FedEx was on schedule and delivered the Elekit TU-8200R stereo integrated amplifier kit I ordered from Tube Depot. Elekit is a Japanese company that’s been in business for about 40 years. They are well-known in Japan for the science project kits they sell to high schools. High schoolers in Japan build projects like robotics and other electronic devices with the Elekit supplied parts and manuals. They are also well-regarded for their audio gear.

Mr. Yoshitsugu Fujita is the Chief Engineer and designer for Elekit. His audio circuits are brilliant. Unlike most boutique stereo amplifiers, which rely on circuit designs originally developed in the 1950s and 1960s, Fujita-san designs outside of the box everyone else is stuck in. His audio gear is vacuum tube driven, but he has no qualms about using solid state devices in the power supply stage. If a DB107 solid state bridge rectifier creates a cleaner power supply, that’s what he uses. He also incorporates transistors in circuit protection schemes, but the signal path is all analog tube driven.

I got to work right away after the delivery came at 1pm. Everything was well packaged and sorted into plastic bags.

One of the key elements of this kit is the R-core power transformer on the left in the photo above. The two output transformers – also very key components – are in the left center of the photo. Once I inventoried all of the parts to ensure nothing was missing, it was time to populate the main board. Over the next five hours or so, I soldered over 200 points on the main circuit board. There are seven boards total to make up the amplifier. These are high-quality printed circuit boards (PCB) with thick fiberglass plates and copper traces on both sides that are well proportioned and 70um thick. The through holes are copper plated.

I finished the main board around 7pm and knocked off for the day – I was getting tired and I didn’t want to make an error in the build. Building a stereo amplfier is like building two amps at once. Each channel (left and right) has it’s own, separate signal path. Only the main power supply is shared in this amp.

Saturday morning after breakfast and coffee, I got back to work around 9am. Assembling the rest of the boards was straight forward. I had to knock off at 1pm to have lunch before going to Donna’s concert. The Viewpoint Concert Band had their first performance of the season. They have fewer musicians than in years past due to covid and other reasons – they’re down by about 30 performers. They sounded great though and put on a good show.

Before I started building this amp, I went Michael’s craft store and bought a pack of craft sticks. These look like a popsicle stick but they’re larger – about 3/4″ wide. I glued two of them stacked together to make it 1/8″ thick, then I cut down the width on one end to make it 3/8″ wide. This was my jig for bending the leads on resistors and setting them precisely 1/8″ clear of the board. I did this because resistors get hot and keeping them up from the board would allow air to circulate around them. I wanted a uniform height for aesthetic reasons. This would be an issue later.

There were a couple of places where PCBs are joined perpendicular to each other and tricky soldering was required. The PCBs had copper pads on each board that aligned with each other but didn’t make contact. I had to solder a triangular fillit that joined the copper pads. This was tricky because both pads needed be simultaneously heated to allow the solder to flow and adhere properly.

After the concert, I got started on the hardware mounting and had everything put together a couple of hours later. Total time spent on the project was around 12 hours at this point – eight hours or so with a solder iron in my hand.

I put tubes in the sockets and it was time to fire it up. I plugged in through my my bulb limiter connected to the APC Line R voltage regulator. It was a disaster. I had a loud hum. I switched it off and looked everything over. I tried switching tubes but the loud hum persisted. I tried a few tests and found the noise was unrelated to the volume control – no matter where the volume control was set, the hum level was the same. I also found that touching the volume control or the input jacks changed the hum – it was lower volume when I touched them.

This made me believe the hum was from a ground loop. I put a jumper from one input jack to a ground point on the chassis and it killed the hum. I hooked up the CD player for a test – no sound output. Bummer. Up to this point, I thought this was the easiest amp I’d ever built. The kit was high-quality and everything fit well. The instructions were good. Somewhere along the line, I must have been a little over-confident and made a mistake.

I pulled the boards out and reflowed the component solder points. I couldn’t see anything wrong. I put it back together and had the same result. I was getting frustrated and tired. It was past 7pm by then and Donna had dinner waiting. I decided to give it a break and think about it for a while.

I thought about it while sipping a Scotch on the rocks and finally gave up for the night. I woke up at 4:30am Sunday morning and thought about it some more. I couldn’t get back to sleep, so I got up as quietly as I could and went back to the amp at 5am. I reconfirmed all of the component locations and values. I can’t tell you how many times I took things apart and checked them – I wasn’t getting anywhere.

I had to take a break at 9am to meet Mike Hall at our coach – he was going to look at the damaged body panel that I temporarily repaired while we were traveling through Utah last summer. He came up with a plan for a permanent fix.

Then Donna and I drove to Scottsdale to meet Alana and Kevin at Merci French Cafe and Patisserie for brunch. Kevin and Alana had left the Painted Mountain Golf Resort in Mesa on Saturday and went to Alana’s mother’s place in Wickenburg – over an hour away. They made the trip back to Scottsdale to spend a little more time with us before flying back to Washington on Tuesday. We had an excellent brunch on the patio at Merci – eating out again for the fifth time in eight days. I was a little distracted, thinking about the amp problem.

