A simple mod for the later H-K turntables

[marcmorin]

Marc, after dealing with the arm-excited subchassis resonances and that of the bottom cover, your suggestions are very interesting to me as an approach I hadn't considered due to my working in isolation. The water pool instrument is brilliant and simple, thnx for that. Your analysis of the suspension spring system in particular is very instructive. Looking at Big Bill's project it would seen a somewhat different approach here is needed, one that doesn't change the motor's suspended isolation but will allow mass loading of the motor body itself. For the 'drain' I'm thinking a lead collar at it's lower end with a modification to the upper end suspension that will support the added mass without increasing the noise transmission to the plinth, yet to be determined. The lead collar should provide the energy drain for all vibration/noise modes including rotational and axial. Am I off-base here?
BTW My e-mail response to you bounced.

Hi, the lead collar should add damping at the boundary of the motor, ie the circumference of the shell. The motor vibration starts in the center of the motor where the rotor pivot point is. that vibration goes as far as the boundary and reflects back to the center, over and over again. The drain in the link I sent allowed for a path past the vertical boundary. If you can get more mass than energy the motor vibration can create vibrating in an equal but opposite phase, they should cancel. A lead collar should be fine but you could attach a center drain to the motor attached to the lead collar. Don't know why the e-mail bounced I have no bloacks on it......please re-send

Marc

 

[Pio1980]

My e-mail eventually got to you and you responded, probably my server.
One variation I'm considering is having a layer of felt between the mass collar and the motor housing to absorb and dissipate vibration as heat. Another possibility is using loose small glass beads in a containment instead of the lead collar as a dead mass loading for the housing. I've found that using this approach in the hollow tube arm of my Souther definitely helped dry it's resonance modes, got the Idea from Bill Firebaugh's sand-filled WT arm. Also used lead mass loading and felt damping to effectively quell the primary LF resonance in the Souther's gantry.

 

[Pio1980]

If the T-60 is like my T-65c then the suspension screws may not be adjustable from the top any longer. It's the bottom end of the screw facing up, with a screw slot cut into that bottom end of the screw. A bit fragile, and seemingly prone to crumbling after this many years. But still easily adjusted by removing the bottom panel to gain direct access to the screw heads.

I just checked the SM for the T55C-T60C and the suspension adjusters are shown as per my T-60 pic. I think someone reinstalled yours inverted for unknown reasons as it appears that could be done. I can see no possible advantage to not having them readily accessible thru the platter from the top, quite the opposite.

 

[skriefal]

Here's a view of the one of the suspension points on my T65c, showing the slot cut into the end of the screw:

 

[Pio1980]

It's rightside up, you loosen the nut and adjust the screw slot.

 

[Pio1980]

How does the H-K sound?

Some brief history;
I got this TT as a get-by 23 years ago after retiring from the Army with my main system in shipment storage. I installed a lower-end Grado and fiddled with some minor mods but could not then figure out a fix for the subchassis resonances and subsequently let it go when my big system became available. It came back to me a couple years ago some time after the PO died with an unusual Denon 103M LOMC and I later worked out the mods in this thread but never got a chance to audition the TT due to being a shameless serial hobbyist with shifting interests. The recent threads on the Linn Sondek and AR 3-point TTs revived my interest in it and I took it out for serious set-up and auditioning with the cheapest elliptical tipped cart on the market (A-T 92ECD) to make it interesting.

Prior reply;
Hi Bill! Just put it into service and played Pure Prairie League's "Busting Out" thru it last night and side 2 of Leo Kottke 1971-1976, sounded real good from an entry-level A-T. Got to do more auditioning before I can say for sure overall but this is interesting. The TT is very sensitive to floor movement as are most 3-point BDs, bouncy-bouncy.

Today;
Illness in the house precluded further listening for several days, this evening got a chance to run some familiar Joni Mitchell albums and side one of Linda Ronstadt "What's New?" with the incomparable Nelson Riddle, a fine recording, under the A-T.
This set-up has far exceeded my modest expectations for it, musically valid, competent and very satisfying even as bargain-basement playback, my strong initial impression is that I could live with this as my only primary TT with this cart. I will be listening for a while to get a better idea of it's longer-term character or perhaps comparable lack of same as I hear no obvious problems or shortcoming at this stage. Very very low background noise floor from the motor or transformer, I hear absolutely nothing under the disc play itself in the silent grooves.
More to follow----.

 

[wlmill]

I am glad to hear that things are sounding well. The AT92ECD does sound pretty good for the price. It truly is a bargain. I could liv with this cartridge also.

