UPDATE Inexpensive Chinese-Made TUBE BUFFER amplifiers. A Review of One using 6J1 Tubes Upgraded to GE JAN 5654W Tubes

 March 18, 2024

#476

UPDATE!

Gentle reader,

It has been a VERY long time since I have written anything about the listening room stereo. I have (after more than forty years) been very happy with the system and thus stopped trying to improve it.

Over the years of which I have been writing this blog, several of my readers have reached out to me via Facebook and we have become Facebook friends. Of them one lives within reasonable driving distance and we have gotten together a couple times. Another lives in the same town my Aunt does in Arizona. So, someday we will actually meet, when we finally go out there for vacation. We talk frequently by phone and both are dear to me.  In the mean time, these two and I have come to call ourselves The Three Amigos. Which is the title of a comedy film starring Chevy Chase, Steve Martin and Martin Short.

One of them, who has a Dynaco Museum in his home, last year came up with the idea of all three of us building a small Chinese-made tube buffer amplifier. 

The one in Arizona had these guitar pick holders custom made for the three made up for all of us and surprised the other two with them. He is a very giving person.

This is what the kit is comprised of and the parts list for it. 

This is the schematic.

This image is from an eBay seller called Yunsirui. What was NOT included with our kits was the clear plastic housing (shown with protective paper covering), switch knob or 12 VAC "wall wart" power transformer.

Sadly, none of us got around to actually building the kits! No excuses. I did provide four 12 VAC transformers and knobs (two for me, more on that later) to all of us. The transformers are for landline telephones. See below.

Note the 4.17 AMP (50VA) specification. Talk about potential GAIN!

The transformers are large and heavy, which makes sense since they have lots of potential power.

I went ahead and bought two prebuilt ones via eBay, just in case I failed at building them. The first time any of you saw the first one was here:

The Robb Collections: UPDATE on Review of SKW Cables "Audiophile" at Bargain Prices? Amazon Exclusive SKW Cables

Never one to leave well enough alone, I bought two "Audiophile Grade" 6J1 tubes which are shown below. I do NOT have golden ears and could not tell any difference between the factory supplied tubes and these.

For many months I have enjoyed this little tube buffer in my "home office" with a vintage all-Yamaha stereo stack and an OPPO universal player. No room to use a turntable with it. The stack sits inches from me. Initially, I had the buffer atop the OPPO. I used QUAKEHOLD reusable adhesive putty to hold it in place since the unit has no feet and the pull of the cables would surely snatch it off the top.

I have had zero problems with the little unit and since I have no idea what "Warmth" means as far as the sound of music, I can only say that it does sound a bit nicer than before. Plus, the gain the transformer provides can really crank out some volume. My neighbors, who put up with my occasionally loud music would draw the line should I decide to see JUST how much louder it could get.

I finally decided to assemble the second eBay-purchased board in the case, etcetera. Prior to doing so, I was looking at other similar (all likely Chinese-made) tube buffers on offer out there.  

To my dismay, the second buffer I already had, produced barely any volume from the right channel! I looked at the board and it's components and it was easy to see that the volume control had been replaced. Since I'd bought it from a Chinese vendor on eBay a while back, I set out to find a replacement from a USA vendor. And did so for just over $13.00 with free shipping.

Being curious, because some vendors offered "upgraded" tubes for additional money, I decided to see what are considered the "best" seven-pin tubes. Here are two sites I looked on to learn more:

electron Tube Data sheets - 6 and 7-Pin Vacuum Tubes 5654W Upgrade – 6AK5 6J1 6J1P EF95 6k4 – Fosi Audio

The latter stated that vintage General Electric JAN 5654W Tubes were the best, but due to demand, are getting harder to find and thus, pricy. I found a pair on Amazon for way less than those being hawked on eBay.

According to the labels, they were made in July, 1987. Which qualifies as vintage by any metric.

The seller wrote:

• Built to the TOUGHEST USA standards for Amplifier.
• JAN 5654W Made by General Electric USA, Higher Durability and Life, Heavy Duty Cycle Military Specification Grade (JAN) , Considered one of the best of the 5654 family of tubes for audio use. Large ring, enhanced mica, green powder word + matte word mark.
• The sound is full, soft, delicate and poisonous, (?) larger soundstage, Treble and bass is more noticeable. Can hear some details that did not hear before while more complex music.
• JAN 5654W Can Perfect Upgrade For Little Dot / Little Bear Amplifier, Directly replace 7-Pin 6J1 / 6Ж1 / 6J1P / 6J1P-EB / 6Zh1P-EV / 6AK5 / 6AK5W and EF95 tubes. It can also replace 6J2/6J3/6J4/6J5 and ordinary 5654. It can used for WE-403A/403B/EF95 Matched Vacuum Tubes replacement.
• Platinum Grade Pair JAN 5654W tubes show you the difference in natural voice reproduction and simple musical. Match it plate current and mutual conductance. Also pass a specialized life test, aging test and audio sound test.5654W tubes are NOS, It's new stock tubes.

In searching though one of my parts drawers, I found some small rubber feet I had saved "just in case" and two of the knobs shown (above) which are splined inside like the On/Off Volume switch is outside. The knobs I had found in the past for these were from Parts Express, and use set screws to secure them.

I tested the new unit on the stereo here beside me and it sounded fine. Next, I got started on the task of pulling the heavy stereo in the listening room away from it's location so that I could get to the back of it.

A 10mm wide-angle-lens shot of the listening room. The system is on a large and heavy glass and steel stand made for a very large HDTV and for many components. I modified it to have casters at each corner.

