Elekit TU-875

Review: Elekit TU-875, Part II

Letter from Hong Kong (23-6): Terrence Lau on Elekit TU-875

Editor: Reader Terrence Lau submitted this as a comment, but it's substantial enough that I took the liberty of additionally publishing it as an article, to keep the flame burning, so to speak. Many thanks for the detailed write-up!

The Elekit TU-875 is by now legendary. Many in the West look for it but finding it is very hard for them. HK people are lucky in that we could easily buy Japanese second-hand. The coverage on TU-875 is piecemeal in this blog, but I urge you to read them!

My early Elekit Overview (here) can be viewed as Review, Part I. For the sake of simplicity, I shall call this current one Part II, even if it comes after many of ELO's more recent articles on the subject, which likely triggered TL's interests.

ELO's articles are harder to classify. They were written in a Diary-like Systems Context. It pays to read

them carefully. The first one documents his Search (here); the second the full evaluation (here).

I got one in mid May 2023 in Hong Kong from a fellow on the review33 site. He was a very polite and nice guy who is similar in age as I, so we had a good chat at his home when dealing. 

It was an original Japanese domestic kit, unopened, and the seller said he had bought it in Japan himself. It had Jan Philips 5963, contrary to what I had seen previously on some YouTube videos where the kit was shown for assembly process with 12AU7EH. What a treat.

At home, it took me the best part of a day to assemble the thing. I made several mistakes in soldering one diode and several D170 triodes, rendering the unit inoperable upon “completion”. During checking I found the upstream PSU and tube boards were OK and concentrated on the lower main board. There I found my mistakes, having reversed the polarity of those parts that I mentioned. After repeated checks, it got to work finally.

It wasn’t difficult to note the “faster” sound of the TU-875 compared to my other preamps, both tubed and SS. Compared with my McIntosh C11 and C20, it sounds so airy and the background is so hiss-less that I had to turn up the volume up to max to confirm this performance. Really, Kudos to the designer of this kit working on a meagre but applaudable 7 volts 1.7 ampères little power supply case (the wall wart doesn’t even qualify to be called a box).

In stark contrast to my McIntosh and my Conrad Johnson PV-8, both the MM and the Line Sections.sound clear and quiet, without being too analytical, but giving huge level of detail and certain warmth in sound. Harmonics are good therefore, and I found it easily to live with, especially for tube rolling. The front single tube is for the line amp with average amplification, while the two tubes near the taller cover on the back are for MM stage with really huge gain as I found out with my trusted OM-3 pickup. I haven’t had the chance to test out the MC stage yet but opinions have it that it should sound just as sweet as does the MM stage as it is built with two J-FET ICs. I’m not doubting.

In pairing this preamp I noted it relatively prefers a power amp with lower damping, for the sound to gravitate towards the bassier side of the spectrum. So, it should be paired with a tube amp such as McIntosh MC240, or even an EL84 one. The TU-875 works spectacularly well with my Ampex 15-watt mono tube amps with 6973, often referred to as the Ampex 6973 mono amplifier. Not to be confused with the stereo version from Ampex, this mono amp was built for 16 ohm loads, the stereo version being for 8 ohm. Alternatively, I will try it with my Nakamichi PA-700.

So my take is that, nowadays, while it's difficult to source as NOS un-assembled, the TU-875 is holding up well in its performance and even at the price I paid, for US$400 in sum, it is a great value on the whole. A bargain I should say. Just the fun of assembling the kit alone is worth everything and every minute. And alas this fun is probably only for those few who will travel the extra mile to first of all get one set to begin with.

Editor's Comments: 1) It's incredible that TL can assemble the thing in 1 day; it's not an easy kit! 2) the original tubes are JAN 5693! Very nice, but of course even older old-stock 12AU7s are even nicer; 3) Ampex 6973 monoblocks, man, these are gems (pic below borrowed from reverb)! Just that 6973's are hard to find! These are fast, fluid amps that outperform even EL84s. 

Nobsound E6 III Douk Phase Microphonics

Click all pics to enlarge. Top, doctorjohn's naked E6 with Audiophiler Caps. Black Rubber O-Rings sandwiching the white Silicone ones. Kinda monochrome Saturn? Actually, they are not needed, but just for show.

Nobsound E6, Part III: Shawn P Reports on his Experience.

