The Metronome

[Steve Cresswell]

care to tell us more about the amp circuit?

Yep, it's a fully balanced design, all the way through.

The circuit only accepts balanced XLR inputs as there is no phase inverter of any kind. The intention of the whole idea was to do away with the phase inverter, as IME the phase inverter is the weak point of a push-pull amp. It is balanced because of this idea; not because of any noise reduction attempt.

The circuit is very simple; 12AT7 input stage, feeding triode strapped EL34s, no feedback. SS rectified power stage supply, with CLC setup, featuring 2200uF of energy storage capacity and a small, tube rectified CLC input stage supply.

 

[Jnoneiliv1]

The foundry patterns for the Metal Monster Met are complete. 3/8" wall thickness. Still 100 lbs. in iron and 33 lbs. in aluminum estimated.

They look very slender, but each pattern is only half depth, so it can be deceiving.

Since I'm unable to delay gratification, I've got some FX120's coming from Madisound. I hope to make at least one set for a friend or two and I might upgrade to an enabled driver later.

MetalMonsterMet | Flickr - Photo Sharing!

 

[Greg B]

Very cool. I'm wondering though - why not go with curved sidewalls and/or heavily radiused edges, since you are casting this thing?

Of course that would make carving the patterns a lot more work, not to mention you may or may not like the look.

Regardless, this could be a great project. I had the (extinct) big brother of the FX120, and it is/was an excellent driver.

 

[xrk971]

Aluminum sandcasting? Wow is all I have to say. Looking forward to seeing the Metal Monster. Appropriate music would be heavy (or light) metal

 

[Jnoneiliv1]

Greg,

I think you'll read the form as more "rounded" when you see it in the casting. The sand casting will have considerable texture and I'll work it a bit by hand and then we'll play around with some patina ideas. I think you'll be impressed by what the texture can do to simple forms. I really liked the look of the Met and wanted to pay respect to Steve's original vision of the Met and the subsequent design work in the community.

Jamie

 

[Jnoneiliv1]

Help, the Metal Monster Met's are alive!

I just wanted to confirm. For the FX120 driver, in the 52" Met design by Jim S., the port should be 3" I.D. by 4" long? It seems huge. I have some 3" PVC pipe though, so I'm good for this.

See the pick of the rough castings. Build images to come.

Jamie

 

[tnargs]

That is amazing, Jamie!

 

[Jim Shearer]

Jamie,

That's right: port is 3" ID X 4" long. No narrow, little chuffy ports here! Designed with MJK's MathCAD worksheets. Not only that, Martin came over & checked them out himself! (That was the time he brought along a tube amp & I discovered that the F120A loves tubes. blew my mind!)

Cheers, Jim

 

[mightym]

Here is a pic of my own FF225WK Mets.

An externally hosted image should be here but it was not working when we last tested it.

These walnut veneered five footers, have been modified since I last talked about them three years ago.
The original Fostex FT17H horn supertweeter has been replaced to great effect by a Monacor RBT-95 planar/ribbon unit.
The treble performance is simply gorgeous.
The best mod I made however was to completely remove the stuffing from the top third.
The only damping they now have is courtesy of a layer of half inch thick wool felt from top to bottom of the inside back panel.
The improvement in overall performance gained by removal of said Dacron fibre stuffing is staggering.
Bass tone is wonderful, and even up and down the range. It is a pleasure to hear walking acoustic bass lines track up and down the fretboard, without emphasis of any particular frequency over another.

I have lived quite happily with these speakers over the three years since they were built, apart from a certain roughness at the top, which was enough to set me looking for an alternative HF unit. The Monacor ribbons fit the bill perfectly, with a sweet, clean and detailed sound that integrates far more easily with the Fostex widebander than the FT17H did.
I'm well pleased.
Amplification is provided by an EL34 balanced, push-pull amplifier built a couple of months ago. A nice push pull tube amp works great with the big Mets.

Crossover is a simple first order and uses a 1uF cap to the ribbon, relying on the efficiency of the tweeter, to compensate for the power drop off below the very high crossover point, rather than the L-Pad adjuster that could have been required If I had gone for a 12dB/octave 2nd order filter crossed lower down at 6KHz

Works beautifully, giving an even response up through the treble range, with no seams audible.

I'm curious how far away from these you listen, my concern is the typical narrow vertical response of the ribbon type tweeters, and the minor angle of the baffle leaning backward.

Your's have inspired me to investigate possibilities for constructing a larger Metronome than the one for my FE126's. Did you consider mounting the tweeter below the FF225?

