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Tube Audio Labs Jeff Korneff Clone 45 Tube Monoblocks Review.I Received these Amplifiers about 7 weeks ago. Short Story - I love them! Longer story below.
I started this purchase by contacting Tube Audio Labs owner/builder Min Yang last Fall. I had heard many good things about TAL. Many happy customers and many different amplifier options. I had read on-line that he was building Jeff Korneff 45 tube Amplifer Clones. Jeff Korneff had quit building Amplifiers around 2010, and the used ones that went up for sale were gone instantly. Also, I had never seen a Jeff Korneff Monoblock Configuration, so a Custom Clone build was definitely an Answer for me, as my System Layout was with the Amplifiers close to my Speakers.
So, when I contacted Min, he was very open to most any customization that I had in mind. Min let me design the Tube and Transformer Layout on the Top of the Chassis, as well as requesting a Mirror Image of the Monoblocks, as this always looks pretty neat. I also got to request my favorite 'Audiophile' grade parts. I selected a Large 17"x 10" Wood Chassis, so there was plenty of room for components.
- Hammond metal-on-wood (walnut) chassis.
- Canadian Hammond power, choke, and filament transformers
- Takman and Kiwame CF signal resistors
- ASC oil filter caps
- Mundorf Silver Supreme oil caps
- Hashimoto output transformers
- Cardas Rhodium Binding PostsOnce we settled on a design, he told me his lead time was about 6 weeks, and since I was leaving for the winter, I did not want to receive them until Spring. So, I paid him ($3,000 - less final shipping of $550) for the Amplifiers with an agreed ship date around Mid March of 2021. I confirmed the design schematic with Jeff Korneff himself (Via E-mail) and yes indeed it is the circuit that he used to build.
So, I have been listening to them now for around 7 weeks. And have settled on the Old Globe Style RCA UX-245 Tubes, Sylvania 6SN7 'Tall Boy' Chrome Domes, and National Union JAN VT-244 (5U4G) Rectifier Tubes. I am driving 115db Oris Horns with these Amplifiers, and I bi-amp with Hypex Class 'D' Amps to my Klipschorn Bass Bins. These are my 3rd pair of 45 Monoblocks. Previously I used Welborne DRD45 amps. Then I built a pair of Welborne Star Chief 45 Monoblocks.
As far as listening goes, I would be hesitant to pick either the Star Chief amps or the Korneff Amps over each other. They are both great Amps! I prefer the design of the Korneff Clones, as I got my preferences. Quite simply these are the best amplifiers I have had in my System. I will say that the Jeff Korneff Clones are a tad quieter than the Welbornes. I can place my ear inside the Oris Horns and I can barely tell they are powered on. I also like knowing that I have a Jeff Korneff circuit design, as these are known to be one of the finest 45 tube Amps around. I had pretty much settled on the 45 tube over 15 years ago, having also owned a couple 300B amps and Welborne 2A3 Moondogs as well. Still own Welborne 300B Laurel Monoblocks. You know the usual 45 Tube characteristics - Spooky, in the room vocals, etc. etc. - These amps do it all in spades!
I also like that the Korneff Amps are Tube Rectified and are completely point to point wired. (In case I want to modify down the road).
I looked at other Amplifiers, but could not find a Jeff Korneff design, let alone Monoblocks... I don't know, but I may have the only Jeff Korneff Clone Monoblocks out there?
Edits: 05/11/21 05/29/21 05/29/21Follow Ups:
I've heard good things about Korneff amps..... It would be interesting to compare with Don Allen's designs.
nt
All that full range effort to drive a compression driver from 500 Hz up ?
No, from 270 Hz. up! --- But who listens to music from 270 Hz. Up?
Hello Cut-Throat,
Very nice amps.
How were the 6sn7 wired on the Korneff clone monoblocks?
I have built this amp and used one 6sn7 triode section per channel in a stereo amp. Very good sounding amp indeed and wanted to build it as mono's as well but was not sure about using the 6sn7.
I did hook up a adapter and ran two 6j5g's but I think they have less gain than the 6sn7 tube.
Best regards OB
Here:
Edits: 07/29/21 07/29/21
I realise the amplifier is similar to the stereo version but what struck me 'different' about it was the way the L/R channels share a common cathode resistor. Surely this changes the sound, for better or worse, but it wouldnt carry across to the dual mono build.
Similarly, with the two 6SN7 triodes within the common envelope - to a lesser degree, but still with some crosstalk between channels (in the stereo build) and out of phase with the output stage. Again, its going to sound different with the dual mono build.
With regard to 'what to do with the other half of the 6SN7' in the dual mono, well considering its fundamentally a different amplifier from the original stereo amplifier, I'd use both halves and set it up as a differential amplifier, this would remove the need for the Ck, and then I'd try taking the output from both in the and out of phase outputs and see what difference that made.
and wish I had a pair. Have always had a hankering for some.
