Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Millett "Starving Student" hybrid amp
New Posts  All Forums:Forum Nav:

Millett "Starving Student" hybrid amp - Page 450

post #6736 of 6757

I am guessing the PSU you found is a switcher. If it was me, I'd not encase this inside the same enclosure as the amplifier itself. It's asking for troubles.

 

As for powering the amp from a lower voltage... Why would you even wanna do that? Tubes benefit from more voltage, not less.

 

It'll work, but you'd have to recalculate all the resistor values. I currently have my output stage working at 25 V just fine. Though the tubes are powered from a 138V rail.

post #6737 of 6757

Hi Kim!

 

I have read a bit about your build of the SSMH and it seems you've had a great deal of trouble, I'm sorry to hear that. What are the key issues that you needed to resolve? You are the only one I've seen with cages around your tubes, Why is that? Why does it not go well with sitting on top of your DAC?

 

The reason for wanting to power it from a lower supply voltage is only because I had found a 30V supply readily available as well. I do believe you're right in that it's asking for trouble to box a switched supply within the amp. In the meantime I found wall warts available in a range of wattages as well, so I'm gonna go for that anyway.

 

What is the benefit of more voltage in this application? Does it reduce noise?

 

My big question now is: Will a 313mA (15W) power supply will suffice? I know the suggested one is around 387mA IIRC. Has anybody measured the actual current draw of the amp? I have simulated the quiescent current to about 151mA/channel. Which only leaves me with 28,65mA to spare if the supply delivers exactly to spec up to its worst case OL protection. If I find one I'll make sure to go with a beefier one though.

 

//Swek

post #6738 of 6757

Wakibaki, tomb,

We now have a fully fledged SS.

Assembled, tested and it still sounded terrible (can string styles)... grabbed my 880's and wow what a difference. Night and day.

 

Anyhow thanks again, much appreciated!  And big thanks to Pete!  I'm off to listen to some music.  :L3000:

post #6739 of 6757

Well, Yesterday I modified it again and I am happy to report I finally nailed it. My amplifier is now quiet to an acceptable level! :k701smile:

 

 

After two years, it was about time. And wow did I learn a lot in the process.

 

I'll borrow my friend's camera tomorrow to take good quality picture. Though it's not much of a MSSH anymore.

 

Quote:

Originally Posted by swek View Post
 

Hi Kim!

 

I have read a bit about your build of the SSMH and it seems you've had a great deal of trouble, I'm sorry to hear that. What are the key issues that you needed to resolve? You are the only one I've seen with cages around your tubes, Why is that? Why does it not go well with sitting on top of your DAC?

 

The reason for wanting to power it from a lower supply voltage is only because I had found a 30V supply readily available as well. I do believe you're right in that it's asking for trouble to box a switched supply within the amp. In the meantime I found wall warts available in a range of wattages as well, so I'm gonna go for that anyway.

 

What is the benefit of more voltage in this application? Does it reduce noise?

 

My big question now is: Will a 313mA (15W) power supply will suffice? I know the suggested one is around 387mA IIRC. Has anybody measured the actual current draw of the amp? I have simulated the quiescent current to about 151mA/channel. Which only leaves me with 28,65mA to spare if the supply delivers exactly to spec up to its worst case OL protection. If I find one I'll make sure to go with a beefier one though.

 

//Swek

 

The only problem I've been fighting ever since day one was noise. For me this project started when I salvaged a transformer from an old stereo. The transformer has many taps, with the outmost set offering a nice 27-0-27 volts. Rectified, it gave me well enough tension for a linear regulated 48 V rail. When I figured that out, I went "Challenge accepted!". The goal of this project was to learn, not to have a final product.

 

The problem is, going this route means introducing mains AC into the enclosure, and bathing the whole thing in electromagnetic interference from the transformer. Those two things together means I'm shooting myself in the foot from the start. Even a perfectly quiet linear PSU will have its output corrupted if the wires pass too close to any wire carrying AC. I learned the hard way how important the layout of the internals is. Once you mix AC and DC together, building the amp becomes a lot more than replicating a schematic. Oh and grounding scheme is the most voodoo thing ever.

 

The cages around my tubes are there because the tubes are so close to the transformer, there was some magnetic coupling between them and the transformer. They picked up a 60hz wave along with all the nastiness of AC. It was ugly. The cages are ferrous and grounded, allowing them to efficiently shield the tubes from electromagnetic fields. Oh and not to mention I keep the amp on my desk surrounded with wifi, bluetooth, cellphone, wireless mouse... Unshielded, the tubes picked up the modulation of these signal. 

 

As for the DAC, I suspect there was some coupling between the circuit of the amplifier and the toroidal transformer inside the DAC. But that's almost expected if I stack them directly on each others. There is no problem if they are side by side.

post #6740 of 6757
Quote:
Originally Posted by the_Samurai_chicken View Post
 

Wakibaki, tomb,

We now have a fully fledged SS.