 

[Pio1980]

This evening I swapped in a Digitrac tombstone and things just get better, this may be the best I've heard from the $20 e-Bay wonder since I started using them. I'm going to listen to this a while before going to the ReVoX Linatrack which also has a Digi tombstone to get a comparison. Initial impression is that the sonics here are better than the Linatrack set-up, more neutral and more natural.
Some have commented that this TT sounds better with the quartz lock turned off, I find it essentially unlistenable with the Q-lock engaged. Fine without, use a comparison with Q-lock to set the free-run speed and listen without the 'Q' lock.

 

[Van_Isle]

 

[Mawerick]

Anyone know for sure if the T55C can be changed from 110V model to 220V model by simply connecting the leads differently on power board? My ex-T60 had the option, so I suspect the T55 is the same, but I'd like to _know_ before opening the table. I've looked at the service manual but it doesn't really say anything about the matter.

I'm currently using a step-up transformer but it's prone to humming, so I'd like to get rid of it.

 

[marcmorin]

This evening I swapped in a Digitrac tombstone and things just get better, this may be the best I've heard from the $20 e-Bay wonder since I started using them. I'm going to listen to this a while before going to the ReVoX Linatrack which also has a Digi tombstone to get a comparison. Initial impression is that the sonics here are better than the Linatrack set-up, more neutral and more natural.
Some have commented that this TT sounds better with the quartz lock turned off, I find it essentially unlistenable with the Q-lock engaged. Fine without, use a comparison with Q-lock to set the free-run speed and listen without the 'Q' lock.

It's one thing to have to hear a slight speed issue during a heavy transient attack (if you do hear it) It's quite another thing to hear a speed control device trying to "repair" a momentary speed issue after the fact by adding a bunch of speed control issues so the logic module (or what ever they use) ends up with a satifactory "overall" speed. The best speed control device on a suspended BD table is to make sure the suspension tuning is perfect.

 

[Pio1980]

Anyone know for sure if the T55C can be changed from 110V model to 220V model by simply connecting the leads differently on power board? My ex-T60 had the option, so I suspect the T55 is the same, but I'd like to _know_ before opening the table. I've looked at the service manual but it doesn't really say anything about the matter.

I'm currently using a step-up transformer but it's prone to humming, so I'd like to get rid of it.

It should be on the data plate on the back. The ones sold thru the Military shops in Europe should be dual voltage and possibly have a Euro-standard plug as does my Army PX sold ST-7.

 

[Pio1980]

It's one thing to have to hear a slight speed issue during a heavy transient attack (if you do hear it) It's quite another thing to hear a speed control device trying to "repair" a momentary speed issue after the fact by adding a bunch of speed control issues so the logic module (or what ever they use) ends up with a satifactory "overall" speed. The best speed control device on a suspended BD table is to make sure the suspension tuning is perfect.

That is exactly what it sounds like to me, I think there are time constant conflicts between the Quartz PLL and the Tach loop vs the give-and-take of the mechanical aspects you cite.
I found similar problems with the first generation Bulova Accuquartz watches that had a Quartz clock basically driving the marvellous tuning fork drive as a motor rather than the fork-and-index running as originally designed as a self-correcting resonant time base. The original design's feedback loop design allowed compensation for shock settling and could either temporarily reduce or increase drive to compensate overstroking or understroking error caused by the fork being affected by the normal bumps in wear. The quartz circuit "patch" overrode this ability and while the timepiece was dead-on-time on the dresser it would gain like crazy in wear at, say, a concert where applause would give repeated shocks to the fork, causing it to overstroke for an extended time and the index pawl grabbing several teeth on the index ratchet rather than just one per. Road-to-hell engineering, the principle of unintended consequences run amok.

 

[Pio1980]

One of my concerns with a resilient belt drive is pitch 'pulling/sagging' from the increased drag of heavily modulated passages. All my in-use TTs since 1978 have been DDs which while not perfect do not exhibit the problem in the same way if at all. The later ones apparently have better balanced overall time constant considerations to deal with such to avoid correction bouncing and other unintended anomalies. I think the thing that idler fans appreciate is that these drive systems do not have drag/correction time constant issues. I did have briefly a non-working Rec-O-Kut 33H rigid belt drive TT that I passed onto another AKer that theoretically would have been a BD without stylus drag pitch droop, like an idler. Not quite the best of both worlds, the rigid belt won't isolate torsional vibration from the motor like an elastic belt tho' resilient mounting of the motor would help with keeping it out of the platter on the uni-plate mounting.

