Here we go for tube amplifier again!
I have this Elekit TU-8900 amplifier for a short time before I sold it. I was enjoying the music with this amplifier for quite a while, and I can say this amplifier is powerful enough to drive my 86 dB sensitivity speakers with lots of dynamic and bass slam.
This Elekit TU-8900 is popular because it is the cheapest 300B or 2A3 amplifier that still made in Japan. This amplifier was coming as a kit, meaning you should install it by your own with the included manual and all parts scattered. Since I bought it second hand, it is assembled from the previous owner already.
In this post, I don't think I would add the same review again because you can find many good reviews about this amplifier everywhere. What I will share to you is actually there are few components that can be easily upgrade for the better sound.
Let's check it out.
Something that makes this amplifier special is the power tubes that can be swap between 300B or 2A3 directly without any modification at all. As you are probably known that 300B running at 5-volt filament voltage, while for 2A3 running at 2.5 volt. The output transformer impedance also needs to match between those tubes since they are different in the specification. When you swap between 300B and 2A3 tubes or vice-versa, the microcontroller inside this amplifier will sense the tubes that you are plugged in and adjust the parameter accordingly.
The driver tubes is 12AU7 and can be swap with 12BH7 for slightly higher gain. Both tubes identical in the filament voltage and pin configuration, so, it doesn't require any particular circuit inside to sense this changes.
When I remove all the tubes and open the top cover, the components inside are easy to access.
The special power module board is in the red color which it function is for the power tubes sensing controller. This power module was pre-built from factory, so I can only guess the circuit inside is quite complex.
Other than that, the other components are through-hole components and easy to replace to the better quality.
Replacing all components such as resistors and electrolytic capacitors will certainly improve the sound, but let's just focus to the critical components first.
The components that need to upgrade first is the components that largely impact to the audio quality because the audio signal will pass through them. The target are potentiometer and coupling capacitor which the quality coming from the factory is lower than my standard.
Elekit guys probably knew that their customer will upgrade those components soon or later. Since those components is the key to better sound, so they are preparing the actual space to accommodate this upgrade.
I replacing the small film capacitor with Russian K-40Y paper-oil capacitor and small potentiometer with ALPS blue. Those new components are bigger in size and fit without any issue.
This simple upgrade is completed just about a hour.
Later I notice the shaft length of the new potentiometer is way too long. So, I need additional time to cut the potentiometer shaft length carefully before the knob can be plug-in fully inside.
This upgrade is working like charm.
The sound is so much improved now because I know how this paper-oil capacitor impact to the music presentation. For the ALPS blue potentiometer, I don't think it improving so much to the sound quality other than its high mechanical durability compare to the small one.
So, before closing this post, I might share to you the reason I sell this Elekit TU-8900 amplifier.
This amplifier is single-ended 300B amplifier which sound wonderful, no doubt about that, but probably this issue is coming from my personal preference especially about the sound quality that I wish to hear from a single-ended tube amplifier like this. Unfortunately, it is not presenting like I wish to hear from it.
This amplifier sound like modern amplifier. We commonly hear clinical and sterile sound from a solid-state amplifier, fast but grainy sound which this Elekit TU-8900 amplifier sounds like. The sound signature is like in the middle of the modern sounding amplifier and the tube amplifier, with the warm tube sounding signature still presenting with this amplifier.
You might asking is the modern sound amplifier like this can be tailored to suit my preference, to sound more like human voice rather than like an electronic?
My answer is probably can, but sacrifice a lot of resources. The answer can be no; just let it is what it is.
After my continue observation with this Elekit TU-8900, I found this amplifier design using negative feedback to lower the distortion. This might good on paper, but not to the sound quality enjoyment.
Other than that, probably using solid state power module sensing also the one cause this sound signature shift to modern sounding amplifier. The missing of tube rectifier can be one of the reasons why using silicon diodes can sound like this as well.
Cheers.
Disclaimer: Any statement and photos in this article are not allowed to copy or publish without written permission from the writer. Any injury or loss from following tips in this article is not under writer responsibility.
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