• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Why has single ended output become popular


2010-11-05 6:44 am
For me it started with Eduardo de Lima paper Whysingle-endedtubeamplifiers.pdf. Relevant distortion figure that we hear can be measured from the acoustic output. From p9 "... the same set up with the other polarity. We can see that the whole 150 Hz till 300 Hz region has reduced distortion and that around 900 Hz we have an increase in it. The overall effect seems to be a reasonable decrease in distortion."

Of course majority of multiway speakers do not have correctly aligned phase of the drivers which render distortion cancellation by SE amplifier ineffective.
"Timbre of instruments" betrays the simple kinds of music. Nobody is talking about timber of instruments in a symphony orchestra, what matters is resolution, so that you hear real complex texture, and not some kind of homogenized sound. Good PP does it better than good SE.

But I AM talking about the timbre of individual instruments within the symphony orchestra and individual voices within an opera. I'm talking about exactly that. Operas and orchestral music aren't just about tuttis where the whole orchestra plays together at high volume. Woodwind instruments are a large part of it, singly, in pairs and in sections. With SE and with DHTs each individual woodwind instrument is audibly more accurate in timbre. For anyone familiar with these acoustic sounds, either musician or concert-goer, this is an enduring joy and a big reason for constructing your audio system to achieve this. For me there's a huge difference between a clarinet that sounds exactly like a clarinet and one that sounds "pretty much" like a clarinet.

Play Bartok's Concerto for Orchestra on a really good SE system with DHTs and then on a PP system - probably but not necessarily with global feedback. I'd be very surprised if you can't hear a difference in the timbre of the orchestral instruments when you listen attentively. Reasons are no doubt some of those already described, pure class A, harmonic spectrum etc.

I fully realise that I'm being ultra sensitive to timbre here, but that's what music is for me. A Steinway is not a Bechstein is not a Yamaha.

I'm not even just talking tube amps here - the best solid state amp I ever heard was a SIT amp, pure SE class A and monster heatsinks. Those old Sony SIT devices that are obsolete now. Nelson Pass has revived SIT amps - he liked the sound so much.

The other thing I have to say is that it's the combination of SE and DHTs that achieve this kind of timbre for me, so I'm talking about two distinct factors, though these are often combined in e.g. SE 300b amps. A really good PP amp with DHTs right through might be pretty close. Not so common, but perfectly possible. Lynn Olsen did it for example.

Last edited:
Aha, we are getting there. Lynn Olson's DHT is not "close", it is better. I am all for DHT. Did you compare your SE amplifier to Lynn's or Gary Pimm's PP?

As to Bartok, this is about single solo instruments. Do you claim that you can hear the timbre of each violin or cello in the string section? That's what I meant.
Aha, we are getting there. Lynn Olson's DHT is not "close", it is better. I am all for DHT. Did you compare your SE amplifier to Lynn's or Gary Pimm's PP?

As to Bartok, this is about single solo instruments. Do you claim that you can hear the timbre of each violin or cello in the string section? That's what I meant.

I've made PP DHT amps with no global feedback. PP 2A3, 4P1L drivers, 01A inputs. Yes - that's a good sound of course. But I don't listen loud in my city apartment, so SE is enough for me, and I do get more of a thrill out of vocals and acoustic instruments with SE. Life's little pleasures.

No - I don't hear the timbre of each string instrument in a section, but you wouldn't anyway in a concert hall unless it were one-to-a-part in early music. I talk about woodwinds because their timbre is so important in orchestral music and so distinctive. Brass is easier to reproduce but woodwinds each have a unique sound signature. The importance of woodwinds can hardly be overstated - they're crucial in all classical music, everywhere in Brahms and Sibelius ..... I could go on forever. And we haven't even started on chamber music and voices.


Paid Member
2002-08-14 1:47 pm
As posted above, SE is only good for certain kinds of music - "girl and guitar". It is not good for complex music, particularly orchestral and choral.

My principal objection towards SE too. What is worse, ownership of a SE amp / single driver speaker, further limits the listener's taste to really lame music the system likes playing. The descent from Diana Krall into Norah Jones is eventually unavoidable :p
  • Like
Reactions: 1 user
Perhaps a bit of difference in terminology.

He id talking about the kink in the hysterious curve at the zero crossing. This kink directly affects the transfer curve when information is smallest (and easiest to lose). A non-parafeed SE amp operates in a linear part of the curve.

This is wrong. You are just substituting the correct term " hysteresis" with the incorrect term "kink".
Andy - I wholeheartedly agree with you re. instrument timbre and under which circumstances you can or you cannot parse them out. What I disagree with is the superiority of SE. In my experience, a PP amplifier can do what SE amplifier does, but do it better. Timbers too.

I can't say you're wrong here - I just haven't yet experienced a PP amp that did timbre better. I only built a couple of PP amps with DHTs and that was 8 years ago. And I did like those amps, even though the filament supplies were a nightmare with DHTs. Three stages, six individual filament supplies each with voltage regs. Arggghhh...... If I did it today I'd build it better with all the knowledge I've gained. Probably 300b outputs and 10Y drivers with a SUT on the input. If I still had my Apogee Caliper Sigs I'd build exactly that, but I've downsized to single unit Alpair 10Ms. My SE amps are big enough - complex filament supplies with chokes and so on. PP would double that. I'd have to be younger and madder....... well, I was once.......

Within my experience I'd go SE for a smaller system and a simpler life. Multiple DHT stages are no joke when you're a perfectionist.

Last edited:
There is no need for individual DC supplies for each filament in a PP DHT. AC works fine for outputs and drivers, it just has to be clean filtered AC, and in fully differential stages all filaments can be tied together. SE indeed requires DC regulators, as there is no common mode cancellation. Another disadvantage of the topology.
@andyjevans. It sounds to me that the accurate timbre you talk of is really just the result of low distortion that would be very good with a SE amp at low volumes due to the distortion profile.

Yes, and the harmonic spectrum. That's important for timbre. But I'd also say that DHTs are for whatever reason superior when it comes to the timbre of acoustic instruments. 10Y, 26, 01A and such as well as 2a3, 300b. Different factor, admittedly, and these could be used in a PP amp though it's rarer that this happens.


2019-12-28 9:16 pm
To answer the OP question - I would say simplicity.

Simplicity for equipment manufacturers (ie digital devices with headphones or Bluetooth etc).

Simplicity for a customer is simply - if I plug my things together does it work first time? If so - happy with purchase. More happy people given the cost distribution. So you'll see more manufacturers selling it.