In a previous post several of us have described the CL MK I amplifier. Batman built this amp and there are now several other headwizers in process of building it.

The team of mains_hum, batman, and runeight still wanted to improve on the MK I in several ways: 1) to remove the complexity of tube regulators, 2) to use the better differential input/feedback input stage, 3) to supply a slow start solid state power supply, and 4) to use constant current sources on the input stages.

One other goal was to use only one power transformer with a single high voltage secondary and one heater secondary. To supply the input stage with its required negative bias, we used a standard back bias technique in the PS to create a -15V supply.

This new amp has been built by mains_hum, Steve Culton, and jwags. They will be posting pics and listening experiences following this post.

mains_hum built a slight variation on the amp which includes special lighting effect and BJT CCSs (instead of Mosfets). Diagrams for both amps are at the following links:

Standard CL MK II

Mains_hum CL MK II Special

This project was great fun to work on, especially collaborating with the rest of the team to work out this design and to hear their descriptions of how the amp sounds. Let us know what you think!!!!

[Edited by runeight on 09-13-2005 at 03:36 AM.]

This one

CL mkII powered
CL mkII underside

is slightly frivolous in having blue LEDs added just for fun.
The valves themselves can be lit blue, but the picture shows how it normally looks i.e. just a power indicator and the knobs lit.

Also, this version uses ordinary transistors rather than FETs for the CCS just to show that BJTs can be used to good effect.

What really matters though is, how does it sound ?
In simple terms, very good indeed.
Replacing the hollow state regulator as seen in the mkI with a FET version really seems to "tighten up" the sound.... not that it was bad in the first place.
Bass is very controlled yet full on when it should be.
Treble is clean yet sweet.

I'm a fan of Sennheiser headphones, and I've auditioned this amp with my HD-600 (300Ω), along with HX-100 (32Ω) portables and MX-500 (32Ω) ear buds.
OK, so using streetware headphones with a valve amp is a slightly strange thing to do but the amp really shows what these cheap headphones can do when given a chance.
And of course, the HD-600 are magic.

Overall, this amp is closer still to a BCJ but considerably easier to build.
And our biggest collaboration yet to ensure it really works !!!

Just for fun, here's what's the amp looks like with all LEDs lit
everything lit
I leave it to you to decide whether it's worth doing or not.
Some folk liked this, others didn't.
Hence the (not shown) switch to leave the valves "normal", yet in a darkened room ....

[Edited by mains_hum on 08-06-2005 at 01:33 PM.]

So.......... THANK YOU!!!!!!!!!!!!!!!

Here is a link to some pics. The copper plate looks alot better in person as the lighting made every spec of dust look like a crater.

bottom view
front view
rear view

Now on to the details..
The build itself went very well as the instructions and documentation was very good. These guys really did a fantastic job making this easy to build. I had two small wiring errors that I was able to chase down without anything going up in smoke. Once fixed everything worked like a champ.
This is my first tube amp. And my first quality headphone setup.
My system is:

Sennheiser HD600s
NAD 542 cd player
And then of course the MK2

Prior to my amp being built I was using a Carver C1 preamp to run my headphones and I thought it hard to imagine it sounding any better than it already did.
Boy was I wrong!!!!

First off the amp is dead dead dead quiet. We are talking so quiet I thought it wasn't working when I first powered it up. Even full volume produces ZERO buzz or hum.

I listen mostly to acoustic music. Pop Piano and classical for the most part. And I have to say this is the best sounding system I have ever heard. Bar none. Nothing even comes close.
The realism and 3d image produced my this amp is nothing short of fantastic. Cymbals sound like vibrating disc of metal as opposed to a frying pan. Cello strings resonate and sound so real you would swear the cellist was standing in front of you.
The amp has more power than I would ever use and the dynamic range has to be heard to be believed. Mozarts "A little night music" in G major at the intro with the screaming violins has such power and realism it gives me goosebumps, even after I know to expect it.
I am not a super experienced audiophile. So they may be other headphone amps out there that approach this level of performance. But I have yet to hear them.
I know this review sounds a little over the top but I am being honest here. This amp is incredible. Hats off to the designers!!

