Bascom's Preamp Chronicles


#1

We’re starting a new topic for Bascom H. King, or BHK as he is known, to write about the upcoming preamplifier. He’ll cover design decisions, failures, successes, ideas - both good and bad - and the journey to design and build his finest statement on the art of preamplification. And how cool is this?

BHK has spent a lifetime designing analog electronics that matter, that make music, that bring joy to people. And he’s asked for space and a forum to share with us his ramblings on the art of analog design.

I look forward to learning from this master. Please help in encouraging him to write deeply and often so we might all learn.


#2

This will be great fun!


#3

Indeed. Bring it on Bascom!


#4

As obvious as it may seem, I would like to hear his take on why his preamp improves the sound in comparison to running the DS direct. I know some still prefer a preamp, I personally don’t, but there is some interaction going on that no one seems to clearly understand. I know Paul had his socks knocked off in comparison to his reference preamp, but my socks are generally well attached and not subject to such easy removal. In other words call me an agnostic waiting for the right explanation to shift me into belief.

Hi Pmotz. You bring up a good point and rather timely as I have been listening to my Direct Stream DAC direct into my power amp as I take my ptototype BHK Signature preamp (1 or 3) in and out of my system to go work on it in my lab. The system without the preamp in it sounds very nice and acceptable but when the preamp is back in there is a very obvious increase in musicality, transient attack, spaciousness, and detail. I am amazed and delighted with this creation. But I must disappoint as I must be in the camp of those who cannot explain it. I just know what it does for my musical enjoyment and that, in the end, is where it is at for me.

BHK

Ah, mistake in the (1 or 3) above. It should have been (1 of 3) Three prototype units of the evolving design.

BHK


#5

A few cues that could affect things would be:

  • Sensitivity match

  • Impedance matching

  • Headroom regime

For a start…

Hi Frode. Those are interesting things to consider at some point in the discussion. However, I am starting out by telling the story of how the BHK Signature Preamp came to be conceived and how the thing evolved to where we are presently in the prototype development process.

BHK


#6

That’s fine :)

My post was a comment to pmotz.


#7

Frode, I’ve heard those mentioned before, but it seems everyone is thinking out loud rather than showing/demonstrating that is the reason. I’m not sying they are wrong, but I’m thinking Bascom is experienced enough to know why this is. As such he has done something during the design to make sure it works and works damn good at that. I think Paul intended this to go a different direction than I thought, though, so may be a while before he gets to answering my question. I can wait…


#8

The idea for a BHK Signature preamp as a product was a result of ideas discussed between myself, Arnie Nudell and Paul McGowan about the BHK Signature power amp design and experience with several very good sounding headphone amplifiers – namely an old Melos line stage/headphone amp and the Pathos Aurium. These headphone amps both had a tube input stage and a solid state gain of one output stage. Well, it seemed that the prescription for a great sounding preamp would be some kind of input volume control into a tube differential amplifier and into a solid state class A MOSFET gain of one output stage running a good stiff amount of idling current for each output phase. The volume control was to be some kind of switched attenuator arrangement. Conversations with the most immanently capable Herr Stadtherr of PS Audio culminated in a tentative schematic design and the process was started. As with the design of the BHK Signature amps, working with PS Audio where I come up with a design concept and initial circuit design, then they implement the design with back and forth conversation about it has worked very well for me. Next, some of the design ideas and leading up to the first prototype unit received by me.


#9

BHK Signature preamp (1 or 3)

Are there two models 1 and 3 if so what are the differences?

magicknow


#10
magicknow said BHK Signature preamp (1 or 3)

Are there two models 1 and 3 if so what are the differences?

magicknow


There is one model if you will. So far, there are three playing prototype units of the evolving design. One is at PS Audio, one is with Arnie Nudell where he is evaluating different tubes for the design that are not NOS ones and can be bought for production and generally commenting on the process, and the first one that I work on and enjoy the sound of.smile

BHK


#11

Wonderful Forum Topic !

I’m also very interested in the differences between Direct (No-Preamp) and Pre-Amplification (BHK Style).

I wouldn’t want to bore the others, but if other people think it would be warranted, it might be nice to hear a “ground up” approach from Bascom on what a Pre-Amplifier is intended to accomplish.

On a number of topics (including really “simple” topics like PRaT), there have been a wide variety of pre-conceptions that members brought to the table. So, if it were not too boring for Bascom, it might be nice to hear all about the most “obvious” of things associated with the design.

