McIntosh Rebuild with solid state rectifier

[Fast996]

My McIntosh C20 was converted over to solid state rectification replacing the original 6x4 rectifier tube by Audio Classics They also upgraded the power supply while doing a complete restoration. Did a beautiful job.
What changes can I expect to hear? Will it sound like a C22?



.

 

[Fast996]

I know this article is about amplifier rectification. But I would not want a tube rectified preamp.
I told Ryan i.wasnt interested in a museum piece but the best sounding C20. I.wont know for sure for a couple of weeks..but I think that's what Ryan gave me after reading and listening.

https://www.mojotone.com/blog/tube-vs-solid-state-rectifiers

 

[clinic-audio]

But I would not want a tube rectified preamp. and can you tell us why ? If you don't want a tube rectifier don't buy a C20

 

[Fast996]

But I would not want a tube rectified preamp. and can you tell us why ? If you don't want a tube rectifier don't buy a C20

Hello,
Please read my opening post,first sentance.
I came to that conclusion after reading and listening to the videos I linked to in my 2nd post.
I think we actually agree. So do you think converting a C20 to Solid state rectification would improve the sound of a C20?

But I would not want a tube rectified preamp. and can you tell us why ?

If a tube rectifier adds it's own distortion called "sag" why would Mcintosh use one...because when they built the C20 solid state rectifiers weren't available. When McIntosh came out with the C22 they used a S.S. rectifier...Why?

The price difference asked for C20's and C22's is substantial. Is it because the C22 is percieved to sound better? Tube rectified vs SS rectified?
Anyway I soon will be able to listen to my SS rectified C20 and will post my thoughts on the sound quality. Maybe i'll like it and maybe I'll find it suffers from rolled off highs and bass that lacks "punch".
Those qualities I don't necessarily care for but then again lot's of C20 owners do.
I do think the C20 is a beautiful preamp and i like the fact that it is point to point wired. I also like the tube compliment used. This was my experiment to see if I could improve the C20.

 

[SaturationPt]

I don't expect as much (if any) improvement from tube to ss rectification in a preamp as I would in an amplifier. Why? The preamp power supply doesn't see significant swings in the current demand, fairly constant therefore the voltage should remain fairly constant. In an amplifier that can see very low current at low SPLs and with low dynamics to a multiple of that current at higher SPLs (the "dumbed-down" version being 10x for double the SPL or 2x the power for a noticable difference) you can see "rail" or supply voltages droop during high output, especially in equipment old enough to be designed before highly-dynamic (esp. digital) music became common.

Tube rectification is a preference, some swear by it, others swear at it. I will say that I prefer SS to tubes in rectification as a perfect power supply with constant voltage is what I always strive for in designs (reduces the need to compensate in other parts of the design) but vintage audio is more about taste and opinion than science. In guitar/instrument amps it's a completely different discussion as the instrument, amp, and speaker create the sound and a certain sound (including distortion) is desired, where an audio/stereo amplifier is designed to pass the sound/music without changes.

We do have one member who has converted all of his Mc tube amps (MC60 x 4?) to solid-state rectifiers years ago and has posted that he is very happy with the results.

 

[clinic-audio]

Please read my opening post,first sentance.
I read it before to post my message
I came to that conclusion after reading and listening to the videos I linked to in my 2nd post.
I don't care about post made by people who don't work on MCINTOSH product since many years . Guitars amplifiers do not interest me
The price difference asked for C20's and C22's is substantial. And do you know why ?
How can you compare two completly differents units with different specifications ? one is 78rpm dedicated not the other one !
So do you think converting a C20 to Solid state rectification would improve the sound of a C20 ?
I think that you have bad informations .C20 is tube rectified , yes, but C22 is SELENIUM rectified which is not the same as SILICON rectified . MARANTZ made more than one unit with selenium bridge and many owner's do not accept to touch or replace them by SILICON diode .
Those qualities I don't necessarily care for but then again lot's of C20 owners do. This is not because they do what they want with their unit that they are right . I will not follow the other regarding what they can say or what they can do . Do they have more than 40 years about working on MCINTOSH units ?
This was my experiment to see if I could improve the C20 ; are you engineer ? more experienced than the staff at factory ?
Replacing many old components in your C20 will improve the result of course but I don't believe that using silicon diode will give you a " wonderfull sound"

 

[Fast996]

