New Jelco 750 on 1210, now getting bass distortion...? Any ideas?

[nickbaba]

Hi gang - Just had the stock Techie arm on one of my 1210s replaced with a Jelco 750, which I know is a popular choice amongst people here. Didn't do the fit myself but it was professionally done by someone who knows what they are doing.
After setting up the arm/ cartridge etc everything sounded fine, except on the bottom end. I could straight away notice a hint of transient distortion on kick drums and deep bass notes. Unfortunately this is a problem for me as I listen to a lot of dance and dub.
I decided to test it out with my usual low-end test track, LFO by LFO, which for those of you not familiar with it, has a sub- bass break which never fails to let me know how my system is handling the bottom end. In this case the answer was not very well at all. The bass was just nastily distorted, and it sounded like the needle was about to skip or jump off the record.
The depressing thing is that the Techie arm, while obviously not the best arm in the world, always handled that sub-bass without a problem.
So...can anyone please offer me some wisdom on why this may be happening and if/ how I can fix it!
Bit of background to rule out some potential issues - nothing else in the system has been changed except the tone arm. Same cart, same headshell (DV20XL & Sumiko). TT stands on sorbothane feet on a granite plinth & speakers are min 6 ft away so don't think it's vibrational feedback. Cart & arm properly setup using a vinylengine protractor & head shell spirit level. Tried to up the tracking force to the max recommended for the cart but made no difference.
Anyone else with a Jelco 750 encountered problems with low end distortion? If so, how did you fix it?
Cheers.

[OneyedK]

Didn't do the fit myself but it was professionally done by someone who knows what they are doing.
The obvious thing to do is to go back to those that fitted the arm.

But you asked for possible causes...
Assuming there is nothing electronically wrong (bad contacts, bad cable, etc.) and you didn't damage the cart when removing, storing or placing it...
1) The arm stands loose in his collar, you should be able to feel this.
One of the reaons why the following exists: http://theartofsound.net/forum/showthread.php?t=7359
2) There's something wrong with one of the bearings, if it's a new arm, trade it in for a new one, if it's 2nd hand, have someone experienced have a look at it.
I'd contact J7 of Audio Origami for such a problem.

And maybe a silly question, but the headshell sits snug in it's socket?

[nickbaba]

Thanks for the suggestions
The arm is mounted on one of Shuggie/Hugo's collars. Can't feel any movement from it within the collar. Headshell is secure.
I will look into the other possibilities - thanks.

[Marco]

Hi Nick,

I presume that the correct geometry has been used, for the cut-out on the arm board, to ensure 100% accurate alignment?

Also, double-check VTA, and make sure that the arm is not sitting slightly 'tail up'. When you've reinstalled the cartridge, you may not have gotten the VTA set absolutely spot on. Also check that Azimuth is spot-on, by using a small headshell weight to determine that the headshell is bang-on level, and that the anti-skate mechanism on the arm is set correctly.

Furthermore, ensure that the bolts fixing the tonearm to the arm board aren't screwed on excessively tightly, and that also applies to headhell bolts, fixing the cartridge to the headshell, both of which should simply be 'nipped up' slightly, from finger-tight.

If all of the above is as it should be, then try applying some fluid-damping to the tonearm, which it has been designed to take. That can often perform wonders, in terms of making the partnering cartridge 'behave' properly.

Let us know you get on :)

Marco.

[chelsea]

Seems strange.
Would have thought you would get distortion all through the range.

Was going to suggest dirty or knackered cart,but not sure you would just have trouble in the bass.

[Tarzan]

l too was going to suggest the cartridge.................:scratch:

[jagdesign]

I use exactly the same setup and don't have any noticeable distortion in the bass. If not setup correctly then the bass can be slightly overblown, perhaps the DV20XL's compliance is a little high for the Jelco. My arm runs pretty much level when playing, 1.9g tracking force and the same anti-skate. I also use the fluid damping, filling the reservoir completely, with the cap backed off about half a turn from being fully down.

I've read different things about what to do with the cap, anyone know if it should it be fully screwed down or not?

What is your deck sitting on Nick?

[Wakefield Turntables]

Have you checked your cartridge tags???? I had the same problem when I got my 1210 back after some mods. I had extremely light bass, now the things shakes the room.

[nickbaba]

Thanks for all the input guys.
I guess I will go over everything from scratch with a fine tooth comb.
First thing I will swap out the cart and try my spare ( Denon DL110) to rule out the cart. Will also check the tags at the same time but since I didn't remove the cart from the headshell ( I just removed the entire headshell) nothing should have changed.
Didn't try the damping oil yet, but slightly nervous that even if it solves the problem, I will just be masking it rather than fixing it. Surely a good clean sound should be possible even undamped. Certainly was from the stock Techie arm.
Will double check the VTA & azimuth etc but already checked it quite carefully with my little headshell spirit level - the little bubble is exactly centred so must be level, no?
TT sits on a granite plinth on isolator feet (sorbothane) quite far (min 6ft) from the speakers so I don't think that's an issue.
Really want to iron this out as apart from this issue I can already hear that the 750 sounds really musical and just want to enjoy it!

[Stratmangler]

Will double check the VTA & azimuth etc but already checked it quite carefully with my little headshell spirit level - the little bubble is exactly centred so must be level, no?

