Feature – Pioneer SX-535 Rebuild

I purchased this Pioneer SX-535 from a local shop. With the exception of the broken face plate in the tuner window, the unit is in great shape inside and out. All original and in working order. So, I decided that this would be a great unit to rebuild.

Power Supply: I replaced the main filter caps with new Nichicon LKG Gold Audio Grade caps at 6800uF @ 63V. A bit higher than the original 4700uF caps but that’s all I could get and no harm done. I replaced the bleeder resistors with new 5 watt resistors. All electrolytic caps on the power supply board (AWR-065) were replaced with new long-life Nichicons or Panasonics, depending on what was available from Mouser. All diodes and resistors were checked and found in good working order. I did add a small heat sink to the 2SD234, mostly because I had one around and, why not?

Control Board: I replaced all electrolytic caps with new, long-life Nichicons or Panasonics. I also replaced all the old Sanyo caps, which are known to fail miserably, with new Cornell Dubilier, DME Film caps. All pots and switches were cleaned with DeoxIT.

Tuner: All 6 old Sanyo caps were replaced with new Cornell Dubilier, DME Film caps.

Phono Preamp: All electrolytic caps were replaced with long-life Nichicons or Panasonics. I also replaced all 4 original 2SC1312 transistors with better sounding Fairchild KSC1845FTA transistors. Resistors were checked and found to be fine.

Power Amp: All electrolytic caps were replaced with long-life Nichicons or Panasonics. The troublesome original 2SA726 transistors were replaced with new Fairchild KSA992FBU transistors. Resistors were checked and found to be fine. I also replaced the original bias pots with new Bournes 362-line pots and was able to set the bias at exactly 15mV for both channels.

Front Panel: I decided to replace all the original incandescent lights with new LED’s. I used a bridge rectifier and dropping resistor to power the whole display properly. I added 10 blue LEDs to the tuner dial, an orange LED for the tuning indicator, and white LEDs behind both tuner meters. I then replaced the stereo indicator with a red LED and appropriate dropping resistor to set the brightness level properly.

And finally, I gave the whole thing a good cleaning, inside and out. Everything works perfectly and sounds absolutely amazing! This unit should deliver great music for another 40 years.

If you have a receiver like this that you feel is worth keeping, you should consider having Seven HiFi perform a full rebuild on it. Not only will this greatly increase the reliability and lifespan of your unit, but it will also regain it’s original, wonderful sound! Contact us today!

Why I’ll Never Buy A Huawei Phone Again

I used to be an Apple iPhone fan. They were expensive but I felt the phones were great looking, worked flawlessly, and Apple’s iOS seemed smoother and more refined. When standing in the cell phone store, looking at all the top-tier offerings between Android and Apple, I always felt that Apple phones were just slightly better, smoother, and more reliable than their Android counterparts. Same price, slightly better phones. Apple it is then.

Over the years I watched the Android ecosystem get better. The phone manufacturers were making better looking phones and the Android ecosystem seemed to work out their bugs and refine their platform. So, back in late 2016, while standing in the local cell phone store and shopping the top-tier phones, all priced about the same, I felt that Apple had lost their edge above the rest or more accurately, I felt that Android phones gained the ground needed to really compete with Apple’s phones. Looking for a change I decided that an Android phone would be my next purchase. But, which phone?

I am a sucker for efficiency. Smooth, clean, lean and mean. It’s why I use Linux over windows (yes, I don’t even capitalize it). I frustrates me to no end when my computer operating system has to ask me several times if I really want to delete a file. “Are you sure?” Yes. “Are you really sure?” Yes. “OK, we’ll put it in the Trash for you in case you made a mistake.” Damn. Right-click on the Trash and choose “Empty Trash”. “Are you sure?” YES!

Almost every Android phone manufacturer feels compelled to take the stock Android operating system and “customize” it to their liking. The result ends up much like windows. They add extra applications that replicate the stock Android apps that work fine on their own. Why? They add their own fat UI code over the top of Android’s stock UI thinking that it’s easier or better looking or more appealing in some way. They add extra applications they think their users will like and add them to the core operating system image so they cannot be deleted, only “hidden”. All this extra bloat simply slows down the system, wastes precious storage space, and gets in my way of doing the things I want my phone to do. So, Samsung, LG, HTC, Motorola, Sony, and the like are all off the table for me. I wanted a stock Android experience and in December of 2016, that meant Huawei’s Nexus 6p.

