ANK 300B Interstage Monoblocks

The mains transformer had a lot of resin on the leads (a little messy if you ask me), and also had damage to two leads. It looks like the transformer was pressed against the leads when being shipped. But nothing that some shrink wrap can't fix. I cleaned off the resin as best I could without damaging the insulation.



Mounting the transformers was not too difficult, although I had to do a little surgery on the rubber strips that ANK provided for the mains transformer. The holes were punched for a transformer with wider spaced mounting holes. Fortunately, there was enough room to drill extra holes and clip off the excess rubber.



The cutout for the copper plate made it a little easier since I could fish my hand underneath while working on the top side.

Mounting the power supply caps was actually a bit more challenging than the transformers, since I had mounted the clamps first, and it's a pretty tight fit. For the next one, I will mount the caps in the clamps before mounting the clamps.



This is the first enclosure I have made using the threaded stud inserts that Front Panel Express offers. For some reason, I had it in my head that these were standoffs with female threads, since that's what I am used to working with.

But of course that's not the case. These are just male threaded studs. I had sized them based on how far off the plate I wanted the PCBs to mount. Fortunately, I have enough clearance to thread female threaded standoffs on top. This will mean that my PCBs will be 5mm or so further off the top plate, but checking the Tent Labs supplies which have the tallest heat sinks, there is plenty of clearance to the bottom plate.

For the second chassis, I will just spec short studs that I can thread the appropriate standoffs onto.

 

Super cool thread. Can’t wait to hear how it sounds.

 

DIY Hifi goals!!!

 

I've done most of the wiring on the backpanel. I'm waiting on some green hookup wire to use to wire the XLR connector ground connections, so I can keep the color for all chassis ground connections consistent.



I decided to change the input circuit a bit from the rough schematic I posted previously. I am going to use a separate load resistor for the balanced and single ended inputs, and move the select switch to the other side of the load resistors. This allows me to use a 10K load on the balanced input, while keeping the 100K load for the single ended input.

The Jensen transformer is optimized for a 10K load. It will work OK with a higher impedance load, but a load higher than 10K requires a separate Zobel network to eliminate ringing due to the mismatched impedance. Since my preamp has a low 33ohm output impedance and plenty of drive, the 10K load (which results in an approximately 13.5K ohm input impedance) will not be a problem. The lower impedance also reduces susceptibility to noise pickup on the interconnects, although with balanced connections this is not much of a problem.



The high-pass input XLR is connected through a pair of V-Cap ODAM 0.47uF caps. Since these caps are effectively in series, this results in a -3db point of about 50Hz. I use stereo servo-controlled subwoofers to cover the bottom couple of octaves, so this reduces the wasted power from the amplifier and also reduces speaker driver excursion below their natural roll-off point.

The load resistors for both the balanced input (transformer secondary) and unbalanced inputs are Audio Note 2W silver tantalums. I'm using these resistors in all locations in the circuit which have an audio signal. These resistors are ridiculously expensive (roughly 250 times the cost of a good quality Vishay metal film resistor), but since there aren't that many resistors in this amp (six per channel in the audio signal path), I figured I might as well go for it. Based on my limited experience with these, and a number of rave reviews in forums, I decided it was worth splurging on them.

 

There's so many great ideas to steal be inspired by in this thread already. What a resource it will be once it's done.

 

Still looks like a rat's nest, but some progress being made.

 

Well, more like a rat's palace. Looks great!

 

Everything is wired up except for the copper insert plate wiring. The copper plate has the three audio tubes (6SH7 and two 300Bs) and the circuitry surrounding these tubes.

Since I changed the input circuit to use the V-Cap ODAMs, the cap size is smaller than the Miflex caps I had originally been planning to use, so threaded holes for the mounting clamps were two far apart. So I am making do with clamps just on one end. For the second chassis, I will stick with one clamp, but move it so that the clamp is in the center of the cap. I'll probably add a few more threaded blind holes for cable clamps now that I now where all the wires need to go.

 

Finally, a shot of how the front panel attaches! It was driving me crazy!

Looking wonderful by the way.

 

Thanks. All you had to do was ask.

Here's the copper plate with components. The rest of the components and wiring gets added after it's installed in the chassis.

 

The wiring on the first amp is done (barring problems of course). I want to install a bleeder resistor on the power supply before I power it up so that the caps don't hold a lethal charge for a long time. I have to dig through my parts bin to see if I have anything appropriate, but I also ordered some 2W 470K resistors online just in case I can't find anything that will work.

 

I realized the next morning in the shower that I had forgotten to connect the ground lines. Oops...

Here's the final inside shot.



I couldn't test the Tent Labs supplies without a load, so I decided to just plug in the 300B and 6SH7 tubes and see how they worked.



A couple minor tweaks to the regulator trimpots and I got pretty close to the desired voltages. The heatsinks on the Tent Labs supplies got pretty warm, but even with the bottom plate mounted they stayed below 50C, so I'm not too worried.

Since the heaters seemed to be working, the next step was to plug in the rectifier and see what happened.



Voltages checked out ok, I turned on a source, and voila...music. Everything seems to be working perfectly. I've only got a cheap speaker connected, but no hum or hiss can be heard.

So I installed the bottom plate to check temperatures again.



Here's the finished first amp. Now on to number two.

 

Absolutely stunning!!!

