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How is 11V peak-to-peak possible here?

mike7877

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So I just got the DX1, sounds great so far - love it.

Upon closer inspection of specs now, I see high gain HP output is rated for 11V peak to peak...

How is this possible? Even 5V both ways is 10V, so...
1697196877346.png

They don't mention that their LNRD boosts voltage.
They do say they don't use off the shelf USB power chips, which is great for this application.

From the E30 II:
"The Discrete LNRD circuit filters out the noise of various 5V power inputs and provides a stable power supply of ultra-low noise reference level."

So it seems to be a filter...

So, how is 11V possible? They've listed it as a spec, and I'm sure if I hooked up my scope (or even multimeter with a <2000Hz tone), I'd see 7.78 VAC RMS (11V p-p)


1697196760288.png
 

voodooless

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I know what a boost converter is - what a stupid thing to do in a low noise device. Making a lot of work for just 0.5V each way, though- wouldntcha say?

Is there any other way?

Each way would mean you'll also need a -5V to get to 10Vpp already.
 
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mike7877

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Each way would mean you'll also need a -5V to get to 10Vpp already.

I was under the impression that you can use the same side hooked up the other way around. I'm a bit of a noob though lol (now slightly less).

Funny that it's not mentioned in the documentation when they talk about the power supply. They only talk about their filtering of the 5V... Why filter the 5V before the boost converter? You'd have to filter it again, unless the boost converter was not no regular boost converter!

I think it's pretty funny that they chose to only increase voltage to 11V - with the amount of current that the op-amps are able to push, they could've raised the voltage up quite a bit higher for better support of 600 ohm loads. 34V would be more than enough for 31V peak to peak, which would be enough for 200mW / 600 ohms.

They could've done 3 gain stages, with the first giving the op-amp +2.5V/-2.5V, the second +5.5/-5.5, and the last +17V/-17V (two configurations of the boost converter, not two boost converters). I'm only saying because apparently one complaint is that the DX1 can be quiet. Wouldn't have cost more than a dollar at manufacture!

I guess it's easy to criticize after the fact. This is the DAC that got Topping on the map, right? That's what I gather from https://apos.audio/products/topping-dx1-dac-amp

edit: graph to support voltage choices

1663622326-THDN-Ratio-vs-Measured-Level.jpg
 

voodooless

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Here is a similar circuit from the E30:

TOPPING-E30-II-e30ii-Digital-Audio-DecoderCOLOR-2-AK4493-XU208-32BIT-768K-DSD512-Touch-Operation-With.jpg


See the voltages: + and - 5.6V. Probably a very similar scheme is used here. Both of these voltages are made by a DCDC from the 5V USB, and probably the filtering is part of the circuit as well.
 
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