Is Ultra Linear the Way to Go For Hi Fi?

[Structo]

I have been fascinated with tube Hi Fi stereos for years but of course most
commercial amps are out of range of my meager income.

So when building a high fidelity amp, is a ultra linear approach to the output
the best way?

I recently read a blurb about a new tube, the Tung Sol KT150.
Reportedly with an output of 75-80 watts per tube.

http://www.thegearpage.net/board/showth ... ?t=1323133

They are kind of an egg shaped power tube.

Mike Matthews is up to something.

[img:640:480]http://3.bp.blogspot.com/-ITN8-6Q31t8/U ... lberto.jpg[/img]

[ToneMerc]

I wager $5 that before Thanksgiving some Zombie will post here wanting to put a KT150 in a Fender Champ.

TM

[Firestorm]

Hi-fi guys usually swear by triodes (300B and the like) so UL is kind of a step in that direction.

As to the new Tung Sols: I sure hope they spent as much R&D on the guts as on the envelope.

[Firestorm]

I wager $5 that before Thanksgiving some Zombie will post here wanting to put a KT150 in a Fender Champ.

TM

What's wrong with a 35W Champ? The trick will be finding an SE OT that doesn't mind 275mA "bias" current.

[xtian]

Yowzer! Beautiful amplifier, man.

Can you recommend a $10K stereo system to play my 128kbps encoded MP3 tracks?

[jjman]

The HiFi guys seem to generally see power and quality as a tradeoff although I doubt they would admit it or describe it that way. Pentode power vs triode (wired) response. UL in the middle. Many other factors including the type of tube. And negative feedback is critical for pentode mode. I can't proclaim to know much about it but I chose UL for my HiFi build, partially since feedback is not "mandatory" in that mode. I used 6v6 SE UL. 6v6 only because I have a bunch from the dark side of tubes we are in over here.

[gingertube]

I use PP 6V6 Ultralinear connected plus parallel shunt feedback from the output tube anodes with ZERO global feedback. ONLY 10 Watts per channel but absolutely stunning. Hammond 1608 Output Trannies.

This circuit but with 6V6 output tubes and 6SL7 for the diff amp.
Cheers,
Ian

[gingertube]

I use PP 6V6, Ultralinear connected plus parallel shunt feedback from the output tube anodes with ZERO global feedback. ONLY 10 Watts per channel but absolutely stunning. Hammond 1608 Output Trannies

This circuit but with 6V6 output tubes and 6SL7 for the diff amp (in lieu of the EL84 and 12AX7 shown, that was stunning too but I personnally like the 6V6 better).

Damn - not sure what button I pressed to end up with a double post.

This amp design (several versions) is called the "Baby Huey" - there is a long thread over at DIYAudio about it, more than 50 of them have been built by various folk around the globe.

One guy in germany says he prefers it to his very expensive push pull 2A3 Filamentary Triode Amp.

The feedback scheme trades output tube gm for reduced rp (which was already reduced by the UL connection). That means that it better drives the limited primary inductance of cheaper output trannies (better bottom end) and also better drives teh leakage inductance and shunt capacitance of the output tranny so better top end as well. This amp has the best stereo imaging I have ever heard.

The Miller Capacitance of at the output tube grids is higher in UltraLinear Mode than in pentode Mode. For this reason and to keep effective Rg1 values low I use current source loaded mosfet source followers to drive the output tubes. This low impedance drive also results in the quietest (blackest background) amp I heard, no hiss or hum noise at all.

The 16K "cross connect" resistor shown, sets the shunt feedback level. 16K is what I used for EL84 outputs, with 6V6 outputs this was reduced to 13K.
This cross connect method also adds a forced AC balance function.

Its a busy little circuit. Does lots of things well.

I haven't tried it yet but I believe it would scale up to a 50W amp easily by using KT88 output tubes.

Cheers,
Ian

[gingertube]

Also the Power Supply I used for your possible interest. The schottky rectified 5V winding for the input tube was done purely because the output tubes soaked up the full 6.3V heater winding capability (only 1.5 A). Using power tranny with more heater capability would mean that is not required. Still a good idea to sit the heaters on +50V or so.

Cheers Ian

[Cantplay]

I think it really depends on what speakers you are driving, and how loud you listen.

The setup I have in the bedroom is almost 100dB sensitive, and it has an amp with a single EL84 per channel.

There is a switch from SET to UL that doubles power to about 3W.

If you have deaf speakers you may need more power.

[img:600:400]http://cgim.audiogon.com/i/vs/s/f/1257218434.jpg[/img]

John

[M Fowler]

I'm think about the 845 SE tube amp myself.

[renshen1957]

I have been fascinated with tube Hi Fi stereos for years but of course most
commercial amps are out of range of my meager income.

So when building a high fidelity amp, is a ultra linear approach to the output
the best way?

Hi Structo,

A book could be written on that question alone.

D T N Williamson concepts for Hi Fi designers back in 1947. One was for lower total harmonic distortion, less than 1%, and the THD should ideally be low order and even harmonics. All Triode circuits (preamp tubes and power tubes) was an easy way to attain these goals.