Also, I don’t think I could ever really tire of hearing about Bascom’s work, so the more BHK is inclined to write, the better - as far as I am concerned.

Cheers,

GM


#12

Thanks Bascom! This is great, a rare glimpse into the working of an analog guru we all appreciate reading. I can’t wait for the next installment.


#13
BHK said ...

Hi Pmotz. You bring up a good point and rather timely as I have been listening to my Direct Stream DAC direct into my power amp as I take my ptototype BHK Signature preamp (1 or 3) in and out of my system to go work on it in my lab. The system without the preamp in it sounds very nice and acceptable but when the preamp is back in there is a very obvious increase in musicality, transient attack, spaciousness, and detail. I am amazed and delighted with this creation. But I must disappoint as I must be in the camp of those who cannot explain it. I just know what it does for my musical enjoyment and that, in the end, is where it is at for me.

BHK

BHK, thanks for being honest! It's funny and frustrating at the same time how many things in this hobby are easy for us to hear but cannot completely explain. My engineering side wants an explanation before accepting it, but my (let's call it) "listening" side just likes to get the best it can. It will be interesting to hear your take on this endeavor.

I like you feel pretty much the same way! My engineering side wants to know the why and my listening side more or less hears the differences in things. Actually, when I was younger, I wanted to be the one that found out the why of it all but I failed and just decided to keep at it and perhaps one day I would.

BHK


#14

I received prototype #1 in early July. I have attached two pics of the unit – one as it is installed in my setup and the other as I first got it. One exception, the little pc board between the tubes was not in it originally. More on that later. The finished units will have a shiny black cover over the metal cover shown here and of course a proper knob, headphone jack, etc. When I first measured its frequency response, I was surprised to see that it was 3 dB down at a little more than 20 kHz. Whoa, not right! It turns out that there was a small capacitor in the input attenuator that was the culprit. I clipped those out and then we had a more proper high frequency bandwidth. I settled on some Philips PCC88 tubes to initially listen to it in my setup. Immediately, I was impressed and became more so with more listening as it broke in. There was this wonderful detail and transparency that made me think that we had created something pretty magical! Also during this time, I had designed and bread boarded a headphone amplifier circuit to go in the preamp. It was not long before it was time for my annual car trip up to Arnie Nudell’s to attend Vail Bravo Festival concerts and test and listen to the preamp and headphone amp and other things on his system.top-cover-off.jpgTop-cover-on.jpg


#15

This is awesome Bascom!


#16

This is so exciting and so funnnnn. I’m loving and hanging on each and every word from Basom. What a treat. And Paul, thank you for making this all possible!


#17

Oh, and thanks for reading and sharing! I am excited as well. I have much to learn.


#18

Paul and Bascom, this is going to be great! Thanks!

One observation so far, the power supply is internal. In an “all-out-assault” on pushing the preamp paradigm envelope, I would have guessed a second chassis to separate the transformer, etc. would have been employed. I am sure it was considered.

And gadzooks, a Shakti Stone in the photo. One of the few things I have NOT tried but have come close so many times. Any comments on the Shakti?


#19

Regarding the preamp-vs.-no-preamp issue: Bascom’s comments about the improvements made by inserting his pre in the chain are very similar to the differences generally noted between active and passive preamps. Passives are felt to be very clean and transparent, but subject to strain and often lacking in dynamic capabilities.

The system in Sound Room One, using a DS straight in, has never seemed to be lacking in dynamic impact–but somehow with the prototype BHK pre inserted in the chain, it’s just more palpable and real…more MORE. ;->

Like Bascom and Paul, I find a theoretical explanation for this to be elusive–more current capability? I don’t know.

But as we all know from cable-deniers and climate-change deniers, theoretical dogmatism is often a front for ignoring/denying problematic and inexplicable truths.

That doesn’t mean that the difference isn’t real.


#20

[big quote of text and pictures deleted]

Good morning.

This is my first post with the new io9 and it’s making things crazy not sure where I am writing

very glad you designing this preamp as you amps in mono will be driving my set of IRS V soon.

If I may suggest something for the headphone side of the preamp

it should have both high and low output imp as some headphones like the hd800 sound best from an amp that is

second a low imp but one with plenty of reserve power for flagship headphones like Hifi man HE6 it needs about 2 watts at 50 ohms

there are others to please but getting those two nailed is a headfi

dream setup

thanks