Vinyl Rules!
Well-Known Member
Anyone know the capacitance of the phono input on the C28?
TIA
TIA
McIntosh C28 Phono Capacitance Question
- Thread starter Vinyl Rules!
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McIntosh did not publish any capactitance loading spec of their phono equalization circuit.
Have you measured a improper frequency response outside of a acceptable tolerance?
I can not say for sure if I ever specifcally measured the response of cartridges with the C28 as I did with the C32 and C33 while making evaluations and auditions for resale recommendations.
I know that cartridge loading became a big selling "feature" pushed by most Asisn midfi manufacturers but as usual for such selling features few consumers had a clue and I would guess that 90% of the mass market tables did not get setup with the much more critical aspects of turntable calibration.
Finally, in the 60s when the basic research to develop the 3rd generation of Mac's phono equalization circuit was being sorted out the turntable cables where the greatest contributor to the capacitive load the cartrigde saw. Not much different than today.
Have you measured a improper frequency response outside of a acceptable tolerance?
I can not say for sure if I ever specifcally measured the response of cartridges with the C28 as I did with the C32 and C33 while making evaluations and auditions for resale recommendations.
I know that cartridge loading became a big selling "feature" pushed by most Asisn midfi manufacturers but as usual for such selling features few consumers had a clue and I would guess that 90% of the mass market tables did not get setup with the much more critical aspects of turntable calibration.
Finally, in the 60s when the basic research to develop the 3rd generation of Mac's phono equalization circuit was being sorted out the turntable cables where the greatest contributor to the capacitive load the cartrigde saw. Not much different than today.
twiiii
Lunatic Member
Mac did not publish the loading. I checked both my original and later C-28 owners manuals. That said using a Cook test record at both 33 and 45 rpm the frequency response I got with my Ortofon Sl 15 MK II and Sl 20 was + 0/-2db. from 20 to 40,000 HZ. Same goes for my C-29. The difference being where was less of a broad droop with the C-29 over the C-28 in the midrange and lower highs, but a slight boost below 35 hz with the 29. The C-28 seemed to be more euphonic and easier to listen to for long periods where the C-29 had better bass and definition. What I didn't like about either pre-amp were the tone control steps were to large. So I had to use my SAE graphic EQ some times to get the balance I wanted. The C-34 has a similar sound to to the 28 more closely than the 29. But the graphic tone controls make it easy to get the sound I like. You do have bass trim controls which can come in handy listening to LP's that aren't required other wise. Its a shame you can't switch them in and out like the C-34 graphic controls. Take the top off your 28 and see if there is a vertical metal piece straddling the circuit board on the left across the middle. It was added to remove the crosstalk in the phono section. It did not make any difference to me but Davie Obrien installed for me for free at a Mac clinic when my unit was 6 months old. So I grinned and thanked him. He also did an update on the low level input connector plate to guarantee freedom from stray hums and buzzes. The volume controls and switches on a C-28 can be an issue so just plan on cleaning them periodically. Because of the extensions on the mode selector and input selector shafts sometime the align meant will shift causing a channel to drop in and out so keep them clean, too. A C-34 removes a lot of those issues with its electronic switching. My pet peeve is the tendency for the balance and loudness controls to become noisy.
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Vinyl Rules!
Well-Known Member
Thank you for the response.
I don’t have any equipment that would permit to measure anything, but I’ve long been curious as to what the phono input capacitance is on the C28.
I was hoping that perhaps someone here might have measured a C28’s phono input capacitance. It should be more available than say, the ingredient list for Coca Cola’s syrup.
Not a important thing to measure........being the state of the typical 100% foil shield with a solid not foam dialectic the cable of the 60s would be quite high compared to today's offerings. However with the input selector switch near the back of the unit the cabling lengths are short compared to many.
Any number of test records have been available over the decades with a frequency sweep test band or two.......yes and a scope is needed but really any cartridge evaluation without these basic tools is really working with both hands tied behind your back.
Any number of test records have been available over the decades with a frequency sweep test band or two.......yes and a scope is needed but really any cartridge evaluation without these basic tools is really working with both hands tied behind your back.
Thank you for the response.
I don’t have any equipment that would permit to measure anything, but I’ve long been curious as to what the phono input capacitance is on the C28.
I was hoping that perhaps someone here might have measured a C28’s phono input capacitance. It should be more available than say, the ingredient list for Coca Cola’s syrup.
Since I have been given dispensation to get on my soap box if I relay Gordon Gow stories and since proper turntable setup and calibration was the most important service he thourghly believed that his dealer's could offer their clients I do have to question you about how you can properly setup a cartridge, table and arm without any test equipment? Without documenting empirical evidence you have have to be just guessing and there goes any real chance for repeat ability.