Since the PAT-6 only has one Tape input, I added a SONY audio/video switch for the TDK CD Recorder unit's output I have in the system. I used the QUAKEHOLD to secure it to the top of the PAT-6.

Here is an overhead view. Note the white power cord snaking away. I only had to unplug the RCA cables from the OUTPUT terminals of the PAT-6 and plug them into the (right pair) RCA outputs of the buffer. I added a good pair of RCA cables to bring the PAT'6's output to the input of the buffer.

Upon turning on the buffer, there was a low-level (and deep) hum. It seemed to me lower than 60 Hertz. "Hmm," I thought, "it didn't do that in the other room. But then, the speakers there only have eight inch woofers. These are twelve inches."

I was referring to the black Cerwin-Vega! LS-12 speakers. Which are the last models made in the United States. The smaller ones are vintage Dynaco A-25XL which have ten inch woofers. I switched to those and the hum was barely audible. Which is why I think it is not AC interference I am hearing.

Playing music, the hum is not audible and it only starts to get louder if the buffer's volume is past 50%. Nonetheless, I set out to eliminate the noise. 

"Okay," I thought, "I'll run a ground wire from the transformer."

Prior to that, I marked one terminal insulator and swapped the two AC terminals. It made no difference. 

The hum was still there! I decided to shield the white power cord. I cut some lengths of good quality aluminum tape and carefully wrapped the cord from the bundle all the way to the right-angle plug in three layers. I then fished the wires through  heat shrink tubing and shrunk it with a propane torch.

The hum seems quieter to me, but that may be wishful thinking. Again, as long as I keep the buffer's volume control below fifty percent, the hum is barely audible and not at all when the music is playing.

UPDATE: My friend in Arizona called and we talked about the issue. He concluded that maybe one of the capacitors is failing in the buffer's circuitry. My next step is to substitute that one back in this room to see if there is a hum, if not, then the one sitting on my PC into the listening room system to see if there is a hum...

In the interim, I have loaded these photos of post-cord-shielding.

I moved the unit away from the SONY switch (and wherever the preamp's transformer sits inside the cabinet) just in case that is causing the hum.

While on the subject, let me find a photo of the inside of the PAT-6 preamp-tuner...

As you can see, the transformer sits smack in the middle of the right side of the unit.

UPDATE TWO: I swapped into the listening room system the unit from the Yamaha stack (below, NOTE: I have since moved the OPPO to the top. I don't know what I was thinking.) and there WAS a hum from this unit, but not nearly as loud. Then, I swapped the transformers and there was no difference.

I first placed each unit on top of the dbx box, which of course, has a transformer inside it. No difference in the hum. Then, I gently placed each on top of the turntable and there was still a faint hum from the office's buffer and the same hum from the listening room unit.

Conclusion: Both the unit and it's transformer are hooked into the Yamaha stack. There is NO hum!* The speakers attached in here are two KLIPSCH KG-4s which have an eight inch woofer and twelve inch passive radiator on the rear. And two of the latest BOSE 301 speakers which also have eight inch woofers. Therefore, neither will go deep enough to reproduce the hum, but will still receive it. *See third update below.

To conclude-conclude, I have purchased yet another buffer board from a different US seller. I will keep you posted.

Third UPDATE March 18, 2024: I received the replacement board (identical to all the other ones I have bought) from a different US seller of these completed boards via eBay. 

It is the one in front. Note, the rubber feet, while the one in the rear is secured with Quake Hold reusable adhesive.

I tried it initially in the Listening room system and the hum was still there! But, only audible on the largest speakers. ARRGH! Here, it is using the power supply with the unshielded cord.

Here, it is powered by the modified shielded cable. I tested them both, since in the Yamaha system it is placed in the Accessory RCA in and out terminals, using my Audio-Technica AIR ATH-AD700 headphones. They are THE best headphones I have ever tried and I have enjoyed them for many years.

They are super comfortable because they rest ON your head rather than clamped to your ears by tension. There are later models now for sale in the USA.

Here is a link to Audio- web page about them: ATH-AD700 | Audio-Technica should you like to get some. Specs on that page note frequency response of 5-30,000Hz.

Prior to bringing the new unit back into this room, I tried a test tone CD played through my  Cerwin-Vega! LS-12 speakers. They have the highest efficiency and lowest reach of the many speakers I own now. Their frequency response is 28-20,000 Hz and efficiency is 98dB, one watt at one meter.

The hum was there as soon as I turned the volume control up from zero. Through my Dynaco A25XL speakers it was barely audible.

I put a test tone CD in starting at 10Hz, nada then 20, zip 30 was audible, but too deep as was 40 and 50. 60Hz, as you are now thinking was identical!

Anyway, regardless of which system these units are installed in, at least in my home, there is an interfering 60 Hertz hum, whether the speakers can reproduce it or not.

I looked on eBay for better (i.e., more expensive) tube buffers but the lowest prices were near $200. On to Amazon I went, I chose two of these: 

【Upgrade】AIYIMA T2 6K4 Tube Preamplifier Bluetooth 5.0 with Treble & Bass Control HiFi Audio Preamp for Home Audio Amplifier System with DC12V Power Adapter

They were offering me a 10% discount. They use 12 volt DC power supplies and have full metal cases which I hope should prevent this hum. They should be here tomorrow, so I'm keeping my fingers crossed that they will work, sound good and be interference free.

Thank you for taking the time to read this article and commenting if you have ideas what might be causing the hum.

Scott Robb

March 18, 2024 Updated

#476