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Old 25th June 2003, 09:57 AM   #1
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Wink High-end preamp for my GC

Ok, here they are, the small boards.
It could be one big board with everything, but as I was doing it the ideas kept coming...

From left to right:

PSU
Headphone amp (OPA2132 / BUF634)
Preamp module (OPA627 / BUF634)
Buffer for the tape loops (OPA627)

I have an Alps Blue 20K log. pot, it's not in the pictures.
All this has been playing on the floor, because the box hasn't arrived yet.
The sound is fantastic, even my headphones kick an impressive sound.
I'll put some pictures of the finished Pre later.
Here it goes, general view:
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Old 25th June 2003, 10:03 AM   #2
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A closer look at the pictures.
Sorry for the lowsy quality, but this second camera I have is a point-and-shoot autofocus and it has no macro ability.
I always get much better photos with my "Rolls Royce" Canon T90 manual focus.
A closer (not much...) look at the Pre and tape loop buffer.
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Old 25th June 2003, 10:08 AM   #3
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Finally, a closer look (not much...) of the PSU and the Headamp module.
Is this page getting too "heavy"?
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Old 25th June 2003, 10:22 AM   #4
Raka is offline Raka  Europe
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Heavy? Not at all, I listened to Metallica St. Anger yesterday, and this is heavy
I'm happy to hear that it sounds very well (pun?!), Does it mate well with your GC?
Which schemes were you using?
I really think that together with your planned small GC, you will have a minnuscule great gear!! Which case are you using?
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Old 25th June 2003, 10:40 AM   #5
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Hi Raka,
Glad to see you listen to all kinds of music.
The preamp mates very well with my GC indeed, it's impressive.
What a shame I can't "send" you the sound...
I based on the headphone amp that's on the BUF634 datasheed, with some changes.
I normally don't do schematics, it's all in my head.
The case for this preamp is 26x6.5x18 cm (WxHxD), and it will be full of RCAs , 6 line-ins, 3 tape loops and 2 pre outs.
Ha!
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Old 25th June 2003, 10:48 AM   #6
PWatts is offline PWatts  South Africa
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Interesting. I've built a headphone amp using an OPA2132 with a BUF634 as explained in the BUF634 datasheet and, no matter how well regulated my supply, short & shielded the connections and decoupled the opamp, there always was excessive noise. I finally gave up and built a discrete headphone amp.
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Old 25th June 2003, 11:02 AM   #7
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Default Huh?

Quote:
Originally posted by PWatts
Interesting. I've built a headphone amp using an OPA2132 with a BUF634 as explained in the BUF634 datasheet and, no matter how well regulated my supply, short & shielded the connections and decoupled the opamp, there always was excessive noise. I finally gave up and built a discrete headphone amp.
ABSOLUTELY NO NOISE!
Did you use the BUF634 inside the feedback loop?
All the caps you see in my boards are there for PSU bypassing, no caps in the signal.
0.2~0.3 mv DC offset.
Op-amps were hand-selected.
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Old 25th June 2003, 11:09 AM   #8
PWatts is offline PWatts  South Africa
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Yes. I experimented a bit with the BUF outside the feedback but it (naturally) was noisy as hell. I've decoupled both the opamp & BUF's supply rails with electro's in parallel with ceramics at less than 2mm from the pins. Maybe my cheap junk closedback ultra-sensitive 18ohm headphones made it more obvious. The noise was much less on a set of 30year old Sennheiser openback insensitive headphones. I always use my junk headphones for testing headphone amps because it's very easy to spot noise with it.
Pierre
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Old 25th June 2003, 11:10 AM   #9
Raka is offline Raka  Europe
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Well, I like very much almost all kind of music, but when I say music I don't mean most of today FM music, (I'm sorry Britney )
Does it better the sound of the GC, or there is nothing like a passive pre?
No schematics? Not even a small one for all of us, green of envy of your sound? please...
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Old 25th June 2003, 11:17 AM   #10
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Quote:
Originally posted by PWatts
Yes. I experimented a bit with the BUF outside the feedback but it (naturally) was noisy as hell. I've decoupled both the opamp & BUF's supply rails with electro's in parallel with ceramics at less than 2mm from the pins. Maybe my cheap junk closedback ultra-sensitive 18ohm headphones made it more obvious. The noise was much less on a set of 30year old Sennheiser openback insensitive headphones. I always use my junk headphones for testing headphone amps because it's very easy to spot noise with it.
Pierre

My Beyerdinamic headphones are very revealing and I hear absolutely no noise.
I test first with some cheap Sennheiser headphones and same result.

And this is without a box, laying on the floor, with non-definitive wiring...
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