Like others here I am seriously intrigued by notion of a preamplifier between my DirectStream and my Power Amp improving the sound vis-a-vis plugging the DS directly into the PA. With my own PreAmp the improvement going direct is massive [to the extent that I’m thinking of selling the PreAmp. It hasn’t even been powered up in a year]. I comfortable with the notion of a great PreAmp design reducing the difference to negligible levels, but going beyond that and having the PreAmp generate an improvement ultimately calls for an explanation. I can only imagine that it has to do with interface issues between the output stage of the DS and the input stage of the PA which are eliminated by the insertion of the PreAmp, but who knows?..
I’m firmly in the camp that, at the end of the day, doesn’t really care provided the product actually does what is claimed for it. But pursuing the technical underpinnings remains an intriguing part of our hobby/profession.
Of course, the experimentalist in me immediately wants to know … what would the DS sound like if it had the BHK PreAmp’s output stage?
I suspect that the digital noise in the DS would be kind of hostile to a good preamp. Tho I’m fond of a good analog volume control, the DS only does attenuation in it’s output stage so I’m not sure that a built in analog preamp would help a lot (or at least one that didn’t add significant cost to the unit.)
Oops, I kind of forgot to talk about some of the design aspects of the preamp. The volume control scheme consists of a balanced input attenuator that switches in large increments of attenuation that drive the inputs of the tube differential amplifier. Like for iexample, 0, -10, -20 dB, etc. The small in between increments of attenuation are accomplished by changing the gain of the tube stage. The overall result is small increments of attenuation (0.5 - 1 dB/step) down to about – 80 dB. The outputs of the tube stage are capacitor coupled to the inputs of the two MOSFET output amplifiers per channel. These are MOSFET source followers with MOSFET constant current sources and with the signal outputs servo controlled for zero DC offset. Idling current is about 50 mA and they can drive down to 1K Ohm loads if needed. Each channel has its own regulated high voltage B+ supply and regulated plus and minus 30V for the output amplifiers. The -30V supply also is used for the tube circuit’s constant current source.
When up to Arnie’s for my summer visit, we first put my preamp prototype into his main listening system in place of the long standing reference, his Aesthetix Calypso. This was another WOW moment of major proportions where the qualities of this circuit pretty much shocked the hell out of us! One of the things that stood out was how much more powerful and extended the bass was. And then there was this greater transparency and ability to hear into the music. Arnie has a separate headphone listening setup away from his main system room. We setup the preamp in that system and then fed the headphone prototype with cables from the preamp output. This sounded quite terrific also and was easily as good if not better than the headphone amps he was using in that setup. Then we set up this arrangement of the preamp and headphone prototype to be driven from his ModWright Elyse DAC over in the main system. Using the new HiFiMan HE1000 headphones - Oh Lordy, what transparency and great sound that was! All in all, this was a very successful revelation of how good this new design is from a sonic standpoint. There were some problems with the volume control having popping sounds when changing volume that have lasted into recent times that are presently being solved. More on some of this and tube testing by Arnie to come.
Bhk , so very kind of you to give more info as I am very hopeful of the final product to be very good.
As for the headphones nice choice in deed . I had the honker demoing that new pair a good choice speaker like for sure fang is a talented man . The headphones are far more easy to drive then the HE6 are. In my own comparisons I still prefured the hd800 and the he6 to them. Although they were a move to being useful in many more amps I felt they lacked in the mids a bit and the he 6 are still my favorite . They were light on the head and had good low end details too. It’s good to know Arnie has new and flagship to compare with . I think the amp Arnie had the hifiman amp if I am correct it’s an ok amp and yours besting it is a good sign of the direction your heading .
The amp to beat or be in the class with is the woo wa5 . For the he 6 anyway getting to that output power is where you need to be . It has more than enough to drive them and it’s my second choice in the hd800 . Now they are something Arnie should acquire for you . They need high output imp and if you get those singing your in . Weather Paul admits or not there is more headphone people than speaker People.
Just go on headfi and see it above any other forums I know of big bucks in advertising going on.
Please do not take me for being a troll. I am not and you and Arnie know far more than I ever will in audio. But I am a headphone guy first and have over 170 k invested in headphones Apms and dacs . Not counting any speakers I am truly trying to help and nothing more .
again thanks for you to take this time to post about your all the BHK ps audio products
Well heck, since dedicated “high end” headphone amps have been mentioned, I might as well throw an additional request into the mix.
Don’t forget the electrostatic headphone connectors when you add headphone connectors. Yes I realize that means a high voltage baising supply too, and specific 5 pin outputs. But hey, a guy can dream can’t he?
Sorry to sound like a broken record, but no on has been able to answer my question in a while, namely, why did AudioResearch go for the 6H30 “supertube” years ago and yet Bascom/Paul are sticking with the 6922/ECC88? Granted there are more types to roll with the 6922/ECC88 than the 6H30, but the transconductance of the 6H30 is on the order of 17,000 to 18,000 vs. 12,500 or so for the 6922 family.
Can this make a difference to the sound? Or doesn’t it matter? Have you tried the new circuit with the 6H30?
