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Old 19th March 2004, 06:27 AM   #1
corbato is offline corbato  India
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Default RIAA and Linestage for life time

I am not getting any younger and slowly it is dawning on me that I should discard the assorted riff-raffs of the past and build a gear that will see me through rest of my life. So here we are. The aim is to build a RIAA and Line stage that will not make me want to change it ever. Can we discuss possibilities with following broad parameters?

- No feedback. As far as possible.
- No interstage/output transformers
- Minimum stages
- Only use any or a combination of following tubes
- 6SN7
- 6SL7
- 6DJ8
- 12AX7
- 6267

My options are limited to the above set of tubes. So esoteric types will not be of much help. In past Iíve built several Ďgenericí types 12AX7ís and 6DJ8 topologies and somehow felt all of them lacking in transparency, detail and LF response.

Thanks in advance.
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Old 19th March 2004, 11:44 AM   #2
SY is offline SY  United States
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Would the presence of a FET in there wound your pride?
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Old 19th March 2004, 12:05 PM   #3
corbato is offline corbato  India
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Not at all..honourable Sir..not at all.
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Old 19th March 2004, 12:13 PM   #4
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Hi,

What types of cartridge do you need to cater for?

Fetsssss....I'll start throwing mayonaise your way soon...

Cheers,
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Old 19th March 2004, 12:25 PM   #5
corbato is offline corbato  India
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Oops.Should have specified that in the begining.

MM. I have Shure V15 and Shure M97. Nothing fancy. I'm assured of its continued availability here for a reasonable outlay.
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Old 19th March 2004, 12:26 PM   #6
EC8010 is offline EC8010  United Kingdom
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So you're looking at passive RIAA equalisation with valves biased for optimum linearity, and a cathode follower line stage to drive cable capacitance. 6DJ8 can make a quiet disc input stage, and 6SN7 would make good succeeding stages. Are moving coil input transformers forbidden, or is your cartridge moving magnet? What sensitivity is the power amplifier?

Edit: Ah, so you actually require 400-500pF of input capacitance. What is the capacitance of your arm and cable?
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Old 19th March 2004, 12:56 PM   #7
corbato is offline corbato  India
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I think I'll actually require 250 to 300pF as a compromise load.

My current and future amp will have an Input sensitivity of greater than 500mV.
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Old 19th March 2004, 10:54 PM   #8
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Default Re: RIAA and Linestage for life time

Konnichiwa,

Quote:
Originally posted by corbato
The aim is to build a RIAA and Line stage that will not make me want to change it ever. Can we discuss possibilities with following broad parameters?

- No feedback. As far as possible.
- No interstage/output transformers
- Minimum stages
- Only use any or a combination of following tubes
- 6SN7
- 6SL7
- 6DJ8
- 12AX7
- 6267
I would say that the above is limiting enough that no matter what, you will be wanting to change.

You have eliminated input/output transformers, that presumably also includes Transformer Volume controls?

For a "limited" Phonostage I'd recommend this one:

http://diyaudio.com/forums/showthrea...624#post335624

Linestages are more difficult. How about a parallel 6SN7 or ECC88/6DJ8 with sone output to grid feedback to get the gain low, the output impedance downs and all? Take a 22k Anode load and individual 1k Cathode resistors plus bypass Cap, 1uF ouput cap and a 220k .... 470k Resistor from output to grid. Then a 100k Resistor from the grid to the 100k Log pot or directly attach the wiper of 470/500k or even better 1M Carbon Track linear Pot.

I have drawn this out in the attached piccie, this stage has around 6db gain << 1K Output impedance. You can pretty much do the same thing also with a ECC88/6DJ8 in the linestage of course, simply reduce the cathode resistors to 750R each.

I think if you slightly scale the Powersupply I suggested for the Phonostage you could use it for the linestage too. Not really my kettle of fish, but you set the groundrules to preclude almost all with any seriously good sonic potential, so what can I do? The results should be okay enough I guess.

Sayonara
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Old 19th March 2004, 11:18 PM   #9
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Hi,

Given the restrictions of the tubelist I personally favour the 6DJ8, both for phono as linestage.
You don't need the gain in a linestage but its high transconductance is always a good thing to have.

While we're talking linestages, I always wondered why no one bothers to design a linestage and headphone amp all in one box?

Instead of using a local NFB loop why not use a good CF and be done with it?

Just my twopence,
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Old 19th March 2004, 11:24 PM   #10
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Hi, Ashok -

I would ditch the 6DJ8 and definitely not use any silicon anywhere near the signal path. Even one transistor and you've lost a lot of potential on your very best analog recordings, IMO. Maybe 6SN7's 6SL7's and 6BX7's or 6BL7's if you want low impedance/high transconductance perhaps with an initial gain stage followed by passive RIAA eq, then a second gain stage/buffer driving a passive gain control with an otherwise passive architecture would seem most satisfactory. I did something somewhat similar about ten years ago and there's no comparison with anything commercial I've heard when playing LPs.
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