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Old 25th October 2012, 03:55 PM   #7481
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Originally Posted by tvrgeek View Post
A crystal is far more stable. To do better, it has to go into a controlled oven for precise temp control. I know of no cap with a small enough temp coefficient for this use. Even humidity and small variations in voltage change caps basic parameters too much.

I wonder as I have been building oscillators for years . COG are about 30 ppm and standard crystals 30 ppm . Some say it is not that , it is the moment to moment changes we hear . I also suspect absolute frequency less important than fluctuations as long as 0.1% correct . An oven is well worth doing . My old frequency meter had one . The cheap 30 ppm resistors seem to match COG well and result in 5ppm when lucky . Ironically more expensive resistors sometimes are not the best match .

As for the 4060 . I was wondering how DAC's work . Do they lock onto the reference given or do they establish a timing sequence when powering the crystal ( i e . the oscillator input fires up the crystal in sequence or receiving the output of the crystal sets the wheels in motion , the later I hope ) ?

If the DAC will accept the 4060 I will run it on a 9V battery for starters . I will pot down the output to start ( to avoid damage to DAC input ) . I will try a bit of shaping as the crystal into such oscillators is not a square wave I seem to remember , I doubt it matters but ...


The inspiration for this came from a very early HI Fi Choice review which was astonished to find a cheap CD player that had poor absolute speed was well liked sonically ( Sansui + 0.4% ) . The investigation found an RC clock . They hypothesized that RC might sound better . some years later the clock became the most suspect component .

Cheap test idea . Record 1kHz on a CD . Test before and after . If no frequency meter handy leave generator running to use as a beat frequency test . It probably will be OK if the generator is warmed up for an hour first . Even reading a clock into a microphone will work as a CD time reference . After one hour see how close . 3 seconds out would be OK .
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Old 25th October 2012, 04:00 PM   #7482
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DVV thanks , great idea and I must have a go at that . I will give that some thought . I would love to have a tweak with something basic like this . Often I find daft ideas work quite well if enough trouble is taken .
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Old 25th October 2012, 04:55 PM   #7483
dvv is offline dvv  Serbia
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DVV thanks , great idea and I must have a go at that . I will give that some thought . I would love to have a tweak with something basic like this . Often I find daft ideas work quite well if enough trouble is taken .
Shouldn't be too hard. Mine uses 8 Philips TDA DACs, their output being a linear signa. This is then taken to the other half of the board, which has another rectifier, pair of electrolytics and 3 pin stabilizers, all of serving only the AD 847, which is in a socket.

Well, you can take the signal from the socket and feed it to a pair of tubes, or a set of FETs and MOSFETs, or whatever.

I don't have the link on this PC, but I'll get it for you. I must also mention that since then, I have see literally a myriad of Chinese copies at 10% of the original price, which makes me suspicious, but thaat you will have to tackle on your own. I prefer to feed Ozzies rather than the Chinese. I find I can trust Ozzies, but not the Chinese.
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Old 25th October 2012, 05:05 PM   #7484
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I was going to order a class D PCB from China ( inc chip ) . My reckoning being they would struggle to clone a Philips chip of that complexity . Wanted to test the specs more than listen 200W for $15 seemed a bit of fun . Want to drive motor with it . Don't give a stuff if it is any good or fails . A little valve amp Separo SE88i seems well made , the exception to the rule .
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Old 25th October 2012, 10:57 PM   #7485
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Quote:
Originally Posted by nigel pearson View Post
The inspiration for this came from a very early HI Fi Choice review which was astonished to find a cheap CD player that had poor absolute speed was well liked sonically ( Sansui + 0.4% ) . The investigation found an RC clock . They hypothesized that RC might sound better . some years later the clock became the most suspect component .
For me a simple "answer" is that digital circuitry, and audio analogue circuitry are a bad mixture. Always. Digital loves sharp transitions, beautiful square waves. Analogue hates these, it yells out, "Interference, interference ...!"

Frank
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Old 26th October 2012, 07:27 AM   #7486
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For me a simple "answer" is that digital circuitry, and audio analogue circuitry are a bad mixture. Always. Digital loves sharp transitions, beautiful square waves. Analogue hates these, it yells out, "Interference, interference ...!"

Frank
This is impossible to argue. I could say in all honesty that my Yamaha CDX 993 does very well indeed on its own, with three separate stages at the output - I/V converter, buffer and output amp proper. The I/V stage uses an op amp (AD826), the other two are fully discrete with dual trannies, current mirrors and the rest of the bells and whistles.

Someone might say that while it does fine, it could do better still in some other way.

I believe - right or wrong - that it's the I/V stage which is critical. Get that right, using a very fast op amp, and you should be home and dry. I find it symptomatic that standard op amps (as Yamaha original had, I pulled it out and stuck the AD 826 inside) seem to lose quite a bit of focus and detail. It appears to me a very fast op amp will by default improve the sound.
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Old 26th October 2012, 01:45 PM   #7487
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My friend John builds magnetometers . His advice to me was to use film caps and an oven . He said COG also acts as quartz . They use a small bunch of various capacitors to match a resistor for near perfect stability . From what I understand this rivals quarts if so ( < 5ppm ) .

John said that some DAC's will be happy with what I am doing ( read very happy ) others not . He said if not happy it will be obvious .

I thought a true square-wave to be best . To use the full 2 to the power 14 divisions might be best . Or less if the caps dictate that . I have a hunch that polystyrene are worth trying . I have some 33 nF lead foil types ( Philips ) . The lead has good aging qualities with the lead out wire ( interesting English there , lead and lead ) . I also have 10 nf standard type ( and values in nf to pf ) . What I hope to hear is less harshness and openness .
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Old 26th October 2012, 03:49 PM   #7488
DF96 is offline DF96  England
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People when talking of CD player clocks always seem to confuse long-term stability with short-term jitter. Quartz crystals, when used properly, are fairly good at both. CR oscillators can be made to be good at long-term stability but are almost always completely useless at short-term jitter. This is because of their very low effective Q; I think I read somewhere that a Wien bridge has a Q of 0.25. Quartz is more like 10000.

It is jitter which matters for audio. Long-term stability, unless really bad, is not noticeable. Just use a good quartz oscillator: no need for ovens, GPS syncing, temperature compensation etc. The circuit techniques for low jitter may have little to do with long-term stability and vice versa; an exception is using good quality crystals, which can benefit both.
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Old 26th October 2012, 04:02 PM   #7489
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You could use an OXCO, bit pricey tough..

http://nl.farnell.com/jsp/search/bro...atchallpartial
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Old 26th October 2012, 04:31 PM   #7490
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Originally Posted by DF96 View Post
People when talking of CD player clocks always seem to confuse long-term stability with short-term jitter. Quartz crystals, when used properly, are fairly good at both. CR oscillators can be made to be good at long-term stability but are almost always completely useless at short-term jitter. This is because of their very low effective Q; I think I read somewhere that a Wien bridge has a Q of 0.25. Quartz is more like 10000.

It is jitter which matters for audio. Long-term stability, unless really bad, is not noticeable. Just use a good quartz oscillator: no need for ovens, GPS syncing, temperature compensation etc. The circuit techniques for low jitter may have little to do with long-term stability and vice versa; an exception is using good quality crystals, which can benefit both.
I think this will be some fun for the winter months . Rotel were very kind to offer upgrading advice . Were it not for the RC reference in that old copy of Hi Fi choice it wouldn't have occurred to me . The good news with this one is I can only use my ears as I doubt my test gear will show any difference ?
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