 

Again, that interior looks great. Busy but not cluttered,

I'm looking forward to what you make of their sound compared to the quality SS amps in your profile. Having just acquired some tube friendly speakers your build has made the idea very tempting.

 

I'm waiting for the panels from Front Panel Express for the second amp. I'm expecting them to arrive this coming week, so I'm hoping to be able to make some good progress next weekend.

In the meantime, I've got the first amp set up in my workshop connected to a Revel F30 speaker. These aren't terribly efficient at 87db/w, but the amp seems to do pretty well driving them. As I get a few hours on them, the sound is getting a bit smoother and the bass a bit more powerful.



While I'm waiting for the rest of the enclosure panels. I've been able to assemble and wire the backpanel, and the copper plate components. This should reduce the time it will take to complete the second amp, since between these subassemblies, this takes care of about 75% of the soldered connections.





This time around, I removed the protective film from the other side of the copper plate and polished it before inserting the components. This made it a lot easier to get a nice smooth polish since I didn't have to avoid getting polish in the tube sockets and could rinse the polish residue off with water and then buff it which worked out much better.

 

This is an excellent threading..!

 

Thanks.

The rest of the panels for the second amp arrived today from Front Panel Express. They do a great job packing the panels to prevent any shipping damage. Here are a few photos.



A large piece of heavy cardboard is used for one or more panels and a sheet of shrink wrap plastic is used to secure the panels to the cardboard. That little orange corner allows you to peel the plastic off to get the panels. The second image shows the top plate panel which has a large number of standoffs. A sheet of foam is used on top of the standoffs to prevent any damage.

I forgot to mention previously that the first step before assembling the chassis is to grind some of the powder coating off on the screw holes so that the screws can make electrical contact with the panel. The powder coating doesn't extend far down into the threaded blind holes, so the threads make good electrical contact for the panel they are being screwed into.



The top, bottom, and rear panels all have counter-sunk holes for the screws. A short touch of the dremel grinder in these holes clears out enough of the powder coating to allow electrical contact with the screws. Having good electrical contact ensures that all panels will be connected to safety ground and will improve EMI/RFI shielding. Just to make sure, I check the connectivity with a multimeter once the chassis is assembled.

I like to use powder-coated panels for my DIY projects because the finish is more durable and harder to scratch when I'm working on assembly. I also like the selection of colors. I've pretty much settled on the grey-white for the main panels on my projects.

Now, on to getting this second amp built!

 

Finish is definitely very nice.. Keep us posted and great work!

 

I see some of your metal parts, like the side panels, have threaded screw holes drilled into the thin sides of the panel. Can this be accomplished with the FPE software, or do you have to write them a note or something?

 

It is sort of supported. For example, let's say you have a panel that is 100mm x 100mm x 8mm thick called "Panel A". You create a second panel that is 100mm x 8mm x 10mm that you call "Top edge machining for Panel A", and indicate "customer supplied material". The drill holes you specify in this second panel are applied to the edge of the first panel. Here's a link describing the process: Front Panel Designer I usually add notes for both files to make sure it is clear. It's a little pricey to do this, but if you need blind holes on the edges, it works well.

 

I finished assembling the second amp today - well, almost. I am missing one tantalum resistor from the kit (in the voltage divider to set the heater DC offset for the 6SH7 driver tube).. Brian is sending it to me and the tracking says it will arrive on Tuesday. In the meantime, I pulled a resistor from my parts bin so I can test everything.

My wife and I have plans for this evening, so I haven't had a chance to test it yet but will tomorrow. I did inspect everything pretty carefully, so I don't anticipate any problems.

The second amp went a lot faster since I had done one already. Hopefully I didn't rush through the build too fast. We'll know tomorrow.

 

The only experience I have with DHTSE was my UX-45 amp and, going along with conventional wisdom, used AC on the filaments. Careful routing of the wires and using hum pots got hum entirely inaudible with very high efficiency speakers.

Does AC sound better than DC? I don't know but this was one great sounding amp.

 

@B. Scarpia - nice amp. Are you still using it?

I powered on my second amp this morning. All the voltages measured ok, but I wasn't getting any sound. I spent a while checking everything over, and finally decided to start swapping. Lo and behold, when I swapped the 6SH7 from the first amp, the second amp started working fine.

I happened to have purchased some cheap 6SH7 off etsy a month or so ago, so I put one of them in the first amp and it is working ok. I'm not sure how good these tubes are, so I've asked Brian to send me another tube. At some point, I'll check with some of the better know tube resellers to see if I can find a good pair.

I am also reading all the reviews of 300B tubes and will probably order a set of one of the more highly regarded tubes. At this point, I'm leaning toward Takasukis.



For now, I'm burning in the amps in my hobby room. Once I get the tantalum resistor from Brian installed, I'll move the amps down to my main system to see how they sound. I will be interesting to see how they compare to my Pass XA60.8s.

Thanks all for following my build thread and all the comments and likes. I appreciate it.

 

The finished product looks fantastic I hope they sound as good as they look jaytor!

 

Can't take my eyes off those beauties. I'm all about woodworking but that metal work makes for a MoMA worthy design.

After I built my current KT-88 P-P Monoblocks 5 years ago the 45 just sat on it's stand looking forlorn. Good as it was, the poor thing couldn't do Mahler properly with my 97dB speakers so 3 years ago it found a new home.

You might look into the KR Audio 300BXLS. I lived with their VA-340 amp some years ago and it was extended top and bottom. Have to adjust the current draw possibly, though.