 

[marcmorin]

One of my concerns with a resilient belt drive is pitch 'pulling/sagging' from the increased drag of heavily modulated passages. All my in-use TTs since 1978 have been DDs which while not perfect do not exhibit the problem in the same way if at all. The later ones apparently have better balanced overall time constant considerations to deal with such to avoid correction bouncing and other unintended anomalies. I think the thing that idler fans appreciate is that these drive systems do not have drag/correction time constant issues. I did have briefly a non-working Rec-O-Kut 33H rigid belt drive TT that I passed onto another AKer that theoretically would have been a BD without stylus drag pitch droop like an idler. Not quite the best of both worlds, the rigid belt won't isolate torsional vibration from the motor like an elastic belt tho' resilient mounting of the motor would help with keeping it out of the platter on the uni-plate mounting.

I'll address what I hi-lighted. Beyond what we talked about in e-mail about how the suspension reacts to this, there is another area to look at as well. I addressed this in a thread about a Nottingham Spacedeck. You want no type of eddy brake in a suspended BD table running a syncronus motor. An eddy brake is in action in the main bearing well due to surface structure of the main well sleeve, the surface of the spindle, the load at thrust, and type of lubrication. The optimum finish of the main well sleeve should be 12 micron (burnished) and a 60 deg crosshatch. The optimum finish of the spindle should be 12 micron (burnished) and 15 deg crosshatch. Those finishes when moving past each other create a perfect 45 deg load. Send me some photos of the thrust system employed in your table via e-mail.

Motor vibration: removing it from the table via isolation still doesn't remove it from the belt. If it is a 24 pole 300rpm motor there still will be a 12.5hz major frequency the belt carries. Divide your motor rpm by the number of poles to find major resonate frequency. An 1800/4pole motor adds a 450hz frequency into a belt/table. The Well Tempered table has a tension rod running from the motor to a 10-12 pound chunk of something (iron or brass or lead) I think the designer had the idea of......"try to get that to vibrate B**ch !!!" I still believe a drain will do a lot more than isolation in getting motor resonates out of the belt/table

 

[Pio1980]

Marc, I'll get back to you on this.
In the meantime I've tweaked it a bit and auditioned some more good material and all I can say at this point is that I am sooooooooooo glad I did not sell this TT.
Oh---My---God!!!

 

[marcmorin]

Marc, I'll get back to you on this.
In the meantime I've tweaked it a bit and auditioned some more good material and all I can say at this point is that I am sooooooooooo glad I did not sell this TT.
Oh---My---God!!!

There's magic in a properly tuned suspended belt drive. Seems like ya can just walk into the music and look around. :thmbsp:

 

[Ilikevinyl]

I have a HK T55C. Thanks for the tip! I have the felt and some stainless steel washers that will work fine for the job.

I did add some adhesive foam rubber (the kind you find in craft stores) and applied it to the subchassis.

Did a stupid thing and removed the cloth material around the springs. You really get a bounce! I wouldn't recommend this. I did notice that when a record was playing if I made contact with the tonearm base I heard less noise.

It now has some problem. If I move the arm into the play position the motor will run for 2-3 seconds and then stop. What would cause this?

I do not like the sound of the original HK platter mat. Sounds dark & veiled compared to my Extreme Phono None-Felt Turntable Mat with Skin on top. This mat is much better sounding!

 

[Pio1980]

There's magic in a properly tuned suspended belt drive. Seems like ya can just walk into the music and look around. :thmbsp:

That is exactly what I'm getting with the Digi Tombstone in it. I can't say that I'm getting any pitch pulling that I can put my finger on, hopefully that'll stay.
A turntable just shouldn't make this much difference with the same cart as in several others but it does, it frankly makes some others I've used sound like incompetent toys with that cart. This just sounds 'right', and by the way I had no idea how close to neutral and transparent my experimental system could sound until this set-up, The Joni Mitchell "Don Juan" and the DGG "Carmina Burana" were a transcendental listening experience this evening. This thing is probably too good for most of my records.

 

[Pio1980]

I have a HK T55C. Thanks for the tip! I have the felt and some stainless steel washers that will work fine for the job.

I did add some adhesive foam rubber (the kind you find in craft stores) and applied it to the subchassis.

Did a stupid thing and removed the cloth material around the springs. You really get a bounce! I wouldn't recommend this. I did notice that when a record was playing if I made contact with the tonearm base I heard less noise.

It now has some problem. If I move the arm into the play position the motor will run for 2-3 seconds and then stop. What would cause this?

I do not like the sound of the original HK platter mat. Sounds dark & veiled compared to my Extreme Phono None-Felt Turntable Mat with Skin on top. This mat is much better sounding!

Did you change anything other than what you mentioned that could affect the highlighted item?