Assembled, tested and it still sounded terrible (can string styles)... grabbed my 880's and wow what a difference. Night and day.

 

Anyhow thanks again, much appreciated!  And big thanks to Pete!  I'm off to listen to some music.  :L3000:


OK - guess it was the coupling capacitors on the output, then.  You could always upsize them if you really wanted to use it with those earbuds/IEMs.  470 uf can make a huge difference and if you've built everything custom, 1000uf might solve the entire issue.  The only thing you have to worry about is the size of the capacitor (they get bigger).

post #6741 of 6757

Question to all the SSMH owners: What's your source for the amp?

 

I am building SSMH and would like to use it as a bedroom headphone system but space is limited so turntable or HTPC as a source are out of the question. This leaves me with DAP (digital audio player) but maybe I am missing something that would also work with SSMH.

post #6742 of 6757

Hi everyone!

 

My name is Jonas and I'm from Uppsala, Sweden.

 

Been working on this amp (12AU7 version) for a week or so after waiting for all parts to arrive. Maybe it's wise to state that this is my first real electrical project ever so I am a novice (who might make stupid novice mistakes, but hey, that's what life is for).

 

After putting it together I tried to power it up and I'm experiencing some problems that I need some help with, I can post pictures and more detailed info if needed.

 

Anyway, I'm using the Cisco 0.38A PSU and my problem is that I don't get sufficient power into the circuit. When I have the tube sockets empty (tubes disconnected) voltage between the drain-pin and ground is 48V. When I insert the tubes, voltage starts to fluctuate (at regular intervals of XXXms). When I have one tube in, voltage at MOSFET drain fluctuate between 10 and 15 volts. At tube pin 1+6 it fluctuates between 3 and 6 volts. I don't know what this could indicate (if I've broken some component or if I have made some mistakes with the wiring). I might add that at first start up, I had the MOSFETs short circuit through improper isolation from the chassis (used metal screws....). Could the MOSFETs have burnt (what does this mean) and causing this behavior? Is there a way to test them using a multimeter?

 

Anyway, if someone has any ideas on how to proceed with troubleshooting I would appreciate it. As I said, if picures are needed I can supply them.

 

Oh, I can post a picture of the (non-working) exterior: http://imgur.com/dt8IlgG

 

/Jonas


Edited by fugelpitch - 2/22/14 at 12:36pm
post #6743 of 6757

Hi

 

Total newbie but inspired by the whole DIY thing :)...

I have had a go at the SSMH and I am very happy with the case and look, but something is not quite right :(

The sound is very quite!!  Probably my interpretation of the schematic to stripboard... (experts out there will probably laugh at the design!)...

Any help or pointers would be greatly appreciated!

(link to pics and a jpg of my board setup - hopefully understandable!!)

 

Thanks....Tony

 

http://1drv.ms/1cBni9e

post #6744 of 6757

Phew!! solved :)

 

Forgot to break the tracks under the 2 vertical resistors (R1, R7)  :)

 

LOVE the sound!!!

 

Thanks to Pete and all who have put useful info on this forum (and the creator / modifier to accept 12AU7's... ) - from total newbie and hooked!! - now looking for next project (where do I progress from here folks?!)

 

Tony

post #6745 of 6757

Hi mates.
I begin to build an SSMH amplifier. Is my firts DIY :atsmile:
I wish to know what configuration you recommend to me for a SSMH 12au7:
10K pot and R16 & R17 10K or prefer 50K pot and R16 & R17 50K?
I will use for headphones from 80ohm up to 250ohm.
Thanks on advance.

 

Cheers

 

toni

 

P.D.(If you can tell me pros and cons, thanks :beyersmile: )

post #6746 of 6757

I'm drawing a PCB with 12au7 version but i'm wondering that does pin 9 of tube need to connect to ground?

post #6747 of 6757
Quote:
Originally Posted by proid View Post
 

I'm drawing a PCB with 12au7 version but i'm wondering that does pin 9 of tube need to connect to ground?

I do not know the answer to your question, but you can get PCBs from Fred. Check this thread for more info:

 

http://www.head-fi.org/t/664191/starving-student-pcbs

 

I have ordered two and they arrived fast (though remember that based on where are you located, they may be shipped across the World). Price is good too.

post #6748 of 6757
Quote:
Originally Posted by proid View Post
 

I'm drawing a PCB with 12au7 version but i'm wondering that does pin 9 of tube need to connect to ground?

Leave pin 9 unconnected, it is the center tap of the two heaters and we need them to be in series

 

cheer

FRED

post #6749 of 6757

Hello
Solved the potentiometer matter now:
Can I use tinned wire? or is prefered use a normal copper for pot and tubes extension cables.
I read in one forum the tinned wire do bright and syntetic sound, is it true?
Thanks so much.

Toni

post #6750 of 6757

Copper is fine, don"t over think it :-)

 

cheers

FRED

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Millett "Starving Student" hybrid amp