Streets Still Works said
Sorry to sound like a broken record, but no on has been able to answer my question in a while, namely, why did AudioResearch go for the 6H30 "supertube" years ago and yet Bascom/Paul are sticking with the 6922/ECC88? Granted there are more types to roll with the 6922/ECC88 than the 6H30, but the transconductance of the 6H30 is on the order of 17,000 to 18,000 vs. 12,500 or so for the 6922 family.
Can this make a difference to the sound? Or doesn’t it matter? Have you tried the new circuit with the 6H30?
Curious minds want to know.
Thanks.
–SSW
Hi Streets Still Works. Yes, I know of the 6H30 and we are going to try that tube out. What we are trying to find is a tube that sounds as close as possible to a Tungstram 7DJ8 which sounds the best in the preamp circuit. We have found a particular brand of 12AU7 that is not NOS but is currently produced and it looks like that is what we may ship with the preamp. Note the preamp has an arrangement for 6V tubes of the 6DJ8/6922 variety and for 12V tubes like the 12AU7. The situation is that the circuit was designed for the 6922 type regarding plate load, current amount and the relation of those to the 6922 characteristic curves. If the mu of a tube is too high it won’t bias correctly as it can’t draw the design current without trying to draw grid current or if the mu is too low, the volume control scheme won’t work right. The 6H30 might be too low in gain but otherwise looks promising. The sound in the circuit which is of primary interest, we will see.
This is ADI cool to have you here a legend in design and implementation.
Paul you are surrounded by people who practically invented hi end audio it’s no wonder your entire product line has increased so. Your Amps and now your preamp not forgetting your new ds dac.
Mad inhabe about 100 or so pairs of tubes I agree to go with a new rather than old nos.
mad I have both rarely does old nos not best out or be close enough to new.
Companies like ps vane and Sophia or Eml
just to name a few
mad an example I have new 101 d relica and a like new old now west 101d yes it’s cool to see a 90 year old rube glowing but unnerving too. And who make a product and ship with Nos not me for sure.
Mr k I am surrounded by you as I love infinity products of old. And plan to buy a pair of garies
G1.2 at some point soon. I honestly had no idea just who you are in this , very cool indeed
Please do your best in the headphone amp side and any help I can be I would happy to assist in.
This is just getting better Paul.
I wish you all the very best in making a world cakes product we all can afford as most products made the concept of less is more is really is really just not true for all. Even my MSB stack with all its bells and Whisles soundsbetter from a great preamp
As I cannot speak for its physical fit or its sonic atributes as well as should it come stock , but as an upgrade they are cheap compared what some spend just look at power cords or still points there Crazy in comparison . I myself have spent about 800 for a vintage we sting house 101D tub set .
Elk said
At $550/pair this is not a reasonable option.
Well, those are interesting tubes and the reference to the website shows some indeed remarkable linearity in their characteristic curves. However, the BHK Signature preamp is based on two 9 pin miniature tube sockets, one per channel and they are dual triodes. Oh, and the filament (one says filament when referring to such DHTs I think) voltage is 5V at 1.4A. No way is the heater supply in the preamp going to power FOUR of these puppies!!
After I got back from my trip to Arnies, I enjoyed listening to my preamp prototype and finally got tired of its major flaw thus far. It had some pretty bad pops when changing the volume control setting and varied in amount with the tubes I put in it. I turned out that the problem was variable differences in two critical DC voltages in part of the input volume control. I devised a simple servo that would make these voltages equal. This helped a great deal so that one could put different tube in with much less if not any volume control popping. It turned out, not surprisingly, that the tubes that Arnie and I liked the best for sound in the preamp were NOS type and not suitable for producing the preamp. So Arnie and I, mostly Arnie, researched various tubes that were being made and were purchasable in production amounts. It turned out that a particular 12AU7 was a prime candidate. However, the initial design of the preamp was to use 6DJ8/6922 types with a 6.3V heater. A 12AU7 has an arrangement that allows 6.3 or 12.6V heater voltages. I had to make socket adapters that would map the 12AU7’s heater arrangement to the one in the preamps tube sockets. I had two of these that I made up in the past from a 9 pin miniature base and wired with short wires to a 9 pin miniature tube socket above the base. I rewired these for the job at hand and sent them up to Arnie. Now the “fun” begins. These socket adapters were not the best workmanship of the BHK – it was not long before Arnie pushed one too hard into the preamp pc board socket and something either shorted or broke loose. When he connected the output of the preamp to the amps, his way of avoiding any startup transients – ha - BAMM!! Put the bass amp and the BHK mono amps into standby. His preamp had to be sent to Bob Stadtherr at PS Audio to fix. Long story short, this happened three times caused by these POS socket adapters. This third time, I insisted that Bob install the planned 6/12V jumpers on the preamp pc board as it will be when produced. Duh, this stopped any problems in using the 12V tubes and Arnie finalized after considerable listening a very good sounding 12AU7 to be shipped with the preamp. Note that this allows all of the great NOS 6DJ6,7/6922 variants to ge used in the preamp. Further software refinements have reduced the volume control popping to virtually nill, with display improvements, and now the remote volume control is working. A working version of the preamp will be shown in the upcoming RMAF. Go check it out!
