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Old 10th January 2008, 09:42 AM   #1
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Default Wanted: 12V Discrete Preamp Design

Hi,

I've searched and searched, but I still haven't found a design suitable for my upcoming project - a preamp to accompany a tripath based Class D.

So, what I'm after, and am hoping some-one can direct me to -

- Preamp with switchable phono stage
- Discrete solid state components
- Powered from 12V DC (it has to live in the same case as the Class T, which uses ordinary +12V. No cheating and using designs which can deliver +/- voltages from AC sources, the power supply will (sometimes) be a battery)

The second requirement I've found can be filled fairly easily, but I've found none that can manage both that and the third.

Any contributions from this boards vast wisdom are muchly appreciated!
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Old 10th January 2008, 01:25 PM   #2
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You can split the 12V into +/- 6VDC with a "rail splitter", like the TLE2426, or an opamp set up as a splitter. Then use one of the conventional low power rail-rail opamps for your RIAA stage.

The problem with using a conventional single-supply setup with a phono stage is that the input is very low, 10 to 20 mV so you can't just tie the non-inverting input to the positive rail through a resistor -- the noise will kill you.

The TLE2426 is a $1.30 part from Mouser or Digikey.
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Old 10th January 2008, 05:15 PM   #3
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Default phonopreamps.com

phonopreamps.com has a pretty good selection of preamps and all appear to run on +12V. I've seen pictures of TC-750 internals and it's completely discrete, but not the most advanced design.
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Old 10th January 2008, 08:37 PM   #4
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Hi,

Obviously I forgot to mention that I'd like the design for a DIY project. I've got a cheap and nasty preamp in the role now, and I'd like to replace it with something substantially better.

I should note that the phono stage isn't the most important, as it's unlikely to see very much use.

Chris
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Old 10th January 2008, 11:04 PM   #5
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The reason I mentioned the +/- voltage thing was that I very much like the look of the below circuit, as well as what I've heard about the sound. Is there anyone out there who can show how it could be modified for a different power supply arrangement, or who could show me a design for a power supply that can give the necessary +/- 15V from an input of just 12V DC?

http://myweb.tiscali.co.uk/nuukspot/.../ls.buffer.gif
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Old 11th January 2008, 03:04 AM   #6
dangus is offline dangus  Canada
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DC-DC converter modules aren't too expensive ($5 to $15 depending). I'd find one that goes 12V to +/-15v, and then use 3-terminal regulators to clean up the outputs.
http://search.digikey.com/scripts/Dk...dc%20converter

The Hagerman Bugle looks like a very good phono preamp; schematics are available if you want to build from scratch, or there's kits on eBay; use the search terms bugle and phono. But it's not discrete. Sorry. Maybe you could build up discrete op-amps?
http://www.hagtech.com/bugle.html
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Old 11th January 2008, 06:20 AM   #7
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The desire for discrete components simply comes from being uncomfortable dealing with IC's - I have a tendancy to cook them in one way or another.

OK, to simplify my needs, forget, for now, about the phono stage. Looking around more, I've found a million phono stage designs, so I can easily build one later - and having it as an outboard component makes some sort of sense. However, I still need a preamp in order to complete my (portable, hence the strictness about the 12V supply) integrated amp.

So, to reiterate - I'm after a preamp/buffer with discrete components (I've never worked with JFET's, either - anyone care to give a good link explaining them?) that will run from a +12V source, or, alternatively, a schematic for a power supply board that can supply +/- 15V from a 12V DC source.

thanks folks, you've been really helpful so far, I just need to keep refining my needs down to something possible!
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