Amplifier Output Impedance - Erin's Gear Synergy Video

[PristineSound]

@RickS, can you merge?

 

[Matt_Holland]

What's not discussed here is another effect of using high output impedance amplifiers to drive very efficient loudspeakers in relatively small listening rooms--the reverberation effect. This, of course, is not on the recording, but added to the "second room" acoustics--your listening room. I strongly believe that this is the "magic" that one gets from using amplifiers of high output impedance: more low-level reverberation induced from in-room acoustic reflections (less than -40 dB SPL...and mostly at lower frequencies).

Chris

Interesting. Has this effect been measured?

 

[Chris A]

Yes. Unfortunately, the K-forum has been down for some time (almost a week). When it comes back up, you can try this (IIRC):

https://community.klipsch.com/topic/157466-speaker-microphone-and-room-reverb-effects/

Chris

 

[krabapple]

Might was well drop this here like I did on the other thread where this is being discussed :


Gee, everything old is new again!

E. Brad Meyer writing about load conditions under which two amps will "sound different":
"The Amp/Speakers Interface, are your Loudspeakers turning your amp into a Tone Control?", Meyers, E. Brad, Stereo Review, Jun 1991, pg 53-56.

 

[PristineSound]

"Nothing to see here."

We know amps who's frequency response are load variant and frequency variant will behave like this. Nothing new. In the realm of accurate sound reproduction, these amps are considered subpar amps and you shouldn't even be entertaining these amps to begin with if your goal is the pursuit of accurate sound reproduction.

If you enjoy some spunk and color, of course you can go for these amps, it's your money and your decision not to mention, sometimes, it's fun to change things up.

 

[JohnnyNG]

Pretty well-known, I think Stereophile has been testing this for ages.

 

[DanielT]

One of the most common pictures of "audiophile" setups includes a single single-ended triode (SET) amplifier mono-amping loudspeakers (either small direct radiating loudspeakers or large horn-loaded designs of much higher efficiency). Also absent from these pictures is any hint of digital PEQ capabilities to rebalance the amplitude and phase response in-room.

SETs are tube-type amplifiers that typically do not have negative feedback to lower their output impedance (because they don't have enough forward loop gain to sustain effective negative feedback). There are also tube-type amplifiers that do have negative feedback and sufficient output transformer capacity. The problem amplifiers highlighted here are generally not the push-pull tube amplifiers having sufficient amounts of negative feedback to lower their output impedance--and this should be noted (...not that I would own any of them).

So when you read that the SETs bring "magic" to the table in so-called hi-fi setups, it's now obvious that it's really the unknowing owners that are using one type of high-output impedance amplifier non-linearity (the subject of this thread) to cover other loudspeaker and room-reflection-induced nonlinearities--without the owners taking the time to acoustically measure what is occurring. This should be one of the takeaways from this thread, IMO.

What's not discussed here is another effect of using high output impedance amplifiers to drive very efficient loudspeakers in relatively small listening rooms--the reverberation effect. This, of course, is not on the recording, but added to the "second room" acoustics--your listening room. I strongly believe that this is the "magic" that one gets from using amplifiers of high output impedance: more low-level reverberation induced from in-room acoustic reflections (less than -40 dB SPL...and mostly at lower frequencies).

Chris

Damn expensive are those tube amps too. Better, for your wallet and flexibility, to instead have an amp that doesn't mess with FR and/or adds distortion, then, if necessary and/or desired, plug in an EQ and get the FR you want. In addition, you still need to change the EQ in the lower frequencies due to the room's influence. That regardless of how good the amp and speakers/subwoofer you have. Something that you and I suspect most people reading this thread already know.

If you want to add tube amp distortion, you can, for example, use @pkane's......

PKHarmonic VST Plugin - Audiophile Harmonics Generator | Distort documentation

PKHarmonic 1.0 is the initial release of this software. Use at your own risk!

distortaudio.org

...for that:

Screenshots from this thread:

What electronic audio products you want tested most

Would like to see a new set of headphones (reasonably priced) reviewed. MEZE AUDIO 105 AER | Wired Over-The-Ear Lightweight Audiophile Open-Back Headphones Regards, Greg

audiosciencereview.com

Edit:
I say as I always do regarding tube amps. It is for those knowledgeable in electronics to keep as a hobby. DIY tube amps, maybe renovating old treasures to keep old stone age tubes working. Making an effort for the history of electronics that is.

