Jump to content

Deep End DIY - My first speaker project


acg

Recommended Posts



HF Filter Box

 

I've been steadily building up the second DSET amplifier but there is still quite a bit to do.  I really, really want to put the first one on its mount in the listening room and measure and listen to it before I do too much wiring on the second amplifier that becomes difficult to undo or modify.  So I have also worked on the first one wiring in some crossover filters and generally dotting the i's and crossing the t's before I make the big lift upstairs.  A few minor mistakes have been found and it would not surprise me to find more.  The safety circuit has also been tweaked and the power supplies now take only a minute or so to drain down, as opposed to 10 minutes in the first stage testing and 25 minutes when 1,200 joules for the second stage power supply needed to be drained.  I feel much better about it now and wish I'd spent the time to tweak that at the time rather than waste so much time waiting for the power supplies to be safe.

 

I've also calibrated the six analogue ammeters on the front of the amplifier as well as the digital voltmeter for checking the DC offset.  The amplifier is DC coupled (no input capacitor) and the DC Offset is managed by the bias circuit and the 0A2 gas regulator tubes, so I needed a simple way to check the DC Offset from time to time.  My dac, a Phasure NOS1a is also DC coupled (so is the preamp) but it uses a 9V battery and a digital voltmeter to check the DC Offset at its output.  I talked with the manufacturer/designer of my dac @PeterSt, and he kindly gave me the type of meter he uses and I got some of them myself and implemented the scheme.  In the photo below, in the recessed region above the 5 led lights (safety indicator lights for power down) you can just see the voltmeter and the switch used to turn it on and off.  It works brilliantly and I love it.  When something is simple it will get used and you don't get much simpler than flicking a switch and looking at the screen next to it.

 

The filter for the High Frequency (HF) amplifier is a 4th order Butterworth, unequal terminations, CLC T High Pass, infinite termination.  Romy uses 3rd order, but I think that 4th order may be more appropriate.  3rd order uses two caps in series with a shunt inductor in between or CLC.  4th order adds a second shunt inductor to the end of the filter so CLCL.  The signal for this channel (>10kHz for RAAL Lazy Ribbon) runs directly through the caps so you need to choose the best ones you can and the best dielectric is air so, like Romy, I chose air-caps.  The problem with air caps is that they are not shielded so you have to provide the shielding.  There is 100kg of power transformers and chokes sitting below and behind the amplifiers and some inductors and output transformers above and inside the amplifier case so magnetic shielding is almost certainly going to be required in addition to the standard RFI shielding.  I'm good with steel, so have encased the filter in a 4mm steel outer sarcophagus inside which an off-the-shelf RFI box sits.  Have a look below, you can see the silver RFI box inside the black steel box.

 

 

 

 

1925583932_HFBox.jpg.8075e14b1217aeb7df1d481eb4ec15eb.jpg

 

 

The wires enter and exit the box via a single shielded cable gland (top right corner).

 

Below you will see the HF filter partially constructed...

 

1785549132_HFBoxfilter.jpg.10112bdfab75ec6972fb8b99ea151966.jpg

 

Two variable air capacitors and two Black Art Audio shielded inductors (potted into steel box and then sheeted with mumetal) sitting on a 1mm thick aluminium plate.  The plate gets screwed into the RFI box and construction of the filter is completed.  There is heaps of room inside the box for more components if necessary.  The 3rd order filter would require a different inductor and a change in value of both the air-caps (which is easy, just twist the shaft until the desired capacitance is reached - must be unhooked first from the circuit).

 

267086622_HFBoxfilterinandwired.jpg.2e9f24845204fe331b715ab89a16d2e8.jpg

 

Then the lid of the RFI box goes on and then (not shown) the side panel of the amplifier to complete the 4mm steel sarcophagus.

 

1600549083_HFBoxClosedup.jpg.2540ea98d1b892e93606d690cadc628d.jpg

 

It's ironic that the channel above 10kHz where all I'll hear is the odd squeak has by far the most complex electronic filter...ha!

Edited by acg
  • Like 5
Link to comment
Share on other sites

Just did the capacitor energy storage calculations for one monobloc amplifier after reading the spiel of a commercial amp producer bragging about having 80 joules of storage in their stereo valve amp power supply compared to most valve amps that have about 50 joules.  I don't know if either of those claims is actually true, but one of my monoblocs has 3,300 joules of energy storage...yikes, that's 6,600 joule for the stereo pair...no wonder they take a heap of bleeding down when the amp is turned off!

