JVC QL-7 plinth question

joeriz · « **on:** 29 Dec 2009, 03:42 pm »

Hello all,

I have a JVC QL-7 turntable that I recently placed back in to service. I am using a Shure V-15 type IV cartridge with a new Jico replacement stylus.

Question: I have noticed that the plinth is -- for lack of a better term -- microphonic. That is, when I tap on the plinth, I can hear it through the speakers. Now, the table doesn't suffer from howling acoustic feedback even when I turn the volume up quite high (or even when I turn the volume up all the way with the stylus in the groove of a stationary LP). However, I can't help but think that this 'microphonic' behavior is not good for sound reproduction.

Does anyone know of a way to reduce/eliminate this behavior? I have read mixed reviews on loading this particular table with clay and its effectiveness with this issue. The plinth appears to be made from MDF.

Any ideas?

Thanks!

Joe

TheChairGuy · « **Reply #1 on:** 29 Dec 2009, 04:06 pm »

Hey Joe,

Lotsa' ideas here to help!

I really adore the JVC tables...from the lowly belt drive JL-A20 I had as a teen three decades ago to the three JVC direct drives I've owned the past 4 years.

The plastic bodied ones seem to be very happy filling them with modeling clay and putting them up on feet. My current JVC QL-Y66F is also mdf and microphony is and was a persistent problem.

See an earlier topic on it: http://www.audiocircle.com/index.php?topic=63108.0

Filling it with clay with help the sonics...but didn't help with microphony. I tracked that down largely to the particleboard bottom. It acts as a huge bellows for sound bouncing waves back in and around the deck and more problematic at higher volumes.

Leaving the particleboard bottom off entirely actually helps....otherwise, what I did to greatly help was the use a heavy mastic-type, damping spray on the bottom board (both sides best). Once dried, replace the stock feet with something more effective...the best combo I came up with is Herbies' Tenderfeet on the table bottom, under that are 4 brass toes pointed straight down into a 3" thick maple platform.

But, there was still a little resonance encountered after all this...I tracked that down to a microphonic top plate. So, I have some 1lb brass weights in 4-5 places around the top deck to damp the energetic

surfaces. Problem now solved.

You won't be able to rid it of 100% of the problems (or, at least I couldn't

), but using the pointers above you'll likely rid it of enough nasties to wholly enjoy the deck. The drive mechanisms in the JVC's are really quite good - when you dial out the other nasty artifacts, they are truly enjoyable decks to listen to

Don't forget the clay inside...it's silly how much better these hollow bodies Japanese decks sound for ~ USD$30 in clay.

Good luck, John

Wayner · « **Reply #2 on:** 29 Dec 2009, 04:45 pm »

Certainly some key issues, as John has pointed out are internal resonance of the plinth, for starters. Easier said then done. I am also a big fan of plasticlay (non-hardening modeling clay) but the MDF is also suspect. Speakers are generally made of MDF as it is a great base material to make cabinets out of, then line them with your favorite flavor of wood veneers. The one thing that speaker manufacturers do to eliminate the internal microphonics is to add internal bracing. This stiffens the cabinet and prevents some energy transfer. As you may be figuring this out on your own, there isn't one simple cure, rather it requires several approaches to a quiet plinth. Not knowing what the internal cavity looks like, I would attempt to glue in some more internal braces to secure the top of the plinth to the sides. Then, plasticlay up as much as possible, staying away from electronics or moving parts as much as possible (don't know if this model is automatic, semi-automatic or totally manual). I would also line the inside of the bottom cover with a thin layer (about 1/4" think) to also help stop noise from ping-ponging around in the plinth.

Many new table designs do do have any hollow in the plinth at all, mostly MDF or MDF sandwiched between some acrylic.

Wayner

joeriz · « **Reply #3 on:** 29 Dec 2009, 06:37 pm »

Thanks, guys.

I will try the clay for starters. My table does not have a particle-board bottom...the bottom of the table is open so that you can see the electronics and the open cavities in the MDF.

John - if I'm reading you correctly, it sounds like in my case the weights may do the most good.

In the back of my mind, I'm almost wondering if an entirely new plinth is in order...

I also have an AR ES-1 that I'm pretty sure I'm going to sell (nice-sounding table but I'm not that into vinyl these days and I'm tired of the fiddly springy suspension and not being able to easily play 45's). With the current plinth of the JVC I'm quite sure I won't be able to get it as quiet as the AR but I'd like to move in that direction as much as possible.

I guess what I'm looking for is a relatively easy way to get the most out of the JVC so that I can enjoy my vinyl in as "hassle-free" a manner as possible.

