JLTi KT88 "Unity Coupling" Tube Amplifier

[Antripodean]

I had been reading about the JLTi EL34 tube amp for some time and as I am building a pair of full range speakers (don’t ask me to design a crossover!!!) I thought it would be good to have a tube amp in the house for the office.

This was about six months ago and when I finally decided to go ahead early this year I spoke with Joe Rasmussen at JLTi to see what was available. He explained that it would be better to get a KT88 version, considering the power needed to drive the speakers I normally use (86dB sensitivity) and also because the amp design was in fact a dual mono construction that could be used as both an integrated and a power amp.

Joe also explained that it would be cheaper overall if I supplied the base amp rather than him. So, I went out looking for a Yaqin MC100B. Low and behold I found one on SNA and had it sent up for modification. Joe put a lot of time into doing the modification and checked all of the wiring to ensure that even circuits that weren’t being changed were correct.

This amp is now in place and it’s a revelation! The easiest way for me to describe the sound is uncompressed. The soundstage is 3-dimensional and all of the detail is revealed in a way that maintains the integrity of the mix in all instances. What this means is that quiet sounds are still quiet but the dynamic range is such that there is room for all the music.

The midrange is superb, which is what tubes have always been good at. The wonderful experience of having the singer in the room is something I have always liked about single ended tube amps. I had a listening session with a lot of different female vocalists and the realism was breathtaking. The highs are wonderful and it is so much easier to discern lyrics that were previously difficult to comprehend. The bass is powerful and authoritative making the whole sonic spectrum balanced and non-fatiguing.

In comparing with my Pioneer SC LX-81, which is no slouch, there is now a wonderful depth to the music. Hearing the breath that surrounds the singer’s voice and the sustained vibration of acoustic guitar brings drama and realism to music.

I haven’t had time to try out all the configurations for this amp. I am currently using the Pioneer as the preamp (it has a remote) and the JLTi KT88 as a power amp, driving my SF Concertos. I would also like to try it as an integrated and also with a different preamp as well as with different speakers. I am already very pleased with the results and can’t begin to say how involving it is to listen to music with this amp.

The modification cost $880 plus freight. A Yaqin MC100B costs less than $1000 so it all works out at less than $2000 for an amazing musical experience. I don’t know if this amp will find its way to the office after all. I look forward to enjoying tube amps all over again

http://www.customanalogue.com/jlti_el34.htm

[Orpheus]

Excellent result, and impressive looking amp.

[Joe Rasmussen]

Thanks for the nice 'review' and if I may say so, I told you that you'd like it.

Cheers.

Joe R.

PS: Will put details on the website plus pic asap.

[Joe Rasmussen]

Before sending the amp, took this pic:

Joe R.

Edited April 17, 2009 by Joe Rasmussen
pic wrong path

[Leon]

Hi Joe,

Welcome to the forum, good to have you here, how's things? Just before anyone complains, you may want to read the forum's site guidelines regarding commercial members...

[Joe Rasmussen]

Hi Leon

Hey, didn't know you inhabited this space. Actually things are very busy indeed, so no complaints except for working too many hours. OK, will take a look at the guidelines, I suppose you are similar in that respect. It's a bit like a member of ASoN and not being blatant and also reasonable about it and just contributing. Actually 'Antripodean' phoned me and just put faith in me as we have an amusing chatter about life and things.

Joe R.

[Keith_W]

Antripodean - that sounds great! Would like to know what modifications were done?

Thanks for pointing him to the guidelines, Leon

[Antripodean]

Hi Keith

Joe says it better on his website, hence the link, but in short it features "Super Linear Triode Mode", "Induced Permeability" & "Unity Coupling". All of this needs far more explanation than I can muster What attracted me to the whole modification was no negative feedback, (a feature of your Cary amp), pentodes acting as triodes (I like the power of PP with the sound of SE) and the idea that the output transformer would always be operating in its optimum range.

I could suggest a listen at my place but given your other gear I think it would be more fun to bring the JLTi KT88 over one weekend for a comparison with the Cary CAD 211. I don't mind losing the contest

I had a thought that maybe this thread should be moved to reviews. Leave that with you

[Keith_W]

If you want me to move the thread to reviews, happy to do so In fact i'll do it now.