 

[Soniclife]

What's not discussed here is another effect of using high output impedance amplifiers to drive very efficient loudspeakers in relatively small listening rooms--the reverberation effect. This, of course, is not on the recording, but added to the "second room" acoustics--your listening room. I strongly believe that this is the "magic" that one gets from using amplifiers of high output impedance: more low-level reverberation induced from in-room acoustic reflections (less than -40 dB SPL...and mostly at lower frequencies).

That's presumably similar to what happens when you play vinyl loud, my assumption is that occasionally I like the added reverb at low frequencies. If this is a real preference DSP seems the sensible way to add it.

 

[tengiz]

What's not discussed here is another effect of using high output impedance amplifiers to drive very efficient loudspeakers in relatively small listening rooms--the reverberation effect. This, of course, is not on the recording, but added to the "second room" acoustics--your listening room. I strongly believe that this is the "magic" that one gets from using amplifiers of high output impedance: more low-level reverberation induced from in-room acoustic reflections (less than -40 dB SPL...and mostly at lower frequencies).

This is cool! What’s interesting is that no audiophile tweak can address it - even in principle. Unlike other old-school "microphonic effects," whether real or imagined, this one is completely immune to remedies like cable elevators, anti-vibration stands, fancy feet, or isolation platforms. None of that will make the slightest difference. The only real fixes involve changing the amp, the speaker, or the room. So, in the spirit of 'if you can’t fix it - embrace it" I can imagine that, for a certain category of audiophiles, it’s actually a welcome feature - not a flaw.

 

[Chris A]

I can imagine that, for a certain category of audiophiles, it’s actually a welcome feature - not a flaw.

Well as you can see from the link in your quote, Bob Carver himself professes to enjoy that reverb effect.

His "Silver Seven" amplifiers pushed the SOTA in the late 80s--at $17.500 (in 1988 dollars...equivalent to over $47K USD today). He kept selling out of those expensive models. He later built a SS amplifier that he called the Silver Seven-t that cost less than 12% of those tube amplifiers but was apparently indistinguishable in sound quality from the tube versions. That was all Bob Carver.

Remember that it was Carver who won The Audio Critic/Stereophile amplifier challenge in 1985. Carver took up physics at university then started building amplifiers inside empty coffee cans, etc. that had more available (clean) power than anything else on the market. He then started Phase Linear corporation selling very powerful but very good sounding amplifiers. The rest is history.

Chris

 

[PGansz]

It's bizarre to me how many people keep saying: "nothing new here". As if everyone in the world is a bad ass electrical engineer and should just be born with knowledge.

There's nothing new about gravity, yet it's taught all year round every year and will be throughout the course of humanity's future.

Seriously people, lighten up. Sharing facts regarding audio equipment to inform judgement in a scientifically literate fashion is a win for all involved.

 

[tengiz]

It's bizarre to me how many people keep saying: "nothing new here". As if everyone in the world is a bad ass electrical engineer and should just be born with knowledge.

There's nothing new about gravity, yet it's taught all year round every year and will be throughout the course of humanity's future.

Seriously people, lighten up. Sharing facts regarding audio equipment to inform judgement in a scientifically literate fashion is a win for all involved.

Allow me to offer an explanation for the facet of the reaction you observed.

Output impedance used to be a basic spec for amplifiers - right alongside frequency response, RMS power, and total harmonic distortion. It wasn't buried in a data sheet like some obscure detail. But as amplifiers with very low output impedance became the norm, this specification slowly disappeared from prominent spec sheets. You can still find output impedance charts in technical documents, but they're usually not included in the headline specs. This omission can make it seem, incorrectly, as if output impedance is now irrelevant. You rarely see it mentioned in marketing materials.

Of course, it's always great - and reasonable people welcome it - when fellow audio enthusiasts learn new technical facts. What's frustrating is that the industry (or whoever's responsible) has allowed this once-basic information to become something you have to "discover" as if it were esoteric knowledge.

 

[PristineSound]

It's bizarre to me how many people keep saying: "nothing new here". As if everyone in the world is a bad ass electrical engineer and should just be born with knowledge.

There's nothing new about gravity, yet it's taught all year round every year and will be throughout the course of humanity's future.

