What contributes most to a change in how an amplifier sounds?

The on off switch.

The speakers with which they are paired.

You didn't mention capacitors, but you should have.

Whether the amp is wired in an ultrlinear or a triode circuit.  

Just like an entire audio system, an amplifier is a chain of circuits and parts that’s only as good as it’s weakest link. At some level, everything matters, but many folks feel that it all starts with the power supply.  In the case of tube amps, I can't help but think the quality of the output transformers is pretty important. 

My amps started as Dynaco 70s, then got a boost in the power supply that helped. Later on they got modified with the VTA circuit boards that address the power supply and audio circuit even further, better caps, etc....a;; very audible improvement with the same output tubes and transformers. Later I changed the output and driver tubes, then upgraded the rectification to SS. All made audible changes that I felt were upgrades. When I finally bi-amped the system in a horizontal configuration, the Dyna/VTA amps went from seeing a 4 ohm load to an 8 ohm load where the tube amps only drive the midbass and tweeters, and that made another very audible improvement. All of these changes contribute to what I’m hearing now, but I can’t say that any one of them was more important than the others. They all add up, and they all matter.

FWIW, I’ve always preferred them in triode.

A good design  helps a lot. 

Output impedience.

If you follow the graphics in Stereophile, you see that the higher the output impedience, the greater the variation in frequency response based on a real life speaker load that is not a simple resistor.

The loudness button.

The transformer is the beginning to great sound.  It has to handle the requirements of a recording.  If you think about it, why do different amplification from the same manufacturer sound different or handle music differently?  Quick Silver just stopped making one of their amplifiers because they could not source the transformers any longer.  We used to use Plitron transformers but they now require a minimum order of 100 pieces.  Designs are not new so depending on what you are looking for, a design is important to the sound and cost.  Power supply is the key to great sound.  That needs to filter AC noise, handle dynamic swings, etc.  Then capacitors and resistors have an impact.  Tubes vs. SS is personal preference.

Happy Listening.      

@bigkidz , I remember a conversation I had with John Barnes (may he rest in peace) of Audio Unlimited quite a while back.  He was talking about a couple of tube amps and I forget how he exactly worded it, but it was to the effect of when when comparing amps and you separate the wheat from the chaff it is the transformer that makes the difference.

The transformer.

Everyone forgets the power supply. It isn't as sophisticated as the amplifier circuit itself but it's actually the direct electrical connection to the speakers whose impedance interacts with the amplifier to great affect. The thing we think of as the amplifier is basically a valve that opens and closes the power supply supposedly as an analog of the input signal. So the better the amplifier does that the closer the output is to the input albeit larger. But that assumes the power supply is robust and pure. If it isn't even if the amp is accurate it's varying a changing source of current and the result is loss of fidelity.

It turns out many circuits are pretty good but power supplies are expensive and you can cheat with little or no change in the classic measured specs. The only thing that changes with a so so power supply is the sound. Power supply is a major factor why costly amps sound so good. There's money to make pretty good power supplies. But I suspect even 6 figure amps can be improved with even better power supplies.

Distortion signature and output impedance. 

1- whoever is listening.

2- location, local, location.

Power supply 

Power supply

Power supply

Power supply, quality of components in critical places, feedback, bias and even chassis design and quality. 

In a single-ended, no-feedback tube amplifier, it largely comes down to the output transformer.  Nothing else can make up for a poor OPT.  In a push-pull amp there's a bit more leeway because the OPT doesn't have to handle a large amount of standing current due to the cancellation.  Add global feedback and you can turn a pig's ear into a decent silk purse, as the saying goes.  But any tube amp is still going to benefit from quality iron.  As others have said, the power supply, the circuit design and other components can all make a difference.  Oh, and the power supply time three, as perkri says. ;-)

@thecarpathian 

😂😂😂👍🤦‍♂️ CLASSIC 

$

I would agree with @helomech on distortion signature. When people describe sound attributes of a power amp, it's likely the sonic signature the manufacturer was designing for. 

Audio Research’s WZ Johnson believed that the transformers were the make of break component in the quest for audio excellence.  

Without a doubt the power supply is critical. There is also the input stage, which if not done well will result in the output stage amplifying distortion and artifacts. 

The meters:  Instantaneous is far superior to averaging.  A common misconception is the color of the backlite illumination matters.  This is a myth.

One might also include OTL. 

