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

[kiwilistener]

30 minutes ago, TheBlackDisc said:

These's are rapidly losing any presentation of “poor man’s” to me.

 

Yep there's nothing poor about this build, at least in comparison to mine. 

Edited August 29, 2023 by kiwilistener

[The Mad Scientist]

2 hours ago, El Tel said:

You are a true Renaissance Man.

I don't know about that - I just stubbornly refuse to be bested by a challenge!

[The Mad Scientist]

2 hours ago, TheBlackDisc said:

These are rapidly losing any presentation of “poor man’s” to me.

In the context of the original Stradivari Homage (£40k) and the newly announced v2 (£50k), mine are still relatively bargain basement!

 

I've done quite a few DIY speakers in the past and they've always ended up with a slightly home-made look to them. This time, I'm aiming for a look that wouldn't be out of place in a hi-fi dealership.

[ENIGMA]

2 hours ago, TheBlackDisc said:

These are rapidly losing any presentation of “poor man’s” to me.

You're missing the point, at the end of the build he will be a poor man 

 

 

[TheBlackDisc]

6 minutes ago, The Mad Scientist said:

In the context of the original Stradivari Homage (£40k) and the newly announced v2 (£50k), mine are still relatively bargain basement!

 

I've done quite a few DIY speakers in the past and they've always ended up with a slightly home-made look to them. This time, I'm aiming for a look that wouldn't be out of place in a hi-fi dealership.

Take the compliment!!!

[BioBrian]

2 hours ago, TheBlackDisc said:

These are rapidly losing any presentation of “poor man’s” to me.

 

It's probably best not to dwell on the name.

 

Doesn't matter how pretty or clever it is, any mention of PMS and it's likely to have zero WAF.

[tripitaka]

Amazing thread! 

 

Congrats for what you have achieved

 

When seeing such expertise I feel slightly awed, yet more than slightly relieved that I never bothered to attempt anything like it.

 

[The Mad Scientist]

12 hours ago, TheBlackDisc said:

Take the compliment!!!

Hehe. Never could recognise a compliment. Well, maybe if you wrapped it around a wet kipper and slapped me in the face with it. Then I'd recognise it. Possibly......

 

I'm a spectrum dweller. Clinically diagnosed as simultaneously co-existing at the extremes of ADHD and ASD. Consequently, nuances in written communication are sometimes lost on me!

Edited August 29, 2023 by The Mad Scientist

[TheBlackDisc]

59 minutes ago, The Mad Scientist said:

Hehe. Never could recognise a compliment. Well, maybe if you wrapped it around a wet kipper and slapped me in the face with it. Then I'd recognise it. Possibly......

 

I'm a spectrum dweller. Clinically diagnosed as simultaneously co-existing at the extremes of ADHD and ASD. Consequently, nuances in written communication are sometimes lost on me!

I’m literally in the same boat -  communicating is a problem both ways - we were doomed for the start.

Edited August 29, 2023 by TheBlackDisc

[The Mad Scientist]

Where it comes to testing the limits of my ingenuity and problem solving abilities, this project just keeps on giving!

 

Trimming the stainless back has proved challenging. Even on the lowest speed with the thinnest stainless cutting disc on a battery grinder, the stainless is getting too hot to the point where it’s compromising the resin at the end of the cabinet. A little sanding and touching up of the resin will be required.

An alternative solution was needed, so I’ve gone down the route of “cold” cutting with my trusty 25 year old jigsaw equipped with a carbide tipped blade.

The other challenge was how to scribe a line to follow with the jigsaw that made sure I had just enough clearance to avoid damaging the carbon finish.

A roughly fashioned scribe with a centre insert the same thickness as the stainless, with a hole drilled in the end to hold a 3.2 mm sharpened tungsten:

 

 

 

Some blue layout fluid and a run round with the scribe gave me a nice, crisp line to follow with the jigsaw:

 

 

 

 

It’s a slow process, but with a little cutting wax applied to the blade every so often, the blade stays reasonably cool and the stainless doesn’t even get warm.

