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-   -   12ax7 srpp dac output (http://www.diyaudio.com/forums/tubes-valves/133180-12ax7-srpp-dac-output.html)

Klimon 14th November 2008 08:20 PM

12ax7 srpp dac output
 
Actually 6n2p srpp; was wondering if people with some more technical expertise have remarks about this circuit. The author seems to hold it in very high esteem compared to other tube stages in that position. Maybe this is a circuit in which the often wrongly-used 12ax7 finds a proper use? fwiw I'm contemplating trying this one with nos tda1541. Link: http://www.lampizator.eu/lampizator/...H/IMG_5501.jpg

Simon

dsavitsk 14th November 2008 09:10 PM

100R is too large of an I/V resistor for the TDA1541. That isn't an SRPP which takes the output from the cathode of the top valve. But, making that conversion, Z out (from the formula in the linked article) is still 35K or so.

kevinkr 14th November 2008 11:43 PM

Yeah I am with Doug on this one, the 12AX7 has really lousy output impedance when used in an SRPP or SRPP like circuit. (The lampizator circuit is using the upper tube as a mediocre ccs to linearize the lower tube.. The output impedance is extremely close to rp and should not go anywhere unbuffered.)

Hate to say it but a conventional voltage amplifier and CF using a single 12AX7A will run circles around this circuit in most applications - learned that the hard way when I was in the "enamored with SRPP" :D phase of my audio development about 10yrs ago. The 6SN7 makes a great SRPP (~10mA@400V) in many instances IMO, but does not have nearly enough gain for the application.

Again the 100 ohm resistor is too large for good dac linearity and should probably be in the range of 20 ohms or so.

A single triode connected D3A would solve all of the problems quite nicely, and is also about an order of magnitude quieter than any 12AX7A.

Eli Duttman 15th November 2008 02:40 AM

Quote:

The 6SN7 makes a great SRPP (~10mA@400V) in many instances IMO, but does not have nearly enough gain for the application.

Kevin,

Would choke loading a 'SN7 SRPP with something like a MagneQuest EXO-99 and buffering it with an IRFBC20 alter the calculus? All possible gain would be realized and linearity is (naturally) a given.

Klimon 15th November 2008 06:53 AM

Thanks, that should save me some time. I'll probably use the 5842 then which I've got on hand. Two circuits are posing as candidates next: Yeo's GG http://diyparadise.com/mar06/gg.html or the input stage of the tubelab se, possibly with orange led cathode bias http://www.tubelab.com/TubelabSE.htm . Any opinions?

Edit: referring to the GG schematic without plate chokes (money money money)

Simon

dsavitsk 15th November 2008 07:01 AM

Quote:

Originally posted by Klimon
Any opinions?

tubelab

Klimon 18th November 2008 07:28 PM

NOted, thanks :)

Simon

devas 11th December 2008 06:50 PM

Hi,

I have a satch dac (tda1541) and experimented output stage with 5842 (and 417a),6n2pn (Lampizator circuit), E180f and D3A.

5842, E180F and D3a were choke loaded; I was quite disapointed with 5842 whereas I use a 5842 Euridice preamp which fully satisfies me, the sound lacked in dynamics and was on the dark side even with i/u 22 Ohms resistors.

I understand the use of 100 Ohm in Lampizator circuit as any values under 80 ohms yielded a harsh and thin sound. With 100 ohms it's quite acceptable but again rather dark and less natural.

Most impressive is the triode connected D3a :top detailed, very large sound, deep and tight bass never agressive even at very loud volume.

But when compared with op-amp configuration I find this latter more delicate and maybe closer to the truth as far as texture is concerned.

Next step is try the universal output stage from DIYsupply.....

Karsten Sømand 11th December 2008 07:51 PM

Hi devas

Thanks a lot for sharing your experiences with us. As you might have seen Lukasz has tried to make the stage as a J-FET stage.

Mr. Dietmar from Austria helped him making a good J-FET circuit. It is claimed having some of the same characteristics as triode tubes (?).

The nice thing is that it will only cost you around 10-20 Euros to make the complete circuit. The article contains detailed explanation about the components, there is a parts list and even a drawing so that you can make your PCB-circuit (which was tested before release!). Please follow this link:

http://www.lampizator.eu/LAMPIZATOR/...JFET_CDout.pdf

Kind regards

Karsten

Klimon 11th December 2008 07:56 PM

Very interesting

Quote:

But when compared with op-amp configuration I find this latter more delicate and maybe closer to the truth as far as texture is concerned.
Kinda reminds me of a tube-guru concluding his journey with non-os tda1541 tube output remarking how hard it was to choose between his home-brew machine and his stock top model pioneer cdp. Not very encouraging :D Considering the not so lowish options you've already tried makes one figure indeed if diyhifisupply can put something even better against that.

Simon


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