustment at all... All in all, we vacuumed a ton of dust, changed the speaker plugs which were oxydized black beyond cleaning, waxed the wood case, and the amp looks and sounds like new without deoldering any cap...
So it might make sense to start mezsuring those caps before making more harm than good...
An ESR meter suitable for in-circuit testing is, however, highly recommended for this task. Dried-out caps may well hold nominal or even higher capacitance, but their ESR will be through the roof.
It does sound like the OP's unit has some issues that may trace back to dried-out small electrolytics or out-of-spec carbon resistors, or just simple contact issues - IOW, the usual things that may plague electronics that old.
It does sound like the OP's unit has some issues that may trace back to dried-out small electrolytics or out-of-spec carbon resistors, or just simple contact issues - IOW, the usual things that may plague electronics that old.
The small electrolytic caps cost about $2 to replace them all with 10000 hour service life grade, the Peak ESR meter is $100. I haven't wasted the money on it. Amp has problems, calender says the e-caps are over twenty years old, out they all go. The dumbest thing I have heard is measuring the ESR of old e-caps then soldering them back in. That is like measuring the air pressure of the 1970 red line tires on your 1970 Mustang before taking it out on the freeway. If you survive that bone-head maneuver let me know. Other than silicon rubber, historic rubber sealant is dirt. A Macintosh might have had the silicon rubber sealed e-caps, they were available in 1975, but paying $100 to find out is dollar foolish IMHO. None of the dynaco, hammond or wurlitzer equipment I have owned has had silicon sealed e-caps. I have a problem with sound, I change them all.
The main e-caps in the power supply, you can check those first level with a DVM. If the rail voltage has sagged from nominal, one is leaking current usually. Sagged rail voltage can cause channel imbalance. Those will be $5 each, maybe more if you have as much as 10000 uf. The freight is $8 minimum to my house; I buy $50 of parts and change them all instead of making several orders and freight charges as I discover one thing after the other.
Also reseating all connectors to scrape off any accumulated oxide is part of imbalance patrol. This includes the wiper on the volume pot, which can be especially troublesome. I've replaced volume pots on all my old hifi and radio equipment that have had significant use. The tone controls don't seem to wear as much.
Anybody with specific MacIntosh experience, that they had silicon sealed (long life) e-caps after a certain date, do please chime in. One famous long life series was the "green" cornell dublier e-cap.It's not the brand, I've found grey CDE e-caps and gold tall CDE cans (cardboard replacement for aluminum tall cans) from the 80's to be real problems.
The main e-caps in the power supply, you can check those first level with a DVM. If the rail voltage has sagged from nominal, one is leaking current usually. Sagged rail voltage can cause channel imbalance. Those will be $5 each, maybe more if you have as much as 10000 uf. The freight is $8 minimum to my house; I buy $50 of parts and change them all instead of making several orders and freight charges as I discover one thing after the other.
Also reseating all connectors to scrape off any accumulated oxide is part of imbalance patrol. This includes the wiper on the volume pot, which can be especially troublesome. I've replaced volume pots on all my old hifi and radio equipment that have had significant use. The tone controls don't seem to wear as much.
Anybody with specific MacIntosh experience, that they had silicon sealed (long life) e-caps after a certain date, do please chime in. One famous long life series was the "green" cornell dublier e-cap.It's not the brand, I've found grey CDE e-caps and gold tall CDE cans (cardboard replacement for aluminum tall cans) from the 80's to be real problems.
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Alright well I looked up the service manual and realized there's only like 20-30 capacitors in the whole amp...I've never done a recap before and just expected there to be a 100+ capacitors that had to be replaced...
1 question is how hard is all the soldering? I haven't soldered in years and really my main concern with working on the Mcintosh is me damaging it, but I also don't really have the money to have someone else fix it and I would just like the experience of working on it myself. I have a Kenwood ka-7300 which I believe also needs a recap and just a general go through so I may just start there.
Also in the schematic the main power supply caps were 2 39000 uf 50v caps lol.
Also where do you guys get caps from and should I replace them with the same type of cap it says on the service manual?
