the home of the turntable

Mission 774 tonearm rewire

snap, crackle and pop

Mission 774 tonearm rewire

Postby ripblade » 24 Nov 2008 22:04

Hi all. Has anyone here any experience rewiring a Mission 774 (original) tonearm. What I'd like to do is lift the ground lead from the signal ground, but the harness is terminated with a 4 pin SIP connector. I picked up a 5 pin 2.5 molex connector and header which looks like it should work, but I was wondering af anyone here has any experience/comments/advice before I bring out the soldering iron.

Thanks in advance.

Glenn
ripblade
senior member
 
Posts: 402
Images: 1
Joined: 05 Oct 2008 19:51
Location: Toronto, Ontario

Postby abril » 24 Nov 2008 22:34

I have disconnected yellow wire and grounded the arm from the base on one of the socket retaining studs - works fine for me ,no hum and no interference even on a DL304 through a MC input.
No need to change the plug and socket
User avatar
abril
contributor
 
Posts: 1543
Images: 146
Joined: 13 Oct 2002 20:48
Location: Cornwall

Postby rhmbus » 25 Nov 2008 08:36

abril wrote:I have disconnected yellow wire and grounded the arm from the base on one of the socket retaining studs - works fine for me ,no hum and no interference even on a DL304 through a MC input.
No need to change the plug and socket

same with me!!!
ray
cd !the curse of the listening classes
(thanks MR N Rockwell)
User avatar
rhmbus
contributor
 
Posts: 635
Images: 1
Joined: 24 Nov 2004 08:31
Location: east london

United Kingdom

Postby audioorigami » 25 Nov 2008 21:00

if you pop the mission sticker of the front of the headshell...the earth pin is just behind
User avatar
audioorigami
senior member
 
Posts: 1146
Images: 105
Joined: 29 Jan 2005 13:53
Location: scotland

United Kingdom

Postby abril » 25 Nov 2008 21:18

The 774 club meet again :lol:

Just disconnect from the cartridge return wire at the tag :idea:
User avatar
abril
contributor
 
Posts: 1543
Images: 146
Joined: 13 Oct 2002 20:48
Location: Cornwall

Postby ripblade » 25 Nov 2008 21:32

audioorigami wrote:if you pop the mission sticker of the front of the headshell...the earth pin is just behind

Yes, I see that. It was in the archives at your website where I first got the idea of lifting the ground from the signal ground. The images clearly show the 5th wire but there is no mention of how you terminated it. Any tips? :)

I did cut the ground (yellow) wire behind the cartridge tag and found no increase in hum; no decrease either. Seems to have made no difference. I installed a Linn Klyde as test case because it hums badly on the right channel with this arm, for reasons which are not yet clear to me.

I rewired a Rega RB 250 in the "Incognito" style with a star ground at the base, but this won't work with the Mission as there seems to be no continuity between the arm and base.

In any event, I plan to continue rewiring the Mission with a silk wrapped copper Litz wire. I'll wind in the black (well, it looks black) wire from the Mission harness, attach it to the ground pin and leave the end float for the meantime.

Thanks again for all the replies.

Glenn
How boring it would be, this endeavor
If all we heard was "perfect sound forever"
ripblade
senior member
 
Posts: 402
Images: 1
Joined: 05 Oct 2008 19:51
Location: Toronto, Ontario

Postby ripblade » 25 Nov 2008 21:51

abril wrote:The 774 club meet again :lol:

As the newest member it is a great honour to have reconvened the club for this emergency session...... :lol:

I had a Mission arm from '84 and sold it with the deck when I replaced it in '91. Things haven't been the same ever since. I bought a Mission 775 SM with the arm installed and a Mission 773 all in one original package just a short while ago. The pickup is well past done of course, but it's been a great feeling to have this great arm back in my possession.

It is wonderful to hear an orchestra in proper tonal balance once again.

Glenn
How boring it would be, this endeavor
If all we heard was "perfect sound forever"
ripblade
senior member
 
Posts: 402
Images: 1
Joined: 05 Oct 2008 19:51
Location: Toronto, Ontario

Postby rhmbus » 25 Nov 2008 22:15

I rewired one of my arm tubes with silk/copper Litz ,Michell silver tags,damped the arm with a length of balsa wood fitted a brass plate at the front for a little more mass and fitted a brass pin at the other end to make contact with the arm tube clamp for earth continuity(must have been bored out of my skull that day).No hum and better tracking with some mc`s and i managed to convince myself it was all worthwhile,but in all honesty the 774 is pretty damned good without all the gentrification.
welcome to the club ray :D
cd !the curse of the listening classes
(thanks MR N Rockwell)
User avatar
rhmbus
contributor
 
Posts: 635
Images: 1
Joined: 24 Nov 2004 08:31
Location: east london

United Kingdom

Postby ripblade » 25 Nov 2008 23:42

Thanks Ray. The arm is good as is, but is also worth the extra effort IMO. I find the balsa wood treatment interesting; I didn't think it would be necessary with the Mission. I did however, plan on trying it with the Rega because IME it is an obvious candidate for damping. I have heard of using sand, but don't think I'll bother because at the moment I have no issues with trackabilty.

