This all reads like an advertisement for high efficiency speakers and low output amps: large power supplies generate more noise and stronger electric fields. So rather than muscle amps first Watt focus seems the better approach.
An Audio Conversation with ChatGPT
This is long but I hope you find it interesting. I learned quite bit and it only took a few seconds to get answers. First some background information.
My Accuphase P4600 Class AB amplifier has four gain settings with associated voltage required to drive the amplifier to full output. The amplifier is rated at 150W @ 8 Ohms, 225W @ 6 Ohms and 300W @ 4 Ohms.
28db Gain requires 1.37v
25db Gain requires 2.05v
22db Gain requires 2.74v
16db Gain requires 5.48v
I use my MSB Discrete DAC as a Preamp. It has two output impedance settings. 300 Ohms that delivers 3.57v and 150 Ohms that delivers 1.785v.
So I have many combinations of output voltage and amplifier gain. If I want access to full amplifier output and have the best technical match I would need to select 28db gain and 150 Ohms or 22db gain and 300 Ohms. In both cases the voltage exceeds the required amount needed. I’ve tried many of these combinations and I consistently find the best sound results when I select 16db gain requiring 5.48v and 150 Ohms delivering 1.785v. This combination provides the most transparent, open soundstage with the greatest depth and the smoothest silken highs. It also provides the blackest background, imaging and instrument separation. The difference is quite clear and preferable.
So I was interested in understanding just how may watts I have available, what headroom I have for peaks and what sound pressure levels I can attain. I have Harbeth C7ES-XD speakers rated at 6 Ohms and never dip below 5.2 Ohms. Their sensitivity is 86db and I sit 2.5 meters from the speakers. I listen to mostly Classical music but also Jazz and Pop. I find that I never register more than 70db on my sound pressure readings and this is usually the peaks. After describing this environment to ChatGPT it responded with the following minus all the formulas it used to reach the conclusions.
Based on the numbers we’ve calculated, you have far more power available than you need to hit a maximum level of 70–72 dB at your listening position. Here’s a brief recap:
1. Power Required for 70 dB:
We found that to reach 70 dB at 2.5 m, you need roughly 0.16 W at the speaker.
2. Your Available Power:
With your amplifier settings (1.785 V into an amplifier that needs 5.48 V for 225 W full output), you’re getting about 23.8 W available at the output.
3. Resulting Headroom:
When calculating the maximum SPL at 2.5 m from your 23.8 W, the speakers (rated at 86 dB at 1 W) would produce around 91–92 dB at that distance in a free-field environment. This gives you roughly 21–22 dB of headroom above a 70 dB listening level. Conclusion:
Since your listening peaks (70–72 dB) are far below the maximum SPL your system can produce (over 90 dB at 2.5 m), you indeed have ample headroom. This headroom not only ensures clean, undistorted sound at your listening level but also helps accommodate dynamic peaks without stress on the amplifier or the speakers.
Then I asked it why does this low gain and power limited combination sound the best. It responded.
There are several reasons why running the amplifier at a lower gain with a lower input voltage can sound subjectively better—even if it provides less maximum power:
1. Optimized Operating Range:
When you set the gain and input level so that the amplifier is not pushed near its limits, it tends to operate in a more linear (and therefore less distorted) portion of its transfer curve. Even though you’re using less power overall, you’re using the amplifier in its “sweet spot,” where it performs most cleanly.
2. Improved Signal-to-Noise Ratio:
High gain settings amplify not only the signal but also any noise present in the signal path. With lower gain and a well-matched input level, you reduce the risk of amplifying unwanted noise. This can lead to a cleaner, more refined sound even if the maximum available wattage is lower.
3. Reduced Clipping and Distortion:
By keeping the amplifier far from its maximum output, you greatly reduce the risk of clipping or other forms of distortion. Clipping introduces harsh artifacts into the sound, so even though you have extra power available, avoiding the edge of clipping is more important for sound quality at normal listening levels.
4. Headroom for Dynamic Transients:
Although you’re not using the full power, having extra headroom means that sudden, dynamic peaks in the music can be handled without distortion. This dynamic reserve contributes to a more natural and engaging sound.
5. Matching with the Listening Environment:
In your scenario, to achieve a comfortable listening level (70 dB) at your distance from the speakers, you only need a fraction of the available power. Running the amplifier with lower gain means you’re better matching the actual listening requirements, which can help maintain clarity and detail without overdriving the speakers or the amplifier stages.
In summary, even though the lower gain and lower input voltage setup yields less maximum wattage, it places the amplifier in a region where it produces a cleaner, less noisy, and more dynamically controlled signal. For typical listening levels (like 70 dB), that clean performance is more desirable than having a higher power output that might be prone to distortion or unwanted noise when not carefully controlled. And some final thoughts about the Accuphase amplifier.
