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General SET question - performance vs push-pull

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Posted on May 16, 2015 at 17:14:29
rogerh113
Audiophile

Posts: 506
Location: San Francisco South Bay
Joined: October 20, 2014
 Hello,

Just started to look at SET amps as an option, and am looking for opinions as to expected improvement. I am wondering if a SET would be a noticeable/substantial improvement to my current amp. Sorry if the post is a bit wordy, but I figure too much info, in this case, is better than too little.

I am currently running a Primaluna Prologue 5 power amp with (what I think) significant tube upgrades - Bugle boy 12au7s and 5751 Sylvania black plate triple mica. The amp sounds very nice. I am running quite efficient speakers (Klipsch Forte 1 with Ti tweeters and rebuilt crossovers), which causes me to run my linestage pre (Mod Squad Deluxe Line Drive) at max of 25% (9 O'Clock). This means I am attenuating my signal by 75% so I can amplify it back up again - too much gain in the amplifier. I did notice a SIGNIFICANT improvement when I went from a pre-amp (Classe DR-4) to the linestage, and I am assuming the elimination of excess amplification from the system was a large part of it. Is it likely that a SET amp would provide a significant improvement to my system? If so, are there any suggestions as to things I should look for/avoid and to watts per side (speakers are supposedly 97db)? If there is any particulary useful book on SET amps, please let me know. I have an engineering background, so I could likely work to understand the technical bits, but my major focus is on the listening side.

Regards -- Roger

 

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RE: General SET question - performance vs push-pull, posted on May 16, 2015 at 17:55:58
Triode_Kingdom
Audiophile

Posts: 10042
Location: Central Texas
Joined: September 24, 2006
 "I could likely work to understand the technical bits, but my major focus is on the listening side."

That's exactly what's needed when the subject of SETs comes up. SETs don't generally measure as well as their push-pull cousins. However, if the reduced power available from a single-ended triode amplifier is suitable for your system, the audible improvement can be significant. There are many theories as to why this is so, but suffice it to say this is one of those arenas best explored and characterized by ear. I will say that I have occasionally come across an audiophile who truly hated SET amplifiers, but as with so many aspects of this pursuit, the cause was always open to much conjecture.

I build most of my own gear, but it appears to me that Bottlehead has an outstanding product. There is also considerable respect for Audio Note products, although they are likely to cost quite a bit more. I think you wouldn't go wrong with either.

 

RE: General SET question - performance vs push-pull, posted on May 17, 2015 at 01:32:11
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 Triode_Kingdom has made an excellent post. (Be aware that I have done the electronic design of most of the Bottlehead SET amps.) I'll try to add some semi-technical thoughts:

Triode output stages have low output impedance and therefor generally do not use feedback; that is IMHO an effect of similar magnitude to the difference between SE and PP. It also has an effect on speaker damping in the deep bass; damping factors of 2 to 5 are common, vs. hundreds in amps with heavy feedback. This is often audible though rarely significant - and of course highly speaker-dependent.

With 97 dB speakers, you can usually be happy with as little as 3 watts if your room and tastes are similar to most audiophiles. Even on recordings with excellent headroom, this gives on average a 6dB margin at normal audiophile listening levels. Of course if you want to reproduce the sound levels of a live rock concert, forget SETs and make friends with a good audiologist! :^)

On the other side of the equation, SETs have very benign clipping behavior, leading some to claim SET watts are subjectively 2 to 4 times bigger than P-P watts.

If you listen to a lot of spectrally complex music (I myself am a big fan of the Mahler symphonies) you may want a little more headroom, just to reduce the IM distortion components. I'd say 5-10 watts.

 

There are other options, posted on May 17, 2015 at 06:18:14
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 The one that comes quickest to mind is triode PP. You'll be down on power (esp. if you go into a Class A amp). You can wire Pentode output tubes as triodes, or you can use a Directly Heated Triode (DHT), such as 300B, 2A3, 45, with lower plate voltages. A DHT class A amp will get you about 2x SET output; and KT88 triode-wired Class A amp about 12-15W. Of course you can use more than 2 tubes per channel to get even more power in both SET/SE and PP.

And don't forget about sweep tubes. Many work well in both SE and PP, and give you quite a bit of power.

 

RE: General SET question - performance vs push-pull, posted on May 17, 2015 at 14:33:04
dth31
Audiophile

Posts: 298
Location: San Diego
Joined: September 3, 2002
 "I am wondering if a SET would be a noticeable/substantial improvement to my current amp."

This is a very difficult question to answer. Within a group of people, you'll likely get some who love SET and hate PP, some who love PP and hate SET, and another group of people in between.

I would be VERY surprised if you didn't HEAR a noticeable difference. Which you would PREFER, or think is an improvement, is another matter. I would urge you to listen to several SET amps before buying one. Even within SET lovers there are those who strongly prefer 2A3s or 45s or 300 Bs: they do sound different!

Personally, I usually prefer SETs but I've also heard PP EL84 amps that I really liked.

Good luck!

 

RE: General SET question - performance vs push-pull, posted on May 18, 2015 at 05:04:39
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 Compare the two topologies for yourself. Try to avoid comparing two different things; horsepower-race, AB1, loop NFB PP to open loop SE. This may be more difficult than it sounds, being as true Class A PP is even rarer than SE...LOL Or, include the HP race amps but don't go and make too many conclusions on the topology based on that data point...heh-heh-heh.