Thanks for sharing this fantastic design with the rest of the world.

John

 

[hajj]

Help, the Metal Monster Met's are alive!

I just wanted to confirm. For the FX120 driver, in the 52" Met design by Jim S., the port should be 3" I.D. by 4" long? It seems huge. I have some 3" PVC pipe though, so I'm good for this.

See the pick of the rough castings. Build images to come.

Jamie

NICE!!!
Finally, the metal metronome!
Care to share some pics of the casting process?

 

[Steve Cresswell]

I'm curious how far away from these you listen, my concern is the typical narrow vertical response of the ribbon type tweeters, and the minor angle of the baffle leaning backward.

Your's have inspired me to investigate possibilities for constructing a larger Metronome than the one for my FE126's. Did you consider mounting the tweeter below the FF225?

Thanks for sharing this fantastic design with the rest of the world.

John

Hi john,

I've often thought about why the tweeter is above the widebander. The slope of the baffle does provide a degree of time alignment with the tweeter above, but then sit soo close and the tweeter is firing over your head. A difficult question to answer without building two versions.

I sit 10 feet from the speakers so am listening in the far field, so the reduced vertical dispersion from the ribbon, does not cause any problems at HF, that I can hear.

Re the design: even after all these years it still amazes me how much this truncated pyramid is liked across the world.

I can't wait to see these metal mets come to fruition.

 

[Jnoneiliv1]

Thanks Jim. I trusted your math, I just wanted to make sure I didn't swap a digit or something.

I'm almost done and I've got a fully process photo's for everyone. It's a faithful rendering the design in iron.

Jamie

 

[Jim Shearer]

Jamie,

I eagerly await your report! It would be fascinating to put the wood & metal units side by side for comparison.

Cheers, Jim

 

[Jnoneiliv1]

I have finished the Metal Monster Mets and they were debuted at one of our local audio club meetings. I'm still working on trying to make a proper listening impression, but I haven't broken in the drivers or hooked up the Mets properly yet. I have a pair of nicely built FH3's at home with a KT88 push/pull, so I hope to try to make a good comparison. I might need to get some better ears than mine to take a listen though.

Anyway, on with the build photo's.

I've posted a complete set of build images at this link to my Flickr site and I'll post a few here.

Metal Monster Metronome - a set on Flickr

Thanks to everyone for the help. I'm really excited about these Met's and I'm so grateful to have such a well done design to copy.

Cheers,

Jamie

 

[vitorio]

Hello all

Ten months ago (post 1041) I started a FF125WF metronome, its finished now. Some pictures:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

My friend asked me to do it active and remote controled. Inside the right box there is a TA2020 and PGA2311 preamp.

The sound is very good, detailed with bass enough. The running period is loooong, they started to sound right after 1 week. First days they sounds too agressive, then gets smoother.

The best thing is its look, every woman in my family likes it. Very high WAF, a really good design.

Thanks you Dave, Jim, Steve and all nice people in this blog.

 

[GM]

I have finished the Metal Monster Mets

GM

 

[hajj]

I have finished the Metal Monster Mets

Gorgeous!

 

[Steve Cresswell]

Hello all

Ten months ago (post 1041) I started a FF125WF metronome.


My friend asked me to do it active and remote controled. Inside the right box there is a TA2020 and PGA2311 preamp.

The sound is very good, detailed with bass enough. The running period is loooong, they started to sound right after 1 week. First days they sounds too agressive, then gets smoother.

The best thing is its look, every woman in my family likes it. Very high WAF, a really good design.

Thanks you Dave, Jim, Steve and all nice people in this blog.

Stunning is all I can say.
Those are simply beautiful.
As you have found; WAF is very high with these speakers and the sound is good.
Best of both worlds really.

 

[toobhed]

Very, very nice, Vitorio!

 

[AmadeusMozart]

The FF105WK metronome is my favourite. Am driving it with an EL84 UL SE amplifier ( diytube.com • View topic - New Build) Has pictures towards the end of the thread and changes have been documented. Monitor is a the Dell U2913WM and the mac mini is running windows with Foobar and am using Equalizer APO 0.8.1 to correct room response. Very satisfied with the setup.

Had some thoughts about putting the FX120 in the FF125WK metronome but Fostex stopped manufacturing the FX120 in 2004 and the driver is using a foam surround. Don't know what the life expectancy of that foam is but I do not fancy buying a 10 year old driver with foam.