Review of AIYIMA T2 6K4 Tube Preamplifier Can this Solid Little Asian Beauty Sing?

 March 20, 2024

#477

Gentle reader,

This video takes over from the previous one here: The Robb Collections: UPDATE Inexpensive Chinese-Made TUBE BUFFER amplifiers. A Review of One using 6J1 Tubes Upgraded to GE JAN 5654W Tubes

The Chinese people have invented many things and were far ahead of much of the Earth's peoples in many ways for many centuries. Today, they are known as the world's factory and have an infrastructure that is the world's envy.

Sure, there are a lot of cheap items that come out of China and land in dollar stores all around the US. But, they are an industrious people and have created items that are designed to attract the West's collective eyes.

My interest in Tube electronics was mainly in the 1970's, starting with Dad's old Hallicrafters multi-band radio. It predated FM, so all I could bring in was AM radio. Later, my little brother found a Bogen Tube integrated amplifier.

I have found a tube radio or two over the years in thrift stores. None of them, including this find from a year or two ago, did anything more than hum or hiss. 

That all changed when one of my readers, who became a real friend, came up with the idea of us three (including another reader / friend) should all build a DIY tube buffer kit. He provided the kits and PCB soldering kit. I found the needed 12 volt AC transformers and knobs. 

This is an image from an eBay seller's auction page. He supplied the transformer and case (which is clear plastic, that one still has the protective paper on it) and knob.

Well, none of us got around to actually building one. I bought a couple completed ones via eBay. The link below is to an article I wrote about finding a major flaw in the ten-dollars-or-so kits. At least when using the massive AC transformers I found: 60 Hertz hum. The Robb Collections: UPDATE Inexpensive Chinese-Made TUBE BUFFER amplifiers. A Review of One using 6J1 Tubes Upgraded to GE JAN 5654W Tubes

Which leads me to this article in which I gave up on cheap Chinese tube buffer kits and bought a pair of REAL tube preamplifiers with solid engineering behind them and real electronics and DC (not AC!) transformers.

This is an image of the inside of the T2 Pro. The standard T2 can also be had in silver. I was looking for a photograph of the inside of the unit. This the closest I could find. A whole lot more "guts" than the ten dollar plastic cased tube buffer. But, these do offer tone controls and Bluetooth input and it's associated electronics.

Some of the images above are from the Amazon page, others were found by doing an image search for the unit. from which one can purchase the AIYIMA T2 6K4 Tube Preamplifier for (at least in my case) less than sixty bucks US. I ordered them on Monday and Tuesday morning, early, the box was on my front porch. Inside were these two boxes.

While "un-boxing" is usually reserved for YouTube videos, I am old school and prefer still images.

While there is an "op-amp" inside, I don't think any digital effects are happening inside. But, I could be wrong. No transmitting either, only receiving. Bluetooth, that is.

Another thing the Chinese are really good at is packing their wares really well.

I'm not sure what I am supposed to do with the stickers.

6K4 tubes are taller than the 6J1 tubes I have been fiddling with previously. Are they "better"? I don't know. Let me know in the comments area below.

The metal case is very well made and the whole unit is heavy for it's size.

Volume control is nicely detented and all knobs are solid metal. All the controls seem to be of good quality. 

I was hoping to get the case off to see what the internals look like. Sadly, more than just the two side screws hold it on. I did not want to break something, so the "guts" will have to remain a mystery.

There could be screws hidden beneath the rubber feet which seem to be made of Sorbothane.

Comparing the two units is like comparing "cheap Chinese crap" and well made precision equipment. 

The fact that the DIY kits and preassembled 6J1 tube buffers are being sold for less than fifteen bucks (ten when I bought the first built pair) after being manufactured, shipped from China, bought from the warehouse should be a clear indicator that they are cheap Chinese crap and not to be trusted. 

I have two stereo systems, plus a nice home theater system, in the house. The listening room uses 1990's Panor-era Dynaco equipment and the stack of vintage Yamaha 500U equipment with an OPPO universal player taking the place of a finicky Yamaha 500U CD player. 

Right now, I am listening to a SACD of Herbert von Karajan conducting the Berlin Philharmonic performing Beethoven's 9th symphony way back in 1963 on the DG label through the AIYIMA T2 6K4 and my outstanding Audio-Technica AIR ATH-AD700 headphones. And, let me tell you, it sound's FANTASTIC!

Here are some more images of this amazing little gem in the listening room system. In order of my trying one of them out first, then moving it down to it's final destination, sitting atop the Dynaco PAT-6 preamp/tuner where it is safe from being bumped.

The system above is the culmination of almost fifty years buying and trying literally hundreds of components and speakers. This AIYIMA T2 is the first change I have made to it in many years. 

NOTE: The unit I added to the Yamaha stack (next to my PC) seemed to have failed the next day! The left channel was weak, then gone altogether. I tried swapping tubes (again) and found it was still limited to the left Channel. Removing the unit and using double-female RCA connectors resulted in both channels working.  Similar to below, but mine are Monster Cable units.

