[dlaloum]

Help !!! 

When I first got the JVC QL-Y5F, I seemed to suffer serious Hum in one chanel, then I messed around with headshells and it was gone...

I assumed that it was just a poor connection with one of the headshells and moved on as everything seemed to be working fine.

(Famous last words...)

Tried to mount my AT150 today - the hum is back...

did some investigation

1) the Hum is limited to the left chanel
2) If the cartridge is connected but shielded from the Headshell there is no hum
3) the Left chanel ground is the ground that is connected to the cartridge body
4) Other cartridges I have been using have plastic screw mounting points, the AT150 is metal at the mounting point, so for the first time the cartridge body is in contact with the tonearm via the cartridge body ground.

So what I have happening is that the tonearm is picking up the hum, and feeding it through the cartridge body ground into the Left channel.

Is this a common problem?
What would cause this problem?

There's a whole bunch of cartridges that this will cause me trouble with...Having to isolate every cartridge when mounting it will be difficult.... this TT is my Sandbox where I experiment with different cartridges and setups.... so this problem is a Royal PITA!!

Any suggestions?

thanks

David

P.S. Mind you it may focus me on getting those Nylon screws.....

[neobop]

Did you ever get the service manual? It might come in handy.

First thing I would do is take a close look at all the exposed wires coming out of the arm, under the table. Maybe the blue one has some insulation rubbed off. I got lucky that way with a tonearm. I found such a spot of exposed wire and a little nail polish fixed it.
Good luck,
neo

[bacobits1]

Is there a separate ground wire coming from the tonearm? Is it connected to your Pre?
Disconnect it. You may have a ground loop.

D

[Wayner]

If you have a volt-ohm meter, you could test the wiring. The blue and green wires are the return for the cartridge wires and they should each be connected to your RCA outer jack, green for the right channel, blue for the left. Then test the incoming red and white cartridge wires should go to the center pin of the RCA plug, red for right channel, white for left channel.

Then you should be able to touch any metal part on the arm with one test lead probe and the end of the ground wire with the other. Using the continuity test of the volt ohm meter should give a tone for positive connection.

You should also cross check each connection like between the blue and the red or white and the green. You may discover that the green and blue also give a tone when touched to the ground (that usually is OK). If you get a weird tone doing the cross-checks, you may have a wiring problem.

Wayner

[dlaloum]

Thanks folks

I will go through and test everything to work out what is grounded to where, and whether there is something funky going on - when I get the time (and patience) to do another dismantling of the TT. (I'll order another Kg of plasticine so I can finish filling her up at the same time!)

For the meantime, I picked up some Nylon M2.5 screws, and in combination with very thin shims (milk bottle plastic cut with a pair of scissors! - less than 0.2mm thick) - I can insulate the cartridge from the arm - it is working well so far.

I Still want to check the arm and cabling, as I have a feeling that improved grounding and wiring may also improve the sound in general...


bye for now

David

P.S. the nylon screws are great - dirt cheap and very very light - less than half the weight of my lightest aluminium ones. Another step to achieving a lighter arm...

[e.man]

well, i don't pretend to understand any of this Topics talk on Elastometors and Effective Mass but i do have one of these TTs.
Thanks to David for posting the fruity photos of his packing job. ( I have made a collection of toilet roll innners).  From the comments that it improves the TT i am interested in the idea but can someone give any before and after impressions before i turn it into an immovably heavy bastard.
Here is something i just noticed.  When i had the TT level with less room under it, because the feet were screwed in, the sound (esp Bass) was more flabby/muddy/indistinct than when i had it level with more room under.  More air under seemed to give a sound with ......   more air.
My TT is original in good order.  Original feet.  Running Ortofon Concorde (early 1980s model)/ Digitrac 300SE.  I have a Stanton headshell on the way to mount a Stanton 680 (late 1970s) / Jico Shibata.
I too like the engineering but my sound (esp bottom end) is a bit thick so i'm looking to tighten that up.

BTW, is there no 'bookmark Topic' on this board. ?

[dlaloum]

I probably should have made some before and after recordings.... sorry about that...

