Thread: DIY 300B SET Monoblocks

Since some of you seemed to enjoy my DIY preamp posts, I thought I'd create a post about my latest project. This is my first tube project so I started with a kit, but I made many embellishments to the basic design.

My amps are based on the Interchange monoblock AudioNote Kit This is a parallel 300B design. I made the following changes to the basic kit.

• My own enclosure with much thicker aluminum panels for better vibration control and a nicer look. The top plate is 6mm thick.
• Transformer coupled balanced input, with a second high-pass input using V-Cap ODAM caps, since I'm using separate servo woofer towers for the bottom 2-3 octaves.
• Soft-start with 12V trigger input and front-panel low-voltage power switch.
• Delayed start outputs - the speakers are connected after a 30 second warmup.
• Tent-labs high-impedance filament supplies for the 300B filaments.
• Pete Millet regulated DC supply for the 6SH7 filament.
• Maida regulator for the driver stage (reduces ripple to 20uV).
• Modified 300B power supply hookup which uses an AC voltage divider to improve the power supply rejection ratio by approximately 20db.
• All resistors are Audio Note non-magnetic tantalums, with all the signal path resistors upgraded to the 2W silver version.

I just finished the second amp this weekend, so I haven't connected them up to my primary system yet. I'm letting them burn-in in my workshop for a few days first. They sound great on this modest system with no audible hum or noise from the speakers when the music stops.

Next on the agenda is to get a set of higher quality 300B tubes. I'm deciding between the new Western Electric tubes or the Takatsukis, and currently leaning toward the former.

Nicely done Jay !!

Thanks guys. All in, I'd estimate about $12K for the pair, not including the $3K I'm about to spend on a set of premium 300Bs. A bit over $5K of that was in all the custom machined enclosure panels.

There are plenty of places to skimp and save some money, but I wanted to build the best amps I could. I do DIY because I enjoy the process of designing (often relying on subassemblies designed by more knowledgeable engineers than I) and building my own gear, so I don't really try to be particularly cost effective.

Also, I ended up not using a lot of the stuff that comes with the kit (although I did get a reasonable discount), so I could have saved some money by sourcing the transformers and the handful of other parts I used myself. But since I was using the base circuit design from the kit, I felt ANK deserved to make some profit from it.

The speakers are Revel Performa F30s that I've had for over 20 years. I don't use them very often since I have several other better systems, but they don't sound bad. But at 87db/w efficiency and a slightly difficult load, they don't really allow these amps to sound their best.

My current main system speakers are 92.5db/w and uses a separate servo-controlled woofer tower for the bottom couple of octaves. I'm looking forward to hearing how they sound in this system.

But I really built these for new speakers I am working on which will be 98db/w and cross over to the woofer towers at around 170 Hz.

Spectacular, congratulations! I currently have my ANK Audio EL34 stereo amp in my system, it was my first kit to build. I built the L4 DAC, and progressed to several Nelson Pass DIY amp designs. It’s a fun hobby. I’m working on a last one or two projects, but will eventually go back to a commercial amp for my end game.

You built your end game - well done.

Thanks for the compliments. I'll report back when the amps are well broken in and connected to my main system.

Really nice amp build and details , now whats the story on the Bicycle ..?




Regards

Thanks guys. I'm certainly proud of this build, but it's always nice to get compliments

now whats the story on the Bicycle ..?

I've become an avid cyclist over the past 20 years. I now own and operate an ecommerce cycling accessories business and ride as much as I can. This photo was taken a couple of years ago on a cycling trip to Provence. I'm about 3/4 of the way up Mt. Ventoux in this photo.

I decided to order a set of the Western Electic 300B Reissues. I placed the order last week and received a matched quad set today, even though they indicate up to a 30 day delay before shipping. They must not be as backed up as they purport.

The tubes come in a very nice wooden box and include fairly complete specs and curve traces for each individual tube.



I installed the amps in my main system yesterday (Sunday) with the help of an audiophile friend. These replaced my Pass XA60.8 monoblocks. After listening to a few songs with the Pass amps, we switched to the SET amps and listened to the same songs.



With the relatively inexpensive Linlai 300B tubes installed, the amps sounded quite pleasant, although perhaps a bit strained at higher volume levels, and a touch less detailed compared to the Pass amps. The new amps still don't have that many hours on them - maybe 75 hours for one and 40 for the other.

Still, they played loud enough that I think they will be a great match for my new speakers (GR Research Line Forces being built) which are 98db/w line sources, compared with my current 92.5db point source speakers (GR-Research NX-Oticas).

After installing the WE tubes this morning, it was immediately obvious that these were a significant improvement. Right out of the box, the improvement in midrange clarity and sweetness was really obvious.

I've spent the last several hours listening to female vocals with light jazz, and with this kind of material, they sound fabulous.

Western Electric says these tubes take up to 500 hours to fully break-in. I can't wait to hear how they evolve with more hours on them.

Fantastic looking amps. I bet they sound fantastic!

Thanks guys. I didn't take any precise measurements but did look at the output on an inexpensive scope. Into an 8ohm resistor load, I started to see noticeable waveform asymmetry and clipping around 32v pk-to-pk, so I'd estimate 14-15w. I didn't think to check bandwidth.

At some point, I'll schlep one of the amps back upstairs to my hobby room and make some more measurements. They weigh almost 60 pounds each, and my back doesn't like carrying that much weight around too often.

As it breaks in, it is sounding better and better. I think they are a touch too low in power for my current speakers, particularly when I turn up the volume a bit. But at more moderate levels, they are sounding very nice. I think they'll be an excellent match for my new speakers.