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The high octane phono preamp
The high octane phono preamp
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Old 14th November 2013, 07:21 AM   #11
jan.didden is offline jan.didden  Europe
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I build this unit myself and use it on an MC with a 1:8 step-up input transformer.
Incredinly as it seems, this 3-transister unit performs as well as the best I've heard!
If your are turned off by phono preamps with dozens of devices that need to be tightly matched and tricky adjustments, this is for you! DIY audio at its best.

Jan
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Old 15th December 2013, 03:36 PM   #12
h_a is offline h_a  Europe
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Hi Jan!

I was away the last weeks and just read your kind post!

Whoa! Cool!

Glad you like it Your kind posting certainly exceeded what I dared to expect!

Thanks a lot for your kind words! Happy listening!
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Old 15th December 2013, 05:11 PM   #13
Joachim Gerhard is online now Joachim Gerhard  Germany
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Just for fun i build a P-P version too. Trouble is that i can not persuade the shunt to make the voltage higher then 27 V. I consulted with Jan and i have tried to adjust the sense resistors but no luck so far. Ether i have made a stupid mistake or there is something wrong with the schematic i have. Jans version works so i am at a loss to explain the reason why. I will post a photo.
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Old 15th December 2013, 05:27 PM   #14
Joachim Gerhard is online now Joachim Gerhard  Germany
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Here are the pictures….
Attached Images
File Type: jpg HOkt 1.jpg (412.4 KB, 1875 views)
File Type: jpg HOkt 2.jpg (479.8 KB, 1819 views)
File Type: jpg HOkt 3.jpg (461.1 KB, 1732 views)
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Old 17th December 2013, 06:55 AM   #15
h_a is offline h_a  Europe
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Hi Joachim!

Great point-to-point build!

By the way, did you build the original single ended version first? Did the regulator work then?

Basically, the opamp simply compares the voltage from the LED (a 1.6 V red LED in my case) with the fraction 1/25.5 of the regulated voltage which is again 40V/25.5 ~ 1.6V. Any difference between these two voltages is compensated by adjusting VGS of the shunt mosfet.

When the output voltage never raises up to the intended 40V, please check that you have a 1.6V LED (not an 1.2 V or so) and your two sensing resistors RP2, RP3.

Alternatively, please check total current draw across RP1 and compare it to the one I mention somewhere in the article. I'm sorry I cannot give you the exact value right now as I don't remember the total current draw out of my head.

Hannes
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Old 17th December 2013, 08:59 AM   #16
quan is offline quan  Australia
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I am interested but too hard to do p2p. Would be great if PCB GB start running down the line.
Quan
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Old 17th December 2013, 09:07 AM   #17
h_a is offline h_a  Europe
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Hi Quan,

thanks for your interest!

Sure, a group buy or a small production run of the boards is no problem at all. However, honestly there has not been too much interest so far.

PS: in case you want to do your own boards, the Gerbers are already online!
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Old 17th December 2013, 10:34 AM   #18
SY is offline SY  United States
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The high octane phono preamp
If I had a PCB, I'd build it in a hot second, FWIW.
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Old 17th December 2013, 03:27 PM   #19
iko is offline iko  Canada
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The high octane phono preamp
Definitely a tempting little circuit. But is everyone happy with a 50A device in that position? I'd definitely choose something with lower capacitance. I don't mean to be controversial... surely you can see why. I mentioned this to the original designer and he had a fit. Just my 2c.
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Old 17th December 2013, 03:42 PM   #20
merlin el mago is offline merlin el mago
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Sorry my ignorance: what's a 50A device?
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