Seriously people, lighten up. Sharing facts regarding audio equipment to inform judgement in a scientifically literate fashion is a win for all involved.

I see your perspective, but consider this:

• There are ample amount of amps on the market that are load and frequency invariant. And has been for decades now.
• This is not new information in the world of amplifiers, maybe it is for some individuals as consumers, but in the world of amplifiers, especially for those who engineers them, this is nothing new.
• The reason why some people are coming here to say "nothing new", or at least why I am doing it, is because Erin's video comes across as if this is some sort of revelation and the video caption itself is also very click bait. Additionally, I can easily see this video be weaponized by the subjectivist community to say: "ah-ha, one of your very own darlings has vindicate us after all the years of you mocking us. I am waiting for Erin to prove cables make a difference." Something like that? Maybe, maybe not?
• Archimago and Gene DellaSala has talked about this topic for years.
• Most often times, load and frequency variant amps are budget amps or (as demonstrated in this video) tube amps. Most half way decent SS amps wouldn't have this problem. You can buy an Adcom amp off of Facebook market place for $200 and it won't have this problem.
• Also did you know that Erin also did a video sometimes back where he DB ABX two SS amps and he heard zero difference?
• Lastly, this topic is frequently talked about on this forum, or at least I have mentioned it few times.

IMO the specs to look for in an amp in order of priority are:

1. Load and frequency invariant, while this is number 1 but most half way decent SS amps are.
2. Power output, this implies thermal management and power supply capability.
3. SINAD, the reason why I put it as number 3 is because the threshold of hearing is rather high tolerance.

 

[PristineSound]

I will say however, there is absolutely value in this video and it should be made. Despite that this topic has been talked about many times over, having this content from another reputable reviewer is only good for the hobby.

 

[levimax]

If you want to hear what your speakers would sound like with a SET amp you can just put a 5 ohm resistor between the amp and speaker. The FR change is easy to measre and it will cost only pennies.

My issue with the video is the word "Synergy" which implies something better. Higher output impeadance is just as likely to make your speakers sound worse than better.

 

[Karmacoma]

• The reason why some people are coming here to say "nothing new", or at least why I am doing it, is because Erin's video comes across as if this is some sort of revelation and the video caption itself is also very click bait.

This.
Erin has made several good educational videos, which makes this move hard to understand. The whole angle of approach he chose in this one to talk about the damping factor is really different. Let's hope he won't keep doing that, I mean he's trying something different obviously to touch a wider public and be catchy i get it but it's a bit of a miss imo.
His previous videos were like '' here's why distorsion/directivity/whatever is important or sucks ''. Now this one could have been called '' ''what is damping factor and why is it important'' (which isn't catchy at all ok) but instead he chose a misleading approach imo, ''no, all amps don't sound the same'', the answer to that question being in the end, without being answered clearly, ''because some amps suck!/are poorly designed, just don't buy them". I might be wrong but there's no real advice here, cos he trapped himself by using the old synergy fallacy to get some visibility, so he couldn't give a real good advice which IS what we expect from him.

 

[PristineSound]

My issue with the video is the word "Synergy" which implies something better.

The word "synergy" has been the marching call of the subjectivists.

The idea of 'system matching" for "synergy" is portrayed as some kind of art, orchestrated by a sommelier who has gone through decades of apprenticeship and training. It portrays audio as some sort of craft by beard artisan men.

 

[RexrothPigeon]

If you want to hear what your speakers would sound like with a SET amp you can just put a 5 ohm resistor between the amp and speaker. The FR change is easy to measre and it will cost only pennies.

My issue with the video is the word "Synergy" which implies something better. Higher output impeadance is just as likely to make your speakers sound worse than better.

Yeah, synergy is really misleading here. Can only hope that was out of ignorance rather than conscious dishonesty.

 

[PGansz]

I don't agree that "synergy" shouldn't be used.
For the very fact it struck a chord with you, is the opposite chord being struck with that community, luring them in, to watch a video about how an amp they likely purchased is coloring their sound. Perhaps even masking their poor choice in speakers.

I state this because that community is more likely to buy subjective-description-only audio components. Maybe even from Crap-ton, and with holes in the cabinet.

I appreciate the discussion folks.

 

[Chrispy]

LOL Synergy is real is just offputting and when I start the video its about stupid tube amps....