[lampee]

Hi Everybody!
 
I would like to share my ideas with you, and if the thought are positive and I will have enough budget, then the project will begin, and I will post the pictures here.
 
The things I would like to build into the amp:
 
- PCB made by me with copper clad laminate, FeO3 acid etc.
- 4channel on the PCB (or 5)
- seperate power supplies (two sigma11)
- variable gain
- balanced / unbalanced selection
- if it is possible, I would like to build a little circuit which could convert one channel to active ground (I don't know if it's a stupid idea or not, I would like to hear the oppinions)
- built in speaker / headphone selection (probably with relay)
- I would like to use the amp as a speaker amp too, like it's mentioned on amb's site, so it would provide 20Wrms to an 8Ohm speaker
- I don't know If it's better to put the power supply into the box or separate, but probably seperate enclosure
- It could happen that I build a 5th channel just to use the amp as 3 channel active ground topology (if the conversion is not possible)
- unbalanced balanced conversion to make the amp get unbalanced and output 20W to the speakers
 
Now please tell me if my ideas are completly stupid or not and share me your ideas with this project or the opinions.
 
Lampee

 

[MASantos]

Hello welcome to head fi!
 
If you wish ti do your own pcb for an m3 you should first speak with AMB and ask his permission as he is the designer and owner of the M3 project.
 
Your idea sounds good, but I think it would be easier to build 2 M3 boards, the 2 sigma11's and a nice stepped attenuator and case. 

 

[regal]

He doesn't need permission for a one off board,  you can build any patented piece of equipment you want for personal use,  thank God we have a few rights left.

 

[nattonrice]

On the other hand if he involves Ti from the start he may be more amicable to giving some pointers if he gets stuck.

 

[K3cT]

I don't understand the point of building your own PCB when a ready version is available...

 

[cobaltmute]

Wouldn't you end up with something a bit  like this?
 
http://www.head-fi.org/forum/thread/449462/the-m4-a-fully-differential-single-pcb-amplifier-with-relay-attenuator

 

[K3cT]

Quote:

Wouldn't you end up with something a bit  like this?
 
http://www.head-fi.org/forum/thread/449462/the-m4-a-fully-differential-single-pcb-amplifier-with-relay-attenuator

That's hella interesting! Thanks for the heads-up, cobaltmute.

 

[lampee]

I thought about built in relay  based stepped attenuator, but I think it will be a long time from the design period to the ready and working amp, so anything could change.

 

[lampee]

Hi Everybody again!
 
I designed the 2 channel board for the m3 balanced, so two of these will drive the headphones and the speakers. The power supply is not in the design yet, but as soon as I have time I will post it too. Please recommend any modifications or simplifications or anything useful for me.
 
If somebody could help me how to modify the power planes on the top of the schematic so it would look like the other two, I would be really thankful. I can't modify the polygons, so I can't put another lineinto it, I can only remove the them.

 

[lampee]

Ok, I corrected the power plane, but I don't think it is necesarry to post the new picture. I will update the project, when the power supply is also intgrated.

 

[francisdemarte]

This is a really interesting thread! Hopefully AMB will chime in and provide some feed back too.

 

[MASantos]

If you wish to make a fully balanced amplifier with make 2 x 2 channel boards? Why don't you go with 1 board with all the 4 channels in it?
 
Also, since you're making this a balanced amp from the ground, take a look at the B24 project from AMB here: http://gilmore2.chem.northwestern.edu/ubb/showpage.php?fnum=3&tid=7227
 
and see how you could apply the full differencial design here. What I am proposing is to instead of just taking the m3 and adapting it with a new pcb, why not take the concept and revamp it a little bit with AMB's permission and make a fully differential headphone amplifier! I believe that would bring much more interest to this project, me included!
 
In any case, good luck! 

 

[lampee]

 
Quote:

If you wish to make a fully balanced amplifier with make 2 x 2 channel boards? Why don't you go with 1 board with all the 4 channels in it?

 
I think the PCB would be too big to make it with the printing-ironing method. Now it's around 4"x4" + there would be the sigma11 attached, so it sould be around 4"x7" or so.
 
I am considering the fully differential design, but I think the OPA627 can't do that, and I can't do the wiring to make it doing that. Could somebody recommend a fully differential state-of-the-art opamp, so the amp could be the best opamp best FD headphone amp.
 
Lampee

 

[lampee]

Could anybody tell me which is the best fully differential OPAMP?

 

[amb]

"Best" how?  Whenever someone ask "What is the BEST of this or that", 99% of the time there is no right answer.
Given that there are not many fully differential opamps out there, it does narrow the playing field to just a handful.  I would look at the OPA1632, but there are others which are also interesting.  Note that using a fully-differential opamp is quite different than a "normal" opamp, and puts some constraints on input impedance and choice of feedback resistor values, how you implement the volume control, and your choice of volume pot value.