Linear Tube Audio MicroZOTL Elekit TU-8150 Klipsch Heresy

Click pics to enlarge. Bottom, wires from RCA to TP3/4. Note the disabled resistors (under the red wire).

Review: Linear Tube Audio MicroZOTL MZ 2.0, Part III, as Preamp
Review: Elekit TU-8150, Part IV
HiFi Basics XI: Pre-amp or not to Pre-, That is the Question
Review: Klipsch Heresy I, Part IV

Linear Tube Audio, Part I (mostly as amp, with my 104 db YL horns), Part II (used as amp in the Living Room with 97 db Klipsch Heresy I).

Elekit TU-8150: Part I (Basic Info; 6AQ5 vs 6V6), Part II (Pentode vs Triode; Input 1 vs 2), Part III (tested with bookshelves).

Klipsch Heresy, Part II, Part III, Part IV (this includes the important comparison with the Elekit TU-8800VK)

Elekit TU-8800, Part II

Minor Modification of TU-8150
After rather exhaustively testing the TU-8800VK and given my fondness of the 6V6 tube, I finally summoned the energy to perform small modifications to my TU-8150.

In TU-8150, Part II, I discussed the topology of this amp. To quickly summarize, compared to the TU-8800, this is a modestly endowed amp, with a much smaller transformer (which is not necessarily a bad thing). It is a sibling of their popular TU-8200 but designed to run the low powered 6AQ5 and 6V6. It is also apparently designed for the desktop. Input 2 (RCA in the back) is routed to the minijack input in the front before going to an op-amp (for amplifying weaker sources like cellphones) and then the 50K volume pot. I removed the op-amp for purer sound. I wrote this:

1) The long signal signal path of the RCA Input 2 is certainly not ideal, but looking at the schematic one can disable R101 and R201 and solder a jumper wire between the RCA terminals and TP (Test Point) 3 and TP4, thus bypassing the Op Amp stage altogether; 2) Even if the Op Amp is removed, because of the associated circuit the signal still passes through 2 more resistors before reaching the 50K main volume pot - the 4.7K resistors (R102 and R202) before pins 6 and 2 of the Op Amp and the 22K resistors (R103 and R203) connecting pins 6 and 7 and pins 2 and 1 before the 50K main volume pot. That is 26.7K (22K + 4.7K) of resistance that can be bypassed if TP3/4 are used. If one uses the RCA Input 2, even with the Op Amp removed, there is a total of 36.7K of resistance before the 50K volume pot, making a total resistance of 86.7K if the main volume is maxed out. One notes that in SET amps the line level signal usually directly goes to the main volume pot, and 100K is the more popular value. One can use jumpers and eliminate those 4 resistors (R102/R202 and R103/R203).

As you can see in the pic above, I did (1) by disabling R101/201 (lifting one end) and wiring the RCA directly to TP3/4 (just before the potentiometer) using the conductors of Belden 8451 (just as I re-wired my TU-8300). For the moment I did not tackle the R102/202 nor R103/203, so if the minijack is used the signal will still see 26.7k of resistance before the potentiometer.

Used in Ultralinear Unlike before, given the somewhat lesser sensitivity of the Heresy I, I opted for Ultralinear Operation.

TU-8150 Used as Integrated Amp I have actually never tested the amp before like that. Suffice to say it played well but volume had to be turned way up and so it was not the most dynamic. Clearly a preamp would benefit it.

LTA MicroZOTL MZ 2.0 + Elekit TU-8150
System used is the same as testing TU-8800VK, except that now the LTA is inserted as a preamp (with Gotham and Belden as interconnect, see below). With the volume knob of the Elekit TU-8150 maxed out (something that cannot be done with the TU-8800), the volume knob of the LTA is around 1 O'Clock:

Turntable (stereo): Thorens TD-124 Mk I with Thomas Schick 12" arm and Goldbug Clement II MC Cartridge.
Turntable (mono): Technics SL-1200 Mk II with Denon DL-102 Mono Cartridge。
Phonoamp: Arcam rPhono (to Gotham GAC-2111 interconnect)
CD Player: Magnavox CDB 262 (to Gotham DGS-1 interconnect)
Preamp: LTA MicroZOTL MZ 2.0 (Gotham GAC 4/1 or Belden 8451)
Amp: Elekit TU-8800 (Belden 9497 loudspeaker cable)
Speakers: Klipsch Heresy I (alnico)
Subwoofer: Pioneer SW-8 (connected to amp with generic cable)

• Bass As soon as I played something (it was Nick Cave's The Boatman's Call)), I was really taken aback. Surely, there was more bass! I dialed back the subwoofer volume a little and listened again. Now, the balance was about right, but it was apparent it is not just a question of loudness, as the bass is even cleaner, better delineated and a little deeper! This is likely attributable to the LTA, which has phenomenal speed and bass (read my LTA, Part I).
  

• Air and Detail Also, given that I had come off the excellent upgraded Elekit TU-8800VK, I was very happy that the combo yielded little to the former here (using 6V6). As a matter of fact, there is a somewhat deeper soundstage, more air around instruments and more minute details.
  

• Transient, Microdynamics and Flow The system's faster transient means enhanced microdynamics and more truthful timbers. Whether it is Nick Cave or Dvorak 9th (Detroit/Paray, Mercury), it is exciting, but never strident and always with enhanced musical flow.

• Power Despite the somewhat more refined and sparkling manner of the LTA + TU-8150, the combo does not sound quite as powerful as the TU-8800. People with less efficient loudspeakers may have different conclusions.