Please read my opening post,first sentance.
I read it before to post my message
I came to that conclusion after reading and listening to the videos I linked to in my 2nd post.
I don't care about post made by people who don't work on MCINTOSH product since many years . Guitars amplifiers do not interest me
The price difference asked for C20's and C22's is substantial. And do you know why ?
How can you compare two completly differents units with different specifications ? one is 78rpm dedicated not the other one !
So do you think converting a C20 to Solid state rectification would improve the sound of a C20 ?
I think that you have bad informations .C20 is tube rectified , yes, but C22 is SELENIUM rectified which is not the same as SILICON rectified . MARANTZ made more than one unit with selenium bridge and many owner's do not accept to touch or replace them by SILICON diode .
Those qualities I don't necessarily care for but then again lot's of C20 owners do. This is not because they do what they want with their unit that they are right . I will not follow the other regarding what they can say or what they can do . Do they have more than 40 years about working on MCINTOSH units ?
This was my experiment to see if I could improve the C20 ; are you engineer ? more experienced than the staff at factory ?
Replacing many old components in your C20 will improve the result of course but I don't believe that using silicon diode will give you a " wonderfull sound"

Fair enough....thanks for the input

 

[Fast996]

IIRC I replaced my selenium rectifiers on my Ampex 350 power supplies because they could be hazardous with age.

 

[clinic-audio]

They could be , yes , but they were not !

Many members does this without knowing when they will fail

The easiest way to know when is to make power consumption control . When your "selenium rectifiers" becomes bad , power consumption will drasticly increase and the best way to act is to use a fuse in serie before the selenium rectifier . Your fuse will burn just before your selenium rectifier will cause to make dammage to your power transformer winding .
Easy don't you think ?

 

[audiocrzy]

Will it sound like a C22?

it will sound as it sounds. I’m sure that will be fine.
Not much you can do about that since the conversion has been done.

 

[Fast996]

it will sound as it sounds. I’m sure that will be fine.
Not much you can do about that since the conversion has been done.

For better or worse. The tech that did the work and all he works on is McIntosh said it sounds "wonderful and warm as it should".

 

[dcgillespie]

I would think it would be very tough for a C20 to sound like a C22 at all -- the type of rectifier used not withstanding -- as their designs are so significantly different.

The C22 is little more than a glorified C11 (said only to emphasized how nearly electronically identical the C11 and C22 are), and as such represent classic McIntosh preamp design. The circuit uses NFB around all the active gain stages to maximize performance, minimize the impact of component and/or tube variations on performance, and to ensure virtually identical performance between the two channels. Active feedback type tone controls are used, as are selenium rectifiers in the power supply. This all works to produce a preamplifier with very good accuracy, frequency response, low noise, and low distortion.

The C20 on the other hand couldn't be more different. Active NFB is still used in the phono preamp section to achieve the various playback characteristics, but that's it. The active gain stages in the line amp section do not operate within any NFB loop, and employ only limited local feedback -- and only at the lower frequencies at that. Therefore, the unit's performance is much more subject to characteristic variations in tubes and components, so that tube rollers should have a heyday with this unit. Passive tone controls are used, as is (obviously) a tube rectifier.

If the rectifier tube was properly replaced with silicon devices (meaning the operating voltages are the same as when using the rectifier tube), then their presence should be all but invisible. Any discussion of voltage sag SS rectifiers tend to minimize has no meaning with a preamplifier, because the current draw from the power supply remains utterly constant regardless of whether a signal is passing through the preamplifier or not. The likelihood it the rectifier change causing any great change in the character of the C-20's sound then is beyond remote.

Purely speculating, because the C-20 is so different from traditional Mac design, I believe the C-20 may have been Mac's answer to the "feedback and SS rectifiers are bad" crowd. It's performance could surely be described as warm and and buttery smooth because of the design approach used. As to how accurate that is is up to each individuals own assessment.

All my 2 cents worth of course.

Dave

 

[Fast996]

I would think it would be very tough for a C20 to sound like a C22 at all -- the type of rectifier used not withstanding -- as their designs are so significantly different.


The C22 is little more than a glorified C11 (said only to emphasized how nearly electronically identical the C11 and C22 are), and as such represent classic McIntosh preamp design. The circuit uses NFB around all the active gain stages to maximize performance, minimize the impact of component and/or tube variations on performance, and to ensure virtually identical performance between the two channels. Active feedback type tone controls are used, as are selenium rectifiers in the power supply. This all works to produce a preamplifier with very good accuracy, frequency response, low noise, and low distortion.

The C20 on the other hand couldn't be more different. Active NFB is still used in the phono preamp section to achieve the various playback characteristics, but that's it. The active gain stages in the line amp section do not operate within any NFB loop, and employ only limited local feedback -- and only at the lower frequencies at that. Therefore, the unit's performance is much more subject to characteristic variations in tubes and components, so that tube rollers should have a heyday with this unit. Passive tone controls are used, as is (obviously) a tube rectifier.

If the rectifier tube was properly replaced with silicon devices (meaning the operating voltages are the same as when using the rectifier tube), then their presence should be all but invisible. Any discussion of voltage sag SS rectifiers tend to minimize has no meaning with a preamplifier, because the current draw from the power supply remains utterly constant regardless of whether a signal is passing through the preamplifier or not. The likelihood it the rectifier change causing any great change in the character of the C-20's sound then is beyond remote.

