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Topping D70 DAC

wadec22

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I have the SMSL M10 arriving tomorrow. I know on paper it is not as robust as the D70 (it's more comparable to the DX7s), but I am still pretty pumped to see how it pairs with the THX.
 

Toku

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Looking at the advertised THD+N for the DAC chips themselves to give a lower bound:
Code:
ES9038PRO: -122 dB
ES9038Q2M: -120 dB
AK4497EQ:  -116 dB
AK4493EQ:  -113 dB
AK4490EQ:  -112 dB
I guess AKM are a bit behind ESS in this area (or more honest), but it looks like switching chips makes Topping's life a bit harder in terms of improving SINAD.
You forgot AKM 4499EQ
S/N 140dB, THD -124dB
That's excellent!
 

trl

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Usually a standalone DAC might measure better than a combo, mostly because there's no PCB and PSU sharing, no EMI/RFI from additional transformer or boost/buck regulators.

Volume regulator? Not sure the scenario, but I assume you're referring to the volume knob, right? It's a rotary knob that controls DAC output volume (volume control it's built-in DAC chip).
 
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Usually a standalone DAC might measure better than a combo, mostly because there's no PCB and PSU sharing, no EMI/RFI from additional transformer or boost/buck regulators.

Volume regulator? Not sure the scenario, but I assume you're referring to the volume knob, right? It's a rotary knob that controls DAC output volume (volume control it's built-in DAC chip).
Volume control build in DAC chip degrade sound qualiry. I prefer resistor ladder like in NuPrime.
 

Toku

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Volume control build in DAC chip degrade sound qualiry. I prefer resistor ladder like in NuPrime.
If so, D70 is a completely unsuitable product for you.
However, if you set the RCA output to the fixed output mode and then add a ladder resistor type volume, you get the desired behavior.
 

trl

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Volume control build in DAC chip degrade sound qualiry. I prefer resistor ladder like in NuPrime.
This is not per our choice, is built-in by manufacturer and enabled later by the designer. From all tests done by manufacturers, the 32-bit volume control built-into the DAC chips are perfectly fine. However, you can add a ladder resistor later and keep the in-chip volume to the max., but that means DIY and tinkering.

My personal point of view of the built-in digital volume control over the resistive-control:
- lowest background noise possible and best SNR-ever, especially if the chip can be firmware programmed to deliver 4.5V RMS (feel free to add a resisitve ladder to Topping D10/30/50/70 and compare measurements with volume to 1/2 under both scenarios).
- cheaper to implement, without adding any active or passive components around.
- no Johnson noise, like the ladder resistors or regular pots.
- however, a noisy input stage (if exists) or a a higher gain-stage (>5X) will make the amplifier less compatible with sensitive headphones (8-16 Ohms IEMs); a resisitve volume control between the DAC outputs (or voltage gain, like O2) and the output buffer may help here a bit.
- with regular resistive volume control it takes me half of sec. (1 turn of pot.) to get the volume from max. to min., instead with digital volume I need 3-4 turns of the rotary knob to do that (I like analog pot. more here because it's faster).
 

tired_guru

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Volume control build in DAC chip degrade sound qualiry. I prefer resistor ladder like in NuPrime.
On the contrary. If DAC uses enough bits inside to calculate it, it is the only method to change volume without any degradation. I am afraid you have no idea how things work. For example ESS DAC uses 48bit (!) word length inside to calculate volume. This is completely audibly transparent and shoud be used wherever possible.

Resistors ladders are great though for amps volume control instead of standard carbon path pots, as long as ladder is built from high precision, SMD resistors (lack of inductance because of no legs for through the hole soldering). You can have then perfect channel balance + very small impact for the sound. Good quality ones like DACTs are extremely expensive but there are a lot of simple contructed stuff on ebay from China which do the job decently.

Still PGA laser trimmed electronic resistors ladder with some encoder can be better solution - you don't have to clean it from time to time to avoid scratching sound during switching steps (once the oxidation or some pollution got inside the mechanism).
 