It is remarkably easy to build a 25W, Class A PP amp, for that power level in SE it is substantially more difficult. Even with the same tube compliment, the PP amp will skew the results with 2x the power. either way, power in Class A is entirely dependent on plate dissipation; if you want power out, you are going to have finals that can stand the standing dissipation.

There are also DH pentode( and beam tubes )that make fine audio finals...60-125W of plate dissipation that allow more power w/o paralleling them to tolerate the idle dissipation.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: General SET question - performance vs push-pull, posted on May 18, 2015 at 06:31:46
rogerh113
Audiophile

Posts: 506
Location: San Francisco South Bay
Joined: October 20, 2014
 Thank you all for the well considered posts and emails. There is a lot of useful information there, and the SET alternative seems well suited to my listening style (musical content vs volume).

I have a lot of homework to do, as there seem to be a lot of options in terms of topologies, transformers, tubes, and so on. I realize that I am unlikely to hit on the perfect SET on the first try, but I want to get real close - better to motivate myself from a positive listening experience, and I prefer to flip equipment as little as possible.

I will try and see if there is anyone local that has a SET system I can listen to. There is a San Francisco audiophile club, but I know little about it. I have only been in one local "audiophile" store, and they only had large self amped speakers - I asked if they sold anything tube, and they said their customers viewed tube equipment as way too much trouble....and this is right in the heart of Silicon Valley!!

Thanks -- Roger

 

SET guys in SF, posted on May 18, 2015 at 08:52:17
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 There are indeed plenty of SET users in the bay area, I'm sure some of them will stumble upon this shortly enough.

 

RE: General SET question - performance vs push-pull, posted on May 18, 2015 at 16:19:33
OldNuke
Audiophile

Posts: 141
Location: Silicon Valley
Joined: November 18, 2014
 Try the Analog Room in San Jose or Century Stereo in Saratoga. Be aware there will be cigar smoke in the Analog Room. Hell, even the Best Buy in Santana Row sells Macintosh. Google tube audio bay area and you can find plenty of places. I don't know about the upper Bay area, things there close down when you aren't looking.
Alonzo

 

RE: General SET question - performance vs push-pull, posted on May 24, 2015 at 06:26:54
rogerh113
Audiophile

Posts: 506
Location: San Francisco South Bay
Joined: October 20, 2014
 Thanks for all of the input. In the process of seeing what was out there in terms of SET amps, I ran into a discontinued project that was too good to pass up. This should be a fun and educational experience for me, building an amp from scratch. I was trained as an EE back in the day of the discrete transistor, and also have adequate skills in soldering and routing. As I slowly plod through putting the amp together, I can work on each aspect of the amp and learn about it. Really looking forward to it. Beyond that, I can eventually (hopefully) get to listen to a SET amp driving my system.

I will no doubt have lots of questions once I get started, so I'll probably be here a lot.....

Regards - Roger

 

RE: General SET question - performance vs push-pull, posted on May 25, 2015 at 14:48:14
rebbi
Audiophile

Posts: 288
Location: Austin, TX
Joined: September 4, 2008
 Roger,
I'll just chime in here to say that I recently made the move from a PP to DHT SET amp and couldn't be happier! I went from a pair for Manley Mahi mono-blocks with a Manley Shrimp preamp to an Audio Note Kits "Kit 1" 300 B SET amp (integrated). In my rig, driving the Reference 3A De Capo monitors, I am thrilled. As trite as this, I feel that this change has shifted my experience from listening to hi-fi gear to something much closer to appreciating musical performances in my home.
I had a ball building the Audio Note Kit 1 and have provided the link to my blog below. There are also lots of listening impressions there. I also started a thread over on Audiogon called "What's The Greatest Bargain In SET These Days?" that has a lot of good info in it.
Have fun exploring! :-D

 

RE: General SET question - performance vs push-pull, posted on May 26, 2015 at 15:27:58
sideliner
Audiophile

Posts: 208
Location: NYC
Joined: August 22, 2013
Contributor
  Since: December 15, 2023
 Speaking from experience, the Forte will sing with a good SE amp. This is a lively speaker in character and hardly in need of the extra dynamics and drive that is the main benefit of the PP amps. I'm fairly certain that you will like the combination of an SET with the Forte's. Go for it!

Just make sure that the output transformer of your chosen amp has a 4 ohm tap since the Klipsch woofer dips to that level for a good portion of its working range. At the very least you'll have the option to experiment for the best bass and overall sound by trying the different taps.

 

RE: General SET question - performance vs push-pull, posted on May 26, 2015 at 16:41:58
rogerh113
Audiophile

Posts: 506
Location: San Francisco South Bay
Joined: October 20, 2014
 Thanks very much for the suggestion to try the 4 ohm output - I tried it on my current push-pull and preferred the sound on the 8 ohm taps. Could be quite different on the SET.

I am pretty sure the output transformers has 4 ohm taps. Scheduled to get the project amp in about a week, and then much will be revealed !! Really looking forward to getting started on the build.

Regards -- Roger

 

RE: General SET question - performance vs push-pull, posted on May 26, 2015 at 16:46:35
rogerh113
Audiophile

Posts: 506
Location: San Francisco South Bay
Joined: October 20, 2014
 Thanks for the link to your blog - interesting step by step descriptions of what I will be doing. My project has no directions and will require point to point wiring - just working off the circuit diagram. Should be great fun.

Glad to hear that you are enjoying your SET - I look forward to hearing mine someday!!

Regards -- Roger

 

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