Shine7 12au7 preamp builds?

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ChiDave

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Joined 2013
#1
Has anyone built this preamp? I'm looking for a low (or variable) gain tube amp.
It would be great if it were easier to find established projects here more easily than sifting through all of the threads. Am I missing anything?
thanks
 
#4
I originally thought all I needed was a quality buffer and volume control since my DAC output is the max that my amp needs. I'm driving my system DAC direct right now. In a perfect world I'd build a preamp where I could select 0, low, or fairly high gain. But, I'd rather not add that complexity to this design.
The reality seems to be even very low distortion preamps with gain can alter the sound in a way that many people think is a change for the better. I assume this has a lot to do with second harmonics, but probably other, more subtle, things as well. I've stopped worrying about the science behind why things like this seem to be true. And hey, I'm building it myself, so why not give it a try?

PS: I'm using a BMC PureDac which they claim adds currnet to improve the "preamp" section's performance. I'm not qualified to delve into analyzing this. At least they say they're doing something to make it work better than simple digital volume attenuation.

PPS: Yes, I'd take a gain of 4 or 6 instead of 10. At least it's not 15 or higher.
 
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#5
0.058% THD - probably mainly second order - at 2V pk-pk output may be enough to colour the sound a little. This is just 70mV RMS input, so you need to put the volume control before the preamp. Other things being equal, a 2V RMS CD player output could give you 1.6% THD. Or you may prefer this! A low distortion preamp would do much better than this.
 
#6
ChiDave said:
Ok. Anyone care to take a look at this design and offer an opinion? I'm going to build this unless someone can point me to a project here with a complete schematic that they're confident is significantly better. The one problem with the Shine7 project is it doesn't include the PSU design.

DIY 12AU7 Tube preamp

Thanks, Dave
Click to expand...

I would have added a grid stopper to first stage to kill RF.
 
#9
sfthurber said:
the shine7 6922 version is much better than the 12au7 version
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sorry, forgot to reply to your other question--there are two respectable 6922 preamp PSUs shown here: RJM Audio - Tube passive phono preamplifier although i'd be inclined to also go with DC for the heaters using LM317 current source for regulation. there's a useful discussion of LM317 and similar current source regulators at: LM317 / LM338 / LM350 Current Regulator Calculator and Circuits. Also, if you haven't looked at Pete Millet's stuff, it's very worthwhile IMHO. http://www.pmillett.com/
 
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#11
ChiDave said:
I'd thought of the 12au7 version because of its lower gain. I will consider the 6922 also. I have Pete's 'Low Mu' preamp bookmarked as another candidate. Thanks for the input.
Click to expand...
FWIW:
got thinking a bit about the 6922 circuit--he's pushing the tube pretty hard in the cathode follower (second stage) and it isn't necessary. changing the load R and the cathode R to safer values (lowering the loadline so the current is around 5ma) would be much easier on the tube but you would have to elevate the heater supply because the cathode will be floating much higher to the point that would exceed the heater cathode breakdown voltage if the heater were not elevated.
 
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