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24.27.41.140
This is 30W per channel, 20Hz - 40 kHz response and less than 0.05% THD at 5W output. I'm hoping all the CAD work and measurements that went into this will transfer to two or three future units. My time to build this was worth about 25¢ an hour. :)
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Buy Chinese. Bury freedom.
Follow Ups:
Nice work.
Nice work there. A bit light on Iron for my personal stuff, but this clearly isn't that. By its specs, the output iron is doing its job. Do try that one with a LTP front end and some local FB instead of the global loop, or the SP10/20 mix around a pair of 6AU6 drivers... :)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Can you describe a bit how you constructed the Chassis ?
Thanks. The chassis was fabricated from a long 10" x 2" aluminum extrusion. It was cut to a length of 14" for this project. The material is 1/8" thick. The front panel is cut from 1/2" 6061 aluminum and is attached to the chassis with brackets bolted to the sides. The two internal sub-chassis are also bolted to the sides. The oak side panels have threaded brass inserts and are attached with screws from inside the chassis. The rear panel is 1/8" aluminum and is attached to brackets bolted to the sides and bottom of the chassis. That's the basics. :)
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Buy Chinese. Bury freedom.
Did you do all the Chassis work yourself or did you contract it out? --- It's very, very nice.
Thanks again. I do all the work myself - cutting, engraving and anodizing. The most difficult and time consuming part is surface prep, and to say I don't enjoy it would be an understatement. I have two more chassis like this cut to size. When they're used up, I'll probably go to Landfall Systems for future projects.
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Buy Chinese. Bury freedom.
Excellent work. I've got a few of the Landfall chassis here...they are quite nice.
Is the front end a concertina phase splitter type? Do you end up using a cap to fine tune your global feedback loop?
The splitter is a DC-coupled LTP. Yes, I tuned the feedback loop and also the HF network at the anode of the preamp tube.
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Buy Chinese. Bury freedom.
I like the bias adjust panel underneath. Do you mind if I borrow the idea on my next project? ;-)
An upper-class design effort on all aspects. Respect!
Joris
Thanks! Feel free to make use of any of the techniques you see in these photos.
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Buy Chinese. Bury freedom.
Very difficult!
I have been lately resorting to a pretty amp with a remote black box power supply connected with Amphenol military connections.
Looks great, professional appearance.
Did you check THD at MAX power output?
DT667
"Did you check THD at MAX power output?"
Yes, but the question puts the cart before the horse. When making the measurement, it has to be decided first what level of distortion will be used in determining that maximum output has been reached. I use 1%, because A) that's the level at which most people can first begin to identify the effect as actual distortion, and B) the amplifier should only ever reach this level on brief, intermittent musical peaks. Here are the final specs for distortion:
5W output: < 0.035% THD, < 0.1% IMD
30W output: < 1% THD, < 1% IMD
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Buy Chinese. Bury freedom.
Very nice work as usual.
How do you do your lettering?
Thanks. The markings were engraved using a CNC mill.
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Buy Chinese. Bury freedom.
Thanks for everyone's kind comments.
This amplifier was built around a transformer set removed from a Harman Kardon TA7000X receiver. The drivers each consist of a 6J32P (EF86) in triode mode driving a hand-selected Telefunken ECC91 (6099 equivalent). Outputs are fixed-bias 6P3S-E. About 20dB of GNFB is applied. The screens of the outputs are fed from main B+ through two 0B2 VR tubes. This reduces screen voltage enough to be compatible with most 6L6 types, including early variants.
Most of the other features that I included are visible in the pics below. If all goes well, I'll do a few more like this in the next year or two.
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Buy Chinese. Bury freedom.
You, sir, have skills. That is indeed lovely work and overall beautiful amp. I bet it sounds as good as it looks.
Lovely work. Great to see the insides too. Looks well planned out.
Thanks for sharing.
and you should get some kind of prize for sticking your fingers in there to do the work. Nice!
The most challenging part of this project was the large amount of metalwork. The physical design began with the premise of hiding all the attaching hardware, excluding transformer bolts. Hardware is only visible on the rear panel and bottom cover. This concept necessitated constructing two separate sub-chassis, and the CAD work was pretty intense. The second most difficult area of construction was dealing with only 1.75" of interior height.
I have a few more raw chassis like this cut to size. Those might not be completed in this same way. It's much faster to bolt sockets and other parts directly to the top of the chassis. That also leaves more space inside for components. I'm not getting younger, so this might end up being the only amp I ever construct like this.
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Buy Chinese. Bury freedom.
The cadd work can be time consuming unless you do it every day. I'm much better at cadd than I am at design so it was a piece of cake for me. That pre planning and level of machine work really makes your amp look that much better. When you did the lettering, how deep do you go and is the coloring done by hand and if so, what is your method?
Ahhh, those details are the nitty-gritty of the process. It's astounding how many posts I've seen on machining and finishing forums asking how to accomplish this. I should probably charge for this highly proprietary information. LOL, here's how it's done:
Lettering is engraved with 0.015" to 0.022" diam. end mills. The depth is typically .006" to .008" with the mill running about 10K RPM. The panel is smoothed one more time after engraving to remove burrs and sharp edges around the work. Next, the surface gets a brushed or swirl finish, depending on the look desired. After that, the piece is degreased and clear anodized. Finally, the engraving is filled with high-quality enamel and left to cure for a day or two. Filling is a process in itself, and the technique requires practice. Essentially, the enamel is flowed over an area containing markings, then most is wiped off with a squeegee. After curing for an hour or two, the area is wiped down with thin, lint-free paper dampened with a relatively slow drying solvent such as Xylene.
Really, if you could see how much time I spend on this, and how much I've spent over the last 10 years perfecting it, you'd think I'm nuts. Actually, I probably am. :)
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Buy Chinese. Bury freedom.
engraving.
That sound like a lot of work.
Great work TK. Looks beautiful.
Enjoy!
Great looking metal work too.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Hot Darn! I enjoy seeing other people's vision being made manifest. Clean lines and no nonsense is what I see and of course being the inveterate whack job that I am... 'Wonder what it sounds Like?', thank you for sharing TK.
The Mind has No Firewall~ U.S. Army War College.
Any chance to see what the underside/inside looks like and could you talk about the tube compliment .....are those el34's?
thanks
I like it.
Omnes feriunt, ultima necat.
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