WolfX700 Measurements of Topping Pre90/Ext90 Preamplifier/ Extender

[win]

Just bumping a previous question: can you use RCA and XLR as switchable inputs? Would really liked to see at least two inputs on something claiming to be a preamp, you almost have never seen something been called a preamp with only one input, this makes it basically a volume control.

has to be... otherwise it would just mix the sources

 

[777]

It's the same low impedance. If anyone what it high, don't buy.

What a shame ! 2k ohm input for a pre-amp ? The industry standard is a 47k ohm. Topping D90 and the rest of the Topping DAC's has a weak output stages, just a simple op-amp with 100 ohm series and a very weak power supply. Why don't you put a additional buffer with a switch ? Who need lowest noise, will choose 2k ohm directly input and for the rest of the people, 47k ohm is a perfect input. This 2k ohm input it's a big disappoiment for the people, maybe is good for a Robocop which want -150dB of noise. You just kill the good sound in the name of perfect measurements.

 

[JohnYang1997]

Too bad! according to what I can see in the AVS threads, I think there is a lot of people like me who aim to combine home cinema and hifi in the same set-up. Since these days most of the DAC or DAC+preamp solutions are all giving stellar measurements, I do not understand why Topping, SMSL or Gustard do not add new features in their new devices which can improve the customer experience instead of being engaged in a race to implement the last DAC from AKm or ESS. It will be much more helpful for them to differentiate from competition.

It's a design consideration that affects the whole product line. It will make larger outcry if the 12V trigger can't be used with other products like current DACs and power/Integrated amplifiers. Then will people also want it on headphone amps?
Yeah it's a shame but it's nothing more than that.

 

[JohnYang1997]

What a shame ! 2k ohm input for a pre-amp ? The industry standard is a 47k ohm. Topping D90 and the rest of the Topping DAC's has a weak output stages, just a simple op-amp with 100 ohm series and a very weak power supply. Why don't you put a additional buffer with a switch ? Who need lowest noise, will choose 2k ohm directly input and for the rest of the people, 47k ohm is a perfect input. This 2k ohm input it's a big disappoiment for the people, maybe is good for a Robocop which want -150dB of noise. You just kill the good sound in the name of perfect measurements.

There's no industry standard first of all.
Secondly if it measures fine it's impossible to sound bad. WTF is 'kill the good sound"?

 

[Veri]

You just kill the good sound in the name of perfect measurements.

I am using the L30 extensively in amp/pre duties and the sound is very good. I'm not sure your criticism is truly warranted :/

 

[Harmonie]

It's a design consideration that affects the whole product line. It will make larger outcry if the 12V trigger can't be used with other products like current DACs and power/Integrated amplifiers. Then will people also want it on headphone amps?
Yeah it's a shame but it's nothing more than that.

If the whole product line is the consideration, then do you consider the trigger at least at the end of the line >> on the power amps that you are currently designing ?

 

[AndyLu]

You just kill the good sound in the name of perfect measurements.

I have read this sentence a couple of times. But how can perfect measurements kill good sound? Seems like a contradiction in terms. To me it does not make any sense. Care to elaborate?

 

[777]

The op-amps has a little bias current in A class, about 0.5mA. At 3Vp-p and 2k ohm load, we have 1.5mA, so, will work in AB class. With 10kohm will remain in A class.
The sound is not just SINAD score for static measurements. It's about the transients, it's about the power supply response in fact. At low input impedance the sound will be transparent but in the same time is a "flat" because the power supply will not be just as fast.

 

[Harmonie]

What a shame ! 2k ohm input for a pre-amp ? The industry standard is a 47k ohm. Topping D90 and the rest of the Topping DAC's has a weak output stages, just a simple op-amp with 100 ohm series and a very weak power supply. Why don't you put a additional buffer with a switch ? Who need lowest noise, will choose 2k ohm directly input and for the rest of the people, 47k ohm is a perfect input. This 2k ohm input it's a big disappoiment for the people, maybe is good for a Robocop which want -150dB of noise. You just kill the good sound in the name of perfect measurements.

