I must say that I agree with JC here. One should focus measurements at realistic levels, not at the extreme. What's the point of measuring a preamp at output levels up to tens of volts when the preceding poweramp usually clips at 2-3 volts input level. And in the case of the JC1/JC2 combo (400 watts), the distortion in the preceding loudspeaker is in the tens of percent.
Nelson Pass has a good point on this matters with his "first watt" philosophy. When I listen to music, my amp seldom puts out more than a few watts, usually even less. The distortion in our ears also increase dramatically with listening level. To be able to detect low level distortion we must listen at 70-80 dB SPL, if I remember the figures from ARA correct.
Nelson Pass has a good point on this matters with his "first watt" philosophy. When I listen to music, my amp seldom puts out more than a few watts, usually even less. The distortion in our ears also increase dramatically with listening level. To be able to detect low level distortion we must listen at 70-80 dB SPL, if I remember the figures from ARA correct.
Sensible, 2 Quad. I have never, in recent years, been a true believer in ultra low distortion for its own sake. I seriously don't believe that .01% 3rd harmonic distortion is audible in a worst case situation. It is just too small of an amount, compared to loudspeaker, analog magnetic tape, and perhaps other distortion sources. I also believe that analog magnetic tape works as well as it does, because it behaves essentially like a fet class A circuit in its distortion profile, which predicts, for example, only .1% or less distortion at -10Vu, which is where most of the signal level is, close to the proverbial 'first watt'. Distortion, in my case is many 100's of times lower than this at this level, even with the Parasound JC-2.
Now, is the JC-2 therefore 'perfect'? Of course not. The CTC Blowtorch has been shown to exceed it, not surprisingly, and I can predict several other quality, (and probably much more expensive) preamps will too. Think of the Parasound as a high level Honda, not a Porsche or a Mercedes.
Now, is the JC-2 therefore 'perfect'? Of course not. The CTC Blowtorch has been shown to exceed it, not surprisingly, and I can predict several other quality, (and probably much more expensive) preamps will too. Think of the Parasound as a high level Honda, not a Porsche or a Mercedes.
I won't disagree that better MEASUREMENTS can be made by using alternative topologies or further complexity. For example, a feedback pair (4) on each input device 'might' significantly reduce this sort of distortion generation. Halcro does something similar. Still, I designed it for 2V out to be very clean and am less concerned what comes after. IF I was building a pro system with +4 to +30dBm output, then this might not be the best solution.
If all we were concerned about was measurements I think we'd all be using good op amps.
But, I think the overall system needs to have good overtones. I mean all stereo systems have some distortion and putting together a system as a whole that has good overtones, as opposed to bad ones, is important. So, maybe a preamp or other gear has some distortion products that are maybe pleasant sounding, but maybe that helps the over sound and experience for the listener to get involved in the music.
That's not commentary on John's JC 2! Just want to mention that I read in stereophile that the JC 2 and Charles Hansen's Ayre preamp are two of his favorites.
But, I think the overall system needs to have good overtones. I mean all stereo systems have some distortion and putting together a system as a whole that has good overtones, as opposed to bad ones, is important. So, maybe a preamp or other gear has some distortion products that are maybe pleasant sounding, but maybe that helps the over sound and experience for the listener to get involved in the music.
That's not commentary on John's JC 2! Just want to mention that I read in stereophile that the JC 2 and Charles Hansen's Ayre preamp are two of his favorites.
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Not necessarily. Most opamps are poor in slew rate and have very low output stage idle current. It is very difficult to find very fast and very low distortion opamp. The ADA4898-1 is one of the very few, and very good sounding.
That's the key, IMO. Small added content of 2nd and 3rd may make sound seemingly more pleasing for many listeners, hiding some natural rawness. But, even 0.03% of 3rd changes natural spectra of acoustic instruments. You may start to have troubles to distinguish if you hear Oboe or English horn. Cello playing in low key may start to sound as Double Bass playing in higher key. Philharmonic orchestra is loosing definition and resolution. For this reason, I do not like sound of tubes, though the others consider them superior.
