A really hot SMD current feedback headphone amp
Nov 19, 2003 at 8:29 AM Thread Starter Post #1 of 33
peranders

peranders

Member of the Trade: Sjöström Audio
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Hi!

Is anybody interested in a small cute SMD current feedback totally discrete built headphone amp?

Those of you who are interested can download the schematics for simulation. I have used the freeware LTSpice.
http://www.diyaudio.com/forums/showt...642#post266642

I got inspired when I did the Diamond buffer. I think the pcb will be four, five times the area of the pcb below, 2.5" x 2.5". The pcb below is 1.4" x 1.475 "

qrv05r0_topview.jpg
 
Nov 19, 2003 at 5:07 PM Post #2 of 33
Very cute, peranders. Can you post a gif or jpg of the schematic for those of us who don't want to install LTSpice? BTW, what's with the Lithops icon over at DIYaudio?
 
Nov 19, 2003 at 8:53 PM Post #3 of 33
Thanks, Morsel. I will post schematics later on. In the meantime everybody can have it if you send me an email.

The amp look like the discrete part of QRV-03 with a diamond buffer at front.

I have started to make the pcb and it will be 2.8" x 1.6". EDIT: 1.875 x 3.000" when it was finished...

Simulated performance DC-25 MHz and low distortion. I expect at least over 5 MHz.

Right now I'm think of if the pcb should have any regualtors on board or not. Maybe Jung Regulators? A little overkill maybe?

Do you know about Lithops, Morsel? I like them and this fall two of my Lithops have flowered! Lithops optica is cool with it's purple colour. I have bought seeds from Mesa Garden and Succseed
 
Nov 27, 2003 at 12:46 PM Post #5 of 33
The size is 1.875" x 3.000". Totally DC-connected and capable of DC-25 MHz according to simulations. I gather that I won't reach 25 MHz but a couple MHz at least.

Pictures can be found here.
http://www.diyaudio.com/forums/showt...threadid=23241

In a couple of days I will start building the amp.
 
Nov 27, 2003 at 5:49 PM Post #6 of 33
I do like Lithops and grew them along with other succulents when I was a kid. I have only seen yellow flowers on Lithops optica, I guess you have an interesting variety. Many of my favorite Mesembryanthemums have purple flowers, though. I also like Drosanthemum, Lampranthus, Conophytum, and many others.

Let us know how your new amp works out. Are you going to try it in a balanced or differential configuration?
 
Nov 27, 2003 at 6:38 PM Post #7 of 33
One thing I've noted on both this PCB and the BUF634 board is that it doesn't seem that copper is used on the boards for heatsinking. For example, the BUF634 spec sheet recommends up to 4 square inches for heatsinking (using thermal vias to the V- power plane helps with the BUF634). With SMT components it is difficult to attach other forms of heatsinks. Thermal considerations, of course, are important for class A amps. I would be interested to learn how warm the output transistors run. For optimal performance, I'd like to use as much heatsinking as possible. Maybe you find that heat is not a problem with your circuit...


JF
 
Nov 28, 2003 at 6:13 AM Post #8 of 33
Quote:

Originally posted by morsel
Are you going to try it in a balanced or differential configuration?


Not really but there are two identical channels so it's not hard to at least use the pcb in balanced mode if you already have a balanced signal.

Quote:

Originally posted by morsel
I do like Lithops and grew them along with other succulents when I was a kid. I have only seen yellow flowers on Lithops optica, I guess you have an interesting variety. Many of my favorite Mesembryanthemums have purple flowers, though. I also like Drosanthemum, Lampranthus, Conophytum, and many others.


Most Lithops flowers are yellow (some are white) unfortunately.... not like cacti flowers.
 
Nov 28, 2003 at 6:18 AM Post #9 of 33
Quote:

Originally posted by JohnFerrier
One thing I've noted on both this PCB and the BUF634 board is that it doesn't seem that copper is used on the boards for heatsinking. For example, the BUF634 spec sheet recommends up to 4 square inches for heatsinking (using thermal vias to the V- power plane helps with the BUF634). With SMT components it is difficult to attach other forms of heatsinks. Thermal considerations, of course, are important for class A amps. I would be interested to learn how warm the output transistors run. For optimal performance, I'd like to use as much heatsinking as possible. Maybe you find that heat is not a problem with your circuit...


The cooling area mentioned in datasheets are often just for a reference. No pcb (ever?) has this copper area at the same side as the part in mind. The groundplane cools rather good. It's no problem to use BUF634 in high speed mode. They don't get overheated on my QRV-04 pcb.
 
Nov 28, 2003 at 6:42 AM Post #10 of 33
Quote:

Originally posted by peranders
The cooling area mentioned in datasheets are often just for a reference. No pcb (ever?) has this copper area at the same side as the part in mind. The groundplane cools rather good. It's no problem to use BUF634 in high speed mode. They don't get overheated on my QRV-04 pcb.


With the BUF634, I use just under 2 square inches and thermal vias down to a very large power plane. I can run 200mA continuously and it stays cool. Seems like a good thing to me.

However, I'm still interested to learn if the output transitors on your Diamond Buffer PCBA get warm, or not.


JF
 
Nov 28, 2003 at 5:09 PM Post #12 of 33
Hi Peranders,

I just read last night in Walt Jung's "Op Amp Applications", I obtained because of your recommendation, that: a large PCB land (1-2 sq. inches) should be used for the collectors for heat sinking purposes (page 6.196 end of first full paragraph).

For your PCB, you could solder an "L" shaped piece of copper under the tab of the transistors for a heatsink. Again, only if it tends to run hot.


JF
 
Dec 1, 2003 at 5:41 AM Post #15 of 33
Quote:

Originally posted by jarthel
/me saw this project and remembers that SMD tantalum resistors they have for sale in the Farnell catalog.
smily_headphones1.gif


Let me say that again. Tantalum resistors!
smily_headphones1.gif


Cool. I can't find them using the UK site. Can you provide one Farnell part number so I can do a search? Have you ordered and used Tantalum resistors from Farnell?


JF
 
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