But I knew that I had to replace the cable, and the rubber-ish stuff in the feet (elastomer) was looking a bit cracked and was stiff....

So I had a good idea that any recording would not show the turntable in its "original" state - but rather in its degraded state....

And once I had the beast upside down and in bits, I wanted to get as much done as possible...

When the feet are raised up - there is definite movement - much of which is absorbed by the rubber in the feet - but there are still vibrations being fed back into the table.... this was exacerbated when I replaced the feet with cones - and had them raised up... resulting in a killer vibrato... urgh!

Dropping the cones as low as possible, got rid of that problem, and the platform the cones are standing on, is in turn on top of some sorbothane pucks - so there are various stages and levels of damping and vibration isolation on my one.

I also picked up some ball bearing based feet to try - but haven't got around to them yet.

Someone else (need to hunt down that posting) - posted his platform composed of Rubber/Cork/rubber mat, cones under the table, and his own custom made ball bearing feet using doorknobs for the cones to sit in - has to be seen to be believed - and yes it works.

You can, when you answer a post, tick the "notify me of replies" checkbox....

bye for now
David

[e.man]

A comment on www.stevehoffman.tv that a Michell clamp would help tighten up the bass.  I like that it is quite lightweight.  Costwise i think it would be about the same as the 'clay/putty'.  Of course results may vary, so has anyone tried this ?

[TheChairGuy]

A comment on www.stevehoffman.tv that a Michell clamp would help tighten up the bass.  I like that it is quite lightweight.  Costwise i think it would be about the same as the 'clay/putty'.  Of course results may vary, so has anyone tried this ?

It might help, but I've not found inner clamps to be of much benefit at all many times tried in the past.  Man, have I tried tho

However, with non-hardening modeling clay in a hollow body of a turntable, returns ,any times its cost of $20-$30 to fill most tables (+ your associated time doing so)

Damping wads a la Dynamat have been found to be inferior method of damping with tables, as well.  Something about that clay (added mass? correct channeling of pent up energy into heat?) that just makes it supremely effective.

The effect afterwards is that you just went up another $500 in table quality.  Unless you have a horrible sounding cartridge or old stylus, it's generally a MUCH more cost effective upgrade than moving up to a newer, pricier cartridge.

John

[TheChairGuy]

David / dlaloum,

Feedback is the bane of all the pretty JVC mdf based tables.  The rosewood looks splendid, but is a pathway for awful levels of feedback.

Here's a two page topic on the JVC QL-Y66F and my various steps to tame down feedback to finally hear how good the table can be: http://www.audiocircle.com/index.php?topic=63108.0

While they don't look as pretty, the plastic bodied JVC's have some of the same advanced Direct Drive technologies as the 'wood' ones. They look pedestrian, but their ills are remedied easily with 7lbs of modeling clay inside and some hard feet of choice pointed down into 3" block of maple.  The QL-A2, QL-A4 and QL-F6 all fit into the 'easy' fix category, but are superior performers at their price otherwise (that is, have fantastic JVC DD technology built in).  Fix the mechanical resonance issues and the sound swell.

The mdf bodied ones, well, I'm not sure the resonance/feedback issue are EVER fully cleared up.  You have to satisfy yourself with good enough.  But good enough still allows these underappreciated beauties to shine and sound great 

The steps:

1. Fill your QL-Y5F with clay (maybe you already did?).  This step, in itself, seems to make feedback WORSE...so you have to do steps #2 and #3 to get your deck back into playing shape again

2. Spray the flexy mdb bottomboard with viscoelastic damping compound outside and in (this is the major culprit for the feedback your experiencing).  That flexy bottom is creating something of a speaker cone, amplifying the feedback back into your deck and music.

3. Sit your deck ultimately on 4 squishy (ie, compliant) feet.  While I much prefer hard feet on every other table tried, on the mdf'ed JVC's hard feet again amplify the feedback issue.  If you don't have squishy feet about (you probably do as you are experienced), just keep the stock rubber feet on until you find something better.  As bad as those stock feet are, the rubber does a so-so job of keeping feedback levels lower on these decks.