No.
All that shows is that the headshell is level.
Best way to check azimuth is with a small mirror - place the stylus tip upon it and view from the front, and you should see if the stylus is standing vertically.

I believe that there is some small amount of rotational adjustment that can be made on the headshell if required.

[nickbaba]

Thanks Chris that's a good tip - didn't realise that.

[Marco]

You can also sit the little spirit level on top of the tonearm's bearing housing, when the arm is placed on the record, and use it to test the VTA.

It's more accurate adjusting it that way, than just by eye :)

Marco.

[DSJR]

Re: 20X - fat in the bass, yes - IMO, but distorted? Shouldn't be...

[Marco]

Which stylus profile is used by the DV?

Some are fussier than others to 'dial in' accurately. I know that the FG S tip, on my SPU Royal, was a ball-ache to get right and would distort and almost jump out of the grooves, with some bass-heavy material, until all adjustment parameters were 100% spot on!

Marco,

[nickbaba]

OK - progress!
Swapped out the DV for the Denon 110... Set it up & made the necessary adjustments & the distortion is gone. So it's not the 750 after all.
Definitely an issue with the DV cart. May mean finessing the set-up, or may be that it's suffered some damage somehow. I've always found it very forgiving on set-up so I'm leaning towards the second possibility. Either way, everything is sounding fine with the 110 for the moment.
Thanks for the input everyone!

[Marco]

Glad you've sorted it, Nick. It was always likely to be a cartridge issue, rather than the arm. At least you've learned some new tips with regard to optimising set-up, which you hadn't considered before! :)

Marco.

[nickbaba]

Yep! Seems like with this hobby/passion/obsession there is always more to learn!

[jagdesign]

I did forget to mention one thing Nick, I'm also using a lighter headshell to reduce the arms effective mass. I haven't got the calculations to hand, but I remember the Jelco's effective mass being a little on the heavy side for the Dynavector. A lighter headshell, the ADC magnesium ones or similar, coupled with the oil damping should help things.

Even with a poor match, I wouldn't really expect distortion, just loose, overblown bass. So maybe the cartridge does need checking...

James

[DSJR]

CHECK THE DIAMOND for cleanliness! Amazing what some stubborn crud all but glued to the stylus can do.. I rejuvenated a Stilton OC9 by giving a very thorough clean..

[Tarzan]

CHECK THE DIAMOND for cleanliness! Amazing what some stubborn crud all but glued to the stylus can do.. I rejuvenated a Stilton OC9 by giving a very thorough clean..


x2- always keep yer tip clean;)

Me Denon sounded like a bag of nails one day- until l cleaned- properly:)

[nickbaba]

Thanks...
I have just noticed, while fine-tuning the VTA, that if I sit my headshell spirit level on top of the arm bearing, as suggested by Marco, that the bubble is not centred. Its not way off but its noticeably off-centre. (The spirit level is actually sitting on the oil chamber, with screw top removed.)
I would say, if you were looking down directly over the bearing, that the arm is slightly out towards the 11 o'clock position, if you see what I mean.
Firstly, is this even a problem as long as my headshell/cart are measuring flat? e.g. the bubble is centred when at the end of the headshell over the cart.
Can anyone please tell me, if I do need to adjust the vertical angle, is there a way to do that while the arm is mounted?

[Marco]

Hi Nick,

Sounds like you need to lower the arm slightly. You can adjust the VTA by unscrewing the allen bolt at the base of the arm, and lower and raise as required until you get the bubble level :)

Marco.

[nickbaba]

Thanks Marco - but I'm not sure the problem can be fixed by adjusting the VTA in this case. The issue is that the arm is slightly out-of-whack in its vertical axis where it sits in the collar. I have included a photo to illustrate, rather than try to describe in more detail.
I think its a question of levelling the armboard, as the TT body itself seems level as measured by my spirit level.
What I'd still like to know is, does this slight off-set even matter if my headshell and cart are flat, as measured by my headshell bubble?

[phonomac]

Hello Nick,
Your photo looks as if you are looking at the level with the arm on its rest? It needs to be on a stationary LP on the platter.

Apoligies if this is grandmother on about sucking eggs.

regards

Angus

[Ammonite Audio]

.............. I think its a question of levelling the armboard, as the TT body itself seems level as measured by my spirit level.
What I'd still like to know is, does this slight off-set even matter if my headshell and cart are flat, as measured by my headshell bubble?

You are correct in thinking that the armboard is not necessarily level, even when the rest of the turntable is! Careful adjustment using washers is required. This is a pain because you need to dismantle the turntable's base, but there's no other way.

The slight off-set does matter, because the headshell azimuth will be correct only at one point, and will vary as the arm crosses the record - you can check this with your headshell spirit level. The error can only be eliminated if the platter and the arm (at the pillar/bearings) are both correctly levelled. In effect, you need to level the armboard to match the platter level, using a bubble level placed on the armboard, then the arm will pretty much be OK in its collar. The arm does not need to be mounted while you are levelling things out. The good news is that you only need to faff around with all of this once!

[nickbaba]

Thanks Hugo - that makes perfect sense.
You are right, the arm as shown in pic was on the rest. Went back & checked it on a record and there is no difference, tbh. The offset is about the same as shown in the pic.
Don't suppose you'd be kind enough to check out my recent post in the main Analogue section and unleash some of your wisdom on my next problem...? :)