Stereomour II mods

[Paul Birkeland]

I'll have to pop by since they aren't all that far away.  I bet they could just whip out bases and finish them in house very easily.

[hmbscott]

Wow! Gorgeous.

[Paul Birkeland]

Wow! Gorgeous.

Yeah, everyone was like "wow, good job building those bases", and I had to break the bad news to them that I have no idea who made them or where they came from.  I sure would like a few more though!

[Mucker]

Nice stuffs fellas! Shunt regulator .... yeah it's cool you are waiting on that because it will give you a good idea just how great the Stereomour II can be. It transformed mine.

[hmbscott]

... Shunt regulator .... yeah it's cool you are waiting ...

Yeah, I'm looking forward to experiencing that!. It's going to be a while. I'm currently breaking in my tubes, and boy did they need it! The first hour of listening was a bit ... it sounded good, but something was definitely a bit off, because I just couldn't settle down to listen through an entire song. It seems like 75% of the break-in happened in that first hour though, and now that I've got maybe 15 hours on it, it is sounding like butter! I'm going to give the stock Psvains a full month or so, and then swap in my RCAs. And then ...

[2wo]

We need a night shot...John

[hmbscott]

It's taken forever, but I have finally finished the Claro Walnut bases for the Stereomour and Moreplay. It was a painstaking process because I am terrible at mitering and this was an amazing piece of wood that I didn't want to F-up (required building a custom jig to do it properly). I wanted to book-match and grain wrap the bases and to try a french polish. It took somewhere between 30 and 40 coats of shellac, but I really wanted to do justice to the spectacular grain.

Over the past few months I have fully burned in both the original Psvane tubes (good) and a pair of matched NOS RCA Black plates (amazing), and damn! The Moreplay & Stereomour can really sing!

Up next, and I'm a bit afraid, because the Stereomour already sounds perfect, the Shunt Regulator upgrade and DC filament supply.

At some point I will talk about the output impedance switching I built in to my Stereomour, it's really interesting. I use it a lot more than I ever expected.

[Karl5150]

Your continued attention to detail has really paid off. Lovely.
Karl

[Thermioniclife]

Great job, love the corner spline's.

[hmbscott]

Night Shot.

[2wo]

"Hot time, summer in the city"

[hmbscott]

I installed the shunt regulator board a couple days ago, and the DC filament board today. The shunt regulator impacted high frequency performance the most obviously, introduced a touch of sparkle and high end clarity. To me, sonically similar to adding a Speedball to a Crack. Sounds even more awesome!

The DC board completely silenced a pretty loud heater hum, which prior to, could be heard from 10 feet away, so very nice!

Like a dunce, I was bending the lead of the very last 0.13 ohm 3W resistor needed to complete the DC filament install, and suddenly the lead snapped off, WTF ?!?! Because, as I discovered, I was "bending" it with my side cutters, doh. F it! Decided to voltage test the amp anyway even though it was missing that one resistor. After staring at the circuit for a couple minutes I realized the added resistors increase the voltage feeding the heater, being paralleled with the existing 0.15 ohm resistors, dropping the resistance to about 0.07 ohms. So, testing without one should be safe.

Turns out in my case my heater voltages are already running a bit hot, the socket with both of the new 0.13's installed was running too high (2.71 VDC), vs almost too high on the socket where I'd only installed one of them (2.62 VDC). I ended up removing all of the new 0.13 ohm resistors to get the correct target 2.5 VDC on both sockets. So accidentally cutting off that lead was the accidentally right thing to do. Hah.

And with that, my stripped-down pimped-out Stereomour II is officially finished. The Stereomour/Moreplay is an absolutely delicious sonic combination, thanks to the awesome crew at Bottlehead for creating them! And thanks to all who have offered encouragement and advice. Much appreciated!

[hmbscott]

I made a couple of upgrades recently: 1) rolled in matched Telefunken ECC81's (Used tested "near" NOS) for the original Sylvania JAN 12AT7WC. I'm becoming a fan of the Telefunken sound! 2) Upgraded my output caps, which were Audyn Cap Plus 3.3uF 800V MKP to V-Cap ODAM 3.3uF 630V. The Telefunken's were put in first and were very nice right off the bat. The caps are more subtle, but don't have a lot of runtime yet. Together the tube and cap upgrades are a nice addition to the amp, most notable is increased dynamics. The amp is also equipped with matched NOS RCA black plate 2A3s, which sound amazing. At this point I don't contemplate making further upgrades.

And, way back, I had promised to discuss my experience with output speaker impedance switching. Initially the amp was connected to 8 ohm speakers. I played around with it a lot at first and noted both louder and more high-frequency emphasis the higher I switched the impedance. Most notable, it sounded more exciting at 16 ohm, but also a bit more fatiguing, suggesting maybe more distortion. It may have reduced the bass at higher impedance settings, but that was hard to detect due to the higher output. 4ohm was a little muted, and at 2 ohm it just sounded lifeless and dull. I think a significant part of that impression might be due to reduced volume at lower impedance settings. I spent a lot of time listening at 16, 8 and 4 ohm, and eventually settled on 8 ohm as the best balanced.

More recently I have switched to 4 ohm speakers and after a relatively brief audition at various settings landed on 4 ohm setting as the best balanced although 8 ohm is not bad sounding either. A side note regarding my speakers, they present a flat impedance load at the nominal value to the amp from 0Hz up to about 5K gently rising to about double nominal at 20kHz.

[hmbscott]

Jon,

Here is my speaker impedance switching circuit, and how I would implement an 8-16 ohm switch. Note these circuits are specific to Stereomour output transformer wiring and might need modification for other output transformers.