Vacuum tube based moving coil stepup? Hmmmm...

[Doc B.]

One of the more interesting of my many very interesting conversations at CAS2011 started with my being approached by a very nice fellow who asked me point blank why I didn't do a vacuum tube based moving coil step up preamp. My knee jerk reply was "too noisy". But he persisted very nicely and really got me to think about it. With an Eros or our big Tube Phono you don't need a whole lot of step up ratio. The more I thought about it the more I realized that if the SeDACtion circuit I was using in our prototype DAC could be quiet enough, we might have just what we needed.

Well, some preliminary tests today show great promise! It's quiet, and I think if we can find the sweet spot for loading my old Van den Hul MC 1 we may really have a killer combo. Anybody interested in such a beast? Don't have gain figures yet, (it shifts around a bit with the input resistance adjustment) but it seems like it should work well with Eros and maybe even Seduction. The presentation has really quick and snappy transients that I haven't heard before from my vinyl setup.

[Tubejack]

Great idea, Doc.  I'm in. 

I was never really happy with any of the iron stepup's I tried - K&K, DIY Altec 4722's, even sold my Bent Audio Mu's that used the S&B TX103's. Built a Hagerman Piccolo that convinced me, in my Bottlehead system, that active was the way to go. I'm currently using a Shelter 501 II/Graham Slee Elevator EXP/Eros, but hey, it's the only sand device in my vinyl chain.  I'd love to see a Bottlehead tube MC headamp.

[debk]

I would be interested also.


Debra

[Grainger49]

I'm sure that a number of MC cartridge owners wonder what range of input impedances and gain ranges would it have?  That is, if there is currently a target.

[Doc B.]

We have a trimpot wired as a variable resistor on each input. That is a very clean and simple way for someone with DIY ability to get exactly the value they want, you just put an ohmmeter across the trimpot and trim it to the value. We could even throw a couple of different pots in to cover different ranges, like a 1K and a 10K. We had no trouble at all trimming the 2K pots in the SeDACtion down to around 100 ohms.

Gain is not determined yet, as I want to try a couple of different tubes and gain trim ideas.

[ajkdc]

I'd welcome an active step-up option.  SUTs are great with cartridges that were designed to use them, but it can be very frustrating finding a good match with those that weren't.  However, I have a strong personal preference (YMMV) against adding yet another separate component (with added cables and connections) to the signal chain - especially at the small signal end of the chain.  Perhaps it could be developed as a separate component first, and the next revision to Eros and/or Seduction could incorporate it as an option that can be built-in.

[xcortes]

Sounds cool to me. I'm happy with my SUTs but would love to try your new approach.

[John Roman]

SeDACtion? So there is a name for the rumored DAC from Bottlehead. Progress is being made, No?

Surley mood today, sorry Doc!

[Doc B.]

The SeDACtion is the tube output stage that we have been using as we develop the Bottlehead DAC. Best bet for info about that project is to look at the Digital forum for updates. I had a good meeting with John Swenson, who is developing the digital part of the DAC, at CAS2011 and the project is moving forward.

Shawn and I listened more today to the SeDACtion circuit as MC step up. Like all of these projects we have to be very careful to only change one thing at a time and listen to the result, and that makes the process a little slower than we would like it to be. So far the concept shows a lot of promise and maybe poses a couple of questions that need to be resolved. We will be doing a few more tests next week to help to determine if it can deliver as we hope it will. I'll keep you folks posted.

No problem with feeling surly, I've been that way a bit myself during this warm weather in a country where the distinction between pop stars and politicians blurs.

[elcraigo]

I would bite on a Bottlehead product like this. I currently use cinemag step-ups.
Would not bother me if changing the input Z required changing a R here or there or a little trim pot is cool.
I personally don't change cartridges a lot, but, I do like messing with the loading.
I'd prefer a separate device even if it required short cables. I have a Sedution.
Add a magic eye to indicate the Z and you are all set, just kidding on the last part - it was beer Friday at work.

[Grainger49]

Beer Friday?? Are they hiring??

[Paul Joppa]

..., I have a strong personal preference (YMMV) against adding yet another separate component (with added cables and connections) to the signal chain - especially at the small signal end of the chain.  ...ext revision to Eros and/or Seduction could incorporate it as an option that can be built-in.

There might be a possibility there. Thinking of an Eros chassis with the stepup plus a Seduction; we'd have to use a glow tube for shunt regulation (not enough heater current for a tube regulator). Not high on the priority list at this point, but it's a concept.

[johnsonad]

What tube are you guys playing around with?

[levlhed]

I'd be interested!

[sl-15]

although my next purchase in the queue is the extended upgrade for the foreplay i am definitely interested. the nice fellow you met is a friend of mine and we listened to his tube pre pre a while back. although there was something wrong with it (which resulted in a lot of noise) it outperformed the transformer step-up we compared it too. my experience with different trannsformer based step-ups is rather limited though. but i would be excited to add yet another tube component to the mix. so yes, count me in!