Maybe one day.
Big J
"... only a very few individuals understand as yet that personal salvation is a contradiction in terms."
It seems that the Korneff SE amplifiers are held in high regard by many.
In terms of the schematic : a tube rectified cap input power supply with a 10H smoothing choke and a two-stage cap coupled signal circuit. The circuit has been lightly modified by the builder.
It looks like a standard 2-stage SE 45 circuit , perhaps there is more to it than the schematic reveals.
Is it the Korneff circuit or the selection of components that makes it a legendary SE 45 amplifier?
DT 667
I'll speculate that the choice of output transformer plays a large role. That UBT-2 (apparently no longer available) has huge magnetic headroom when used with a 45.
My Actual Build uses Hashimoto output transformers. Which was a substantial upgrade.
Interesting. Hashimoto is certainly a good name - do you have a model number or link? I'm always interested in good-sounding transformers and what characteristics might be associated with the sound.
The circuit of the amp is an excellent example of classic simplicity - nothing exotic, just everything done right.
Closeup Pic.
Thanks!
Hashimoto H-20-3.5U; details easily found on the web. I was very interested to see that a 3.5K primary is being used, as opposed to the 4.8K of the UBT-2. The best 45 amp I've heard happened to use a 3K primary.
In any case, the rating of 80mA DC provides pretty hefty headroom for a 45!
"The best 45 amp I've heard happened to use a 3K primary."
what 45 amp would that be Paul ?... parafeed ?... I have a pair of tfa-2004 to use.. thanks
Neat primary arrangement; offers the ability to run different g2 ratio if applied to a pentode final... :)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
This is a Schematic that was drawn by Craigtone Audio on DIY Audio. It was under the Tutelage of Jeff Korneff Himself. So this is what he was building.Jeff was inspired by an Article called 'Old Glory' that appeared in a Magazine called 'Glass Audio' by Eric Barbour, who put the Amp together using sub Par 'Spare Parts'.... Jeff may have tweaked that original schematic, but the one you linked to was the Schematic of the 'Jeff Korneff' Amplifier, as certified by Jeff.
Edits: 05/17/21
Could someone post the recommended values for B+ and B2+, please. (I would like a rule against using "B+", without defining its value on a schematic). It would be very helpful if someone with a working amp could measure and add some voltages on the schematic too, with expected currents through the tubes.
Edits: 06/10/21 06/10/21 06/10/21 06/10/21
There I circled it for you....
Great! Thanks very much!
"Korneff 45". Jeff Korneff adapted the circuit from a Glass Audio design using old Sansui PP transformers. That design was likely taken from the RCA Tube Manual.
A quote from another audio website regarding the "Korneff" SE 45 design.
Not sure about the RCA tube manual reference. I'd need to look in my copy to see if there is a similar circuit in that old text book.
DT 667
And here was that Article that Jeff Himself sent me. He also sent me a list of the Modifications that he had done to this Design.
Schematic shows a cathode resistor which is common to both 45's ..
I have Monoblocks, so I would have separate ones of course.
as posted above.
Korneff does not seem to favor the cathode bypass multi-cap arrangement in his schematic.
The austerity of a single cathode bypass capacitor does have an appeal to some designers.
Thanks for posting.
DT 667
Jeff Korneff also sent me the following e-mail. He also told me to share this and his schematic as well.
***********************************************************************
Kevin,
That 45 amp was a take off on Eric Barbour's Single Ended Glory for under $100. I attached that schematic. You can download and enlarge. I never bothered with a written schematic of my own, the changes I made were all in my head. You could build the amp exactly as shown, PP transformers and all, and it will sound great. My first build was a mono version very similar to this one, even using the Sansui/Hashimoto outputs, just to see what might be there. I was totally taken in. Don't forget Eric was using junk box parts to build a great sounding amp. Genius.
The changes I would make as a final build to get the full 2 watts, not in any particular order:
use a Hammond 372FX power transformer (a nice transformer, better than 200 series)
use a 5u4 (octal) or 5Z3 (4 pin) rectifier with 20uf/500V electrolytic input cap and 20K 12W load resistor at B+ take off
use separate filament transformers for the 45's with 100 ohm 2W hum balance pots
use 1500 ohm -5W or better- 45 cathode resistors (if separated, above) with say 30uf-100uf / 100V bypass caps
use a pair of true SE 5K outputs from Electraprint- or your maker
use a pair of 50-50 uf/500V dual section electrolytics after the choke pairs
the Heath W series 46-12 (#?) chokes look nice refinished, seems to me they were ~10H, 150 ohm?
use min 2W 6SN7 plate load resistors
suggest using coupling caps to be 0.22uf (not 2.0), 400V or better, try Mundorf silver Foil in Oil
I would personally skip the mylar bypasses across the electrolytics
seems to me I used a 50 or 100uf/16V electrolytic for the 6SN7 bypass cap
It all fits nicely on a 10 x 17 chassis- photo attached. Aluminum.