The Huawei Nexus 6p was Google’s flagship phone released in September 2015. It was a large phone (phablet) and sported a great camera, wonderful display, plenty of storage space (up to 128GB) and decent battery life. It has an 8-core (4 high performance cores, 4 lower performance cores) CPU and came with stock Android version 6 “Marshmellow”. In December of 2016, the Nexus 6p was discontinued in favor of Google’s new Pixel phones which meant I could pick up a Nexus 6p for a decent price! I found a new 128GB unit on NewEgg.com for $500.00 and took delivery of it on December 20th. 2016. Merry Christmas to me!

I loved this phone. It was bright and powerful, with a big display (good for my eyes), plenty of storage, good battery life, and felt solid in my hand. I had a few complaints though. The audio output was not loud enough to properly drive my high-end headphones. A headphone amplifier like the Objective 2 Headphone Amplifier fixed that for me. The new USB C charge port meant I had to replace several phone charge cords I already owned, a fun game phone manufacturers like Apple like to play every once in a while. But, overall I loved the phone.

On December 27th, 2017, at about 1:30 pm, my beloved Nexus 6p shut down on it’s own and rebooted back up. I noticed only because of the flash of the white “Google” display on boot. Once it got to the point it should have shown the log in screen, it rebooted again, on it’s own. This kept up, endlessly and I never got to the log in screen. A quick search on the internet told me everything I needed to know – my Nexus 6p had developed a hardware failure known as a “Bootloop”. This means that the phone continually reboots itself until the battery has depleted. You never get to the point where you can log in and use the phone. It just simply reboots endlessly. Now, I have a phone I cannot use. A very expensive paperweight.

So, why is this? What happened? Well apparently, this is a hardware failure in the phone’s main Snapdragon 810 CPU! An XDA Developer / Member named “XCnathan32” found the failure and developed a workaround that will allow the phone to actually boot and run! There is a trade-off though. The fix is to disable the 4 high performance cores in the CPU and run the phone strictly off the 4 lower performance cores. Still, it’s better than a paperweight (bricked) phone. It’s not a fix that most people would be able to do though. You really have to be a computer geek with a good understanding of the internal workings of operating systems, phones, Android developer tools, custom ROM images, and the like. You also have to be lucky enough to have your bootlooped Nexus 6p phone unlocked before the bootloop started or else you will not be able to flash these custom ROM images to the phone in the first place. There is a way to get the phone to boot long enough to unlock the phone so you can flash a custom ROM image on it. The trick is to heat the phone up hot enough that the CPU will automatically shut down the high performance cores due to overheating and actually boot. What a mess! I would guess this stuff is above and beyond what most people would be able to accomplish on their own. Still, if you have a Nexus 6p and it is in a bootlooped state and you feel like you want to tackle the issue head on, check out this forum thread to try and get your phone back up and running somewhat.

So now what? Well, some people have reported that they were successful in getting a replacement or a fix under warranty. Some have reported that Google replaced their phones with new Pixel phones. I purchased mine from New Egg. It came with a 1-year warranty and I’m 7 days over that warranty. Nothing for me. There are several people out there with useless, bootlooped Nexus 6p phones and cannot get it fixed or replaced because they are out of warranty. Still, to have a very expensive phone only last just over a year is simply unacceptable. Google seems to have washed their hands of the issue stating that this is a hardware issue, not an Android issue, and I agree with that. In my opinion it is Huawei that should be replacing these phones as they are the manufacturer. As well, what does this say about Qualcomm Snapdragon CPUs? Why are they not responsible for this?

Since Huawei, Google, and Qualcomm have not taken responsibility for this obvious hardware failure like they should, a class-action lawsuit has been filed on our behalf. You can check this out and add you name to the list if you like. I have!

Link: https://chimicles.com/google-nexus-6p-battery-early-shutoff-bootlooping-class-action-investigation/

Link: https://www.xda-developers.com/google-huawei-nexus-6p-class-action/

Link: https://9to5google.com/2018/03/08/google-huawei-nexus-6p-bootloop-issue-class-action-lawsuit/


Light Up Your U-Turn Orbit!

