DHT preamp

[johnsonad]

To quote the boss on AA, "Thank you very much for the plug. It just so happens that we will be investigating a DHT preamp in the fairly near future." 

Sooooooo, is this this secret preamp you all have been working on and is it the same one used at the Pacific Northwest Audio Society presentation?  Just fishing for details, a little something to drool over

Aaron

[Doc B.]

The DHT preamp is one idea of several preamp concepts that we are working on, and will probably be experiment number four in the series. We've completed one and two, which use IDHTs. #one was demo'd at the meeting, a pair of 7233s with a 5687 as dual shunt regulator. It already whupped #two in our listening room a few weeks ago. #two was a pair of shunt regulated 5670s with transformer output. Today we hope to finish construction of experiment number three, which is a conceptual cousin to #one that could sound as good or better and be less expensive. The "winning" prototype might be considered as a replacement for Foreplay - but only if it sounds better, and we haven't built and listened to all of our ideas yet.

#4, the DHT version of this concept, would be a high end product intended to go with our Tube Repro, Tube Phono and some form of high end power amp that is yet to be determined. It has some unique requirements and PJ is chipping away at the last tricky bits we have left to work out.

[Jim R.]

Sounds great, and I'm all ears on this too.  My only real requirement aside from low noise and great sound is the ability to drive at least 15-foot interconnects, and it would be nice if it had a headphone output too.

Will definitely be staying tuned for this.

-- Jim

[Doc B.]

15 foot cables - no problem. Headphones - we now have two and plan soon to have three kit choices that are optimized for that job. This project is really about the very best way we can drive line level equipment. That doesn't require quite as low an output impedance as headphones do, and that allows us to do some things to optimize the sound of the preamp that are not possible with a tube headphone amp.

[Jim R.]

That's fine, and thanks for the explanation.  I've already got more headphone amps than I can use at once, just trying to save a bit of space, but if that compromises the sound, then I'll gladly forego it.

-- Jim

[johnsonad]

Thanks Dan for the info.  I'll be keeping an eye out for both the kit and the high end DHT preamp.  Can  you say which tubes you intend to use in the DHT pre yet?

Aaron

[Paul Joppa]

I should probably add that we have already found that a preamp that can drive a 600 ohm load usually sounds better than one that can't, even if it's just driving a 100K load. So all of the preamps under investigation could drive a 600 ohm headphone, though most of them would still prefer one with a flat impedance.

There's a reason traditional pro/studio headphones had 600 ohms impedance. IMHO, it's the low battery voltage of iPods (and Walkmen before them) that has led the drift to lower impedance phones. Of course, I'm not  a headphone guy, but if I ever get a pair they will be 600 ohms!

[Doc B.]

The DHT we will use for a preamp? PJ is working hard on coming up with a way to use a low and hot 300B without smoking the load transistors. You probably thought I was going to say something wussy like a 26, huh.

BTW, #1 beat #3 with a first round knockout punch yesterday afternoon. Poor #3 sat there all compressed and wirey while #1 laid on its midrange weight and smoothness and just walked all over the other preamp. We will attempt to resuscitate #3 for a rematch, but at this point it looks pretty much like we have a champ.

[johnsonad]

Wow... The 300B would have been the last DHT I would have guessed   I look forward to hearing it someday and hopefully #1 even sooner

[johnsonad]

By chance has #1 spent time in the ring with the Foreplay yet?  I'm curious to see who will be the next champ

[Doc B.]

As it turns out #3 just needed to break in and it has now replaced #1, with tighter bass and a little bit quicker and cleaner sound overall. We have yet to compare it directly with a FPIII.