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Old 22nd February 2010, 11:57 AM   #1
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Question Tube Buffer? 12ax7?

Hi, I am a long time lurker now with a dilemma. I have enjoyed David Vorhis mod (The Last Pas, The Audio Amateur, four1982) to the Dynaco PAS2/3 for many years now. Now I am finally ready to copy some of my vinyl to CDs. The CD burner (Philips CDR778) has an unknown input claimed to be 50k/500mv = 0 DB? I wish to add an inverting buffer (the preamp high level is now inverted), "tape output" to feed this unit from the output of the cathode follower which would be simultaneously feeding a ST70 with a natural input of about 470k. Of course I wish no gain and no color. Are there any tried and true buffer circuits (CF?) that fit the bill. I do not wish to reinvent the wheel.
Best Regards to all
Bill
Tampa, FL
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Old 22nd February 2010, 02:05 PM   #2
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Im not an expert or anything, but you cant just take phono out of the table, into a tube buffer, and then to a cd burner.

First you need to run the phone through a phono preamp to get the levels back to normal and as close to cd dac levels as possible. That normally is 1.5-2vrms. You wont get squat out of a normal phono out.

Phonopreamps.com Home Page

Phono Preamp ? Phono Pre Amp - Tube Preamplifier - Phono Amp ? Bellari

Once its up to cd levels you can run it through a tube buffer, but why since your converting to digital? Now all the sweet tube sound is on the recording, but then your sending through a dac, and then through a tube again. Id stick with all solid state for the recording phase to get the least amount of color, since your not really amplifying the signal nor buffering to a hard load.

Heres what i would do if i really really wanted a tube in the recording path.

a tube preamp:

A High-Precision Stand-alone Phono Preamplifier

Then into a high quality pc sound card as a 24bit/96-192khz wave.

Then run it through a program that will take a sample of the slient part of the recoding and remove the background noise from the recording. Then relevel to 95% of zeroDB (remember you sampled at a much higher rate then cd). Then out put it as the standard 16bit 44.1khz wave and burn using a real pc cd burner. If you look at burnt disc analizers, you will find computer burners burn with a lot (talking magnitudes) less parity bit errors then the stand alone ones.

Heres a quick explanation of the errors:

Taiyo Yuden Silver Inkjet Printable 8X DVD-R Media 600 Pack in Cake Box - SuperMediaStore.com
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Old 22nd February 2010, 02:19 PM   #3
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You have missed that I am coming from the inverted high level output of my pas 3. I am trying to make a non loading (to the PAS) "tape output" from my PAS.

Regards,
Bill
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Old 22nd February 2010, 02:34 PM   #4
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The Cavalli OCL Buffer
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Old 22nd February 2010, 03:51 PM   #5
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Location: Monroe Township, NJ
Quote:
Originally Posted by wttaylor View Post
Hi, I am a long time lurker now with a dilemma. I have enjoyed David Vorhis mod (The Last Pas, The Audio Amateur, four1982) to the Dynaco PAS2/3 for many years now. Now I am finally ready to copy some of my vinyl to CDs. The CD burner (Philips CDR778) has an unknown input claimed to be 50k/500mv = 0 DB? I wish to add an inverting buffer (the preamp high level is now inverted), "tape output" to feed this unit from the output of the cathode follower which would be simultaneously feeding a ST70 with a natural input of about 470k. Of course I wish no gain and no color. Are there any tried and true buffer circuits (CF?) that fit the bill. I do not wish to reinvent the wheel.
Best Regards to all
Bill
Tampa, FL

The "normal" setup in a full function preamp is for the recording O/Ps to be connected to the O/P of the source selector switch. The recording O/Ps may or may not be in parallel with the line stage, depending on the position of the tape monitor switch.

If you want to install the recording O/P buffers internally, "sand" is your only option. The DC heater supply in a PAS can't support an additional tube.

Obviously, if you build an external buffer, anything goes. The 1st order of business is to choose between internal and external.
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Old 22nd February 2010, 04:18 PM   #6
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Should have mentioned that I am not using the internal supply except for the heaters. However, I had envisioned this as an external stand alone box.
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Old 22nd February 2010, 04:41 PM   #7
Jim W is offline Jim W  United States
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Location: Brookfield, WI
Isn't it a bit of a waste to bother with a tube buffer when you're connecting it to a solid state CD recorder? I'd be there's a fair amont of "consumer grade" electronics in that recorder. If you're a DIY type of guy, I'd just use a simple opamp buffer. Otherwise using the line stage of a preamp or receiver to buffer it would work too.
Regards,
Jim
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Old 23rd February 2010, 11:14 AM   #8
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Inside the CDR, very few components before the DAC. Those that are there have been suitably upgraded. I am still a purist within my constraints.
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Old 24th February 2010, 12:28 AM   #9
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Location: Monroe Township, NJ
WT,

You said an external buffer chassis. An ECC99 with its sections set up as a cathode followers (1 per channel) should do the job. O/P impedance will be close to 100 Ω. CCS load the CFs with 10M45S ICs. A bipolar PSU avoids a cap. at the buffer's I/Ps.

The 50 KOhm CD recorder I/P impedance places comparatively little pressure on the O/P coupling cap. value. A 680 nF. part will do very nicely. Perhaps Soviet surplus PIOs can be sourced for this job.

Oh yeah, captive interconnect cables, at both the I/Ps and O/Ps, eliminate both mechanical connections and expense. Short, braided, unshielded, I/P cabling holds the capacitance the phono section has to drive down. Shielded cabling of some length is OK on the O/P side, as ECC99s run with a healthy IB.
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Old 24th February 2010, 01:21 AM   #10
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I followed Eli right up to the "10M45S ICs"? and lost him again at the "soviet surplus PIOs". I am old and need a decoder ring.
Sorry for my ignorance, I don't tweet, IM, face or text either.
Thanks for the help
Regards,
Bill
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