• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hi-end definitive vacuum tube phono pre

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#22
analog_sa said:
Don't know. I generally hated all mica caps i've tried. It's possible there are excellent ones i haven't tried.
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Mica's do go bad...physically broken...so do ceramics. In fact, one of the problems with ceramics is that they can vibrate.

I use polystyrene when I can, but these are limited to 100V and you have to be careful soldering them.
 
#24
One bad thread here in an ocean of good ones....Well, this is certainly not AA
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Yeah, you're right. I just happen to be reading the interview at lunch today and I just had to vent when I got back to work. I get an occasional email telling me that I am being slammed by the guru of the week over at AA, but I don't care. The inmates are running the show over there. I never even signed up for that one. Too much like RAT.

All zoos have signs "don't feed the animals" for good reason. And, I observe that Andrea did not take the bait...
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I was dumb enough to be baited by a troll once. It raised my blood presure too much. Turned the computer off for a few days, until I realized that there are a few people out there with nothing better to do. There are a lot of people here who genuinely want to learn and a some who share their designs willingly. I often get emails from newbies who are scared off by a few that tell them that everything they are contemplating sucks, but offer nothing better. This is quite confusing to a newbie.

Does tubelab sacrifice tubes to impress the ladies? Or does tubelab sacrifice tubes because some tubes were born to die in the name of science?
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Well, I haven't impressed anyone yet, and my wife thinks that I am flippin nuts! The last glowing tube was out of sheer boredom! The next ones will be in the quest for a big P-P amp! I got some $1 sweep tubes at a hamfest, I guess some were born to........

Or, the DCR of his Kung Fu was low enough, but he didn't understand it was the ONLY reason his rig sounded so good.
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I wonder what the DCR of that little National chip is, or the 7805 that is powering it? OOPS, it must sound like s***. Quiet s***, but s***. I can't seem to find a $4 tube that is as quiet, maybe I need some better tubes, or some better Kung Fu!
 
#25
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Hello Andrea
thanks for sharing.
You wrote “no compromise phono preamplifier”. But I can see some compromises.

First: The cathode bypass cap. It is not in the signal path but it has a strong sonic influence. Signal current causes voltage droppings and these are added (or subtracted) to the input signal between ground and grid.

Second: At high signal frequencies, there is more signal level at the grid of the input triode than at the output triode. Means dynamic loss at high frequencies.

Third: You have transformers in the signal path.

LG Darius
 
#26
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Vlauga said:
planet10

Strange... For some reason in your reference there is no my solution with a minimum crossing of sound currents plus fullpower work in regime A2 ...
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Hi Vlauga

thanks for the link to your schematic, excellent. Your output is a “part three Loftin White” . I would recommend this for Andrea #1. A output loop is formed by C2, transformer and tube, the so called ultrapath. The cathode bypass is eliminated from the output current loop. 🙂 This is an advantage you can get from a transformer and Andrea should take it, shouldn't he?

Kind regards,
Darius
 
#27
Re: This posting was erased from this thread ...

oldeurope said:
Hello Andrea
thanks for sharing.
You wrote “no compromise phono preamplifier”. But I can see some compromises.

First: The cathode bypass cap. It is not in the signal path but it has a strong sonic influence. Signal current causes voltage droppings and these are added (or subtracted) to the input signal between ground and grid.

Second: At high signal frequencies, there is more signal level at the grid of the input triode than at the output triode. Means dynamic loss at high frequencies.

Third: You have transformers in the signal path.

LG Darius
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There are compromises in each and every amplifier, Darius

In your RIAA 2007 you have noisy, unlinear coupling triodes, a very strange current source and a very long what you called "signal path". Please talk about that.

Regards,
Reinhard
 
#31
I would use the circuit as a starting point. Another that used something like this as a starting point but went on to develop something I believe is a bit special is here from what I've heard from others http://diyaudioprojects.com/mirror/members.aol.com/analogengineer/6gu5ph.html It developed further with a thread on Intact Audio Forum.

IMHO, you should eliminate all cathode bypass caps by using either diodes to bias or fixed bias.

RC all in one EQs work better at low Z so design for that. If you want to spend more, most reckon LCR EQ to be better again. Steve's LR may even be better still.

Designing the EQ from scratch will require you to be able to measure very very accurately or sim with good models. It is almost impossible to calculate accurately without a very big spreadsheet and a ton of patience IMHO. Forget using one equation to work it out.

You might also want to think about parafeed but be careful, it ain't easy 🙂

I love phono stages and it's virtually all I've done for ages in DIYery. So much to find in there not only in the circuit but how you build them, how you power them and so on.

Good luck! I hope you get some decent feedback here.

My Site http://www.izzy-wizzy.com/audio/preampnew.html

cheers,

Stephen
 
#38
Andrea,
the transformer are NEVER neutral in any schematic you use.
Mainly when you try to drive a big triode; if you haven't a good test set you can't reach the best results. (we spoke together two days ago about this)


Ciao


Walter
 
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