Logic DM-101

snap, crackle and pop
jdjohn
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Logic DM-101

Post by jdjohn » 26 Jan 2019 05:37

Decided to start a new thread for this better piece of British engineering - Logic DM-101 turntable.
Logic DM101.jpg
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Although the motor looks a little puny...
Logic DM101under2.jpg
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...the belt pulley is substantial, and IMO it is a very sufficient drive system.
Logic DM101 pulley.jpg
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The plinth/base is made of MDF, and has a few layers:
Logic DM101 chassis1.jpg
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Logic DM101 chassis2.jpg
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jdjohn
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Re: Logic DM-101

Post by jdjohn » 26 Jan 2019 05:47

Here is the sub-chassis. The tips of the main bolts at the three main corners ride in bushings. or grommets of sort, that are suspended with short springs under the main chassis.
Logic DM101subchassis.jpg
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From research/reading I have done, it may be advantageous to replace all the springs involved in the sub-chassis suspension.

Oh, by the way, the Grace 704 tonearm I bought for this deck doesn't exactly line-up... :(
Logic DM101 Grace1.jpg
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...so I am fabricating a custom armboard :D

Alec124c41
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Re: Logic DM-101

Post by Alec124c41 » 26 Jan 2019 14:54

Nice. We had a couple of members that praised that turntable.
I put a Jelco arm on an SP-10 cut for an SME, as yours is. I put a thin plate over the area, to cover the holes. Someday I might improve on this.

Cheers,
Alec

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Re: Logic DM-101

Post by jdjohn » 26 Jan 2019 16:18

Apparently the Logic Datum tonearms are pretty good (and cheaper), but they're rare on this side of the pond.

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Re: Logic DM-101

Post by goatbreath » 26 Jan 2019 22:29

My DM 101 and my Michell Mycro both sound a good bit better than my Linn Sondek..
The Mycro is really neutral..The DM101 is magical and at times dramatic and exciting..
The Bass on the Logic is really special..I'm using a Hadcock GH220 and a Shure M75 ED on mine..
This is the second one I have owned..Visually they aren't much,soundwise they are..
Set the insert centre section so it is slightly lower than the base..
Route the tonearm cable so it is part of the suspension..

The Logic Datum arm was made by Syrinx..
Gimball arms suit this deck well,if something chimes,it is magical.
The note just hovers in mid air and it is really clean..

The one I have this time is the slightly later Electronic..
It came with a Syrinx PU 3..
The one before,same one as yours came with a Hadcock GH220 ss..

Aha,I'm just looking closer,my first one was a Mark 2 as it had the central spring..
That sat into a cupped retainer that was bolted across the circular hole in the middle of the plinth..
It looks like you have a mark 1..Unless you have detached that part..

There are a few DM101 owners on here..
Hopefully there will be a Mark 1 owner if that's what yours is..

The Linn has a smooth easy going on vibe,so still nice..
I get fireworks I have never got from other decks with the DM101,with Hadcock GH220 ss and M75 ed.
I tried a SME 3009 Improved on one once,it works,but no magic..

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Re: Logic DM-101

Post by goatbreath » 26 Jan 2019 22:35


jdjohn
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Re: Logic DM-101

Post by jdjohn » 27 Jan 2019 00:16

Thanks for chiming-in, GB. I see that the Hadcock GH220 is a unipivot like my Grace 704, so maybe I can conjure up some magic as well :D I'm having to fabricate a tonearm board first.

The sub-chassis does sit a little lower than the top right now, however, it seems to tilt towards the front a bit. I won't know for sure what I've got until the arm is mounted and that weight is applied. I may have to get some new springs like you did. In my reading/research, I've seen mention of a counter-weight that attaches underneath the suspended chassis in some instances.

Also, even though I got a new belt (since mine came without one), it is running a tad slow. The belt seems to be riding properly, right on the bulge in the middle of the pulley, so I'm not sure what my next move should be to get the speed right. Maybe replace the capacitor in the power supply?

Btw, I believe mine is a Mk1 based on your descriptions.

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Re: Logic DM-101

Post by goatbreath » 27 Jan 2019 01:10

The counterweight sits on the top of the subchassis on the other side opposite to where the arm hole is roughly..
Looking at yours,it doesn't have it..Another Mark 1 indication..Looking up google images should find a picture..

The Hadcock GH220 ss is strangely for a Hadcock actually a gimball bearing arm..
Which makes people condemn it sometimes,with the wrong cartridge it is bass light..
As with all Hadcocks of yore,the wiring/soldering falls apart..
When working in the right combo though,magical..
Hadcock products were very Home Brew..

I've never tried a Unipivot on the DM101.. :)
So I will read this thread with interest..

The Capacitor,I have only replaced one in a Thorens Belt drive when it decided to start running backwards occasionally..So I don't know enough there..
The belt..I used a Thorens TD 150/160 etc size as an emergency belt..
I'm not sure how far off it is though.
The present belt I got for mine I have the Electronic speed control at complete minimum..
That means a non electronic may run fast with the belt I got..
That was from an E bay shop called Malvern Audio in the UK..