• vs TU-8800 In some ways this is a non-comparison. Elekit vs Elekit Although under the same roof, the 2 amps are quite different, especially in gain structure. The TU-8800 basically cannot be used with an active preamp (particularly if one plays vinyl) whereas an active preamp is needed to max out the TU-8150's performance. Of course, if I install the Op-amp back into the TU-8150 (as initially tested in Part I)  I'd have more gain but it is still likely not as high as the TU-8800 (or 8300 for that matter). That said, I'd think the TU-8800 is better built and more versatile, though for someone who prefer lower-powered tubes like 6V6 it is likely an overkill. LTA vs Elekit TU-8800 Let me clarify this. There are 2 facets to this: We are pitting 1) the LTA (as preamp) against the preamp section of the TU-8800. Now, I don't have the schematics of the TU-8800 so I don't know whether it has an active preamp gain stage or is just an amp with a passive volume knob (latter more likely). But the result is clear - I prefer LTA + TU-8150 to TU-8800(VK) on its own, but this is because I can get away with 6V6 (not many can), and the LTA preserves its own sterling attributes used as a preamp; 2) LTA as amp vs TU-8800 I think I prefer the more subtle sound of the LTA, but it loses out in sheer grunt. Contributing Factor of the Active Preamp To my thinking, part of this is due to the contribution of an active preamp. I have written extensively about this - unless I am faced with an amp with very high input sensitivity, I prefer to have an active preamp (especially since I am a vinyl addict). The "scientific" basis is not certain (just as "science" is used as a refutation of vinyl), but that's what my ears tell me. For more on this, read the HiFi Basics part that finishes this article.

• Note: I do think a little more power will not be remiss. The LTA will be staying in the system as preamp. I am going to rotate some amps more powerful than the TU-8150. Next up will likely be the AES AE-1 300B amp. 

HiFi Basics XI: Pre-amp or not to Pre-, That is the Question This is excerpted from a very long previous article. Regular readers may want to skip it. I am just using this opportunity to turn this into a HiFi Basics Article for indexing purposes.

DIY, Preamp, Passive Volume Control, First Watt and Low Powered Amp

• Is an Active Preamp necessary? Audiophiles are divided into the pragmatics and the theorists. The former will try anything if it makes the system better. The latter believes in numbers and have strong beliefs on many issues. There can be no more contentious issue than whether an active preamp is necessary. Take the standard CD player output of 2V, if you run that directly into your amp, it will be ruinously loud. So the preamp actually attenuates the signal going into the amp. The classic active preamp has gain, sometimes a lot, but in the end the signal is also attenuated before going into the amp. Many people take this to mean a passive preamp is all one needs. Why amplify and then attenuate? In theory this is correct, but in practice things are very different - the setups I have heard with passive preamps (including my own and those with source going directly into an amp with a passive volume) easily number more than a hundred, and in no more than a handful of instances did I not long for an active preamp. Let's look at this in detail.

• Passive Volume Control (PVC) Basically this is a volume pot. You can easily build one with a cheap volume pot, or you can spend thousands using boutique parts and ultra expensive resistors. My Audio Synthesis Passion V (a pic from the net to the right) costs a lot, and the cost of the parts add up to more than the second-hand price! Here are some factors influencing performance: Amplifier Sensitivity Amplifiers with high input sensitivity, such as Leak, works well with PVC, whereas those with low sensitivity, like Quad, would not. Source Output Most CDPs output a standard 2V, but there are exceptions. The vintage Muse Model 2 was supposed to be a very refined sounding DAC, but it has an unusually low 1V output. I heard it once many years ago in Opera Audio in HK. The late Stanley Chu had it in a system with 300B amp and Klipsch La Scala, but I just found the sound dull. On the other hand, Audio Note UK is known for the very high output of its DAC's. My vintage DAC-2 (here) has a monstrous 10V max. It was designed to be able to drive AN amps (those with volume knobs) directly. High Source Outputs work better with PVC. This is why imho people who play vinyl should NOT use PVC. Signal Loss and Buffer One reason why preamp with gain drives the amp better is that a PVC by nature can only use a short interconnect. Preamp with gain can drive much longer interconnects. Even more important, many active preamps actually buffer the output, which has a great advantage in impedance matching. Transformer Volume Control (TVC) This is now all the rage. Since a transformer naturally "buffers" the output, it has advantage in impedance matching with the amp. Some can even have gain, which is a plus, especially for those who use analog sources. But TVC's are not without problems: 1) expense - all are very expensive, more so than a very good active preamp; 2) non-linearity - I don't care what they claim; ALL of them cannot be linear across the range due to the compromises in winding; in fact, non-linearity can be severe. All the claims for better cores, wires etc are exaggerated. It is ironic that the DIY enthusiast can put so much faith into TVC, as they cannot easily measure the TVC's performance under dynamic condition. That said, some do sound reasonably good.

• First Watt I am a firm believer of First Watt, which has to be: 1) of good tonal quality; and 2) of good dynamic capability. The former is not hard to achieve, but the latter is often ignored. In forums I see many DIY people using flea powered amps with PVC for "pure" sound, but most of those setups are severely lacking in dynamics. There are many people who like the "economy" of an integrated amp, but in almost all cases their "integrated" amp is just an amp with a PVC, incapable of a glorious first watt. There is a reason why a company like Audio Note, which specializes in low-powered amps, use high-gain everywhere else, be it a CDP, preamp or phonoamp (I am actually not a fan of their sound, but I know why they do what they do).

• DIY Woes This is too big a topic for this article, so I shall be brief: I have literally come across hundreds of DIY people in my audio life and, sorry to say, much of the experience is a waste. Too much trust in science and material, too little cognitive insight, too much reliance on internet opinions, too little equipment to compare with. I don't care what you DIY, have a good source (say, an old 16-bit CDP or turntable), integrated amp (say, the cheap NAD 3020) and loudspeaker (say, the Yamaha NS-10M) on hand to compare, and be honest with your failures.