DIY Schroeder Tonearm???

[velvetsunrise]

Hi Fran, Sorry i cant be much help, i get very little needle chatter, and cant feel any vibration at all in the gallows.

If the gallows it actually vibrating, i would be surprised if the source of the vibration is the actual needle in the groove, it would require a fair amount of energy to cause the gallows to vibrate, and it would have to travel up the suspension thread.

Is there any vibration from the Turntable motor or main bearing, this woud seem a more likely source for vibration of the Gallows.

Just a thought!

[seanb]

hi fran could you rig it up to another turntable to try it out as i dont think it is the arm looking at the photographs you have posted good luck sean

[woodturner-fran]

Hi guys,

yeah I know - is weird!

OK, so the TT is a lenco in a mass loaded plinth. Absolutely no rumble etc etc. In fact you can tap the plinth with the volume right up and no sound through the speakers. But if you have the volume up, and you rattle the tonearm wiring, I can hear microphonics.

Yes, I know its hard to believe, but that 6mm (ie 1/4") top plate, the one that the arm is actually suspended out of is vibrating!! And it has to be coming from the needle since I can't feel any vibrations say, on the bottom plate, or on the armboard. Its like the arm is resonating (test track is 300Hz BTW) and its draining out through that plate. I know I could maybe make the plate more massive, but surely it would be better to get rid of this earlier in the chain. Oh, and the arm I had in there previously is a roksan tabriz and it showed none of this behaviour.

It actually had me scratching my head for ages yesterday because I thought it was an alignment issue, so I aligned the thing about 5 times yesterday with lofgren, then baerwald etc etc. It sounds exactly like mistracking, but it seems it this resonance. Luckily I felt this vibration or I'd be still looking at alignment.


Any help greatly appreciated!! I'll post up some photos later.


Fran

[velvetsunrise]

Fran,

Just wondered,

did you use the super glue technique to cut the suspension thread, if so, is it possible the glue has run into the suspension thread and caused it to go stiff?

[woodturner-fran]

No, I actually didn't use any glue - its cut neatly for me with a razor blade.


mystery continues!!

Fran

[berlinta]

Hi Fran,
Your pics, as nice as they are, don't show the thread attachment/exit point on the armwand. It kinda looks as if the thread comes out on the very top of the wand. The magnets are rather small it appears and the counterweight has a waaay low cog.

All of this amounts to a tremendous restoring force which will lead to large VTF differences depending upon the record thickness, warps and, possibly important in this case, misleading readings on your tracking force gauge. If you don't want to change the general layout for now, first make sure to measure VTF EXACTLY on record level(like,150gr. pressings). If you use a Shure gauge or any other gauge where the measuring level is above record level, you will end up with too low a VTF "in action".

Can you make out any rotational(around the armwand axis) movement while mistracking occurs?

Don't worry, we'll straighten you out :-)!

Cheers,
Frank

[bgruhn]

Originally Posted by woodturner-fran

Hi guys,

yeah I know - is weird!

OK, so the TT is a lenco in a mass loaded plinth. Absolutely no rumble etc etc. In fact you can tap the plinth with the volume right up and no sound through the speakers. But if you have the volume up, and you rattle the tonearm wiring, I can hear microphonics.

Yes, I know its hard to believe, but that 6mm (ie 1/4") top plate, the one that the arm is actually suspended out of is vibrating!! And it has to be coming from the needle since I can't feel any vibrations say, on the bottom plate, or on the armboard. Its like the arm is resonating (test track is 300Hz BTW) and its draining out through that plate. I know I could maybe make the plate more massive, but surely it would be better to get rid of this earlier in the chain. Oh, and the arm I had in there previously is a roksan tabriz and it showed none of this behaviour.

It actually had me scratching my head for ages yesterday because I thought it was an alignment issue, so I aligned the thing about 5 times yesterday with lofgren, then baerwald etc etc. It sounds exactly like mistracking, but it seems it this resonance. Luckily I felt this vibration or I'd be still looking at alignment.


