Who's using Harbeth with tubes, what speaker model and how many watts per channel?

• #167

Even tubes can improve the sound of Harbeths with SS amps.  While I prefer the H360, H390, H590 with my 30.1's and 40.2's... I did try my Class D Audio (brand) SDS 470C amp yesterday, and found my Harbeths sounded about as impressive as with my Hegel H590. Though, I was using the Schitt Yaggdrasil R2R DAC (which is superb), and the Audio Research Reference 5se tube preamp - which improves the overall sound quality of the 470C. The benefits of this set up is you get the spacious, airy, holographic sound of tubes, but with the bass and mids control of a powerful SS amp.  

So... a class d SS amp, can drive Harbeths very well... if... you have the right class d SS amp driven by the right sources and preamps.

I should also note that I also have just tried my Audio Research Reference 5se tube preamp in combination wth the Audio Research Reference 150se tube amp driving my 30.1’s and 40.2s... and the sound is sublime.

While the bass slam and control is not as great as with the SS amps I noted herein - the details, air and holographic stage is a bit better, and the organic tone, tenor and texture of the sound is a bit better. And the bass may actually may be a bit more real sounding. Real live bass may not have quite as sharp leading and trailing edges as with the SS amps I noted.

Regardless - all of these amps sound superb with the Harbeths - which have impressed me more than I thought they ever could - being box speakers. They sound very much like Quad 57’s, but with more bass slam - which means with the right set up they sound as good as it gets!

M30.1 Here with Air Tight ATM-2 at 80w KT88.
try some Audio research and Primaluna with lower than 80w but prefer more above 60W.
Also prefer KT to EL tubes.

30.2/ 40th.  Luxman MQ-88uC 25 watts. Using the 4 ohm taps.  Sounds glorious in my small 12’ x 13’ room.  Fully treated by GIK.

My Harbeth C7 sits idle most of the time since I got Gershman Avant Garde. Occasionally I switch to C7 with Plinius or Audio Research SS amp. I think C7 works fine with 50 wpc solid state amp in a small room.

i thought it is the nature of semiconductors/transistors that allow them to react faster and also their ability to pass more current without strain or overheating -- once again, given good power supply capability they are gating...

separate question ralph - you make otl amps, how do you handle low impedance loads and are otl’s fundamentally better than transformer coupled tube amps? i think back to my experience in the 90s with fourier otls... man that was quite memorable, those 32 6as7’s lighting up all at once --- wow!!

Tubes and transistors are the same speed. Think about the fact that old tube color TVs had chroma amplifiers in them, one for red, blue and green, and had to have bandwidth from DC to about 10MHz. Although not exactly the same, the ability to make bandwidth and ’speed’ are closely related. Just FWIW, the output sections of our amps have full power bandwidth from DC to well past 30MHz. Its our voltage amplifier section that limits bandwidth (and done intentionally). In most tube amps, its the output transformer that limits speed.


Its good to have lots of capacity in the power supply of any amp- it can reduce IMD at higher power levels.


If the OTL and transformer coupled tube amps are on a load that is friendly to both amps the OTL will be more transparent and obviously wider bandwidth (and more speed). However low impedance loads don’t work for most OTLs although we make some that can handle low impedances just fine (the MA-2 and MA-3 in particular). But IMO/IME low impedance loads and heavy phase angles are not not good for any amplifier (tube, solid state, class D) because in all cases the distortion will be higher.


At least in the world of high end audio, keeping distortion down is paramount to obtaining smoother, more detailed, more transparent and overall more neutral sound. The ear converts all forms of distortion into some form of tonality; hence the brightness of solid state, caused by higher ordered harmonics and IMD. Distortion is also why many tube amps sound ’warm’; this is caused by the 2nd and 3rd harmonic. But if you play a solid state amp on a higher impedance speaker it will sound smoother and more detailed since you have less distortion. You might think that the low distortion of solid state amps as inaudible (this has been the myth for the last 50 years) but if it were we would not be having a tubes vs transistors conversation!


We handle lower impedances with our smaller amps by the use of an outboard device called the ZERO (www.zeroimpedance.com). But the funny thing is that even solid state amps sound better driving lower impedances if a set of ZEROs are used and this is entirely due to the fact that you are reducing distortion.


Class D amps have problems with low impedances too- its no worries doubling power as load impedance is halved; class D amps have the lowest output impedance of any amp made (our prototypes have output impedance of only a few milliohms). But they have filters at their output, and the quality of the filter is directly affected by the load impedance- many are designed for 8 ohms. But they too have lower distortion into higher impedances.


Since this is an issue for all amps, I really don’t see the point of the speaker being hard to drive! You need a lot of power, and finding an amp that is simultaneously high power and able to sound like music at the same time is a challenge! Plus you get thermal compression caused by voice coil heating- something that is not nearly so severe with high efficiency speakers, which is part of why the latter sound more dynamic. The speaker cables become hyper critical. Finally an easier to drive speaker does not have to take a back seat when it comes to distortion and resolution- often they have less distortion and greater resolution. It does get progressively harder to make deep bass with higher efficiency, but there are simple ways around that problem.