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Old 9th March 2012, 09:54 PM   #1
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Default Joy of birth - a new preamp brought to the world

My narcissism makes me want to share this. A few hours ago, I finally brought to the world another healthy tube preamplifier. This one already has an almost identical older brother, so I'll give this one to adoption.

The newborn has two 12BH7 or ECC99 tubes and a healthy bandwidth up to 450kHz (-3dB), four inputs and an Alps volume pot. Output coupling capacitors are Obbligato Premium types.

Just some tube-a-rotica for your weekend...
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File Type: jpg pre21_insides.JPG (180.7 KB, 585 views)
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Old 9th March 2012, 10:27 PM   #2
DF96 is offline DF96  England
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Very helpful for those who wish to listen directly to longwave broadcasts on their supertweeters.
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Old 9th March 2012, 10:48 PM   #3
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Originally Posted by DF96 View Post
Very helpful for those who wish to listen directly to longwave broadcasts on their supertweeters.
Yep, I know the BW is a bit over the top. 150kHz squares come out just nice at 20Vpp. Still, I just don't see any reason to limit it. Doesn't sound overly bright at all.
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Old 9th March 2012, 11:40 PM   #4
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How are you doing the front panel graphics?
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Old 9th March 2012, 11:51 PM   #5
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I love the 12BH7A although find that black plate CV5042 to be nicer sounding.
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Old 10th March 2012, 02:34 AM   #6
Mr. dB is offline Mr. dB  United States
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Got a schematic you can post?
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Old 10th March 2012, 08:36 AM   #7
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Originally Posted by boywonder View Post
How are you doing the front panel graphics?
I use the same type of decal film that comes with model aircraft kits etc. I just print it out with a laser printer, cut them out, dissolve the base out in water, then transfer on the aluminum front plate. After they're dried, I apply several thin coats of lacquer. Between 5 and 7 coats is usually enough to make the edges of the films disappear. It's not silkscreening, and works only on light backgrounds, but given that you need no special tools besides a good knife for the cutting of the markings from the sheet, it gives quite nice results.

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Got a schematic you can post
Maybe I could... Basically it's just a CCS loaded ECC99/12BH7 common cathode directly coupled to a CCS loaded cathode follower, which uses the second half of the tube. I applied the basic topology by another finnish designer. It was originally using ECC82's, and was point to point wired, had a tube rectifier, and a lot less idle current. It also had both channels passing through the same tube, with the idea you could use a different tube for the different stages, giving you a possibility of varying the sound using for example an E80CC in the first stage and so on. I opted for a possibly better channel separation in my PCB version of the thing. The PSU is also slightly different, with SS rectification and more capacitance. Sounds and measures better than the original.

I'll try to remember posting the schema when I get home from work.
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Old 10th March 2012, 10:06 PM   #8
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Here's the schematic for one channel. Pretty simple.
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Old 11th March 2012, 12:14 AM   #9
tictac is offline tictac  United States
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Do you have a drawing of your power supply and the voltages needed for the preamp stage?
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Old 11th March 2012, 12:33 AM   #10
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Quote:
Originally Posted by Adolf Corkscrew View Post
Here's the schematic for one channel. Pretty simple.
Hey, that's nice! Looks like something I'd do! (except I'd drop the cathode bypass capacitor in the first stage)
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