If you are shopping for a new turntable, the U-Turn Orbit is a very popular choice. It’s well built, American made, sounds great, and has several upgrade options you can choose at purchase time, or as an after-purchase upgrade path.

One of the coolest options U-Turn offers is a full acrylic platter over the standard MDF platter. The acrylic platter is much heavier. It smooths out the rotation of the platter for better speed consistency. It’s also more dense which helps tighten up the bass and deliver more detail out of your records. It also offer some really cool lighting effects!

It’s a simple modification / addition to your U-Turn Orbit that really accents the turntable, and your listening room!

There are several colors available and we can even install multiple colors!

Contact Us to get your U-Turn Orbit colorized!


6DJ8 Vacuum Tube Headphone Amplifier

The Circuit:

I’ve spent a long time studying vacuum tube circuits, specifically audio amplifiers. Vacuum tube amplifiers are generally speaking, pretty simple in nature. Over the years, manufacturers have tried designing very sophisticated preamps, tightly regulated power supplies, various tone equalizer circuits, and fine-tuned the power amplifier sections with various degrees of success. Most of these design changes do a good job of actually improving vacuum tube amplification in some way. However, most of the improvement is in the pursuit of better numbers, including the price, but not necessarily the sound in your ears! That’s why I decided to build the 6DJ8 Headphone Amplifier. It’s a single tube amplifying the signal without anything else in the way. I would describe the 6DJ8 Headphone Amplifier design as elegant. It is clean, simple and smart.  If it’s tube sound you want, this is it!

This amp was inspired by Bruce Heran’s, Do-It-Yourself, 6DJ8 Headphone Amplifier Project. There were several things I liked about this amp. It’s single-stage design did not use any coupling capacitors that can “color” the sound of the amp. No negative feedback is used. It uses current production E88CC (6DJ8) tubes, and there are plenty of new-old-stock (NOS) 6DJ8 tube options available on the market as well. I liked the emphasis on the power supply design to provide clean, stable and quiet power to the power amp sections. I liked the idea of using filtered DC on the heater circuit instead of hum-inducing AC. The only thing I didn’t like about his version was his use of solid-state diodes (or a bridge rectifier) on the B+ supply. I was concerned about the noise from the diodes, even “low-noise” diodes, tainting this clean power supply. I also thought about cathode stripping as the B+ hits the cold tubes right after power-on, and this can strip the cathode coating, shortening the life of the tube.

Then I came across Matt, at CascadeTubes.com who built one of these amps. He used a current production, EZ81 (6CA4) tube rectifier for the B+ supply instead of diodes. The rest of the circuit was the same.

For my version, I tried to combined the best of both worlds. I borrowed Matt’s EZ81, tube rectified B+ design with Bruce’s solid-state DC heater supply.

For the heater circuit, the bridge rectifier and two 4700µF capacitors on the DC heater supply provide clean, filtered 6.2V DC to the heaters of the tubes. 6.2V is just within the 6.3V specification for 6 volt tubes and is perfect for getting them warmed up quickly and safely. For the B+ supply, the slower warm-up time for the EZ81 tube rectifier to start conducting means no cathode-stripping DC will hit your expensive output tubes before they warmed up and ready to handle it. All of this means this amp will provide optimum conditions for your expensive 6DJ8 (E88CC) tubes to operate in, both extending the life of the tubes and increasing the performance of the amp.

A note about the bridge rectifier: The original schematic called for a 2 amp bridge rectifier, which would be fine for powering only two tubes. Adding the tube rectifier added another 1000mA of current consumption to the heater circuit with a total current drain of ~1.8 amps! I don’t care for running parts at their maximum so I used a 10 amp part in my build. My bridge rectifier requires a heat sink at 3 amps or better. Even though I’m only pulling just shy of 2 amps, my sample still runs quite hot! I put a decent little heat sink on it to help keep it cool. I chose to omit the heater supply voltage regulator found in Bruce’s original plans. While it’s not a bad idea, I didn’t feel the need to regulate the heater supply.


I designed the whole amp, chassis, wood base, and schematic using LibreOffice Draw. I then ran my designs through one of the best engineers I know: my dad! He was able to double-check and troubleshoot the design with me, and then re-create the drawings in AutoCAD for manufacture.

