Lampy cd player

[Richard]

Yes. Though I will repeat again, what you see on the scope is not real, whats real looks a lot less like noise.

Hi Nick, as in your previous post?;

Its what I would expect with no reconstruction filter. If the frequency was a sub multiple of 44.1khz, then you would see the clear steps, one at each sample period. But because the scope is locking on the 1khz (or whatever) then the 44100 steps a second happen at different parts of the 1kHz sine wave, so you see the blur of each pass of the dot on the scope traces a different path. If you had a storage scope and just took one sample you would see the staircase that is the different value every 1/44100th of a second.

So the trace is down to the way the scope locks on so ignore it (or at least pay it less attention)?

Whatever the reason I wasn't bowled over by the sound of this valve stage in NOS or 4x (both without a reconstruction filter), somewhat heavy and dark despite showing flat. Although the trace was a lot better in 4x the sound was better in NOS.

I'll try Thorsten's as it seems to be what more folk would go for as suitable and I've plenty of ecc88/7308 types. It also has a filter so I can try it with NOS and 4x again and try to ignore the trace (but I will have little look ).

[Nick]

Yep, for me, I would be looking at a buffer stage with a bit more current through it. Given that I doubt you need that much gain, I would have thought a CCS loaded 6n6p would work well, or a 6n6p or ecc88 mu follower if you wanted to stay away from SS.

[Richard]

Well, before pulling it down I thought I'd give it another listen in the light of the crash course you gave me yesterday and some reading up.

Maybe it's relaxed the mind a bit but it didn't sound too bad running 4x into the valve stage (where I left off yesterday). Switched the disc into the stock player and thought, nah, swings and roundabouts even against the stock player. Then thought that it had sounded a lot better than that with NOS so put it back for another listen and it blew my socks off The difference between 4x and NOS is far more obvious with the valve stage. So played a few more tracks and have decided it can stay awhile. I might build Thorsten's in the other player without pulling this one down so there's a better comparison. I still have another stock one so there's still a control, to stop me getting off course. Trouble is this could get dangerous and I could end up locked in a dark room for 4 years surrounded by 100 cd players like Lukas and almost certainly sectioned or divorced...

[pre65]

Trouble is this could get dangerous and I could end up locked in a dark room for 4 years surrounded by 100 cd players like Lukas and almost certainly sectioned or divorced...

I knew you'd fit in here.

[Nick]

The difference between 4x and NOS is far more obvious with the valve stage.

Now here is the thing. I wonder exactly what it is that you are hearing between 4x and NOS?

[Mike H]

So the trace is down to the way the scope locks on so ignore it (or at least pay it less attention)?

Yes the 'scope can only "lock" onto one frequency at a time, the others will be "free running" and look like just a splurge.

At which point I might have a play with the triggering band filters, if good enough, see if I could lock onto some of the more HF stuff and get a more proper butchers at it

 

[Nick]

It won't do you any good, the sample rate and tone rate are not locked together so you can't lock on them both at the same time. You may get more sense if you find a common frequency between the two, but its so much simpiler just to record a test tone at 882Hz

[Mike H]

That's right you can't.

How to waste hours looking at traces


 

[Richard]

Trouble is this could get dangerous and I could end up locked in a dark room for 4 years surrounded by 100 cd players like Lukas and almost certainly sectioned or divorced...

I knew you'd fit in here.

[Richard]

The difference between 4x and NOS is far more obvious with the valve stage.

Now here is the thing. I wonder exactly what it is that you are hearing between 4x and NOS?

What I'm hearing, or why I'm hearing it?

Bro Jonny and GerryB came over yesterday afternoon to pronounce on the project so far,
hmm it does look like a milk crate
is the top off to let the smoke out
I put screening in mine
has the display got an off button
and other such useful things were being discussed when I hit the play button,
wow
bl**dy hell
followed by a bit of peace and quiet whilst we listened to the music,
Kill to get Crimson, Golden heart, Artic Monkeys, Led ZepII, Lynard Skynrd, Van Morrison, Joni Mtchell, Tracy Chapman, Graceland, Donna Summer , err, no not Donna Summer.
Compared the players against each other and against some of the same albums on vinyl.
We philosophised a bit,
it's like Raquel Welch
eh
well you might fancy her
'spose
more so without clothes
maybe
but not without skin
urgh, yeah see what you mean
a bit like a lotus 7
yeah, but there are potholes and it rains been there
yeah.

4x may hide the truth, paper over the cracks but we preferred NOS in every case between these 2 players. Gerry and I had heard the comparison between the two using opmaps last week but it is much more obvious now. But NOS doesn't quite sound right, not at first after 20 years of OS anyway. I'm not even trying to explain this in normal terms of bright, tinkly, etc. It's something you have to hear. It's very clear, very tuneful, bright and powerful but doesn't take your ears off. It's like winding up the colour on the tv after watching black and white, at first you say no, turn it down, then you adjust and like it. It is that different, OS sounds veiled and smeared in comparison so it may be partly a timing thing, it certainly times well according to Jonny anyway. But then MP3 was raised. Rawness, the sense that it was really good but that something was still missing. Perhaps it just lets us hear the shortcomings of 44.1. Time will tell

[Richard]

That's right you can't.

