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Paul Spencer

DIY audio: what are you building?

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8 hours ago, betocool said:

Marc, how did you get 200V out of 24V? A special transformer?

 

Cheers,

 

Alberto

I have using this simple trick for years in all sorts of amps. Easy to implement in preamps where current demand low but I've  used it low power tube power amps also.

 

From the 24VAC wall wart connect it to the secondary of a 24V step down tranni. In other words connect the second tranni backwards. Out of the primary comes 240V. Once rectified 1.4 times this. I use Jaycar 24VAC 1A wall warts and a small step down 150mA 24V tranni as in the image.

 

Because the wall wart is also powering the filaments it tends to load it up - 630mA. With a result instead of 240V out if the now step up tranni a lower voltage is presented. Usually I use this method for small tubes with far less demand on filament current. But 200VDC HT is sufficient for this build.

 

I have two wine box 6L6 power amps (2W pc) and I use two 300VAC 12V toroids in the same way. These I have in an external seperate enclosure. In the wine box I have the rectification (diode bridge) and filtering. Works a treat. Also in this amp I series the filaments (6V each) and run 12V AC to them direct off the first toriod which is driving into the second toriods secondary. 

 

In some preamps, where I have the space, I use bigger step downs (backwards) and 3A step down as the primary tranni. Some may argue regulation but as long as the trannies are scaled to the job at hand and lots of filtering storage caps (the build above has 400uf) and current demand is not high it's not an issues. And you get double mains filtering and isolation you wouldn't get from a single tranni. 

 

Hope that helps.

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On 04/11/2018 at 9:38 AM, CamSemp said:

Yeah the ply on the front of the woofers has a fairly nice face. However I've decided to make things hard for myself and I've got a roll of Silver Wattle veneer to apply to the whole lot. That said, I haven't actually done a cut diagram to see if I've got enough from one sheet to do it all. May do the baffles in black or something.

 

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Looking good Cam.

Silver Wattle should have some nice natural lustre to it like most of the acacia species.Shellac would bring that out nicely.

You might find that angling the top boxes to align the front baffle so it is parallel with the grain direction will give a more interesting look as well as meaning you use a bit less width of the veneer sheet.

I will post pictures of my Kairos boxes when they are finished.Just sprayed the last coat of lacquer today.

 

Jon

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11 hours ago, THOMO said:

Looking good Cam.

Silver Wattle should have some nice natural lustre to it like most of the acacia species.Shellac would bring that out nicely.

You might find that angling the top boxes to align the front baffle so it is parallel with the grain direction will give a more interesting look as well as meaning you use a bit less width of the veneer sheet.

I will post pictures of my Kairos boxes when they are finished.Just sprayed the last coat of lacquer today.

 

Jon

Thanks Jon. Can't wait to see yours! Not quite sure I understand what you're saying with the grain direction? Do you mean having the grain on the sides running at the same angle parallel to the front baffle?

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3 minutes ago, CamSemp said:

Thanks Jon. Can't wait to see yours! Not quite sure I understand what you're saying with the grain direction? Do you mean having the grain on the sides running at the same angle parallel to the front baffle?

Yes.That is how I did mine using solid timber .I guess see which you think look best but if you are struggling to get enough width out of the veneer it will save about 20-25mm across the sheet.It meant I could get the full depth out of the boards I had but I also quite like the look .

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Ordered the PCBs to build a First Watt M2X.

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I made some posts a few weeks back about using wire wound resistors or carbon film resistors for a "L" pad for my Altec 511B horns to work with 12" woofers. I found the wire wounds bright and felt the carbon film pad, of the same value, better sounding. Well here I am weeks later and I haven't changed anything where in the past I would only last a day or two before going back to carbon film resistors.

 

I only just realised I haven't  changed the pad for weeks so it tells me I'm comfortable with the attenuation level and sound. Just raising the level 1db (in 21) and using wire wounds was too bright. Same level with carbon, (though I can tell the level is raised a little) not too bright. I like to think a good balance.

 

And that's the beauty of DIY. Us DIYers are not stuck with what a manufacturer gives us, we are free to try different and many varied alternatives, cheaply, untill we are happy with the result. For me $1 worth of carbon film resistors has given me many hours of music pleasure and a long term satisfying result.

