C2 headshell weight - Friday project

the jewel in the crown
amagasakii
member
member
Canada
Posts: 158
Joined: 18 Jun 2017 04:14
Location: BC

C2 headshell weight - Friday project

Post by amagasakii » 23 Nov 2019 10:46

The AT91 cartridge I'm using on my SL-65B is probably a bit light for the arm. It's within the counterweight balancing range but just barely; I had to push the counterweight as far inwards as possible.

Previously I'd used a standard 6g shim-style headshell weight that came off the Toshiba of a friend. This type of thing:
LP-Gear-Shim-Spacer-1g.jpg
(7.52 KiB) Downloaded 131 times
I didn't like how it looked, but genuine Garrard weights are rare here.
434289987_o_1_.jpg
(16.49 KiB) Downloaded 131 times
As rare as lead hen's teeth. So I threw together my own tonight, in typical amateur fashion.
bad-weight-1.jpg
(9.25 KiB) Downloaded 131 times
It's four pieces from a strip of $3 hobby shop brass all soldered together. Unfortunately I didn't think things through, and I tried to put it together in two steps. I spent a lot of time aligning, filing, smoothing and shaping the "weight" bit, then tried to solder the perpendicular "mount" to it...immediately melting the solder in the "weight" and turning the whole thing into a sloppy mess. #-o

tl;dr: it's not as pretty as I'd hoped, but it clocks in at 5.25g, fits into the cartridge carrier very nicely, and the tonearm responds well to the added weight.
prettier-weight.jpg
(19.83 KiB) Downloaded 131 times

DSJR
long player
long player
Wales
Posts: 3078
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: C2 headshell weight - Friday project

Post by DSJR » 23 Nov 2019 12:14

I was brought up to have the inertia as low as possible for arms like this, so the counterweight being as far forward as possible is a good thing for me, as long as the arm can balance out.

One thing, accepting the AT91 is a conical tip and not so sensitive to the steep autochange tonearm angles (VTA) -

The C2 used to come with a little black plastic 'wedge' to get the cartridge more parallel with a single record. One way round to cater for the tonearm sloping downwards in the 65B and related models and the other way round to correct for the too-tall platter of the AP76 causing the arm to be tail-down (the related SL72B had a smaller lower platter). I'd recommend it if you could consider fabricating one if you mainly play single albums as high frequencies will thank you for it as regards less disssssstortion...

amagasakii
member
member
Canada
Posts: 158
Joined: 18 Jun 2017 04:14
Location: BC

Re: C2 headshell weight - Friday project

Post by amagasakii » 24 Nov 2019 08:01

Well shoot-- I was under the impression the extra weight was needed, but I guess not. Well, at least it kept me occupied for a little while! :-)

I'm mainly using this thing as a changer-- do you have a picture of the wedge? I can't seem to find anything on Google and I'm not sure I can picture it. I assume the mounting screws go through it?

cafe latte
vinyl addict
vinyl addict
Australia
Posts: 11613
Joined: 11 Oct 2009 04:27
Location: Cattle property near Ravenshoe Qld Australia

Re: C2 headshell weight - Friday project

Post by cafe latte » 24 Nov 2019 09:04

amagasakii wrote:
24 Nov 2019 08:01
Well shoot-- I was under the impression the extra weight was needed, but I guess not. Well, at least it kept me occupied for a little while! :-)

I'm mainly using this thing as a changer-- do you have a picture of the wedge? I can't seem to find anything on Google and I'm not sure I can picture it. I assume the mounting screws go through it?
The at3600 and the at91 are both lowish compliance so the weight you made is needed and cart will perform better conical or not. Compliance has nothing to do with this.
Chris

DSJR
long player
long player
Wales
Posts: 3078
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: C2 headshell weight - Friday project

Post by DSJR » 24 Nov 2019 17:58

You misunderstand I think. If the cartridge will balance out in the arm WITHOUT the extra headshell weight, then the 2g or so tracking force can still be applied with no hiccups. If the cartridge won't balance out at all, as happens when low mass ceramic type cartridges are used, then obviously you MUST add extra mass to the C2 and fitted cartridge so the counterweight can balance it out. This isn't the same thing as 'effective mass,' of which the 65B/SP25III arm has plenty and no more needs to be added :D.




I thought the Rega Carbon cartridge had the same conical tip of the AT91. Apparently it's advertised as elliptical, so won't be 'quite' as suitable for an autochanger like this where the VTA varies with each record played.

