The Christiansen "DG" 300B Amplifier Build Thread

[tomchr]

Aluminium is a bit more user friendly than bronze - at least judging by your experience polishing bronze. The only thing with aluminum is that it sometimes can be a bit hard to get paint to stick to it. If you use an etching primer, it's no problem. I find the Rustoleum rattle cans work quite well for this. Just don't sand the aluminum with sand paper finer than 320 grit. You want some surface roughness for the primer (or clear coat) to grip onto.
 
Spray painting with rattle cans can be a royal pain, though. It took me nearly two weeks to get acceptable results on my 300B build. I think next time, I'll look into anodization. 
 
Of course, if you have access to a bead blaster, you're in phat city. Bead blasted aluminum with a clear coat can look really good.
 
~Tom

 

[sceleratus]

Hi T,
 
Correct-a-mundo.
 
1) Get it anodized.  I'll probably have a couple panels cut.  With the heat sinks I'll still be at some minimum anodize charge.  Best
2) Use my buffing wheel and compound and try to make it look billet...   Cheap and I can do it in my garage in a day.**  Trouble is I don't think T6061 sheet is the same as T6061 that's CNC'd.   I miss my 57 Chevy.  sniff
3) Powder coat.  There are places that will do that cheap.
4) Paint.  From my hot rod days I have some bad az industrial metal primer.  Yup.  Need that for sure.  Hot liking the paint option.
 
**Tip I found that's great.  Get a hard rubber cone bit.  Not only does it remove the burrs in an instant, it'll give the cutouts a mirror finish.
It's best to get an inexpensive pneumatic hand held grinder from Harbor Freight for a couple bucks, but a drill will do.

 

[tomchr]

6061-T6 aluminum is 6061-T6 regardless of how you machine it. It machines really well. 
 
For the surface prep, I'd ask the anodizing shop for advice. They may do their own prep anyway, so you might be wasting your time getting that mirror finish on the parts. If you're responsible for the prep, definitely do a good job as any imperfection will show.
 
Don't powder coat the heat sink. Powder coating (or painting) adds an insulating layer of paint. This increases the thermal resistance (i.e. makes it harder for the heat sink to get rid of the heat). Only black anodizing will help getting rid of the heat. Black anodized aluminum is pretty close to a black body radiator - the most efficient radiator out there. Black anode is what you want.
 
~Tom

 

[sceleratus]

  6061-T6 aluminum is 6061-T6 regardless of how you machine it. It machines really well. 
 
For the surface prep, I'd ask the anodizing shop for advice. They may do their own prep anyway, so you might be wasting your time getting that mirror finish on the parts. If you're responsible for the prep, definitely do a good job as any imperfection will show.
 
Don't powder coat the heat sink. Powder coating (or painting) adds an insulating layer of paint. This increases the thermal resistance (i.e. makes it harder for the heat sink to get rid of the heat). Only black anodizing will help getting rid of the heat. Black anodized aluminum is pretty close to a black body radiator - the most efficient radiator out there. Black anode is what you want.
 
~Tom

 
 
 Thanks for making sure, I wasn't going to powder coat the heat sink.  I would only anodize it.  
For the back plate I'm going to polish it using Dico TC6 Tripoli and a bonnet.  It should produce close to a mirror finish.
 

 

[sceleratus]

I'm looking into the single driver speakers using either a Fostex or Markaudio driver.  There are a number of builders that offer either plans, make [size=small]flat-paks, or complete speakers.   I could easily assemble a flat-pak but I'd have to have someone put on the veneer.  It's not something I'd like to do for the first project and I'm sure there are special tools needed to make the job look professional.[/size]
 
[size=small]I found a gentleman that will take his Markaudio M10 design and modify his enclosure to match the amp design.  Just adding dead space instead of using stands.[/size]
 
[size=small] I'm just not sure the one driver designs will fit my listening tastes.  I like classic R&R more on the mellow acoustic side.   Dylan, The Dead, Knopfler, but I do like vintage Stones and Zeppelin.[/size]
 
[size=small]For two drivers, I'm looking at ZuAudio, but they leave me with the impression of form and marketing over substance.  There's also a small builder named Sonist that Jack likes a lot.  They're a two driver configuration but I'm not liking the cabinet and they need stands.  I don't like stands.   This is where the Zu Omen fits better for me aesthetically.[/size]
 
[size=small]Here's the modified layout for a Bob Brines M10-A10 speaker that would match the amp.  This too may be aesthetics vs what the overall best speaker would be, but it would be great to match the amp.[/size]
 
 

 
 
 
 
[size=small] [/size]

 

[sceleratus]

Can sub woofer circuit could be added? YES

I found this circuit. I like it because it's on the output from one OPT, rather than some I saw that had op-amps on the input side....
Any preamp would mung up the headphones as well.

Any other design suggestions of this type would be appreciated. If I could add a Sub, I'd me more incline to try a single driver speaker model.




Reading the description further,

Voltage divider R1-R2-P1 is designed for use with the output signal of an average output amplifier of around d 50 W. The crossover frequency of the network may be varied between 50 Hz and 160 Hz with P2. The values of R3, P2, and C1, are calculated on the assumption that the subwoofer amplifier to be connected to K1 has a standard input resistance of 47 kΩ.

