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Old 4th May 2012, 10:02 PM   #5121
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Default DAC's

http://www.datasheetcatalog.org/data...ic/mXyzrzw.pdf

I loved this DAC . Where are we now with this today ? Alan Mornington West's Quad 67 had this as far as I remember ? If you have the time read spec sheet . This was my introduction to understanding digital the easy way . I can not beleive there is a better chip if 16 bit . Not least to get it to work should be a no brainer. NOS , I know . Sorry .

This was the CD player that changed my mind . Opera had vertical dimensions and it was not digital sound anymore .

Alan was apparently very concerned how small the box was . The CD66 was best forgotten .

I am not the worlds greatest CD fan and have heard many that are great I can assure you . CD 67 is where I feel I belong with CD . My favorite CD player is Garrard 401 with Niam Arrow and Lyra Helicon if asking .
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Old 4th May 2012, 10:24 PM   #5122
a.wayne is offline a.wayne  United States
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What about Rega Digital... ?
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Old 4th May 2012, 10:25 PM   #5123
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Default Dither

Reading the amp noise debate reminds me of dither . I seem to remember Martin Colloms devised a - 90 dB test for CD players in the early days . Some showed in excess of 30 % distortion whilst the new dithered ones were 3% . It could have been higher level ,however the 20 db improvement is the question not the exact level . I was told by a friend to ignore it as hiss form master tapes would dither my CD player . Perhaps that's why the best sound in the early days was from Analogue masters . I know people who used Analogue Dobly A and said it was digital to their bosses .

Could it be simply the transistors are acting as switches at low level ? I have the feeling that is something assumed . Just never saw the words before .

Is it dither also in amps ? Should make the amp switch faster marginally .

Martin has a fascinating RFI test coming soon . Not quite sure what , he was being vague but excited . He said to me it will cause many people to rethink if I am allowed to slightly guild the lilly on his exact words .
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Old 4th May 2012, 10:34 PM   #5124
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Default Wayne / Rega

My friend bought a Rega CD recently . I want one . I am getting his cast off Cambridge . At last a blameless product in my life ( Cambridge I believed use a famous designer ) He has a Naim CD player I can have . Too big . .

I think Terry at Rega even designed that chip ( set specs ) . He was a musician who liked guitar amps and played with them ( pulled them apart ) . He trained himself and is one of the most gifted engineers I now of . Roy said to me he is so proud of him . Roy employed him when another caused problems . Roy persuaded Terry he could learn on the job . Terry's first amp was PE Texan revised . It was OK . Roy said they were astonished that Terry learnt about digital and could converse at the highest level .

Last edited by nigel pearson; 4th May 2012 at 10:43 PM.
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Old 5th May 2012, 06:58 AM   #5125
dvv is offline dvv  Serbia
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Quote:
Originally Posted by john curl View Post
I use the AD825, myself.
A good choice, no doubt. A Danish company made money by selling them as replacement op amps for just about anything spinning a CD, in their day.

But do take a look at AD 818/828 (single/dual), John. Just for fun, check out their say 50 kHz distortion. The odd thing is, the 818 was never intended for audio, rather for photocopy machines, scanners and such like.

And if you should current boost it, well, then you're in for a bit of fun. Then it turns really serious.

For a cream, try current boosted, venerable OPA 37, the uncompensated OP 27 version. THAT sounds very serious, despite its age.

The one I can't make up my mind about is the AD 829. According to its Data Sheet, it is God-given for audio, yet somehow it doesn't do as well as I would have expected it to. Perhaps I am being unreasonable, perhaps my expectations were unrealistically high, I don't know.
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Old 5th May 2012, 08:05 AM   #5126
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Default Is noise useful ?

A very famous British amplifier somehow got into production without any bias . I suspect a few thousand got sold . We called it class C then. However more correctly I suppose zero bias class B .

Funny thing is it sounded half decent . When I asked the man responsible he said he was learning electronics then . How refreshingly honest of him . When I said how come it sounded OK . He said , that's easy . It had enough hiss .

He went on to beautifully bias the amp and not use complex Vbe ( which I find less good than some think even in famous worked examples ) .

DVV . He used a telecom op amp inside it . He said because it was ultra fast . He had special permission to buy it . It was sourced via his old company where he was a telecom engineer . I never knew what it was . Again it wasn't the sort most would use . He very carefully decoupled it .

If asking I will never tell who it was .

Last edited by nigel pearson; 5th May 2012 at 08:28 AM.
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Old 5th May 2012, 08:51 AM   #5127
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Default Video op amps

http://www.farnell.com/datasheets/61847.pdf

Picked this out today . Typical video amp . Look at distortion given . Looks like it would work as a normal voltage amp .

The previous amp . I remember NE531N was said to be a workable replacement .

Last edited by nigel pearson; 5th May 2012 at 09:04 AM.
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Old 5th May 2012, 10:00 AM   #5128
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
http://www.farnell.com/datasheets/61847.pdf

Picked this out today . Typical video amp . Look at distortion given . Looks like it would work as a normal voltage amp .

The previous amp . I remember NE531N was said to be a workable replacement .
Why would you want to use an op amp which cannot use more than +/- 5V, or 12.6 V single?

I would have thought this severely limited their usable dynamic range in the audio bandwidth, already considered by some to be limited at +/- 15V, or three times the rail voltage of this one?

What's wrong with well known amps, like AD 818, 825, 826, 828, 829, PMI/AD OP 275, and so forth?
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Old 5th May 2012, 10:07 AM   #5129
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
...

DVV . He used a telecom op amp inside it . He said because it was ultra fast . He had special permission to buy it . It was sourced via his old company where he was a telecom engineer . I never knew what it was . Again it wasn't the sort most would use . He very carefully decoupled it .

If asking I will never tell who it was .
What does "ultra fast" mean?

These days, finding op amps with slew rates of 2,000 V/uS or more is no big deal. In my view, once you get past the 1 V/uS per every peak volt of output, it's sort of like the damping factor, get over 10:1 open loop and it doesn't matter any more.

In practical terms, since many op amps can deliver 24 V peak to peak, some even more, get your slew rate at that value plus a bit more, and it doesn't really mean much any more - for audio.

True, with the exception of two op amps I like, OP/OPA 37 and 275, all of others are well over 200 v/uS, but I doubt the good sound obtainable from is dependent on wild slew rates.
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Old 5th May 2012, 10:12 AM   #5130
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Default Magnets

D V V . I agree
I sent out inquiries for magnetic amps . I got this ! What planet is it from or am I being cynical ? Tell me it's great . I need to have dreams

http://www.google.co.uk/url?sa=t&rct...xTi3ng&cad=rja
HOW about this.
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