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12ax7 srpp dac output

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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/REFERENCES/SATCH/IMG_5501.jpg

Simon
 
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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.
 
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
 
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.....
 
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/FETISHIZATOR/JFET_CDout.pdf

Kind regards

Karsten
 
Very interesting

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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Eli Duttman said:



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.


Hi Eli,
I have actually used a very similar circuit to drive 2A3 without the mosfet, it actually behaves like a mu-follower, but bass performance is very dependent on the available inductance. I was using 100H MQ chokes and found that something higher than that would be better still - I don't think 200H is overkill, but since I also used the dcr of the choke to bias the upper tube high value chokes aren't that practical. The gain however is still only 20 (even with a mosfet buffer) which is useful for driving a 2A3, but not enough here.
 
Hi,

I haven't done mods in the Satch Dac but for the output caps, as I consider that it works well enough as it is. The only thing I had in mind was to implement a Tentlabs Dac clock.

As I said before the 6n2p circuit sounded to me crispier and thinner than the other tubes I had tried, perhaps even crispier that the op-amp option. All my tests were made with EZ80 tube rectifier of different brands, the change of this latter affects the sound a lot.
With a classic i/u resistor of 22/33 ohms I had to put the darkest ez80 (Siemens or Sylvania) to get the balance right.
With 100 ohms I had to put the brightest ez80 (Tungsram) and it was still on the dark side.

It's not bad but I don't consider it worthwhile on my system for sense of detail,balance and tone appeared better to me with the d3a or the op-amp configuration. But this is just my opinion.
 
Yes I tried in NOS configuration and found that there was less air between instruments and definitely prefer the soundstage in OS.

Before the Satch I had a tda1545 Monica with a tube output stage and tried to convert with all my heart to the religion of NOS but I think I'm still a non believer of unique truth and rather always open to enlighted contradictions...
 
diyAudio Senior Member
Joined 2002
Hi,

If you want to use an SRPP circuit for this kind of application the 6DJ8 is a pretty good candidate.

It does I/V conversion nicely and still has enough gain left (considering the SRPP topology).
Load it so you force current flow with say a 1K bleeding resistor at the output , or determine by circuit analysis if you can and you should have low enough Zout with reasonable distortion figures.

After that I'd recommend (as usual) a well regulated, neutral sounding PSU, for best results since all SRPP circuits have low PSRR.

The TDA 1541 provides good symbiosis so results should be sonically pleasing...for a DAC.:D

Another option is to use a //ed 6DJ8 and CCS that with a J-Fet or similar constant current diode around 30ma with a regged B+ of 24VDC.
Zout will probably be higher than the SRPP circuit but gain will higher too.
One of the advantages of this circuit is that you won't need a raw B+ higher than 40V which allows for used of top of the bill SS* components in the rails. (* Did I just write this?)
I'd need to look at the actual numbers as I'm just writing this from long term memory storage.... :rolleyes: ;)

Cheers, ;)
 
Google brought me here: I'm looking for a new output stage for my TDA1541. I'm using a 28 Ohm I/v resistor with a 6211 SRPP. I am deeply in love with the sound but seriously lack gain. The 6211 is extremely microphonic btw. I was looking for tubes with a mu of around 100 and the 6N2P seemed a good candidate. After reading this the D3a seems a better choice, but I haven't made up my mind yet :dunno:
 
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