While we're here, another issue I've noticed developing with these arms as they're getting long in the tooth, is the Sorbothane damper in the counterweight seems to be losing its structure. On mine the weight sags backwards slightly, but I doubt it's any concern sonically. Still, it would be nice to know if any members have found a resource for replacing it.

By the way, I've tried the search engine in this forum but it returns too many results to be much help. If any one can point me to any previous threads covering these topics I'd greatly appreciate it.

Glenn
How boring it would be, this endeavor
If all we heard was "perfect sound forever"
ripblade
senior member
 
Posts: 402
Images: 1
Joined: 05 Oct 2008 19:51
Location: Toronto, Ontario

Postby abril » 26 Nov 2008 16:41

Mine had to be worked on as a necessity as the wiring was in a dreadful state when I bought it.
Cardas wired tube (J7 may remember rewiring the plug for me) :D
New external wiring.
Tube was sand loaded with DL110 and DL160 but now have a DL304 and sand removed
The sorbothane damper unfortunately gets mistreated on many by peoples adjusting the counterweight and not using the thumbscrew.
Tried many other arms in the years since I've had it including rewired and Technoweighted RB250/300 and still found nothing to touch it.
User avatar
abril
contributor
 
Posts: 1543
Images: 146
Joined: 13 Oct 2002 20:48
Location: Cornwall

Postby audioorigami » 27 Nov 2008 00:19

yes m8 i memebr it well!!

i now how the tools to make new rear weights with a harder plastic insert that will last a lifetime
User avatar
audioorigami
senior member
 
Posts: 1146
Images: 105
Joined: 29 Jan 2005 13:53
Location: scotland

United Kingdom

Postby ripblade » 03 Dec 2008 20:24

Well, it's done!

Image

Image

I preparation for the re-wire, I needed to take care of some nasty business beforehand involving trueing the flats on the mounting block. The sample arm I have has the block offset sufficiently to force either a shim, or raising the pillar several millimeters in order to obtain the correct VTA. Since neither solution was satisfactory, I set up my Unimat lathe as an end mill and trued the flats on the block, removing as little of the alloy as possible.

The results not only look good, but sound better. Removing the paint is, I think, the biggest structural change behind this, resulting in a considerable increase in micro-detail, with a pleasing oomph added to the upper bass spectrum, filling out the bass quite nicely.

With that done, I proceeded with the re-wire, beginning with the interconnect to the preamp. The Mission table you see in the photo uses RCA jacks to output the signal. Great from a convenience standpoint, but not very satisfactory from an electical one.

As this was my first attempt with the copper Litz, I proceed the way I would with normal teflon coated wire, but the results weren't satisfactory. Conventional wire spirals well and stays put with little effort, but the silk wrap resisted my attempts to spiral the wire strands. I've since concluded this wire must be braided.

Upon completing the IC portion of the wire, I now had a solid (if less than ideal) electrical connection between the 4 pin SIP and the preamp. Despite the loose winding of the strands within the shield, the replacement wire offered up a considerable increase in the stage, with a generous amount of atmosphere around each instrument. Despite this obvious improvement, the bass seemed a little lighter in the bottom end, and the treble, though more than adequate, had a more delicate, refined and silky texture compared to what I'm used to hearing.

In rewiring the arm itself, I followed standard proceedure in preparation, but added braiding to the routine to keep the wires closely spaced. This was my first time braiding anything since a time as a child at summer camp. It took awhile to descipher the intructions I found on the web, but after a few mis-starts, I found the braiding sequence quite straightforward and before long, the 'memory' was in my fingers. I abandoned my plans for the 5th wire as it a seemed an unnecessary complication.

The cartridge tags are scavenged from a db25 jack, trimmed and ground to a shorter length, and covered with colour coded shrink tubing to maintain tension on the cartidge pin and protect the wire at the joint.

The result? Well, it was certainly worthwhile! I have not heard better sound from a record. The 3 dimensional sense of space is incredible! The dynamics are very large and fast, and a certain amount of the bass that was lost in muddling the IC wiring seems to have been restored somewhat. The biggest unexpected benefit is with regards to continuous surface noise - it seems to have disappeared. Well, certainly reduced considerably compared to anytime previous.

I have to say that I'm hooked on braided Litz wiring. I expect to replace more wiring soon, beginning with redoing the IC portion of the signal chain. I expect this will restore the bass hammer to it's fullest impact.

Thanks for all your help!

Glenn
How boring it would be, this endeavor
If all we heard was "perfect sound forever"
ripblade
senior member
 
Posts: 402
Images: 1
Joined: 05 Oct 2008 19:51
Location: Toronto, Ontario

Postby abril » 04 Dec 2008 08:54

Great to see another in use,doing what it does best - playing music :!:

No damping I see.
User avatar
abril
contributor
 
Posts: 1543
Images: 146
Joined: 13 Oct 2002 20:48
Location: Cornwall

Postby Beltway » 04 Dec 2008 15:47

Nice work. That braided wire looks great.
User avatar
Beltway
senior member
 
Posts: 505
Images: 31
Joined: 23 Dec 2005 02:43
Location: Calgary, Canada

Next

Return to Turntables and Tonearms


Design and Content © Vinyl Engine 2002-2013

faq | site policy | advertising | hifiengine