You're looking for 275 plate volts for the 45 (plate to cathode), 56 volts dropping across the 45 cathode resistor, about 160 plate volts at 6SN7. You will need approx a 335V supply off the rectifier to get to these voltages. Using any other rectifier choices than those I mentioned may/will necessitate the use of a different power transformer rating.
Other notes: I did tidy up the 6SN7 and 45 filament supply voltages with 5W cement dropping resistors to put them "on the money". The amp was buss grounded to a power transformer mounting bolt. Also, the amp was dual switched to allow for preheating the 45's before B+ voltage could be applied- the B+ switch will do nothing without the 45 preheat switch being on. Don't be tempted to use high capacitance values.
The amp was built to run USA old stock 45's. If using overseas versions you would want to consider their specifications.
It's a power amp and will want a preamp ahead no matter that it could be driven directly from some sources. Seems to me the input sensitivity was around 2.6vac .. not sure now. But more than 2.5 and less than 3.
Be safe. High voltages can be lethal.
Hope this helps, feel free to share, Eric did!
Jeff
JDM said he has been trying to contact you regarding the TAL/Korneff 45 amplifiers.
DT667
No one has contacted me.....
Have him e-mail me at kdbmeb@gmail.com
"No one has contacted me....."
Have him e-mail me at kdbmeb@gmail.com
CT's contact info has been forwarded to JDM per request, sir.
DT667
I would imagine your Korneff 45 has rather low gain and probably needs an active line stage to get full volume. Is that right?
Your amps look very nice!
Volume is no problem at all, as these Amps are just driving my 115db Oris Horns. I bi-amp and so the Bass (Klipschorn Bass Bins) are driven by Hypex Class D Amps (500 watts per channel).I've never had to push the volume of the 45 amps even slightly. With that said, I do use a Don Sachs Active Pre-Amp, not because of Low Gain, it is because it sounds a bit 'lifeless' without it. I have always used a Tube Pre-Amp because of this.. I have tried driving it directly from my DAC, and I always felt I was missing something (texture, layers, depth of music etc.)
Edits: 05/16/21
Of course, having 115 dB efficient speakers definitely opens some doors for low power amplifiers.
Cut-Throat,
What speakers are you running with your 45 amps? I'm on a hunt to find out a bigger list of what speakers people are pairing with 45's successfully.
Thanks!
I am using Oris Horns (Orphean System) - 115db. I am Bi-Amping. I use Klipschorn Bass Bins and power them with Hypex Class D Amps with a built in Active crossover. I use a Don Sachs Model #2 Pre-Amp.
http://www.bd-design.nl/contents/en-us/d71.html
Edits: 05/15/21 05/15/21
Killer Speakers! Did you design them yourself?
The Speakers are Oris Orphean System:Here: http://www.bd-design.nl/contents/en-us/d71.html
They are meant to be Bi-Amped as they only Include the Horn, Crossover, and Concentric Driver with Mid Range and Tweeter.
You have to add your own Bass Bin and Bass Amps. So, I added the Klipschorn Bass Bin and Hypex Amps with built in active Crossovers.
And I ordered the Horns unpainted, so I had to build Stands for them and get them painted. So, I found a Pair of used Klipschorns, and just used the Bass Bins, then I ordered a pair of Bass Amps and matched the Bass Bins and Crossovers to the Horn System and I was 'In Business'.
Edits: 05/16/21
About 2000, I was looking to get into SET and had narrowed down to Welborne and Bottlehead....I went Bottlehead. As you know, both are SS rectified.
What do you think tube rectification brings to the sound that differs from SS?
I have Laurels and Moondogs, neither currently in systems. I also have a Korneff stereo 45 built by Oliver Sayes. Excellent amp. Currently I rotate it in and out of my main system with a Sean Casper 10Y. If you love the 45, I see a 10Y in your future.
Ciao,
"Starting in the middle of a musical sentence and moving in both directions at once." - John Coltrane.
Cpwill
Anyone with a schematic to share?
106dB horns so power is not a huge issue.
Actually, the Welborne DRD45, you were given a choice of Tube or SS rectified. When Welborne upgraded the DRD45 to the 'Star Chief' 45 amps, he only offered SS Rectification, as he thought it sounded better.I do not currently have an opinion on the sound of SS Rectification vs. Tube Rectification. You can google it however, and find all sorts of Opinions.
Edits: 05/13/21
nada aqui
--------------------------
Buy Chinese. Bury freedom.
nt
1 1/2 to 2 Watts is all you need.
Hard to beat the sound of a globe 45 at any price, if one has sensitive speakers that will accommodate the low power.
And they look great.
nt
Love all of it.
KP
Love those low powered SET amps. I just wish I had good speakers to enjoy them with.
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