27 replies to this topic

[Warren M.]

Joe Rasmussen of Custom Analog Audio, in the Southwest suburbs of Sydney, provided me with a JLTi KT-88 Mk2 amplifier for my turntable presentation at the Audiophile Society of NSW. Before I decided to use it, I had a listen in his own home. He was also showing off his newly modified Oppo BDP-95 universal digital player (Bluray, DVD-n, SACD, CD, music server) which he modestly describes as, after modification, the best digital player you can buy regardless of price. It was indeed amazingly good. The amplifier was pretty good too. I liked what I heard.

A little background to the amplifier (apologies to Joe, if I get anything wrong here). Joe takes a superbly built Chinese amplifier, in this case the Yaqin MC-100B, based on a 1960s push-pull dual mono tube amp design, using KT-88 tubes as the main amplifiers and 12AX7s as the input tubes. Build quality is exceptional and would require thousands of dollars if Australian labour was to be used to produce the same finish etc. On the other hand, Yaqin does not try to address the problems associated with a push-pull design (e.g. great impact but lacking micro details). At under $1K shipped to Australia, you'd hardly expect them to!

That's where Joe comes in. In the Mk1 version he made some major circuit changes and added in a few very clever bits of technology, resulting in a tube amp with the impact of a push-pull and much of the micro detail of a single-ended design. In the Mk2 version, just released, Joe has replaced the 12AX7s by 12AT7s and reworked the circuit for radically better sound. The cost to upgrade an existing Mk1 version was $300 or to modify a Yaqin MC-100B was about $1000 as I remember it.

It is funny how some things just happen together. I heard the JLTi amp at Joe's and started thinking about finally replacing my Arcam Alpha 10 / Alpha 9 combination, which has been my amplification system in one form or another for well over a decade.

I looked on eBay for the prices of Yaqin amps and discovered that someone was selling a JLTi Mk1 2nd hand. I couldn't resist! I won it at Auction and, after a few days of listening - it definitely did not sound as good as the Mk2 I'd heard at Joe's or at the ASoN presentation - sent it off to Joe for upgrading.

I've now had it in my home for a few days. It is hard to describe the difference in sound, and, surprisingly, I'm still coming to terms with some aspects of it.

The thing which is most striking about the amplification is how "honest" it is. This is a bit of a two-edged sword. For instance, my CD player (a modified Arcam Alpha 9 CD) is a very fine performer. But aspects of its performance, for better or worse, have been hidden from me up til now. Something I would call "digital edginess", which I have heard on lesser CD players (including more expensive ones), is much more obvious now than it was through the Arcam amps. A considerable veil has been lifted off the music, but that veil has also been lifted off the non-music. On balance, the CD sound is much better than before, but you can tell by comment that the amp is forcing me to reconsider the quality of my CD player. As for my tuner, it sounds absolutely fantastic, especially on 2MBS FM live broadcasts (my tuner is a Sansui TU-X701 which is a wonderfully musical tuner). I haven't switched back from my Alpha Genesis to my Shelter cartridge on my Once/PU7 turntable system, so I shall not make comment about phono yet, except to say that voices sound amazingly lifelike - beyond any sense of realism I got with the Arcams.

The JLTi is considerably noisier than the Arcam duo, most apparent when listening through headphones. But the noise is very easy to live with as the music sounds so much more like ...music.

More later as I experiment.

[ATTACH=CONFIG]38123[/ATTACH][ATTACH=CONFIG]38124[/ATTACH][ATTACH=CONFIG]38125[/ATTACH]

Cheers
Warren

Edited by warrenmmmmm, 20 November 2011 - 07:53 PM.

[datafone]

I'm surprised about the noise that you mention? Is it a product of the amp or the source?

Do you know what Joe has done to improve the Yaqin in the Mk2 version? Hmm...scratch that last question, would maybe on a need to know basis

But this noise you mention has me intrigued?

Edit:Forgot to mention that I like the dual supply aspect of these amps

Edited by datafone, 21 November 2011 - 11:06 AM.

[Warren M.]

First I should mention that the Arcams' preamp is extremely quiet. Through my headphone amp (-112Db noise), open circuit, using the Arcam Alpha 10 as a preamp, I can just hear the faintest hiss through my AKG 701s. I have not used the Arcam Alpha 10 as a preamp into the JLTi KT-88 as a power amp (you can switch the JTLi to be a power amp or an integrated) to listen whether the noise is preamp only, power amp only or both.

I also think I may have been a little too hasty in my comments. This particular amp has to go back to Joe for a check-up - it was one of the first Mk1-to-Mk2 upgrades and, also being one of the first Mk1 units he had ever done, required some additional stuff done which was not "standard". Once he checks it all over and makes sure it is 100% right (or 50% left and 50% right), I'll be in a better position to make absolute judgements about its noise level and the rest of its performance.

I certainly did not notice any residual noise whatsoever coming from the KT-88 either at Joe's home or at ASoN.

Regards
Warren

[datafone]

Heh...I see, I was imagining more noise than that, and surprised that Joe didn't address it.