I have been trying to correlate the old school testing procedures that we were taught by McIntosh's factory people, yes a amp and speaker company invested their employees time to teach us turntable setup. Gow was personally heavily invested in this and therefore, with the renewed interest in record playback I feel I should honor him and his legacy by passing on what I was taught 40 years ago, while I still can.
New laptop based o'scopes offer a interesting new wrinkle to capture cartridge performance, camera eyepieces to USB inputs offer a whole new way to share stylus wear information.
So back to my question: how do you know a capacitance change will affect your performance if you do not even know if what you have has been maximized?
So does anyone in the SF Bay Area know of a shop that will fully-instrument and set up a turntable?
I just bought an expensive TT at a specialty shop 3 days ago where the cartridge was mounted and aligned by sight with a protractor. The shop owner told me the VTA was fine as is (I trust that he's right), and I was sent on my way. When I got it home, one of the cartridge mounting screws was loose and so I had to realign it with my own protractor. So I guess that's representative of the current state of customer service.
For his reviews, Michael Fremer (AnalogPlanet) uses powerful microscopes and software to show exact angles to align the VTA and azimuth of the stylus itself allowing that the stylus might not be perfectly straight in the cantilever which itself might not be perfectly aligned with the body - most people align by sight of the cantilever or the body. He uses a no-longer-available app plus test record to measure speed and W&F and that's as far as he goes.
Begs the question, how precise do these adjustments need to be to make any noticeable sonic inprovements?
So I would love to find the magic shop that would fully instrument all 3 of my TTs and check stylus wear, fine tune cartridge alignment, tracking force, anti-skate, speed and electrical loading. Running spectrum sweeps at various loadings would be interesting.
But the best I can do is what I've done and trust my ears. But I am considering buying more test equipment / tools because, who provides this service? (Maybe True Sound in SJ?)
BTW, the new TT sounds really good as is.
Well I can not make any referrals but I can suggest what you might look for in respect to what the principles at McIntosh held via two intertwined incidences.
Must have been in the early spring of 1979 and I had on my desk a copy of HPs rag in which a product was being promoted to fine tune the VTA of cartridges. It was a collar with a rack and pinon adjustment to allow the setting by ear on the fly.
The magazine was setting on my desk when I answered it and on the other end of the line was a McIntosh VP, Dirk Roos, calling for my boss. Since he was on a another line and Dirk wished to hold for him we entered in a back and forth about VTA and he questioned me about my turntable knowledge. Just a year out of college and my chain hifi store work I knew how to mount a cartridge, alighn it with the manufacturers supplied grid, balance and set the tracking and dial up the antiskate.
My boss got off the other line, I said goodbye to Dirk, and switched him to my boss.
Ten minutes later my boss came out of his office, face bright red, sweat dripping, tie askew, and very unhappy. He had just has his ass chewed.......big time, I thought I was a goner.
He assured me I was OK, but since he was just informed that he was absolutely negligent in not properly training us, he had days to create a advertising mailer because Roos was coming to town to personally train me in proper turntable setup and we needed a clinic to provide a variety of tables to setup.
First thing Dirk did when he arrived was to show me how to disassemble our Wild M5 microscope and clean it. Then how to use it to I sure that the cartridge manufacturer bothered to mount the diamond with its wide axis perpendicular to the cantilever.
It is unreal how many are not on correctly.
So it starts with a Wild M5 scope, with a rotating stage. Expensive yea, but doing setup right has to start somewhere and if the wear contact surfaces are dog tracking the groove walls all the alighnment and tweaking will be a fools errand.
He gave me a Dennison sound protractor to alighn the cartridges and then we began the process of trial and error to solve my personal setup problem a Ortofon M20 moving coil in a SME 3009ii arm.
Set the tracking force, antiskate and observe gross mistracking in the bass using a shure test record and the shure CPEC. Do a active resonance test find the cartridge styuls is too stiff and is a mismatch to the low mass arm. So grab a AkG P8es and start over.
Quick setup with tracking and antiskate and the tracking is so much better so now we can dial in the most important parameter for stereo playback the channel crosstalk. The AkG could approach 40 dB which was better than average and all the azimuth and VTA tweaking could not nudge it to a better number.
Now with a scope we could actually see if there was any mistracking of the wave forms and could balance the antiskate setting to equalize it between channels.
So now we are in 1981 or so. Gow is in town for a seminar and we get talking about turntable setup and I ask him how his search for a turntable and arm partner is going.
He reveals he is still searching but should have prototype cartridges arriving any day from his friend in Japan. He picks up the phone calls Bingamton and has the five of them Fedexed overnight to us.
