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Old 26th June 2007, 04:25 AM   #1571
dsiroky is offline dsiroky  United States
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I'm glad it's working. And hope others get to enjoy this great project.

I definately got a bad batch of DACs. Last night I pulled some fresh ones from a tube and one of those also sounded like static. All had the same markings (tda1543). So I think I just got unlucky here.

The project has been fun - and good sense of accomplishment.

I've ordered some replacement DAC chips to fill out the missing 7 chips and hopefully will have it finished soon.

I'm starting to think about what case to make for it. Part of me wants to make something in cedar, however I worry about heat disipation. I could route vents in the top - but perhaps aluminum is better.

I notice some enhancements since the Di8 pcbs were finalized - do any of those enhancements also apply to Di16?
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Old 26th June 2007, 04:34 AM   #1572
dsiroky is offline dsiroky  United States
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Default CD vs HDD transport

I think HDD transport is better than CD (imo) for a couple of reasons.

While in theory if the disc is perfect (if there are no transfer issues) the CD media can be just as good.

CD rom is not as fast - particulary if the media is scratched, laser lens dirty etc. What can happen is the ecc routines can kick in to try to recover difficult to read parts of the disk. Seek time on optical media is still slower (burst read is ok), but during ecc seek time is important. Overall transfer rate is slowed down, and cpu usage can go up.

When you read the bit perfect copy from the hard drive it's already bit perfect and has gone through the process.

in short

#1 HD transfer rate is faster and buffers into RAM very fast

#2 HD image is already bit perfect (assuming it's ripped lossless etc)
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Old 26th June 2007, 08:33 AM   #1573
ecdesigns is offline ecdesigns  Netherlands
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Hi anatech,

Thanks for your reply [post #1569]

Quote:
By comparison, a CD image on a HDD is always read error-free.
Don't bet on it!

This remark I made doesn't imply that the CD image itself is error free (after ripping), but that the HDD reads the file without errors.


Quote:
This can be shown by how long it takes to rip a CD and what the error options are. So be careful when you make assumptions. Always remember the old Pentium math error. Who knows what is swept under the rug! So your file is read out bit perfect, but it may differ from the intended image by a fair amount. Also, the better CD transport will always present you with lower error data than a cheap one. Home machines do not typically re-read several times because the read-play operation is real time
Yes I agree that the error options selected prior to CD ripping, does affect the way the CD image is read. I also mentioned using CD paranoia mode when ripping CDs.

The old Pentium math error didn't affect file integrity, if I am correct it was an error in the (integrated) math co-processor. I remember using my first pc, it ran on 8 MHz, it didn't even have a math co-processor.

Yes, sometimes it's not very clear what happens between reading the CD image and outputting it as digital sound data. But doesn't this apply for a CD transport as well? Perhaps sound quality is the only indication of what really happens inside a CD transport or a computer based music player.

My Sony CD changer has a RAM / anti-shock buffer, so it can do a significant amount of re-reads. Still it's not a High-End CD player, the transport mechanism resembles that of a CDROM drive.

There are correctable read errors (read errors are 100% corrected and the data remains bit perfect), and uncorrectable read errors (read errors are compensated, but data is no longer bit perfect). I agree that given the worst case scenario for reading a damaged CD, the CD transport that has the best laser pick-up and servo system is more likely to retrieve the data correctly. But when a CD image is already stored on a HDD, and it get's damaged for whatever reason, it's very likely, the error correction routines are able to fully restore the damaged data. In the worst case, the exact CD image can be restored (bit-perfect) from a back-up drive.

