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Multi-Way Conventional loudspeakers with crossovers

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Old 27th September 2017, 02:29 PM   #11
system7 is offline system7  United Kingdom
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Click the image to open in full size.
Too nice to throw away, for sure.

Looking at the scorch marks, the electronics was insufficiently ventilated. Sort of issue you'd run into with a near prototype.

With the low price of second-hand amplifiers in junk shops, I'd think that going passive is a very real possibility. My own view, is that if you design for easy impedance, you really don't need any exotic amplifier for a very good sound.

And you do that by using an old BBC BW3 design like the LS5/9:
Rogers Loudspeakers › LS5/9

This speaker is still made, and still sounds good. It uses passive RL bafflestep and impedance correction: mh-audio.nl - Home

Just calculate for BW3 and 10R bass and 6R tweeter and 3500Hz, and the values drop out: 2-Way Crossover Calculator / Designer

But it's down to your friend really. FWIW, I believe the D28-2 is a ferrofluid design, so an oil-change might be in order.
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File Type: png BW3 Theoretic Values 3500Hz.PNG (19.0 KB, 109 views)
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Old 27th September 2017, 07:08 PM   #12
chrisb is offline chrisb
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Looks like your client is stuck between a rock and a hard place, and Steve is right that the enclosures are too pretty to throw away. The amps appear to have suffered the same fate as many plate amps on commercial powered subs over the years - inadequate thermal dissipation - and there's often no affordable option other than to replace. This is certainly the type of failure mode that makes outboard amplification very appealing. It may well be too early to conclude that the higher efficiency class D amps that are currently in vogue are categorically immune to the same system design oversight.

MiniDSP offers a couple of models of ICE powered plate amps with full DSP functionality, and Parts Express' Dayton brand have lower cost - but far less flexible - options as well.

Full-Range Plate Amplifiers in the Speaker Components Department at Parts Express | 333
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Old 27th September 2017, 08:00 PM   #13
Lojzek is offline Lojzek  Croatia
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I recommend the most elegant and failure proof solution, passive crossover and integrated DIY amp, as you would find in the appropriate forum here. I have built G.Randy Slone design and will keep it forever. The transparency is unsurpassed by anything I have listended thus far at home and I am able to repair it, if needed.


Post your Solid State pics here.
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Old 27th September 2017, 08:46 PM   #14
chrisb is offline chrisb
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Lojzek, to clarify, do you mean internal passive XOs with a single outboard stereo power amp, or something else?

OnC - I'm not sure it's been made clear yet, but was the lower section housing the amp a completely isolated enclosure? If not, and if those are vario-vents for porting of woofer section seen above the heat sinks, completely removing the amp modules could have an impact on the net volume for which the system was tuned. Perhaps not a huge factor, but worth keeping in mind.
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Old 28th September 2017, 01:02 AM   #15
system7 is offline system7  United Kingdom
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AFAIK, the woofer is high Qts around 0.8. So you really can't give it a box that is too big. Almost a car parcel-shelf woofer.

I am sure Lojzek means a stereo amplifier and a passive crossover. TBH, that design (attached) looks a knockout!

What is special about it Lojzek? TBH, I prefer to leave these things to Rotel and Sony and such. The main problem with Class AB is that everytime it switches from plus to minus, you have to pass through the power transistor switching, which introduces a little discontinuity and a blip of noise. It's quite easy to design an average amplifier with lots of compensation on the feedback, but hard to design one that is fast but stable.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

This is the 20wpc output stage of my competent Rotel RA-931 amplifier. A Class AB design from about 20 years ago and still going strong. It's the switches that get a bit vague over time, and need a clean with an aerosol switch cleaner.
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File Type: jpg G.Randy Slone Amplifier.JPG (88.5 KB, 28 views)
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Last edited by system7; 28th September 2017 at 01:09 AM.
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Old 28th September 2017, 02:25 AM   #16
Old'n'Cranky is offline Old'n'Cranky  Australia
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Yep. Way too pretty to let die in a dump or corner.
Of that both the owner and I agree.

I've redone the tweeters. Didn't touch the fluid. Looked ok.
On DATS sweeps they now measure within spitting distance of each other and sound identical. As far as I can tell anyway
Could be placebo but I'm sure they sound smoother and a little more extended.
One tweeter originally sounded low and distorted.
I'd imagine damage to the voice coil when the amp died.

If he decides to go passive, I was going to do it right.
Mic'd sweeps and go from there.

If he goes for the active dsp plate option.
Well, I'll still have to do mic sweeps and listening tests.
But then I can play with settings through a pc...
Should (HA) be a faster process.

EDIT.
sorry, the vario vents...

three chamber cabinet.
very bottom of cabinet is a sealed enclosure purely for the electronics.
next section up has two vario vents through the back wall to the outside world.
This section also has three vario vents into the main upper cabinet that houses the bass and tweeter.

Last edited by Old'n'Cranky; 28th September 2017 at 02:29 AM.
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Old 28th September 2017, 04:29 AM   #17
eriksquires is offline eriksquires  United States
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Here are the 2-channel, DSP enabled plate amplifiers I was thinking about:

Plate Amplifiers : PWR-ICE125

Sadly they are not cheap, $325 each, but very nice amp sections.

Best,

E
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Old 28th September 2017, 07:26 AM   #18
Old'n'Cranky is offline Old'n'Cranky  Australia
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yup. thats the one i've suggested to him.
310 from PE. + $$ conversion and shipping......
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Old 28th September 2017, 08:03 AM   #19
Lojzek is offline Lojzek  Croatia
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Quote:
Originally Posted by system7 View Post
What is special about it Lojzek? TBH, I prefer to leave these things to Rotel and Sony and such.

What's special is that it performs better than Rotel 931 and I happened to own one, it has built in automatic current limit while output short circuited or heavily overloaded, DC voltage protection and turn on delay, current mirrors below differential amp, electronic input switch and I get to feel good that I managed to put together some electronics.

I agree it's not essential if you can live with any decently built commercial amp and Rotel counts for sure. I even have the same tuner 935 AX.

@chrisb: Sure, I meant stand alone stereo amp and internal passive crossover filter as usually found in passive speakers.
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Last edited by Lojzek; 28th September 2017 at 08:06 AM.
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Old 28th September 2017, 02:50 PM   #20
phase_accurate is offline phase_accurate
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I think I have seen this speaker in a special "speaker-issue" of the German DIY magazine "elrad".
I know that I still have all these mags but I don't know where at the moment.

Regards

Charles
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