ANK 300B Interstage Monoblocks

Improving PSRR through this part-injection of the B+ supply into the output is also the hallmark of John Broskie's (writer of Tube CAD journal) own Aikido topology, with which I built my line stage. It's considered to be a very neutral sounding design, rather than 'tubey', but I'm not certain how much that may be attributed to the Aikido noise reduction method.

The Aikido circuit utilises a pair of resistors forming a voltage divider instead of additional capacitors, but it too requires the solving of an equation based on the mu of the tubes employed. It's good to know that similar noise rejection techniques might be available for other topologies as well.

PS - fingers-crossed you get all the parts in your ANK delivery...

 

Yes, this looks like a nice design. Are you happy with the way it sounds?

I had considered building a preamp using some of the Aikido boards as my first tube project, but I've already got a preamp build underway (almost done) - my second DIY preamp - so I decided the 300B SET amp would be more interesting to start with. I may circle back to the tube line stage in the future.

I will certainly keep track of what is included, but I am replacing so many of the standard kit parts that I'm not too worried. As long as the transformers and copper plates are in the shipment, I can get to work on completing the top plate and follow up with Brian on any missing parts I need.

 

Completely satisfied with it once I found the right tube complement, although I haven't had a lot of experience with standalone preamps. But I am considering a full rebuild with a tube rectified power supply and some additional goodies.

I have to say, I find ANKs own Mentor preamps to be very enticing. And what a great match for someone who has a pair of their monoblocks...

I remember being much impressed with your AMB Alpha-24. What's the new preamp?

 

It's a two chassis design, with transformer and first stage power supplies in one chassis, and the audio circuitry with local shunt regulators in the second chassis.

The audio circuitry consists of a AMB A24 unity gain input stage which feeds a Khozmo balanced switched attenuator (the same one as I used in my first preamp). There are two separate output stages. One is another AMB A24 and the other is a Salas DCG-3, operated fully balanced (one 2-channel DCG-3 for each of the two stereo channels). Both output stages are set up for 6db gain. The A24 is used to provide a single-ended output to drive my subwoofers.

Each channel has two Salas UltraBib +/= shunt regulators - one to supply the +/- 12V power for the A24 boards, and one to supply the +/- 17V power for the DCG-3. The DCG-3 is DC coupled to the attenuator since it has a DC-servo built in. The A24 is AC coupled using some high quality film caps.

The A24 boards and the DCG-3 boards are built using Z-foil resistors (same as my previous preamp), but I changed up the attenuator resistors a bit. This time, I'm using Takman REY shunt resistors and Audio Note silver tantalums for the series resistors.

Below is a photo I took a few weeks ago when I was doing a layout check. This was before I had any of the power transistors installed. After taking this photo, I decided to redo the base plate to spread things out just a bit more, so there is now about 10mm between the heatsinks, between the attenuator and the A24 boards, and between the A24 boards and coupling caps.

When I had first designed the base plate, I had planned a different configuration of the front panel, but now I have a bit more space to pull things forward. On this build, I'm only going to have the OLED display and a single knob on the front panel. Input selection is done by pushing in the volume knob (or using the remote).



The power supply chassis has a custom 400VA Toriody transformer that has 9 secondaries - 4x17V, 4x12V and 1x7.5V. These feed four separate simple DC power supplies (schottky diodes, CRC filter bank) - two for each channel. The outputs all connect through a 14 conductor umbilical cable to the main chassis, where they feed the shunt regulators. There is also a separate 5V regulated supply for the digital circuitry in the Khozmo attenuator.



I'm working on getting it all wired up now. The power supplies, including the shunt regulators, are now all wired and tested. So now I'm working on all the audio connectors. Even with spreading things out a bit, it's still a tight fit so it's taking a bit longer than my first preamp did. But I need to get this done before I can put too much more time into the 300B amps since my workshop is getting a bit overly cluttered.

 

Exceptional! I'm almost speechless.

 

Thank you. My previous (current) preamp was a nice improvement in SQ over the Parasound JC2 I was using, so I wanted to see how much better I could do. I have been working on this since the beginning of the year, but I have a hard time working on only one thing at a time so I've also modified my Purifi monoblocks to use tube input buffers, built a stereo Purifi amp for my bedroom system, and started working on crossovers for my new speakers and this 300B build while trying to finish the preamp. I'm going to spend most of the day today wiring up the preamp so hopefully I'll make some good progress.

 

Three boxes arrived today from ANK. These contained the eight transformers.

My hobby room/workshop is starting to look like a scene from a tv show where the bad guys rip apart a home or apartment looking for the hidden document. I had to set up a temporary table to unpack the boxes.



The transformers were very well packed with lots of protection.



Not my favorite packing material, but it does provide good protection. Very heavy duty cardboard boxes, and all the Styrofoam filled up a large contractor garbage bag. The transformers look great though, and this will allow me to confirm most of the measurements for the top plate. The last thing I need to measure before being confident in the measurements is the copper plate.

 

Oh those are purdy.

 

Now that's a lot of iron!

 

Here is my preliminary design for the top plate. This will be machined from 6mm aluminum and powder coated. I tried to minimize the holes that would be visible from the top.



The underside is a lot more complicated. There are a lot of studs for holding the PC boards, and threaded blind holes for various mounting brackets. All told, there are 136 through holes, blind holes, studs, and machined cavities.



I still have a few measurements to confirm (copper plate dimensions and hole positions, and the mounting holes for the 50W resistor used in the power supply), but I think all the other measurements are accurate and I think I have found a place for everything. I had to make a few adjustments from my previous layout, but it's pretty similar.

