New 300B pre-amp?

[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.

[Jim R.]

Dan, Paul,

Do you see any issues with this preamp driving 16-20 foot ICs?  That would be into SR-45s, Stereomour (built as a power amp), and possibly paramounts in the future?

Trying to get a sense of how the new room will be configured and right now I'm leaning towards keeping the main rackk next to the listening chair and running some long interconnects over to the amps which will be situated near the speakers.  I'm trying to keep the space between the speakers as free of acoustic interferences as possible, but I also don't want to run 1.8 watts through 20 feet of speaker wire.

Thanks,

Jim

[Paul Joppa]

Should be no problem. I estimate 50 meters of cable before you see any HF rolloff, and plenty of current margin above that. That's a theoretical estimate of course, but gives you a good idea.

[Jim R.]

Paul,

Thanks -- that helps a lot and also solidifies my plans for the new room.

-- Jim

[Chris]

50 meters!  ... that is great and responsible engineering.. thank you for engineering in all that flexibility Paul...

[Doc B.]

Just to give everyone a heads up on this project - we have another that is ahead of this one in terms of release, but we are currently working on studying the best way to heat the 300B filaments. We hear a difference in the quality of the noise floor with different schemes and need a little time to refine our approach. Which led, yesterday, to our needing to look at the noise on the scope. Which led to having to go inside the scope to figure out why the acquisition board on the scope was flaking out. Which led to PB picking up some new batteries on his way home, to solder in today. Some days doing one simple thing ends up being like building a ship! Hopefully the scope will behave and we can get some useful data and move forward.

[tuffy_puppy]

hi all,  question for jim:  what is a source for quality i/c in the 16-20 range?  i have a situation where almost all of my listening is streaming from my pc to my bottlehead preamp located 16 feet away.  i did locate an i/c from parts express ($70).  not the highest quality.  don't know where else to look.  suggestions??  thanks, don

[Jim R.]

Don,

I currently have a pair of Crimson Music Link speaker cables that are 20' long and they use the same cable with different terminations for their interconnects, so it would be a simple matter of swapping banana plugs for RCAs.  Not cheap though.

You can diy a deceent pair from cat-5 or 6 by braiding the pairs and then connecting all the solid color wires together at each end, and then all the striped pairs at both ends and putting some sleeving over them -- and possibly some groud braid as a shield if you want -- or just use cat-6 as it is and do the same thing for terminations.  The earlier usually requires that you use (if you can find it) cat-5 with twisted pairs that are bonded together.  You could also use mogami star quad abling of various sizes, but really good quality is, for the most part, going to cost some money.  Some of the DH labs cabling could be decent too.  There are a zillion ways to do this, but what level of performance, shielding, etc. will vary greatly with each approach and setup.

For me, the Crimson cables are some of the best I've heard, including many of the insanely priced ones, and while not exactly bargain basement pricing, aren't outrageous compared to most of the boutique cables -- figure $350 for a 1 meter pair of interconnects, and about $525 for an 8-foot pair of speaker cables.  These are my favorite overall and go well with BH gear.

HTH,

Jim

[johnsonad]

Status update please

[Paul Joppa]

Pretty much all the circuit design issues are resolved - PB just sorted out an impedance question for his snazzy gain controls today. And we have a pretty nice-looking chassis layout. It's 10 by 12 inches, same as Stereomour, and dual-mono the hard way - two power transformers(!). Next up is to build another prototype, this time with all the production parts and component values. That may or may not be the actual production prototype (the one that will be in the manual).

[johnsonad]

Thanks Paul   Does the single chassis allow room for different attenuators (ladder, etc), and other user specific mods?  It sounds pretty full  given the single chassis layout.

Regards,

Aaron