Any help greatly appreciated!! I'll post up some photos later.


Fran

Hi Fran, First I must compliment you on a very nice job building this arm, beautiful. Next I suggest that "we" of this thread do some rethinking of the previously held belief that energy won't drain out through the suspension thread. Your problem and my experience seems to say otherwise.

Next, for some easy and quick trouble shooting hints: take the cartridge mounting screws out and hold the cartridge on with some double sided sticky tape, several layers, and see if that makes any difference.

As for the microphonics when rattling the tone arm wires, grab the wires firmly with several fingers at a point between the arm and where you apply the rattle. Should damp out any microphonics there. This will most likely generate some hum though. If there is no change, there is something different to consider.

Do you have any damping inside the arm wand? If not try some black electrical tape, a few layers and maybe wrap it with sewing thread on the outside. This worked well for me on an experimental linear tracking arm.

Lastly I suggest getting some modeling clay and see what can be done with damping areas of the gallows assembly. I found damping the bottom plate most effective. None of these parts are going to self resonate. The arm wand will have a resonant signature, but so what if you are not coupling energy into it. I believe the best approach is keeping the energy out (isolating) rather than trying to drain it out once it is there. This of course is begging the issue of what to do with that energy if it is still locked up in the cartridge. I think the modifications to cartridges such as fancy wooden shells and special gluing to selected areas inside the cartridge are attempts to deal with this energy at the point of origin.

Lotsaluck,

BillG

[Renron]

WTF,.....Wood Turner Fran...... coincidence? LOL

I seem to recall that Mr. Davidson had similar issues with his counter weight he had at first. Remember that really cool looking one that was under-slung on both sides? It gave him trouble(s) and he went a different route, more mass centered on the longitudinal axis of the arm wand.

His Uberness, Frank, mentions this as a possible point of trouble as well.
Imagine the point where the string exits the top of it's connection inside the arm wand as the axis point for micro-rotational wobble. The arm wand is a pendulum and that attachment point is the fulcrum, it can wobble in 3 planes, X,Y,Z.
Try removing your counterweight and wrapping some lead / heavy solder around the arm tube in lieu of the counterweight.

I could be completely off track (no pun intended) but it's easy to try and worth a shot to see if it helps.

An awesome looking build, and I'm jealous of everyone who's completed theirs, working or not.

As always, Big Thank You to Frank (Mr. Schroder) for helping us with his expertise and background. Bless you.

Bgruhn, any photos you could share with us?
Ron

[woodturner-fran]

First of all, I want to say thanks so much to all of you for your help so far.


Frank, I read your post earlier today and have been thinking ever since!! I'm going to modify the arm as you suggest. I am measuring VTF at above record height, and I'll bet it is making a hell of a difference. The second thing you mention about the COG of the counterweight being too low - I have another counterweight that I think will slide right on to try out. Lastly, what you mention about the magnet size. I bought 8mm (dia) x 5mm magnets from ebay. They certainly feel very strong, and I think were what was used by another member here - IIRC I asked what were people using.... although its a while ago now.

If you remember a few pages back, I mentioned that I though the arm was quite "stiff" in vertical movement. You advised me to move the bottom suspension point down to lower in the arm. Well, I did that - see the drawing below gives you an idea of what I did. Essentially, I made a filler piece to take the position of the bottom knot lower.

Now as I looked at what I've drawn, it seems to me that the string passes through that narrow "chimney" and I wonder if that's effectively making the pivot point higher (by binding on the thread). Although when I did this, it certainly "felt" better that it did.

I can't see any movement around the axis when the mistracking happens.


Pic:

[woodturner-fran]

So what I'm thinking of trying is:

1. different counterweight with higher COG
2. Drill the filler piece shown above out bigger so that string only moves on lowest pivot point


After that, I'll see how I get on!

Thanks again to you all for your help!


Fran