Audio Note Kit - L5 Mentor - build experience

Hi all,

Adding to here yet another Audio Note Kit build thread. This time it will be the Mentor L5 preamp.

Intro

Some intro. I have for more than a decade this custom made preamp. It is quite a beast with a simple line stage driven by a very beefy powersupply and regulation circuit. I honestly don't understand how it work. The sound coming out is good. The only issue I have with it is that it is a bit noisy.

So recently having gone back into audio I am looking into a new tube preamp. I have been brought up with tube amps and although I recently switched to class D power, I want to keep the preamp tube to give it a bit of tube flavor.

Initially I was looking at kits around $1-2k. But upon learning about the ANK series of preamp, I was quite hooked. I was going to just get a L4 but I also wanted a stereo attenuator instead of dual mono, ANK gave me a good deal so I ended up with the Mentor plus stereo attenuator. Why stereo attenuator instead of dual mono? My current preamp has dual mono, it is a pain to try to get both side to the same level, it mostly involve turning back to 0, and then count to 12 or 13 on each side. Honestly I don't see the benefit of dual mono.

Build

So anyway, onto the build. I was promised to get the part in 3 weeks. And having gone through all the build thread here in SHF, I already have the expectation that some parts will be delayed, and some will be missing, etc. Two large boxes arrived as scheduled, it was like early Christmas.

With the expectation that some parts are missing, and some indeed are missing. The line board resistors and cap, all wires and the attenuator were not there. Turned out that they are being ordered from a different source. I wish it had been communicated that way. I am currently still waiting for that shipment to arrive.

However, I do have enough parts to build the power supply side which is where I started. I received the shipment on Friday but was due to travel out of town Saturday morning to run a marathon. Well I don't have much in terms of patience so I started on the most simple part which is the tube rectifier board.

to be continue...

 

GL and thank you for sharing this. These build threads are some of the most fun and solid information sharing on the forum.

 

The boxes are huge. Total 53lbs.

 

I first worked on the rectifier board. I have been working late all week and I was looking forward to some fun time building it before going out of town on Saturday. The board has a grand total of 5 components. 2 tube sockets and 3 capacitors. The kit comes up with nice Mundorf 4 poles filter caps and a supreme 0.22uF filter cap. However it also come with cheap Chinese 5U4G rectifier. I have a few rectifier tubes in my collection that I will roll in after the Mentor is burned in correctly.

Somehow I managed to screw up one of the sockets. It wasn't sit in fully. Now one of the tube has a very slight slant. I made some attempt to correct it but no amount of solder suckage was able to free it up.



Some of the build I see cotton tubes are used for the exposed capacitor leads. I don't have that on hand so I covered them up with shrink wrap. I don't think they serve much of a purpose other than looking pretty and maybe prevent electric shock (there are numerous other exposed HV pads anyway... so... )

 

On Sunday evening after I came back from running a very poor marathon, I jumped in and worked on the filament supply board. (Well, more like limped in..) It's purpose is to supply the 6.3V DC needed for the filament of the 6sn7 and ecc99 line board tubes.

The capacitors supplied are Rubycon YXJ. I don't know how good they are and Rubycon isn't known for audiophile grade caps. I might swap them out. Anyone have recommendation on 16v 4700uF caps for filtering purpose? I am not stressing at the moment since this is just the filament supply.

Pretty straight forward except the heatsink for the regulator. I didn't set the regulator on the heatsink before soldering it. I trimmed the end and it was too short for the hole. To workaround it, the heatsink is upside down which give enough clearance. It will be fine, I might get new regulators and swap these one out later if I go ahead and swap out the caps.

 

Next I mounted the power supply transformer and the large and medium chokes. Those things are heavy.

The custom wounded PS supply caps has 5 input and 14 output leads. On the input side there is a input board that interfaces with the outside power lead and switch. It lays out the 2 primary windings that can then be hooked up in series for 240v or in parallel for 120v. ANK supplies this piece of clear plastic that is supposed to be the cover for this little PCB. It doesn't have the matching middle screw hole and I don't see what covering this board would do. I put it behind the back of the board at the moment before I figure that out. This cover is not mentioned in the instruction manual.