Amazon quickly sent a replacement T2 preamp, and took the back one back with free shipping. The new one did the same thing! I thought, "Wait a minute, what if I unplug the transformer rather than using the unit's on/off/input selector switch? Let's see if that helps." THAT did the trick! 

So, in both systems (both rooms) I remove the transformer from the AC source and plug it back in each time I turn on the system. Both channels come on every time. Yay!

Below are some information I have gleaned from the Amazon page as well as AIYIMA's own web site:

"AIYIMA T2 6K4 Tube Preamplifier Bluetooth 5.0 with Treble, Midrange & Bass Controls, Hi-fi Audio Preamp for Home Audio Amplifier System with DC12V Power Adapter.

Item Dimensions LxWxH         4.69 x 3.74 x 1.22 inches

Voltage                 12 Volts

Manufacturer                 YIMA TECH

Mounting Type         Surface Mount

Brand                 AIYIMA

This Bluetooth 5.0 equipped Vacuum Tube Preamplifier has Bass/Medium/Treble controls, has really sound good quality. (sic)

It lets you enjoy sweet and warm sound quality associated with Tube equipment.

1 pair Stereo RCA inputs and Bluetooth Audio input (includes antenna) with manual switch mode. 

2 pairs Stereo RCA outputs can connect to two amplifier devices.

Equipped with DC12V/1A power supply. 

Can be upgraded using the 6K4 tubes design for easy replacement. Designed so the tubes can be replaced to 6J1, 6J2, GE5654, 6J3, 6J4, 6J5, 6*1N, 6AK5, etc.

Build quality is very solid, the unit is surprisingly heavy.

The power circuit is completely separate from the audio circuit, minimizing interference for a clear sound. 

This AIYIMA T2 is a preamplifier use for Audio Component Power Amplifiers.

And/or it can be connected to a pair of powered speakers and a rear amplifier.

Equipped with warm sounding 6K4 Vacuum tubes. These tubes can be replaced with: 6J1, 6J2, GE5654, 6J3, 6J4, 6J5, 6*1N, 6AK5, etc.

Because the design has current passing through the tubes, the tube must be fully inserted during use!

Both Bluetooth and RCA audio input modes are selectable.

Use Bluetooth 5.0 Version, it can offer high bit-rate transfer and supports AAC, SBC, APTX, APTX-LL, APTX-HD. 

And the RCA input (red/white) is compatible with most audio devices, such as computers, tablets, laptops, phones, TV, CD player, etc.

Dual Channel RCA output.

This upgraded T2 tube preamplifier can use for most home audio amplifier (such as A07), or connect your active speakers directly. It provides you with clean and warm sound!

Dual Channel simultaneous output. This T2 tube Preamp is special, as it can directly output connected to 2 Amplifier devices.

Nice buttons design and knobs layout with: Treble, Medium, and Bass Control, it can achieve different sound style. This upgrade T2 is a perfect Tube preamp for your home Audio system. Use it to achieve purer music experience.

Use the NE5532 Dual Op Amp Chip. The op amp chip can be replaced to double op amp chip, such as OPA2604, OPA2314, LM4562, JRC5532, etc.

Note: If there is no soldering technology, it is not recommended to replace the op amp chip. Poor soldering will cause noise, which will damage the sound quality!

With DC 12V Power Adapter. This T2 Tube Preamplifier can not be used in cars, turntables, also it cannot be used directly for headphones or passive speakers. Please know it.

Note: To ensure sound quality, please use a good audio cable. 

Thanks!

Specifications:

Tube Model                 6K4(Can upgrade Replaceable)

Chipset                 6K4+QCC3034+NE5532

Bluetooth Version 5.0supports AAC, SBC, APTX, APTX-LL, APTX-HD

Operational amplifier chip         NE5532*2

Distortion         =0.15%

Frequency response range         20hz-20khz (±1db)

Signal-to-noise ratio         =100db

Volume adjustment range         ±6db

Audio Input mode         Bluetooth or RCA

Audio Output mode         RCA

Input voltage                 DC12V

Product information:

Item Dimensions LxWxH         4.69 x 3.74 x 1.22 inches

Voltage         12 Volts

Manufacturer                 YIMA TECH

Mounting Type        Surface Mount

Brand       AIYIMA

Number of Channels         2

Product Dimensions         4.69 x 3.74 x 1.22 inches

Item Weight         1.15 pounds

ASIN         B0BCKCDQR7

Item model number         AIYIMA T2

Date First Available         August 30, 2022

Country of Origin         China"

It does come with a warranty, which is good. I downloaded the manual, such as it is. At this point, both are working perfectly. Whether they in fact adds "sweet and warm sound quality associated with Tube equipment", I don't know. It does NOT add anything negative, that is for sure!

Thank you for taking the time to read this rather long article. I tried to get all of the specifications columns aligned vertically with the Tab key, but, every time I rechecked in Preview mode, they were still misaligned. OCD sucks sometimes. I mainly use mine for good, not evil.

Feel free to comment below or on Facebook.

Scott Robb

March 20, 2024

#477