Thanks,
Joe

TheChairGuy · « **Reply #4 on:** 29 Dec 2009, 07:46 pm »

Quote from: joeriz on 29 Dec 2009, 06:37 pm

Thanks, guys.

I will try the clay for starters. My table does not have a particle-board bottom...the bottom of the table is open so that you can see the electronics and the open cavities in the MDF.

John - if I'm reading you correctly, it sounds like in my case the weights may do the most good.

In the back of my mind, I'm almost wondering if an entirely new plinth is in order...

Thanks,
Joe

Joe,

No bottom to your deck...did it maybe come off over the years? It doesn't sound correct - not having a bottom at all on the table

If no bottom - where are the existing feet? Are they in the corners of the table, where each side is joined? Every table needs feet or supports to isolate (and drain) the stored energies in all objects.

Actually, it's a tri-fecta of things that will tame the problems you have and improve the sonics.

The clay is just great for overall sonics....but dodn't tame the microphony much at all.

Damping the mdf bottom did a whole bunch...but so did leaving the bottom off (if that is your only option with this table)

Wayner's idea is probably a good one, that of creating cross-braces for the jiggly frame, but I'm no woodworker and this wasn't going to happen for me

Changing out the feet and isolation was very important if you can.

The weights on top, were perhaps the least important...but a good last step after all the others are dispensed with. Read the previous topic on my JVC QL-Y66F....it's only 2 pages overall (not like some of hte opus' I've started around here

)

It's likely a good sounding table yo uhave there...it just needs a little love and attention to get it sounding great. Unless your AR table was significant modded and has outboard dedicated power supply now....you'd do well to spend a little time with the JVC to enjoy your vinyl. That's my opinion, of course, not shared by all

John

Norman Tracy · « **Reply #5 on:** 29 Dec 2009, 09:38 pm »

Joeriz asks "In the back of my mind, I'm almost wondering if an entirely new plinth is in order.."

Be careful, there lies a path to madness.

Of course maddness with tunes beats sane in silence any day.

See also:
http://www.porterhouseaudio.com/index.php?option=com_content&view=article&id=56%3Aplinth&Itemid=74
http://www.soundfountain.com/amb/sp10page.html

Happy New Year to all!

joeriz · « **Reply #6 on:** 29 Dec 2009, 10:43 pm »

John,

It looks to me like there never was a bottom. The feet are atttached where the MDF sides come together. If I get a chance, I'll snap a picture. This is the exact table that I have...unfortunately, no shots of the underside:

http://www.thevintageknob.org/VICTOR/QL7/QL7.html

My AR has a Rega RB-250 arm on it; other than that, it is stock. So far, I like the sound of the AR better but I have a feeling that with a bit of work, the JVC could be a nice-sounding table.

Joe

TheChairGuy · « **Reply #7 on:** 29 Dec 2009, 11:04 pm »

Joe,

Have at it - the JVC's are worth the efforts, all in all

I have the aforementioned QL-Y66F...and also the QL-F6. Another terrific effort from them...with a plastic base it is less resonant; tho it doesn't look quite as upscale (however, it sounds it with 7lbs of plasticlay inside)

http://www.thevintageknob.org/VICTOR/QLF6/QLF6.html

Regards, John

joeriz · « **Reply #8 on:** 30 Dec 2009, 05:31 pm »

Snapped a pic of the underside of the QL-7 today...

Joe

Wayner · « **Reply #9 on:** 30 Dec 2009, 07:36 pm »

Hmmmmm, that is interesting. Beside needing new feets, I'm not sure how to even get inside of this unit. Looks like you can't from the bottom. Looks like you could stuff some clay on the bottom tho.

Maybe we need a picture from the top or off to the side a bit.

Wayner

Wayner · « **Reply #10 on:** 30 Dec 2009, 07:40 pm »

Oh, I get it. The end of the tone arm is in the little box in the upper right hand side of the photo. I also see the transformer for the table thru the slots in the drive unit, under the platter.

There possibly is no hollow in this plinth. Looks like the only place for some clay is right underneath as in the photo. Put some new feet on and fill up the hollows with clay. Stay away from the DD motor/vents.

Wayner

joeriz · « **Reply #11 on:** 30 Dec 2009, 11:57 pm »

OK, here's the latest. I was at Home Depot today and picked up a length of 3/4" dowel (the 'sides' of the underside of the plinth are 3/4" high). I measured the areas under the table where I could add bracing and it now looks like this:

I cut the pieces long enough such that I had to work them in a bit and they sit in the plinth nice and snug.

I also picked up some non-hardening modeling clay today and have begun stuffing the bottom of the plinth. And, as luck would have it, I happen to have some spikes lying around from an old pair of Target speaker stands that - lo and behold - fit the screw holes where the old feet are. aa So I will give those a whirl...

