Mark,
The name Kevin Gilmore does ring a bell, although my memory is pretty foggy from those days (can it really be 30 years ago?) I don't particularly recall your name though, I must admit. You wouldn't happen to have any pics of store personnel from those days that can be scanned and sent by private mail to me, by any chance? Just a thought. Trying to jog my neurons.
Brian (now a dedicated swamp rat living in Florida)
The name Kevin Gilmore does ring a bell, although my memory is pretty foggy from those days (can it really be 30 years ago?) I don't particularly recall your name though, I must admit. You wouldn't happen to have any pics of store personnel from those days that can be scanned and sent by private mail to me, by any chance? Just a thought. Trying to jog my neurons.
Brian (now a dedicated swamp rat living in Florida)
custom wound transformers available
There is a guy on the web who can custom wind any transformer, and replicate any transformer. I talked to him once when some lieing spelling? creep from Audiogon sold me Nestorovic mono's with one bad transformer. I had sent the amp to Nestorovics house for overhauling, and replacement of caps and old parts. I found this guy after some searching. He was going to rewind it, but Mile kept it and gave me a new one for free. So if anyone has an old dead mac transformer, we could do a group buy of fresh wound replicas. So Mac tube stuff is clonable. I'd like to see a clone of the Counterpont 5.1 preamp, updated.
There is a guy on the web who can custom wind any transformer, and replicate any transformer. I talked to him once when some lieing spelling? creep from Audiogon sold me Nestorovic mono's with one bad transformer. I had sent the amp to Nestorovics house for overhauling, and replacement of caps and old parts. I found this guy after some searching. He was going to rewind it, but Mile kept it and gave me a new one for free. So if anyone has an old dead mac transformer, we could do a group buy of fresh wound replicas. So Mac tube stuff is clonable. I'd like to see a clone of the Counterpont 5.1 preamp, updated.
Easy for you to say, probably got a heap of spare CBT's lying around.
(on the lookout for a 465B, btw, your fault)
If construction of a spectrum analyzer would be part of a MR-78 tuner thread, i'd sure would like to combine them.
My reference was to the front plate of the Sequerra Model 1, the front handles, digital display and the touch control buttons.
As the Sequerra was a copy, copying its esthetic design for a McIntosh clone not only combines the great looks of a McIntosh chassis setup with the extraordinary looks and userfriendlyness of the Sequerra, but it also has a funny streak.
With such a tuner clone design thread i'd be interested in a GG amplifier to drive a headphone set too.
With the parts available nowadays a tuner clone thread is a hell of an idea.
I've been desiring a tube design tuner for ages, just this afternoon i told mrs N. about the sound of the Philips tube tuner at my elderly home in my childhood days.
(on the lookout for a 465B, btw, your fault)
If construction of a spectrum analyzer would be part of a MR-78 tuner thread, i'd sure would like to combine them.
My reference was to the front plate of the Sequerra Model 1, the front handles, digital display and the touch control buttons.
As the Sequerra was a copy, copying its esthetic design for a McIntosh clone not only combines the great looks of a McIntosh chassis setup with the extraordinary looks and userfriendlyness of the Sequerra, but it also has a funny streak.
With such a tuner clone design thread i'd be interested in a GG amplifier to drive a headphone set too.
With the parts available nowadays a tuner clone thread is a hell of an idea.
I've been desiring a tube design tuner for ages, just this afternoon i told mrs N. about the sound of the Philips tube tuner at my elderly home in my childhood days.
If anyone decides to clone the MC1000, let me know because I have three cases of brand-new meters. They are made by Modutec for Mac. I considered using them on the Pass Monster project but decided that would be too weird looking. Besides, the Monster will be well over 1000Wrms.
-Casey Walsh
-Casey Walsh
iirc plitron makes tube output toroids, with a -3db range of 20hz to almost 220khz (not a typo, you read it right). the only problem is the $300.00 price tag...... not only McIntosh amps or similar designs could benefit from this, but in pro-audio, i could see it as an upgrade for Marshall, Sunn, etc... amps. a nice wideband output transformer with no parasitic resonances, etc....
MC 2505
There is a lot that can be done to greatly improve the sound of the 2505 solid state Mac.
If collectors think it sounds good as is then they are stuck with an inferior sounding amp.
You can chuck out the input driver board. In fact no system needs a pre amp. And that extra gain stage. But, I digress. That board is not good. It has feed back, too many parts in the signal path. Like a cap directly at the input!! Just remove the board. And connect the inputs directly to the output printed circuit board.
