New power amp has a (gulp) tube inside!


#1

As some of you are aware, we’re heavy into building designer Bascom King’s greatest masterpiece, the new PS Audio power amplifier. And yes, it has a tube input stage (with a drop in MOSFET solid state valve option) that will really differentiate this product from anything we’ve done over the last 40 something years.



Of course we understand that if there’s going to be a tube, then there’s going to immediately be the desire to replace those tubes with personal choices of different types, brands, and so on. Hey, if we’re joining the tube nuts might as well jump in with both feet.



To make this easy, the back of the new amp chassis (a PerfectWave P10 chassis) will have a pull out drawer that will look a little like an old fashioned laundry chute. Opening it will expose the tubes. The engineers have sketched a way to make this safe and easy. By placing a metal shield between the high voltage supply and the tube on the user side, we get both shielding and safety.


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#2

BTW, once this tube circuit is working and voiced the way we want, it’ll then become the basis of our new preamp. “Just” add a volume control and input switching and you’re good to go.


#3

Very cool! A great way to keep the look of the product and provide easy access.


#4

So no glowing in the dark tubes visible through the front panel :wink:


#5

Well it looks like you chose the two tube route, I say that assuming the white “cylinders” are the tubes. More of that tube magic! Of course only listening will tell. Still planning on taking a prototype to Munich? As for the preamp, if it’s the same circuit wouldn’t that be redundant gain stages? That’s OK? I’m asking from an "I don’t know " point of view, not trying to second guess you. Would you also assume there would be synergy between amp and preamp because of this? Gotta look at the long term impact on my current components …


#6
pmotz said: As for the preamp, if it's the same circuit wouldn't that be redundant gain stages? That's OK? I'm asking from an "I don't know " point of view, not trying to second guess you. Would you also assume there would be synergy between amp and preamp because of this?

Yes, I have the same question. If the idea of the amp is to get rid of a preamp and connect the DS directly, then adding another similar input stage might be either too much or (who knows?) in perfect synergy.

#7

How will the unit display the number of hours on the tube? How will the tube hour counter be reset by the user?



Granted, it’s expensive to add a display just to show hours, so one could conceivably put a USB port or SD card on the front panel and the user could insert a memory stick, the PWA writes a file to it, then the user can read that on his computer. A bit more of a pain than a direct display, but at least a way to show total hours on the tube.



Then, of course, one needs a button to reset the counter.



Also, let us know if Bascom is still considering the 6H30, as it seems to have some performance advantages. Unfortunately there’s only one manufacturer (2 brands) and that’s in Russia, so it’s up to you if you want to limit the tube type to something that has fewer options. (Or, what the heck, change the heater/circuitry such that we can opt for a 6922, 6H30, or the MOSFET with a switch on the PWB next to the tube.)



And, oh, please be sure and give us a 5VDC trigger as we can’t leave the tube on forever like with solid state!



–SSW


#8
streets still works said: How will the unit display the number of hours on the tube?

:-))

Alekz said: So no glowing in the dark tubes visible through the front panel

Part of the appeal of tubes is the glow and sound when warming up and cooling. But I have always found full case units with an input tube or two with little windows more than a little corny, especially those that additionally incorporate mirrors.

#9

I am with you Elk. I could never bring myself to have a visible window for the tubes. It reminds me of a place I once visited in Amsterdam where they had these poor women hookers displayed in windows for the leering eyes of prospective customers. That was just degrading and cheezy and I could never bring myself to do that.



I want to keep this simple so I don’t think we will have a tube hour counter. I’ll request the 5v trigger, it’s a good idea.



Two tubes are used, one for each channel. Each tube is really two in one, but this circuit is actually a diff pair - which, of course, uses two.



As to the preamp. Yes, indeed, it will be yet another stage between DirectStream and the amp - just as any preamp would be. But there are two reasons we want to do this. In some cases the preamp sounds better than straight in. Not sure why, but there it is and if you’re going that route, might as well stay within the ecosystem.



Secondly, our Asian customers won’t buy a standalone power amp without a matching preamplifier. Not sure why that is but that’s what we have to deal with. If we’re going to be successful selling amps to our Asian friends, they require a matching preamp. Who am I to refuse?


#10
Paul McGowan said: . . . this circuit is actually a diff pair - which, of course, uses two.

Yes!

Paul McGowan said: our Asian customers won't buy a standalone power amp without a matching preamplifier.

This is interesting. In the U.S. we like to mix and match, although there is a contingent that insists upon matching equipment.

Would there be any value in providing direct access to the output stage of the amp for those with a PS Audio preamp? Or is this a bigger headache than I am imagining?


#11

Nice design approach!



The little window approach is not to my taste either. Not that I have anything against tube fetish, but I just don’t think it looks good.


#12

Get one of these hour meters and you can power it off of the 5VDC trigger:



http://www.jameco.com/Jameco/Products/ProdDS/2095074.pdf



Oh well, at least we have the 5VDC trigger . . .



–SSW


#13

that’s a nice little meter. Can’t say I’ve ever felt the need for a meter on any tube gear that I’ve had in the past, but maybe having one would change my perspective


#14

I actually have a tube hour meter on my AR LS-26. I changed the tubes at 4000 hours and it did sound better after the new tubes burned in . . .



I seriously think it’s a good idea to have one.



–SSW


#15
To make this easy, the back of the new amp chassis (a PerfectWave P10 chassis) will have a pull out drawer that will look a little like an old fashioned laundry chute.


You're going to be sorry you said that.

"What, so like switching to tubes will be like adding softener?" =))

I assume you know I kid since I use a hybrid amp myself. But a question. Will the amp have a user-capable means of setting tube bias?

#16

I’ve never heard of bias adjustments for input tubes. Do other amps have that feature?


#17
streets still works said: I seriously think it's a good idea to have one [hour meter].

It's a fun gadget, but I am insufficiently OCD to require this level of precision. I know roughly how much I listen and a simple mental calculation reveals whether it is a reasonable time to consider swapping tubes.

I am much more curious to learn whether PSA installs the tubes upside down as it does SD cards.

#18
stevem2 said: I've never heard of bias adjustments for input tubes. Do other amps have that feature?

None of which I am aware. But this is hardly definitive.

#19

@tony22 No, the tubes will be run with a MOSFET constant current source, unlike many other means people have used in the past. Because it’s a constant current source, the exact amount of current will be passed through the tube as needed, so whatever tube you put in will adjust just to where we want it to be.


#20
Elk said: This is interesting. In the U.S. we like to mix and match, although there is a contingent that insists upon matching equipment.

I experimented with mixing several times but failed miserably. Since then I always use the same manufacturer for both power and pre- amp. The pre must match the power amp. And the power amp must match the speakers.

Currently I have PassLabs x1 and x250.