Edited August 31, 2023 by The Mad Scientist

[ICUToo]

3 hours ago, The Mad Scientist said:

Where it comes to testing the limits of my ingenuity and problem solving abilities, this project just keeps on giving!

 

Trimming the stainless back has proved challenging. Even on the lowest speed with the thinnest stainless cutting disc on a battery grinder, the stainless is getting too hot to the point where it’s compromising the resin at the end of the cabinet. A little sanding and touching up of the resin will be required.

An alternative solution was needed, so I’ve gone down the route of “cold” cutting with my trusty 25 year old jigsaw equipped with a carbide tipped blade.

The other challenge was how to scribe a line to follow with the jigsaw that made sure I had just enough clearance to avoid damaging the carbon finish.

A roughly fashioned scribe with a centre insert the same thickness as the stainless, with a hole drilled in the end to hold a 3.2 mm sharpened tungsten:

 

 

 

Some blue layout fluid and a run round with the scribe gave me a nice, crisp line to follow with the jigsaw:

 

 

 

 

It’s a slow process, but with a little cutting wax applied to the blade every so often, the blade stays reasonably cool and the stainless doesn’t even get warm.

Looking great- this is a wonderful thread, thank you.

And I've never heard of carbide-tipped jigsaw blades! Thankyou! I own most of the tools, now I have to get this one:)

[Rob Wright]

Wow. Just wow. What an absolutely amazing project.

[The Mad Scientist]

Progress has been slow - partly due to work, partly due to an old back injury (from a road accident back in '93 when I was rear-ended by a truck) rearing it’s head again (my second osteopath visit seems to have done the trick) and partly due to one of my neighbours complaining about noise…

 

The weather has also been ridiculously hot this week. After a bit of reorganising, I’m now working in my air-conditioned man-cave which has certain benefits:

 

1. It’s a balmy (from a Celtic/Nordic perspective) 18°C in there.

 

2. It’s well insulated (thermally and acoustically), so it’s cool to work in and no matter how much noise I make, I’m not disturbing anyone.

 

3. With local dust extraction and environmental air filtration, it’s surprisingly clean.

 

Anyhoo, after jigsawing the stainless on the first cabinet to within ~2 mm of the carbon skin, subsequent grinding with an 80 grit flap disc followed by a Norton Vortex rapid blend disc was painfully slow, so a better method was required.

 

From previous (though inadvertent) experience, I learned you can cut stainless steel with a carbide cutter on a router. There are limitations, however. Linear cutting speed for carbide on stainless shouldn’t exceed about 115 metres/minute. For a 1/4" diameter (6.35 mm) cutter, that’s about 6000 rpm.

Cue this little bad boy:

 

 

10,000 to 30,000 (no-load) rpm. Under load with a 1/4" cutter, it’s just about perfect.  I'm using a downcut spiral solid carbide bearing guided cutter which gives an exceptionally clean edge. The only downside is that it throws the chips downwards, so even with dust extraction, about 50% of the chips land on the floor

 

After routing (gingerly), followed by a polish by a Norton Vortex rabid blend disc to remove the machining marks, I’m getting there:

 

 

First cabinet stainless trimmed flush, epoxy flatted back ready for a little touching up, then the final coat prior to sanding and polishing:

 

 

The second cabinet needs a couple of build coats, then it’s due for the jigsawing and routing treatment to finish off the stainless. There’ll be no heat damage to the resin from grinding, so this one should be a little more straight forward  Then I can progress with fabricating the plinths.

 

Which reminds me, I need to check how much argon I have left in my tank.

Edited September 10, 2023 by The Mad Scientist

[ENIGMA]

Very nice, i bet you cant wait to start polishing.

[The Mad Scientist]

4 hours ago, ENIGMA said:

Very nice, i bet you cant wait to start polishing.