I was a bit puzzled how Joe managed to convert the pentodes to work in triode mode without losing power. Typically you lose about 50% power output by doing this? I had a look at the website and Joe talks about "hiding" the screen grid - an explanation which more or less went over my head

In any case, any hope I had of Joe modifying my triode amp is now out the window!

Apart from (maybe) installing that Linearity Enhancement Module. Hmmm.

If you're in Melbourne, I wouldn't mind exchanging visits?

[Antripodean]

The really interesting part of the modification is that it is not actually a conversion to triode mode, rather it is virtual triode mode. So it's a PP behaving like an SE in effect. I used to have an 845 SE and it is not 'euphonic' like that amp was (which can actually be fun). The explanations go way over my head too but it does come down to 'hiding' the screen grid to achieve this.

Joe is good to talk with about whether something should or could be modified, especially with tube amps. I am always looking for value in hifi so it was an easy decision to go the whole hog, so to speak, rather than spending money on simply changing the wiring which wouldn't have brought the improvements I was looking for.

[scuzzii]

I had been reading about the JLTi EL34 tube amp for some time and as I am building a pair of full range speakers (don’t ask me to design a crossover!!!) I thought it would be good to have a tube amp in the house for the office.

This was about six months ago and when I finally decided to go ahead early this year I spoke with Joe Rasmussen at JLTi to see what was available. He explained that it would be better to get a KT88 version, considering the power needed to drive the speakers I normally use (86dB sensitivity) and also because the amp design was in fact a dual mono construction that could be used as both an integrated and a power amp.

Joe also explained that it would be cheaper overall if I supplied the base amp rather than him. So, I went out looking for a Yaqin MC100B. Low and behold I found one on SNA and had it sent up for modification. Joe put a lot of time into doing the modification and checked all of the wiring to ensure that even circuits that weren’t being changed were correct.

This amp is now in place and it’s a revelation! The easiest way for me to describe the sound is uncompressed. The soundstage is 3-dimensional and all of the detail is revealed in a way that maintains the integrity of the mix in all instances. What this means is that quiet sounds are still quiet but the dynamic range is such that there is room for all the music.

The midrange is superb, which is what tubes have always been good at. The wonderful experience of having the singer in the room is something I have always liked about single ended tube amps. I had a listening session with a lot of different female vocalists and the realism was breathtaking. The highs are wonderful and it is so much easier to discern lyrics that were previously difficult to comprehend. The bass is powerful and authoritative making the whole sonic spectrum balanced and non-fatiguing.

In comparing with my Pioneer SC LX-81, which is no slouch, there is now a wonderful depth to the music. Hearing the breath that surrounds the singer’s voice and the sustained vibration of acoustic guitar brings drama and realism to music.

I haven’t had time to try out all the configurations for this amp. I am currently using the Pioneer as the preamp (it has a remote) and the JLTi KT88 as a power amp, driving my SF Concertos. I would also like to try it as an integrated and also with a different preamp as well as with different speakers. I am already very pleased with the results and can’t begin to say how involving it is to listen to music with this amp.

The modification cost $880 plus freight. A Yaqin MC100B costs less than $1000 so it all works out at less than $2000 for an amazing musical experience. I don’t know if this amp will find its way to the office after all. I look forward to enjoying tube amps all over again

http://www.customanalogue.com/jlti_el34.htm

Great review.

Did you swap tubes over as well or are you still using stock ones?

I wonder if Joe can mod a Melody SP9......

Couldn't help but notice the SACD players on his site.

[Antripodean]

I am using stock tubes at this stage. I didn't want to introduce more variables and more expense at this stage. Joe assures me that I can go tube rolling in the future

I think if you have a schematic for the Melody then I am sure it can be modified. I always think starting with a good amp and making it even better is an excellent strategy. My Yaqin has been dragged kicking and screaming out of the 1950s

I have the JLTi modded Oppo and it sounds great. I only have 4 SACDs but it sounds superb. Out with the jitter and in with the music!

