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Old 5th June 2015, 09:49 AM   #1
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Default Hypex UcD400 OEM unbuffered input?

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

Last edited by Windforce85; 5th June 2015 at 10:16 AM.
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Old 5th June 2015, 10:50 AM   #2
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Windforce85 View Post
Why I cannot see my post?
Because you have edited it, and as a member with a low post count your posts need to be read and approved by a moderator before going live.
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Old 5th June 2015, 10:51 AM   #3
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I'm sorry Mooly, I think I'm too impatient...
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Old 6th June 2015, 06:13 PM   #4
Koifarm is offline Koifarm  Netherlands
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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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Old 6th June 2015, 06:16 PM   #5
Koifarm is offline Koifarm  Netherlands
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More info. See picture.
If there is DC on the output of the dac board you need to ad a capacitor(10uf) in the signal line.
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Last edited by Koifarm; 6th June 2015 at 06:40 PM.
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Old 7th June 2015, 07:48 AM   #6
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9Vrms, wow. So maybe it will be better to use LME49610-based headphone amplifier to drive it. For example - voltage output from ES9018 DAC + LME49610 drive stage + UcD400 OEM core. What do you think?
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Old 7th June 2015, 03:48 PM   #7
Koifarm is offline Koifarm  Netherlands
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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.

Last edited by Koifarm; 7th June 2015 at 03:51 PM.
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Old 7th June 2015, 05:08 PM   #8
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http://www.audiophonics.fr/images2/4...0Schematic.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.
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Old 7th June 2015, 09:16 PM   #9
Koifarm is offline Koifarm  Netherlands
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Quote:
Originally Posted by Windforce85 View Post
http://www.audiophonics.fr/images2/4...0Schematic.PDF

On this schemate I need to replace just R19 and R22 with higher values?
Try 1k for R19 and R22. Do not forget to check if there is DC at the output. How do you plan to control the volume?
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Old 7th June 2015, 09:21 PM   #10
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Would it be a good idea to control volume at the DAC's output using this solution?


Lightspeed Attenuator a new passive preamp

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.

Last edited by Windforce85; 7th June 2015 at 09:34 PM.
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