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PostPosted: January 3rd, 2023, 1:52 pm 
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I have been using tube preamps and passives in my system for decades, and always unfairly dismissed using solid state linestage use. I do have a PassDIY B1 buffer, but it is capacitor coupled (on both ends), and therefore have to deal with the sound of these components. However, recently, experimenting listening to my DAC (Chord DAVE) as a preamp revealed the colorations these can have. Also having a vinyl system complicates just using a digital only system, and I have been experimenting with digitizing vinyl on the fly using an ADC to limited success. However, it would be better to not go through the conversion if I can help it.

I picked up the Wayne's BA 2018 board and parts kit from the DIYAudioStore and finally built. Wayne Colburn, for those you do not know, is the preamp designer at Pass Labs. This was just a throwaway project to the DIY community, as both Wayne and Nelson Pass is prone to do. It is a DC coupled discrete opamp design, with JFET input (using Toshiba 2SK208 SMT JFETs), and BJTs for current sources and output stage. Just completed the build a couple days ago and it is breaking in on the system. It is possible to adjust the gain via the feedback resistor, the default is 3.7 with a 10K resistor, but I have set it at around 2.5 using a 22K resistor to better fit in with my overall gain structure (been using passive attenuators for years, all my amps have enough front end gain). I find the clarity and transparency to be better than my recent 12SN7 Aikido linestage, and the drive and control that the active gain stage results in my tube amplifiers sounding more solid and powerful. The problem I have found with passives is often a slight thinness or lack of body, although they can be very transparent. The new linestage is absolutely quiet and very detailed sounding, with an expansive soundstage and a hint of warmth (but not so much as to be a coloration).

I am using a bipolar +/-15V power regulated power supply from a Pete Millett LR Phono stage that I am not using currently, the preamp is cased in a spare Hammond extruded aluminum enclosure I had on hand. I started with a NOS Alps Black Beauty 50K conductive plastic stereo pot, but just received a pair of 50K Mono series attenuators from Hong Kong (Design by Mr.K) that are very nicely built, similar to the Khozmo, and they went into the preamp this morning.

Anyway, I am coming around to the sound of a low gain solid state linestage, finding it works really well with tube amps. I am already using a solid state phonostage (iFi iPhono3 Black Label) that I found is significantly better than all my DIY phonostages I have built over the years. So maybe there is something to this solid stage stuff after all. Still using tube amps (I have enough of them!).

Some gratuitous pics follow.


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PostPosted: January 3rd, 2023, 2:20 pm 
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Another example of what I have been saying for years. Any audio technology when properly implemented can yield superior results. The problem is almost always in the implementation.

Tom


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PostPosted: January 3rd, 2023, 2:37 pm 
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I find it interesting that Wayne Colburn offers up a DC-coupled DIY design yet is manufacturing and selling an AC-coupled design (Pass Labs XP-12 Preamp) and using aluminum electrolytic coupling-capacitors to add insult to injury. :angry-banghead:

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PostPosted: January 3rd, 2023, 2:53 pm 
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DIYers can deal with setting the output offset (though a servo would work). Also any commercial design needs to connect to any equipment and user error.

David


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PostPosted: January 3rd, 2023, 3:24 pm 
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David McGown wrote:
DIYers can deal with setting the output offset (though a servo would work). Also any commercial design needs to connect to any equipment and user error.

David

It's interesting you say that since Wayne used that (". . . needs to connect to any equipment. . .") as his reason. Yet much older products were AC coupled (Threshold FET-9) and there was not one sticking electrolytic in the signal path.

The irony here is that the XP-12 had the means to dial-out DC offset and offset differential. :angry-banghead: I got it down to .7-mv and it's stable. :thumbup: I replaced the output caps with bobbins and added test points to revisit the offset.