This will also bypass the low quality volume pots. That are a pain to use anyway. I use a transformer volume control and switching unit. Works wonders.
Don't use headphones? The you can eliminate a switch in the signal path and connect output directly to the transformer.
Bypass the large caps with good quality film. Next you could replace those big caps with something better. Have not tried to replace the big caps yet.
These changes worked. And the sound improved a lot.
Now I want to try and remove the feed back loop. Which most of the time does two things. Improves the everything from the bass on up to the highs. But, you then limit your speakers to those that are easier drive and in most cases sound better. The bass suffers the most with the wrong speaker. But, again speakers that require an iron fist are not the best sounding most of the time anyway.
I have a service manual. And when I get chance I will post the output section. As I am not sure of all of the parts that belong to the feedback loop. There are many people on here who would be able to sort it out. And that would be really helpful.
There is a lot that can be done to greatly improve the sound of the 2505 solid state Mac.
If collectors think it sounds good as is then they are stuck with an inferior sounding amp.
You can chuck out the input driver board. In fact no system needs a pre amp. And that extra gain stage. But, I digress. That board is not good. It has feed back, too many parts in the signal path. Like a cap directly at the input!! Just remove the board. And connect the inputs directly to the output printed circuit board.
This will also bypass the low quality volume pots. That are a pain to use anyway. I use a transformer volume control and switching unit. Works wonders.
Don't use headphones? The you can eliminate a switch in the signal path and connect output directly to the transformer.
Bypass the large caps with good quality film. Next you could replace those big caps with something better. Have not tried to replace the big caps yet.
These changes worked. And the sound improved a lot.
Now I want to try and remove the feed back loop. Which most of the time does two things. Improves the everything from the bass on up to the highs. But, you then limit your speakers to those that are easier drive and in most cases sound better. The bass suffers the most with the wrong speaker. But, again speakers that require an iron fist are not the best sounding most of the time anyway.
I have a service manual. And when I get chance I will post the output section. As I am not sure of all of the parts that belong to the feedback loop. There are many people on here who would be able to sort it out. And that would be really helpful.
Yes, please post the service manual!
Your post makes me wondering how it is possible that the amp still works. I would be very interested wether you really connect the input to the output stage - which would really be a shot in your own knees, since you at least loose power (reduced output swing, since no vas). The cap at the input protects usually from DC or acts as lowpass filter, both can lead to serious troubles if removed, like decent DC at the output right into your speakers.
Honestly I really hope that it's not that worse.
Your idea to run the amp openloop is also incredible, it shows impressively that you don't know how the frequency response looks like in this case. Besides all other troubles.
Maybe you want to consider to stop modifying until you have more electronics knowledge?
All the best, Hannes
Your post makes me wondering how it is possible that the amp still works. I would be very interested wether you really connect the input to the output stage - which would really be a shot in your own knees, since you at least loose power (reduced output swing, since no vas). The cap at the input protects usually from DC or acts as lowpass filter, both can lead to serious troubles if removed, like decent DC at the output right into your speakers.
Honestly I really hope that it's not that worse.
Your idea to run the amp openloop is also incredible, it shows impressively that you don't know how the frequency response looks like in this case. Besides all other troubles.
Maybe you want to consider to stop modifying until you have more electronics knowledge?
All the best, Hannes
He either doesn't have a schematic, or doesn't understand how it works.
Let's look at the power amp section first.
The DC resistance from the base of the input resistor to ground is only 1760 ohms! It's bootstrapped to the feedback node for a higher input impedance, but since he plans on eliminating the feedback it will only be about 3.6K from the amp section input to ground.
Not many preamps will like that.
The gain is only about 10dB.
Not many preamps will like that.
It's DC coupled on the input.
If the source has any DC on it the amplifier will have a huge current flow in the output stage (driving an autoformer).
If the feedback is removed there will be 0.7V on the output (because it's a quasi-comp design without a Baxendall diode), and it will probably blow up.
Now let's look at the preamp.
It has about 20dB of gain (to make up for the low gain of the power amp).
It has about 200K input impedance (so a tube preamp can drive it).
It's AC coupled (so it doesn't blow up).
The gain controls are useful in matching levels with non-McIntosh equipment. Many preamps have too much gain in their line stages, especially with high efficiency loudspeakers.
If you just freshen up the caps and add some film bypass it will sound great. Here is a list for the MC 2100, the schematic is virtually the same.
--------------------------------------------------------------------------
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.
Let's look at the power amp section first.
