Wanted to ask. Did anyone here try a single end DHT amp (not a PSE) with zero negative feedback on a Klipsch speaker?, and any thoughts vs push pull amps? (or PSE). I was mostly thinking of either a 300B or 2A3 SE amp (which I understand have a different sound to 845 and 211 SE amps but probably sound better than those in the midrange at least).
Yes, many times, as you probably know I design and build them and have done so for over 30 years and 25 years commercially. It all comes down to a few things: How loud do you listen in your room, How big your room is and what type of music do you play. I quote the last point because if you have a large room and play your music loud, don't expect a 2A3, or even a 300B amplifier to provide undistorted sound. Check out my article in Sound Practices Magazine "Speaking out", issue 9, pages 20 & 21 from 1995. Although this was written nearly 30 years ago it is still relevant today.
I’m no technical expert, and those with more technical knowledge please feel free to correct anything here that is wrong, but my understanding is that these efficient horn loaded speakers will probably be working within the first watt of power, most of the time, in most situations (unless one listens to a lot of dynamic classical in larger rooms at longer listening distances). With standard material that is not dynamic, not as much power is needed as one might expect, especially with very efficient speakers.
Correct. However, the power often quoted by most manufacturers is widely inaccurate.
With pure SE DHT amps with zero feedback, the first Watt of power is more linear and cleaner than other amps. In theory the results should sound better in some key regards than other designs due to this. (Better purity and less smearing in the mids and highs).
Correct. One thing to note is that the power figures quoted by most SET amplifier manufacturers are vastly out. When they quote 8 watts for a 300B amplifier, on the bench into an 8ohm or 16 ohm load they barely measure 4 watts. That is at about 1% distortion. At 8 watts the distortion figure will be 10% to 20%. The Tron Atlantic 300B amplifier I make measures a true 8 to 9 watts at less than 1% distortion. Low distortion and good power can be achieved with good design and excellent output transformers. The latter is super critical for good performance and the transformers need to be large. The transformers I use on the Tron Atlantic are huge and are designed for 2 x 300Bs. I use them for just one 300B, so the bass performance is very good.
Compromises compared to other amp designs could however be, as already mentioned, some lack of bass driver control with some speaker designs (due to the zero neg feedback), and how the amp interfaces with the impedance characters of the speaker, which is more critical when using an SE tube amp than push pull (I’m not familiar with the exact situation there with regards to Klipsch speakers). AFAIK they don’t have impedance flattening networks inside them like some horn speakers do to make them more SE amp friendly. Maybe some mods could however be done to the speakers if not.
As soon as you move away from a Single-ended Triode design, as in one triode driving the loudspeaker, the purity of sound you mention above will rapidly start to degradate. If you need more power it is better to use a single more powerful Triode like a 211, 845 or a GM70. There are other larger triodes but these require very high voltage power supplies which become extremely dangerous for manufacturing, servicing and repair, as well as being in a domestic scenario.
Getting the noise level low enough with an SE amp with zero feedback can be a challenge as already mentioned. From what I have read and have experience of myself, more elaborate and expensive PSU designs can help, as well as (also already mentioned) having 2 stages in the amp only instead of the usual 3 you see in most production SE amps. That’s more likely to give lower noise.
I have been saying this for over 25 years, in that you need to design specifically for high efficiency loudspeakers if you want top performance. The gain needs to be correct, so you have good control of the volume range, as well as extremely low noise circuits. Any noise will modulate with the audio frequencies being amplified through the amplifier and huge degradation will be heard, especially if you have very high resolution loudspeakers.
The Cornwalls are high efficiency speakers. If do to the maths regarding their efficiency rating (102 dB), average listening distance in a room with a normal amount of reflections, then it’s likely any amp you use will probably be working in the mW range most of the time, with most material, unless you want hearing damage from continuous high dB levels.
Correct. You can use a push pull valve amplifier 20-25watts, but once you move away from a SET you will start to lose the purity and linearity of the Triode design. For a start, a push pull amp will require more gain stages and the use of feedback to keep everything in check. The feedback will reduce the gain but in practice the gain is still usually high at 500mV to 750mV for full output. Not forgetting the source Analogue or Digital will be outputting 2 volts, plus there will normally be a preamplifier in-between as well.
I read a few times that 20-25 watt amps are considered to be generally the limit with these speakers in domestic situations. With an amp of that max power potential you have a max vol potential of over 110dB, after an average listening distance/ average size room and reflections are taken into account. 40-50 watts or will work but that kind of max power potential probably isn’t needed for these speakers, unless you really need the 119dB max quoted output (if you have a huge room in a manor or something…)
Anything more than about 12watts in a normal sized domestic living space will be wasted, unless of course you are using your Cornwalls for parties, or playing disco or heavy rock music at very loud levels.
After reading around many say that the Cornwalls sound a bit more ballsy with a PP amp rather than an SE amp, which can sound smoother and purer. However Chris on some forums has some Living Voice Tone Scouts with the same efficiency rating . When he got them he had a Radford Push pull amp and a Border Patrol SE 300B amp. He told me the Border Patrol sounded a lot more dynamic and better in the bass than the Radford with them, to his surprise. I suspect that’s at least in partly down to a better first watt of power.
You can get very good bass from a SET amplifier providing it has been designed correctly and it uses large good quality output transformers, good circuit design and good power supplies. As a guide the output transformers need to be about the size of the valve they are connected too. This is why good SET amplifiers cost money. It's like trying to design a supercar for the cost of a family saloon. The compromises are just too much to expect the proper supercar performance and experience. You cannot make a cheap SET amplifier because the parts required are expensive. That is to do the job properly.