So this is my CL Mk II. Some contruction notes:

I took my sweet time on this; I actually began in January. My design is based on the Bottlehead amps which make up the rest of my system. I started with an aluminum chassis plate, polished with a wire wheel, then drilled and cut holes, fisnishing with several coats of gloss lacquer. The tranny bell had to be stripped and polished before it too received a coat of the lacquer. It also has semi gloss black on the sides. The base is maple and has a nine layer hand-rubbed finish. Built the power supply first, then promptly blew it up by wiring a FET backwards. (I highly recommend to anyone building this that you build the PS first; makes it easier to find wiring errors.) After getting the PS right, I completed the circuit part. Well, not really as I wired my CCS boards wrong. While trying to figure THAT out I blew another FET. Jeff came to my rescue with some CCS boards he built, and we finally got this sucker working.

OK, how's it sound? (Like I'm going to say, "uh, it's OK"...) For starters, it's dead balls quiet. It's definitely better than the Cavalli Jones: better, tighter, bass; bigger soundstage; more details revealed. And the tube sound...this is what good audio is all about! I'm currently running it with my TT into my Bottlehead Seduction phono stage, and it kicks some serious burro. Using TungSol Black Plates and gold pin Amperex PQ 6922s. The sound is just fantastic.

Hats off to mains and runeight and Batman for their design/layout/construction help. As usual, if it weren't for them, I wouldn't have been able to build this.

http://mysite.ve..._CL_MkII_2.JPG"

To help Steve and jwags818 with the construction, we made three-layer pictoral drawings of the wiring. Each layer of the drawing shows the wiring of a different section of the amp. To see one page, click HERE We've also created a list of parts with part numbers from the usual American suppliers. Some of the circuits of the amp are built on perf boards to simplify constrution. We made drawings of these circuit boards to assist with their construction. What was the most fun was making a dimensioned drawing of the chassis mechanical layout and watching jwgs818 bring it to life with CNC machinery.

To help those who may be interested in building the conventional version, I've assembled a zip file that contains the pictoral wiring guide,drawings of the ciruit boards, the parts list and the dimensioned chassis. This file can be downloaded from HERE Note that the pictoral drawings are "printed" on pdf "paper" that is 17x 22 inches. One can zoom the drawings 200% and see the fine detail of the wiring of any part. I also have a pictoral drawing for Steve's Bottlehead layout if anyone is interested in that.

[Edited by Batman on 08-07-2005 at 04:35 PM.]

Jeff

I can't think of anything else these guys could have added to this amp to make it any better. I did add a stepped attenuator here recently and another level of focus was achieved. But it was great before I added this. Now it is even better.
Thanks again to Rune Eight and Mains Hum and Batman for an incredible design. I listen to my amp 40+ hours a week.
It is the first thing I turn on when I get to work in the morning and last thing I turn off on my way out the door.
Worth every penny I paid to build it and then some.

;-)

Batman, btw I'm still in the process of procuring parts (75% complete now) for a mk1. ;)

Jeff

The only change is that that pass mosfet will dissipate a little more than twice the power as before. It will need a good heatsink to relieve it of the 10W that it must shed. The error mosfet will dissipate about 600mW and will need a small heatsink.

[Edited by runeight on 10-09-2005 at 07:41 PM.]

well for starters you'd cut down on the likelihood of having AC-induced hum straightaway.

"Is anything to be gained by using DC on the filaments?"
Possibly.
But ....
If you twist the cable pair and lay them flat to the (earthed) top plate all should be well.
Thus far no one has needed to use DC 6.3V for this amp, which is deliberate to avoid rectifying and smoothing 3.5A with the complication and expense that it adds.
By all means try, and post the results .. that's what DIY is all about ... could be a CL mkIIa