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PostPosted: January 3rd, 2023, 3:31 pm 
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If you build the Bride Of Zen (https://www.passdiy.com/project/preampl ... ide-of-zen) with depletion mode MOSFETs (or power JFETs) you can at least eliminate the input cap. Either way, the B1/BOZ designs are inverting, so you'll need to take that into account... I bet at the current & load impedance needed for a B1 or BOZ stage, you could relatively easily build a 1:1 output transformer, gets rid of the output cap, and you can fix the phase reversal as well ;) Probably make a decent headphone amp too (if you go for that kind of thing) :music-listening:

Roscoe

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PostPosted: January 3rd, 2023, 3:50 pm 
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David McGown wrote:
However, recently, experimenting listening to my DAC (Chord DAVE) as a preamp revealed the colorations these can have. Also having a vinyl system complicates just using a digital only system, and I have been experimenting with digitizing vinyl on the fly using an ADC to limited success. However, it would be better to not go through the conversion if I can help it.


So, at this point, with the Dave, if you were running a digital only system, do you think there's anything to be gained by having a separate line stage?

Roscoe

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PostPosted: January 3rd, 2023, 4:12 pm 
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Walt,

Not arguing with you, and good to know about use of coupling E-caps on the XP-12. Using tube amplifiers, a few mV of DC on the input really is not going to be an issue, it is not enough to upset the bias of the input stage and there are usually coupling caps (and an output transformer) that is going to filter out any DC through the amp. Only a problem with DC coupled solid state amplifiers where any DC at the input can be amplified and be presented across the speaker terminals. Not good. Of course, can have the same issue with leaky output caps (Jensen PIOs being infamous) on a tube preamp. Double plus not good.

BTW, what is your impression on the XP-12? I consider this little BA linestage as an experiment, and if I am sold on using a solid state linestage, may want to be shopping around for a nice unit at some point, since my solid state design skill are, well, non-existent. Of course, I still have other tube based alternatives to explore for low gain/buffer stages, like DHTs or triode coupled power pentodes, either cap or OT coupled. That can end up being a major project, getting a quiet heater supply is the biggest issue for DHTs.

Also, what is your view on back to back E-caps (with a bias voltage at the ++ or -- junction)? I have also heard that small value WIMA polycarbonates are ideal for bypassing the ELNA Silmic E-caps that PASS Labs tends to use for coupling. I picked up a few to try on my Pass DIY Pearl II phonostage when I get a chance.


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PostPosted: January 3rd, 2023, 4:20 pm 
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Roscoe Primrose wrote:
David McGown wrote:
However, recently, experimenting listening to my DAC (Chord DAVE) as a preamp revealed the colorations these can have. Also having a vinyl system complicates just using a digital only system, and I have been experimenting with digitizing vinyl on the fly using an ADC to limited success. However, it would be better to not go through the conversion if I can help it.


So, at this point, with the Dave, if you were running a digital only system, do you think there's anything to be gained by having a separate line stage?

Roscoe


If I were running a digital only system, I would not even bother with a linestage with the DAVE. I will have to AB the two once the linestage is broken in to see the impact on the digital side. The DAVE has 3VRMS unbalanced (6VRMS balanced) output and very low output impedance, more than capable of driving my amps. I have tried it, and the result is excellent. This is all a grand exploration of the best way having an integrated system.


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PostPosted: January 3rd, 2023, 4:27 pm 
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Roscoe Primrose wrote:
If you build the Bride Of Zen (https://www.passdiy.com/project/preampl ... ide-of-zen) with depletion mode MOSFETs (or power JFETs) you can at least eliminate the input cap. Either way, the B1/BOZ designs are inverting, so you'll need to take that into account... I bet at the current & load impedance needed for a B1 or BOZ stage, you could relatively easily build a 1:1 output transformer, gets rid of the output cap, and you can fix the phase reversal as well ;) Probably make a decent headphone amp too (if you go for that kind of thing) :music-listening:

Roscoe


There is also a revision to the B1 that is run from a bipolar supply and DC (with an offset nulling pot at the output). Very simple complimentary pair (2SK170/2SJ74).

David


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