[kevin gilmore]

So i was crusing another forum and came across this a few days ago
and ran into this.

http://diyaudio.com/forums/showthrea...highlight=6ar8

and then decided that for those people that wanted a tube front end
and solid state output then this was the ultimate item as it had all
sorts of things going for it like ultra low inherent distortion without feedback,
the volume control of both channels with a single pot, balanced input
without a transformer, balanced output without a transformer. In short
really sweet. So i bolted a solid state output to it. With a servo of course
because as everyone knows i don't like caps in the signal path. There is
of course one cap in the signal path, but it is in a place where you can
go absolutely nuts with a high quality cap.

http://gilmore.chem.northwestern.edu/hybrid.gif

All open loop, no feedback. About 100mw into 300 ohms at .03 % thd.
(verfied with berkley spice). No i have not built one yet, i won't even
have the tubes till later this week. These tubes are available and cheap.

The tuberollers might have a problem with this one however.

 

[PeterR]

Here 's a more space efficient version for those on dial-up...

 

[rudi]

Full of feed-back and dangerous for headphone

The third harmonic made by input pentode dostortion is compensated by feed-back. Poor idea coming staight from component databook! very far from Hi-end.

Very low power ( for sure not enough for to drive HD650 - Rs1 )


Very dangerous for headphone. ( if the power output transistor burn, you say good by to your headphone in few minutes )

Altough Mr Gillmore don't like my projects, he nont' like my company, my face and my name, I don't have anything personal against him. I consider his projects pittoresuqes but honests.

I don' t want fight anymore, I dont' want make another flame, I'm not interested in any battle vs Gillmore.
Use this is only as constructive contribution on this 3d.

Designing an Headphone ClassA Amplifier is simple and don't need any guru, you can learn from my diy website www.rudistor.com/sound-lab (theory is only in italian, sorry)from Elliot Sound website, from Nelson Pass (the zen )and many many others.

Use caution with alchemic design!!!

I have posted only to allert possible diyers on the limits and danger of this design, as a costructive contribution only!

rudi

 

[Nik]

This is very, very interesting for me even if I cannot understand all that the designers are telling...

I hope this discussion will be a lesson for many builder...

Thanks to Gilmore and rudi !

Best!
Nicola

 

[eric343]

Quote:

Originally Posted by rudi Very dangerous for headphone. ( if the power output transistor burn, you say good by to your headphone in few minutes )

Kevin is known for leaving things like that out of his schematics.

 

[Nik]

Quote:

Originally Posted by eric343 Kevin is known for leaving things like that out of his schematics.

Hmmmmmm !!!!

Rudi is known for NOT leaving things like that out of his schematics

Best!
Nicola

 

[eric343]

Quote:

Originally Posted by rudi Very low power ( for sure not enough for to drive HD650 - Rs1 )

Quote:

Originally Posted by kevin gilmore About 100mw into 300 ohms at .03 % thd. (verfied with berkley spice)

Um...

 

[Nik]

Quote:

Originally Posted by eric343 Um...

"hum" are you saying ???

Best!
Nicola

 

[eric343]

KG says the design can put 100mW into HD650s, Rudi says it's too low power to power HD650s. (100mW is definitely capable of doing the job)

 

[Nik]

Um...

 

[kevin gilmore]

quote
Full of feed-back and dangerous for headphone

Absolutely no feedback of any kind. The servo runs at sub 1hz
region.


quote
The third harmonic made by input pentode dostortion is compensated by feed-back. Poor idea coming staight from component databook! very far from Hi-end.

If rudi would have even bothered to look up the 6ar8 he would have realized
by now that this is a voltage steering balanced tube similar to a cathode
ray tube, and nothing like a standard pentode. Once again absolutely no
feedback of any kind. There is no miller effect, and distortion products
are so far down compared to rudi's simple triode input circuit there is
no comparison.

quote
Very low power ( for sure not enough for to drive HD650 - Rs1 )

Um, plenty of power. The output power was specified for that
distortion level. For high impedance headphones you could always
boost the output rails to +/-24 volts and get way more output
power with little increase in distortion. For low impedance headphones
it is no different from any other single ended class A output device with
a resistive or current sink load. Just like a Szekeres. Just like the
rp5 and rp5cav too.

quote
Very dangerous for headphone. ( if the power output transistor burn, you say good by to your headphone in few minutes )

True. But you can say this about absolutely every single dc coupled
higher power headphone amplifier out there. Including any of the
buffer (diamond and otherwise) amplifiers. The solution is also very
simple. A simple opamp integrator and a relay protector. My mig
and mig2 amps absolutely require this sort of thing because it takes
a minute for the tubes to warm up.

What rudi is really saying is that he does not know how to do a decent
protection circuit, and therefore relys on huge miserable sounding electrolytic
output capacitors instead.

I threw this out because there are a few diy people out there that will
definitely build and play with this thing. I'm certainly going to build one.

Quick changes the 20k servo resistor should be 100k and the one
and only cap in between the two stages can be as high as 1 to 10
uf depending on how much physical space you have. Lots of nice
teflon, paper in oil, beeswax, and silver mica's out there.

The 9 volt battery can and should be replaced with a very well
regulated shunt supply.

By the way it is spelled pittoresques

 

[Nik]

This is very interesting...

But how do you judge (in sound performance) this your project respect to your others (Lite, V series, Reference... SS ) for headphones?

Best!
Nicola

 

[rudi]

I can't believe!!!

Gillmore is joking or the design is copyed the and he don't know how it works.

Everybody knowing basic electronics can understand, both stages have a huge feed-back. The worst kind of feedback as in all KG design. A solution that make the projects easy to build and tune, but very far from what is considered purist Hi-End.

I'm not a diyer but a producer, so is not fair if I post too much in the forum.
I leave the 3d, everybody can contact me by PM

regards
rudi

 

[kevin gilmore]

Haven't built it yet. Therefore i have no idea how it sounds. But for
people that have built the 6ar8 as a preamp it evidently sounds very good
indeed. And definitely not your typical tube sound.

Rudi needs to think outside the box a little.

Todays project (warning: very huge only so you can see the label)
http://gilmore.chem.northwestern.edu/twt.jpg

I've had this around (brand new) for years. Just picked up the right
magnet for it yesterday. 50 ohm input, 50 ohm output, should drive
hd300's just great. 16db of gain. ZERO to 5ghz frequency response.
Direct coupled too. 15k noise temperature (about .7db NF).
I only have one, otherwise this would be a great stereo amplifier.
No i don't expect many people out there to build one of these.
Go and look up the price on the thing then add up the magnets and
power supplies and you will know why.

Think of it as a very big brother to the 6ar8.

 

[cosmopragma]

Quote:

Originally Posted by Nik This is very interesting... But how do you judge (in sound performance) this your project respect to your others (Lite, V series, Reference... SS ) for headphones? Best! Nicola

Please, Nik,
this is a bit ridiculous.
Asking for info about the SQ of an amp which isn't built yet . ....