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Design Help

post #1 of 7
1/23/06 at 2:45pm
Thread Starter 
Please bear with me, I am trying to learn the ropes of design, and for some odd reason , university doesn't teach me much about Tube design in my engineering degree.

My latest project, is to modify my Pioneer DV-578A DVD-A/SACD player. I am looking to grab a line out from the DAC, and run it through a tube stage.

My tentative design is attached. Does anyone see anyhting blatantly wrong with what I did? Its a simple cathode follower, with a unity gain opamp for buffering. Should my opamp have any gain, since its going to be a lineout for my other amps?

Thanks in advance!
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post #2 of 7
1/23/06 at 3:16pm
I'm not sure this makes any sense. A cathode follower is a buffer, so I am not sure why you want to stick the opamp in the way, especially if you are just driving the next gain stage which should have a high enough input impedence that a pure tube buffer is fine. Also, this isn't quite a cathode follower which would only require 1/2 of the tube and a few resistors. But, most importantly, it is not clear what you are hoping to accomplish with this. Running the line out of your cd player through some sort of "tubey" filter is not going to do anything good -- especially if that filter is just a cathode follower which is not the best sounding circuit in the world, and does not impart that much of a "tubey" sound. If you want to use a tube for your cd player, you should take the current output (Iout) from te dac chip and use some tubes for the i/v conversion. As you have it, it seems that the player still does the i/v conversion, and then you are simply running it through an extra filter. You might look around for Thorsten Loesch's generic tube i/v stage for some ideas (i don't have the link off the top of my head.)

On the other hand, if this is actually a preamp (a buffered passive preamp), then you still don't need the opamps. You should, however, take a look at SY's heretical unity gain preamp over at diyaudio as it is a very well designed example of what you are trying to do, and there is a great deal of explanation. Here's part 1 of that http://www.diyaudio.com/forums/showt...threadid=58757 as well as part 2 http://www.diyaudio.com/forums/showt...ight=heretical
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post #3 of 7
1/23/06 at 5:13pm
Thread Starter 
Wonderful! I'll look in to that. Thanks!

I guess I'm looking to replace the SS preamp thats in my CD player for a tube one.

It's really more of a learning project.
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post #4 of 7
1/23/06 at 5:30pm
For what it's worth, I designed a PCB for a cathode follower buffered passive preamp. I have never built it, however, so it may not be error free. http://www.ecp.cc/cathode_follower.html Also, there is no PS so you would be on your own there.
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post #5 of 7
1/23/06 at 7:01pm
Thread Starter 
Although I keep scouring the net, I cannot find a good article on this design. How do I go about calculating the resistor values for the circuit that you have on your website?
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post #6 of 7
1/23/06 at 10:02pm
Maybe try this? http://www.glass-ware.com/tubecircui...Followers.html It's a slightly different circuit, but not much. Also, my circuit was straight from Morgan Jones' book, so that's probably worth a read.
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post #7 of 7
1/23/06 at 11:24pm
Thread Starter 
Quote:
Originally Posted by dsavitsk
Maybe try this? http://www.glass-ware.com/tubecircui...Followers.html It's a slightly different circuit, but not much. Also, my circuit was straight from Morgan Jones' book, so that's probably worth a read.
I asked for that for christmas.. all I got was 3x 6922's, a 6x4, and an AKG K240s.

Thanks for all the help!
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