[HFFan]

Quick question for D400EX owners, why does it not have 12V Triggers?

On the other hand, the comparable Topping E70V has convenient 12V Trigger ports.

Especially when it is only equipped with the very limited "Dimmer" function. You can't make the screen stay on only when tracks are playing. And you can't make screen to time out only when no tracks are playing. It's either always on or turning off after a specific time between 5-60 seconds.

Is there any workaround?

 

[HermannS]

I just had a look at images of the SMSL SU-10. There we have it, the Vref trimpot solution for the IV stage, and also the capacitor multiplier (which I would rather call a Zener-transistor regulator) for +/- 12V. Also remarkable: no supply bypassing for the op amps?

 

[Head5]

I don't think there is a zener transistor regulator because between colector and emmiter is 0.6v plus voltage of the op-amp current × output impedance of capacitive multiplier. Sometime maybe I'll remove the power supply and I'll use my lab power supply with 13v for exemple. If is zener regulator, then the output voltage will remain the same. I think that diode is just for safe there, anti reverse voltage.

 

[HermannS]

I don't think there is a zener transistor regulator because between colector and emmiter is 0.6v plus voltage of the op-amp current × output impedance of capacitive multiplier. Sometime maybe I'll remove the power supply and I'll use my lab power supply with 13v for exemple. If is zener regulator, then the output voltage will remain the same. I think that diode is just for safe there, anti reverse voltage.

Well, I think it is. I annotated a close-up of the circuit and it looks exactly like the one I found here: https://electronicsarea.com/transistor-zener-diode-voltage-regulator-circuit/
The capacitor C2 is in parallel to the Zener, supposedly to reduce its noise. It is bigger than the others, I guess at least 22µ. You basically drew the circuit yourself earlier, just the Zener was missing in the right spot.

 

[Head5]

No, I think it is not zener voltage regulator because the votage between base and collector is very small, max 0.6v. That means 0.6v/2200ohm= aprox 250uA. All op-amps sink aprox. minimum 10mA bias current. That means will must be an aprox. 10mA/100(transistor gain)= 100uA in the base of transistor for the 10mA op-amps current. So, 250uA-100uA= 150uA current for zener diode. So, 150uA×11v= 1,6mW dissipation for zener diode. For me is too small current for zener diode to work properly.

Maybe I am wrong, we must to see exactly what is there

 

[HermannS]

You have a point there. I also wondered about the large R value. All regulator circuits I found on the interwebs have 500 Ohms or less. However, the circuit topology fits 100%. I think I am going to measure across the diode and see what's up with the reverse voltage.

 

[Head5]

First time I was thinking at a Darlington transistor but the base-emmiter voltage is only 0.6v, not 1.2v. Who knows, maybe is a Sziklay pair transistor and then R=2200 ohm is ok.

 

[HermannS]

It's annoying that there is absolutely nothing to find about this transistor in any SMD code table I know :-/. And BTW, the devices with the scratched-off markings are dual op-amps. It is a well-known filter circuit for DACs. ESS recommends the same. I tried the OPA1612 and the LME49860 and neither one did beat the original in terms of sound quality. SMSL has found an unknown gem apparently and did not want anybody to find out.

---- edit

So, the output voltages of the circuits are not symmetrical. I measured:
out: -10.76, +11.08
Zener voltage minus side: 11.41, plus side: 11.7
According to the regulator formula above, the output voltage is Vz - Vbe, which fits the measurements perfectly. Vbe is around 0.65 in both.
Measuring tiny SMD parts is always stressful. One slip of the test tip and boom, the device can die

 

[Head5]

11.08v + 0.70v = 11.8v That is the voltage at the base of the transistor, ok ? Don't forget about Vinput, 12v. This voltage, 12v, is the voltage at the collector of the transistor. So, we have Ucb=12-11.8=0.2v The 2200 ohm resistor is between C and B. So, we have Ucb/2200ohm= 0.2/2200= 90uA !!! This current is too small for base resistor and zener diode. And much more, Ucb=0.2v is too small, the transistor is near saturation region. Any variation of the input voltage will affect the operation of the transistor. In my opinion it would have been better that input voltage to be bigger than 12v, maybe 13v. Anyway, all the power supply is a crap. They design it like a butt.

That op-amps, scratched-off, double op-amps in fact, there are special because has big capacitors at the outputs. You can not use opa1612, lme49860, etc... If you want to use it, you must to remove all the output capacitors. Toppins use OPA1612 there but with very small capacitor at output. The most probable, that op-amps are something like LM7322 wich accept big capacitors at the output.

 

[HermannS]

I am enjoying this conversation. I am thinking about the A26 as my next project (hobbies, what can you do :-D). It has very good genes, so to speak. The D400 is limited by design, although it really performs best of all the DACs I had so far, and none of them were slouches.

 

[Emilar]

I am enjoying this conversation. I am thinking about the A26 as my next project (hobbies, what can you do :-D). It has very good genes, so to speak. The D400 is limited by design, although it really performs best of all the DACs I had so far, and none of them were slouches.

There is no need to switch to A26. Going from an ok output stage to a little bit better one is not going to cut it.
These AKM Dacs shine when the whole opamp stage is bypassed. Tap the signal as close to the output pins of the ak449x as possible. Then fully balanced into a good output transformer and into your preamp. You will never look back.
I did this with all my AKM Dacs 4490, 4493, 4495....
Even just 4 Siemens MKV caps going straight balanced into my amp sounds way better than with the opamp stage.

Greets Klaus

 

[HermannS]

That's an interesting idea, Klaus. Care to share any links where I can study some designs?

 

[Emilar]

 

[Emilar]

That is my double AKM Ak4495 attached to TPA 3255 bypassing opamp stages on both devices. Input is a diy Dante board by Monism.

 

[HermannS]

Woopeee, I like the DIY looks! :-D How did you choose the transformers?