The Joe`s capacitor...

[Bigun]

What do we know about soundstage - what affects it ? - I had assumed it was something that depended on quite subtle details but certainly it needs good channel separation (which we can measure), low noise (which we can measure), good phase coherence (which we can measure). Then there is the speaker, which must have good phase coherence, appropriate frequency dependent dispersion and lack of inappropriate diffraction artifacts from edges. Then there is the room, reflections from surfaces can spoil things. Can we trace all this back to requirements at the signal level at the output of the DAC ? - then we can ponder what a capacitor might be doing to influence them.

 

[Coris]

I think we can do...
Starting with the speakers (in your quite right list), and ending with the room, all these factors are constant in the "soundstage equation". These factors are always the same, with/without the cap in place. So one can well appreciate the difference between a good and poor soundstage quality.
With a device of a certain channel separation, low noise levels, and phase coherence, but without the cap in place, one get a result, and a certain soundstage quality. Mounting the cap in place everything become better in the soundstage. That capacitor might be doing to influence something... And my personal assumption is that may be the phases coherence the area, where it happen the "magic"...

 

[Coris]

There is enough logic to bind this cap, placed over DAC outputs with the parameters of DAC circuit and/or the circuits after the cap, then appreciate the whole as a DAC system/behaviour. I did the same assumptions, that this cap effect over the resulted sound, it may be in connection with DAC output parameters. Therefore I was enough surprised to hear the same effect when applying the cap over the differential inputs of an preamp device. Using the cap on DAC outputs AND on preamp inputs, it multiply the effect, and it make it behaving more sophisticated. With two caps in the same stereo chain/channel, one get the possibility to adjust somehow this effect, in a quite different way than only adjusting the amount of the effect, by modifying the DAC cap value. So, my (new) assumption was that this cap/filter it act in a particular way and it have impact over the audio signal, when is placed it supposedly over any differential signal path point in the audio signal processing chain, but not necessarily just at the DAC outputs. However I appreciate that the DAC outputs is the the very right place for this way of filtering.
So, recently came Ken with the information that he got the same effect when placing the cap/filter over a non-deferential signal path, however at the DAC outputs...

So, it still be not enough very clear about the circumstances this effect occur...

 

[Max Headroom]

Personally, my bet is still that this capacitor thing is altering the internal behaviour of the DAC so that it functions more per what it's spec's would imply. Why I say this is because I get the same sort of audible behaviour change by utilising the time dimension. IOW, I "hammer", condition the DAC over a decent time frame, hours typically, till I get the optimum performance - from cold, the sound is gray, dead, flat as a tack, mifi quality; as the DAC comes to life the detail in the soundstaging starts to emerge, and the audio becomes worth listening to.

This has to be done every time the DAC is powered up - so obviously a right pain in the ... 🙂 if you just want to listen for enjoyment straight up. The "Joe" capacitor possibly short circuits this conditioning period, making it largely unnecessary.

I find that my system sounds 'all wrong' initially with cold start.
I let the system idle for 30 mins or so, 10 second shut down, reboot and then it's ready to play music.
After this initialising I don't find sonic changes of particular note...clarity, depth/side imaging is all there from the warm restart and does not appreciably change.

Not sure about this 'thrashing' business....how do you protect your ears from changing due to loud/distorted sounds until the system comes 'on song' ?.

Dan.

 

[DF96]

For this cap not to totally stop the audio it has to be placed at a very low impedance position in the circuit. It is very likely that such a low impedance position either arises from a virtual ground via feedback or a low impedance transformer winding. In both cases the situation is likely to be (or mimic) a low value inductance. The cap will interact with this to give a peak then rolloff. The exact shape will depend on local circuit details, but it is likely to be audible. It is not improving the circuit, but adding a bump to the frequency and phase response. Any small change can be perceived as an improvement when someone has told you to expect this; only a large change for the worse will definitely be heard as worse by most people.

Simply adding a low pass filter elsewhere will not add the peak, so will not have the same effect.

 

[SY]

The cap will interact with this to give a peak then rolloff. The exact shape will depend on local circuit details, but it is likely to be audible. It is not improving the circuit, but adding a bump to the frequency and phase response.

Are you implying that not a single advocate of this "effect" has bothered doing a simple frequency response check?

 

[DF96]

Are you implying that not a single advocate of this "effect" has bothered doing a simple frequency response check?

The famous Joe did some frequency response plots, but I could never work out whether they were measurements or simulations. When I became awkward he said the opamp virtual ground I was discussing was not the real issue and soon after that the thread was closed.

Response plots of magnitude alone might not help much as a big peak would be audibly obvious. Assuming a small peak this could get lost in measurement error, but there could be significant phase issues - but people often forget about phase when measuring frequency response.

Now an interesting question might be: why does a somewhat underdamped second-order rolloff at the top of or just above the audible range seem to cause so much pleasure to listeners?