Purely speculating, because the C-20 is so different from traditional Mac design, I believe the C-20 may have been Mac's answer to the "feedback and SS rectifiers are bad" crowd. It's performance could surely be described as warm and and buttery smooth because of the design approach used. As to how accurate that is is up to each individuals own assessment.

All my 2 cents worth of course.

Dave

Thank.you for such a informative explanation. I think.because as you state

"Therefore, the unit's performance is much more subject to characteristic variations in tubes and components,"

I voiced the preamp.with very good components, I think.the C20 will sound fine.

 

[Fast996]

Had time to take the bottom cover off my C20....Audio Classics did a beautiful job on my C20 and I doubt there's another C20 voiced like this one

 

[egellings]

In a preamp, a rectifier with a bit of excess voltage drop is not an issue because the current draw is pretty constant in small signal circuits like that, and the supply voltage won't get bounced around by the preamp following an input signal. Nice thing about the tube is the slow start it provides.

 

[analog addict]

They could be , yes , but they were not !

Many members does this without knowing when they will fail

The easiest way to know when is to make power consumption control . When your "selenium rectifiers" becomes bad , power consumption will drasticly increase and the best way to act is to use a fuse in serie before the selenium rectifier . Your fuse will burn just before your selenium rectifier will cause to make dammage to your power transformer winding .
Easy don't you think ?

Somehow the logic in this approach eludes me. After going through all the trouble to do a complete restoration on a piece like my C-22, why would I want to take an extra step to add a fuse? Merely to monitor a component that could otherwise be replaced with an arguably better performing component, and in the case of a new/modern diode, likely to outlast me? And that's if selenium held its characteristics, which they don't as their voltage and current handling characteristics deteriorate they age, and this is before total failure.

Now if you could make a valid argument about the sonic characteristics of a selenium rectifier being superior to that of equivalent silicon diodes, then I could understand.

But if that were so, someone would be making a buck making new ones to sell to people like us.

http://w3hwj.com/index_files/RBSelenium2.pdf

 

[twiiii]

Fast 996: I envy your professional Ampex collection. Not so much the 8oo series Crowns. I am not that familiar with the Studer C-37. I had a 4 channel 300 using 354 electronics with a custom Bias oscillator, a AG 350-2, AG 500-2/4, A 300-2, an AG-300-2 and a AG 440 C/2 that replaced the AG 350-2 and 300-2. Two B-77 HS 2/4 and two A-77 IV with Dolby. All the tape machines have been gone since 2008 when I mixed everything down or dubbed everything to CD. Sticky Ampex tape prompted me to get rid of all tape machines including Nakamichi cassettes and Sony DAT Machines. Sony Professional VCR's, to.

 

[Fast996]

Fast 996: I envy your professional Ampex collection. Not so much the 8oo series Crowns. I am not that familiar with the Studer C-37. I had a 4 channel 300 using 354 electronics with a custom Bias oscillator, a AG 350-2, AG 500-2/4, A 300-2, an AG-300-2 and a AG 440 C/2 that replaced the AG 350-2 and 300-2. Two B-77 HS 2/4 and two A-77 IV with Dolby. All the tape machines have been gone since 2008 when I mixed everything down or dubbed everything to CD. Sticky Ampex tape prompted me to get rid of all tape machines including Nakamichi cassettes and Sony DAT Machines. Sony Professional VCR's, to.

twiii i still have all mine....they will need a peterbilt and a cat loader to bury all my stuff with me...lol. The Crowns are no slouch....I love this hobby,thanks

 

[trainbuftony]

My guess is that you're not going to be able to discern a difference and if you have a test bench. You'd be hard pressed to find a difference there.
Reason being as dave described the amp is all class A. Its always drawing the same average current through th tubes regardless of how loud your music is playing. Monitor your b+ with a volt meter and crank it if you don't believe me! The tube rectifier did exactly the same thing with more voltage drop.
The audio circuit doesn't care how the B+ was made. As long as you have a constant uninterrupted supply. If Audio Classics did the work, you're 200% safe to plug in and enjoy. If anyone claims they hear a drastic difference encourage them to get their ears checked. Maybe the space between them as well...
As the world gets hotter, we can all appreciate solid state rectification for its lack of a filament supply, and its lower voltage drop. Feel free to check my math, but voltage drop=heat every day of the week and twice on Sunday. I'd say solid state is better just from a raw heat perspective.
In your amplifier it likely make no difference.
The power is probably dropped over a resistor to approximate the sag in the rectifier at load. 6 of one, half dozen of the other. Be happy, you have a very nice preamp

 

[Pio1980]

It's one less expendable part that slowly fades over time, otherwise sonically indifferent overall.