What dac and what headphones? How was the dac connected to the computer and to power? What OS? What software?
If you are like most people trying to perceptual testing at home on whatever equipment you have around, then you probably made a number of mistakes that made the overall system sound worse than an mp3.
OTOH, a CD can be astonishingly good, but almost nobody has heard a CD on a system that accurately reproduces what is encoded on it.
If you are like most people trying to perceptual testing at home on whatever equipment you have around, then you probably made a number of mistakes that made the overall system sound worse than an mp3.
OTOH, a CD can be astonishingly good, but almost nobody has heard a CD on a system that accurately reproduces what is encoded on it.
OK don't quote me on this. We did not use a PC we used a PI with linux and we complied each of the codecs from source. We used a
IQaudIO DAC Pro and HD600 headphones. It was a blind test but was done as a joke as everybody claimed compressed audio was audible over uncompressed. Some people were much better than others at detecting MP3. Certainly you can be trained better to tell the difference once you understand what these codec can do to the signal. The thing with MP3 is it did not continue to get better as the bitrate was increased - there was a floor.
Low distortion in every stage.
This is what I have been experimented for some time. First move was changing the driver circuit for the 300B SE amp. I got the Monolith PP interstage and drive it with 6DJ8. The PP drive surely provide very clean and low distortion signal for the 300B. The amp sound amazingly good indeed.
Second move was changing the differential balance 6SN7 RC drive to PP plate choke for the differential KT66 PP amp. The result is real good that makes it sound so natural and smooth like the 300B SE amp.
When you look at the distortion at each stage of the traditional tube amplifier, you would realize the driver stage in the power amp having large amount of distortion. For example, like the Sun Audio 300B, the 6SN7 output signal to the 300B would have about 5% distortion which drives the 300B for full output power. Such large distortion that mixed with the 300B stage may not show that much in the THD measurement. However, our ears are much more sensitive to determine the THD doesn't mean much.
Johnny
This is what I have been experimented for some time. First move was changing the driver circuit for the 300B SE amp. I got the Monolith PP interstage and drive it with 6DJ8. The PP drive surely provide very clean and low distortion signal for the 300B. The amp sound amazingly good indeed.
Second move was changing the differential balance 6SN7 RC drive to PP plate choke for the differential KT66 PP amp. The result is real good that makes it sound so natural and smooth like the 300B SE amp.
When you look at the distortion at each stage of the traditional tube amplifier, you would realize the driver stage in the power amp having large amount of distortion. For example, like the Sun Audio 300B, the 6SN7 output signal to the 300B would have about 5% distortion which drives the 300B for full output power. Such large distortion that mixed with the 300B stage may not show that much in the THD measurement. However, our ears are much more sensitive to determine the THD doesn't mean much.
Johnny
@baudouin0 Thank you. That's helpful. HD600 are pretty good, maybe a minimum these days. Still have a pair myself. Looks like there are some problems with RPi hat dac though. RPi radiated and conducted EMI/RFI are pretty bad, and it does affect dacs. Also, RPI GPIO is very jittery. That's why Iancanada makes all those various products to fix what's wrong with RPi for audio.
Anyway, I've tried the RPi stuff a few years ago. Did some listening tests for Allo for their Katana dac. They also sent one their RPi substitutes, USBridgeSIG. Also tried the Iancanada stuff and posted pics of how to improve some of the noise problems. In summary, I'm pretty familiar with the sound that results and it how compares to some of he best dacs available today. IMHO and IME what you have there is not suitable/reliable for perceptual testing.
Anyway, I've tried the RPi stuff a few years ago. Did some listening tests for Allo for their Katana dac. They also sent one their RPi substitutes, USBridgeSIG. Also tried the Iancanada stuff and posted pics of how to improve some of the noise problems. In summary, I'm pretty familiar with the sound that results and it how compares to some of he best dacs available today. IMHO and IME what you have there is not suitable/reliable for perceptual testing.