I will keep you posted.

Thanks for the advice, gents!

Joe

lazydays · « **Reply #12 on:** 31 Dec 2009, 04:17 pm »

Quote from: Wayner on 29 Dec 2009, 04:45 pm

Certainly some key issues, as John has pointed out are internal resonance of the plinth, for starters. Easier said then done. I am also a big fan of plasticlay (non-hardening modeling clay) but the MDF is also suspect. Speakers are generally made of MDF as it is a great base material to make cabinets out of, then line them with your favorite flavor of wood veneers. The one thing that speaker manufacturers do to eliminate the internal microphonics is to add internal bracing. This stiffens the cabinet and prevents some energy transfer. As you may be figuring this out on your own, there isn't one simple cure, rather it requires several approaches to a quiet plinth. Not knowing what the internal cavity looks like, I would attempt to glue in some more internal braces to secure the top of the plinth to the sides. Then, plasticlay up as much as possible, staying away from electronics or moving parts as much as possible (don't know if this model is automatic, semi-automatic or totally manual). I would also line the inside of the bottom cover with a thin layer (about 1/4" think) to also help stop noise from ping-ponging around in the plinth.

Many new table designs do do have any hollow in the plinth at all, mostly MDF or MDF sandwiched between some acrylic.

Wayner

there's a sound deadening compound out there that you actually aply with a paint brush. The stuff will work it's way into nooks and cranys much easier than some of the clay type compounds we normally think of using. I'm going to hunt the stuff up for you all the first of the week, and let you all know.
gary

joeriz · « **Reply #13 on:** 31 Dec 2009, 09:22 pm »

I finished stuffing the table with clay last night, put the spikes in place, and set 'er back up to play some tunes (which it is doing now as I type this). Here are the latest photos:

There is a definite improvement in both sound and in microphony. I can't quantify it at this point but it's a plus in both categories for sure. The microphony, in particular, is markedly decreased when I tap on the plinth. This improvement is much more noticeable on the tonearm (right) side of the plinth, less so on the left. So far I'm unable to tell if this is a function of the bracing or the clay but I will keep experimenting. There is a little over 2 lbs. of clay in there now and there is room for a bit more. I will probably also mess with some different feet at some point.

Just wanted to give you the latest and say 'thanks' again.

Happy New Year!

Joe

Wayner · « **Reply #14 on:** 31 Dec 2009, 09:47 pm »

Joe, it looks like you have room for lots more clay, load 'er up! Good job and I think you will reap many rewards later as you start to listen to some of your favorite LPs. 4 hockey pucks under those feet might help. Hockey pucks are usually around a $1.00 each, and are a pretty good thump stopper.

Wayner

WireNut · « **Reply #15 on:** 26 Jun 2013, 08:09 pm »

(This thread is originally a few years old)

I have an opportunity today (6-26-13) to purchase a JVC-QL7 table with an Audio Technica 2002 cartridge and stylus (probably original) for $175.00. Do you all think it would be worth $175.00? Also, I’m not sure if it would be an upgrade from my current Technics SL-D3.

What I do like about the JVC compared to my Technics is that the arm height is adjustable and also the arm has set screws at the headshell to allow for rotation/alignment.

What I don’t like about the JVC is that it’s a manual table but I believe the arm should lift up at the end of play and the table should stop, does that sound right? That would be fine if it does.

I should probably audition it but if I purchased it today that's not possible.

Any thoughts

JackD · « **Reply #16 on:** 26 Jun 2013, 09:24 pm »

Wirenut

The QL-7 is manual, A7 is auto-lift and the Y7 is auto-return. I have an A7 and Y7.

Here is a link to the TT.

http://www.thevintageknob.org/jvc-QL-7.html

Jack

WireNut · « **Reply #17 on:** 26 Jun 2013, 09:34 pm »

Quote from: JackD on 26 Jun 2013, 09:24 pm

Wirenut
The QL-7 is manual, A7 is auto-lift and the Y7 is auto-return. I have an A7 and Y7.
Jack

So at the end of play it just sits there and spins?
I don't think that's something I want.

JackD · « **Reply #18 on:** 26 Jun 2013, 09:38 pm »

Yep, unless you use something like the Q-Up. It is a better deck all around, but not for you if you want some form of automation.

WireNut · « **Reply #19 on:** 26 Jun 2013, 09:48 pm »

Quote from: JackD on 26 Jun 2013, 09:38 pm

Yep, unless you use something like the Q-Up. It is a better deck all around, but not for you if you want some form of automation.

Ok. Talk to me about the Q-Up. Where can I buy one, approx cost, do they work very well, difficult to mount.

Thanks