  • Like 1
Link to comment
Share on other sites



1 hour ago, acg said:

Just did the capacitor energy storage calculations for one monobloc amplifier after reading the spiel of a commercial amp producer bragging about having 80 joules of storage in their stereo valve amp power supply compared to most valve amps that have about 50 joules.  I don't know if either of those claims is actually true, but one of my monoblocs has 3,300 joules of energy storage...yikes, that's 6,600 joule for the stereo pair...no wonder they take a heap of bleeding down when the amp is turned off!

Man.  You don’t need battery storage for that solar system you put in!  Just have amps on during sunny days!

  • Like 1
  • Haha 1
Link to comment
Share on other sites

  • 2 weeks later...

So, the first DSET is still downstairs on the electronics bench and I am back to work for a while, but not too hard and not for too long (I hope).  I've added all the filters and checked and tested and changed some more things and decided that it was time to see if I could get any music to play.  Several crappy drivers and speakers that I had scrounged for just this purpose were wired up and I pressed the go button to stream some Tidal.

 

313735084_FirstMusicTesting.jpg.6879d84808c02e8c025681aaf56282ea.jpg

 

 

 

It works!  I have sound.  Kind of a weird sound with the mix and match driver selection but at least it is comprehensible.

This is the front of the amplifier where it wraps around the chassis pillar for the horn stack...

 

 

1028441234_AmpFront.jpg.9a44bcc7c80a5efd6808311b79c38cbe.jpg

 

Plenty of thought has gone into the speaker cables largely because there are plenty of them and I would prefer for them to be hidden completely from view.  Five of the six channels exit the amplifier in the well that fits around the horn stack pillar where they are nicely hidden, and the bass channel exits from the side closest to the Bass Cannons.  I've thought about different types of speaker wire from exotic to simple and in the end I have gone with simple Duelund 16GA tinned copper wire.  I've used this before with fullrange speakers and it is fine.  The big benefit for me is that it is black and the individual wires are tinned:  black to hide it and the tinning because these speaker wires will not be terminated in any way, no spades, bananas or whatever, just crushed in the binding posts of the driver one end and directly soldered to the output transformer on the other end.  Inductance and capacitance should not be an issue for such band limited amplifier channels, and even the Injection Channel that runs fullrange will run 14dB or so down.  Terminations seem to be the major issue in speaker cables, and these Duelund wires when used this way will eliminate a joint/termination each side of each binding post while proving resilient to oxidation in a tight crush joint at the transducer.

 

 

Anyway, music has been playing downstairs for a couple of hours now and the only temperatures that I am concerned about are the 3 final anode resistors (15k 12W) for the first stages of A/B/C.  The hottest of those according to my thermal camera is about 140C (280F) so it might pay in the long run to parallel a pair of 30k 12W resistors even though the datasheet specifies 350C maximum and there should be decent airflow from the chassis fans at that part of the case.

 

A hopefully minor problems are left to solve with the HF Channel not drawing enough current and the DC Offset at input not able to be zeroed out, then it will be upstairs for the beast.

 

 

The next DSET is also taking shape...

 

1577496043_NextOne.jpg.d9655e3dc91ba6b1f428d7ff377da81b.jpg

 

 

 

 

 

 

 

 

Edited by acg
  • Like 6
  • Love 1
Link to comment
Share on other sites

Currently streaming the cricket telecast on my work computer and using the DSET to listen to the commentary...a perfect symbiotic relationship drawing 400w to listen to the cricket...or a prime example of power wastage?

Link to comment
Share on other sites

I've not yet measured them but the amp channels should be about as follows:

 

Bass Channel - 9w into 1r impedance.  With a more sensible speaker load and output transformer to match this channel will make about 17watts.

Midbass/Injection Channel - about 9w I think.  This burns only half of the power tube so it may be a little higher.

Upperbass Channel - same as ^^

Fundamentals Channel - 2w or maybe a bit less

Midrange Channel - depends on the DHT power tube used.  From 2w or so with a 45, 3W with 2A3 to maybe 4w with YO186.