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Yep its was a PI3B+ but using separate plugin audio card. We asked for people to provide a couple of mins from their CD collection that would be of critical listening. We took the wave file and with a script compressed and decompressed the wav file. This gave a original wav file, a mp3 wav and an aac wav. We did not tell them which was which but they could play them as many times as they wanted.
I think this is the right track. On the bench is a CCS loaded pentode RC coupled to a 813 UL SE output. The driver in its current iteration swings ~140 Vp-p at 0.015% THD, equal parts 2H and 3H with high current delivery. ~20 dB of feedback is employed from the secondary. Seat of the pants opinion but the sound was much more receiver/solid state when the driver THD was ~2%.
Feedback appears to be a tool with strict requirements and not a magic wand.
Blameless means no known sources of measurable avoidable distortion are present in a 3-stage design, not that the amp is perfect. This leads to precise current mirror input pair, EF-VAS, advanced compensation, good thermal management, PSRR control, extended beta output devices, correct PCB layout, best bias point, BJT outputs (not FET), and a few other things. In other words no "mistakes", hence "blameless". That's how Doug Self describes it and he invented the term.
As an example many amps have the feedback pick-off point wrong and this limits the distortion floor considerably sometimes. Its a mistake that shouldn't be made once you know the issue.
Yep he did, and you can take the same approach to valve amp design. Not over design but making sure each stage works as expected, including the power supply, mitigation of hum etc. With a valve amp there's a limit to amount of GNFB that can be applied. The trick seems to be to make the amp as linear as possible without it and then apply the feedback.
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This is an amp (schematic)
that i remember being syrupy, exaggerated mid-range, and old tube sound…
The screens will be connected to HT through the windings. The 220k will form a summing junction of the 6sl7 grid so its gain is -1. Yes this amp will drive the output tubes with difficulty at 10KHz - so your going to get slew rate limiting and a fuzzy sound. Oddly this amp should not have a lot of 2nd harmonic being a PP if its phase invertor is working. Interesting to post.
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That's an old floating paraphase inverter and probably contributed to the "syrupy" sound.
One place that's pretty easy to draw a line is between regulated and unregulated circuits. (I'd put CCS in with regulation)
No, It's a floating paraphase. The voltage divider sends a portion of the AC signal to the second 6SL7 grid.
The Conrad-Johnson is a completely different circuit. It looks like a voltage gain stage direct-coupled to a cathode follower, which is in turn direct-coupled to a long-tail pair phase splitter/driver. It's going to have much better drive and bandwidth than the simple paraphase.
caryking,
1. Your Post # 30 is an early Cary push pull 807 amplifier. Right out of the service manual . . . Right!
This amplifier has fairly direct signal path, and fairly direct negative feedback paths, 1 global, and Ultra Linear.
Simple.
2. Your Post # 35 is much more complex, has perhaps 10 transistors in the IC Regulator Op Amps.
Some might not consider that schematic to be a vacuum tube amplifier.
This amplifier does not have fairly direct signal paths, and has Ultra Linear, plus 2 direct negative feedback paths (like the Dyna Stereo 70).
It seems to need lots of adjustment to make it perform optimally. What happens to that as the tubes age?
Complex.
If anybody thinks that a regulator can not affect the sound . . .
Then ask if they think an electrolytic cap in the B+ can not affect the sound.
3. Back to double blindfold testing.
1. Your Post # 30 is an early Cary push pull 807 amplifier. Right out of the service manual . . . Right!
This amplifier has fairly direct signal path, and fairly direct negative feedback paths, 1 global, and Ultra Linear.
Simple.
2. Your Post # 35 is much more complex, has perhaps 10 transistors in the IC Regulator Op Amps.
Some might not consider that schematic to be a vacuum tube amplifier.
This amplifier does not have fairly direct signal paths, and has Ultra Linear, plus 2 direct negative feedback paths (like the Dyna Stereo 70).
It seems to need lots of adjustment to make it perform optimally. What happens to that as the tubes age?
Complex.
If anybody thinks that a regulator can not affect the sound . . .
Then ask if they think an electrolytic cap in the B+ can not affect the sound.
3. Back to double blindfold testing.
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