Hypex UcD400 OEM unbuffered input?

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Hello everyone!

I consider buying two Hypex UcD400 OEM amplifier modules for cheap. This version of UcD have an option of unbuffered signal input to drive power stage directly. Unbuffered input impedance is 1.8 kOhm.

I will connect DAC from this link:

audiophonics dac1798 - dac 24bit 192khz - cs8416 + pcm1798

with single ended outputs from pair of NE5534 opamps.

This DAC output impedance is 120 Ohm at 1 kHz and max. voltage level at 0dB is 2V.

Will it drive UcD400 core without issues? Should I use buffered input? UcD400 OEM has differential inputs. How to connect it do the DAC with SE output? Is it doable? I want to keep sound path as simple as possible without signal degradation. UcD and DAC will share one enclosure.

I also don't know where to connect signal ground.

I wrote recently to Hypex company but I don't know if they are willing to help me and loose their time on me becouse I buy second hand amps and now I can't afford for new ones. I burned my old amp and I need Hypex urgently.

Thank you,
Damian
 
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NE5534 can drive the 1,8k of the unbuffered UCD. But you need at least 9Vrms to drive the UCD to his max. Change NE5534 circuit to give 9Vrms, often you have just to change one resistor. Unbuffered input for unbalanced on the Oem UCD is signal +on pin 31, ground on pin 5,6,7,8 , Signal - on 27 also to ground.
 

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if you want to use as less parts as possible, just modify the output opamp of the dac. Change the feedback resistor of the opamp. Make the value of the resistor 4.5 times higher. NE5534 can perfect drive a 1k8 load. Do not forget the place a capacitor in the signal path to the unbuffered UCD. If you can not do that yourself use the buffer on the ucd.
 
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http://www.audiophonics.fr/images2/4993/DAT1796 Schematic.PDF

On this schemate I need to replace just R19 and R22 with higher values?

If this is that simple and there is no other parts to replace I can do this with ease.

There are OPA2134 instead of NE5532 in I/V stage in my current DAC.

I am also thinking of 9V battery powered power supply for digital section of this DAC. This is relatively simple DAC but in many trials it reveals to be very good sounding DAC for that price.
 
Would it be a good idea to control volume at the DAC's output using this solution?


http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html

The plan is to be as cost-effective as I can.

Another cool idea which comes to my mind involves some investment. First I'd extract RAW current output from DAC and feed it into the battery-powered IVY buffer from Twisted Pear.
Then tune it to supply balanced output at level suitable for UcD power stage. IVY seems to be adequately strong to drive it flawlessly.
 
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Adjustable feedback resistor would be good solution in the case of eventually tuning gain of DAC output stage to the UcD inputs level.

TL072 buffer in UcD is the first candidate to the upgrade. I want more flexiblity among good buffered and unbuffered inputs. I consider OPA1642 or LME49880 instead of TL, with some minor tweaks around components quality in signal path and feedback loop. These two have very similiar requirements with greatly improved performance.

What do you think about these opamps for UcD buffer?
 
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Adjustable feedback resistor would be good solution in the case of eventually tuning gain of DAC output stage to the UcD inputs level.

TL072 buffer in UcD is the first candidate to the upgrade. I want more flexiblity among good buffered and unbuffered inputs. I consider OPA1642 (or even better and newer OPA1652) or LME49880 instead of TL, with some minor tweaks around components quality in signal path and feedback loop. These IC's have very similiar requirements as TL with greatly improved performance.

What do you think about these opamps for UcD buffer?
 
I like no opamp at all, but tubes. But this is personal.

In the past i tested several opamps, my favourit are DIP8 versions of LM4562 and OPA827. But the most you get out is that you give the opampstage his own good power supply.
 

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