WolfX700 Measurements of Topping Pre90/Ext90 Preamplifier/ Extender

[JohnYang1997]

Can someone explain, for us idiots , what defines a line-level source component that is "robust" enough to mate well with the Pre90's 2k ohm input impedance? I have seen only "modern" equated with "robust" here, plus an example of an Accuphase tuner.

To put it another way, it seems to me that a lot of modern line-level source components do not include output impedance in their specifcations. For example, my Oppo UDP-205 lists output impedance only for the headphone output, not the line-level outputs. So how would I go about determining whether or not that component would work okay with the Pre90?

I think I have explained in one of the previous posts discussing all cases that may have issues. So UDP-205 is fine regardless of what output impedance of that thing actually is. You only need to turn the preamp up a bit in the worst case scenario.

 

[YSC]

I would say higher output impedance is suspectable for noise pick up and interference. Regular power amps have input referred noise of about 1k to 2k ohm resistor. I would say 2.5k(corresponding to 10k pot/attenuator) is as high I would go, 12.5k (50k pot/ attenuator) is certainly too much to me.

Or if I have a resistor used in series list can we have a formula to deduce the output impedance? Nice if I can learn about this, Googling makes me confused

 

[JohnYang1997]

Or if I have a resistor used in series list can we have a formula to deduce the output impedance? Nice if I can learn about this, Googling makes me confused

There really isn't. Best way is to add a buffer. But then it's something else. Or you can reduce the input impedance further. 2k is quite low on the look but usable.

 

[YSC]

There really isn't. Best way is to add a buffer. But then it's something else. Or you can reduce the input impedance further. 2k is quite low on the look but usable.

O, so even if having a resistor value we can't compute theoretical value of output impedance, I thought it was my stupidity resulting in this

 

[JohnYang1997]

O, so even if having a resistor value we can't compute theoretical value of output impedance, I thought it was my stupidity resulting in this

Output impedance changes across the range. 0 at maximum and nil position and 1/4 of the resistance at 50% position. And in between else where. You can calculate it but there's no way to minimize it without changing topologies or adding a buffer.

 

[YSC]

Output impedance changes across the range. 0 at maximum and nil position and 1/4 of the resistance at 50% position. And in between else where. You can calculate it but there's no way to minimize it without changing topologies or adding a buffer.

ic, can I understand how's the calculation? as I am interested to get one, not trying to optimize or lower that, but I can try to avoid those >1kohm output impedance values and use digital solution from dac instead to feed my 8030C instead of using the high gain active preamp like I currently do

 

[JohnYang1997]

ic, can I understand how's the calculation? as I am interested to get one, not trying to optimize or lower that, but I can try to avoid those >1kohm output impedance values and use digital solution from dac instead to feed my 8030C instead of using the high gain active preamp like I currently do

Just use as normal, it should be fine. As nothing is bothering you.
For most cases you may not go over 50% position (which is usually about 2-3 o'clock already). In normal use it's under 12 o'clock(which is about 25%) right? So no big deal for the most part. When it's at noisier position it's probably really loud already so it won't be so audible either.

 

[YSC]

Just use as normal, it should be fine. As nothing is bothering you.
For most cases you may not go over 50% position (which is usually about 2-3 o'clock already). In normal use it's under 12 o'clock(which is about 25%) right? So no big deal for the most part. When it's at noisier position it's probably really loud already so it won't be so audible either.

ic, that's perfect for me then, I am really liking the Khozmo look and then the volume currently I use is either with dac and the digital volume is at 20-30, and paried with a DACT modded Taurus with 26db gain I always keep the knob at -50 to -60db depends on song and digital volume at 80-100, if so the 48 step khozmo would fit as the sole preamp or use as a pre for taurus if any noise occurs

 

[Cortes]

Output impedance changes across the range. 0 at maximum and nil position and 1/4 of the resistance at 50% position. And in between else where. You can calculate it but there's no way to minimize it without changing topologies or adding a buffer.

