AudioCircle
Industry Circles => Audio by Van Alstine => Topic started by: 13mh13 on 16 Oct 2016, 11:58 am
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From Audio Basic days, I recall FVA note some mods to Harman Kardon turntables.
What was this? Also, which Audio Basics issue(s) was this noted in?
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The mod moved the power transformer and the power supply circuits outside of the turntable considerably reducing the hum.
The procedure for the T60 was outlined in an old Audio Basics article. #83 or 84??? Frank had all of them archived at one time.
I did this to my HK 720 turntable which was a precursor to the T20/30/60 series and their variants. This model was distinct as it had the timing marks on the turntable platter edge and a neon strobe illuminating the marks.
It played music well. I still have mine but not currently in use. Moved up to a Well Tempered Amadeus.
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Thx ... found many refs in the Audio Basics PDFs, and notably:
http://www.avahifi.com/images/avahifi/root/audio_basics/ab_pdf/ab1985.pdf
The T60 fetches quite a hunk-a change in the used marketplace. As does a lot of "vintage" gear. I mean really!! 2x as much as brand new a Pro-ject?!!!
Speaking of HK tt's, the T65C is the one I wouldn't mind having. It improved the T60 quite significantly (i.e., tonearm and electronics; cosmetically almost same as T60)
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it would be interesting to do a shoot out between vintage decks and new entry level models. Speed accuracy isn't that great in the latter.
The MicroSikeii tone arm used in the HK decks was pretty good. But adjusting VTA is a pain
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That would be the Microrace tonearm by Ito.
If anyone is interest, I have the AVA outboard power supply available.
Ron
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I'd have to say that HK styling -- from any era -- is outstanding. I think it's called "design language", which for HK is (and remains) very modern and timeless. Even HK product catalogs are coffee-table showpieces.
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That would be the Microrace tonearm by Ito.
If anyone is interest, I have the AVA outboard power supply available.
Ron
You, sir, are correct about the tone arm.
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I have studied the Harman Kardon T60C manual.
A friend Cinderella-found a T60 in a Thrift Shop.
This post was motivated by this thread of removal of the T1 AC Transformer
and substitution of an outboard external Power Supply.
My Idea is to re-purpose older HP 18.5Vdc power bricks with SwitchMode technology
retaining most of the original Turntable components except T1 AC Transformer and AC Cord.
My ideas are attached in one JPEG but are based on the Harman Kardon Service Schematic on page 13.
found at https://elektrotanya.com/harman_kardon_t55c_t60c.pdf/download.html as the free download.
my re-draw:
(http://www.audiocircle.com/image.php?id=179376)
John R. Ottawa Canada CET-III 1979
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Updated;
I am matching a HP Laptop power brick to this outboard modification.
Most HP bricks are 18.5V output (closer to 19 unloaded).
In addition , the original internal power is close to 17V, but the input Full Wave Bridge
drops any external source by 1.4V if the attachment is at the two Transformer Secondary
connection points.
an update Schematic is attached to this post.
Only two series diodes are used.
A COAX barrel connector matching the HP Power brick plug was mounted in the AC cable hole
vacated by the AC cord. Thus, the integrity of the T60 case preserved without (ugly) drilling.
T1 transformer and AC original Mains 2wire cable/hole strain/plug removed.
note : using a 12Volt as originally suggested in 2006 posts is too low and will cause the
Quartz-Lock servo loop to become unstable. I am matching the original Power Supply voltage
after the input FW bridge at +/- points per the marking on the 1983 factory schematic.
I will solder the series diodes internally into the T60 case to minimize any external shorting issues.
takeaway: the length of most HP Laptop cables is about 6FT (2meters), enough to get any
source EMF (far) away from the pickup.
I will post a third time with pictures after we modify with the COAX barrel jack inline or mounted.
(http://www.audiocircle.com/image.php?id=179411)
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There's two simultaneous threads on the same mod to 30yo H-K TT's???
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Updated;
I am matching a HP Laptop power brick to this outboard modification.
If the original transformer is not working then your mod might work.
If the transformer does work then you are re-inventing the wheel, just follow the AVA T60 mods and you are good to go.