1 question is how hard is all the soldering? I haven't soldered in years and really my main concern with working on the Mcintosh is me damaging it, but I also don't really have the money to have someone else fix it and I would just like the experience of working on it myself. I have a Kenwood ka-7300 which I believe also needs a recap and just a general go through so I may just start there.
Also in the schematic the main power supply caps were 2 39000 uf 50v caps lol.
Also where do you guys get caps from and should I replace them with the same type of cap it says on the service manual?
Also sorry for all the replies I keep remembering something I want to add after I press reply... I'm currently an Electrical engineering student at UW and have access to high-grade signal generators and oscilloscopes, but don't have a personal ESR and would prefer to avoid buying any expensive equipment, since I'm broke and in college lol. But what equipment would I need? And it sounds like I won't need an ESR if I'm replacing everything.
The Peak "ESR70" I believe is the model number of the capacitance meter that newark.com sells, that goes up to 10000 uf. Some tech on organforum says he uses his a lot. He was repairing guitar amps though, saving every penny on those repairs matters to the customers more than repairing it and forgetting it for 30 more years. They get banged around so much they have many more problems than overage parts.
Wow, 39000 uf mains caps, those will be so expensive it might be worth checking them. If they are mallory blue screw top "computer grade" I might just measure voltage on them without an ESR meter. I've had a few of those Mallories in the junk box from 1972? that measure fine with the DVM ohms scale (you can estimate leakage some by watching how fast the resistance climbs versus a new cap). Mallory computer grade might have been another silicon seal rubber cap: they were certainly the most expensive cap Allied Radio mail order sold in the seventies. If you're in college it might be worthwhile to set up a signal generator, a resistor load, and a sensitive RMS voltmeter, and measure ESR on the 39000's by Kirchoff rule calculation. Particularly when the Peak ESR70 only goes to 10000 uf. Don't forget signal generators usually have a 600 ohm output impedance.
Not ALL caps need replaced, just the electrolytic ones. By 1975 film technology was good enough they last nearly forever, (except an infamous French brand) and disk caps have always been pretty good if the coating was complete. (I hope Mac used mil-spec disk caps, the rot gut grade salesmen tried to push on little amp companies were infamous for having incoming inspection problems. Read John Curl on caps, he was shown a lot of **** disk caps. I specified centralab mil spec ceramic caps for Ford Aerospace to be installed in JSC space center MCB, hundreds of them, no problem. Electrolytic caps have a plus on one end, or a few non-polar ones have NP after the voltage. In the schematic electrolytics have a curved bottom plate.
Carbon comp resistors over 100k can drift high a little due to moisture. Measure them, this is a problem before 1960 mostly, or with brands other than Sprague or AllenBradley mil-spec clones. Again, more of a problem in guitar amps or TV's. I like modern metal film resistors from Vishay or multicomp. Replacing the ones 100k and over sure took some hiss at idle out of my dynaco amp and preamps. Use the 2 or 3 watt ones if you can fit them in, the 400 mw metal film resistors are so short they might arc over with 30 years of dust on them.
Getting good volume pots these days is a trick,the new ones I bought for the dynaco hifi amps have had a life 1/3 or 1/4 of the original milspec centralab ones. With and imbalance problem, you definitely you need to check your volume pot for same resistance both sides without jumping around when you move it. Or do it voltage at power on with a good AC scale on an analog VOM (not a DVM, they produce random numbers on music I've found, except maybe the $200 fluke RMS meter 177, which is still limited to 1.5 khz) I like my Simpson 260-6XLPM analog meter with the 2.5 VAC and 20 vac scale.
Oh, the heat sink compound and the mica washer on the output transistors deteriorate based on time. The fan, if one, also is hours used limited.
Wow, 39000 uf mains caps, those will be so expensive it might be worth checking them. If they are mallory blue screw top "computer grade" I might just measure voltage on them without an ESR meter. I've had a few of those Mallories in the junk box from 1972? that measure fine with the DVM ohms scale (you can estimate leakage some by watching how fast the resistance climbs versus a new cap). Mallory computer grade might have been another silicon seal rubber cap: they were certainly the most expensive cap Allied Radio mail order sold in the seventies. If you're in college it might be worthwhile to set up a signal generator, a resistor load, and a sensitive RMS voltmeter, and measure ESR on the 39000's by Kirchoff rule calculation. Particularly when the Peak ESR70 only goes to 10000 uf. Don't forget signal generators usually have a 600 ohm output impedance.