If you use CDs regularly, disk surface damage accumulates, no matter how careful you handle the CDs. With a CD image it's possible to maintain CD image data integrity, regardless of the amount of times it's read.
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Old 26th June 2007, 02:17 PM   #1574
tubee is offline tubee  Netherlands
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Maybe off topic here, maybe not, but want to report anyway:

I have swapped the two standard 15A diode bridges in the hybrid (tube/fet) poweramp in discrete bridges of 4 hexfreds, and added snubbers (zobel network) on the PS, with great result.
First did one channel, and checked for visual differences on the scope with the untouched channel. The latter showed small hf spikes in the recovery part of the AC waveform on diode. The snubbered/hexfredded channel showed no HF spikes, and a smoother waveform. The HF is reduced mainly due to the snubber i guess. (1ohm/100N mkt in series)

Sound: depth in soundstage is more accurate now, the recordings sound more dry when it's recorded in a heavy dampened studio, and when available on tracks, the room information is better performed, now i hear a room has a ceiling and a floor, eg is mostly rectangular. Percussion cymbals show more it's particular body-sound (groundtone) not only the "hit". But there is a small difference in bass, it sounds some warmer/ maybe less defined.
Overall a nice mod.
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Old 26th June 2007, 04:14 PM   #1575
maxlorenz is offline maxlorenz  Chile
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Hi gentlemen, Tubee,

OT:
Did you see what happens on the scope with hexfreds but without snubber?

I snubber my normal type rectifiers with exact values you use, as you may guess only copying from what I read, not calculating anything. It does improve sound.

While I have also snubbered Hexfreds, I can't asure it made a sonical change

Hexfred are supposed to need different values of C and R for the snubber to behave in an optimal way (not over/underdamped). But i guess you confirmed good response with the scope. Maybe changing scale?

I could not help noticing that you changed your avatar
Could you explain what is it???

Bye,
M
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Old 26th June 2007, 04:36 PM   #1576
anatech is offline anatech  Canada
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Hi -ecdesigns-,
Quote:
This remark I made doesn't imply that the CD image itself is error free (after ripping), but that the HDD reads the file without errors.
Although not entirely true, a hard drive is orders of magnitude better than a CD. Both formats require error correction. I guess most people don't understand that the raw information coming from either media is an RF wave, both form what is known as an eye pattern. The hard drive firmware is designed to catch errors and do a re-read of the defective block. They are both subject to noise and mechanical vibration. The CD format is more sensitive to this overall for a couple of reasons.

So we agree with that one small issue in mind. Nothing is perfect but the hard drive is better once you have the data in there.
Quote:
The old Pentium math error didn't affect file integrity, if I am correct it was an error in the (integrated) math co-processor.
Yes, correct. This did affect any operation that used the math co processor. I threw that in there only to illustrate that we should be careful about making assumptions.

Quote:
There are correctable read errors (read errors are 100% corrected and the data remains bit perfect), and uncorrectable read errors (read errors are compensated, but data is no longer bit perfect).
Yes, a C2 flag is bad and triggers interpolation, substitution of a previous value or a mute (cheap systems). A C1 flag make be correctable as long as the flag doesn't trigger the C2 flag (correction failed).
Quote:
the CD transport that has the best laser pick-up and servo system is more likely to retrieve the data correctly.
LOL!
Yes, that's what I've been saying for years!! That's why it's completely silly to use a cheap transport with an expensive DA stage. Once the data is corrupt, it's garbage. Not amount of re-clocking or anything else will fix it at this point.

I do agree that once you have the image successfully ripped with the best transport you can get, with good error correction routines, you will probably have better playback than a regular CD player can achieve. Sound quality may be a different matter though.

Just be aware that data errors can creep in at any point. I imagine an expensive hard drive will have more accurate data than a cheap one (better correction too). Errors can also creep into the data transmission on the bus due to noise or anything else. Attention to all these things may be important. Once you've done your best, relax and enjoy the music.

I'm not disagreeing with you ec, just trying to avoid oversimplifications.

-Chris
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Old 26th June 2007, 04:42 PM   #1577
tubee is offline tubee  Netherlands
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Quote:
Originally posted by maxlorenz
Hi gentlemen, Tubee,

OT:
Did you see what happens on the scope with hexfreds but without snubber?

