New 300B pre-amp?

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
 
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.
 
50 meters!  ... that is great and responsible engineering.. thank you for engineering in all that flexibility Paul...
 
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.
 
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
 
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
 
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).
 
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
 
Paul Joppa said:
... PB just sorted out an impedance question for his snazzy gain controls today... and dual-mono the hard way
Click to expand...

Does this mean there will be separate left/right gain controls?  Having the ability to fine tune channel balance would be a MAJOR plus in my book.  Thanks.

Gerry
 
Remember that there's only one tube per channel so a 12 x 10 in chassis should have enough space. It's 120 sq in vs 60 of the FP2 and 80 of the FP3.
 
There are two tubes per channel, a 300B for the voltage amp and a 6BQ5 for the shunt regulator. We were assuming the chassis would be 10" x 12" until PB started trying to fit in all the XLR jacks for balanced inputs and outputs yesterday. Those have required an increase in the layout to 12 x 12. Even though it's "just a preamp", there is a lot of stuff in this puppy - two power transformers for the dual mono supplies, big shunt regulator boards, a fairly sophisticated regulator for the filament supply, a very trick 63 step coarse/fine volume control (that in my opinion will not automatically be upgraded by putting in a different attenuator) probably optional input and output transformers for balanced operation, and all of this needs to be laid out so that there is ample room between your hand and the hot tubes when turning the knobs. My hunch is that we are close on the layout, and we will hopefully be ordering some parts for the functional prototype in the next week or so.
 
Maybe you could offer the kit with/without XLR to save some people some money. I know that I'm not interested in balanced. I have too much invested in RCA cables, and I dont think balanced is needed in short cable runs.
 
Yes, at this point that plan is that transformer balanced inputs will be an option, the coarse/fine stepped stereo attenuator will be an option with the basic version being a stereo volume pot and balance control pot. We are investigating other options as well. The kit will be available with and without 300Bs. PB is shooting for an under $1K price tag for the basic version w/o 300Bs. Not sure if we will make it, but we should get close.
 
Dan/PB/PJ, could you tell us a little more about this fancy attenuator you have created?  My ideal attenuator would have 1dB (or less) steps where each channel can be adjusted (for balance) but overall volume increased in stereo (one control). 
 
Doc B. said:
Yes, at this point the plan is that transformer balanced inputs will be an option...
Click to expand...

The following is related to the balanced option.  Allen Wright stated the balanced operation only made sense if it were used in the entire system.  In other words from source component to preamp to amplifier.

Putting aside the fact that the new 300B preamp may be used with other amplifiers, why even offer the balanced option if the Paramount amplifier itself is not balanced?  I
 
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