Not ALL caps need replaced, just the electrolytic ones. By 1975 film technology was good enough they last nearly forever, (except an infamous French brand) and disk caps have always been pretty good if the coating was complete. (I hope Mac used mil-spec disk caps, the rot gut grade salesmen tried to push on little amp companies were infamous for having incoming inspection problems. Read John Curl on caps, he was shown a lot of **** disk caps. I specified centralab mil spec ceramic caps for Ford Aerospace to be installed in JSC space center MCB, hundreds of them, no problem. Electrolytic caps have a plus on one end, or a few non-polar ones have NP after the voltage. In the schematic electrolytics have a curved bottom plate.
Carbon comp resistors over 100k can drift high a little due to moisture. Measure them, this is a problem before 1960 mostly, or with brands other than Sprague or AllenBradley mil-spec clones. Again, more of a problem in guitar amps or TV's. I like modern metal film resistors from Vishay or multicomp. Replacing the ones 100k and over sure took some hiss at idle out of my dynaco amp and preamps. Use the 2 or 3 watt ones if you can fit them in, the 400 mw metal film resistors are so short they might arc over with 30 years of dust on them.
Getting good volume pots these days is a trick,the new ones I bought for the dynaco hifi amps have had a life 1/3 or 1/4 of the original milspec centralab ones. With and imbalance problem, you definitely you need to check your volume pot for same resistance both sides without jumping around when you move it. Or do it voltage at power on with a good AC scale on an analog VOM (not a DVM, they produce random numbers on music I've found, except maybe the $200 fluke RMS meter 177, which is still limited to 1.5 khz) I like my Simpson 260-6XLPM analog meter with the 2.5 VAC and 20 vac scale.
Oh, the heat sink compound and the mica washer on the output transistors deteriorate based on time. The fan, if one, also is hours used limited.
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MC2125 caps (compare the schematic with the 2205, they're the same with an extra set of outputs on the 2205)
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?
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?
Just wondering, why would adding those capacitors make any difference? Like the 47uF at the power supply pale in comparison to the 39000uF so wouldn't they essentially do nothing? I'm still a little fuzzy on amp design so I'm not sure why those caps would make any difference.
Also I think my plan is going to be get a baseline and measure max power and distortion with and without power guard. Can I use a wire wound resistor as a dummy load or do I really need a non-inductive resistor? Is there anything else I should benchmark before making changes? And can I use like a spectrum analyzer to measure distortion or an oscilliscope? I have access to a spectrum analyzer, signal generator, oscilliscope, DMM and DC power supply at the lab.
Then I plan on going through the amp and checking for any loose solder joints, using deoxit on all knobs/switches/rca jacks and the main filter caps and anything else to deoxit while I'm at it? Also replacing all electrolytic caps. Then after all that I'll fire it up and see which if any of the problems I listed are still there and measure power output again and distortion etc. Then if everything is going swimingly at this point I'll potentially go through and make those cap mods listed above and then retest for anything that could potentially change. Also I looked up about the meters going wonky but I'm not quite sure I understand what I would have to do to it or what cable needs to be replaced. I'll probably go through it and do all the recapping etc. and see how that effects the meter readings.
Is there anything I'm missing? I've never done any amp work and haven't soldered in years so I wanna make sure I'm not missing some vital step. Is there much risk of me doing something dumb and breaking something? I really don't want to risk the amp if theres a high chance of me causing damage to it, tho I am pretty confident I can handle it. And is there anything else I can do while I'm ripping everything open? Maybe something to give the amp some love after 40 years of pretty much constant use?
"Just wondering, why would adding those capacitors make any difference?"
Research: bypass caps.
" Like the 47uF at the power supply pale in comparison to the 39000uF so wouldn't they essentially do nothing?"
They make the bass tight, see above.
" I'm still a little fuzzy on amp design so I'm not sure why those caps would make any difference. "
Do more research.