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trl

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Built-in DAC volume control has the perfect channel volume match ever, not even +/-0.1dB difference. It's also easier to control it via software and remote control, no need for expensive motorized pots.

However, a pot in the middle, placed somewhere between the gain stage and output buffer will definitely lower the output background noise and very sensitive IEMs will feel better with pots instead of DAC's digital volume control. Basically, between the DAC and headphones jack there's no electronic active or passive circuit to lower the background noise, so all the internal noises of the components will end up in the headphones. So, lot of care in the layout design and care when choosing the low-noise components as well are needed.
 

tired_guru

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Basically, between the DAC and headphones jack there's no electronic active or passive circuit to lower the background noise, so all the internal noises of the components will end up in the headphones.
Interesting.

I guess this digital volume control itself on the DAC's side, has no bigger impact than a lot of what's going on inside the DAC itself during signal processing. I guess you meant lowering general internal noises from the DAC itself, not the digital volume alone. But this depends how well PCB is designed, how speed signal part is separated from analog output part, how many layers is being used, how were ground/VCC planes placed, is the ground connected in a star fashion + all kind of EMI/EMC requirements met.

I used to design this kind of circuits, also measuring very small signals using differential circuits, filtering in digital & analog domains, processing them with multi point calibration for some non-linear sensors. Difference between bad and state of the art implementation using exactly the same components can be drastic.
 
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trl

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[...] I guess you meant lowering general internal noises from the DAC itself, not the digital volume alone. [...]
I'm only thinking that between the DAC and the headphones jack there are lot of active and passive components that generate electrical and thermal noise. Placing a resistive potentiometer or ladder array between DAC's output stage and gain stage of the headphones amplifier will reduce the background noise. Of course, this may only help with >100dB/mW low-impedance headphones.

My test IEM's are Superlux HD381f having 16 Ohms internal DC-resistance, 103dB/mw, 120.5dB/V sensitivity. To drive them with peaks around 100dB (normal peaks for an average listening of 80-85dBFS) the amplifier needs to apply 90mV RMS, so an amplifier with less than 9uV of background noise will be needed for an attenuation of 80dB (usually we don't really hear a noise 80dB lower than music's peaks). So it's really hard for an amplifier to provide such low numbers, especially if internal gain is high (>5X) and there's no resistive divider in there to lower the output volume.

P.S.: With volume to the max. (input RCA shorted, no music playing) Burson PLAY v1.6 with AD8599/AD797 and custom linear PSU is having the lowest background noise from all my amps (compared with Matrix M-Stage HPA-3B with medium-gain, Objective2 with a gain of 3.3X, Burson FUN, ASUS Essence One). For the above "test", the analogue volume control was set to around 7V RMS with 1KHz sines, then all input sources went muted, so I can wear the sensitive IEMs and A/B test the internal noise. If notching down the analogue volume controls down to zero value, then Objective2, HPA-3B, Essence One and FUN are the winners, in that specific order, then follows the PLAY combo. Of course, the noise difference I'm speaking about are so tiny that during the day this test can't take place, so only during a very quiet night this can happen.
 

tired_guru

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103dB/mw, 120.5dB/V sensitivity
You should check out new JDS atom to drive these. In unity gain mode. First be sure that the dac connected to the amp is fully separated from PC ground (optical + some reclocking of samples on the DAC's side). There should be no possibility to create ground loop even if the dac uses 3 prongs plug because atom is using only 2 prongs. So it should provide benchmark environment for how dark is the background of the atom during quiet passages in the night :) You may be shocked ...
 

Veri

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And, when will we see products coming out using the AK4499EQ chip?
Asahi Kasei Microdevices Corporation, (AKM), has developed a new D/A converter, (DAC), the AK4499EQ. It is the latest, “VELVET SOUND|VERITA”, product, following the prior generation flagship DAC, the AK4497EQ. The AK4499 adopts Current Output architecture, which is the first among AKM products. It achieves the world’s highest class of low THD+N and high S/N. Samples will be available in January, 2019, and Mass Production starts from May, 2019.

So no, devices to be using it will take a while yet. Maybe by summer/end-of-year...
 
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