The Accuphase P-4600 is designed with a very high level of performance and low distortion in mind. Although its rated output is 225 watts, much of its sonic magic comes from operating in a pure Class A mode for a significant portion of its output range. Here’s how to think about it:
1. Design Philosophy of the P-4600:Accuphase amplifiers are built so that—at typical listening levels—the output stage operates in its most linear (Class A) region. Many high‐end designs like the P-4600 are engineered so that the devices remain in Class A for anywhere from roughly 10–20% (and in some designs even more) of the full-rated output. For a 225-watt amplifier, that suggests that pure Class A operation might extend up to around 20–40 watts per channel.
2. Everyday Listening Levels vs. Maximum Output:
In your typical listening scenario (for example, when you’re hitting around 70–72 dB at your listening position), you’re using only a tiny fraction of the maximum 225 watts—on the order of a few tenths of a watt at the speakers. This means that in day-to-day use, the amplifier is operating very far below its rated maximum and is comfortably in the Class A regime.
3. The Benefit of Having a 225-Watt Amp:
Because you have a high-rated amp, you have plenty of headroom. This allows you to use a lower overall gain and ensures that even when you do increase the volume (within reason), you’re still likely to remain in the clean, linear portion of the amplifier’s operation. In other words, the high maximum power rating gives you flexibility and helps keep the amplifier in its low-distortion Class A mode during normal operation.
4. An Approximate Range:
While exact bias conditions are proprietary, many reviewers and experienced users suggest that for Accuphase designs like the P-4600, the output stage remains in pure Class A operation for output levels on the order of 20–40 watts per channel. That means under normal listening conditions—even if you dial up the volume beyond your current 70–72 dB level—you’d likely be within the Class A zone until you get into the higher output demands. Once you push beyond that, the amplifier may start shifting toward Class AB operation for very high-power peaks.
• For everyday listening (70–72 dB), you’re using only a very small fraction of the amplifier’s potential—and you’re deep in the Class A region.
• The P-4600 is designed so that for a significant portion of its output (likely roughly 20–40 watts per channel), it operates in pure Class A.
• The high wattage rating is not “wasteful” at all—it ensures that you have plenty of headroom and can run the amp at lower gain settings for the best sound quality, while still having the capability to handle demanding music passages without distortion.
So, even though you might only be using, say, 0.2–0.3 watts at the speakers for your typical listening level, the amp’s design ensures that all of that output (up to perhaps 20–40 watts) is delivered in the pure Class A region. This is a key reason why many enthusiasts appreciate the sonic qualities of the Accuphase P-4600.
19 responses Add your response
That is very interesting and enlightening really. The amplifier in my main system is a Conrad-Johnson 27A, 36 watts, class A. My speaker rated efficiency is 89 db at one meter. My listen levels and musical choices are similar to yours. At no time has there ever been any indication that my amp is stressed at all and this explanation seems pertinent to my situation as well. Thank you for sharing. |
One thing I’ve learned when using ChatGPT and other AI resources in my day-to-day work environment is that the quality of the AI’s output is very dependent upon the amount of detail in your initial query and subsequent follow-up queries. Even the basic AI search capabilities that Google uses in its current search engine can have excellent results. The adage "garbage in, garbage" holds very true for AI. It can be a great tool to use, especially when searching for more sources of information to use. I think you’ve demonstrated that hi-fi enthusiasts can/could use ChaptGPT or other AI tools to help them better match components on a measurement level to help narrow the field of potential choices and that would help someone, especially if they’re just getting into the hi-fi hobby, to avoid expensive mistakes trying out various components when building up a system. Many of us rely upon several "squishy" factors when determining whether or not an upgrade is worth the effort. Those squishy factors are hi-fi reviews, recommendations from friends or forums, and most importantly our personal listening environment, tastes, and ears. As the OP has demonstrated, AI can help dial in your system by eliminating a lot of trail and error in that process. I'm surprised that I haven't thought of using AI in this way before but will in the future. So thank you for this. |
Yes it’s amazing how important it is to get the right match between amplifier gain and pre output voltage. And to understand why a high powered amp running at its lowest gain and limited watts can actually sound the best in certain circumstances. Also high wattage is actually needed so that when you use the lowest gain and input voltage there is still enough residual power to provide significant headroom. These concepts I really didn’t understand before. When purchasing my amplifier I had also considered the Bryston 4b3. That amp had two gain settings: 28db and 22db. I would have used the 23dv setting so it would have been similar to my Accuphase 22db setting which I did not prefer when compared to my Accuphase 16db setting. So when purchasing an amp/pre combo it’s important to listen to these various mixes of gain and output voltage. To me the sound is noticeably different. One isn’t bad and the other good. They are just different and you will likely strongly prefer one over the others. One other advantage running at low gain and low output voltage is I can set the volume on my DAC/PRE at a very high position. This eliminates any potential for digital volume loss. My DAC volume range is 0-106. I have it set at 88. |
@jfrmusic The above is a bit of hallucination. The level of class A operation has nothing at all to do with this. You can't hear the 'transition' and the amp isn't any more linear in the 'class A' region than it is a few Watts above that. If this was a real intelligence with access to the knowledge available on the internet, ChatGPt would have know this. But all 'artificial intelligence' is prone to hallucination as DeepSeek has shown. The other bits about gain riding and such are spot on. All I'm saying here is that you do have to be wary.