 

Those yellow clips for the IEC and power switch were quite hard to attach. And honestly I am not convinced they will sound good. I am considering taking them out and use direct solder onto the lugs and then wrapped it up with shrink wrap. For now, I just want to focus on getting this to function and then make small improvements later.

The green wire coming out of the power transformer, and the black one at the bottom of the IEC goes to a common ground point on the chassis. This thing better not have a nanovolt of hum.

 

I have built a couple of these kits. If you look closely at the press on clips you will see that they are not a good fit on the terminal blades, quite poor actually. Because of this I soldered all the connections and covered with heat shrink. A much better connection, just don't overdo the heat on the power switch.

 

That's great to know. I will do the same.

 

Rubycon made the famous Black Gate caps - considered the best sounding caps int he history of the world - so I dunno about Rubycon not being noted as a good sounding cap maker - of course these things may be system dependent just like tube choices.

 

I guess this is where my nightmare starts.

I received the package from hificollective. It is missing ALL the caps, no hookup cables, and the wrong attenuator.

 

You're going to love the Mentor. I love mine so much. It's an incredible preamp. Just give it a month to settle in once you're done building.

 

@Ilovefooty : Thanks. That's a beautiful build you got there.

A couple of questions. What caps are those on the filament board? I got that yellow AN-A cable, but the supplied length is just enough for the long selector switch to attenuator run. was the length from the attenuator back to the line board included?

 

The build continues. I hooked up the transformer secondary cables to the rectifier and filament board and since I don't have the remaining of the hookup cables, I only managed to hook up the bleed/shunt resistor. That enough to do some voltage check.

the filament measure 6.1 to 6.13 volt, and B+ is around 276-278 volt.



The rectifiers are glowing quite nicely. A bit of light after the disappointing afternoon receiving that package.

 

The caps on the input board are V-Caps and Mundorf - see photo below.
Yes, the length of the yellow AN cable was included.

 

Wow, a marathon and you still had the energy to work on it?!? Looking good! No mention of the power jumper PCB in my EL84 instructions either.
These pictures are helpful. I think I'll be redoing my IECs at some point, soldering would be cleaner and I can shorten the extra wire. It also feels weird
to use the included red wire as my ground.

 

Man, gotta love all that iron and those C-Cores!

 

Absolutely beautiful! Love seeing other builds. I think I should upgrade my pot to a Khozmo.

 

@Ilovefooty that's a beautiful build. the wires are all wrapped up and clean.

 

Marathon: building only take sitting down.

The L5 instruction also have good step by step details. I looked at @Ilovefooty 's build and learned a bit about how to do that plastic cover piece and I have fixed it nicer now.

After a couple of email exchanges with Brian. He promised he will have the missing pieces sent out next week. Patience is not my thing!

 

I have totally forgotten Rubycon makes Blackgates! speaking of which. I have a couple of these leftover from a unrealized project a long time ago. still measures good. 220uF is ok for cathode bypass. I will experiment with it after finish building with the stock components.

 

Meanwhile, I am just putting together whatever I can. Not much more can be done without the hookup wires and caps.

I elevated the resistors like recommended in another build thread. Looks quite cool that way. Those tube bases are the best that I have ever touched. Top quality stuff. Tube insertion is smooth and effortless. The legs are machined and not those cheapo bent metal found in cheaper bases.

 

I sense that there is a moral to this story, but it seems to be alluding everyone out there in build-a-kit land.

 

I am not a manufacturer - but I just don't really understand why it is so hard to simply put 4 XYZ caps and 8 ABC resistors, And Transformer Value Q into a bag And then place all the bags in a box and mail it out.

But then there is a reason for that saying, "Good Help is Hard to Find."

 

It's interesting reading threads like this as someone who has been doing rebuilds and component upgrades for the better part of 25 years and looking at the images and being critical over every aspect of construction from component choice to wiring technique, soldering finish, electrical potential danger and then you realise everyone has to start somewhere. HOPEFULLY it doesn't kill them first.