High Frequency Channel - 2w or maybe a bit less

 

Speaker channels are all somewhere near 109dB/w/m with the bass channel lower at about 100dB/w/m.  I've not decided on how I will use the midbass/injection channel yet, but this channel is easy to modify to 17w output if required just by turning on the second triode in the tube.  

 

 

  • Like 1
Link to comment
Share on other sites



On 01/02/2019 at 11:32 AM, acg said:

So, the first DSET .... works!  I have sound.....

Well done. That's a great achievement.  Thanks for the great photos. If this the very first amplifier you have designed and built? 

Link to comment
Share on other sites

@Nada, the basic circuit was not designed by me, but all the peripheral circuits and  protocols plus layout, components, parts, cables, chassis et cetera were certainly all me, and quite unique.  I did breadboard a single channel of the amp a few years back and was impressed enough with what I heard to push forward with the big 6 channel monoblocks.  The power supplies for those fullrange valve amps are built and boxed and one day I will also put the amplifier into its own cases as well....make it an all valve home theatre in my office...haha.

 

Then there is a solid state preamplifier that is 85% built and tested and the chassis is designed and about to be laser cut.  Likewise for a Class A PP SS amp that should be cased up in the next month or so once I get around to it.  I have also built two phonostages that await boxing up and final testing.  However all these amplifiers are based on someone else's circuit boards and sound testing and are very, very simple and very, very quick in comparison to the process for the DSET amplifier, which has taken thousands of hours all up in planning and execution.  I've really enjoyed it all so far and to think four years back this was all well outside of my comfort zone!

  • Like 3
Link to comment
Share on other sites

  • 2 weeks later...

Soooo, something happened on Sunday morning...

 

28799867_DSETonthestack.jpg.1936f0c6fdf29dcde949e7995767a19f.jpg

 

O. M. G.  a DSET is on the horn stack!

 

Two mates wandered over on Sunday morning and we put on some Pink Floyd, carted the amp upstairs, polished the roller cup isolation mounts that this thing sits on and then tried to sit the 100kg amp on the stack...oh sh&t it does not fit!  It was hung up!  We took notice of what was grabbing the amp in the wrong place and with much sweat and steady effort from the three of us removed it to the carpet...the table was too far it seems.  The amp is a tricky wriggle to get in place and requires quite a bit of finesse and control over its movements which was fine when we three were putting it on but it was a big effort getting it off.

 

I consulted my CAD model and found the issue.  I had installed the valve assembly for the pneumatic isolation to the left instead of the right so it took 10 minutes to swap the parts from the right horn stack to the left one.  With the bits pointing in the correct direction we hefted the big fella back up onto the stack, put some air in the pneumatics and got her sitting there in the right place and all jiggly on the isolation.  We three then took some step back into the middle of the room to ogle the new creation and right on cue PF blurts out...


 

Quote

 

Come in here, dear boy, have a cigar,
You're gonna go far,
You're gonna fly high,
You're never gonna die,
You're gonna make it if you try,
They're gonna love you.


 

 

Which although is perfectly timed for the occasion, is quite ironic when the actual meaning of the lyrics are considered in the context of the entire song.  It was a nice moment anyway.

 

 

783116898_DSETonthestack2.jpg.84b96e86b82b1d04f2b7a4e5fc79c276.jpg

 

Please ignore the sweaty hand prints on the black powerdercoating, but the whole thing looks absolutely fantastic in my opinion.  It is unique, purposeful, a little bit plain and industrial but that was the goal and it is still lovely in the scheme of the entire installation.  I am very happy. 

 

I had an enormous urge to hook everything up and light her up and listen to something with the horns and cannons that I have in the room.  I was very, very tempting, but I was just a little too excited and would have glossed over something important for sure, so the rest of the day was spent getting minor details sorted that hopefully means that once I start her up I won't have to power her down to get these other things done.  One of the minor things is the humpot for the DHT Channel that I have blown twice.  It goes off the end of the track, which is easy enough to do , and it fries that little part of the track and it is caput.  The circuit has been modified to alleviate this issue and the final parts should arrive today which means I may even get some glow happening tonight...maybe.

 

 

 

 

  • Like 8
Link to comment
Share on other sites



 

It's missing a couple of channels, nothing had been measured or tuned, but frometh comes sound.  Yay!  Kind of an appropriate song considering how long this has taken me thus far.