Looks….If the amp looks ugly it will play as such. LOL

My experience is that the color of the housing is the most influential determinant. A shiney black case produces less harmonic distortion. And I agree that a good on/off switch can make a critical difference. 

In SET amplifier:

1. Output tube.

2. Driver tube.

3. Coupling between stages (transformers and capacitors).

4. Cathodes (cathode or fixed bias, cathode bypass capacitors size and quality, resistors).

5. Signal transformers quality. Output, interstage, input.

6. Power supply. Fist capacitor quality. B+ capacitors quality and size. Voltage stabilization. Power transformers and chokes.

I had a 300b integrated SET amplifier from 2005.

I tweaked a lot of different things:

1. Interstage capacitors.

2. Tubes working points.

3. Cathode and load resistors.

4. Power supply capacitors. Including increased value of capacitors from 100uf up to 3500uf per each tube b+.

5. Cathode capacitors. Including increased value of capacitors from 100uf up to 100000uf.

6. Added interstage transformer for driver and input tube.

7. Added a separate power transformer for drives and input tubes.

8. Build a new 300B SET with external power supply.

9. Changed driving tube from 6f6 to 6v6 and 6L6.

10. Changed output transformers.

I didn’t try to do:

fixed bias, voltage stabilization, SRPP, choke load (LC coupling), direct coupling and many other things.

Hardly any mention of AC cable.  It makes a difference, and it's something users can often change, unlike most of the other components.

@knotscott

You certainly know your way around the inner workings of the mystery boxes in an audio system and how cool to have you as a neighbor. So much knowledge between your ears.

Seems like the power supply and transformers, no surprise, dominate how an amplifier sounds. I’ve always wondered why amplifiers don’t have a second Power chassis but this clearly would be impractical. Capacitors certainly influence the rebustness of amplifier dynamics and I would guess these wear down overtime.

I, like you, pursued biamping, and I use a MC 901 pair from McIntosh. a more safe approach for me by ensuring added amplifiers Will get along and avoids additional interconnects. I upgraded all the small tubes with NOS telefunken but have continued with the same power tubes I'm not sure how much these will influence sound but quite a price tag to replace them all.  

You have a nice size room and a lovely space. My amplifier does quite well in a 20 x 16 room but is deserving of a much larger space.

@alexberger 

You need to have a play date with.  @knotscott 

I saw your YouTube channel wondered how it might be you could do a narrative of the types of work you do with your system.  Inspiring to see people with all this knowledge and putting it to good use.  Very very technical stuff.

Hi @emergingsoul ,

This is a good question.I thought about it, to make stuff about tweaks on youtube. But my English is not good enough to do it. English is my 4th language. I am also not a good speaker in general. For me it is much easier to write.

Reminds me a bit of the old story where organs of the body are having a fight over who was most important.  Can’t remember what the plot twist was — something like the little toe saving the day.

But the moral was the organs make up a team, all of which is “most important” depending on what is going on.

Don’t forget how you isolate them from resonance and vibrations. 

All of it contributes.  The weight of an amp is its most important spec.

About twenty years ago I bought a pair of old, used Altec-Lansing 1568A mono amplifiers in nice shape, they had spenent their lives in a rack.

Those 1568A’s are simple, lightly stressed designs, made to run 24 hours a day, using two EL34 tubes in a push-pull configuration to deliver a clean 40 watts.
They also have some of the finest transformers ever put in an amplifier, second only to the legendary output trannys found in the Harman-Kardon Citation II.
Any tube amplifier made today, regardless of price, except for some insanely expensive Ongakus, has transformers that cannot hold a candle to those on those Altecs and the H-K Citation.

But the Altecs also had anemic and primitive power supplies. Too simple.

Upgrading a tube amplifier power supply is really not too difficult, and these had plenty of room to work in.
So I went to town on these, replacing the PS caps with new oversize electrolytics with poyptopylene bypass caps.
I also also added a filter choke. A slight hum disappeared completely, All the signal caps were updated with Polypropes. All the resistors were replaced with new carbon films
Finally two NOS sets of Philips EL-34’s finished the job.

Those old Altecs put my McIntosh MC-60’s to shame. Greater slam in the bass, smoother mids, and the highs were just plan gorgeous, silky and detaled, into my JBL C50/S7 speakers.
I soon sold the Macs for $2000, and the total cost of those Altecs including the mods was about $700.00.

