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In Reply to: Guess I've been TOLD posted by kavakidd on April 11, 2015 at 16:06:13:
There are very good technical reasons that a tube integrated amplifier shouldn't have a phono stage.
Tube phono stages benefit from clean, regulated DC heater power. This is not a reasonable implementation for all the heaters in an integrated (too much current). So, to add that bit to an integrated, you have to add a dedicated winding to the power transformer just for the heaters.
The next thing you'd want for a good tube phono stage is very well filtered, if not regulated B+. You don't really need much voltage, maybe 250-350V is plenty, but your tube integrated has B+ rails at 450-550V (and they aren't well filtered, because your integrated is push-pull class AB). So you get to shed a ton of that voltage and add a lot of parts to get the noise down, or you take the same steps as the first problem, and add another winding to the transformer.
You've added 2 windings to the PT, but there probably isn't enough room on the bobbin for 2 more windings, so you really need another PT. Since low level phono signals are pretty delicate, you should design the power transformer to run at a lower flux density, just to be safe. So now you need to toss the old transformer for the integrated and wind a new one, probably on a larger core.
After all that, you need special shielding inside the integrated, so you may need to add an enclosure around the phono preamp to shield it from what's going on in the power amp.
It's these kinds of issues in the design process that prevent many tube integrated amplifiers from having phono preamps.
In a solid state amp, the voltages are already lower, and a lot of the phono preamps will just be a couple opamps and a few other parts, so they can pop in on a card and not face the same challenges.
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Follow Ups
- RE: Guess I've been TOLD - Caucasian Blackplate 09:55:03 04/12/15 (1)
- Thanks for that explaination - airtime 06:51:43 04/13/15 (0)
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