Indeed!

 

I'm very much looking forward to the polishing stage. Then I can wire the connectors and fit the drive units

[The Mad Scientist]

Finally, the first cabinet has had all of its touch up repairs, been flatted back with 120 grit, and now has its final coat of resin, ready for final flatting and polishing:

 

 

My original plan was to mirror polish the stainless, but given the satin look of the embedded aluminium, I decided that a satin polish would be more fitting:

 

 

I picked up a reasonably priced burnishing grinder and a selection of drums this week.  More photos to follow.  I Invited Mrs. Mad Scientist out to have a look at the nearly finished cabinet. “Ooh, it’s big isn’t it?”   I was kinda hoping for some comments around the aesthetic appeal of my artisanal blend of stainless steel and carbon fibre…

 

Edited September 15, 2023 by The Mad Scientist

[The Mad Scientist]

They say the measure of a good craftsman is how well he can hide his mistakes.

On that basis, I reckon I’m not doing too badly.

I didn’t tighten the depth stop enough on my router when doing the second bass driver cutout.

The cutout should have been 5.7 mm deep.

Oops…

 

 

 

 

5 mins to chop a 9-ish mm thick ring from an offcut of 12 mm ply with the circle jig:

 

 

Glued up and tapped into place:

 

 

Phew!  I learned this trick many years ago. My router collet was worn and it threw this cutter out and straight through £1000 worth of solid oak worktop I was fitting in my kitchen:

 

 

I fitted a pull-up power socket strip with an aluminium ring surrounding it made from an old computer case to hide the hole

[The Mad Scientist]

First cabinet sanded all the way from 240 grit to 2000 grit, and now onto the cutting/polishing:

 

 

Nice mirror finish coming up:

 

 

[The Mad Scientist]

The first speaker is finished and relocated into the house while I continue with the messy work on the second one. The kitchen has the best light in the evening, so I wheeled it in there to take a few photos. The dolly is a makeshift arrangement to facilitate moving it around. Going from the shed down the steps to the house was interesting. I made up a big dolly to transport the air compressor into the shed when it arrived and I kept it just in case. It’s been extremely useful throughout this build. Screwed the timber supports to the big dolly, wheeled it gingerly down the steps, unscrewed them from the dolly, carefully slid it in through the French doors, turned it upside down onto a towel and screwed on the castors.

Tips the scales at 50.4 kg now, so moving it around is a proper challenge.

 

 

 

 

 

 

Whilst I had it upside down in the shed, I took some measurements to make an aluminium template for cutting out the plinth sections, and whipped out the mag drill to drill the 21 mm holes for the sections of stainless pipe that will join the top and bottom panels and fit around the mounting studs:

 

 

Mag drills are ridiculously good at cutting clean holes quickly in metals, but it took about 20 minutes of set up for literally 20 seconds of drilling.

[ENIGMA]

A very satisfying build.

[BRS]

Absolutely stunning. Well done and thank you for sharing.

[Rob Wright]

What an absolutely amazing project.

[The Mad Scientist]

Thanks for the kind comments everyone.

 

The second cabinet is nearing completion too.

 

Looking forward to having them in the lounge for a play before getting on with the plinths.

[Janus77]

The finish looks incredible.  Great job.  

[The Mad Scientist]

I've had a few setbacks in the past week.

 

1. My Mirka sander died a death about a third of the way into sanding the final coat on the second cabinet.

 

2. I caught a nasty case of COVID.

 

3. I had an issue with microcrystallisation in the latest batch of epoxy hardener, resulting in lots of little white flecks in the final coat.

 

The Mirka is on it's way back for evaluation/repair/replacement under warranty. In the mean time, I picked up a cheap 6" (£70) Erbauer sander from my local Screwfix store. The Mirka Abranet sanding discs fit perfectly, so all is good, well apart from it's 3 kg heft compared to the Mirka's 1 kg!

