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Alternate source for Millet-Hybrid PCB - Page 3  

post #31 of 589
Quote:
Originally Posted by individual6891
Will a diamond buffer be absolutely necessary? Modifying another circuit are you absolutely sure you can guarantee stability?..Which would require extensive prototype testing..

Diamond buffers designed from scratch to fit a specific circuit run into stability problem - is there such a thing "universal diamond buffer" out there? I maybe wrong, but I was under the impression that diamond buffers were very sensitive to the components around it..
Yep, that's a problem. What I was getting at was that there are quite a few topologies out there. There is not one universal diamond buffer, but several different implementations. Component selection is, of course, the key.

It may be best to leave the output buffer as a DIP8 part and not even mess with trying to get something on the PCB. That would make the whole prototyping issue much easier by reducing the number of things that can go wrong. It also would let me reduce the board size and still leave an option for those who want to pursue a diamond buffer.

To answer your question, no, a discrete diamond buffer is not necessary.

-Drew
post #32 of 589
Does the BUF634T get hot in the millet hybrid circuit? Of course a DIP8 package would be preferred, but maybe there was a reason pete chose the TO220 package?
post #33 of 589
Quote:
Originally Posted by individual6891
Does the BUF634T get hot in the millet hybrid circuit?
It doesn't even get warm. The heatsinks are totally unnecessary.

-d
post #34 of 589
Quote:
Originally Posted by individual6891
Does the BUF634T get hot in the millet hybrid circuit? Of course a DIP8 package would be preferred, but maybe there was a reason pete chose the TO220 package?
No more than in any other headphone amplifier. The BUF634's thermal protection circuit kicks in at 175C which is very, very hot. I suspect that he chose the TO220 package because it is the most thermally conservative one available. Pete didn't address his choice of buffer package in the AudioXpress write-up, but considering Ohm's law, the output buffers ought not to dissipate more power from this amplifier than from a solid state model.

-Drew
post #35 of 589
Dip-8 it is then
post #36 of 589
Dip8 will also allow for easy stacking of BUF634s like in the Pimeta.

My only other suggestion is to allow plenty of space for electrolytic and film caps. It might be nice to give multiple hole options so people can easily use the Blackgates or Panasonics of their choice.
post #37 of 589
I've started on the redesign of Pete Millett's amplifier. I've reduced the board size from 32 square inches to about 26. There is still plenty of work to do, especially with the electrolytic cap placement and some of the currently awkward routing, but this should give everyone a feel for where the board is headed. I've left some space around the buffers for anyone who wants to experiment a bit. There is not enough space around some of the caps and I'll fix that. The signal inputs have a nice ground plane except for one spot on the left channel grid input.

Please, please, please, if you have any interest in this project, post some suggestions for things that you'd like to see included in a basic, low cost, easy to build entry level tube amplifier.

Board image (no fill): http://img.photobucket.com/albums/v4...wd/millett.jpg

Board image (fill): http://img.photobucket.com/albums/v4...llett_fill.jpg

Rendered image: http://img.photobucket.com/albums/v4...ybrid_head.jpg

-Drew
post #38 of 589
Thread Starter 
Drew, I know this runs contrary to the current layout (which I like a lot ) but I think conventionally minded people might have expected the volume on the short end of the board with the tubes running back in line behind it. That way you might fit this thing in a standard hammond case (not my plan) and use an external powersupply.

Personally I'm envisioning it in a case somewhat like your Ascent with a center pot just like you've got it now. But that's just me.

Any thoughts?

Nate
post #39 of 589
Aye, a lengthway PCB would allow for a larger variety of enclosure options.. Maybe even a possibility of fitting into into eurocard size?
post #40 of 589
Drew, could you possibly change the trimpots on the board to Bourns type 3296? They are a bit larger, but much easier to find replacements for than the current type


/U.
post #41 of 589
Roger dodger on the three previous suggestions!

-Drew
post #42 of 589
A quick update. This is single Eurocard sized, 100x160mm. The usual caveats apply - very preliminary and needs substantial refinement, but I'm interested to hear if the general layout seems acceptable.

http://img.photobucket.com/albums/v4...brid_head3.jpg

-Drew
post #43 of 589
Yeah that looks quite nice..

Any chance of leaving about 3-4mm space on the sides (down the lengths) so they might fit better in cases with PCB slots (hammond, bopla etc). Also make sure there's enough space for mounting holes in the corners for those who don't use a euro-card pcb enclosure.

Also any chance of changing the trimmer pot to use 3 x 0.1inch spacings as Nisbeth suggested? Or maybe even a way of using both layouts like you have done in with the vol pot? Though this isn't a major issue, the trimmer pot spacing is still widely available, just though some people may prefer to use the bourns.
post #44 of 589
Quote:
Originally Posted by drewd
A quick update. This is single Eurocard sized, 100x160mm. The usual caveats apply - very preliminary and needs substantial refinement, but I'm interested to hear if the general layout seems acceptable.
Sure does !

/U.
post #45 of 589
Quote:
Originally Posted by individual6891
Yeah that looks quite nice..

Any chance of leaving about 3-4mm space on the sides (down the lengths) so they might fit better in cases with PCB slots (hammond, bopla etc). Also make sure there's enough space for mounting holes in the corners for those who don't use a euro-card pcb enclosure.

Also any chance of changing the trimmer pot to use 3 x 0.1inch spacings as Nisbeth suggested? Or maybe even a way of using both layouts like you have done in with the vol pot? Though this isn't a major issue, the trimmer pot spacing is still widely available, just though some people may prefer to use the bourns.
Yes, I'll adjust the routing to leave some space for the grooves and I'll put some mounting holes in the corners - good ideas.

I'll also use the Bourns trimmers. I'm going to look through the DigiKey and Mouser catalogs and make sure that the component sizes on the board match what is available from those catalogs.

-Drew
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