Will this work with 8W-10W ?

EDIT:
Forget the above. It's too much BS for my needs. Circuit....separate Sub, sub amp.
If a single driver won't do it, I'll go with a two driver speaker...

 

[tomchr]

With a mass loaded transmission line (MLTL) design, you can get rather extreme bass with a full range driver. No need for a sub. I ran a sim with a 5" TangBand speaker (W5-1611SA) and was able to push it to about 38~40 Hz -3 dB.
 
Designing a speaker is more than just putting a driver in a box. Much, much more. Don't design your own unless you want to experiment and learn. Either build a kit, use known-good plans, or buy a speaker.
 
~Tom

 

[sceleratus]

  With a mass loaded transmission line (MLTL) design, you can get rather extreme bass with a full range driver. No need for a sub. I ran a sim with a 5" TangBand speaker (W5-1611SA) and was able to push it to about 38~40 Hz -3 dB.
 
Designing a speaker is more than just putting a driver in a box. Much, much more. Don't design your own unless you want to experiment and learn. Either build a kit, use known-good plans, or buy a speaker.
 
~Tom

 
Yup,
 
I wouldn't dream of designing my own.  I picked up on the fact that it's not just a box with a six inch hole but one acoustically engineered for a specific driver.
Good to know about the bass on an MLT.  That's one of the designs I was looking at.  It's built for the Markaudio A10.  That option is now back in play.
 
Thanks for watching out for me.

 

[nikongod]

Unless specifically designed for it, modern speakers with crossovers may not play nice with the Zo of your amp. 
 
Stick with single drivers. There are plenty of designs about. 

 

[tomchr]

As long as the impedance curve of the speaker is reasonably flat, there won't be a problem driving it with a tube amp. That goes for any speaker, actually. The impedance curve of a full range driver in an enclosure is not perfectly flat either...
 
With a 2-way design, the XO frequency tends to be around 1-2 kHz. So you get a directivity change right where the ear is the most sensitive. The XO frequency is a compromise between getting decent SPL out of the tweeter (sets the low limit) and avoiding cone breakup of the woofer (sets the high limit). With the low slopes of passive XO filters, this tradeoff becomes very hard and nearly all 2-way speakers will exhibit some amount of woofer cone break-up (rude sounds in the midrange) as a result. Using electronic line-level crossovers (digital or analog) will help as the filter slope can be made much steeper, hence, the amount of rude sounds emitted by the woofer can be minimized and the XO frequency increased slightly to allow the tweeter to operate closer to its comfort zone.
 
In a full range speaker, the tradeoffs are mostly tied to the driver size. A smaller size driver will have better performance in the highs, but won't be able to produce low bass loudly. And vise versa for a big driver. Getting a small driver to produce low bass is a game of tuned loads and peak excursion. So basically, expect a full ranger to be able to produce low bass in the right enclosure, but don't expect it to rock the house off its foundation. For DIY speakers, the TABAQ is a good place to start. Pete Millet's design based on the Jordan JX92S is another interesting one. I do have some concerns about the Jordan drivers. Specifically, that the diaphragm is made from insanely thin aluminum foil and dents really easily. Personally, I'm also not a fan of metal speakers as they tend to accentuate the cone break-up, resulting in harsh highs.
 
~Tom

 

[sceleratus]

Dave at Planet 10 sent me the Fonken-167.  Based on the discontinued Fostex FE-167e.
The bottom of the cabinet is a sealed void.  In the photo I  noticed a version with a woofer.  Would that be on a passive crossover? 
I found this source with many crossovers to choose from.
 

 

[tomchr]

  Dave at Planet 10 sent me the Fonken-167.  Based on the discontinued Fostex FE-167e.
The bottom of the cabinet is a sealed void.  In the photo I  noticed a version with a woofer.  Would that be on a passive crossover? 
 

 
It could be a passive radiator. So basically a speaker diaphragm without a voice coil driven by the pressure inside the cabinet. But I don't know. I'm sure Dave will be able to answer that question.
 
~Tom

 

[sceleratus]

He did. Needs an amp and an input channel.
The 167 is obsolete so the plans are obsolete.  They were provided as an example.
 
There are a dozen other plans.  Pick a driver and take your chances.

 

[tomchr]

  There are a dozen other plans.  Pick a driver and take your chances.

 
Pretty much. I've listened to Dave's designs as well as some where his enclosures were used with other drivers. They all sounded good. The only driver I didn't like so much was the Mark Audio CHR70 as it tended to suffer from a rather harsh cone break-up (pretty evident in its response curves as well). That's another driver with a diaphragm made from Reynolds Foil. Me no like.
 
~Tom

 

[sceleratus]

I dropped off the materials to have a new rear panel cut from T6061-T6  0.08" AL-LOU-MINI_YUM
Since the cost of materials and cutting for a 24" x 48" was the same as a 24" x 24", I had extra panels cut.
 
I moved the filament stack from the center to the left and reduced the depth by 1.50" 
 
If anyone wants a set it will only be the cost of postage.
 
 
UPDATE:  I picked them up today and they look great.
I polished the rear plate I am going to use.