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Old 13th January 2009, 10:31 PM   #1
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Default Need help: tube DAC and Phono pre-amp

Hey everyone,

I am just starting on the DIY journey and hoping for some guidance from you more senior people out there.

I only listen to music from two sources: Turntable and Computer.

My question is:can i build a pre-amp that is half DAC and half phono pre-amp that both use tubes within one casing?

any and all advice is welcome.
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Old 14th January 2009, 09:13 AM   #2
kmaier is offline kmaier  United States
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Suppose you could, but I'd prefer separates if possible, at least for the phono stage as you have high gain there and less noise in the enclosure would be better. There are many phono designs posted here as well as line level stages which you could easily adapt for your needs. One interesting small DAC you could consider building into the same enclosure would be the AMB Gamma-1 DAC. As you are planning to use USB, you can essentially just mount it inside and have it powered from the USB port and it becomes completely isolated from the rest of the preamp. Here's a link:

http://www.amb.org/audio/gamma1/

Regards, KM
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Old 14th January 2009, 12:23 PM   #3
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This can be done, although I'd shield the phono preamp from rest of the circuit for best results. For phono preamp I would recommend two high-gain stages separated by a passive RIAA equalization circuit so you wouldn't have to use any feedback (many circuits like this float around the net for your reference). Although this is probably blasphemy for some, I'd try some very common (and cheap!) dual triodes like ECC83 or 6N2P for the first version as they work fine for me, unless you already have a stash of exotic NOS tubes many people would recommend instead. If you're not completely satisfied with the resulting preamp you can substitute many other types with quite little effort once you have a working build.
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Old 14th January 2009, 03:00 PM   #4
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You could easily have one preamp if that's your wish, though I'd also use a second box for the phono section.

I use a RAKK DAC which has a USB option for your computer:
http://www.kandkaudio.com/digitalaudio.html

Inside your preamp you then need the couple of boards from the RAKK, then a tube output stage. If you use a differential pair of tubes with a current sink underneath you can use this both for the DAC which goes directly in and for the phono stage. You may even want to use a solid state phono stage through the tube output. A good simple one is here - see page 12. This is essentially the original Michel ISO design (though it's from Walt Jung I believe)
http://www.linear.com/pc/downloadDoc...26,P1293,D1612

The RAKK boards are tiny, and the phono stage above would be very small, so you should have room for everything. In my own preamp I've been having good results with the 1J6g into the Hammond 124b.

andy
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Old 14th January 2009, 11:44 PM   #5
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Quote:
My question is:can i build a pre-amp that is half DAC and half phono pre-amp that both use tubes within one casing?

Zack,

Certainly all functions could be put into a single case. IMO, a more important question lies in the advisability of such activity. Digital electronics are noisy! It could be a royal PITA keeping the digital garbage out of the analog circuitry. AC mains filters and an internal Faraday cage are distinct possibilities.

Perhaps a better concept is building a DAC that stands alone and building a full function (phono and line) preamp in a 2nd "box".

Hmmm, how about 2 fully enclosed chassis in a common wooden frame? The outer wooden construction would keep everything tidy and present good cosmetics. Is SOAF an important consideration?
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Old 29th October 2010, 03:41 AM   #6
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any luck/progress so far jazzmanzack? I'm also very interested in a Tube DAC with phono
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Old 7th November 2010, 05:56 AM   #7
regal is offline regal  United States
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I have often thought that a phono type preamp (without the EQ) would be the best means to implement a tube DAC. One could use an ideally low passive I/V resistor. My concern is noise amplifying these mV signal levels, so I have yet to invest in the experiement. Please do share your results, it could be quite a development.
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