The chassis is 1/16″ brushed stainless steel. It’s pretty to look at, as well as rigid enough to handle the weight of all the transformers. The stainless steel chassis will also last forever and never rust, and it shines up quite well.


To go with a good design, you need good parts. This amp is so clean and simple, the few parts it has are really going to count!

The original plans called for Edcor power and output transformers. I’m already a fan of Edcor so no argument there! Unfortunately, I couldn’t find a suitable Edcor choke so I’m using a Triad choke instead. All power supply filter caps are Sprague Atom (blue) capacitors with the exception of the heater supply filter caps. Those are 16V Nichicon Black capacitors. All power resistors are wire-wound and rated 10 watts. I also sprung for the excellent quality Alps Blue Velvet volume control.

A few notes about parts: I feel I should have used 1% tolerance resistors in the whole amp even though they are more expensive. I have found that even a few volts difference in plate voltages between output tubes *can* make a difference in the output volume in that channel and lead to an unbalanced stereo image. Most tube vendors offer tube balancing for free or a small extra charge. If you are ordering new production tubes, be sure to get them balanced. If you are ordering new-old-stock (NOS) tubes, have the seller check and balance the pair as close as possible. This will help keep the stereo image balanced properly.


I read through the forums of the original project and learned that transformer placement, especially the power transformer, was crucial to keeping noise and AC hum out of the amplifier circuit and ultimately out of your headphones! The trade-off is the overall size of the amp. It was suggested that a minimum of 7″ should be kept between the power transformer and the output transformers to keep things quiet. I choose to put the power transformer as far back as possible and centered in the chassis, while the output transformers are pinned as far front and towards the edges of the chassis as possible, giving me roughly 7″ of space between power and output. Also, the output transformers are rotated 90° to the power transformer to isolate them even more. All the noisy, high voltage AC is in the rear-center of the layout including the IEC power connector, fuse, and power switch. It’s all much quieter DC and filtering going forward from there.

Results – The Good:

  • While it’s not going to earn any fancy art design awards, I think it looks pretty decent! All screws are stainless steel to match the brushed stainless steel chassis.
  • The custom wood base really shines and can be made with any hardwood and stained to any color. It could even painted!
  • The impedance switch to select between the 32Ω and 150Ω output transformer taps helps find the best match to your headphones.
  • It uses current production tubes so there are plenty of new stock out there at cheap to reasonable prices.
  • There are plenty of NOS (New Old Stock) tube options available on the market at various prices.
  • This amplifier does not use any coupling capacitors in the signal chain to color the sound of the amp. This means that your tube choice is all that matters in the overall sound character, allowing anyone to fine-tune the amp to their specific taste and headphone choice!
  • It’s a solid performer and will run until you shut it off.
  • The amp sounds absolutely amazing no matter what tubes I use! The background is completely black with only a small amount of hiss with the volume wide open and no input signal.

Results – The Not So Good:

  • The Edcor power transformer hums in the chassis a bit, as most Edcor transformers do. With headphones on, you don’t hear it at all so it’s not a real big issue.
  • There’s no balance control so you must get matched output tubes or you *might* notice one channel is louder than the other. As well, make sure that you get the same voltages on all the output tube plates!
  • On my build, there is no physical protection for the tubes sitting in their sockets on the top of the amp deck. I personally like it this way and think it adds a nice visual to the amp. But, these tubes get very hot and can burn anyone who doesn’t know better and tries to touch one. This is not for toddlers!
  • The amp uses only a single gain stage and therefore, only offers a *decent* amount of gain. This amp will get plenty loud enough to drive most headphones out there. However, there are some sources that just don’t offer enough output voltage out of the headphone jack to sufficiently drive the amp and can leave you wanting more gain. Keep this in mind. I have a 7″ Android tablet that simply cannot drive this amp well enough. To be clear, my Android tablet doesn’t get very loud using it’s own speakers. The rest of the sources I’ve tried like the Nexus 6p, the iPhone 4S, 5S, & 6, the Google Pixel 2, and a Sony CD player are absolutely fine.

Special thanks to Mike Amos for hand-crafting this beautiful wood base for the amp!