I snubber my normal type rectifiers with exact values you use, as you may guess only copying from what I read, not calculating anything. It does improve sound.

While I have also snubbered Hexfreds, I can't asure it made a sonical change

Hexfred are supposed to need different values of C and R for the snubber to behave in an optimal way (not over/underdamped). But i guess you confirmed good response with the scope. Maybe changing scale?

I could not help noticing that you changed your avatar
Could you explain what is it???

Bye,
M
Hi Maxlorentz

I realised also later the possibility to look with scope on hexfred only. Maybe some other time, temporally snubbers off and look.
Yes the value's are standard as recommended. The snubber compensates the paracitic capacity's from the toroid used. I wanted to enlarge the spikes to measure the frequeny but couldn't manage, Resolution of lend scope is only 20Mhz. But the spikes where fine, so it must have been in the mhz range.
The best way is to measure (with speaker workshop or so) the secondairy winding of toroid in calculate the right value's of snubber.

Well, how do you like the avatar?
It is a side two disc label of an 1978 LP fom Gruppo Sportivo my brother had. Dutch band. Have a CD from them, very joyful music.
The funny thing is when you put the LP on the TT, there is something growing between the leadsinger his legs......

The tokyo thing below is a part of lyrics from a song of them, and i own such make car too.
http://users.skynet.be/JePe/LP%20Pag...%20To%2078.htm
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Old 26th June 2007, 05:11 PM   #1578
Christer is offline Christer  Sweden
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Quote:
Originally posted by anatech
Hi -ecdesigns-,

Although not entirely true, a hard drive is orders of magnitude better than a CD. Both formats require error correction. I guess most people don't understand that the raw information coming from either media is an RF wave, both form what is known as an eye pattern. The hard drive firmware is designed to catch errors and do a re-read of the defective block. They are both subject to noise and mechanical vibration. The CD format is more sensitive to this overall for a couple of reasons.

So we agree with that one small issue in mind. Nothing is perfect but the hard drive is better once you have the data in there.

Read errors certainly occur in both cases. If the error is not possible to correct, it is easy and quick to reread data in the case of a hard disk, which is not usually possible for CD. That is a big difference, apart from different error rates.

Further, there are permanent errors, which cannot be corrected even by rereading indefinitely. In the case of hard disks, that means we had a write error. I must say I cannot remember ever experiencing a write error with hard disks during some 30 years of using computers. My guess is that write errors on healthy hard disks are so rare that it is more important to worry about losing data because of disk crashes. I suppose permanent errors are rare, at least, also on CDs. It is very seldom that EAC fails to read a whole CD correctly, but it sometimes has to do a lot of rereading to make it. A CD player doesn't have that option.

Since you raised the important point that digital data is actually represented as anaolog data that has to be discriminated, many read errors probably are caused by varying quality of written data, but as long as it is possible to recover by rereading the data a couple of times, it is hardly to be considered a permanent error. Obviosly, that type of error is more problematic on CDs, where we cannot reread.
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Old 26th June 2007, 05:19 PM   #1579
anatech is offline anatech  Canada
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Hi Christer,
Quote:
I must say I cannot remember ever experiencing a write error with hard disks during some 30 years of using computers.
You are so lucky!
I deal with voice mail servers, and disk errors all the time. To give you an idea, voice mail systems are normally programmed to do hard drive maintenance every morning around 2 ~ 3 AM. Real voice mail anyway. Some cheap systems are too stupid to do this. The files in question are wav files and database files. This is accelerated wear for sure.

It's nice to know someone else understands how this stuff works!