The standard amp uses a lot of cheap parts (resistors & caps) so still even more room for improvement for you down the track, if it takes your fancy

With the MC-10L I had, the signal passed through three circuit boards before reaching the preamp, by-passed the difference was very noticeable for the better

[zenelectro]

I certainly did not notice any residual noise whatsoever coming from the KT-88 either at Joe's home or at ASoN.

Regards
Warren

WRT amplifier noise contribution: unplug the amp from source and *short the IP's of the amp (to
gnd)*, then listen to how much noise it makes.

A lot of people will unplug an amps IP's and hear noise, this can be significant due to
thermal noise of IP gnd ref resistors, which will not be heard in normal use when it is
plugged into a source.

If your amp is still noisy with the IP's shorted then you have a problem (or it is a poor
design).

[Joe Rasmussen]

Hi Guys

I know this is not the correct place, but since it was mentioned here above:

I didn't exactly say the upgraded Oppo BDP-95 was the best player regardless of price, more like it simply on another level to anything I have heard before, and I have heard a lot.

Yesterday a client picked up his upgraded Oppo '95 and he called this morning. He has a Meridian 800 DAX which he reckons about three years ago was around $40.000 - WOW!

How did the Oppo square up?

He said the Oppo was smoother, more analogue and revealed subtle details in a less pushy way and upfront way, it was SUBTLE and REFINED. It also revealed the Meridian to have a glare that was missing in the Oppo. He said he was very happy. Which also made me happy.

I must then make a comment about the JLTi KT88 Mk2 amp. I have been in audio for over fourty years (yes, I was knee high to a grasshopper) and I have not seen better value, I found them quite amazing. I've got far more expensive amps here and I don't feel like I have to turn them on.

I has a talk with Warren about the noise and since the noise is quite low with inputs shortened (as zenelectro correctly point out), and he also said the noise varied with the position of the Volume Control, that it seems to be a source noise rather than the amp. If he wants it, I can lower the gain of the KT88 amp which is a bit above average, that would make source noise less apparent. As Warren said, and nobody else has heard or mentioned a noise problem in the Mk2, whether listening here or elsewhere. So it seems some detective work is required to sort out why Warren has a problem. I am sure we can.

Cheers, Joe R.

[datafone]

I often consider that I should have bought one of those for the transformers... instead of the MC-10L, mono supplies would be nice

[56oval]

..............................................

Edited by 56oval, 10 December 2011 - 11:47 AM.

[datafone]

That's another way, and never too late to do it

[Warren M.]

Man! That is good service. I delivered the JLTi KT-88 to Joe on Friday morning, along with 4 KT-120 tubes. He fixed a fault in the left power transformer, replaced the KT-88 tubes by the KT-120s, checked everything out, had a friend audition it on Sunday morning, and delivered it back to me at yesterday's ASoN meeting.

I switched it on at 6:30 this morning, gave it about an hour to fully settle, and re-adjusted the bias (two of the tubes required the slightest re-biasing to bring them back to within .001V of 0.45V).

Noise appears to be less than -90dB (via my CD player) and all above 10Khz - I've heard noisier high quality solid state amps. Absolutely no audible hum at full gain, even on headphones.

I listened to Cat Stevens "Tea For The Tillerman" (Quality Records vinyl 200g reissue/remaster) side 1 - wow! This evening I get to trial a MiniMax phono in place of my modified Jasmine. Should be a real treat.

Cheers
Warren

[datafone]

Be interesting to hear the difference with the MiniMax over the Jasmine.

You like the KT120's?

How do they sound to you Warren?

[Jehuty]

Congratz warrenmmmmm, sounds like a worthy upgrade to Mk. 2.

Joe has always been very supportive and helpful to me too, he's definitely one of the nicest guys in the industry

[Warren M.]

You like the KT120's?

How do they sound to you Warren?

It is a little difficult to tell how the KT-120s compare to the KT-88s that were originally in the amp. My first indication is they are superb - exceptionally quiet, midrange sounds nice, deep sonorous bass, and very fast. Top end is somewhat strident at the moment in absolute terms. Keep in mind they are still brand new. With another 30 hours on them, I expect they will sound considerably better. I would not expect them to reach their optimum until about 100 hours' use, but the differences after that first 30 hours until they have reached optimum should be subtle. In the meantime the sound is already way more musical than my Arcam amps, which kept me very happy for over a decade.

Others with KT-120s rave about them and Joe greatly prefers them to stock KT-88s. So does Elson Silva, who uses them extensively in his amps.

Be interesting to hear the difference with the MiniMax over the Jasmine.

At my ASoN presentation, the improvement going to the brand new MiniMax was stunning, with the obvious limits associated with brand new tubes. However, it is not necessarily going to be the same in my home, where lots of other acoustic compromises are at play.

If I do buy the MiniMax, I might replace the pair of stock 12AX7s with Psvane tubes. Not cheap but apparently the most musical 12AX7s out there. The 12AT7s in the JLTi KT-88 input stage might also be a contender for Psvane tubes, but only once I have given the KT-88 long enough to properly settle in.

Edited by warrenmmmmm, 28 November 2011 - 03:58 PM.

