Although he likes my autoformer-based passive pre, my brother is reluctant to give up his active line stage pre. The problem is that he never gets the volume knob past about 25%, so he's throwing away most of the input signal only to amplify what's left.
He acknowledges it loses bandwidth compared to my autoformer (particularly at the bottom end) but he likes the "drive" it brings. I don't hear it, I think he likes the colouration. It's a beautiful hand-crafted balanced differential pre using 4 x 12AU7 valves, which have a mu of about 17.
So I have started thinking about building him a line stage with a much lower gain. He doesn't need ANY gain - I'm driving the same power amps (45 output tube) into the same speakers (Lowther DX3 + subs) with my autoformer.
I was wondering about a balanced differential line stage based on low-mu DHTs, perhaps the 71A (mu=3). I couldn't find anything in a brief search this morning. Has something like this been done and are their circuit diagrams I could look at ?
He acknowledges it loses bandwidth compared to my autoformer (particularly at the bottom end) but he likes the "drive" it brings. I don't hear it, I think he likes the colouration. It's a beautiful hand-crafted balanced differential pre using 4 x 12AU7 valves, which have a mu of about 17.
So I have started thinking about building him a line stage with a much lower gain. He doesn't need ANY gain - I'm driving the same power amps (45 output tube) into the same speakers (Lowther DX3 + subs) with my autoformer.
I was wondering about a balanced differential line stage based on low-mu DHTs, perhaps the 71A (mu=3). I couldn't find anything in a brief search this morning. Has something like this been done and are their circuit diagrams I could look at ?
Ive done a pre with 3A5s. Not very low mu but dht. My current pre can take 6AS7 which is low mu. Precently I have 6BX7 in there b/c I need some gain. This pre can take all the octals with same pin out so 6SN7 and 6SL7 as the highest gain tubes. But I prefer the lower gain of 6BX7 and 6BL7.
Sorry not much help. But my point is yes u can build a pre with low mu tubes.
Sorry not much help. But my point is yes u can build a pre with low mu tubes.
oops sorry. It even says 'Balanced differential' so there really should be no ambiguity...
I'm usually so good at reading headlines (and very little else) so dunno how I missed it.
71As are not that cheap, and they're probably not tightly matched, you wont buy tens of them to find two matched sets, or..? So DF96's tip is definately a must.
Yeah I was starting to think that way, reading about the Balanced Aikido.
Balanced Aikido
I fancied doing it with DHTs, but as has been said finding matched sets will be difficult and they are not cheap.
Balanced Aikido
I fancied doing it with DHTs, but as has been said finding matched sets will be difficult and they are not cheap.
I' ve found great assistance for my current project here:http://waltjung.org/PDFs/Sources_101_P1.pdf http://waltjung.org/PDFs/Sources_101_P2.pdf
Also a lot of info in Merlin Blencowe's book.
Also a lot of info in Merlin Blencowe's book.
Here you go. Amplification is only some 1.7 times. THD at 5 Vpp is negligible (~0.007%).
The 50 mA CCS can be constructed in many different ways. In simplest mode it can be a LM317 voltage regulator with two resistors.
Attachments
No. Have only compared CCS plate loads to decent plate chokes. Despite the obvious attraction of low weight, low cost and high hum resistance, chokes tend to win every time. Obviously imhSo.
I have just build one with OPT LL1692a and 4p1l...you use the opt in a step-down setup, so you trade tube gain for a low impedance.
Kevin has a lot of very good sounding CCS and very reasonable priced....plus he gives always great support on your projects.
http://www.kandkaudio.com/images/Input Stage for 2 Stage PP Amp.pdf
On the discussion chokes vs. ccs:
I will test this in the very near future myself. It is quiet easy to do when we talk about anode choke vs. ccs. But I believe it is nearly impossible to exchange the CCS with a choke in the tail as most chokes have not inductance or to high resistance (talking about true Diff pairs).
Only exception I found was the work of Thomas Mayer: VinylSavor: The Ultimate Line Preamplifier
VinylSavor: 10Y Differential Line Preamp, Part 2
Looking at the poctures, Thoms seems to have used four Anode Chokes, one per tube, but at the cathode.
Indeed the idea of hybrid CCS would be intersting where you have a tube (or maybe choke ?) sitting on top of a transistor-CCS. I found this idea with an 6LW6 intersting: CCS Circuits | Tubelab
Kevin has a lot of very good sounding CCS and very reasonable priced....plus he gives always great support on your projects.
http://www.kandkaudio.com/images/Input Stage for 2 Stage PP Amp.pdf
On the discussion chokes vs. ccs:
I will test this in the very near future myself. It is quiet easy to do when we talk about anode choke vs. ccs. But I believe it is nearly impossible to exchange the CCS with a choke in the tail as most chokes have not inductance or to high resistance (talking about true Diff pairs).
Only exception I found was the work of Thomas Mayer: VinylSavor: The Ultimate Line Preamplifier
VinylSavor: 10Y Differential Line Preamp, Part 2
Looking at the poctures, Thoms seems to have used four Anode Chokes, one per tube, but at the cathode.
Indeed the idea of hybrid CCS would be intersting where you have a tube (or maybe choke ?) sitting on top of a transistor-CCS. I found this idea with an 6LW6 intersting: CCS Circuits | Tubelab
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...cant change the text anymore: I am actually not sure how he uses the four anode chokes of the first article as there are just many in this amp (looking into the second article)...the four chokes at the filament maybe/most likely will be only filament choke as Thomas likes LCL filament supplies...
Well...in the older days there have been schematics and even white papers and I believe this is tremendous...I would regard the way Thomas is sharing today more like as a teasing...for potential customers on his build quality and for us diy-guys to use our brains and figure the stuff out by using a forum like this.
Typically his circuits are very, very simplistic ...for very good reasons. So, it should not be too hard to fogure it out...
Typically his circuits are very, very simplistic ...for very good reasons. So, it should not be too hard to fogure it out...
If you would have done some searching you would have found enough about Thomas' basic circuits and preferences.
Since he has gone "commercial" he does not feel the need, quite understandably, to publish all the details.
On the other hand he has been, and still is, on this forum on a regular basis, providing his advice "for free".
Not long ago I stumbled upon a DIY site of someone in your country who charges just for advice, what about that?
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