When we got back home, I finally wised up and quit looking for a visual clue. Instead I measured voltages throughout the circuit. The schematic identifies 29 points to take voltage readings. All looked perfect until got to number 29. The reading was impossible. I should have had around 6 volts for the heater filaments, but I found -30 volts. What? How could I have negative voltage there?

Looking at the schematic led me to the solid state bridge rectifier. It was installed properly, so I scratched my head again. I was using a headset that resembles the one used by dentists to magnify things in front of their eyes. The one I bought had five different lenses with magnifying powers of 1x – for eye protection only, 1.5x, 2x, 2.5x and 3x. I used the 2x lens because it allows greater depth of field than the stronger magnification – above 2x, you have view from a precise distance or things get out of focus. It also has an LED lamp to make me look like a cyclops while lighting up the working area.

With this headset on, I was searching the board around the DB107 rectifier chip when I saw something reflect a tiny bit of light. There was a fine line of solder – no thicker than a strand of spider web – across two terminals of the rectifier chip. Bingo – this was enough to short the rectifier. I used a braided copper solder wick to clean it up the solder joint. That should take care of the lack of sound and the voltage issue, but it didn’t explain the hum or ground issue.

I traced the ground circuits and resoldered the triangular fillits where the grounds went from one PCB to another. Then I put it all togther without the top plate on the chassis. I plugged everything in and it was silent – no hum. I turned the CD player on and I had sound. Hooray, I fixed it. All along, Donna kept reassuring me by saying, “You’ll find the problem, I have no doubt.”

I took the amp back to the bench and put the top and front cover plates on. I plugged everything back in and put on some music. Oh, no! Now I had nothing coming from the left channel. I took it apart again and traced back from the left channel input jack. Fujita-san cleverly marked all of the left channel components with odd numbers and all of the right channel components with even numbers. So I went to the resistor R1 to start checking and I found it bent with the lead touching the lead of R3 mounted perpendicular to it. This shorted the signal path to ground. Remember how I set the resistors all 1/8″ high? When I put the chassis back together after I fixed the original problems I must have accidently pushed R1 over onto R3. Problem solved.

This stereo sounds fantastic. It’s unbelievably good. Donna doesn’t exactly share my passion for chasing tone and good sound. When I say something like, “Listen to that bass and how clear the highs sound,” she usually says she just wants to enjoy the music, not dissect the sound. But when she heard this amp for the first time, right away she said, “That really sounds good!” The amp looks good to me in a simple, somewhat industrial way.

Tube amps do sound good. I know, I’m a retrograde analog man in a digital world. But vacuum tubes naturally create an emphasis of second order harmonics – that is, they accentuate the octave above the fundamental frequency. Acoustic instruments naturally do the same thing. It’s a euphonic response and people find the tone pleasing. Solid state amplification creates higher odd order harmonics – the 3rd, 5th, 7th, etc, of the fundamental which most humans perceive as harsh or even unpleasant. Solid state designs require complex circuitry to try to work around this.

In my last post, I mentioned my concerns about the future availability of CD players. I decided to buy the Cambridge Audio AXC35 player after thinking about it for a day. I went online to Crutchfield and found out they had sold out since I last saw it the day before! Luckily, I found it on Amazon for the same price and placed the order. I went with the Cambridge Audio unit which is made by a company based in London, England because of the Wolfson Digital to Analog Convertor (DAC) in it. The Wolfson DAC is made by a company in Ireland and is a very good DAC. The DAC is a key component of a CD player.

Information stored on a compact disc can’t be amplified directly into music. The information is a series of microscopic pits in the disc separated by lands. These become a series of zeros and ones. The DAC takes this information and converts it to a waveform that represents the frequencies of sound. This waveform can now be amplified and sent to a speaker. Magic!

The Cambridge Audio CD player arrived on Monday. Now my stereo system is complete – new CD player, new amplifier and new speakers. It sounds so good, I can’t put it into words.

Enough stereo talk – let’s get to the food. Thursday night, Donna made garlic butter chicken with riced cauliflower, mushrooms and asparagus. She seared the chicken thighs on the stove top, then baked them in the oven

Donna is back on the Bright Line Eating plan, which means I’m sort of on the plan. But I get to cheat some. Monday she grilled wild caught Alaskan salmon and served it with Brussels sprouts in bacon horseradish sauce.

Last night ,she made lemony shrimp and bean stew – this was a new dish for us and really tasty.

Alana and Kevin picked a great week for their visit. The temperature was around 80 degrees everyday. Early this morning, that changed as rain moved in and we’ll be lucky to see 60 degrees today. The forecast looks good though, as we should be in the 70s by Friday.

*Just so you know, if you use this link to shop on Amazon and decide to purchase anything, you pay the same price as usual and I’ll earn a few pennies for the referral. It’ll go into the beer fund. Thanks!