When the five showed up, first thing under the microscope they all went. Next get the tonearm in this case a 3009iii to have the correct mass to get the arm/cartridge resonance correct. To do this I needed to add a lead plate between the cartridge and tonearm head to add mass.....trial and error, with unknown prototype cartridges, but this has to be dialed in if you expect good bass response. Next crosstalk in this case a remarkable 45 dB. Find the lightest optimum tracking force by observing the wave forms on a scope and then dial in the antiskate.
It takes practice and commitment, in the case of a lab grade scope a expensive investment.
So to me a sign of commitment would be a stylus microscope and then of coarse the know how to use it.
Turntable setup was really Gow's top priority and since it was mine also ( room voicing didn't hurt also) it was always a common bond between us.
Must have been in the early spring of 1979 and I had on my desk a copy of HPs rag in which a product was being promoted to fine tune the VTA of cartridges. It was a collar with a rack and pinon adjustment to allow the setting by ear on the fly.
The magazine was setting on my desk when I answered it and on the other end of the line was a McIntosh VP, Dirk Roos, calling for my boss. Since he was on a another line and Dirk wished to hold for him we entered in a back and forth about VTA and he questioned me about my turntable knowledge. Just a year out of college and my chain hifi store work I knew how to mount a cartridge, alighn it with the manufacturers supplied grid, balance and set the tracking and dial up the antiskate.
My boss got off the other line, I said goodbye to Dirk, and switched him to my boss.
Ten minutes later my boss came out of his office, face bright red, sweat dripping, tie askew, and very unhappy. He had just has his ass chewed.......big time, I thought I was a goner.
He assured me I was OK, but since he was just informed that he was absolutely negligent in not properly training us, he had days to create a advertising mailer because Roos was coming to town to personally train me in proper turntable setup and we needed a clinic to provide a variety of tables to setup.
First thing Dirk did when he arrived was to show me how to disassemble our Wild M5 microscope and clean it. Then how to use it to I sure that the cartridge manufacturer bothered to mount the diamond with its wide axis perpendicular to the cantilever.
It is unreal how many are not on correctly.
So it starts with a Wild M5 scope, with a rotating stage. Expensive yea, but doing setup right has to start somewhere and if the wear contact surfaces are dog tracking the groove walls all the alighnment and tweaking will be a fools errand.
He gave me a Dennison sound protractor to alighn the cartridges and then we began the process of trial and error to solve my personal setup problem a Ortofon M20 moving coil in a SME 3009ii arm.
Set the tracking force, antiskate and observe gross mistracking in the bass using a shure test record and the shure CPEC. Do a active resonance test find the cartridge styuls is too stiff and is a mismatch to the low mass arm. So grab a AkG P8es and start over.
Quick setup with tracking and antiskate and the tracking is so much better so now we can dial in the most important parameter for stereo playback the channel crosstalk. The AkG could approach 40 dB which was better than average and all the azimuth and VTA tweaking could not nudge it to a better number.
Now with a scope we could actually see if there was any mistracking of the wave forms and could balance the antiskate setting to equalize it between channels.
So now we are in 1981 or so. Gow is in town for a seminar and we get talking about turntable setup and I ask him how his search for a turntable and arm partner is going.
He reveals he is still searching but should have prototype cartridges arriving any day from his friend in Japan. He picks up the phone calls Bingamton and has the five of them Fedexed overnight to us.
When the five showed up, first thing under the microscope they all went. Next get the tonearm in this case a 3009iii to have the correct mass to get the arm/cartridge resonance correct. To do this I needed to add a lead plate between the cartridge and tonearm head to add mass.....trial and error, with unknown prototype cartridges, but this has to be dialed in if you expect good bass response. Next crosstalk in this case a remarkable 45 dB. Find the lightest optimum tracking force by observing the wave forms on a scope and then dial in the antiskate.
It takes practice and commitment, in the case of a lab grade scope a expensive investment.
So to me a sign of commitment would be a stylus microscope and then of coarse the know how to use it.
Turntable setup was really Gow's top priority and since it was mine also ( room voicing didn't hurt also) it was always a common bond between us.
You might try Berkeley Stereo. They have a pretty decent service dept(I've brought a couple things there myself, although not a turntable) so I know they're fully equipped. Worth a call. They're nice folks, too.
http://www.berkeleystereo.com/home.html
Thanks for the tip. I like to stop in there whenever I'm up that way to see what (used stuff) is available. Once I asked them if they could align my MR71, and the person did not know what that meant - but I may have asked the wrong person.
The main (only) service person who helped me in 2017 was a guy named Kent. He worked on some Dynaco MKIII's and did a good job. He knows what an alignment is, although whether he knows how to do it is another thing. Kind of sad though that somebody working there didn't at least know what it is.