[Joe Rasmussen]

Hi Keith

Joe says it better on his website, hence the link, but in short it features "Super Linear Triode Mode", "Induced Permeability" & "Unity Coupling".

I have decided not to use Super Linear Triode Mode as that term is also used to describe another technique used by another designer (who graciously publishes his circuits). But I found that Virtual Triode Operation has been used to correctly describe it, hence VTO.

But VTO on its own has not been universally accepted when others have tried it. I do believe and have floated this on another place, that VTO gets exposes the output transformer and its low level lack of resolution, especially with the most common type which is silicon steel cores (other cores are very expensive when used as power outputs). The LEM module constantly keeps the transformer busy, so much so that any audio signal below about 60dB SPL (soft but clearly audible) keeps having the same Permeability and hence resolution. It will surprise many that tube output transformers have a strong similarity with DACs used in digital playback: At very low level they have poor resolution.

The beauty is that it complements VTO. Where VTO adds real dynamics and power (in an audio and not measured sense) it can also sound just a bit uncouth and rough-and-ready because it exposes other short-comings. The LEM adds the opposite, the matching refinement that comes from better linearity. Sound wise 1+1 now equals 3 or 4 and not 2.

Most amplifiers that are routed in 50's technology (and that applies to almost all PP amplifiers using Pentodes like KT88, 6550, EL34 and so on) can be converted. But the Unity Coupling can be tricky as it relies on getting rid of global feedback. The gain goes up dramatically and some way needs to be found to lower gain and also fix the raised noise floor that results. But I have done this to a variety of amps, from Jadis to Dynaco and the new (and fantastic value) Chinese Yaqin amplifiers.

The Yaqins also gets a 'constant current source' on the driver stage. The SRPP input stage sounds nice but I have real problems with it - sounds oh so smooth and oh so boring in the long run. This gets converted into a classic single Triode voltage gain stage - it may be classic but this into a high impedance load on the Anode means current is almost constant and sound quite glorious (note my repeated use of the phrase "constant current" - this is high in my audio vocabulary). This is one thing we don't need to reinvent.

Anybody in Sydney (or visiting) is welcome to drop in and have a listen. Guys (and gals) who come here know that they will not get any exposure to pressure salesmanship. Bring CDs, SACDs or vinyl and we have fun listening to music and it gives me a break from work.

Joe R.

[Joe Rasmussen]

Great review.

Did you swap tubes over as well or are you still using stock ones?

I wonder if Joe can mod a Melody SP9......

Couldn't help but notice the SACD players on his site.

On the first one, always keep the tubes that was used to set up the amp in the first place, don't burn any bridges. But in most cases cooking with tubes is OK, but sometimes it can lead to unexpected results. Also change the tubes in stages and never all at the same time.

Re the Melody SP9, its tube complement of KT88 etc leads me to think that it is doable. Nice looking attenuator using Beyschlag resistors (pic on their website). That's the brand of resistor I use as well. This amp is likely Ultra-Linear, so expect half power when converted to VTO (or any other form of Triode), but it wound sound half power, promise.

SACD players? Different subject...

Joe R.

[mwhouston]

I had been reading about the JLTi EL34 tube amp for some time and as I am building a pair of full range speakers (don’t ask me to design a crossover!!!) I thought it would be good to have a tube amp in the house for the office.

This was about six months ago and when I finally decided to go ahead early this year I spoke with Joe Rasmussen at JLTi to see what was available. He explained that it would be better to get a KT88 version, considering the power needed to drive the speakers I normally use (86dB sensitivity) and also because the amp design was in fact a dual mono construction that could be used as both an integrated and a power amp.

Joe also explained that it would be cheaper overall if I supplied the base amp rather than him. So, I went out looking for a Yaqin MC100B. Low and behold I found one on SNA and had it sent up for modification. Joe put a lot of time into doing the modification and checked all of the wiring to ensure that even circuits that weren’t being changed were correct.

This amp is now in place and it’s a revelation! The easiest way for me to describe the sound is uncompressed. The soundstage is 3-dimensional and all of the detail is revealed in a way that maintains the integrity of the mix in all instances. What this means is that quiet sounds are still quiet but the dynamic range is such that there is room for all the music.