How to waste hours looking at traces

Indeed, Nick saved me that but the distraction was there, the seeds of doubt sown, I left off listening and spent hours reading up. It needs a period of digestion now, live with it a bit, see how it goes, or I'll be chasing my tail trying to make snap judgements

[andrew Ivimey]

Hello Richard et al, I've missed the boat here. What is 'NOS' and what is '4X'?

I've got a 'last year's model' lampucera board and intend to get digging with tiny soldering iron and then add a valve. I like the idea of what a 6N6P can give and don't need the welluy of SRPP output, so we shall see.

I bought another hongker DAC board last year and am very impressed mostly so when coupling it up to a DVD player that cost £20 - very impressive. But this board is stacked and crammed and far too complicated for me so the lampucera DAC is for me the place to begin 'sperryments.

I intend to use lampy with DVD so whatever player I am using I can use CD & DVD and, I hope, be bale to resolve DVD-Audio (I have this with a Pioneer deck anyway) and compare SACD output. I want better!

[Nick]

What I'm hearing, or why I'm hearing it?

No what I meant, was that in theory the only difference is that there is 4 steps in the trace in the same time as there used to be 1. One of the advantages of over sampling is it allows the reconstruction filter to be set higher so out of the way of the audio. But you don't have a reconstruiction filter now, so I was wondering just what process was causing what you were hearing.

I am trying to find references to just what the lack of reconstruction filter is meant to do (positive or negative), other than make the trace look better. References I found indicate its to remove low frequency images from the resultant sound. Anyone got a handbook on digital audio on hand?

Maybe Andrew L (or someone he works with) has some info on the pratical effect on the lack of reconstruiction filter?

[Neal]

Yep, Principles of Digital Audio....in essence this is what the book is saying: the output low pass filter (correct name anti-imaging filter) is needed to remove all frequencies above the half-sampling frequency, in just the same way as one is needed in the A to D process dictated by the Nyquist sampling theory.

So this filter is converting the stepped output into a smooth waveform. The stepped wave form (PAM or pulse amplitude modulation) contains artifacts of the sampling process. The shifts in levels (steps) represent high frequency components not present in the original signal, the anti-aliasing filter removes these components.

It goes on to say: Some question the need to filter out these components above the Nyquist frequency as the original wave form is re-created and because they are above the limit of human hearing.... but these components could cause a modulation in downstream equipment through which the signal passes affecting the audio signal.


So I guess all the extra HF hash present in the NOS output may upset something else in the system...I would expect a wide bandwidth amplifier to be affected, maybe with our valve amps with limited bandwidth are simply unaffected by any of this...

One more bit: Over sampling shifts the artifacts well away from the audio band where the demands placed on the low pass filter are less, meaning simple analogue filters can be used instead of complex digital ones.

[Richard]

What I'm hearing, or why I'm hearing it?

No what I meant, was that in theory the only difference is that there is 4 steps in the trace in the same time as there used to be 1. One of the advantages of over sampling is it allows the reconstruction filter to be set higher so out of the way of the audio. But you don't have a reconstruiction filter now, so I was wondering just what process was causing what you were hearing.

The following explains, I think, why I found a larger 4x v NOS difference with the valve player comparison.

I've not checked but have seen refs to Tda1541 being suitable for NOS and 4x.

In this player I moved from 4x to NOS and back again etc by completely bypassing the 4x filter chip 7220 (cutting tracks) and taking the signal from the 7310 decoder straight to the 1541 dac. The 7220 was kept just for mute control. So a true comparison of 4x v NOS should be with 4x apllied before the dac and reconstruction after it, against NOS before the dac and no reconstruction filter after. How much effect just a reconstruction filter/low pass filter after will make to a NOS output I don't know yet.

Now I come to consider what we were doing in the 2 sessions that we compared NOS to 4x, firstly with opamps, then with valves, I realise that the first time was wrong and the second right (and wrong) which may explain the bigger differences in the second session.

With opamps we compared 4x with a reconstruction filter (stock cdp) against NOS with reconstruction filter (modded cdp). That was correct for 4x but not for NOS. There was a clear difference between the 2 but NOS was strange. I most likely wouldn't run it this way.

With valves we firstly compared 4x with a reconstruction filter (stock cdp on opamps) with NOS without a reconstruction filter (modded cdp on valves). The difference was huge but I didn't take on board much listening (one track and a check for noise and hum) before hooking in the the devil scope and becoming distracted. In panic mode I put 4x back on the modded player running without a reconstruction filter. It scoped better but not clean and sounded poor, about the same as the stock player running 4x correctly. If your question is why was it that bad, it may just have seemed that bad on a quick listen, and I was a bit miffed it neither sounded good nor looked good on the scope.

I didn't compare much further that day, but the following day it still sounded poor and not worth the effort expended so far. So I returned to 4x with reconstruction filter (stock cdp with opamps) against NOS without reconstruction filter (modded cdp with valves) for our much longer listening session.

As I see it this is now a correct comparison of the 2 players (although not a level playing field for any 4x v NOS of course, that would need 4x on the valve player with a correct reconstruction filter, and that had been thrown out with the opamps) and the NOS valve player wins out by a huge margin.