Downside: These Altec 1568A amplifiers are just plain ugly to look at.
Just put them somewhere you don’t have to see them.

Stock

Modded

Marc Stager
https://silversolids.com/

The listener

The room

The speakers

In that order.  

Of course it’s also nice to have an electricity supply, a switch to control that, and, I kid you not, a volume control is absolutely necessary.  
 

42

The cathodes are one of very important issues in SET tube amplifiers.

Some people use a fixed bias solution for the SET output stage. But there is the same issue in the input and driver stage and most designers do nothing to solve this problem. The problem is there are 2 signal paths (input and output) that go through each cathode. There is a Lynn Olson article about it.

There are 3 solutions: using fixed bisa, using batteries and using huge value capacitors (DIY enthusiast Yuri Makarov is another of this 3rd solution).

I tried the huge value capacitor solution (100,000uF with AN Kiasei NP 50uf bypass) in my SET amplifier first stage and driver stage.

The result exceeded my expectations. Much bigger 3D soundstage, better instrument separation, deeper and more controlled bass.

The most difficult was the solution for the output tube cathode. I afraid to use fixed bias. I think it is not safe. I also can't use 100,000uF because it is a strong output tube current for a long period of time after switching on while big cathode capacitors are charging. So I put 7000uf + 50uf AN Kaisei + 50uF Kemet DC-Link. It worked but I could hear the drawbacks of Kaisei capacitors. So I added Siemensk MKV 5uf + Duelund Cu-Sn bypass + 6000ps SGM3 silver mica.

In addition to my cathode experience,

I assembled a new 300B amplifier with external power supply. Most parts were reused from my previous amplifier but the basic break-in took 2 month. After that I started to recognize whatever I tried to do and tweek the sound of my SET amplifier was always sterile. And it was very strange for a 300B set amplifier.

In the end I decided to change the driver tube from 6f6 to 6v6. And I have to change the cathode resistor to increase 6v6 idle current. I bought a new AN tantalum resistor for it. At the same time I decided to change the input stage  (6sn7) cathode resistor from Vishay Z-foil to the Shinkoh tantalum resistor that I used previously in the driver (the value of the resistor is matched). The difference between driving tubes 6f6, 6v6, 6L6 is another story, BUT since I changed Vishay Z-foil to Shinkoh, my amplifier no longer sounds sterile anymore.

Application 

In short, speakers and listening environment. 

IMHO amplifier is more important than speakers and sources. 

Reminds me a bit of the old story where organs of the body are having a fight over who was most important.  Can’t remember what the plot twist was — something like the little toe saving the day.

But the moral was the organs make up a team, all of which is “most important” depending on what is going on.

@davetheoilguy    when you go into cardiac arrest, I think the answer to the above will be clearer.

@immatthewj 

When you die a horrible painful death from liver cancer, screaming for relief to come, think the answer to the above will be clearer.

Seriously, what a horrid thing to say.  Grow up and get a life.

All the organs were deciding who should be the boss....

"I should be in charge," said the brain , "I run all the body's systems, without me nothing would happen."

"I should be in charge," said the heart , "I circulate oxygen and nutrients all over."

"No! I should be in charge," said the stomach, "I process the food that gives us energy."

"I should be in charge," said the legs, "without me the body couldn't go anywhere."

"I should be in charge," said the eyes, "I allow the body to see where it goes."

"I should be in charge," said the asshole, "I am responsible for waste removal."

All of the other body parts laughed at the asshole and insulted him. So he shut down. Within a few days, the brain had a terrible headache, the stomach was bloated, the legs got wobbly, the eyes got watery, and the heart pumped toxic blood. They all decided that the asshole should be the boss.

What is the moral of the story? Even though everybody else does all of the work some asshole is usually in charge.

@davetheoilguy , the heart perfuses all of the organs, including itself and the liver; the liver will die if it is not perfused for a long enough period of time (cardiac muscle will die a lot quicker from absence of perfusion).

When heart rhythm that produces a pulse ceases, one is clinically dead. Liver function can cease but that does not meet the criteria for clinical death. Liver cancer can have a favorable prognosis, and if it doesn’t you will still have time to get your affairs in order as quality of life declines. On the other hand, if you go into cardiac arrest, if you are not in the right place and around the right people your life expectancy usually drops to under ten minutes.

I think we’ve strayed a little off topic…..