GC Preamp Suggestions

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#401
I have not seen many schematics being shown in this thread to go with the pcbs, so I just want to know if any of the board designs incorporate a cap in the same location as C10 in THIS schematic. I think I remember reading that it was a good idea, but correct me if I am wrong.
 

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#402
incorporate a cap in the same location as C10 in THIS schematic. I think I remember reading that it was a good idea, but correct me if I am wrong.
Click to expand...
We talked about that cap,
go back to post #26 - #29 or thereabout🙂 I guess this thread is running a bit too long, to follow everything, said in here:xeye:
CarlosFM recommended 200Pf, and PMA insisted that 18Pf was better. Alcaids curves shows that 200Pf is too much. I have used the 18Pf in that pos.

Steen🙂

BTW. Have you guys in mind to decide on a particular design for a groupbuy? I dont think the linestage can be much better, when looking at some of the designs here😎
 
#403
Hi DC Dave,
go back one page: http://www.diyaudio.com/forums/attachment.php?s=&postid=637655&stamp=1115553605
in that layout you find two small pads under the opamp, the left one is for R2, the right one for C10. You have to use smds at this position.

Better to use 4.7k for R4 and 470R for R3. For a headphone-amp you may (if you want) rise up gain to 21 (so done in the buf datasheet).

So you can see, the layout above can be used for 'your' headphone amp.

I'll still put all amp-modules (line loop, headphone and preamp) from carlos on a single euro pcb (100 x 160 mm) and post all data files in carlos' preamp thread.

Michael
 
#404
BTW: because of the higher gain you can use cheaper opamps (so you did in your schematic). You can also use a double opamp (OPA 2132), costs less then the single version and reduces layout dimensions (you need 2 capacitors and 2 elkos less than in single opamp version).
 
#405
steenoe said:
We talked about that cap,
go back to post #26 - #29 or thereabout🙂 I guess this thread is running a bit too long, to follow everything, said in here:xeye:
CarlosFM recommended 200Pf, and PMA insisted that 18Pf was better. Alcaids curves shows that 200Pf is too much. I have used the 18Pf in that pos.

Steen🙂

BTW. Have you guys in mind to decide on a particular design for a groupbuy? I dont think the linestage can be much better, when looking at some of the designs here😎
Click to expand...


The BUF634 app note talks about that cap and which combinations to use it with. In all honesty I tried the 18pf with my OPA627 version of this preamp and I think it was better without it. I am running with a gain of around 8 so stability is not a concern, I suspect if you were running at unity it might be more important.

G.
 
#409
DC Dave said:
I have not seen many schematics being shown in this thread to go with the pcbs, so I just want to know if any of the board designs incorporate a cap in the same location as C10 in THIS schematic. I think I remember reading that it was a good idea, but correct me if I am wrong.
Click to expand...

I started using the recommended 200pf cap.
Later I changed it for 47pf.
Smaller values are better.

Btw on your schematic the input coupling cap (C1), if you must use it, can be 470~680nf.
4.7uf with 100k to ground doesn't do much to remove DC-offset from the source.
 
#410
carlosfm said:


I started using the recommended 200pf cap.
Later I changed it for 47pf.
Smaller values are better.

Btw on your schematic the input coupling cap (C1), if you must use it, can be 470~680nf.
4.7uf with 100k to ground doesn't do much to remove DC-offset from the source.
Click to expand...


The only reason I chose the 4.7uf was b/c I have a bunch of BG caps in that value laying around. Is their a better value for the resistor in this case to remove DC offset? Or should I just ditch the BG in this application and go with the small cap?
 
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