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Millett "Starving Student" hybrid amp - Page 411

post #6151 of 7056

wow...I just finished etching a board and populating mine for a plastic enclosure... I hope I dont have too many noise issues with it. The amp will be standing up when finished...I took the pictures with it laying down. I hope to finish it in the morning.









Edited by vixr - 7/7/12 at 8:05pm
post #6152 of 7056

Looking good vixr!

post #6153 of 7056

After a few hours of research, I came to the conclusion that not having at least a ground plane is a bad idea. I also found that the unshielded tubes will pickup the interference from wifi networks.


All this is leaving me very disappointed in my design. I expected the electronics to be more troublesome, but it turned out the casework is the thing that makes me scratch my head the most. confused_face.gif


Now I'm thinking just scraping the case and rebuilding the amplifier inside an Hammond 1444 enclosure. Not the sexiest thing, but possibly more functional. Edit: Just found out Hammond 1455 have slide out bottom. I'm so ordering one from my local supplier, today.



On a different note, I'm currently testing the NOS Sylvania 12AU7 I spent almost 50$ on. I can barely pick any difference between them and the new Sovtek 12AX7. Just for fun, I'm currently using one of each in different channel. Using software balance, I only have to move the balance by 7% to get the volume equal on both channel. That's far less significant that I was led to believe.


And I honestly could never tell which channel has which tube in a blind test. Which forces me to conclude that, for the SSMH, spending 50$ or more on the tubes alone is probably not a good idea.

Edited by KimLaroux - 7/9/12 at 12:13am
post #6154 of 7056

here are the latest pics of my MHSS.









post #6155 of 7056

Well, that's a novel chassis. If you aimed for Extravangant, I believe you didn't fall far off. It looks like the type of prop you bring to a science fair. Mind if I dub it "The Unorthodox Millet Hybrid"?


Lemme know if you get humming or interference issues. On my part, I have an hammond 1455 on order. I should receive it this week end. I'll reshell the whole thing into the aluminum enclosure and take the opportunity to change the MOSFET heat sink for something more efficient. I'll then see what I can do to shield the tubes themselves. I'm thinking a cage made of perforated metal.


I learned an important lesson with this build: There is more to an enclosure than just looks. Or at least it is so with these types of audio amplifiers.


The question that haunts me right now is, is this only relevant to P2P wiring? Because from what I have gathered, amplifiers built on PCBs don't seem to mind plastic enclosures.

post #6156 of 7056

Hahahahaaa!!!   It is unorthodox... I'm using a home made PCB with a ground plane and a wall wart for power, so I have my fingers crossed that there will be no noise. I have some metal braid to put over the volume wires, or where ever its needed, just in case. The other purpose of building it tall like this is it will also be a headphone stand...picture my HD-600s hanging on the amp. I dont know about P2P being more prone to noise, but I used metal cases and a ground plane on both of the others I've built...zero noise. Good luck with the new build.

post #6157 of 7056

I received the hammond enclosure yesterday. I'm really impressed by this thing. It's made of 2mm thick aluminum and even their largest case (6.5" X 8.66") is impossible to bend with your hands. I was concerned I'd have to reinforce it to support the transformer, but this won't be necessary after all.


I also got a bunch of bigger heat sinks. All I got to do now is figure which one to use.


Hammond_HeatSink_Choices_2.jpg Hammond_HeatSink_Choices_3.jpg


Either way I'll cut the excess from the heat sink, so it won't look exactly like that. The one on the left picture is too long, and the one on the right picture has tabs that aren't used in my application.


I ordered a couple of step drill bit from Amazon, so I suppose I have until I receive them to make up my mind. Any inputs?

post #6158 of 7056

I like the one on the right...

post #6159 of 7056

Cool design Vixr! I really like that.


 Kim, interesting what you said about picking up wifi interference. I built my MHSS quite a while back, when you could still get the 19J6 for a couple dollars. All components are exposed on top of a perfboard, except resistors. They’re inside the enclosure with Cat5 P2P tying everything together. The amp always sits in front of my computer monitor and I listen to it often.


Pic:  http://bellsouthpwp2.net/k/a/karlet/BigCaps2.jpg


 When I turned it on last night I was getting a clipping noise in both channels. The noise level was independent of the volume control. I swapped the Cisco power supply with another but same issue.  I was about to open the case and test for a bad connection when I noticed moving the amp changed the sound. Moved the amp just a few feet away from the desk and the noise disappeared. Never had interference issues previously.