The DC resistance from the base of the input resistor to ground is only 1760 ohms! It's bootstrapped to the feedback node for a higher input impedance, but since he plans on eliminating the feedback it will only be about 3.6K from the amp section input to ground.
Not many preamps will like that.
The gain is only about 10dB.
Not many preamps will like that.
It's DC coupled on the input.
If the source has any DC on it the amplifier will have a huge current flow in the output stage (driving an autoformer).
If the feedback is removed there will be 0.7V on the output (because it's a quasi-comp design without a Baxendall diode), and it will probably blow up.
Now let's look at the preamp.
It has about 20dB of gain (to make up for the low gain of the power amp).
It has about 200K input impedance (so a tube preamp can drive it).
It's AC coupled (so it doesn't blow up).
The gain controls are useful in matching levels with non-McIntosh equipment. Many preamps have too much gain in their line stages, especially with high efficiency loudspeakers.
If you just freshen up the caps and add some film bypass it will sound great. Here is a list for the MC 2100, the schematic is virtually the same.
--------------------------------------------------------------------------
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.
A cap at the input is not needed these days. I am not worried about blocking DC. Its band limiting is why you don't want it. And a direct path though a cap is not good for sound quality. Which is why people are always searching for the perfect coupling cap. Or use transformer coupling. The best solution is not to have them there. Like an Ultra Path design.
I admit. I am a tube fan and know tube ciruits. Solid state is not my area. Class B is new to me. I prefer class A. Both in tube and solid state. When its done well. Class A really works.
This an experiment. And I am willing to do just that. If I remove the feed back and it sounds worse then back it goes.
Taking out the input board was a plus. Its not going back in.
I have more than enough gain. Using a CD player with 12AX7 output stage through a Transformer volume control to a pair of Spendor SA2 speakers. They are rated at 8 ohms 88 dB, 15 to 200 watts. They work just fine on a 2A3 amp at 3 watts.
If I lost gain some place. I can't tell. The point is to get better sound. So, some gain loss is not an issue. And as I stated before. Taking out feed back does change the number speakers that can be used. To me most speakers sound bad and are really poorly designed. And most of those are because the speaker designer does not care if its a friendly load to an amp. And that to me is the mark of a poor designer. Anyone can stick cones in a box. And that is what you get most of the time. Poor sounding, hard to drive, mega buck junk.
It is not common to remove feed back and have an amp blow up?
I could be wrong here in the solid state world.
I have up loaded the power supply schematic. And the output stage will follow. Because, I have to go reduce it to fit my scanner.
I am on here for advice. When I post the output stage. And it can blow up without the feed back. Then please explain why.
The schmatic files are too big and did not up load. I have to look into how to reduce them.
I admit. I am a tube fan and know tube ciruits. Solid state is not my area. Class B is new to me. I prefer class A. Both in tube and solid state. When its done well. Class A really works.
This an experiment. And I am willing to do just that. If I remove the feed back and it sounds worse then back it goes.
Taking out the input board was a plus. Its not going back in.
I have more than enough gain. Using a CD player with 12AX7 output stage through a Transformer volume control to a pair of Spendor SA2 speakers. They are rated at 8 ohms 88 dB, 15 to 200 watts. They work just fine on a 2A3 amp at 3 watts.
If I lost gain some place. I can't tell. The point is to get better sound. So, some gain loss is not an issue. And as I stated before. Taking out feed back does change the number speakers that can be used. To me most speakers sound bad and are really poorly designed. And most of those are because the speaker designer does not care if its a friendly load to an amp. And that to me is the mark of a poor designer. Anyone can stick cones in a box. And that is what you get most of the time. Poor sounding, hard to drive, mega buck junk.
It is not common to remove feed back and have an amp blow up?
I could be wrong here in the solid state world.
I have up loaded the power supply schematic. And the output stage will follow. Because, I have to go reduce it to fit my scanner.
I am on here for advice. When I post the output stage. And it can blow up without the feed back. Then please explain why.
The schmatic files are too big and did not up load. I have to look into how to reduce them.
"Also my amp is a 2505 not a 2100 or 2105. I don't know if those are the same."
The front end design and rail voltages are the same on the MC250/2505/2100/2105/2300.
OK, delete the input coupling cap if you like. Now you will have several volts on the input to deal with.
If you want to scrap everything but the power supply, go ahead and have at it.
The front end design and rail voltages are the same on the MC250/2505/2100/2105/2300.
OK, delete the input coupling cap if you like. Now you will have several volts on the input to deal with.
If you want to scrap everything but the power supply, go ahead and have at it.
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