Doctorjohn and his NYC friends on Microphonics; Phase Reversal...etc

Editor: The Nobsound E6 wildfire is ablaze on two continents (at least), and I see no sign of ablation. I surmise there are several reasons for this: 1) Now entering cheaptubeaudio preservation stage (i know we are very small compared to the UN...), the E6 is already endangered species (no more large tube stash for continual production; how that increases its allure!); 2) although the tube in question is “flawed”, its great sound potential is worth all the wrangling (I repeat: I discourage most people who are not tinkerers or tweakers to get this thing; also not for measurement and “scientific” people - not at all); 3) a truly dedicated audiophile is a masochist who somehow perseveres, or even enjoys obstacles. In case you are in doubt, if you are someone who buys things from Amazon or Ebay or Aliexpress and compare and return most of them, you are not one! Just do the world a favor, don’t get it and then return! Try not to be a Polluter!; 4) I expect this E6 thread to go on for quite a bit longer! Gauging what my NYC friends are doing, I wouldn’t be surprised if it reaches beyond Part V...

Part I, Basic information on the Preamp and Essential Info on the Tubes.

Part II, Caps Mods and Reception by our friends in NYC.

Part IV should come soon too, on cap mods etc.

In this Part III first we’ll first hear from our HK author Shawn P. His mentioning of Schiit Vali I is extremely interesting to me. Then I’ll show you some of the things my friends in NYC and I have been discussing, and they are of import.

Shawn P
To echo with doctojohn’s Part 1, quite a while ago, we discussed the E6. I thought that was interesting as the only DHT I knew of were the 300B and 845 (and its closely related ones). Let alone, DHT preamps.

Since I like the 300B and 845 so much, I thought a DHT preamp would be nice and likely be my cup of tea. I did a bit more research and eventually I realised that I already had experience with DHT preamp with Schitt Vali (1st generation) which utilised 6088 for the preamp section and I had been quite happy with the sound of it. The realisation further reinforced my belief that I would enjoy a DHT preamp. [Editor: The 6088 is a tiny nuvistor-like Direct-Heated Pentode wired as triode in the Vali I. Like the 2J27, it's also prone to microphonics. I also have the Vali II, which did away with this tube but is not inspiring.]

I spent a bit more time on TB and found that there were not that many DHT preamps and I thought perhaps it was due to the fact that small DHT tubes had microphonic issues.

Nevertheless, the Douk E6 caught my eyes as it was nicely priced and did not seem to be a fake tube preamp with opamp. The E6 page on TB has a warning that HV rail runs at 100V and that sounded like a real tube preamp to me.

Contacted doctorjohn and told him about my new find, and he told me that he also had his eyes on this little guy for a while and perhaps my mentioning finally got him to pull the trigger and the rest was history.

Ok, how does it sound?

I had the E6 connected to my APPL 845 initially. When I first turned everything on, the E6 had serious microphonic issues and merely touching the volume would cause ringing. Needless to say, the music would cause ringing as well and I had to turn down the volume in order to mitigate the issues. Eventually, I connected the E6 to the APPL 300B which had less power and did better with the microphonics. In fact, the APPL 300B was a better match with the E6 in the sense that E6 could contribute more to the APPL 300B. The APPL 845 was doing quite ok without a preamp.

Rubber bands were introduced to the tubes and the microphonic issues were further reduced to a point that it was not too much of a problem. At least not materially disturbing my listening.

The first CD I tried out with this new setup was one of my Jazzclub CDs, “Jazz for Lovers”. on the song “Dream a Little Dream of Me” by Laura Fygi, the problematic area was usually the high E String guitar plugging towards the end of the song. With some amplifiers, the plugging could die down prematurely, and it could also sound a bit rough. With the E6, the plugging extended nicely and it was nothing edgy/rough at all. Smooth but not muffled.

Another song from “Jazz for Lovers”, “Do It Again” by Shirley Horn. I am of the view that this song is the most challenging song of this CD, not that it did not sound good but I have always felt that the music and Shirley’s singing did not match. The music reminded me of some Hong Kong black and white movies from the 60’s (粵語長片) in which, goofy guys would do some goofy acts with similar music at the background. Whereas Shirley was asking you to “Do It Again”. Kind of odd. No worries, the E6 had the ability of making sure Shirley was the “leading actress” and the music was only in a supporting role. With E6 in the chain, Shirley was speaking to me and asking me to “Do It Again” and the goofiness was gone! Shirley's singing became “3D” if you want a modern term with visual elements to relate to.

My general impressions (initial) with the E6 were very good. APPL 300B was musical but with the E6 it became more enjoyable. Music had more extension with E6 and it became more musical. Perhaps additional even order harmonic distortions or some may simply refer to it as “even order harmonics”.

Well, I still need to plug in the Russian tubes. I heard they sound even better."

Doctorjohn and Fellow NYC Friends
Now, these are very experienced people, as I have mentioned in Part II. Their actions regarding the E6 truly astonished me. But before we get to these crazies, a fact.