 

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On 01/10/2018 at 1:29 PM, Muon N' said:

I also wonder how Mal went with that build

He'll be finished by Christmas....    ;) 

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On 11/10/2018 at 9:09 AM, mwhouston said:

12" woofer with a Fo of 25hZ and effcienecy of 96 or better db

You'll likely need to revisit one of these parameters.   As you will need a very high power motor, and very low compliance to ever get the sensitivity up that high, with the Fs staying so low.

 

FWIW, an example of a pretty extreme driver is the Tannoy HPD (dual concentric) woofer.   ~25Hz, ~94dB, 12"

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11 minutes ago, davewantsmoore said:

You'll likely need to revisit one of these parameters.   As you will need a very high power motor, and very low compliance to ever get the sensitivity up that high, with the Fs staying so low.

 

FWIW, an example of a pretty extreme driver is the Tannoy HPD (dual concentric) woofer.   ~25Hz, ~94dB, 12"

I guess what you want and what you need are always at odds. Currently very happy with the Poly cone 12" woofer in sealed 60ltr box with 92db efficiency. The woofer has an fo=25Hz and gives me a 31Hz -3db point. With 150W class D amps driver the woofer and horns plenty of power and dynamics with detail.

 

And I really don't want to spend anymore money on this project though I'm recycling the bass boxes and paid stuff-all for horns and compression drivers.

 

As I have been doing for some months now I'll just enjoy the music and finishing boxing the horns. Wife thinks they are ugly. 

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Meniscus Audio Kairos kit speakers in solid curly jarrah.

26mm thick curly jarrah with the sides laminated on to 12mm MDF .

The sides are glued onto the 12mm MDF which is rebated into the sides with a dry joint where the timber meets to allow for movement.

These are 17litre sealed.

The jarrah is quite unusual being more of light brown colour rather than the usual deep red.

Finish is satin 2 pack lacquer.

 

I guess I need to make some matching stands!

Or finish the three way version.

 

The Kairos white paper-

http://meniscus.lightningbasehosted.com/wp-content/uploads/2016/02/Kairos-Write-up.pdf

IMG_0233 (2).JPG

IMG_0224 (2).JPG

IMG_0222 (2).JPG

Edited by THOMO

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1 hour ago, THOMO said:

Meniscus Audio Kairos kit speakers in solid curly jarrah.

26mm thick curly jarrah with the sides laminated on to 12mm MDF .

The sides are glued onto the 12mm MDF which is rebated into the sides with a dry joint where the timber meets to allow for movement.

These are 17litre sealed.

The jarrah is quite unusual being more of light brown colour rather than the usual deep red.

Finish is satin 2 pack lacquer.

 

I guess I need to make some matching stands!

Or finish the three way version.

 

The Kairos white paper-

http://meniscus.lightningbasehosted.com/wp-content/uploads/2016/02/Kairos-Write-up.pdf

IMG_0233 (2).JPG

IMG_0224 (2).JPG

IMG_0222 (2).JPG

 

Looks very, very nice, how do they sound?

 

SS

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18 minutes ago, Sub Sonic said:

 

Looks very, very nice, how do they sound?

 

SS

They sound quite like the Sonus Faber Cremona Auditors I had.That sort of composed and refined sound but probably a bit more weighty sounding.What is nice about these compared to the Sonus Fabers is they sound best closer to the wall whereas the Auditors had to be brought about 1.5 metres out to sound their best -which gets a bit silly in some rooms.The fact they are sealed rather than ported probably helps in this regard.I would say they are a lot better than the Dynaudio Contour 1.3s I had  and also the Lenehan ML1s and Osborn Eos Special Editions which I have also tried [although the Osborns have fantastic treble courtesy of the Seas Millenium tweeter].The Kairos have a better/more natural midrange than those speakers and at least as good as the Sonus Cremona Auditor -which is saying a fair bit because they excel in that area. I reckon they compete with similar commercial speakers in the $4000-$6000 price range.Maybe a fair bit more than that.These Satori drivers would generally be found in pretty expensive speakers.

As I have said elsewhere I prefer 3 ways but as two way stand mounts go these are very good.Dynamics of course are a bit curtailed but that is the nature of the species and a good sub would probably help in that regard.

Edited by THOMO

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