-Chris
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Old 27th June 2007, 07:10 AM   #1580
ecdesigns is offline ecdesigns  Netherlands
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Default HDD errors

Hi Christer,

Thanks for your reply [post # 1578]


Quote:
I cannot remember ever experiencing a write error with hard disks during some 30 years of using computers
HDD hardware does indeed encounter read / write errors, this is no wonder regarding the vast amount of data stored on a few small disks or platters. The data density is very high, even the slightest flaw in the magnetic material deposited on the platter surface, a servo glitch or just an interference spike on the power supply is enough to cause errors

Write errors can be detected immediately after writing, they can then be corrected, in order to make sure the data is stored correctly at that moment. Read errors are a different problem, now the error needs to be corrected with the remaining information.

HDDs usually have multiple discs (platters), a R/W head is located over each of the two platter surfaces. The spindle motor revs these platters up to 4200...10000 RPM. Due to the bernoulli effect, and the shape of the small ferrite R/W heads, they float above the disc surface on a very thin cussion of air. During power-down, the R/W heads are moved to the landing zone, where they will make physical contact with the platter when the spindle motor speed has dropped. Then the R/W heads are mechanically locked in place to avoid damage to the platter surface that contains user data. The R/W head assembly is usually electromagnetically positioned, and rotates on multiple very high precision bearings.

HDDs can be damaged by wear of the bearings, too high temperatures, shocks / vibrations during use, and minute dust particles (smoke) that enters the sealed compartment trough the air filter and is deposited on the platter surface. It causes the R/W heads to stick to the platter surface, friction can result in spindle motor start-up failure or R/W heads breaking off their supports.

The most common problems are heat, and repetitive movement of the R/W head assembly between specific physical platter locations (this depends on the operating system disc access). By moving very frequently to specific locations on the HDD surface, the R/W head assembly ball bearings wear unevenly, and develop play on specific locations in the bearings, since they don't make full revolutions like with the spindle motor. If the play gets too high, the heads may touch the disk surface during positioning. This causes a head crash (head physically touches the platter surface and scratches the thin layer of deposited magnetic material, in this event, even one or more heads can brake-off, and cause irreparable damage). This R/W head positioning problem can be avoided by periodically re-locating frequently accessed data on the platters, this could be done dynamically, or during de-fragmentation.

So a HDD with 3 platters would have 6 R/W heads. One platter surface is used as servo track, it contains positioning data for the other 5 R/W heads. These servo tracks ensure very accurate positioning, and compensate for temperature fluctuations. During formatting, data is written to the blank platter magnetic surface area. The area is divided in tracks and sectors, when a unrecoverable R/W error occurs, the track / sector is flagged as bad spot, and is avoided for future data storage. But this isn't enough, more errors can, and will develop during HDD service life.

It's unacceptable that data integrity is compromised, therefore advanced error correction mechanisms are used. In fact even a DVD would be completely unusable without these error correction techniques, if I am correct, a substantial amount of DVD disk space is reserved for error correction information. These error correction systems include redundant information that is used to check / re-construct information (ECC), so it's not just re-reading only. The more ECC bits are added to the user data, the more errors can be tolerated / corrected. New techniques (SMART) can even increase reliability by dynamic flagging of bad tracks / sectors.

If the errors are so severe that the data integrity is compromised, the HDD signals an uncorrectable read error, the data is now corrupted and needs to be replaced.

And that's only the HDD hardware error correction, the operating system can continue to increase reliability be storing (important) data twice, on two different physical locations on the disk, or adding more redundant information to correct severe HDD errors that can't be corrected by the HDD hardware. But this takes time, so it's a compromise between both speed and reliability, same applies for the HDD hardware error correction mechanisms.

So when talking about "read errors", you have to include the entire HDD hardware and computer operating system error correction mechanisms. The output of the combination of both, result in 100% error free data, up to the point the errors get too severe to correct. It's safe to say that in such an event, it's very likely there is a serious (hardware) fault, something is damaged and needs replacement. So the retrieved data is either 100% correct, or it is corrupted (unusable), the gap between these extremes is filled by the (multiple) error correction mechanisms used. The amount of added redundant data determines how much errors can be tolerated before the data becomes corrupted (unusable).
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