[datafone]

Nice, and I agree...they need a lot more time, and will reach a point of very noticeable change.

Lot of enjoyment coming

[Warren M.]

It is a little difficult to tell how the KT-120s compare to the KT-88s that were originally in the amp. My first indication is they are superb - exceptionally quiet, midrange sounds nice, deep sonorous bass, and very fast. Top end is somewhat strident at the moment in absolute terms. Keep in mind they are still brand new. With another 30 hours on them, I expect they will sound considerably better. I would not expect them to reach their optimum until about 100 hours' use, but the differences after that first 30 hours until they have reached optimum should be subtle. In the meantime the sound is already way more musical than my Arcam amps, which kept me very happy for over a decade.

Others with KT-120s rave about them and Joe greatly prefers them to stock KT-88s. So does Elson Silva, who uses them extensively in his amps.

At my ASoN presentation, the improvement going to the brand new MiniMax was stunning, with the obvious limits associated with brand new tubes. However, it is not necessarily going to be the same in my home, where lots of other acoustic compromises are at play.

If I do buy the MiniMax, I might replace the pair of stock 12AX7s with Psvane tubes. Not cheap but apparently the most musical 12AX7s out there. The 12AT7s in the JLTi KT-88 input stage might also be a contender for Psvane tubes, but only once I have given the KT-88 long enough to properly settle in.

The KT-120 tubes have now run in for several weeks. The stridency I spoke of has completely disappeared. Replaced by a wonderful fluidity.

A week ago I replaced the very nice GE 12AT7s by Psvane A-Grade 12AT7_T tubes.
CD reproduction has improved in a very major way, with a much more analogue sound, for instance much more subtle crescendos and diminuendos and a markedly wider and deeper soundstage. Undoubtedly worth the $100 asking price for the matched A-grade pair from Grant Fidelity in the USA.

I also replaced the MiniMax's 3 stock 12AT7s (1 matched-halves for stage 1 amplification and a matched pair for stage 2 amplification) with Psvane A-Grade 12AT7_Ts. In combination with the changes to the JLTi, the MiniMax has also shown marked improvements in most areas, taking it to a standard which should not reasonably be available at the price, but the Psvanes are not meant to reach optimum before about 300 hours so there still may be some audible improvement (in both the JLTi and the MiniMax). As soon as one arrives, I'll be swapping the stock 6X4 rectifier tube in the MiniMax by a NOS military grade Mullard, which is supposed to be the best sounding and quietest 6X4 out there. Hopefully the noise floor will lower further with that in place (the MiniMax does have a moderately high noise floor compared to the quietest solid state phono preamps I've heard).

Of course I can't really separate the MiniMax performance from the JLTi, given that phono is passing through both, but the results are pretty amazing.

All in all it has been a very eventful couple of months in my amplification life, and has all been very positive.

Cheers,
Warren

Edited by warrenmmmmm, 01 January 2012 - 12:06 PM.

[Dasher]

Thanks for taking the time to post your thoughts, I enjoyed the read:)

[heman_]

Warren, How do you connect the Rel sub to the amplifier?

[datafone]

Warren, I have read that the KT120's draw more heater current, was this OK without any modification?

Cheers
Ian.

[Joe Rasmussen]

Warren, I have read that the KT120's draw more heater current, was this OK without any modification?

Cheers
Ian.

I have used them for six months and no problem. Also, I recommend using 45mA to bias them and that means only a bit more than 20 Watts Plate Dissipation and less stress on the power transformers (there are two of very adequate size). I don't expect there to be any problems.

Cheers, Joe R.

[datafone]

Looks good Joe

[Joe Rasmussen]

Looks good Joe

You know, I keep finding ways to improve this amp... nothing has quite amazed me as much as this, and I've been around for a long time.

Cheers, Joe R.

[Warren M.]

Warren, How do you connect the Rel sub to the amplifier?

The REL sub is designed to connect to the same speaker connectors as the main speakers, via the RELs very high impedence connectors. I think the resistance is over 1000 Ohms (that's a guess - I'm not in the same country as the documentation or the sub at the moment), so the result is effectively the same speaker load with or without the RELs attached. It works a charm.

[kesa32]

Hi , sadly l have to move my 100b on as l need the cash for a new pj for the ht room and l rarely use it these days

Mine was joe's first modded one and is pictured on his web pages, l've since installed new Shuguang "Black Treasure" KT88-Z's ( probably done 20hrs ) and replaced the 12AX7's with NOS 5751's black plate triple mica's

Will be putting it up in the "for sale" section shortly

[datafone]

A real shame you have to sell it mate, but it will be a nice acquisition for someone here

[kesa32]

Hi lan, yeah l'm not happy about this , but moneys tight and it unfortunately has to go..........also selling my Hawthornes and Cinemag Audio Transformers

l'l Revisit 2ch audio when things come good in a couple of years

[datafone]

Sometimes well have to juggle things to meet priorities, and like you say you can revisit later
The good thing is those items will be easy to move

[kesa32]

Thanks lan , yes patience is a virtue hey

[kesa32]

Hi guys, l've listed it on ebay , as for some reason my listing did'nt get approved / lodge here ??