As for the 'wedge,' The screws did pass through it and if you Google Garrard C2 carrier, you'll see various pics some of which showing this little thing, but not always if you click on them... I use one on my AP76/AT120E. You can see how 'tail down' the tonearm is and if you expand the image, you can see the wedge (just) across the top of the cartridge.

gallery/image/47749/mini

cafe latte
vinyl addict
vinyl addict
Australia
Posts: 11613
Joined: 11 Oct 2009 04:27
Location: Cattle property near Ravenshoe Qld Australia

Re: C2 headshell weight - Friday project

Post by cafe latte » 24 Nov 2019 20:11

DSJR wrote:
24 Nov 2019 17:58
You misunderstand I think. If the cartridge will balance out in the arm WITHOUT the extra headshell weight, then the 2g or so tracking force can still be applied with no hiccups. If the cartridge won't balance out at all, as happens when low mass ceramic type cartridges are used, then obviously you MUST add extra mass to the C2 and fitted cartridge so the counterweight can balance it out. This isn't the same thing as 'effective mass,' of which the 65B/SP25III arm has plenty and no more needs to be added :D.




I thought the Rega Carbon cartridge had the same conical tip of the AT91. Apparently it's advertised as elliptical, so won't be 'quite' as suitable for an autochanger like this where the VTA varies with each record played.

As for the 'wedge,' The screws did pass through it and if you Google Garrard C2 carrier, you'll see various pics some of which showing this little thing, but not always if you click on them... I use one on my AP76/AT120E. You can see how 'tail down' the tonearm is and if you expand the image, you can see the wedge (just) across the top of the cartridge.

gallery/image/47749/mini
What is the effective mass of the arm in question?
Chris

amagasakii
member
member
Canada
Posts: 158
Joined: 18 Jun 2017 04:14
Location: BC

Re: C2 headshell weight - Friday project

Post by amagasakii » 25 Nov 2019 21:16

First, my apologies. I referred to the cartridge as an AT91; rather I meant it's in the AT91 family along with, as I understand it, all the other AT carts with this body. It is in fact the AT3600L, 2.5-3.5g tracking force, conical tip.

As far as the weight is concerned, I'll give it a spin with and without the weight. My inexperience is showing again! I thought that the extra weight would only apply to downward force on the tonearm but, after doing a bit of reading, I think I've also increased the mass the cantilever is experiencing in side-to-side motion. Since this turntable has the dubious honour of playing all my horrible, warped thrift store finds, this might be problematic.

Chris, initially I thought this tonearm expects heavier cartridges, so the extra weight is beneficial. DSJR is saying that, as long as I can balance it and put down the correct VTF, the weight is unnecessary, which of course now has me questioning myself, seeing as how I could indeed balance it without the weight. Can you explain why the weight is beneficial? I'm genuinely curious, because I read other threads with people saying just that-- whichever tonearm they were using responded better with additional weight.

Thanks!

DSJR
long player
long player
Wales
Posts: 3078
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: C2 headshell weight - Friday project

Post by DSJR » 25 Nov 2019 22:28

The AP76 tonearm is, I believe, lower effective mass than the SP25III/SL65B arm. The headshells look alike, but the AP76 one is a plastic moulding where the 65B/25III version is cast metal.

I don't remember the exact figures, but the AT91 or 3600 styli should be perfectly happy in the 65B tonearm. AT have recently revamped their European range and the sole remaining AT91 is the AT91R with 2g tracking, red stylus housing and an aluminium cantilever rather than the 'carbon/plastic' one. The 65B in good fettle and clean acting auto trip (I prefer not to lubricate these parts and keep them dry) should happily track at 2g and maybe a smidge lower, the drag of the arm bearings preventing much in the way of lateral instability here should any arise.

amagasakii
member
member
Canada
Posts: 158
Joined: 18 Jun 2017 04:14
Location: BC

Re: C2 headshell weight - Friday project

Post by amagasakii » 26 Nov 2019 04:46

The headshell or the tonearm carrier is cast? The headshell on my 65B is definitely plastic. Metal would make it a heck of a lot easier to re-solder that wiper contact when the time comes!

I did try the elliptical stylus from my Dual on the 65B. It seemed perfectly happy to track down to ~1.5g, the minimum for that stylus, but that was only on pristine discs. I've got today's thrift score (handful of minty $2 Dave Brubeck LPs) spinning at 2.5g on the AT3600L and it's perfectly happy. Thanks, helpful bearing drag! :-D

cafe latte
vinyl addict
vinyl addict
Australia
Posts: 11613
Joined: 11 Oct 2009 04:27
Location: Cattle property near Ravenshoe Qld Australia

Re: C2 headshell weight - Friday project

Post by cafe latte » 26 Nov 2019 05:09

amagasakii wrote:
26 Nov 2019 04:46
The headshell or the tonearm carrier is cast? The headshell on my 65B is definitely plastic. Metal would make it a heck of a lot easier to re-solder that wiper contact when the time comes!

