A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

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#9,082
dddac said:
This is already the case since a couple of years without any problems. The 2sk208 was obsolete or hard to get, so I took the 2sk3666-3 as replacement.
I never had any issue with stability nor heard of any so far. So please send me your test report showing the sensitivity and instability versus the 2sk208. I will look into it. For me there is no reason for any worries. The current throug the FET is 400uA and with the 2k trimmer you will be able to get a negative UGS of max 0,8 Volt Which is more than enough to get a stable value even when the spread of this FET would be at the max of 3mA. In case you refer to turning the trimmer in regard to sensitivity, you could replace the 2k trimmer with a 1k or 500 Ohm. This will give you more turns per Ohm, making it may be a bit easier to set the 40mV. May be a mother note. The 40mV is not a critical value, like 40,000 or so 39,5 or 41 will also do the job nicely for example
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Yes, you are right. Thanks for the explanation.
Thank you.
 
#9,083
I have one more question about the power supply for the DAC.

I have a blue motherboard with 5V tentlabs SR and 4x dddac board with tentlabs SR. Original Doede power supply with 13V output voltage.
The current consumption at No track is 930 mA, but the output voltage varies from 12.8 to 13.2 VDC. Temperature Talema Blue transformer is raised.
Can you tell me what the problem might be?

If I connected only 2x DDDAC current consumption is 530 mA and a beautiful stable voltage of 13VDC. 4x dddac - 4x200mA + blue MB with Tentlabs SR -130mA Thank you.
 
#9,085
No, the problem is that after warming up for about 1 hour or more when trying to set 13VDC there is a problem to set because the voltage changes up and down. With 2x DDDAC boards the current is 530mA and everything works without problems and after heating it is possible to set stable 13VDC
 
#9,086
well in standard stock the 12 Volt power supply does not have very large headroom. See my blog on this topic. Also mains voltage can reduce this. But anyway, I have two questions. 1: does it work fine with 12,5 Volt? Which is my recommended voltage setting. 2: if you say" changes up and down" what in terms of measurement is this? what is DC, AC ? Frequency of up down? Drift ? could you be more precise what you are observing?
 
#9,087
I think the blue Talema transformer in your 12VDC source can no longer handle a 930 mA load and therefore the output voltage changes up and down from 12.8 to 13.3 VDC.
I tried the Salas L-Adapter and everything works beautifully with a stable 13VDC output (L-adapter and 75VA transformer with one 15VAC winding).

1.I did not try 12.5 VDC because UA7810 needs at least 12.5VDC and there is still a 4R7 resistor which will make a voltage drop of about 0.5VDC
2. Uup and down in VDC. It kept changing uncontrollably.

Maybe if I put a more powerful transformer in your power supply, everything will work as it should.
I have another 150VA transformer with two secondary windings - 2x15 VAC. But it will probably be necessary to cool the transistor better.
 
#9,088
No the 7810 need only 2 volts, hence the recommendation of 12.5 Volt. So try it.

Yes, most people add a larger Transformer anyway as it improves sound also !
In regard to cooling, this is also discussed at my blog.
 

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#9,089
Hi there!

I currently have a 2-deck Tent-Version with decent 2,2 uF caps at the output (xlr only). The DDDAC is only used for my mid/heights, cutoff frequency 150Hz. I2s input and power supply is top notch.
I‘m thinking of an upgrade and I wonder, what will be the better point to invest in:
  • 2 additional decks
  • or highest grade output caps
  • or output transformer

what do you think?

Thanks,
Thorsten
 
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#9,090
Hi,

I would recommend to try an output transformer. Until now I have tried the stock output caps, Jantzen Silver Z 6.8uF caps, Cinemag 15/15B output transformer and Sowter output transformer. This is also the order of my preference with Sowter being the best.

I think you are located in Germany!?! I have the Jantzen caps and the Cinemag lying around. Just send me a PM if you like to try them.

Regards,
Michael
 
#9,091
Not sure about the cinemags, but for the sowters you would need 4 DAC decks anyway to get the needed output impedance. But I would guess too, that 4 decks + sowters delivers best results ,(it's also what I use, but I have to say I never tried expensive caps)

Greetings
Oli
 
#9,094
I tried the same little Chinese ones, but in the 600: 600 version, with 4 boards. The inductance is about 4H. There are only E sheets in the core.

Not suitable for DDDAC, they have a lot of distortion at 2.4V RMS and low frequencies, probably the core is not big enough. The frequency range is limited to barely 40kHz -3db and secondary compensation is needed. Save money for something better.

I will try to rewind them bifilarly, it will expand the range a lot on high frequencies, we will see what will happen with that distortion at low frequencies. If I manage to get a higher inductance with a thinner wire and a larger number of threads, maybe it will be good, I don't know.
 
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#9,096
There is a problem for single board DAC, the higher the output impedance, the harder it is to implement a transformer. It may work with some 10k:10k, but that's not for sure. You should have a buffer between the DAC and the transformer, but that then negatively affects the sound.
 
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#9,098
600: 600 ohm transformer usually require a low impedance source, 50ohm or less on the primary, the less - the better. The secondary must be compensated with a parallel resistor (1.5-2.5kohm) to obtain proper squares without overshoot. If you don't have an oscilloscope, it's hard to set it up. I used the potentiometer on the secondary and watched when the response was correct. It would be better to add at least one more DDDAC board, and then try with a transformer.
 
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#9,099
Thanks for the reply. Maybe the best route then is save up my pennies for another board and trafos, however being in the UK the cost and availability of parts now with customs and courier rip offs are just crazy, that is even if the store delivers to UK as some are not interested due to the hassle of paperwork and VAT returns 🙁

I just looked and the DAC modules are out of stock due to scarcity of components so that kind of halts any progress for a while.
 
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