[happybob]

I'm not an electrical engineer, but I know there are quite a few of you engineers on this forum. Hopefully some of you can help me with this.

I own both the MHDT Lab Paradisea+ DAC and the PS Audio Digital Link III DAC. I've tried them both on my Simaudio I-3 Integrated Amp, which has a digital volume control with buttons. When I use my PS Audio Digital Link III DAC while no music is playing, I would notice a popping noise every time I push the volume up button on the amp. I was told that this is due to DC output from the PS Audio DAC, which is normal since it uses a direct-coupled design and thus can have up to 25mv of DC in its output. I could not replicate the popping noise when using the Paradisea+ DAC or other CD player or changer. I was told that most CD players use output coupling capacitors that eliminate all DC and can degrade the sound, and most likely my integrated amp cannot tolerate any DC on its input by design.

Since I'm not that familiar with all these DC business, can someone explain to me if the popping noise is really due to the DC put from the PS Audio DAC? Is it normal for an integrated amp to have inputs that cannont tolerate any DC? What are the advantages and disadvantages of having output coupling capacitors? Do most popular DACs (such as Benchmark DAC1, Paradisea, Lavry, Stello, just to name a few) use them?

Thanks.

 

[germanium]

Quote:

Originally Posted by happybob /img/forum/go_quote.gif I'm not an electrical engineer, but I know there are quite a few of you engineers on this forum. Hopefully some of you can help me with this. I own both the MHDT Lab Paradisea+ DAC and the PS Audio Digital Link III DAC. I've tried them both on my Simaudio I-3 Integrated Amp, which has a digital volume control with buttons. When I use my PS Audio Digital Link III DAC while no music is playing, I would notice a popping noise every time I push the volume up button on the amp. I was told that this is due to DC output from the PS Audio DAC, which is normal since it uses a direct-coupled design and thus can have up to 25mv of DC in its output. I could not replicate the popping noise when using the Paradisea+ DAC or other CD player or changer. I was told that most CD players use output coupling capacitors that eliminate all DC and can degrade the sound, and most likely my integrated amp cannot tolerate any DC on its input by design. Since I'm not that familiar with all these DC business, can someone explain to me if the popping noise is really due to the DC put from the PS Audio DAC? Is it normal for an integrated amp to have inputs that cannont tolerate any DC? What are the advantages and disadvantages of having output coupling capacitors? Do most popular DACs (such as Benchmark DAC1, Paradisea, Lavry, Stello, just to name a few) use them? Thanks.

I'm not an engineer either but I can tell you a small amount of DC that is present on most any D.C. coupled DAC is of little consequence because most recievers are capacitor coupled anyway. The only times the small D.C. at the output will negatively affect anything is if your preamp is D.C. coupled also & sends amplified D.C. through the volume pots at that will make the pot sound scratchy, also there are a very few D.C. coupled power amps at the very high end that can overheat & even destroy the speakers when presented with D.C. at the input. The popping when the player mutes is a result of D.C. at the output though I seen even capacitor coupled players pop as well. Ive even had the popping go down to a lower level when the output capacitor was replaced by a wire instead but that is rarely the case. Digital volume contols will make a popping noise when there D.C. at the input as well.

D.C. coupling can have it's distinct advantages though in the sound quality as they tend to sound more open with better soundstage than a capacitor coupled one. One has to use really top grade capacitors before a capacitor coupled amp can sound as good & those capacitors are extremely expensive & very large for a given capacitance, consequently they ae rarely used. A 400volt 100uf Solen Fast Capacitor is about as big as your fist, it is a first rate capacitor though that doesn't cause any coloration.

All my sound system has D.C. coupling except my cheap SACD player as they didn't use a differential output DAC on it so it would take major modifications to D.C. couple it & I'm not up to that level of expertise.

Note; D.C. coupling is different than direct coupling in that a D.C. coupled amp will actually amplify D.C. & direct coupling will not as there is a D.C. blocking capacitor going to ground in the negative feedback circuit that controls the gain of the amp in a direct coupled amp but not in a D.C. coupled amp. D.C.coupling implies direct coupling as well of both the input & the output but goes the extra step to get rid of the cap from the negative feedback circuit.

 

[germanium]

Deleted

 

[happybob]

thanks germanium. that was a very good explanation especially coming from a non-engineer.

my ps audio digital link iii is currently being modded by rick cullum. he offered me the option to add the coupling capacitors do get rid of DC if i was distracted by it, but did mention that it will affect the sound quality. the popping noise doesn't really distract me since it's not there during music playing, and i just wanted to make sure that it's a normal behavior of the DAC. i think i'm going to choose not to get those coupling capacitors so the DAC can sound at its maximum potential.