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Older McIntosh Equipment - Where does the higher THD rating come from?

Refugee

Refugee

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I was curious what y 'all's thoughts were as to which components contribute the most to higher THD ratings on older solid state 70's McIntosh equipment vs. modern.
It could be capacitors, transistors, resistors, pots and switching, or board layouts. Caps need to be changed out anyway, but does doing a recap significantly reduce THD or just bring you back to original spec? The easy answer is all of the above and that is probably true, but what components carry the most bang for the buck where THD is concerned?
What do you experts think?

Maybe this should have been posted as a survey but I thought people might have more to say than just clicking one category of component. I believe it to be a more nuanced question than a survey could satisfy. Honestly, I don't know - it might be cut and dry.
Let me know.
 
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I kind of have my doubts that changing any of those components for modern equivalents is going to do much for the THD other than possibly restoring it to original spec. A lot of it is just circuitry design, not so much component limitation. Quasi-complimentary output stages (all NPN or PNP parts) tend to have more distortion than fully complimentary stages (NPN/PNP pairs), though the technical fine points of all that are beyond my understanding.


one possible caveat here is if the original number is THD or THD+N(oise). Less-noisy components will lower that number somewhat just because the noise floor drops. If the original number already eliminated the noise from the measurement it won't change.
 
Refugee said:
I was curious what y 'all's thoughts were as to which components contribute the most to higher THD ratings on older solid state 70's McIntosh equipment vs. modern.
It could be capacitors, transistors, resistors, pots and switching, or board layouts. Caps need to be changed out anyway, but does doing a recap significantly reduce THD or just bring you back to original spec? The easy answer is all of the above and that is probably true, but what components carry the most bang for the buck where THD is concerned?
What do you experts think?

Maybe this should have been posted as a survey but I thought people might have more to say than just clicking one category of component. I believe it to be a more nuanced question than a survey could satisfy. Honestly, I don't know - it might be cut and dry.
Let me know.
Click to expand...
Is this supposed to be a technical/theoretical question or something you would actually consider?

The technical answer is parts tolerances are much better today. Does that mean you could improve the sound with this upgrade? Maybe, but maybe not. You are trying to fix the inaudible. If the number is at or below 1%, you are more than fine. Plug it in, let it fly, enjoy the music. That's a great amp.
 
Closer matching of better transistors and perhaps increased use of op amps, and better ones at that.

Agree with @DesertRatt that the caps Mac used then and now contribute nothing to distortion. If they used ceramic coupling caps back in the day, perhaps.... but Mac was much smarter than that back then.

Let's not neglect the crazy aunt in the attic - IMD. This is rarely a concern nowadays but at the dawn of the solid state era it certainly was. Improved semiconductors and architecture are the main reasons for improvement.
 
I seem to recall c_dk (RIP) mentioning that he was able to obtain better test measurements after replacing with modern components. That is to say, better than what x model tested when new. He was always very interested in this.
 
Yeah, I also recall that with several different preamps that crossed his bench.

There are discs out there which have various tracks recorded with various levels of distortion embedded into them. If you believe you can tell the difference between .1 and .01% THD, then you owe it to yourself to prove / disprove that.
 
damacman said:
Yeah, I also recall that with several different preamps that crossed his bench.

There are discs out there which have various tracks recorded with various levels of distortion embedded into them. If you believe you can tell the difference between .1 and .01% THD, then you owe it to yourself to prove / disprove that.
Click to expand...
...or even 1%. RR spoke about listening tests they often did and said THD in LF could be as high as 40%(!) before becoming objectionable to sample groups. In a Mc product, THD is the least of my concerns.

As I remember it, he enjoyed making improvements to the MA6100, C26 and C28 which benefited the most by the updates he was doing.
 
62caddy said:
...or even 1%. RR spoke about listening tests they often did and said THD in LF could be as high as 40%(!) before becoming objectionable to sample groups. In a Mc product, THD is the least of my concerns.

As I remember it, he enjoyed making improvements to the MA6100, C26 and C28 which benefited the most by the updates he was doing.
Click to expand...
He also had a C35 which he had totally refurbished which was used for comparative purposes. I miss the constant Gordon Gow stories.
 
hopeless said:
Is this supposed to be a technical/theoretical question or something you would actually consider?
Click to expand...
Theoretical. I change as few parts as possible because I love the sound of the amp. It was just a question that was nagging at the back of my mind.
DesertRatt said:
The transistors were no where near as good as today. NO - caps will not lower THD.
Click to expand...
There is a lot of talk out there about the newer caps "improving the sound"; if not THD then what? frequency response? Phase shift? Snake oil?
I think the older film caps are polyester and polypropylene is said to be better.

damacman said:
There are discs out there which have various tracks recorded with various levels of distortion embedded into them. If you believe you can tell the difference between .1 and .01% THD, then you owe it to yourself to prove / disprove that.
Click to expand...
I doubt I can hear the difference. Especially at my age and exposure to machine noise throughout my career. I have, however, fooled myself into believing that I can 'feel' the difference. The newer systems I have heard with better specs seem to fatigue me after a while at higher volumes.

Thanks for the replies, all.
 
Afaik, the Mac amps were originally designed as laboratory grade reference amplifiers with the lowest achievable distortion and ideally having no sonic effect on the signal. Experience and technical advances in design and parts have made distortion lower, the amps by definition should have no effect in the signal, sonic or otherwise.
 
You do realize all Mac components always exceed their published specs by a large margin. My C-34 was rated at .01 distortion with 100 db signal to noise for line inputs below 2.5 volts and the phono spec was 90 db signal to moise below 2.5 MV input. But when it went in for repairs 5 years ago the distortion was below .005 % from 20 to 20,000 HZ and the Signal to nosie was 6 db higher than rated and the pre-amp was almost years old.
 
