AR 77XB feet dilemma

[palo2]

Hi,
Am presently modifying an AR77XB with a self built solid Blackbutt plinth (Australian Hardwood EX 65x19mm floorboard), a 12mm thick plywood sub base is to fit into the underside of the rebated plinth. My idea is to mount 4 rubber with inner spring feet (EX an MSC turntable) rebated partly into the ply sub base. This would look quite the part and achieve some further isolation of the turntable's outer support structure.
Has this been done before? and Does anyone see any problems with this?
Maybe it would conflict with the AR's 'T' bar sub-chassis!
Any thoughts would be appreciated.

[Alec124c41]

Unnecessary, I think.

Cheers,
Alec

[palo2]

Thanks Alec,

I live in a fully timber framed house which I owner built some 20 years ago, the TT is to be installed into a cabinet so transmission of noise from human traffic/speakers may be a concern. I no what every one has said in the past "mount it off the wall on a bracket" would possibly fix the perceived problem of vibration transmission, but I think that this would cause some conflict with the "dearly beloved" as she would look at it as an eye saw in our small dining/living room. Therefore I was interested in the conventional TT spring feet idea.
Regards Paul

[pogo]

Thanks Alec,

I live in a fully timber framed house which I owner built some 20 years ago, the TT is to be installed into a cabinet so transmission of noise from human traffic/speakers may be a concern. I no what every one has said in the past "mount it off the wall on a bracket" would possibly fix the perceived problem of vibration transmission, but I think that this would cause some conflict with the "dearly beloved" as she would look at it as an eye saw in our small dining/living room. Therefore I was interested in the conventional TT spring feet idea.
Regards Paul

I sympathize with your problem. I've lived with a wall mounted turntable in the past. But I don't think adding a springy feet to a sprung chassis turntable is a particularly good idea. "Conflict" maybe isn't the word, but it would certainly interact. Could actually make your problem worse. However, if you decide to do it anyway, I'd love to see a picture of it and hear about the result. Actually I'd like to see a Blackbutt plinth, in any case.

[palo2]

Thanks Pogo,
Yes you might be right, however I think I will take a punt on the sprung feet design, as it is an experimental project. If it doesn't work out I can remove the feet and experiment with other ideas (cones, Sorbothane, cork etc) or at worst change the ply sub base.
I remember reading that additional mass may be required to be added to the plinth base to alter resonances and would therefore compress the action of the feet springs. Maybe the AR trick of inserting foam within the springs would aid in the dampening again all just ideas at this point. I also recall Technics 1200 TT's having a dual isolation system so maybe this might be a worthy call!
This project is an unknown as the original AR77XB was not a running rig, as the original tonearm was removed and the T bar had been crudely modified to accept a Grace 707 arm which was retained by the previous seller on EBAY. I therefore no not of the sonic abilities of the original or previous modified TT, so I have very little, apart from this terrific forum and the world wide web to compare notes upon. The only tools are the lugs on the side of the head to gauge the sonic performance with! Yes I will upload some picks, when available, as pictures always are far more informative than the spoken.
Regards Paul

[palo2]

AR 77XB stock item

[gkimeng]

What you really want from the feet is not more spring, but damping. Either softer rubber or about an inch of felt. In order for springs to do anything you'd have to have the entire base bouncing as much as the subchassis does now, and the resulting double spring is astronomically more likely to amplify your problem as it is to hit just the right combination to improve the situation.

[palo2]

Good reply gkimeng,
Yes I think you may be wright on the mark, as it may even amplitude or extend longer the ability of recovery of a external shock/resonance. It does seem that I would be better off pursuing a theme of dampening for the outer housing. What do you think of filling the feet springs with a silicone sealant material which is encompassed by the outer rubber section of the foot.
I,m still sold on the aesthetics of exposed/raised feet similar to most direct drive formats of turntables ie Technics or similar.

[palo2]

This is the plinth fitted

[palo2]

And part of the wiring and switch connection completed.
Note I have installed the shielded power cable which been rebated into the plinth with a snug fit, works well!


The IEC power fitting, 0.22 cap and RF trap I have recycled from an old computer!
The wiring is as noted incomplete at this stage.

[pogo]

I like it! Nope, I misspoke -- It's beautiful! But not at all what I thought a wood called "blackbutt" would look like. Okay, so I don't know common hardwoods in your part of the world. I just like saying "blackbutt".

[palo2]

Yes your right, come to think of it I can hear some where Bubba Gump saying "I gotta get me some of that Blackbutt"!

[palo2]

Feet are fitted, filled the inner portion of rubber feet full of silicone sealant, then inserted the springs back into it twisting as it went in to reduce air pockets around the spring. This was capped off with the top flange of the foot which sit to the underside of the base.

The silicone, once it was set, achieved the much required dampening as the springs can only now compress marginally if weight is applied.

Feet fitted into rebated ply base

Looks good ! Will be interesting to see how it performs.

[palo2]

Base preliminary fitted with the feet have achieved the desired stability.

It gives it a low profile similar to the original AR 77XB, the feet and base board have been given a paint with metalic black, offsets well against the Black butt timber plinth.