 

[SY]

Why are you feeding OT drivel?

 

[abraxalito]

All a DS DAC does is 'hammer' even on no signal. In fact silence will probably condition better than a signal.

Curious - which DS DAC did you observe? When I looked at an AD1955 it traversed 3 or perhaps 4 levels with no signal and vastly more with a large signal present.

 

[fas42]

All a DS DAC does is 'hammer' even on no signal. In fact silence will probably condition better than a signal.

A key weakness of DS DACs that a lot of people experience in use is that they can be poor at resolving low level information - why precisely, and what the best method for circumventing this I would not claim to know, I just worked out some practical approaches that worked for the equipment at hand.

Something like the Mola Mola DAC is using yet another, "extreme", engineering approach, which appears to be yielding very good objective and subjective results - the industry is still learning how to achieve optimum performance.

 

[Coris]

I think there may a good point to direct the discussion to a more factual approach: measurements.
Can we agree to a measurement setup, what to input, and some assumptions about what we should see/measure?

 

[SY]

How about a simple frequency response measurement of the CD player or DAC output with and without the cap? Pretty easy to do.

 

[Mark Whitney]

How can you measure above the audible range of a DAC? (a frequency response above 20kHz)

 

[SY]

Soundcard spectrum analyzer. A 192k soundcard can readily measure to 90kHz.

 

[Mark Whitney]

Well that takes care of the output. How do you get the DAC to process a signal above 20kHz?

 

[chip_mk]

Well that takes care of the output. How do you get the DAC to process a signal above 20kHz?

You play hi-res test files through it.

 

[DF96]

Do we know what the circuitry of the DAC looks like ? - the output stage and power supply that might possibly interact with said Capacitor

I wondered that.

 

[Mark Whitney]

The datasheet of the PCM1794A, which Joe uses in his examples, is not very helpful on many of design problems. Things like output impedance, out of band noise or the DF filters to name but a few.

 

[Coris]

Well, I can measure quite high over 20khz. Up to 200Mhz. FFT too. I did actually, and no any significant differences. But I can do it again and take a closer look.
I can use ES9018 DAC. This is capable to do the conversion at 80khz without problems. I do not had yet the possibility to generate a higher frequency (digital file) to really test how much it can this chip. BTW, I use so far this cap/filter on the same ES9018, and opa1632 as I/V stage.
Previously I used the cap over the outputs of an PCM1792 (same opa1632 as I/V) with also good results.
There is a little problem here. I can not know if the generated digital file (sine-wave) is just perfect, without artefacts, and so. But it looks however quite fine on spectrum analyser (through ES9018).

 

[Joe Rasmussen]

Tap, tap, tap, tap, tap, tap, tap, tap.... phone rings...

"Hi Mike, it's Joe - going to Campbelltown?

"Yes, tomorrow."

"Can you drop your Oppo off, I am doing an experiment, mind being a guinea pig?"

"What's going on, what are you up to?"

"I can't say to much except I am also getting in touch with a few other Oppo owners, so you have to trust me on this."

"Sounds very mysterious Joe."

"No, not really - there is a reason behind this and for that reason I can't tell you. But you may have to bring back your Oppo a second time."

"OK, why a second time?"

"Well, I am going to do is what I do with the other Oppos brought in, I will toss a coin. Heads, something is done to your player, tails nothing - but you will be kept in the dark, OK? - That's why you may have to bring it back a second time."

"OK, I get it, let's do it."

------

Wrrrr, wrrrr, wrrrr, wrrrr.... phone rings...

"Hello, Custom Analogue Audio."

"Hi Joe, it's Mike."

"Oh. Hi Mike, you ready to report in?"

"I sure am."

"Mike, you sound a bit excited."

"Yes, but not for the reason you think."

"Well, now you have me..."

"No, listen Joe, I set up the Oppo, let it warm up a bit and I heard it instantly."

"You did? Do you reckon that I did something to the player or is this just a placebo effect?"

"You gotta be kidding me. But that is NOT what got me excited, something else happened and you could have bowled me over with a feather."

"OK...?"

"My wife was in the room, she never pays no mind and after less than 60 seconds of silence, she turns around and says 'That's different, I can't put a finger on it... but I like it.'"

"Amazing?"

"Unbelievable!"

"I have a smile on my face." 🙂

"Joe, I am telling you, you are going to be busy."

"Don't know about that, there is a steady stream and well over fifty conversions out there - and the forums have gone beserk..."

"Yeah, I know what they can be like, they are a bunch of flame throwers."

"Yeah, they want to hurt you, but I am way past that."

"Goodonya!"

-----

This is an encapsulated but true story, not even the names has been changed - this actually took place.

Peculiarly, other wives of other Oppos owners have responded similarly - and they are not audiophiles.

In view of the above, what constitutes a blind test?

Cheers, Joe

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