[analog97]

Reading the blog, it appears there is a physical limit to design a high power tube amp.  DRATS!!  Apparently unless one compromises in the design and uses feedback, it's not doable.  Feedback is JH's "line drawn in the sand".  Without a high powered amp in the Hag line-up, there is a serious marketing hole, so maybe some compromise is in order.  I am guessing that 90% of speakers are <90-91 db efficient.  So, if there is this physical limit, can you go SS?  My conceptual idea would be to design 3 SS amps, all utilizing the same PCB's.  They would be a 50W, 100W and 250W amps.  One would obviously need different toroid sizes and electrolytic caps, etc....I don't think this far-fetched and maybe one could achieve an economy of scale.  3 parts lists, but each uses the same boards.  I am not an engineer and have never designed any electronics, so maybe this concept is laughable!!  If so, just putting in another plug for a big amp or sending in my regrets...

[barpc]

Can't speak to the issues related to the "high power" tube amp and am not sure that it is impossible, but I'll let JH respond to that as he wishes.

However, as to your suggestion re SS amp, might I propose a hybrid?  Input circuit, common to all three power levels, being tube and output being SS.  George Kaye's Moscode, Jolida, JLTI amp, all have done this, or something similar, and a DIY half kit would be cool.

Not that JH has any time to do other than put this in the back of his mind, right now -- stick to your schedule, sir!  It's important to your company.

Brad Rush

[BobM]

Generally with SS amps the higher output levels equate to more output amplifier transistors or mosfets. The problem here is that you really want to try and match them up. That's impossible from Digikey unless you buy more than you need and throw out the rest. Also with more transistors you need to beef up the power supply, which involves more than just a bigger transformer. You also need better heatsinking and a larger case.

All in all, I don't think you could use the same boards for each, unless you design for the big boy and scale down the necessary components for the small fry. There's also a whole lot of implementation tricks that go into the mix. Jim is great at those sorts of things for tubes, with all of his experience designing in that space, but SS may be a new animal for him.

I do agree that perhaps a few amp designs, both tubed and SS would certainly round out the product line-up. Then I guess it would be on to speakers, or turntables. Can you imagine a DIY cartridge? 

Enjoy,
Bob

[hagtech]

Personally I have no interest in SS amps.  They're just way too easy to design, practically anyone in electronics can do it.  That's why there are already dozens of available kits out there.  It makes no sense for me to do a copycat product.  I prefer to focus on difficult, innovative, and ground breaking designs where there are few peers.  My business can only exist if I offer something of more value than the next guy. 

So in that respect, I am sticking with tubes.  They require more ingenuity and there is less competition.  They can also sound better!  It plays to my strengths.

For the power amp, I'm not sure if I've bumped into physical limitations, only practical ones.  You can always throw more and bigger tubes at it.  There are the GM70, 6C33, and transmitter tubes.  What I did discover was that every high powered tube amp out there is using feedback.  Hey, sometimes it makes sense.  I could copy them, but that is pointless, especially given the super low cost of the imports.  Some of the Chinese amps retail for less than my raw part cost!  Of course, my design is superior, but you wouldn't know that by a cursory review of specifications.  It would be stupid for me to play their game on their field.

The PA-20 (or PP-20) design I came up with was a compromise.  I set myself into a corner with severe restrictions.  All tube, no feedback, available parts, reasonable size and cost.  So it was not a cost-no-object where I could make it the size of a refrigerator.  I made it very practical.  It is compact, uses low cost tubes and transformers.  It is all about topology.  Now to get the performance out of it, that is where I lose power.  I sacrifice power for a low output impedance, low distortion, good behaviour and stability.  That is, I choose maximal sonics.  And in my particular case, the power suffers.  I pull 225 watts out of the wall to generate roughly 20W or 25W of audio output.

That's just the way the cookie crumbles.  As for real-world speakers.  Well, low sensitivity and complex crossovers are a crutch for inferior design, just like feedback.  Maybe those aren't the speakers you really want. 

And so I choose my path - above and beyond ordinary hi-end offerings. 

jh

[samplesj]

As for real-world speakers.  Well, low sensitivity and complex crossovers are a crutch for inferior design, just like feedback.  Maybe those aren't the speakers you really want. 

I thought you were looking at Maggies?  High sensitivity magnepan is an oxymoron.

Of course I'm not knocking them at all.  I like my 3.6's with Hagtech Cornet2/Clarinet/Chime and Dodd 120 monos just fine .

[hagtech]

Yes, you got me there.  I should have limited that statement to boxes and cones.  There are the radialstrahler and other technologies that probably do no apply either.   I am still considering Maggys as a future upgrade path.  And I think the PP-20 could actually be a good fit, although bi-amping starts to get expensive.

jh

[TomW16]

Thanks for the reference to the blog analog97.

This PP-20 project has piqued my interest.  Good luck with the project Jim.  I am interested to hear how it turns out.

Cheers,
Tom

[hagtech]

Hadn't thought of bridging much.  But if you connect the outputs of two PA-20 (each 14Vrms @1 ohm) in series you get double the voltage swing and double the impedance.  You go from 20W single to 60W double (bridged). 

((14V*8/(1+8))^2)/8 = 19.36W
((28V*8/(2+8))^2)/8 = 62.72W

Doubling amplifiers doubles the voltage not the power.  Oh wait, it does.  The correct comparison is one amplifier into 4 ohms...

((14V*4/(1+4))^2)/4 = 31.36W

So I should specify the PA-20 as ~20W into 8 ohms, ~30W into 4 ohms.

jh