 It turned out to be the new wireless modem/router sent by my ISP when I upgraded my service this week. Until now I had a modem from the ISP but connected my own Linksys wireless router. It sat about a foot or so to the side of the amp. Never had any issue.

post #6160 of 7056

Indeed, we bath a electromagnetic radiation nowadays. In here we have two wireless routers and at least a dozen machines connected to them. On my desk I have my laptop and my phone connected with wifi to the router under the desk. At this point, the only solution is to shield the amplifier. I can't live without wifi, but I can live without the amp. wink.gif


Though building a tube amplifier that is shielded from wifi is an interesting challenge. Here's a picture of my progress so far.




It's the first time I use stepped drill bits. It's quite a pain to use with a hand drill, and I'd venture to say they would be less so from a press drill.


Machining is done, next step is to paint the enclosure in a piano finish black. biggrin.gif I'll then assemble the amp, and see if the tubes still pick up wifi. They probably still will. If they do, I'll build a Faraday cage around them.

post #6161 of 7056

I need a new headphone amp and it looks like it would be really fun to build one but I know next to nothing on how to read schematics and most of the knowledge required to build an amp. Is this an easy enough project that I could pick it up on the way or is there an easier one I should look in to?

post #6162 of 7056
Originally Posted by audio snob View Post

I need a new headphone amp and it looks like it would be really fun to build one but I know next to nothing on how to read schematics and most of the knowledge required to build an amp. Is this an easy enough project that I could pick it up on the way or is there an easier one I should look in to?


I would not recommend starting with this amplifier if you can't even read a schematic. I'd recommend it only if you can find one of the original kits with the PCB, but from what I know, these are not available anymore. To build this amplifier now, one only has the schematic to work with. You have to acquire all the components and then either construct your own circuit board or build the amplifier with point-to-point wiring. Sure you learn a lot of things along the way, but it might be too steep of a learning curve if you start from nil.


If you search on ebay for "headphone amp* kit" you will find hundreds of complete kits ranging from 10$ to 200$. At around 20$ you can buy a RA1/Cmoy kit, which can be built quite easily. If you never assembled electronics, I would recommend you buy such a kit and assemble it just to gain the experience. If you find it enjoyable, then you can get a Project Sunrise II for 200$. Don't forget the enclosure when considering these kits. Some of them come with pre-machined cases, which makes things a lot easier and often allow for a cleaner finish. Buying an enclosure separately add to the final cost and complexity, since you have to machine it yourself. 


Either way, you will need the same tools: a soldering iron, solder, solder paste... a multimeter, pliers, wire cutter, flush cutter... If you don't have the tools, you'll have to acquire them before you start any electronic projects. I also recommend you read forum threads and web pages related to the kit before committing to them. These are good resources that can makes things clearer, or simply conclude that a particular kit is to be avoided.




As for my Starving Student, I started the final assembly today. Here's a picture of what my desk looked like this morning:




I think the paint job turned out alright. Sad I don't have a camera good enough to give it justice. Can anyone guess the one thing that's missing in this picture? biggrin.gif

post #6163 of 7056

Ok ill look through ebay for something like that. Thank you for the advice. I believe I have all the tools that are necessary for this and more. Are there any easy kits that sound very good or is it more for the sake of building than sound?

post #6164 of 7056

no chance anyone has a 12au7 version in a schematic file/pcb layout program or in a format I can send to a cnc?

post #6165 of 7056

I just finished version 2 of my MSSH.


I think it looks cleaner than the first version.

778edc75_Hammond_Finished_22.jpeg aa0e2ab2_Hammond_Finished_24.jpeg


The enclosure is shorter than the original, but it's both wider and higher internally. I had to rebuild the whole PSU from the ground up to make up for the lost length, while making use of the extra width. I think the end result is pleasant looking. Of course I learned many thing from the original design, which were lessons applied to the revision.



The new enclosure fits perfectly atop the Audio-gd NFB-12.



I built Faraday cages around each tubes in an effort to shield them from EMI. They are made of steel mesh, which were grounded. I expected this to be the end game for interference, but WiFi still gets trough! I just don't understand how this can be, 2.4Ghz has a wavelenght of about 12cm, while the holes in the mesh are 1mm. They do keep the AC hum out of the tubes though. I tried the amplifier before installing the cages and there was bad magnetic coupling between the transformer and the tubes. It's gone with the cages.


I guess I have to redo my homework... confused_face(1).gif

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