Is a preamp needed?

[majingotan]

We had a recent detailed discussion here about this on another thread. The summary is: a passive preamp can be more transparent than an active, under certain conditions. The conditions are mainly: the passive preamp is well engineered (ladder attenuator with metal film resistors), your upstream sources have low output impedances, your downstream devices have high input impedances, and you use short, low capacitance cables.

Any objectifiable references for that conclusion? At least with my Schiit Saga preamp reviewed here at unity volume, Passive is audible transparent at 120dB SINAD while active is about 97dB SINAD (still inaudible unless playing a -90 dB test tone)

 

[MRC01]

The passive may or may not measure better at unity volume. But unity volume (say, 2 Vrms) isn't the comparison that matters because we don't listen that loud. The 50 mV level is a more relevant test, which is typically 70 to 80 dB SPL with most headphones. Yet being 32 dB quieter than unity gain, a typical active preamp will have around 32 dB worse S/N ratio (plus or minus), so now the 120 drops to 88 dB (more or less). Amir's measurements of full scale vs. 50 mV SNR shows this theoretical estimate to be roughly true. Yet the passive is still around 120 dB or better (thermal noise of metal film resistor) even at these lower levels, which we actually use when listening.

 

[Novak]

We had a recent detailed discussion here about this on another thread. The summary is: a passive preamp can be more transparent than an active, under certain conditions. The conditions are mainly: the passive preamp is well engineered (ladder attenuator with metal film resistors), your upstream sources have low output impedances, your downstream devices have high input impedances, and you use short, low capacitance cables.

Thanks that's useful.
Does dac or streamer/dac providers communicate about their output I impedance? Usually much lower than power amp?

 

[MRC01]

Input and output impedances are usually shown in specifications. Solid state devices are usually 100 ohms or less output, 20k ohms or greater input. You want at least a 10:1 ratio and these typical impedances give 200:1 which is more than enough. The attenuator is in the middle and you want at least 10:1 on each side (e.g. a 10 kOhm attenuator having worst-case output impedance of 2.5 kOhm @ -6 dB attenuation). Also, most normal cables have low capacitance so normal lengths won't be a problem. However, there are exceptions so one should confirm before using a passive attenuator.

 

[MRC01]

That is exactly what I do with my RME. I use a passive preamp that was custom built with excellent attenuators and switches. If you don’t have impedance matching issues with your amp this kind of setup has vanishingly low noise and distortion and allows the DAC’s SINAD to be put to optimal use. It also works for my phono setup.

Amen to that. That's exactly what I did for 10 years, having built a 10k passive attenuator about 20 years ago. Here's more info on passive attenuators, for those who are interested.

 

[Novak]

Same thing here, I put a passive pre between dac and amp. I found a passive pre with a remote control which is nice

 

[MRC01]

Note: the RME doesn't need a passive attenuator as much as some other DACs might. Its unique "ref level gain" feature automatically reduces the gain at lower volume levels, which reduces noise & distortion at low volumes. The result is that the RME is among the best performers in Amir's 50 mV measurements.

However, a passive attenuator could provide better SNR/SINAD at low volumes with most other DACs that use conventional attenuation (either digitally or a pot). With these, SNR typically drops 1:1 (or worse) with volume. And a passive doesn't.

 

[lucadoc]

Same thing here, I put a passive pre between dac and amp. I found a passive pre with a remote control which is nice

Could you give some references of passive pre in the range 200€ 500€ that would be worthy with a Dac and ncore amplifier? Thanks

 

[Aldo]

What do you think of the DAC TOPPING DX7 pro?

 

[Jimbob54]

What do you think of the DAC TOPPING DX7 pro?

Aldo, I think you would do better checking the review and comments https://www.audiosciencereview.com/...-dx7-pro-dac-and-headphone-amp-reviewed.9446/

 

[Aldo]

Message modified and translated

I'm sorry... I got a little carried away when I woke up this morning!
but I was a little disappointed in your answer!
In the language of Shakespeare:

I'm sorry I didn't read the 54 pages of comments. However, yours is quite short.
Given its price and its SINAD, I don't see what's wrong with it? If it's not the impedance of its headphone output, but here it's not the subject.
Thank you for enlightening us, he argued, if your time is not too precious and since you have read the 54 pages of comments of the TOPPING DX7 pro.
To read you.

 

[Jimbob54]

Je suis désolé de ne pas avoir lu les 54 pages de commentaires. Cependant, le vôtre est assez court.
Vu son prix et son SINAD, je ne vois pas de quoi on peut lui en vouloir? Si ce n'est pas l'impédance de sa sortie casque, mais ici ce n'est pas le sujet.
Merci de nous éclairer, argumenta-t-il, si votre temps n'est pas trop précieux et puisque vous avez lu les 54 pages de commentaires du TOPPING DX7 pro.
Pour vous lire.

With respect, your English posts were far more comprehensible on this English language based forum.

 

[Novak]

Could you give some references of passive pre in the range 200€ 500€ that would be worthy with a Dac and ncore amplifier? Thanks

Sorry I don't know in this price range.

 

[lucadoc]

Ok, I imagine that the pre would be more expensive

 

[Novak]

Ok, I imagine that the pre would be more expensive

passive preamp are often too expansive for what is really in the box but produced in small batches (handmade?). So yes, it can be.
But I am sure there should be passive pre options in your budget that other folks might know (Khozmo should be in your range)