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Denafrips Ares II + Topping Pre90 impedance issue

bsas

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Hi,

So, I have the Denafrips Ares II DAC that I really like. I used to use it on my Aiyima 07 integrated amp since it has a volume control, but I recently got a VTV Purifi (EVAL1 buffer) amp that I love too, but, now I have to control the volume on the Ares 2. For that I recently got the Topping Pre90 preamp to be able to use it as an XLR preamp with volume control.

But, after that I notice that this combination doesn't sound right. After some reading and digging on the Pre90 review post I learned that it is an impedance mismatch between the Ares 2 and the Pre90. Sorry for my own ignorance, but I barely understand this impedance issues when we talk about line level (RCA or XLR) signal.

So, I don't want another DAC. What should I do? Any recommendation of something that can go between the Ares 2 and the Pre90 to "fix" the impedance issue? Can someone explain to me the reason why the impedance on those have such a huge effect? Can I just use the RCA inputs on the Pre90 with the RCA outs of the Ares 2 instead of the XLR and have no issues?

Thanks!
 
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roderickvd

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Oh wow, the Pre90 only has 10KΩ unbalanced in and 2KΩ balanced in? I think that's poor for a preamp, particulary when it's technically not difficult to have a buffer of 1MΩ. You'd be OK going unbalanced in from the Ares II. Given short enough cables you will probably never notice the drop in noise rejection, but you will notice a drop in volume. I don't know but your Purifi amp should have plenty of headroom?

The electrical and in turn acoustic effects of damping have been discussed at lengths on this forum and elsewhere. Just keep the ratio output impedance to input impedance 1:8 or better (1:10 and on) and you will be fine.
 
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bsas

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Oh wow, the Pre90 only has 10KΩ unbalanced in and 2KΩ balanced in? I think that's poor for a preamp, particulary when it's technically not difficult to have a buffer of 1MΩ. You'd be OK going unbalanced in from the Ares II. Given short enough cables you will probably never notice the drop in noise rejection, but you will notice a drop in volume. I don't know but your Purifi amp should have plenty of headroom?

The electrical and in turn acoustic effects of damping have been discussed at lengths on this forum and elsewhere. Just keep the ratio output impedance to input impedance 1:8 or better (1:10 and on) and you will be fine.

Purifi is fine, the problem is that it doesn't have a volume knob so in my mind I thought about the Pre90 as a volume control (the Purifi is 400W, aka, loud as f**k).
 
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bsas

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The latest firmware for the Ares II has digital volume control, if you fancy that. You can flash your current unit with it.

True… but I am never fully sure how much quality one losses with digital volume control :(
 

gvl

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For starters make sure you only have one set of inputs connected on the Ares, there’s a warning about it in the manual. If the issue is real you can indeed try the RCAs, it may work better due to higher impedance on the Pre90 for single ended. If that fails too you’ll need a different preamp with high input impedance. Or use digital volume control as suggested earlier.
 
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pvehling

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I’ll wager a dollar it’s low.
I deleted my message because I found on the forum that the A90 is essentially the same exact as the Pre90.

@roderickvd you said "Just keep the ratio of output impedance to input impedance 1:8 or better (1:10 and on) and you will be fine." So output impedance of D90SE is 100 ohms, and Pre90/A90 discrete input is 2K ohms.. so that ratio should be good? I guess I'm not understanding the ratio. 1:8+ would mean that anything over 800+ohms is fine, right?

Ares II output impedance spec says 1250 ohm balanced, so the issue is that it's not a great ratio to input impedance of the the Pre/A90? Wouldn't even be 1:2..
 