There's another aspect to this. Differences between (pre) amps are often related to how they handle large signals and overloads. It may well be that at the 1-watt level, differences are moot. But it's when the 20, 50 or 100 watt peaks occur that differences become audible.
So there are good reasons to build preamps that can output 10V RMS if only to make sure that they never clip. These are good reasons to make sure the distortion at high output levels stays low.
After all, why build preamps that can output more than a few volts in the first place.
jan didden
I agree here with John.
In an interview the conductor Eliahu Inbal talks about liveness of listening with audio systems. He stated that the system must not be perfect to become liveness because our mind can add the structures of music. He's opinion as well is simplicity. And I agree here with him.
I'm coming from the tube edge and now I'm doing my first experements in solid state - as well with interstage coupling, an old technology from the past. Still learning because I didn't have a look to solid state for the past 20+ years. But what I can say is that the circuits with simplicity are sounding better, even when the distortion are higher.
Clipping even on transients is very bad, .01% or EVEN 0.1% doesn't mean much when the amp is in clipping. However, any sort of clipping, could upset the preamp, completely, and therefore a higher than minimum necessary preamp power supply, such has +/- 24V can be an advantage. The other surprise to me was that 'Stereophile' actually used a 600 ohm load on some of the tests. I didn't design it to drive 600 ohm loads. Why would I?
Johnloudb said:
I did a typo here. I meant to say that I read that the preamps are two of John Atkinson's favorites.
PMA said:
But, how much slew rate you need to reproduce audio frequencies at preamp level output? 25v/usec like the OPA134 isn't good enough?
I think if low distortion at high output levels is the goal, then the op amp wins. I don't see how the low bias current is an issue if it doesn't translate into distortion.
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This is a good question, but the same good question might be why we are trying to get low distortion. We probably need a lot of margin in all possible parameters.
Yes, OPA134 is not sonically good enough for me.
Just my two cents. One of my recent line stages uses an Opamp as the amplification device and then a discrete buffer at the output. The Opamp is able to swing 20mA clean into 600 Ohm, so it should be good enough to drive the system on its own. The load is a 5m long 75 Ohm video cable that is terminated with 10kOhm at the input of the poweramp. The poweramp has a high sensitivity and my speakers are high sensitivity too and 300mV are enough for really loud sound. From the standponit of simplicity i should take out the buffer because it is not necessary. The subjective results though tell me that the buffer should be kept in the system. This is just an example from my own experience where more components in the signal chain gave a subjectivly more transparent sound. By they way the buffer does -120dB distortion at 20kHz@1V into a 600 Ohm load. Off cause i isolated the Opamp from the capacitive load of the cable when i tryed the Opamp on it´s own.
Yes, but low idle current and weak output, not robust enough. I agree with you that the buffer, operating at high idle and capable to drive everything helps a lot.
The designers have different philosophies and experience with solutions that work for them. That's why not always we agree on the one and only one solution.
Joao, I don't completely understand this statement.
Does he mean that it is not necessary for the system to be perfect to become lifelike?
jan didden
Hi Joachim, what is the point of using a 5m long 75ohm video cable if it is anyway terminated by 10Kohm? Shouldn't a regular good shielded cable do the same job? I find 75 ohm video cables expensive and inconvenient (rigid...) to use, are there any good reasons to?
I used a Klotz Microphone cable before that is more or less the studio standart in Germany but the 75 Ohm Video cable was more transparent to my ears. It has foamed PE and a sodid core inner wire and is double shielded with a braid and conductive textile. It is not that stiff and i do not use it because of 75 Ohm termination. I tryed that out of cause too but i do not like the loss of 6dB and i do not think that a 5m audio cable has to be treated like a transmission line. a lot of cables have come and gone but this coax works for me. Besides, i also tryed the Opamp linestage a had being talking about here with a cable of only one meter and in that case too it sounded better with the buffer in the signal chain.
Never heard about Klotz Microphone cable, but obviously you are a cable audibility believer... Thanks for clarifying.
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