Not sure about the "industry standard 47k ohm" though.
I remember that figure in the past, but that's about phono-input and LP33, vinyl times.
Maybe @restorer-john can respond.

 

[777]

We do not want to rely on a regulators. We want to sink the minimum variable curent required by music from the local capacitors because that current can be very fast. If we starving local capacitors, we will rely on the first capacitors which are bigger. The chain up to the output stage will be more longer and more slower. The result is a "flat" sound, uninvolved. That's what we feel in our ears. So, maybe we do not hear the noise from the couch but we feel the flat sound.
If you want a minimum noise, low resistances, then you must have a very hefty power supply which mean much more money. In our case, we must to buy an expensive DAC with hefty power supply and output stage.

 

[EdW]

Not sure about the "industry standard 47k ohm" though.
I remember that figure in the past, but that's about phono-input and LP33, vinyl times.
Maybe @restorer-john can respond.

I recall an input impedance of 100k ohms being typical for a line input so that drive levels wouldn’t be significantly affected if driven from 10k or 600 ohm sources
EDIT: As an edited afterthought I guess these higher input impedance levels are a throwback to the days of valve/tube amplifier stages where impedance levels are generally higher. But the issue is that these impedance levels passed into most semiconductor amplifiers almost by default and so some CD players etc. will even have a 1k resistor in series with the opamp O/P - possibly in an effort to prevent instability with capacitive loads?
I would like to be able to use older equipment with the preamp though.

 

[ririt]

What a shame ! 2k ohm input for a pre-amp ? The industry standard is a 47k ohm.

Can you please elaborate: what are the consequences of this 2k ohm value when you want to associate it with a power amp?

 

[Joaquinín]

Low input impedance is particularly problematic when the source output impedance depends on the frequency, such as in case of capacitor coupled outputs which are common in older gear, and you end up with low frequency droop. There's nothing good about low input impedance, in this instance it's a side effect of omitting the input buffer with the only reason to post a good SINAD value on this forum. If you think about it, it's those with legacy gear who should be the target customers for such a preamp, yet due to its low input impedance it may not be an ideal pairing.

Do you think an Accuphase T-101 tuner (output impedance: 200 ohm) will not give its best with this preamplifier?

 

[EdW]

Do you think an Accuphase T-101 tuner (output impedance: 200 ohm) will not give its best with this preamplifier?

I don’t know the Accuphase tuner - I’d imagine it would be just fine - providing it can source the necessary current into the load of the preamp at max modulation without a significant increase in in distortion. My caveat here is because I suspect it has a discrete amplifier class A O/P stage with limited current capability. So you may need to check with Accuphase.

I can understand the wish to avoid a voltage follower buffer in the preamp, which would solve the problem, in the design of the preamp from a purist technical viewpoint. It would likely as not degrade the THD+Noise a dB or two. But it’s a shame that there isn’t at least one high impedance input on the preamp for completely universal compatibility.

 

[Music1969]

Relay of course.

Hi

What are the advantages of relay over stepped resistors?

 

[solderdude]

Easy to make remote control (without resorting to a motor) but requires power supply and R2R alike configurations.
You can make more 'steps' with relays as well by clever usage of the relays.

 

[Trouble Maker]

I see your 50Hz power in there.

 

[jruser]

So, based on that measurement from Wolf, this has granular volume adjustments down to -24db, but lower than that are jumps of -5db and -10db. Am I interpreting that right?

 

[gvl]

Do you think an Accuphase T-101 tuner (output impedance: 200 ohm) will not give its best with this preamplifier?

It has a DC blocking capacitor on the output and the output impedance is likely higher than 200 Ohm on low frequencies, hard to say without measuring it but it might sound lean with a low impedance input on the pre.

 

[somebodyelse]

I have read this sentence a couple of times. But how can perfect measurements kill good sound? Seems like a contradiction in terms. To me it does not make any sense. Care to elaborate?

The unusually low input impedance improves measured noise performance with the AP as a source, but causes a more audible frequency response problem when used with a variety of real-world source devices, particularly older ones.