 

 

Having COVID has been a proper b@ll-ache. Besides feeling like death warmed up all week, I've had a perpetual sinus headache and little enthusiasm for progressing with the project. To add insult to injury, my taste buds are shot and I can't even enjoy a whisky. No matter how smoky or peaty, all I can taste is vanilla sweetness.

 

The flecks were a real pain.

 

 

 

 

 

I contacted Easy Composites' tech guys. Apparently, the XCR skinning resin hardener is prone to crystallisation if not stored correctly. I can only assume this happened during storage/transit as since delivery, it's been in a 20°C air-conditioned environment.

 

Fortuitously, the process is reversible. Simply heating to above 50 °C and maintaining the temperature until the crystals dissolve does the trick:

 

 

Unfortunately, the offending coat had to be sanded back completely and redone.

 

Given that everything had already been flatted back for the final coat previously, I ripped it back with 120 grit, recoated with fresh, decrystallised resin and cheated by starting with 400 grit (skipped the 240 grit first stage as the finish was already really smooth).

 

Yesterday, I felt well enough to do the sanding, so I worked my way from 400 through to 2000 grit followed by a final cut and polish.

 

I then fitted the Neutrik connectors and soldered and fitted the drive units.

 

Completed the wiring up of the speaker cables  today and fabbed a couple of temporary plinths from laminated poplar ply to get them set up.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

So, I finally got to firing up Roon and listening to some favourite tracks this afternoon.

 

For those who don't know my setup, I stream from a Synology Rackstation (RS3617xs)-based Roon Core via PoE powered RPi 4Bs. The RS was purchased when I was working professionally as a photographer - I wanted the means to shift lots of big files around fast after a gig and have seamless automated off-site backup. I no longer shoot professionally, but the RS is still invaluable, running Roon, a dozen IP security cameras, a Plex server and hosting files and providing on and off-site backup.

 

My main rig consists of a Benchmark DAC3 HGC, HPA4 and dual mono AHB2s. The crossovers are external, mounted in carbon fibre wrapped boxes (shown earlier in the thread) with everything wired throughout with Canare 4S11 speaker cable. I use the 4S11 as intended - as a starquad cable. Both reds to + and both whites to - to leverage the ridiculously low self-inductance, low resistance and moderately low capacitance.

 

Left and right speaker cables are different lengths for neatness. Call me a heretic if you like, but the differences in inductance, capacitance and resistance are barely measurable, let alone audible! I can share the measurements and calcs for the skeptics if required. The differences are so far below the threshold of audibility that they are completely negligible.

 

OK, onto my initial listening impressions.

 

My previous speakers were standmounts utilising some of the best Scanspeak drivers that money can buy and they were very, very good. Within the sweet spot, soundstage was good and instrument placement was pinpoint accurate. On some recordings though, if the vocalist wasn't dead centre, there was a kind of disembodied unnaturalness to the soundstage.

 

With these, there's a huge "wall" of sound. The soundstage is wide, tall and has phenomenal depth. I've heard wide-baffles criticised for lacking the pinpoint accuracy of narrow baffles, but these just sound natural. Live recordings are superb - the whole ambience is recreated in my living room.

 

My Kansas Smity's House Band CD rip takes me right back to Ronnie Scott's jazz club where I first heard them play this set.

 

Another  unusual trait of these speakers is their ability to play well at low level. I used to have to crank the level on the standmounts to bring the sound out of the boxes and really make them listenable, but the PMS play incredibly well at ridiculously low volumes.

 

I'm sitting listening at 23:00 on a Sunday night at 45 - 60 dBA (herself is in bed) and not feeling like I'm missing anything.

 

Troels has really smashed it with this design. I really can't fault it.

 

I've never heard the SF Stradivari Homage, but if this design comes close to its namesake, I'd say they're well worth their 40k price tag.

Edited October 1, 2023 by The Mad Scientist
punctuation