 

Most of the remainder of the parts arrived yesterday. There are a few resistors that Brian didn't have in stock, but I have already received a tracking notification from HiFi Collective for these. I haven't done a thorough inventory (mostly because I am not planning to use all the parts anyway), but all the key parts I looked for are present.

One of the copper plates has a slight mark on it, but I think it should polish out ok. It doesn't look like the copper plate has been sealed in any way. One place in the manual says that it is "coated in a high gloss clear coating so that it is protected from scratches and will never change color", but another place says "we also recommend that you buy a spray-on copper protector to seal the copper plate". I suspect they realized that is better to leave the protective coating on it while assembling and they spray a protectant after assembly. This will require masking the tube sockets, but that's not a problem.



I am planning to order the machined enclosure parts for the first monoblock on Monday. This always makes me nervous that I've made a mistake and will have to modify (never looks good) or refabricate an expensive part. Since this enclosure has over 300 precisely measured holes and standoffs, there are a lot of possible mistakes. Fingers crossed.

 

Well, I placed an order with Front Panel Express for all the panels I needed for the first monoblock. But like many businesses, they are suffering from supply chain challenges and informed me that they are out of stock of 6mm and 8mm aluminum. They have a shipment coming in but it is currently stuck at the port.

I have planned to use 6mm for the top plate since it has a lot of holes and holds a lot of weight. So, I can either wait for their stock to arrive, use a 5mm panel instead, or go all the way up to 10mm. I am going to wait until later this week to see if they have any new information, and then make a call. My wife is going out of town for a few days in early Nov and I was hoping to use this opportunity to focus on getting the first amp built.

 

Knowing from experience the Front Panel Express pricing structure I'm sure that's going to be a pretty penny! I'm also sure it'll look fabulous - I am a fan of the powder coat finishing myself.

 

Yeah, the enclosure is definitely going to be pricey, but I haven't found another vendor that does as good a job and also has the tools to make it easy to design the panels. I've used Modushop enclosures for a number of my builds, and they provide nice enclosures for the money but don't offer near the flexibility.

Given the amount of handling that is required for a DIY build, it is very hard to keep anodized aluminium from getting scratched during the assembly process. Powder coating is a lot more durable. I also like the flexibility in selecting colors. For the 300B build, most of the panels are going to use Gray White powder coating, but I'm going to use Ruby Red for the side panels and transformer cover. The Ruby Red is a pretty close match to the red on the output transformer (looks ok next to it, anyway).

As I mentioned in my previous post, Front Panel Express is running out of stock of all their thicker aluminum panels. They have a shipment at the port waiting to clear customs, so I decided to wait until this shipment arrives instead off compromising on panel thicknesses. Hopefully this won't delay things too much.

In the meantime, I'm going to try to finish my presmp build. If all goes well, I may be able to get this done this weekend.

 

OT: Is it you on the bicycle in your avatar pic? And is it Mont Ventoux in the background?

 

Yes, and yes. One of my favorite areas to ride. I love riding in Europe and have ridden up Ventoux about a dozen times, mostly up the Bedoin side. This was taken a couple of years ago.

 

I received the panels I was waiting for from Front Panel Express today. Here's a photo of the complete set of panels to build a single monoblock amp.



I test fit the panels together to make sure everything fit. Here's how the enclosure will look when assembled.



The copper plate is inserted with the bottom side up. The other side has protective film on it so you can't see the copper. When finished, the plate will look a lot nicer with a (hopefully) scratch-free polished finish.

The red box covers the mains transformer, choke, and power supply caps.



The real test will be when I check all the holes and standoffs to make sure the transformers, tubes, PCBs, etc. fit correctly. I hope to make some progress checking these over the weekend. So far, though, I'm pretty happy with the way the enclosure turned out.

 

Oh my goodness!

 

Truly next level. And the one above that.

 

Wow! The tube shaped vents!!

 

Thanks all. My neighbor, who is also a member here, gave me the inspiration for the vents.

 

Nice! I've never been to Europe to ride. A local-ish climb I like is up Hurricane Ridge in Washington State. Start at near sea level in Port Angeles and you'll have almost a mile of elevation gain to the top of the ridge. Almost a mile. Almost. You'll have to ride back down the hill a little bit and back up to get the GPS to register a full mile of climbing. It's a very scenic climb.

 

It is a nice climb. I've done it a couple of times. The descent can be a little dicey when it's windy, but still one of the most challenging climbs in the PNW.

One of my favorite climbs in our area is McKenzie Pass, in early June when the road is still closed to cars. Not as big a climb as Hurricane Ridge, but the high Alpine meadows are gorgeous and the lava fields at the top are pretty cool.

 

One small observation if I may, Audio Note have very little to do with your build, no transformers, no design input for at least 20 years, a few resistors, nothing but distance between the Canadian supplier and AN in the uk and yet somehow by association, the current AN UK logo is engraved on the top cover. The ANK logo just didn’t quite cut it. I’m not sure how to consider this, maybe when I next see a Bugatti Veyron badge on a Volkswagen, I Will better understand why someone did it.

 

I realize that Audio Note UK is no longer directly associated with ANK, but I decided to use this logo for a number of reasons.

I have no intention of profiting from the use of the logo and have text on the backpanel indicating that the design is based on the ANK kit.

This particular kit was developed when Audio Note Kits was still part of Audio Note UK and was designed by AN engineers (although I have admittedly made a lot of changes to the design). ANK's own website shows the AN logo on this kit as you can see in the photo I posted in the first post in this thread.

While the transformers aren't made by AN, almost every other component in the base design is, including many that I have upgraded to their premium version (e.g. 2W silver tantalum resistors),

And I think the AN logo looks cooler than the ANK logo.

Sorry if you are offended by this.