The midrange is superb, which is what tubes have always been good at. The wonderful experience of having the singer in the room is something I have always liked about single ended tube amps. I had a listening session with a lot of different female vocalists and the realism was breathtaking. The highs are wonderful and it is so much easier to discern lyrics that were previously difficult to comprehend. The bass is powerful and authoritative making the whole sonic spectrum balanced and non-fatiguing.

In comparing with my Pioneer SC LX-81, which is no slouch, there is now a wonderful depth to the music. Hearing the breath that surrounds the singer’s voice and the sustained vibration of acoustic guitar brings drama and realism to music.

I haven’t had time to try out all the configurations for this amp. I am currently using the Pioneer as the preamp (it has a remote) and the JLTi KT88 as a power amp, driving my SF Concertos. I would also like to try it as an integrated and also with a different preamp as well as with different speakers. I am already very pleased with the results and can’t begin to say how involving it is to listen to music with this amp.

The modification cost $880 plus freight. A Yaqin MC100B costs less than $1000 so it all works out at less than $2000 for an amazing musical experience. I don’t know if this amp will find its way to the office after all. I look forward to enjoying tube amps all over again

http://www.customanalogue.com/jlti_el34.htm

After having built a KT88 SE UL amp and even after having to run EL34s in place I can agree that these amps are incredibly good sounding. I had to use (originally 5881s) EL34s because I cut the base whole too small. The cct. I am using is going to be very different to what has been run in this thread but SE UL pentodes produce, not only exceptionally good music but 3D sound staging.

I had built a few Spare Time Gizmo’s 6T9 amps and loved the sound stage and clarity. This got me to build this amp which supports Edcor XSE (inexpensive) OPTs, diode rec. (not enough room for valve rec. with choke filtering) all on a big timber base. The schematic is very simple. It has to be to let the music through. I am now supporting a matched pair of Black Sable EL34s. It just got better.

Though this is not a Vacuum State upgraded amp I can only support the call for SE UL pentode designs. The whole timbre of my system has changed like never (and I mean never) before. Now to build a good one.

Edited May 12, 2009 by mwhouston
missed some detail

[Antripodean]

I have to say I agree with you Running the KT88s in triode mode is sounding great. It's great that you are building your own amps. Opens up a world of possibilities and modding.

BTW I heard there was a recent 'amp blind shoot out' at the Audio Society of NSW (ASON) and the JLTi Vacuum State modded EL34 came up as the winner I am waiting to read a write up on the site but I understand it was up against SS and other tube amps. I like that it was a blind test and I am interested in their methodology as well.

[A9X]

BTW I heard there was a recent 'amp blind shoot out' at the Audio Society of NSW (ASON) and the JLTi Vacuum State modded EL34 came up as the winner I am waiting to read a write up on the site but I understand it was up against SS and other tube amps. I like that it was a blind test and I am interested in their methodology as well.

I hope that's available online sometime. I'm curious about these amps mainly because I've built most of Allen's preamps and the PP1C and PP2C poweramps; then modified them. Some of the first 'audiohile' tube gear I built from schematics Allen gave me years ago.

Not sure who designed this beast, but there will be a fair amount of VS influence I expect.

[Joe Rasmussen]

I hope that's available online sometime. I'm curious about these amps mainly because I've built most of Allen's preamps and the PP1C and PP2C poweramps; then modified them. Some of the first 'audiohile' tube gear I built from schematics Allen gave me years ago.

Not sure who designed this beast, but there will be a fair amount of VS influence I expect.

I can tell you that the Vacuum State schematics you have built not only have Allen Wright in them, but also a LOT of Joe Rasmussen in them. Indeed I built the first PP1C design/schematic into an old Dyna EL34 amp and got Allen to listen to it. There is a lot more... we go back a long time.

BTW, it says you are a westie, so am I. That is what we here in Sydney West call ourselves, so is that where you are too.

Cheers.

Joe R.

[Joe Rasmussen]

MY COMPUTER CRASHED!!!