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pvehling

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I connect my Ares II to Gustard P26. According to Ares II product page, rca and xlr have these output impedances
Analog Output
  • RCA at 2.0Vrms, 625 Ω
  • XLR at 4.0Vrms, 1250 Ω
and Gustard P26 User Manual, rca and xlr input impedances are:
Analog input:
RCA:Input impedance 47k
XLR1 & XLR 2:Input impedance 47k

I connect using xlr so by the numbers, I guess it should be ok, right?
I believe from what @roderickvd said, you'll be absolutely fine with 47k input impedance, which is nearly 38 times the output impedance of the balanced output of the Ares
 

roderickvd

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I believe from what @roderickvd said, you'll be absolutely fine with 47k input impedance, which is nearly 38 times the output impedance of the balanced output of the Ares
Correct.
It’s nice to see some manufacturers are actually doing the right thing and not just trying to hit highest rankings on ASR.
Actually I think the Pre90 misses the mark as a preamplifier, generally. A golfing panther from @amirm and a test with 200 ohm source impedance seems to ignore that besides nice graphs a good preamp should have a high input impedance and low(ish) output impedance.

Testing with a 200 ohm source to the 2000 ohm Pre90 still yields a 1:10 damping factor, so is not representative of the situation with even higher impedance sources. Also, the problem with low input impedance is not for the preamp, but for the source, so turning up the APx555 to 200 (which probably has no issue dealing with the higher loading) and then measuring the preamp out only seems to obscure the fact that this preamp just doesn’t have all the hallmarks of a great preamp.

Some might say that ideally sources should be buffered and have a lower output impedance. Such an argument does not take away the fact that preamps should still have high input impedance — which is technically not particularly hard or expensive to do either.

The Pre90 might work fine in a chain of other Topping products only, I don’t know, but I could not recommend it as a preamp generally.
 

pvehling

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Isn't 1250ohm output impedance for a DAC pretty high though? Seems like most modern DACs I've been looking at are far lower, generally under 400ohms. Regardless, it's a bummer the A90 Discrete is so low because it's the perfect size for my shelf. Oh well.
 

roderickvd

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True but again that does not dismiss the necessity for a high Z input on a preamp. The AMB b22 I built myself had one as high as 1 Megaohm! Even a rather normal 50K or 100K would be heaps better than that lowly 2K.
 
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Veri

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Isn't 1250ohm output impedance for a DAC pretty high though? Seems like most modern DACs I've been looking at are far lower, generally under 400ohms. Regardless, it's a bummer the A90 Discrete is so low because it's the perfect size for my shelf. Oh well.
The RCA input impedance is better at 10k though. So that can be an option to use.
 

nn_in

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Good information here.Thank You .
I have connected denon DNP 800ne optical output to Ares2 Dac XLR output to Topping PA5 Power Amp. Iam not sure if are any impedance mismatch issues here between Ares2 and PA5.
One issue is i need to manually operate the volume pot on Pa5 as there is no remote.
If i replace Ares2 with Topping D30 pro i can get remote volume operation .Is the D30 pro compatible with Pa5 ? I have not seen folks use this combination .
 

gvl

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Good information here.Thank You .
I have connected denon DNP 800ne optical output to Ares2 Dac XLR output to Topping PA5 Power Amp. Iam not sure if are any impedance mismatch issues here between Ares2 and PA5.
One issue is i need to manually operate the volume pot on Pa5 as there is no remote.
If i replace Ares2 with Topping D30 pro i can get remote volume operation .Is the D30 pro compatible with Pa5 ? I have not seen folks use this combination .

Can’t you control the volume on the Denon? I mean if it has volume control, I don’t know.
 

pvehling

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Good information here.Thank You .
I have connected denon DNP 800ne optical output to Ares2 Dac XLR output to Topping PA5 Power Amp. Iam not sure if are any impedance mismatch issues here between Ares2 and PA5.
One issue is i need to manually operate the volume pot on Pa5 as there is no remote.
If i replace Ares2 with Topping D30 pro i can get remote volume operation .Is the D30 pro compatible with Pa5 ? I have not seen folks use this combination .
PA5 input impedance is about 10K, so it should be fine for the Ares 2. New firmware on Ares 2 allows for volume control, but not sure of the quality.. Using the analog volume on the PA5 might have the best sound quality. D30 is definitely compatible with PA5, but if you already bought the Ares you could test out that volume control and see how it works with the remote. It has a remote right?
 
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