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Old 28th March 2016, 04:19 PM   #1
jdrouin is offline jdrouin  United States
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Default Tube Phono Preamps

I'm looking to build a tube phono preamplifier (first time) for a recently completed Tubelab SE 300B, and would like some recommendations for kits or schematics.

I'm currently using a Rega Planar 3 turntable with an Ortofon OM5E cartridge rated at 4mV output.

The input sensitivity of the 300B amp measures at 0.707V, so if I'm correct, the phono preamp would need to put out about 0.7 to 1V. With a 4mV cartridge, the phono preamp inputting directly to the 300B amp would need to provide a gain of about 38db, according to the KAB calculator. Does that seem right?

Years ago I heard a George Wright WPP100C driving a pair of SET monoblocks (a one-off precursor to the Mono 7; it was a 300B designed to sound more like a 2A3), and was utterly blown away by the detail, musicality, and 3D depth/breadth of the soundstage. I realize recapturing that in a first time build is highly unlikely, but I've got to start somewhere.

So far, the following projects seem applicable. Does anyone have opinions as to the sound qualities and suitability to my power amp? Any other projects I should consider?

* Glassware Tetra Sans PS (I'd use the Janus or PS-1 power supplies)
* Glassware PH-1 (would probably use the PS-1 power supply)
* Bottlehead Seduction or Reduction (new or used)
* I have Kevin Kennedy's (aka KTA and kevinkr here) Little Book of Preamplifier Projects, and the 1-tube and 2-tube per channel designs look eminently feasible and affordable.

Thanks!
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Old 28th March 2016, 06:00 PM   #2
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You have all sorts of options. Contact member Jeff Yourison about the tweaked RCA setup. It's reasonably easy to execute and does keep cost control in mind.
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Old 28th March 2016, 08:46 PM   #3
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Here is the tweaked RCA Classic phonostage that Eli, Buzz and others have worked on. The power supply will follow if you're interested. (I thought Merlin had just posted it, but it's gone at the moment.)The range in values shown is intended to keep a key RC product constant.
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Old 28th March 2016, 08:49 PM   #4
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Here is the power supply I used, again with Eli's valuable mentoring.
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Old 28th March 2016, 08:49 PM   #5
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It's here again.

Click the image to open in full size.
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Old 28th March 2016, 09:42 PM   #6
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Subscribing as I'm in a similar boat. My phono preamp is next in line for the upgrade merry-go-round. Is there a thread or write for the posted schematic?

Sorry I'm just gawking and not contributing
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Old 28th March 2016, 09:56 PM   #7
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Quote:
Is there a thread or write for the posted schematic?
Scan the archives here and over on AA. More than 1 thread will turn up.
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Old 28th March 2016, 10:04 PM   #8
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Morgan Jones' Valve Amplifiers book is known mostly for power amplifier design information, but it winds up with a couple of very intelligent preamp designs. The second one is fully balanced.
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Old 28th March 2016, 10:12 PM   #9
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The original thread was spread over several forums, one of which was lost to hacking.

There are a few builders out there. Here is my original quick prototype build. It could be done more compactly in a nicer enclosure; this is mostly point to point, and is set up to allow changing out the capacitors for experimenting. (The enclosure is a Fat Daddy-o 9" x 13", 2" deep cake pan, inverted.)

I like the new Mullard reissues, the Sovtek LPSs, and some older RCA mil-spec tubes in it.

The power supply is on the right, and the actual preamp channels are on the left. The heat sink is for the 12V heater regulator; it gets only mildly warm. I used a mix of 'styrene and mica in the equalization section, and the output caps are GE surplus with Panasonic film and foil bypass. The large black decoupling caps are Solen.
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Old 28th March 2016, 10:24 PM   #10
jdrouin is offline jdrouin  United States
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Thanks for the information. I have a copy of an RCA tube manual from 1959 that seems to have that same circuit (#19-15, on p. 364), though of course without the MOSFET follower.

I take it you like the performance of the RCA phono pre? Any idea what the frequency response, total gain, and RIAA accuracy are?
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