At least one person with an existing power amp emailed me directly the morning my hard drive, only two months old, went belly-up in seconds. Lost record of all emails since February 15. Not able to reply as I don't have email addresses. Dar'n it!

Joe R.

[andyr]

MY COMPUTER CRASHED!!!

At least one person with an existing power amp emailed me directly the morning my hard drive, only two months old, went belly-up in seconds. Lost record of all emails since February 15. Not able to reply as I don't have email addresses. Dar'n it!

Joe R.

C'mon, Joe,

You haven't backed up your PC since Feb 15 ... shame on you!

Once a week's good (as the actress said to the bishop) but, realistically, once a month is probably reasonable.

Regards,

Andy

[A9X]

I can tell you that the Vacuum State schematics you have built not only have Allen Wright in them, but also a LOT of Joe Rasmussen in them. Indeed I built the first PP1C design/schematic into an old Dyna EL34 amp and got Allen to listen to it. There is a lot more... we go back a long time.

Allen told me you designed the crappy bits, which he designed out when you weren't looking.

BTW, it says you are a westie, so am I. That is what we here in Sydney West call ourselves, so is that where you are too.

Cheers.

Joe R.

My therapist told me I had to post my location that way, to come to terms with the reality of it all and deal with the shame. How can a Northern Beaches boy have fallen so far?

Though, I must admit the Winnie Reds in the AC/DC T shirt thing is pretty cool.

[Joe Rasmussen]

C'mon, Joe,

You haven't backed up your PC since Feb 15 ... shame on you! :o

Once a week's good...

I am now backing up every day, no excuses.

Joe R.

[Joe Rasmussen]

Allen told me you designed the crappy bits, which he designed out when you weren't looking.

Well, I am looking and the crappy bits are still there. Maybe not so crappy after all. :o

My therapist told me I had to post my location that way, to come to terms with the reality of it all and deal with the shame. How can a Northern Beaches boy have fallen so far?

Though, I must admit the Winnie Reds in the AC/DC T shirt thing is pretty cool.

So when are you coming and visiting me? Just look on the map and see where the M5 and M7 meet and there I am. BTW, I used to be an Eastie, but the cost of building a house... well, you know what I mean. I miss Maroubra Beach.

Joe R.

Edited May 17, 2009 by Joe Rasmussen
... because I make mistakes :-(

[mwhouston]

Since my last (and first) post concerning Valve, SE UL amps I have upgraded my Electro-Harmonix tubes to Black Sables. Yes another Vodka swilling tube but these are both matched and cryogenically treated.

Usually tubes take 50 hours of play to get them to really settle. Not the Sables. These came out guns blazing to make a sonic impression not easily forgotten Now not only had I depth around individual performers or whole groups that depth had extended laterally to the total width of the sound stage.

For a few hundred dollars these are well worth it. They replaced a pair of date matched only common tubes but not electrically matched tubes. To gain the finest detail in music and to paint an expansive 3D sound stage the tubes have to be matched and the amp built with a perfect balance of channels. My sound stage 'tends to hover in mid air and extend way behind the wall to which the speakers back. This "hover" pleases most listeners though some prefer a more solid sound scape. For me I like the feeling the sound is being projected into the space between my Osborn Eclipse.

I also bought a pair of NOS Siemens rumored to be the best of the EL34s. Yet to be auditioned.

[A9X]

Well, I am looking and the crappy bits are still there. Maybe not so crappy after all. :o

Some years ago, maybe 01 or 02, you sent me some info about techniques for forcing balance in O/P stages. Is the current amp a development of that?

I can't recall what you called it, but I did find the papers in my filing cab during the move.

So when are you coming and visiting me? Just look on the map and see where the M5 and M7 meet and there I am. BTW, I used to be an Eastie, but the cost of building a house... well, you know what I mean. I miss Maroubra Beach.

Joe R.

I'm out here for the same reasons. I miss Narra and North Curlie the most.

Well, I'd sure like to come and have a listen. I gave a mate who's interested in the Elsinores, and I'm currently working at Hoxton, but even so it's not that far from home. I'll give you a call soon when I'm sure of my exact movements to arrange.

Cheers.