 

 

 

 

  • Like 6
Link to comment
Share on other sites

16 minutes ago, Silent Screamer said:

I'm thinking it could be a little bit bigger... said no one, ever.

 

The horn on top is a head strike hazard...without the big upperbass horn underneath that sucker gets everyone once, or twice.

  • Haha 1
Link to comment
Share on other sites

31 minutes ago, acg said:

 

It's missing a couple of channels, nothing had been measured or tuned, but frometh comes sound.  Yay!  Kind of an appropriate song considering how long this has taken me thus far.

 

 

 

 

That sounds surprising good !!!! Very promising.

Link to comment
Share on other sites



1 hour ago, acg said:

 

The horn on top is a head strike hazard...without the big upperbass horn underneath that sucker gets everyone once, or twice.

That’s that.  We’re shutting the site down pending pin notice and review by Worksafe with union shop steward present.  Could be months.....

Link to comment
Share on other sites

10 hours ago, Silent Screamer said:

First thoughts? Impressions? Obviously won't be 100% out of the box, but are you happy with it?

 

First impressions are ok.  Certainly better than it could have been or probably should be considering what is missing and what is yet to do.  It sounds much, much better in the flesh than the video captured with my phone, but there is still a lot to do to get it up to scratch.  Had someone over last night, a non-audio person, and they thought it sounded fantastic...so much bass...but, well.

 

My biggest surprise was how coherent things sounded:  it did not sound like there were multiple sound sources, just the one combined source.  I was not expecting that straight from first power up.

 

10 hours ago, davewantsmoore said:

What a milestone!!  :D:D

Yes, it is a huge milestone.  First sound four years into the project...yikes!

 

10 hours ago, Nada said:

That sounds surprising good !!!! Very promising.

It's not too bad, and yes, I think it is very promising.  

 

8 hours ago, Mat-with-one-t said:

That’s that.  We’re shutting the site down pending pin notice and review by Worksafe with union shop steward present.  Could be months.....

 

Haha.  Bradsy copped two hits on Sunday while helping me lift the amp into place, but as far as I am aware he is yet to register an incident.  Lucky there are no sharp edges up there...

 

  • Like 1
Link to comment
Share on other sites

5 hours ago, acg said:

 

First impressions are ok.  Certainly better than it could have been or probably should be considering what is missing and what is yet to do.  It sounds much, much better in the flesh than the video captured with my phone, but there is still a lot to do to get it up to scratch.  Had someone over last night, a non-audio person, and they thought it sounded fantastic...so much bass...but, well.

 

My biggest surprise was how coherent things sounded:  it did not sound like there were multiple sound sources, just the one combined source.  I was not expecting that straight from first power up.

Sounds like you're well on track, nothing worse than putting in a whole lot of effort and being totally disappointed with it. Obvious missing a big horn it won't sound quite right, and phone camera video leaves a lot to be desired in terms of reproduction (BTW turn your camera sideways) but what I could hear on the video sounded pretty damn good for a first fire up to me.

Link to comment
Share on other sites

15 minutes ago, Silent Screamer said:

Sounds like you're well on track, nothing worse than putting in a whole lot of effort and being totally disappointed with it. Obvious missing a big horn it won't sound quite right, and phone camera video leaves a lot to be desired in terms of reproduction (BTW turn your camera sideways) but what I could hear on the video sounded pretty damn good for a first fire up to me.

 

It's pretty good.  I just played the clip back just now and you can hear my kids either fighting or playing very vigorously downstairs.  I should have closed the trapdoor...haha.

Link to comment
Share on other sites

2 minutes ago, acg said:

 

It's pretty good.  I just played the clip back just now and you can hear my kids either fighting or playing very vigorously downstairs.  I should have closed the trapdoor...haha.

lol my brain filtered out majority of the kids fighting, I was in critical listening mode. Playing it back and listening to them as well, they are far more present than I heard the first time. Sounds a bit thin, but it's exactly the same if I turn off one on the channels in my active xover, it will sound a bit thin. Clarity sound very nice. Bass I am not hearing a great deal of, but that is more probably due to this POS Gigabyte laptop I am using that won't play back below 130Hz. So even if the phone camera is picking it up my laptop is not playing it. All and all I think it shows great promise and look forward to that post that says, it's all done come and have a listen.

Link to comment
Share on other sites



  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...
To Top