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Old 18th January 2015, 10:13 PM   #1
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Default DAC and External (Vintage) Preamp/Integrated Amp

Is it possible to get lower volages than 2 VRMS/lower powers from DACs? ... And use external standalone preamps or preamps from integrated amps?

AFAIK some old vintage preamps have attenuators and others don't. Some people even modify their pres to take up to 7 VRMS (for ex.: Sansui's AU-999).

How do you handle high outputs from DAC/CD players when connecting them to vintage preamps/power amps?
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Old 18th January 2015, 10:33 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by matijaudio View Post
Is it possible to get lower volages than 2 VRMS/lower powers from DACs? ... And use external standalone preamps
How do you handle high outputs from DAC/CD players when connecting them to vintage preamps/power amps?
Many older preamps have the inputs go directly to a volume control, so there's no overload problem.
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Old 18th January 2015, 10:50 PM   #3
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And many haven't. For ex.: Sansuis. Some models have built-in attenuators. And you can always add attenuators to the line (I saw them small as RCA connectors).

DACs have opamps pre preamps. I'm new into HiFi/Audio, so correct me if I'm wrong. Is it possible to use external preamp instead and get the signal at it's source (before opamp in line)?
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Old 19th January 2015, 12:59 AM   #4
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Depends on the DAC design - many DAC chips have internal opamps and its impossible to get the signal prior to these. Most designs which aren't using chips with on-board opamps use them externally. A minority use a current out DAC chip followed by passive I/V and non opamp-based amplification.
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Old 19th January 2015, 01:39 AM   #5
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abraxalito, thank you!

So in designs with by the book IC implementations, precise clocks and good PSUs the difference should be minimal or virtually none. Is it correct?

What is the difference between IC opamping and use of "external" (onboard) opamp? In dynamics? Less distortion?

As far as I Googled both popular ICs (ES9018 and PCM1794) permits passive I/V implementations. Examples are audiodesign's and DD's.
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Old 19th January 2015, 02:00 AM   #6
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In my experience the problems with opamp sound quality are down to PSU quality. That is - opamps are much more demanding of power supplies than most designers realize. So you can undo a lot of the damage to SQ which is laid at the feet of opamps by improving their supplies.

There is an exception to this principle though, that's when an opamp is being fed with fast edges direct from a DAC chip - I don't believe the SQ problems introduced by such an opamp can be fixed up with better supplies. The opamp shouldn't be fed such out of band (OOB) signals in the first place, so a passive filter is in order between the DAC and the opamp.

IC opamps tend to be built on CMOS processes because the digital parts of those chips need CMOS. CMOS is my last choice of process technology when looking at an opamp for audio use. Using external opamps allows them to be BiFET or bipolar which are more appropriate where SQ is the main issue.

Yes dynamics is the issue - a poorly decoupled opamp squashes the perceived dynamics.
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Old 21st January 2015, 10:10 PM   #7
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How much power would you recommand for ESS9023 based board (with IC's opamp)? 5, 10 W? (1, 2 A @ 5 V)?
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Old 21st January 2015, 10:38 PM   #8
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Agree with all the above posts from abraxalito.

It is not about quantity (a supply of a few tens of mA are enough for your average opamp) but about quality.

Since opamps have no HF PSRR, the best way to screw up the dynamic performance of a good opamp is to apply resonant decoupling. That is very easy to do : just add a 100nF ceramic in parallel with any low-ESR capacitor, ceramic, film, oscon, whatever. Then add one ceramic per opamp and connect it all together with highly inductive traces. Then connect to DAC. This pretty much guarantees all the kinds of fail than can happen, will. For extra fail, use a regulator that is unstable with the chosen capacitors.

Bulletproof recipe is 1uF or larger X7R SMD, plus high-ESR cap around 50-100 mOhm, aluminium tantalum whatever, with reasonably low inductance, ie not more than 3.5mm pin spacing. I like Panasonic FR/FM electrolytics, cheap, very high quality, no microphony, very reliable. Add suitable regulator and you're good to go.
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Old 21st January 2015, 10:53 PM   #9
00940 is offline 00940  Belgium
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The most simple answer to the original question would be to build a simple attenuator into an RCA cable and be able to use any modern DAC...
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Old 21st January 2015, 11:00 PM   #10
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Btw, while I agree with everything peufeu said, I can't make sense of abraxalito's comments, unless we're told what he means in technical terms by "dynamics", how they are "squashed" and how to measure these things in practice.
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