New 300B pre-amp?

[Frank Mena]

Somewhere i read that a 300B pre-amp was in the works.  Fiction....?, yet to be finalized....? wish-full thinking?  somewhere on the to-do list?

Thanks in advance.
FM

 

[earwaxxer]

I second the interest on the 300B pre. I would wonder what sort of character that tube circuit would have, and how complex would it have to be.

 

[jrihs]

I third it! Its on my B-day wish list. Which is fast approaching in May though. Any chance of a spring release?

 

[ironbut]

Heard it! Not ideal conditions and it was sourced by the proto DAC so I can't honestly say what was contributing what,.. but it does exist.

 

[Grainger49]

There is a picture of the Bottlehead display at a recent gathering. 

Here:

http://www.bottlehead.com/smf/index.php/topic,2659.0.html

 

[Doc B]

Yes, the prototype exists. PB is working on a second prototype, a finished version in the style of the Tube Phono. It is the best preamp I've had in our system at BHQ. It will be a kit, intended to work with Paramount in particular but also as a great preamp for just about anything you can throw at it. Don't have a price yet, don't have a release date yet. We still have to work out some details regarding layout and parts choices.

In conjunction with working with the preamp prototype we made a change in the system yesterday. The SR45 amps we built to run the tweeters have (relative to the Paramounts) low input sensitivity, and that was forcing us to turn down level controls on the active crossovers that feed the mid range and woofer Paramounts to the point where we just couldn't quite get the system jumping with some sources. Also I had a sense that they were running out of steam into the Raal ribbons when we really cranked it. So yesterday Shawn brought in a pair of his Paramounts to replace the SR45s. This allowed us to turn up the level controls on the mids and woofers - a lot.

This combination of all Paramount amps driven with active crossovers with the 300B preamp ahead of them is now rockin' the house with 56 watts per channel. It can go very loud and sounds very quick and relaxed doing it. It's one of those "now I have to listen to all my favorite stuff all over again" kind of changes. Plan to spend a generous portion of time listening this weekend.

 

[BNAL]

Doc,

Were the Paramounts also 300Bs?

 

[Doc B]

Yeah, all 14 of the Paramounts in the system are 300Bs - one on each tweeter, four on each midrange with secondaries wired in series, two on each 4 woofer array with each amp running two parallel wired woofers. The math says the system should now be capable of 106dB peaks. It's now time to revisit our room treatments to better tune the room to handle higher levels.

 

[earwaxxer]

wow! 56wpc of 300B power! Delicious!

 

[johnsonad]

Will the output be transformer coupled?  Are you able to give us a ballpark on input and output impedance?

 

[Brillo]

Doc - With the Tode progressing so well, will attentions be turned to the 300B preamp? Would love to hear an update on this one...

 

[Doc B]

We are making some changes to speed up the release of new products. That should start in May. So hopefully we will be able to get a bunch of new product ideas out this year - Tode, the DAC, the 300B preamp and a few other ideas I've been musing on.

 

[jrebman]

Hope one of those other ideas will be a 2-way electronic crossover with adjustable gain, frequency and phase -- maybe even a couple of different slopes?

-- Jim

 

[Paul Joppa]

Hope one of those other ideas will be a 2-way electronic crossover with adjustable gain, frequency and phase -- maybe even a couple of different slopes?

-- Jim

Here's the thing that always stops me when I look at a fully-adjustable crossover:

Starting point is a first- or second-order Sallen and Key circuit with cathode followers. Two dual triodes, just like Foreplay or Seduction; possibly another tube for shunt-regulated supply voltage. With no adjustments, it would make a reasonable kit. This is basically what Doc B uses in the Big Rig (I think there are four of them).

adjustable gain: high-pass, low-pass, left and right, that's 4 knobs. For uncompromised filter accuracy, they will need buffers - two more dual triodes.

Adjustable frequency: as above, but each of them is a dual pot. You can't cover any more than an octave that way, so there's a range switch for each as well. That's eight more knobs, total 12.

Phase: Forget it, the only useful way to do this is to implement a variable time delay on each output, which is easy with digital and ridiculous with analog.

So, even without phase you have 12 knobs and at least five tubes. Now think what a b*&^%h it is to wire up the three knobs on a Foreplay or Stereomour. Think about upgrading 4 mono pots plus 4 stereo pots plus four rotary switches. Think about the cost of all those premium pots and switches...

 

[jrebman]

Paul,

Ok, gotcha.  Figured I was asking for a bit much .  I also don't really want to go the digital eq route either, the one exception may be to use a 4-channel dac and use the digital crossover feature in PureMusic, but I don't want to take my nice clean audio and send it into a cheap A/D converter and then to another dac which is probably not up to the same sonic standards as a dedicated source dac.  I'm also trying to stay away from CF circuits as much as possible, but that isn't always practical either.

-- Jim

 

[Paul Joppa]

If we made a non-adjustable kit, here's what I would do. Get a cheap adjustable crossover - Rane is local here and makes several models; there are many others. Play with it until I had a pretty good idea of what crossover function I wanted. Then, build a tube version with those slopes and frequencies.

For the Big Rig, we actually made measurements of the drivers and designed a crossover specifically for them, then implemented it. We've made a few small alterations since, but one or two subtle adjustments can be done by soldering easily enough. It's the initial stages, if you don't have detailed measurements of the individual drivers as installed, where you'd want to do lots and lots of experimenting and listening and therefor need a highly adjustable crossover.

 

[johnsonad]

Will the output be transformer coupled?  Are you able to give us a ballpark on input and output impedance?

Must have been missed by those in the know.  Doc, PJ, can you answer this yet or is it still in the works? 

 

[Doc B]

It will be cap output, single ended 500 ohms or so output impedance. With an option to add a 1:1 trans with CT secondary if you want to run balanced.

 

[Roger]

Is it possible to have an approx time for when the 300b-pre will be released? Will it be an all-out kit, or will you offer various options?
Roger

 

[Doc B]

As I mentioned a few posts below, some changes will be happening in May and we should have a little better sense of a schedule for when new things will be coming out after that.