New 300B pre-amp?

[Gerry E.]

... PB just sorted out an impedance question for his snazzy gain controls today... and dual-mono the hard way

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

[xcortes]

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.

[Doc B.]

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.

[earwaxxer]

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.

[John Roman]

She's picking up speed now!!!!!!!

[xcortes]

Yep, I thought about the regulators after posting. Why constrain to 12 width? Go to 19!

Saludos

[Doc B.]

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.

[ironbut]

Oooh Boy!
The balanced in/out sounds peachy to me!
Need any beta testers?

[johnsonad]

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). 

[Gerry E.]

Yes, at this point the plan is that transformer balanced inputs will be an option...

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

[Doc B.]

Balanced output is not necessarily from a fully differential output. As sweet and bright a guy as Allen was, he used to make me crazy by mixing the definitions. He was talking about push-pull circuits inside the amp (or as George Wright use to call it, push and shove circuits).

Balanced connection simply means that the impedances are balanced between the signal wires at both the source and load end of the cable. It's a technique for wiring equipment together with cables the improves the common mode noise rejection, not an amp topology.

[Paul Birkeland]

Hello Aaron,

We plan to offer the stepped attenuators as an upgrade, and so far they have outperformed all other attenuators that we have used. 

-Paul

[johnsonad]

PB, I don't doubt that it is a great attenuator but can you tell me if it will allow for stepping of each channel individually to comp for balance? It's a PITA to move 150 lbs speakers to get a good center image.

Thanks,

Aaron

[Doc B.]

It's a stereo attenuator, one switch for both channels. My suggestion for balance trim would be to put trimmers in the amp inputs. That will allow for changes in gain throughout the system as tubes age.

[johnsonad]

Team BH, what is the attenuator resistance range for this preamp? Hopefully 10k or 50k will work? I really would like a remote, (for once) and have an ideal in mind.