|
Good to know and I’ve wondered about this, and any discernible differences just before / during / after transition from Class A to AB. So then, what % into Class AB is it that you know or can hear you are no longer in Class A and now into AB? When my current amp was reconfigured from Class AB to Pure constant-on Class A operation, the amplifier did sound different, noticeably, particularly so at 1-2hrs of full warmup for whatever reasons I cannot begin to technically explain or try to. |
Ive been tinkering with AI: ChatGTP, Gemini and CoPilot. ChetGTP gave a quite informed and refined answer, which indicates the OP has built up a ’memory’ in ChatGTP of similar enquiries from to and fro interrogating its responses from which ChatGTP has learned to provide better responses to the OP. This type of answer is a really good starting point and quite probably cuts very close to the chase. But it pays to verify with human analysis and observation. IME ... Gemini is also very good but needs a bit more work to get an answer as good as ChatGTP. Copilot M365 (subscription) is not in the same league, and its online chat app is not very intelligent or good at responses. ChatGTP gives better responses than CoPilot M365 even after I used all my GTP-4o mini quota, that is the free backup AI is better than MS paid premium AI. Someday I’ll try Gemini Advanced to see how that compares to Chat GTP-4o mini. On the audio subject, I use dual mono Devialet at 440w per channel to each drive a stand mount speaker. While the volume dial is not what I’d call low (often abput -14dB), the sound level is usually relatively low (not close to what the volume dial suggests, or how loud it sounded at -14dB when the noise floor was higher). For those who dont know, Devialet is Class A voltage driven with Class D current. |
So then, what % into Class AB is it that you know or can hear you are no longer in Class A and now into AB? @decooney If the amp is at all competent you won't know/hear any transition. IOW there isn't a percentage. |
Good to know. And this could open the door for me to look at other Class A/AB amps I’d potentially consider for the future over my current pure Class a 50w amp. A different angle to the question, please:
The tech is an expert in the brand I have, and really pressed me, multiple times, to permit him to reconfigure it to "pure Class A", "constant on", using different transformer taps, at his very strong suggestion. I went for it. Tech indicated it would be "smoother sounding", "more bottom end", "less grain to the sound", possibly more texture and nice tone. Biased up from 47C to 50C at the heat sinks now, right "at the ceiling limit" for this amp, as I was informed. All of that turned out to be TRUE with the sound, after getting 80-100hrs on the amp. What type of Class A is it?: I’m guess I’m still hung up on what Class A sound really is with a Class A/AB amp, compared to what "Pure, constant on" Class A amplifier configuration is and how I can hear a difference now configured as Pure Class A. And, exactly how he told me it would be. Not sure how to explain it, but i do hear a difference at low volume. Maybe you can explain it in a technical sense, I can only report what I hear that now sounds different as reconfigured. This has me currently excluding Class A/AB amps that I probably could be looking at more. That’s all. |
Since we're on the topic, do you think there is any perceptible sonic difference between a "pure" class A amp and another amp which is running in class A but will soon move into class B? Suppose, for the sake of argument, they are nearly identical amps except one is Class A all the way and the other is Class AB but stays in class A for a while. In those early phases, then, any perceptible difference you think? |
@hilde45 There's no correct answer for all amps- you have to take it on a piece by piece basis. Customers say our class D amps sound better than class A amps they've heard. @decooney There's no 'class A' sound. There is only what sounds musical and right (neutral). The amp you're talking about apparently benefited from the mods done to it- that's all you can really conclude. I've got a class B tube amp here in the shop that we recently refurbished. It was made by Electro Voice in the mid 1950s. It has no artifacts that you can either hear or measure that might lead you to think its a certain class of operation. When you play it, it sounds like a good tube amp. Put another way, its all in the design and how competent that design is, as well as how competent the execution. |