I use Herbies Tenderfeet sitting atop brass feet, but are equally pleased with a combination of Vibrapod/Vibracone - 4 each to a table in each corner.

John

[dlaloum]

Hi John

thanks for that link - exactly the one I was thinking of....

I think my toilet roll trick seems to have done the job as an alternative to the sprayin of the bottom board... as I am using the plasticene as a spring between the bottom and top boards effectively...

I have been thinking of using a 5th foot in the center as well to provide a bit of upward pressure to assist this....

You think I should dump the cones/platform/sorbothane and go back to a simpler setup with squishies directly under the table?

One thing I noticed is that the squishies in the Jose Garcia pictures are mostly of the firm variety... rubber layers on top of cork, ball bearings, and the square blocks at the bottom - all of which are of firm to very firm varieties (and the ball bearings are downright hard).

What are the tenderfeet like in terms of soft/hard-ness?
I currently have different size/diameter sorbothane pads... which have a tendency to be at the soft end of the spectrum...

bye for now

David

(always thinking of ways to improve, frequently lack the time to implement improvements!)

[TheChairGuy]

Yes, 5 squishy feet likely better than 4...forgot I had that setup with the herbies tenderfeet and brass toes.

As the name would suggest, the herbies feet tend towards tender  (that is, medium tending toward soft).  They're made of silicone, which has damping and draining properties alot better than any sorbothane I've found.

You can make your own pretty effective cheap silicone feet by buying dimpled silicone coasters for glasses and pots at a kitchen store. A big pot holder may cost $9.99 (US, Cdn or Aussie) and you can cut into much smaller pieces to make your own feet.  Making 1" squares and stacking 3 on top of one another (the dimples hold the stack steady) make great feet.

Maybe I will take a pic of it to show everyone very cheap yet effective DIY silicone feet.

The range of colors is nice, too.

John

[dlaloum]

You can make your own pretty effective cheap silicone feet by buying dimpled silicone coasters for glasses and pots at a kitchen store. A big pot holder may cost $9.99 (US, Cdn or Aussie) and you can cut into much smaller pieces to make your own feet.  Making 1" squares and stacking 3 on top of one another (the dimples hold the stack steady) make great feet.

Maybe I will take a pic of it to show everyone very cheap yet effective DIY silicone feet.

The range of colors is nice, too.

Now you're proposing "fruity"on the outside? 

[TheChairGuy]

David, there might be beige out there...all I remember seeing is bright orange, blue, yellow and reds.

2 x 7" squares of these dimpled silicone potholders are $11.19 + shipping in the US.   That's 98 square inches of silicone to cut up as needed.  You can make over 40 x 2" squares as feet and, as mentioned, there pretty effective (especially when you double or triple them up stacked on one another)

http://www.amazon.com/MIU-Silicone-Pot-Holders-Set/dp/B0006IVZFU

I live in San Francisco...we tend towards 'fruity' here , ya know 

John

[e.man]

The steps:

1. Fill your QL-Y5F with clay (maybe you already did?).  This step, in itself, seems to make feedback WORSE...so you have to do steps #2 and #3 to get your deck back into playing shape again

2. Spray the flexy mdb bottomboard with viscoelastic damping compound outside and in (this is the major culprit for the feedback your experiencing).  That flexy bottom is creating something of a speaker cone, amplifying the feedback back into your deck and music.

3. Sit your deck ultimately on 4 squishy (ie, compliant) feet.  While I much prefer hard feet on every other table tried, on the mdf'ed JVC's hard feet again amplify the feedback issue.  If you don't have squishy feet about (you probably do as you are experienced), just keep the stock rubber feet on until you find something better.  As bad as those stock feet are, the rubber does a so-so job of keeping feedback levels lower on these decks.

I use Herbies Tenderfeet sitting atop brass feet, but are equally pleased with a combination of Vibrapod/Vibracone - 4 each to a table in each corner.

John

Thanks for the steps John.