The original Williamson amp design did not have Ultra Linear transformers. Later variations on the design incorporated UL. To borrow a phrase from KOC UL produces Triode like performance from Pentodes and Beam Tetrodes, (including speaker damping) not normally found without NFB. UL produces a local global feedback without the addition if NFB. More about negative feed back in a bit.

As was posted earlier, Hi-Fi designs involve compromises.

Class A (either self biased tubes or in Hi Fi fixed bias) eliminates cross over distortion inherent in Class AB, but has less power. Triodes have less power than Pentode/Tetrodes. Yet, some design use Pentodes/Tetrodes wired as Triodes (or as some in the Triode camp call these, Pseudo-Triodes), others use Push Pull fixed bias Class AB for power.

Generally SE is a preferred method. But there is a limit to power in SE designs unless one steps up to High Voltage (1000V DC and higher) and jump from receiving to transmitting tubes.

Headroom, Bandwidth, damping factor of the Power tubes are other factors.

Ideally, Hi-Fi amps should have very large bandwidths. To achieve this large and expensive output transformers are required.

The Japanese seem to excel in specialty EI transformers for Hi Fi however Toroidal Transformers have gained fans in this market.

All this costs money.

NFB narrows bandwidth and power, but lowers distortion. On the other hand, Transient Intermodulation Distortion will increase if too much NFB is used. This relates more to Transistor Consumer Grade "Hi Fis" of the 1970's and 1980's when amps were sold on specifications rather than on sound, but can be true with tubes, too.

I have read recently (in the last two years) that UL causes more distortion than originally thought, and is in some circles falling out of favor. This hasn't been my experience.

So there are a variety of different philosophies as to how to achieve a sonic goal and I haven't scratched the surface. There are output Transformer designs used by McIntosh, Output Transformer Less designs, and others. The speakers run the gamut from Electrostatic, Planar, Ribbon, Horn tweeters, multi driver (woofer, midrange tweeter, tweeter, super tweeter) Satellite Subwoofer systems, etc.

However, How High does your Hi in Hi Fi have to be?

I have a Fisher X 202-C Control (integrated) Amplifier, one of the last of Avery Fishers Tube amps before the company switched over to Solid State. The Integrated Amps of the C series (but not the receivers) have been looked down upon by many Fisher aficionados as compromise designs, etc and have a reputation of being second rate.

Well that hasn't been my experience, too.

I put on an LP (Vinyl Record) of a Hard Days Night (analog cut masters) on my Bang and Olafsen Beogram 2404 turn table (not a Linn Sondek LP). With PolkAudio Speakers and a preamp that's fueled by Tesla (not JJ) E83CC tubes (built on the Telefunken equipment that made the Ecc803) the result was jaw dropping. You felt like they were in the room and in some tracks, spookily so.

A number people, including myself have found sonic nirvana restoring vintage equipment. However, that has driven up the prices.

Another option is to build a Dynaco amp from a kit.

The Dynaco ST-70 comes in a kit form from a number of sources:

http://www.diyaudio.com/forums/tubes-va ... ase-2.html (check out post number 12 on the page).

Triode Kits start at $699 the last I checked.

Other companies start in the same price range.

(the kits contain PCBs plus options for upgrades)

That maybe pricey for some but a bargain for others. The Dynaco's are good sounding amps.

Best regards,

Steve


PS As to the comment xtian's comment "Can you recommend a $10K stereo system to play my 128kbps encoded MP3 tracks?"

Actually valves/vacuum tubes improve the listening experience of digital material. I hear details in online digital source materials not so frequently revealed on Transistor amplifiers. Even MP3 tracks sound better (although most of the data was compressed and lost in the process)

My wife loves to watch programs from her homeland as streamed over the internet. These historical dramas have besides lovely incidental music/soundtracks full scale battle scenes with bomb explosions, rifle bullets that sound like they just missed you, machine gun fire, and outgoing and incoming mortal rounds, hand to hand combat involving Chinese swords versus Japanese guntō. I have hit the deck once or twice.

And I have mistaken spoken female dialogue for my wife's voice on more than one occasion, which is most unsettling.

Youtube recordings of everything from Bach Organ Music, Cantata Symphonia, HAD amps, etc. sound great, or should I say sounded great.

I can't get my tube amp back from my wife.

[Phil_S]

I knew a guy - maybe 15 years since we've crossed paths except on Linkedin - who had a pair of traditional monoblock amps rigged for stereo. This is the kind of thing you can build on the cheap (relatively speaking). I don't think I ever heard a better hi-fi. His actually lived in two separate chassis, one for the L and one for the R channel with input taken from a turntable. No balance control

[M Fowler]

I noticed on the Dumble FB that Airbloom has 40 ST-70 transformers maybe he'd sell some.

[renshen1957]

I knew a guy - maybe 15 years since we've crossed paths except on Linkedin - who had a pair of traditional monoblock amps rigged for stereo. This is the kind of thing you can build on the cheap (relatively speaking). I don't think I ever heard a better hi-fi. His actually lived in two separate chassis, one for the L and one for the R channel with input taken from a turntable. No balance control

Hi Phil,

+1 on your comment. Mono Blocks have a number of advantages, maybe in a DIY design with speakers from Edrosa. However, most Mono Block kits or amps in need of restoration were expensive. Great sound and no possibility of cross talk or power supply issues.

Best regards,

Steve