416C defined source Z phono

the road not taken.
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reVintage
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Post by reVintage »

New ideas!

Just found some WE 416C. With their mu of 300 they will probably be somewhat hard to tame :wink: ! Have checked the Ua/Ia-curves and 10mA/150V will probably be OK.

I have two options:

1. Transformer load them with in the ballpark of 8:1 and place a second gainstage after the LCR. This will reflect ca 80k (with respect to the 1,2k secondary-load) to the 416 and still leave us with ca 30dB gain.

2. Place a tube impedance-converter after the 416 via a 1:1 bifilar and take the lowish 120-130mV output directly from the LCR. Will then need a line-stage with ca 20dB gain.
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Lars
reVintage
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Post by reVintage »

Below is what I came up with.

With 10mA through a primary that is gapped for 5mA, 40mA is needed through the secondary.

My idea is to use the voltage-drop through the secondary to bias the second gain stage.

The only problem is that the secondary DCR must be matched.
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dave slagle
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Post by dave slagle »

Hey Lars,

Typed in a long reply last night and must have only hit Preview... here is a shorter version. (maybe we should split this off)

I played with the 416 about 8 years ago with the hopes of driving a tango EQ-600P through a substantial step-down. I could never get the 416's to bias up properly before they fried. Not sure if it was bad tubes or user error.

I really like the idea of the defined source driving the LCR through a fixed resistance. Why not swap (or wire) the transformer loading the 416 for a tapped choke (autoformer) and direct couple? Then i would look at a 1:1 on the output and you have 12dB extra gain and much better bandwidth. With that 12Db of gain you could either go to a lower mu tube at the output (two high Gm tubes may not ive the most foriving sound) or you could increase the stepdown in the 416 autoformer which should also buy you some bandwidth. Of course this are just some thoughts based on my tastes... feel free to ignore :-)


dave
reVintage
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Post by reVintage »

Hi Dave,
I am also attracted to the bifi 1:1 idea. So I have been working on it for a few days. The 416C will probably be a wild horse to tame :twisted: . It has a theoretical Ri of ca 5k so some kind of buffer is needed. So back to my 180H/10mA, 4650/3600ohm Slagle bifilar 8) ! Ideally more inductance is maybe be good as the sims with 416C indicates -1dB at 20Hz, would go for 300H if that was possible........

When I saw Prazzas thread about crossovers I got the idea of a BJT buffer. Below are three versions, the first two being from the Walt Jung concept. The third one is a no gain version of an old concept from the sixties with "current PI" as used in the JLH 10W Class-A.

When simmed the 3rd is the winner IMHO.
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Lars
dave slagle
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Post by dave slagle »

hope you don't mind, I split this off for clarity and ease of following. The original thread is possibly the best here and I personally find 50 page threads impossible to go back over. Anyways, back to our regular discussion :-)

I absolutely thing Iron is the way to buffer the 5K source. I know I may be repeatin myself, but I am not a fan of low ratio transformers which is why the 416 really appeals to me. Things just get better from a winding (and bandwidth) perspective as you get beyond 4:1. the problem comes when you need gain the 10:1 is self defeating. (unless you have a gain of 300 to begin with). I just mentioned the tapped plate choke since my hunch is it will sound better than a transformer and your LCR lends itself to direct coupling.

The buffer idea is appealing because you will get the full gain (yikes!) and then your second tube could be something you really like the sound of without consideration of gain. I'll be the first to admit that i do not understand the sand circuits, but with a working spice file I can play with the values and learn :-) I'm glad you are following the prazza thread, and if the some of the "buffer work" overlaps we all win.

dave
reVintage
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Post by reVintage »

Thanks Dave,

Great idea to start this as a new thread.

My idea with this second "bifilar to buffer"-idea was to eliminate a second tube in the RIAA. You will get in the the ballpark of 120mV out from the LCR with 5mV in.

This way you could directly feed it to a AVC or TVC and a 20dB preamp. The other sources should then be connected wíth stepdown transformers :wink: !

Frankly, I am no "Master of Sand" either! I play around in LTSpice and learn by doing :D .

You will have to add BD139 and BD140 to your LIB/CMP to make the file work. I got mine from Fairchild.
Brgds
Lars
DowdyLama
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Post by DowdyLama »

I played with the 416s last year.
I could get them to bias, but could never get them to sound good...had to install 3k3 grid stoppers to avoid unprovoked oscillation - I finally gave up on them.

Please keep us informed - I'd love to figure out how to make music with them :?

Jim
reVintage
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Post by reVintage »

This is the other driver idea!
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