@Yohn,
I understand that impedance mistmatches are an issue. But one can't use that argument always as is done very often with jitter in DACs to justify anything.

This is a very good (professional)DAC with its own volume control:

Now with the GoldPoint, or maybe whatever stepped attenuator:

Noise floor with the external attenuator is lower. So, using normal cable lengths as most of the hobbists here do, what's the benefit of passive mode in the Pre90, the Shiits or whetever, over a humble stepped attenuator?. Looking at this graphs I get the impression that those pre-amps look like over-engineered for something ordinary resistences can do.

I'm sure I'm missing something, but I'm struggling to understand what. Of course, I'm always speaking of passive attenuation.

 

[MusicNBeer]

@Cortes, the only thing you're missing is most active preamps have high input impedance and low output impedance so users don't have to worry about compatability of components.

If you're going to have 2K input impedance, there's absolutely no reason not to go passive. Max output impedance of a 2K pot is only 500 Ohms! I use a 10K pot in my Goldpoint passive to be more forgiving of the source component.

 

[JohnYang1997]

@Yohn,
I understand that impedance mistmatches are an issue. But one can't use that argument always as is done very often with jitter in DACs to justify anything.

This is a very good (professional)DAC with its own volume control:

Now with the GoldPoint, or maybe whatever stepped attenuator:

Noise floor with the external attenuator is lower. So, using normal cable lengths as most of the hobbists here do, what's the benefit of passive mode in the Pre90, the Shiits or whetever, over a humble stepped attenuator?. Looking at this graphs I get the impression that those pre-amps look like over-engineered for something ordinary resistences can do.

I'm sure I'm missing something, but I'm struggling to understand what. Of course, I'm always speaking of passive attenuation.

These aren't comparable. The pre90 which I did not talk about is not comparable to things like that. You get good performance and some voltage gain as well as low output impedance but more importantly it's the input output switching, saved volume, remote, screen etc. Also you get way more steps with relay controlled here. A good stepped attenuator will cost 200 dollars itself, for a passive preamp on the market it will likely be 600+. And I don't want to say about this but pre90 will be cheaper than that with all that extra functionalities.
If you include regular potentiometer volume control then L30 is just over 100 dollars with pristine signal path.
The beauty is that you can choose whatever that fits your use case. And it's fine. I'm not here telling everyone to buy a pre90.

 

[Tigi]

Hi @JohnYang1997, is there a chance that you will produce the A90 with a remote control in the near future? I see the A90 as the ideal ultimate headamp/pre combo solution for a reasonable price, but the remote control is really missing here.

 

[Billy Budapest]

View attachment 95896

Thanks. I thought the extender unit would have had a source indicator on it, but no big deal.

 

[Rja4000]

Hi
Thanks for this review !

For a Pre, THD+N and/or IMD+N vs level is very important, IMO.
Is there a chance you measure that ?
(I know. We always want more...)


EDIT: OK, I see you published dashboards at -20, -30, -60 and -90dBr
Not exactly the plot we're used to, but that gives enough of an idea.

 

[JohnYang1997]

Thanks. I thought the extender unit would have had a source indicator on it, but no big deal.

It's on the main unit.

 

[JohnYang1997]

Hi
Thanks for this review !

For a Pre, THD+N and/or IMD+N vs level is very important, IMO.
Is there a chance you measure that ?
(I know. We always want more...)

https://www.audiosciencereview.com/...ext90-preamplifier-extender.17635/post-573276

 

[Rja4000]

https://www.audiosciencereview.com/...ext90-preamplifier-extender.17635/post-573276

Yes, thanks. Just found them.
I just edited my post

 

[raif71]

I suppose I can just get the ext90 only and use with existing amp?

bump

 

[hmscott]

I suppose I can just get the ext90 only and use with existing amp?

I think I saw commented that an idea was to add support to the A90 for the extender, but the extender uses a proprietary interconnect - many pins - to connect the main unit to the extender.

So unless a future device from Topping comes out that supports the extender interconnect cabling it will only work with the Pre90.

 

[okok]

what is the attenuator in this?