Phase Being an extremely simple single-stage triode (albeit strapped) amplifier, the E6 is PHASE REVERSED by nature of the design. This is a complicated question. Theoretically, with a phase reversed component in the playback chain, provided none of your other components reverses phase (the usual scenario), you should compensate by having your + and - loudspeaker cables reversed (either on amp or loudspeaker side, but not both) in both channels. Simple, right? Yes, and no. The younger among us, such as ELO and Shawn P, and mrgoodsound, likely listen to mostly recent recordings, which are mostly phase-correct. In their case, it’s advisable to do the reversal. But for older folks like Andy and friends in NYC, who hold and play tons of old vinyls, it’s not so simple. Many (say, half) of the older recordings are phase-reversed to start with (which is why many insist that a phase switch is mandatory on phonoamps and DACs). In this case, reversing the loudspeaker + and - will not be desirable in half the situations. Such may be the case with Andy who, as mentioned in Part II, uses the Citation I phono stage for RIAA. The Citation I has a Phase Switch (so no need to do adjustment with loudspeaker cables), and Andy reports no significant difference with the majority of material.

Not so for those who play mostly newer stuff. In a private communication, Shawn P reported that the image snapped into focus when compensated for phase reversal. And then there is my case. Although I love old recordings I listen mostly to newer stuff and I find compensating for the reverse phase desirable, but perhaps not absolutely mandatory. SO! You must try for yourself to see if it matters with you. It’s free!

And then there is the issue of some of the loudspeaker systems, particularly some of the older ad-hoc horn systems, where DIY (or even stock) crossover designs etc may have some of the drivers out of phase. The effect can be unpredictable. BUT, aside from a little diffusion, I maintain it’s not night and day usually. Us horn users are not pin-point imaging people, and prefer presence, and it can be a different story. YMMV.

Microphonics continue to be an issue. In Part I I have shown how the tube originally comes in a Full Metal Jacket (FMJ) for a good reason - the metal covering, and inner cardboard rings are there to damp the microphonics. In removing the FMJ for the sake of looks, Nobsound has made the E6 more prone to microphonics. Here’s the breakdown:

• Stock Chinese tubes are naked, without FMJ. Some have very mild microphonics; others more severely affected. You can temper the microphonics by applying Tube Dampers (like one for similar sized 6SN7, which could be cheap or expensive). But I suggest you get Industrial O-Ring’s, which are dirt cheap. For those who can buy from Chinese TB, there are ones made from rubber and others made from silicone. You can use any that’s the right size, and you may find them locally too. Important to know: the diameter of the 2J27 glass tube is 29 mm. So, you need rings with inner diameter of 29mm or less. See one of the bottom pics for how to calculate. It’s likely the smaller and tighter the better the effect. Or, to start cheap, you can use some Thick Rubber Bands and wind them around the tubes (both my NYC friends and Shawn P have employed them with success). beside these more conventional approaches, you shall find many innovative tactics in the attachments at the bottom. Madtubeaudio!

• As detailed in Part I, you can buy Russian tubes from TB here or from Ebay. The Russian ones come in FMJ. As mentioned, the diameter of the FMJ tube is slightly too large to be inserted into the E6. So, you can do as I did, and remove the FMJ. This of course makes it more prone to microphonics, but the Russian tube is inherently superior in this respect and quite manageable so far even without O-Ring dampers

• Or, if you want to use it as is, which is definitely better for microphonics, and it saves you the hassle of removing the FMJ, you alternatively have to remove the E6 chassis (L pic: Andy's with Russian Tubes). You would need a regular Philips screwdriver for the 2 RCA socket screws and, perhaps a little trouble for some people, a small hex bit (likely from a jewelry hardware set) to unscrew the 8 chassis screws. I stick 4 small 3M sticker feet to the bottom of the circuit board and place it on a rubber slab, but any insulating material would do. Voltage is low and unlikely to cause anyone trouble. You can also choose to re-attach the front and rear (gold) plates by the RCA socket screws, but then they would be wobbling a bit and I think that’s not so good for isolation.

• Any Downside to Damping Rings? I haven’t really done any A/B. Andy mentioned: “...two of these stop the ringing entirely but they also take away some upper harmonics in music...” This is true in my experience as well. I have used many Audio Research stuff, and in many of their later stuff they used damping rings. Invariably, I’d prefer to have a little microphonics than to have them totally damped out. The effect is just as Andy mentioned. So, use judiciously, only when necessary (which certainly varies with individuals).

• Advice: With microphonic tubes, when changing cables etc, just turning down the E6 volume is not enough. If your amp has a volume knob, turn it all the way down, or turn it off. Give the preamp some seconds to settle down before turning the amp volume back on, and then gradually. One time, with the Chinese tubes, I was in haste and only turned down the amp volume a little. Well, I heard a loud ringing through my loudspeaker tweeters and I moved quickly to turn the amp off. After that, I have been more careful.

Kevin's Rubber Wrapped Tubes and Modified Caps, just one of many iterations

Andy's Ultra-Zen Tea Cups! Yes, they work!

Yes, Andy's Fluted Glasses Work Too!