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Old 13th August 2004, 03:43 AM   #1
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Default 12v tube output stage for cs43122 based dac?

I am building a dac for use in a 12v enviornment. I am using the cdb43122 board schematic for reference, but would like to replace the opamps with an analog tube section. Does anyone know of a 12v stage that i could incorporate into the design? I also require a 12v remotely controlled analog volume control balanced in balanced out. I was wondering if something like the musical fidelity "missing link" style buffer would work since it was designed to work with 12v.
Thanks
Hans
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Old 13th August 2004, 07:19 AM   #2
Wodgy is offline Wodgy  United States
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Are you just interested in a tube buffer, or do you also care about preserving the analog low-pass filter? Would you be willing to switch to a passive (e.g. transformer-based) filter?
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Old 13th August 2004, 11:02 AM   #3
Previously: Kuei Yang Wang
 
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Default Re: 12v tube output stage for cs43122 based dac?

Konnichiwa,

Quote:
Originally posted by mbcouple
Does anyone know of a 12v stage that i could incorporate into the design?
Why limit yourself? You can get off the shelf 12V to 72V DC-DC converters quite inexpensively, the result is you get 84V HT a few dozend milliampere from a 12V feed.

Quote:
Originally posted by mbcouple
I also require a 12v remotely controlled analog volume control balanced in balanced out.
There are various IC's, though they dramatically degrade the sound. I think you are better off using a classic pot or a relais switched resitor array, either system is easily made compatible with 12V DC supply systems and balanced or not connections.

Quote:
Originally posted by mbcouple
I was wondering if something like the musical fidelity "missing link" style buffer would work since it was designed to work with 12v.
Actually, the missing l(st)ink does not do much to help the sound, except making it a little louder, which makes sure it subjectivley sounds preferable in A/B comparisons where the level difference is not corrected and a lot less transparent.

Secondly, that thing was run from 12V AC which where put onto Voltage doublers, giving actually a 48V supply, so no, it was not designed to work with 12V.

Sayonara
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Old 13th August 2004, 03:58 PM   #4
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Thank you very much for your input. Unfortunately i am not much of an electrical engineer. I can follow a schematic very well, but anything over a simple ciruit, i really cant design on my own. I do like the idea of using a dc-dc converter. Can you point me in the direction of a project that i can adapt to my one. I can combine several onto the same pcb. I aggree with not using an ic. I want a completly analog everything post dac. I want to eliminate the opamps, and use something like a motorized pot. I have 2 12v tube based balanced 3 way active crossovers that i will be using, and also 12v balanced hybrid tube amps. Looking for the ultimate organic sound in a car envoirnment without loosing any resolution.
Thanks
Hans
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Old 13th August 2004, 05:00 PM   #5
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by mbcouple
I do like the idea of using a dc-dc converter. Can you point me in the direction of a project that i can adapt to my one.
I am not aware of one. I got interrested in that in the process of designing a (hopefully) commercial Valve Phonostage. The electrical safety issues can be all circumvented and pushed to a cheap OEM of generic powersupplies by using 12V to feed the phonostage.

DC-DC Converters are easy and if you need to, you can stack them to any more or less sensible voltage.


Quote:
Originally posted by mbcouple
use something like a motorized pot.
You could use a simple "shunt" attenuator using a stereo pot.

I'd probably suggest using a shunt attenuator and a suitable linestage with valves and a the HT generated with DC-DC converters. Look up the differential circuits by Allen Wright. Getting 144V +B (2pcs 72V DC-DC converters daisychained) would be likely enough to operate them, the DC offset from the DAC would give enough bias to stack the differential amplifier directly onto a J-Fet.

Sayonara
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Old 13th August 2004, 08:02 PM   #6
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Quote:
Originally posted by mbcouple
Thank you very much for your input. Unfortunately i am not much of an electrical engineer. I can follow a schematic very well, but anything over a simple ciruit, i really cant design on my own. I do like the idea of using a dc-dc converter. Can you point me in the direction of a project that i can adapt to my one. I can combine several onto the same pcb. I aggree with not using an ic. I want a completly analog everything post dac. I want to eliminate the opamps, and use something like a motorized pot. I have 2 12v tube based balanced 3 way active crossovers that i will be using, and also 12v balanced hybrid tube amps. Looking for the ultimate organic sound in a car envoirnment without loosing any resolution.
Thanks
Hans

If by project you mean one using a DC-DC converter, you will find that they are rare in print and even more so on the web, especially if you are after one using encapsulated black box converters. There was one in Glass Audio around '89/90 using an encapsulated DC-DC converter generating 250Volts for a portable valve mixer. Around the same time in Audio Amateur there was a discrete DC-DC converter design for a car amp. And that about covers the last three decades, though there may be other projects out there.
Your best bet for information on encapsulated DC-DC converters would be to visit the manufacter websites.

http://www.cdpowerelectronics.com/
http://www.tracopower.com/
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Old 13th August 2004, 09:25 PM   #7
agent.5 is offline agent.5  United States
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http://www.tubecad.com/january2001/page10.html


12VDC to 72VDC converter. You can get them at Mouser for $15 a piece.
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Old 13th August 2004, 09:31 PM   #8
Knarf is offline Knarf  Denmark
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Steve Bench has a number of DC-DC converter PSU projects intended for tube service on his home page. Never tried any of them though.
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Old 13th August 2004, 09:39 PM   #9
agent.5 is offline agent.5  United States
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Once you have the +72VDC of B+ using the DC converter, or 144 if you uses two, all you need is a cathode grounded design. Just follow the calculation below and you should be fine.

http://www.tubecad.com/articles_2003..._Amplifier.pdf

For balanced to SE, try the Broskie Cathode Follower

http://www.tubecad.com/october99/page9.html
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Old 13th August 2004, 09:45 PM   #10
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by mbcouple
I do like the idea of using a dc-dc converter. Can you point me in the direction of a project that i can adapt to my one.
I remembered one example, it is in the Tubecad.com Journal.

http://www.tubecad.com/january2001/page9.html

Here the salient point, how to make 12V into 84V:

Click the image to open in full size.

The converter is the Newport Components NMT1272SZ, costs around 15 Bucks and is good for 42mA. If you stack two you can get 156C and use a differential version of pretty much any classic Voltage Amp & Cathode Follower

Something like this should answer the purpose.:

Click the image to open in full size.

The volume control Pot needs to be logarithmic. The high value series resistors pad down the DAC's output as the Linestage has a bit like way too much gain. There are other ways and options, like using just one ECC88 with +84V & -72V as buffers after the volume control, I hope this gives you some ideas.

Sayonara
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