Does anyone care to ask an amplifier designer a technical question? My door is open.

@shkong78

Many people believe that SET tube amplifier give more mid range magic than Push pull tube amplifier.Do you agree on the notion as designer of tube amplifier?If so, could tell me why it is so?

There are some things about SET amplifiers that can be magic. I have always found the simplest circuit that can do the job well will do it best.

Here are some things that are special about SET amps

• They have very simple circuits
• THe output transformer runs on only one side of the BH curve never crossing through zero.
• They are class A by nature.

Not all SET amplifiers are good, they are often light on specs. The important specs are

• Distortion vs level and frequency. His helps avoiding a really bad one.
• Damping doesnt matter so much if you are using it in a bi-amp situation where it only drives the midrange/tweeter. Use an adequate SS or tubes amp for the bottom.
• Some are noisy. Many don't spec noise. Somehow you have to find out.

Explore the idea of Bi-amping with a line level crossover. We have developed a nice mono amp where the crossover is built in. The bass part is push pull about 15 watts and the top is SET at 2.5 watts. Because IM distortion is eliminated less power is required.

Ramtubes 11-26-2018:

HI, Roger here with a question.

I would like to hear how each of you figured out how much power you needed to buy in watts?

I would appreciate the following information in your response.

Your listening level LOUD SPL (preferably measured at 1 meter from the speaker with a REAL SPL meter. Your low listening level. If you are using a cell phone app then you have confirmed it?

Your speaker sensitivity?

Listening Distance from speakers?

How many watts at your load is the amp is rated to supply?

As I mentioned earlier in the thread I listen to a lot of classical symphonic music that has been engineered with minimal or no dynamic compression. Two such recordings, which I believe have just about the widest dynamic range in my collection, are Stravinsky’s “Firebird Suite” on Telarc (Robert Shaw conducting the Atlanta Symphony), and Prokofiev’s “Romeo and Juliet” (excerpts) on Sheffield Lab (Erich Leinsdorf conducting the Los Angeles Philharmonic). I have examined the waveforms of those recordings using a professional audio editing program (Sound Forge Pro), and by doing so I have found the difference in volume between their loudest notes and their softest notes to be approximately 55 db, which is (to me) amazing.

Correspondingly, at my 12 foot listening distance I have measured peak SPLs on those recordings of close to 105 db, with the softest notes being in the vicinity of 50 db. I used a Radio Shack digital SPL meter for these measurements, set for C-weighting and fast response.

My speakers (Daedalus Ulysses) are rated at 97.5 db/1w/1m, and have a very flat impedance curve with a specified nominal impedance of 6 ohms. My 12 foot listening distance corresponds to 3.66 meters. Putting aside room effects for the moment I assume that SPL produced by a box-type dynamic speaker such as those falls off at 6 db per doubling of distance, which means an 11 db reduction going from 1 meter to 12 feet. I conservatively add in 3 db to reflect the presence of two speakers (as I understand it that figure will actually be closer to 6 db at my centered listening position when both speakers are producing similar signals), and I add in perhaps 3 db for “room gain.”

97.5 -11 + 3 + 3 = 92.5 db at the listening position for 1 watt per channel. Let’s call it 93 db.

I add in about 3 db of margin to the 105 db I want my amp/speaker combination to be able to produce at the listening position. So the required minimum amplifier power (into 6 ohms) is:

105 + 3 - 93 = 15 dbW (decibels above 1 watt)

15 dbW = 32 watts.

To answer your question about my amplifier, for several years prior to just recently I was using a VAC Renaissance 70/70 MkIII, rated at 70 wpc. I recently changed to a Pass XA25, which is specified as a class A amplifier rated at 25 wpc into 8 ohms and 50 wpc into 4 ohms. Per JA’s measurements, though, it is capable of 80 and 130 wpc into those impedances. I presume that most of that increase represents the amp’s capability after leaving class A, although per JA’s comments some of the increase apparently reflects differences in the distortion percentages the ratings and measurements are based on.

Best regards,

-- Al

Thanks again, Roger.

Cary has had notoriously bad measuring amplifiers for as long as I can remember. They have long been the poster-boy amps when people want to argue the "measures awful, but sounds great" stance. Personally, it’s been far too long since I last heard a Cary amp for me to have an opinion on the sonic performance.

I just read the Stereophile review of your amp. Congratulations, it really does impress upon the reader that you know what you are doing!To see JA actually impressed with the measurements of a tube amp is really something.

As for this comment you made to someone else:

I would like someone to tell me why spend big bucks on cone speakers when there are better technologies.

I’m wondering which "better technologies" you are referring to.

Do I infer correctly from your comment to me about the QUAD 57 vs the Alan Jones monitor, that you are speaking of, for instance, electrostatic speakers?

If so, I can tell you why I prefer cone speakers.

I first fell in love with electrostatics in the 90’s and first owned the Quad ESL 63s. As did another audio pal. The shock of not hearing any box sound, and that amazing transparency and "hearing in to the recording" sensation were at first intoxicating. But after a while I found the sound too disembodied, too ghostly, like peering through a window in to another room where the music was happening, but it wasn’t "moving air" in the room I occupied. When I’d play my little old Thiel 02 monitors there was such a difference in palpability, aliveness and "thereness" that it just re-enforced what I was missing. That was the case even after I added the Gradient dipole subwoofers to the Quads. Still among the best sub/panel matches I’ve heard.


I still love to "visit" electrostatics (the Quad ESL 57s being my favorite), for their unique qualities. But every time I listen to an electrostatic, of any make, I come away happy to have moved on to cone speakers.That includes every hybrid I’ve ever heard: The cones seem to add some body, but only within their frequency range. As the frequencies climb up to where they are handled by the panel, the sound character changes to my ears to that ghostly quality, so I am always aware of this discontinuity.

I’m not sure if this problem is solvable. Though, one brand I find intriguing is the JansZen speakers, using the electrostatic panels in more of a sealed box design. I wonder if those might maintain the palpabiity and body in the sound, but I’ve never heard them.

Ramtubes,

My bad. I rarely go to shows. I meant showrooms. Audio store showrooms I presume are set up to show the gear at some approximation of optimability.

By “more power” I’m just going by where I set the volume control before and after. It was a surprise, as I thought there would be less, and I was pleased because in my layman’s view it meant less stress on the tubes and circuitry.

There wasn’t much more volume, as the goal was simplicity, as you say; stability, as I have observed; and even more transparency in the mids, as I have also observed, though the Jensen caps also had something to do with the transparency eventually.

So, if you are building OTL triodes too, Jon is not correct. There are more than three. But are you using the same design approach? You guys should talk to each other!

Also, I’m not sure what you mean by better technology than cone speakers. First off, the Altec is a horn/cone hybrid. That aside, while electrostatics have their virtues, they don’t move air the way a cone does, as someone here also observed. That’s what I mean by the dynamic punch of the Altecs. I’ve heard some great horn speakers, with prices in the stratosphere. 

The serial number on my Altec dates them as 1954, the year I was born, lol. If it ain’t broke...