Alec124c41
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Re: Logic DM-101

Post by Alec124c41 » 27 Jan 2019 02:28

If you are running a tad slow, see if you can find a thicker belt.

Cheers,
Alec

phats
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Re: Logic DM-101

Post by phats » 27 Jan 2019 10:30

This is def. a mk 1 Logic. Beutiful turntable, built like a tank. I do note an after-market footer (spike) in your pictures. Springs can be a bit finnicky. Except for finding new springs (which I did find daunting considering the math involved, resonant frequencies and such) you can always insert little damping rubbers. I had some deflex material about and that worked very nice. Enjoy your Logic, it sounds superb!

Kind regards, Stef.

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Re: Logic DM-101

Post by jdjohn » 29 Jan 2019 21:35

GB: I see now that the Hadcock GH220 SS is gimbal...interesting how the regular GH220 (no SS) is a unipivot. Regarding the belt, I estimate the one I have is .4mm thick, but I know where I can get one that is .7mm, so maybe that will sort-out the speed issue.

Stef, you are right that mine has some aftermarket spikes. Kinda cool, but kind of a pain since I've had to find make-shift disks to put the pointy bits in.

Quick update: I finished my homemade armboard for the Grace 704 tonearm. I used MDF for it just to get the deck functional, and left it unpainted, so it looks pretty amateur. I used a bench-top drill (where you strap-in a power drill) for drilling the precise holes.

Finally got everything assembled last night and took it for a spin, but now with all the weight on the suspended sub-chassis, I see I have a suspension problem since the bottom of the platter is rubbing the top of the motor pulley when I add a record #-o It's borderline depending on the weight of the album. When I used an old, thin album, it didn't scrape, and sounded pretty good - had to use low volume, though, due to the lateness of the hour. My first attempt at playing revealed a grounding problem in the right channel of the tonearm. The green wire in the cartridge sled was dodgy (and broke when I pulled on it), so I had to basically replace the wire and re-solder into the sled.

I see now that I need to properly route the tonearm cable through the channel in the plinth. Maybe that will provide more support for the suspension like GB mentioned. Otherwise, next step will be to replace the springs. Anyway, here is an updated pic as it currently stands. I've got a Technics EPC-205CII mounted on the tonearm, and you can see the raw look of the MDF armboard :lol:
IMAG1478.jpg
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jdjohn
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Re: Logic DM-101

Post by jdjohn » 30 Jan 2019 04:47

UPDATE: Properly re-routing the tonearm cable through the plinth's trough, with a little slack, seems to have fixed my suspension issues. Here's a corrected pic of the underside...with a convenient glass reflection :)
Logic DM101 cable susp.jpg
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On the right, you can see the cable (from plug and red arrow) taking a little dip before going back up into a channel in the plinth. Then the cable exits the plinth (blue arrow) after being routed around the front of the spindle bearing housing.

After correcting as shown, the underside of the platter no longer scraped the top of the motor pulley :D I did, however, need to fine-tune the suspended height of the sub-chassis via the 3 hex screws (and knurled circular lock nuts) for dialing-in the height/leveling of the sub-chassis. The running path of the belt is key in adjusting the suspension. It is highly recommended to run the main platter inverted on top of the sub-platter for accurate weighting, running of the belt, and fine-tuning the suspension adjustments. Go ahead and put a test record and clamp on top to make sure the total weight is correct for leveling purpose.

phats
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Re: Logic DM-101

Post by phats » 30 Jan 2019 11:58

Hi John,

If I may be so bold, one of the Logic characteristics was the direct coupling of the tonearm to the subchassis, in other words: that was a specific design for them. As the intended Datum tonearm has a round base as well (Linn-spacing?) it should be possible to couple your tonearm directly. If not, no harm done..... if it sounds nice, all is well.

Kind Regards, Stef.

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Re: Logic DM-101

Post by jdjohn » 30 Jan 2019 20:01

Hi Stef,

The flange of the tonearm base on the Grace 704 isn't wide enough to align over the mounting holes, and the orientation of the holes won't work either. I tried to make it work, but the geometry just isn't there. I may have been able to secure one of the three flange holes by moving it all the way to the edge, but obviously that wouldn't suffice, not to mention trying to get it mounted at the right spindle-to-pivot distance. I see a Logic Datum II arm for sale on eBay over in the UK, so may consider it. Thanks for the information.

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Re: Logic DM-101

Post by goatbreath » 31 Jan 2019 04:00

My Logics used a Metal mounting plate with an oval SME type of hole that you slid the arm along in the case of he Hadcock..
It had 4 bolt holes..
The Syrinx had a similar plate,but with just a mounting hole sized cut out..
The Syrinx has the same mounting distance as Linn Arms but has single point mounting..

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