"Also I think my plan is going to be get a baseline and measure max power and distortion with and without power guard."
Waste of time, but go ahead if you like. At the risk of repeating myself: Even though this changes no measurable performance specification, it will change the sound more than you can believe.
"Also I looked up about the meters going wonky but I'm not quite sure I understand what I would have to do to it or what cable needs to be replaced. "
Google: ribbon cable.
" Is there much risk of me doing something dumb and breaking something?"
At the risk of repeating mysel: 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.
Research: bypass caps.
" Like the 47uF at the power supply pale in comparison to the 39000uF so wouldn't they essentially do nothing?"
They make the bass tight, see above.
" I'm still a little fuzzy on amp design so I'm not sure why those caps would make any difference. "
Do more research.
"Also I think my plan is going to be get a baseline and measure max power and distortion with and without power guard."
Waste of time, but go ahead if you like. At the risk of repeating myself: Even though this changes no measurable performance specification, it will change the sound more than you can believe.
"Also I looked up about the meters going wonky but I'm not quite sure I understand what I would have to do to it or what cable needs to be replaced. "
Google: ribbon cable.
" Is there much risk of me doing something dumb and breaking something?"
At the risk of repeating mysel: 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 bypass caps DJK recommends have less self inductance than the big electrolytic ones, so they help pep up the slew rate. makes for more accuracy at high frequencies, and because of feedback, other frequencies, too. That is a tweak, a design improvement, to be done IMHO after the amp is putting out the same gain and rated wattage on both channels.
I use 5 ohm 225 W Dale log resistors to load down my amp for test. They are inductive, but so are speakers, IMHO. If the amp is not rated for 4 ohm load, use the more expensive tapped 10 ohm ohmmite resistors, and set to 8 ohms. Or you can build a massive array of 4.7 ohm 5 watt resistors or something, depends on what time you want to burn building a load. Just soldering a 14 ga wire to those big logs took a 130 W pistol type iron. I've had trouble with amps wimping out on gain and wattage since 1970 and my dynaco ST70, so load resistors and an analog voltmeter are your friend to check up on volts out. remember scope pp voltage is 1.4 x average voltage read on a meter.
I use 5 ohm 225 W Dale log resistors to load down my amp for test. They are inductive, but so are speakers, IMHO. If the amp is not rated for 4 ohm load, use the more expensive tapped 10 ohm ohmmite resistors, and set to 8 ohms. Or you can build a massive array of 4.7 ohm 5 watt resistors or something, depends on what time you want to burn building a load. Just soldering a 14 ga wire to those big logs took a 130 W pistol type iron. I've had trouble with amps wimping out on gain and wattage since 1970 and my dynaco ST70, so load resistors and an analog voltmeter are your friend to check up on volts out. remember scope pp voltage is 1.4 x average voltage read on a meter.
"scope pp voltage is 1.4 x average voltage read on a meter. "
Oscilloscope P-P voltage is 2.828 x the RMS voltage.
"I've had trouble with amps wimping out on gain and wattage since 1970 and my dynaco ST70, so load resistors and an analog voltmeter are your friend to check up on volts out."
The 2205 puts out 200W into 4Ω, and weighs in at 85 pounds! (it is not going to wimp out).
It will drive as low as a 1Ω load (in stereo, or 0.5Ω in mono), so whatever value you come up with should work. A 50W resistor will be fine if you throw it into a bucket of watter while testing.
Ribbon cable that was cleaned (and needs to be replaced).
Oscilloscope P-P voltage is 2.828 x the RMS voltage.
"I've had trouble with amps wimping out on gain and wattage since 1970 and my dynaco ST70, so load resistors and an analog voltmeter are your friend to check up on volts out."
The 2205 puts out 200W into 4Ω, and weighs in at 85 pounds! (it is not going to wimp out).
It will drive as low as a 1Ω load (in stereo, or 0.5Ω in mono), so whatever value you come up with should work. A 50W resistor will be fine if you throw it into a bucket of watter while testing.
An externally hosted image should be here but it was not working when we last tested it.
Ribbon cable that was cleaned (and needs to be replaced).
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