Troels Gravesen's PMS (Poor Man's Strad) DIY build

[The Mad Scientist]

To fit the edge pieces, I had to notch with the band saw and kerf bend like I did with the curved plywood:

 

 

Welded  up prior to grinding:

 

 

Ground back, ready for second pass:

 

 

Second pass weld:

 

 

Second pass ground back and given a pass with a stainless wire wheel:

 

 

Surface prep reveals a couple of imperfections needing more welding:

 

 

 

 

After more welding, grinding and 40 grit satinising, the first finished plinth:

 

 

 

Stan giving the QC sign off on the second plinth:

 

 

 

[ICUToo]

So wonderful to see your work laid out- lots to learn from you and inspirational attention to detail.

May I ask- what is the reason for the shape of the plinth? It looks far more complex than it "needs" to be but I am certain that there is a good reason for the shape?

[BRS]

EXCELLENT WORK!!

[ENIGMA]

1 hour ago, The Mad Scientist said:

I

 

Great work.

 

I've used several of those glass leveling devices on projects but at times if I use them too much my work gets a bit wonky.

 

Not sure if I have to calibrate them after several uses or if I'm excessively using them.

Edited May 31 by ENIGMA

[The Mad Scientist]

6 hours ago, ICUToo said:

So wonderful to see your work laid out- lots to learn from you and inspirational attention to detail.

May I ask- what is the reason for the shape of the plinth? It looks far more complex than it "needs" to be but I am certain that there is a good reason for the shape?

A big slice of plagiarism and a sprinkling of engineering

 

I basically just copied the shape of the plinth that SF uses on the Stradivari:

 

 

 

With the PMS though, the ports are on the bottom, so the plinths needed to be scalloped to give enough clearance for them to breathe:

 

 

Dimensions were a bit of educated guesswork on my part, but I knew they needed to be deep enough to support a big, wide and heavy (> 50 kg) speaker with a 5° backtilt.

 

SF seems to use solid plate for theirs - I was concerned about "ringing" with solid plate. (As an aside, I have a kindling bucket for the wood burning stove which I made from 2 mm thick Corten steel. When it's empty, just clapping your hands in the room makes it ring like a bell, so I always keep it full.)

 

The blasting shot fill makes the plinths completely inert and takes their weight up to 17 kg each. I got the idea from Korff's Hawaphon, which I used on the internals of the cabinet.

 

I can't remember if I mentioned it earlier in the thread - Hawaphon is great stuff, but you have to be really careful with it. Any damage to the plastic cells and it leaks tiny BBs everywhere. The BBs are small enough to find their way into the voice coil gap in a driver's magnet. I missed a few strays on my first cabinet and it cost me a new midrange!

Edited May 31 by The Mad Scientist

[The Mad Scientist]

My next part of the journey is figuring how to make these fully active, incorporating time and phase alignment and room correction.

 

I need 1 more Benchmark AHB2, a crash course in Acourate, a multi-channel DAC and a means of running the crossover filters that will

 

1. Take a USB digital from a RPi Roon end-point

 

2. Take a TOSLINK from the TV

 

3 Apply the DSP and feed the output to a multi-channel DAC to give the 6 outputs (3 each L&R) to the power amps.

Edited August 20 by The Mad Scientist

[Keith_W]

8 hours ago, The Mad Scientist said:

My next part of the journey is figuring how to make these fully active, incorporating time and phase alignment and room correction.

 

I need 1 more Benchmark AHB2, a crash course in Acourate, a multi-channel DAC and a means of running the crossover filters that will

 

1. Take a USB digital from a RPi Roon end-point

 

2. Take a TOSLINK from the TV

 

3 Apply the DSP and feed the output to a multi-channel DAC to give the 6 outputs (3 each L&R) to the power amps.

 

Fortunately for you I am putting the finishing touches on a guide to Acourate which I will give away for free PM me if you want to read it. It's more comprehensive than Mitch Barnett's book. 

 

If you want to take TOSLink from the TV, what you need is a multi-channel interface and not a multi-channel DAC. If you need 6 outputs, the usual candidates are: RME Fireface UCX, Motu Ultralite Mk.5, and Merging Hapi or Anubis if you feel like spending a lot of $$$.