I did try the elliptical stylus from my Dual on the 65B. It seemed perfectly happy to track down to ~1.5g, the minimum for that stylus, but that was only on pristine discs. I've got today's thrift score (handful of minty $2 Dave Brubeck LPs) spinning at 2.5g on the AT3600L and it's perfectly happy. Thanks, helpful bearing drag! :-D
I cant find the effective mass of this arm. What I will say is the AT3600l is good with effective mass of 18-20g so if arm is less than this I would be adding the weight.
Chris

DSJR
long player
long player
Wales
Posts: 3078
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: C2 headshell weight - Friday project

Post by DSJR » 26 Nov 2019 10:16

The 65B arm is getting on for that I reckon. Are you aware what adding mass to the headshell is going to actually DO to the cartridge behaviour? I'm not sarcastic here, just generally asking. At the time of ceramic pickups, Garrard suggested an arm-cartridge resonance of around 20Hz was quite ok - and most ceramic pickups offered far lower compliance than a 3600L. Please don't worry about it, but if it makes you feel better, then who am I to stop you.


This really is going back forty years now, but I did have an SP25 III for a while and I have it in my head the headshell was a solid casting, unlike the identical looking one on the AP76 arm which is slightly 'twisty' if abused. If I have it wrongly, I do apologise.

The 65B in perfect tune may well go down to 1.5g tracking as the basic under-deck parts weren't much if any different to the later 125SB which could offer low tonearm bearing friction/drag. It's just that now, I have no idea on the state of the greases used in the horizontal tonearm pivots and of course the trip pawls on the main cam can all but seize.

Lastly, don't track too low with a given cartridge, as this is worse for hf tracking as too heavy. I know the AT91 and related AT105, the evergreen-for-decades AT95E and AT110E and of course the 91-derived Rega Carbon, which I need to get out to check if the diamond is in fact elliptical as currently claimed. All of these seem to like 1.8 to 2g for clearest sound in a variety of decks here from a 60mk2 (with which I prefer to use something like a Stanton 500 really) to my Dual 701 which'll take most things out there to high sonic standard at obscene price levels (sounded fab with a Koetsu Black for example). I admit I don't how different the 3600L is to the 91 apart from price (and maybe packaging, as we used to obtain OEM AT95E's on 'egg-trays.'

A70BBen
senior member
senior member
Posts: 839
Joined: 16 Feb 2014 21:56

Re: C2 headshell weight - Friday project

Post by A70BBen » 28 Nov 2019 15:58

You are correct. The SP25 Mk III and Mk IV (also SL65B and 60B) had the rectangular counterweight secured by a setscrew. It was similar to those on prior SP25s, the AT60 and the AT6, but had less rounded contours and was lower-mass due to the reduced mass of its integral tonearm head with C2 cartridge slide.

The SP25 Mk V introduced the round counterweight retained only by a friction fit of its rubber collar on the atmshaft.

DSJR
long player
long player
Wales
Posts: 3078
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: C2 headshell weight - Friday project

Post by DSJR » 29 Nov 2019 16:48

Somehow, we *seemed* to jump from the SP25IV straight to the 125SB here in the UK, but I think some intermediate models are about here. By then though, the Pioneer PL12-D became the low cost model to buy and these sold in the tens of thousands back then in the UK.

A70BBen
senior member
senior member
Posts: 839
Joined: 16 Feb 2014 21:56

Re: C2 headshell weight - Friday project

Post by A70BBen » 30 Nov 2019 04:19

I have a Garrard UK catalog that shows the SP25 Mk IV, 125SB and 35SB. The SP25 Mk IV was idler drive, same as the SP25 Mk III but with a synchronous motor instead of induction. 35SB was belt drive with the straight SP25 armtube and a pivot assembly based on the AT6. Apparently when Garrard exhausted its supply of straight armtubes, the S-shaped armtube similar to the 125SB's was substituted on the belt drive chassis with AT6-derived tonearm pivot to make the SP25 Mk V. By that time, Garrard was using "parts-bin engineering" to make "new" models by swapping around interchangeable parts.

All of these were based on the classic 1960 Autoslim chassis.

DSJR
long player
long player
Wales
Posts: 3078
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: C2 headshell weight - Friday project

Post by DSJR » 30 Nov 2019 12:10

Must have been the snooty (early high end) dealers I worked at then as a 'Saturday Boy.' By the time I started there full-time (late 1975), all these things had gone and our lower cost decks were the last Pioneer PL12-D's (then the 112-D), Technics SL 20 (great with a Stanton 500EE), JVC JLA 1 and feedback prone JVC JLA 15...

Post Reply