1.  Stuffing it with clay makes it WORSE !!   

2.  I am collecting toilet roll inners so i'm hoping David is right with " I think my toilet roll trick seems to have done the job as an alternative to the sprayin of the bottom board... as I am using the plasticene as a spring between the bottom and top boards effectively...".  I would follow his example of packing it tight.

  Maybe if i drop the TT down i could stick a Squash ball under the middle of the board.  Would that help even without doing anything else ? 

3.  My feet are in good order and i don't have anything else about so i'll stay with those.

If i want to try the clamp idea what about that idea of using a Hockey puck ?
Trouble there is finding a puck in country Australia. 

[TheChairGuy]

I found I couldn't dial out a significant measure of the feedback I was experiencing until I sprayed the bottom board with viscoelastic goop.

My original JVC QL-Y66F had an electrical issue for a spell.  While I shelved it for a few months contemplating where to take it to be fixed - another one went up for sale (as it turns out, locally) on ebay so I bid, and won, it.

This gent mostly attacked the problem by making an entirely new bottomboard out of heavier wood stock.  However, it wasn't completely quelled this way. I STILL had to mount the table on some feet with 'give', ie, something not entirely hard.

Once I did that (finally deciding on the Vibaracone/Vibrapod ensemble as about the best) I have been virtually feedback free with the JVC.

Vibracone: http://www.elusivedisc.com/prodinfo.asp?number=VIBRACONE
Vibrapod: http://www.elusivedisc.com/prodinfo.asp?number=VIBRAPOD3

John

[e.man]

The steps:

1. Fill your QL-Y5F with clay (maybe you already did?).  This step, in itself, seems to make feedback WORSE...so you have to do steps #2 and #3 to get your deck back into playing shape again

2. Spray the flexy mdb bottomboard with viscoelastic damping compound outside and in (this is the major culprit for the feedback your experiencing).  That flexy bottom is creating something of a speaker cone, amplifying the feedback back into your deck and music.

3. Sit your deck ultimately on 4 squishy (ie, compliant) feet.  While I much prefer hard feet on every other table tried, on the mdf'ed JVC's hard feet again amplify the feedback issue.  If you don't have squishy feet about (you probably do as you are experienced), just keep the stock rubber feet on until you find something better.  As bad as those stock feet are, the rubber does a so-so job of keeping feedback levels lower on these decks.

I use Herbies Tenderfeet sitting atop brass feet, but are equally pleased with a combination of Vibrapod/Vibracone - 4 each to a table in each corner.

John

It seems i am limited to step 2.

Seeing as step 1 makes it worse and i will not be doing step 3. Cos my TT is a bit exposed and has taken a nudge in the past enough to move it, (not while playing), the screwed-in stock legs get the nod here cos the TT can't be pushed off them.   I do like the look of those Vibrapod/Vibracone tho.

Step 2  is to spray the flexy bottom board with "viscoelastic damping compound".  Is this basically spray-on rubber ?
Then i might see about a rubber 5th leg in the middle.  Still wondering about a squash ball for this.

[TheChairGuy]

Yup - spray on rubber it is.

If it's Dynamat or other audiophool brand it's about $16 a can. Essentially the same stuff is made for the auto industry by 3M and others and costs less than half of that.

Take your choice - either works like a charm to reduce the howling feedback caused by the flexy bottom board on these mdf JVC Direct Drives. The final sonic results are worth the $ and efforts applied to them, normally.

John

[e.man]

I have sprayed the base board with 2 cans of auto sound deadener . Keeping with the theme i put in a 5th leg of a rubber auto suspension bush.   It was the right size and happened to be there.  Possibly it's a bit hard.
I have moved my speakers in the mean time so can't comment on the absolute change but can compare to my other TT.  I think it has made it less 'flabby' sounding but still is missing some 'snap' like from snare drums that the other TT has.
Any suggestions how i can get that ?
Carts around the $100 mark ? 

[e.man]

Q-Damping ?

What's Q-Damping ?
The instruction says to set it to the same as the combined Tracking Force/Anti Skate dial.
Why ?
What if i want different 'damping'?
If it's always supposed to be the same why put 2 dials ?