Hey all!
Has anybody ever built a preamp with D3a tubes or knows someone who did?
I was able to get my hands on some D3a tubes for little money and right now I am thinking about what I could do with them and since I already have an amazing tube phono pre and power amp I thought why not replace my old 6sn7 pre with a new one and why not with D3a's...
I know that they have a very high gain and are propably better used in the driver stage of a power amp, but a preamp with D3a's shouldn't be a huge problem, right?
If anyone has something that could be of use for this project please share it with me! (Especially schematics as a starting point for this project would be much appreciated 🙂
Thanks,
Brzzl
Has anybody ever built a preamp with D3a tubes or knows someone who did?
I was able to get my hands on some D3a tubes for little money and right now I am thinking about what I could do with them and since I already have an amazing tube phono pre and power amp I thought why not replace my old 6sn7 pre with a new one and why not with D3a's...
I know that they have a very high gain and are propably better used in the driver stage of a power amp, but a preamp with D3a's shouldn't be a huge problem, right?
If anyone has something that could be of use for this project please share it with me! (Especially schematics as a starting point for this project would be much appreciated 🙂
Thanks,
Brzzl
Hi there Brzzl,
I'd do a better phono preamp with those tubes:
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Link for inspiration
I'd do a better phono preamp with those tubes:
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Link for inspiration
I'm assuming you'd be using the D3a wired triode, right? IMO, you won't need anywhere near the gain you'd get from a D3a, unless... You use negative feedback to reduce gain, as in an anode follower (plate follower).
http://deewm.com/Webcache/The_Valve...ack/Triodes_with_Local_Negative_Feedback.html
Anode Follower Circuits
i would have done so, however, my first phno preamp already uses D3a's and my second one has C3g tubes so thanks for your input on this subject but I'm pretty happy with my current phono pre's.
Thanks for the reply and yes I'd be using the D3a's as triodes.
I was thinking something along the lines on the websites you linked. Despite that, I would like to stay away from feedback if possible but I might give it a try anyway.
It just had the thought that i could use a stepdown transformer after the tubes what do you (opinions from others are also appreciated🙂 think of that idea?
The only sensible way to build a line stage using D3A is with a step down transformer. I have done something similar using c3g and is not bad at all. Balanced with permalloy UTC LS-51.
mu of 70 in triode mode, doing a line amp will be hard work, you will need to reduce gain from about 35 to about 5 using plate to grid feedback, in an inverting configuration and that may not sit well with some audiophiles...
hint: look at the Camp Amp topology...
hint: look at the Camp Amp topology...
I use D3a with 2:1 stepdown. I note that euro21 sims with ~Lpri that I have; same winder.
From what I've read so far you are wanting to use D3a as a 'line-stage' and not phono preamp, questions follow:
1. How much money are you prepared to spend on parts?
then:
a. What is the max output level of your source component/s.
b. What is the input sensitivity of your amplifier.
c. Are you planning on keeping this amplifier.
d. What is the input impedance of the amplifier.
e. Can you re-think your gain structure, perhaps bypass input stage on the amplifier to account for the voltage gain of the D3a - sometimes integrated is better 🙂
I would be open to trading D3a for E280F -bell curve (tested) from 100 pcs Siemens Master Pack.
Cheers,
HK
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Yeah, but the difference is that a D3a has a gain of 70 in triode mode compared to 40 of a C3g wired as triode...but I think that with a different stepdown trans that reduces the output even further I would be fine
1. I would say that we keep the price point open for now and discuss various ways how I can build a line pre with D3a's or maybe other tubes if someone wants to trade tubes for my 10 D3a's...
a. 1.6V Rms, 1.7V Rms and 2V Rms
b. Current F6 in main system: 0.57 V (1W) / 2.83V (max Out)
c. Yes i plan on keeping the amp but one of the next firstwatt diy amps might replace it
d. 100k
e. That won't work with the F6
With sources with such a high drive level, D3a can not be driven directly!
With 2 Vrms = 5.6Vpp you will need a triode biasing with at least -4V which is impossible for a D3a. The max you can use will be something around -2 to - 2.5V, better would be -1.7V with a max drive level of 1Vpp.
See the triode curves in D3a datasheet.
A solution would be to have a 4:1 step down input transformer or a resistive voltage divider to reduce drive level. As an output transformer you will need at least a 6:1 step down (2V -> 0.5V -> 20V ->3.3V).
With 2 Vrms = 5.6Vpp you will need a triode biasing with at least -4V which is impossible for a D3a. The max you can use will be something around -2 to - 2.5V, better would be -1.7V with a max drive level of 1Vpp.
See the triode curves in D3a datasheet.
A solution would be to have a 4:1 step down input transformer or a resistive voltage divider to reduce drive level. As an output transformer you will need at least a 6:1 step down (2V -> 0.5V -> 20V ->3.3V).
You are making some excellent points. The only way this topology would make any sense is if you insist on using a 600R attenuator after the input transformer. Which may have some merit.
The entire idea of using a high mu valve in a line stage is just wrong. I think AN do this in some models but i cannot see the point, unless Qvortrup got a super cheap deal on suitable transformers.
With the C3g i was mostly interested to compare the sound against my reference 6N30P in practically the same circuit. I was also curious to see how different the distortion would be for the same output, as output swing is much larger.
Surprisingly the distortion with the C3g was very slightly lower. The sound was really not bad but i still prefer the bass, dynamics and focus of 6N30P.
This thread is a useful reminder that the availability of valves should never be a deciding factor for a design. Even cost wise the valves represent just a tiny fraction of the entire design.
Okay thanks for all the various inputs on the topic of a D3a line preamp. -I think that I won't try a D3a line preamp. Anyone interested in trading 10 D3a's for C3g's, 6n30p's, 6sn7's or 6as7's please dm.
Can someone please close this thread? Thanks.
Can someone please close this thread? Thanks.
Is there a compelling reason not to try a bit of plate to grid feedback? Very easy to undo if you don't like it and almost no expense to try.
Not really..
I surely will give it a try if I have enough parts lying arround but I won't buy much for this test other than a couple of resistors and caps. I think that I should have enough to test this idea though...but even than I'd not need 18 D3a's so if anyone is interested in trading 10pcs of them for other tubes I could use more of, that I mentioned in my last post, feel free to send me a dm (even if you have other tubes than I listed because maybe I can put them to good use someway).
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