Outragous Idea....DIY EMT 240

[gyraf]

Foil is apparantly 24K gold electroplated according to the manual - which leaves the question what the material base is. A good guess would be a metal which is prone to oxidation - why else the expensive coating..?

I might be wrong, but I smell a bit of smokescreen around this design. It may not be impossible to DIY.

Drive amplifier has a simple limiter - pickup amplifier has a 1:1.1 downward expander to keep noise down. Uses a Motorola MFC6040 voltage-controlled amplifier (OTA? Never heard of it before..) for this. Modern semiconductors should certainly give better noise figures anyway.

Jakob E.

 

[Walrus]

The MFC6040 is an electronic attenuator....
http://www.electro-tech-online.com/attachments/datasheet-parts-requests/22071d1220420303-needed-pin-layout-mfc6040-attenuator-mfc6040.pdf

 

[mad.ax]

-"why else the expensive coating..?"

maybe to compensate for the lower sound's velocity in the base material used?
Though sound's velocity in gold is still much lower than in steel (about 3240 for Au, compared to 5960 m/s for steel)
Aluminum foil may be a good candidate for DIY. It has a sound's velocity of 6374 m/s.

Axel

 

[abbey road d enfer]

Reading the manual is interesting. The actual mass (and additional damping due to their presence) of the transducers seems to be a very important factor. Seems to be the reason why they chose piezo drivers and moving-coild pickups, not the other way around.
I don't think a gold coating (which may be of the sub-micron type) would significantly change the "acoustic" properties of the base material, especially in view that gold cannot be plated directly on steel (it has to be copper-plated first), unless it was sputtered instead of plated.
I cannot imagine that the 240's material could have been aluminium, which in its purest forms has too much damping, and is very difficult to plate. Now maybe one of the high-Cu-content alloys, may be?
A significant part of the complexity of the 240 is due to the desired acoustic insulation (the 240 was clearly targetted at OB vans). The basic foil may be not terribly difficult to DIY...

 

[abechap024]

Nice! Great samples comparing the 140 and 240. I've never had the pleasure of comparing both side by side before : to my ears it sounds like the 240 is a little more shimmery then the 140. I can't help but think there is a good diy hidden in this thread somewhere. If we can just figure out the mechanical aspect. I have some little speakers I'm converting to pick-ups but I need to pick up a few Peizeos for the drivers. I'm going to start doing some tests...what the heck. maybe that cookie sheet idea isn't that bad. I'm looking at a Pyrex casserole dish and I think that just might be the ticket to do some tests on just how tight the aluminum foil has to be to get a usable sound. seems like a relatively simple experiment. have a peice  of aluminum foil laying on a table, put the casserole dish face down tape the aluminum foil as tightly as you can around the back.
I'll report back, worst thing that could happen is there will be no usable sound at all.

 

[abechap024]

Oh and i was looking at the roll of aluminum foil I have and its 18 microns thick too. Same as the original spec gold foil. too bad it isnt a roll of gold.... ;D

 

[Michael Tibes]

If I get the german manual right, then the foil is simply pure gold, and the foil is made in a galvanic process.

Michael

 

[abechap024]

There must be significant sonic differences in the gold and aluminum. Otherwise EMT surely would've used some other cheaper metal...  It would be interesting to hear the difference. So I got an Idea, but not the means to implement it. Granted its a very ghetto way to tighten the foil it might be usable for some good testing. First tape the foil on a cake pan like the picture.. then find another cake pan the same size (I need to round one up..) and set the foiled cake pan inside the other cake pan of the same size. In my mind it seems like with some careful adjustment, the pressure should tighten the foil all around. A little like an embroidering fabric holder...(don't ask me how I know that..) I searched the whole house and haven't found another pan that the foil ban can slip tightly into. If anyone happens to have 2 matching pans you could try it out. If not i'll get another pan sooner than later.

 

[abechap024]

heres some pics to better illustrate what i'm talking about...
http://img3.imageshack.us/gal.php?g=dsc04705s.jpg

 

[haima]

abechap - i think you'll need a way to raise & even the tension, might be hard with your method.

once you have the foil at tension, you'll need to attach the pickups/driver somehow of course.

i imagine the pickups & driver components that attach to the foil would need to be very light weight, and only attach at a small point, so as not to dampen the small area of foil completely.

 

[mad.ax]

Find (or make) a frame, one or two inches bigger than your cake pan.
Bond or tape the foil on the frame, and place the frame on the cake pan.
By adding some weight on the frame you can tune the foil tension...

You could use piezo for both driver and pickup, those are cheap, small, and not heavy.

Axel

 

[haima]

interesting concept michael... like a drum...

i wonder if you would get some buzz as the foil vibrated on the edge of the "cake tin"?

 

[Kit]

The slightly pricier DIY option;
http://www.palmermetals.co.uk/Sheet/GoldSheet/22CaratYellowGoldSheet/default.aspx

 

[abechap024]

Excellent, going to rat shack to pic up 2 peizos. great Idea with the frame. and that gold isn't quite as expensive as i would've thought. we'll see if we can get any usable sounds out of this contraption!
AC

 

[haima]

the thinnest that gold sheet palmer metals will go is 0.5mm - the EMT i s 0.018mm no?

you'd probably be looking for "foil" not "sheet" to get down to 0.018mm - should be a lot cheaper, and probably work better

good luck with your test! i hope the aluminium foil doesn't tear...

 

[mad.ax]

quotes:
"The slightly pricier DIY option"
"and that gold isn't quite as expensive as i would've thought"

The price is about 30£ per square centimeters.... That means 23455.53 UK Pounds for a 12 X 12 inches sheet...

With that kind of money, I would consider some other options than DIY!

Axel

 

[Wagtbtoobz]

Hi , Tu as les plans exacts de la 240 ?  Pierre

 

[David Kulka]

The circuits for the drive and pickup electronics in the 240 are unconventional and incredibly complicated.

 

[mad.ax]

@Wagtbtoobz: I don't have access to anything but what is in this thread (EMT240 wise), do you?

@David Kulka: Don't we love unconventional and complicated stuff around here?
I think the most important is the mechanical part... Once we have a foil, driving and pick up could be achieved different ways...
And perhaps in a better one than the original.
Take the 140 for instance, despite expensive and hard to find tubes, the sound is not in the electronics, but rather in the iron!

Axel

 

[gyraf]

I still do not believe that the complete foil is 24K gold as claimed in the manual: seems to me this would be too soft and loose too much energy by deformation when transferring surface waves. Not sure tho..

The 240 pickup transducer takes it's mechanical input energy from a rather large area of the foil - in effect cancelling some of the higher-frequency content due to phasing-out. I wonder if we couldn't just use an electrostatic pickup system - like a condenser microphone - for an area that big, it should be possible.

Also consider this:

The 240 changes it's reverb time by simple damping by giving off energy through moving surrounding air and a damping plate (like the 140). But what if we put the foil assembly inside a container where the air could be removed? Vacuum pump, and you (should) have the possibility of rather long decay times.



Jakob E.