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Old 1st January 2003, 07:27 AM   #31
Electrons are yellow and more is better!
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Quote:
Originally posted by Pan
I have a LC Audio DAC with PCM1702K, AD811 and BUF634,

it sounds like S_H_I_T up to ... let´s say an hour or so, then it sings. So when I use it I leave it on 24/7 (of course :-).

/Peter
What did you do to remove the "skit" sound?
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Old 1st January 2003, 11:49 AM   #32
Pan is offline Pan  Sweden
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What I menat was after pluggin it in it sounds very bad, that is when it is cold.

After it gets warm it sounds veeeery good. It takes about 30-60 minutes or so.

Haven´t used it for some time now because I have a SCD-XB940 with LClock and Zapfilter which is sooo nice, especially with SACD.

Before I forgett about the Zapdac completely, I will try to improve upon it with on board LClcok and sync wire to transport.

Also do something with the analog section. Either use a Zapfilter, or try to do something "innovative" such as feeding the 1702K into a Jensen transformer to get a balanced signal, then use BUF634 with batteries on the output. I don´t know if it would work with a transformer though, instead of the AD811 which is the I/V stage now.

/Peter
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Old 2nd January 2003, 07:28 AM   #33
jcarr is offline jcarr  United States
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ppl: What was the general range of resistance that you use to buffer the output capacitance of the current source/sink?

BTW, note that if you use current-regulator diodes, in practice the amount of current will change as the voltage across the CR diodes varies. With Zener diodes also, the voltage output will change according to the amount of current. If possible, I recommend incorporating measures to prevent the voltage across CR diodes and the current through Zener diodes from changing.

Re the AD797, I have also tried it, but must admit that I don't find much wrong with it, other than noting that it needs good bypassing and prefers a guard ring on the inverting input node.

Currently I am working on a prototype for a commercial phono stage with a 797 in the front end, and it sounds surprisingly good. Good bass and rhythms, good ability to decipher complex harmonies, good dynamics, quite relaxed and stays out of the way of the music. Granted, I have put in some interesting tricks (and there is still more that I want to do), but this circuit is definitely opamp-based.

I will be bringing a prototype to the Las Vegas, so anyone who visits the Immedia/Scantech room at "The Show" can check for themselves what it (Lyra Erodion) sounds like.

I don't think that opamps are the be-all and end-all of analog amplification, but I suspect that in many cases the perceived problems with opamp circuitry have much more to do with implementation issues than the opamp chips themselves.

regards, jonathan carr
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Old 2nd January 2003, 08:27 AM   #34
ALW is offline ALW  United Kingdom
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Default Jonathan

Thanks for that post, my experience of the AD797 was as a drop-in listening test to a simple headphone amplifier.

I use this as in general it's a highly revealing and simple way to evaluate sonics of different devices, but I'd freely admit it's optimized for different devices (JFET i/p) and layout would be different were I to do it now (I built it 7 years ago, and still use it daily).

Will re-visit the AD797, as I fancy doing a simple phono stage myself and the noise figure of the AD797 is tempting.

I'll reserve further judgement until I've looked in some more detail.

Andy.
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Old 2nd January 2003, 08:37 AM   #35
Electrons are yellow and more is better!
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Quote:
Originally posted by Pan
After it gets warm it sounds veeeery good. It takes about 30-60 minutes or so.
Are you really sure. My DIL08 chips gets warm in less than a minute...if we talk temperature...

If you had talk about a big tube amp I'd agree with you.
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Old 2nd January 2003, 08:40 AM   #36
Electrons are yellow and more is better!
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Default Re: Jonathan

Quote:
Originally posted by ALW
Will re-visit the AD797, as I fancy doing a simple phono stage myself and the noise figure of the AD797 is tempting.
Don't forget that only a MC pickup can take advantage of the low noise. An ordinary MM pickup needs noise figure less than 10 nV/SQRHz. Less than 4 nV doesn't improve noise performance at all.
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Old 2nd January 2003, 08:49 AM   #37
jcarr is offline jcarr  United States
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Andy:

Note that I am using the AD797 as the input stage of a two-section design. For applications that require lots of voltage swing into lowish impedances, I believe that the TI/BB OPA551 or OPA552 may be more appropriate than the AD797. Or perhaps you could consider adding a unity-gain buffer chip after the 797.

regards, jonathan carr
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Old 2nd January 2003, 08:57 AM   #38
ALW is offline ALW  United Kingdom
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Default MC

Jonathan / Peranders,

I am using MC (a Linn Klyde).

My intention would be for a two-stage design, so no problems there.

Any views on active vs. passive equalisation?

Andy.
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Old 2nd January 2003, 09:57 AM   #39
jcarr is offline jcarr  United States
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Andy:

Passive RIAA is better for overload margin, and tends to do a better job of maintaining the proper RIAA response at all frequencies (active commonly results in a rising HF response, and although this can be corrected via another network, there will be some sonic penalties). Active RIAA has better sn ratios, but the complex feedback load may on occasion require the use of phase compensation to avoid ringing or instability.

In my experience, active can sound at least as good as passive when implemented without phase compensation and with careful design techniques, but passive is the easiest to get good sound from (usually requires less design know-how).

Hybrid is also good, but because passive and active tend to have different "sounds", unless the RIAA curve is spot-on, the circuit can sound somewhat discontinuous. Passive or active only seems more tolerant of RIAA error than hybrid, and passive (subjectively) seems the most tolerant of all.

hth, jonathan carr
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Old 2nd January 2003, 09:58 AM   #40
Electrons are yellow and more is better!
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Default Re: MC

Quote:
Originally posted by ALW
Any views on active vs. passive equalisation?
I think this a typical "taste" question. There are pros and cons with both.

If you want inspiration of the passive approach, check here
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