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Old 15th April 2011, 01:14 PM   #1
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Default valve phono stage on a budget

Hi

New to the forum. I have an old Croft valve pre amp/phono stage which is either in need of refurb/ugrade/mod or i could do to build a phono stage (valve) from scratch, on a budget, to use with leak stereo 20. MM and MC capability wanted.

Anyone out there have any specs or know somewhere/someone on t'net where i might find something.

Yours in hope

Rauza
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Old 15th April 2011, 08:28 PM   #2
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Depends what the "budget" is like.

A pair of ECC85s with plate load CCS set about 7mA and 0.82V Schottky bias (around 135V on the plates if I recall) makes a nice phono gain stage of ~50dB, enough for some of the medium output MCs. For low output MC carts, you'll need a SUT. Suggest the Hashimotos.

Use passive equalization, all in one.

The power supply should be VT rectified. Follow up with at least two stages of LC filtering. The use a single CCS and gas shunt tubes. A 150V and 75V give a nice output of about 225V, that the plate CCS can draw on. Rig for 14-25 or so mA through the gas tubes during normal operation. Don't even think of using the gas tubes without the common CCS upstream, they'll be noisy.

Following the 2nd ECC85, use a follower (I'm partial to the 6SN7/6FQ7 types, but ECC99 and others will work well). Look up Broskie's or Yaniger's servo stages; use those for a DC coupled output.

I expect you'll have it done by the start of the work week. LOL

Oh yeah, the Siemens tubes sound nice, but when you're ready to lay down a bit of cash, find a pair of Telefunkens. Mmmmmmmmmmm.

Stuart
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Old 16th April 2011, 12:32 AM   #3
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LOMC is out, if holding costs down is important.

Undoubtedly, there are better phono preamps available. However, you will be (IMO) hard pressed to better the cost/performance of a tweaked RCA setup. The Sovtek 12AX7LPS is inexpensive and exhibits excellent noise behavior.
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Old 16th April 2011, 12:41 AM   #4
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Here are some options:

http://91.201.116.112/acustica/6c17k.zip

http://pics.qip.ru/102JZ6D.jpg
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Old 17th April 2011, 02:37 PM   #5
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Default preamp SD3 by sound design

Hie there
my name is johnI have a 4 box SD3 4 box preamp in need of some scometic diagrams peter bruty built the preamp worked with croft I am after a 3 valve phono stage ECC83 valves can you help
kind reegards
john
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