My C-34 preamp was built in 1990 and when a switch broke a few years go after the switch was rebuilt it surpassed signal to noise specs by 6 db and the distortion measured below .005 % full spectrum when rated at .01% which is again 6db less distortion , too. I know my C-29 surpassed it specs by a larger margin when it was traded in on the pre-owned C-34 in 2006. I bought my C-29 as the first one to Texas because my C-28 had so many mechanical issues. The only Mac that never met specs was the original C-22. It was supposed meet a .02 % spec but Davie O'brien told the spec was supposed to be .08% which it easily met, unless a tube went south on you. 240's, 225's, and 275's all reached down to .04 % distortion at full power thru the midrange and upper mids and middle highs. Normally being just below 0.2% a the extremes at full power. The Mc 3500's had even lower distortion. If fact their distortion levels were below the MAcs first SS models. 2300's, 2105's, and 2505's. Staying below .07 at the extremes and .02 in the mids and lower highs. In fact other manufacturers tube units today can't match Macs performance.

So all you have to worry about if you want to improve things is get rid of any carbon resistors which can cause noise in the phono stages and will decrease signal to noise ratios. Better caps are quieter and have less DCR so you have to be care full replacing caps doesn't change resonances of the circuits in some circuits. Placement of wiring and isolation of power supplies can help especially with the older noisy phono sections I discovered auditioning a C-24 vs an original C-22. Thats why I waited for the C-28. Its a great pre-amp but you have to replace all the RCA connectors, perform the factory posted upgrades and keep all those controls cleaned and lubed when necessary. Thats why I changed to a C-29. The mechanical issues went away 90% of the time. The newer preamps all the switching is done very near in the input and out put receptacles and low level stages are very close to the connections, too, which increases signal to noise and lower distortion. Today if you don't have great signal to noise that measures as distortion. I think the power supplies are quieter also which helps too. What I would worry about is if DACS are inside units as some older and less sophisticated designs can cause issues with some others pre-amps.

The only controls I have to clean on the C-34 are the balance and loudness controls every few years after the tape monitor switch repair/rebuild. Takes about 10 minutes. . Never buy a pre-amp with out gold receptacles, that goes for power amps, too. Whether RCA or XLR. Some folks love tube sound. I don't accept for the MC 3500 MK 1. The problem with it is you need to check it with great test equipment every 500 hours or so to replace tubes that wander out of spec or become noisy. We used three for Live PA systems back in the late 60's and 70's much preferring them over the 2300's. I would rather focus on the quality of the source material. It's also why I am not that fond of streaming.
 
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Now as far as Power amps go its the quad balanced circuitry that cancels a lot of the distortion. I don't know who developed it first. Mac has patents on it, but Accuphase has been using it almost as long. Me personnally I would rather have direct coupled amps with out autoformers rather than than quad circuitry with autoformers. But that is because of the speakers I chose a long time ago and not the fault of Mac autoformers. Speakers in infinite baffles that aren't well damped need all the control they can get from an amplifier. That series resistance in the autoformer makes for less control when it comes to the back EMF of the speaker due to cone movement. My speakers are bi amped so that helps the amp of either type as their is no series resistance or complex impedance generated by the crossover to compromise the control of the amp over the woofers in this case. Quad balanced amps at first really helped increase signal to noise and lower distortions to way below the .005% distortion spec so common now days.

Now Accuphase's Quad amps are direct coupled and might be a another choice, but their pricing is so prohibitive. Amps like Crown and Krell and a few other SS manufactures damping factors were to high and made the sound above 70 hz just to dry and austere. So I was glad when the 7200 and 7100 DC low distortion amps came along. Since then Mac has improved circuit design with better quality components to get the signal to noise within 3 or 4 db whether un balanced or qual balanced as far as specs are concerned. MY HT amps only have a S/N of 113 db and that is more than plenty for me as I seldom listen at over 104 db and the speakers are rated at 95.5 sensitivity. Maybe if I had Jubilees or older big Altec or Big JBL where the speakers are rated at 110 db sensitivity I might be able to hear the difference, but I don't.


I can place my ears right up against my Left and Right HT speakers and not hear a thing. The HT eq's are the noisiest pieces in the amplification chain for the HT system. The MQ 107 is the noisiest piece in the Stereo system rated some where around 90 db signal to noise. But the speakers are only have a 89 db sensitivity rating at 2 watts because they are 4 ohm. No noise there either. Here again the amps are only rated at 117 db signal to noise.

The Stereo speakers being much newer in design have much lower in distortion and are more revealing etc. Both systems are voiced. But when it comes to producing the natutal sound of concerts I recorded, the older speakers are most natural in reproducing the original sound. That doesn't make them right. Its just that with where the mics were placed, the types of mics used and the electronics used at the time to capture the sound the older speakers reproduce the sound concert experience more accurately. Now the line arrays of the newer system produce the sound more accurately for sure. Its a very enjoyable, revealing, and accurate portrayal of what was recorded, its just not the concert hall experience. Two different things for sure. So thats why I have kept my older speakers, with unbalanced direct coupled Mac amps. First 7200's and 7100's, then a 206 and now two 207's to save space. I need 12 channels with my 7 channel HT system. The rears don't need to be bi-amped, but could and why I have the two spare channels. I even have the extra plug in cards for the electronic crossover to add two more channels. The wire is run. It would just mean a day to Scan-171006-0005.jpgIMG_4040 2.jpegput it all together for very little improvement, I don't require from the rear Symphony Speakers.
 
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