UcD400 Q & A

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mimmo

mimmo

Member
Joined 2014
DIY Ucd180HG vol pot value question

Sorry for postin into wrong thread!
The following question is now posted in "Ucd180 questions" thread

Hi,

I recently rebuild my Hypex Ucd180HG amplifier and added a input selector switch and also a vol pot. Previously it was being used as power amp.

After my modifications some problems occurred (all inputs, same problem);

1. Signal can be heard even when the pot is turned down
2. Volume gets too loud very quickly
3. Pretty much no bass.

Wiring should be all fine and correct. Vol pot is Alps Blue 10K.

I tried with an attenuator plug/interconnect cable and this seemed to give me more adjusting room bit the pot and treble/bass were much better in balance. Though the max vol pot position is not even too loud. (The latter is probably caused by my attenuator being maybe tad too much. I have to check the resistor values I used on it.)

Problems were not present when amplifier was used as power amp.
Nice, if someone has some hint for troubleshooting the problem.

Best,
M
 
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G

Grizlek

Member
Joined 2010
Let me ask general question :

UCD (phase shift feedback loop that contains output filter inside loop, I am considering single R//RC feedback, basic Bruno Putzey's design) vs IRS2092 (phase shift self oscillating without output filter in feedback loop)

Subjective sound quality ?
THD?
etc ..
 
E

emptyroomsystems

Member
Joined 2016
Hello All,

I just tried to upgrade my 400AD modules by removing the BDX33/34 transistors and connecting the 12V supply to my HG power supply. I measured the power supplies and checked all connections. I see that the amodules are not starting up anymore and see that the amplifer enable connection is put on both modules towards 11 Volts.

I am not aware of a schematic where I can check much deeper, but what can have gone wrong?

Kind regards,


Harrie Munnik
 
E

emptyroomsystems

Member
Joined 2016
Baka said:
Have you measured the output voltage of the BDX33/34 before the mod?

In HxR version the output should be around 15V.

Try to raise the voltage to 15V.

The input opamps are working at +-12V.
Click to expand...

No, I did not measure the voltage. The voltage now comes from the HG power supply. There are no HxR regulators on this older version of the UcD400AD. I cut away the transistors just like it is on the instruction that came with the powersupply. It is not easy to raise the voltage. I would need to build another power supply with additional regulators.

I am now thinking of putting the transistors back and see if the modules still work. I hope they are not :RIP:

The strange thing is that the amplifier enable goes toward 11 V when powering up. I read somewhere on this thread that it should go towards 0V? Or did I misinterpret that?
 
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E

emptyroomsystems

Member
Joined 2016
emptyroomsystems said:
No, I did not measure the voltage. The voltage now comes from the HG power supply. There are no HxR regulators on this older version of the UcD400AD. I cut away the transistors just like it is on the instruction that came with the powersupply. It is not easy to raise the voltage. I would need to build another power supply with additional regulators.

I am now thinking of putting the transistors back and see if the modules still work. I hope they are not :RIP:

The strange thing is that the amplifier enable goes toward 11 V when powering up. I read somewhere on this thread that it should go towards 0V? Or did I misinterpret that?
Click to expand...

I just figured out that with the new supply for the opamps the amplaifier enanble switch dows not work anymore. Connecting this to the powerground solved the issue.
 
L

lucpes

Member
Joined 2003
AD823

Hmm... another chip I like is AD823.
Will use that, as it sounds musical and somehow forgiving on lesser recordings and very good at micro-details.
Will let you guys know how the UcD 400 HG/HxR sounds on my Wharfedale Opus 2-2 speakers vs the LM4562. Source is a Benchmark DAC2 (all original LM49860 inside) and right now sound is a bit too neutral for my taste.
 
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lucpes

Member
Joined 2003
AD823

I swapped the opamps for AD823 and it sounds better.

Also changed the small supply capacitors for UKA1H101MPD 100uf/50v at the primary regulators and UKA1C221MED 220uf/16v at the opamp supply after the HXR regulators.

Changed the output filter capacitors for 2 x WIMA 0.33uf/250v MKP (farnell part 1890269).

Also, the input capacitors are now WIMA MKS2-2.2U/50 instead of the 680nf originals.

All parts

Should've done the mods in steps to evaluate the quality of sound but all in all sounds more clear now.
 
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Malefoda

Malefoda

Member
Joined 2006
rx7france.com
Baka said:
There should be no cap overheating in a good ventilated enclosure.
If you are making a caps replacement each one has to be 105C rated.
Click to expand...

OK let me reformulate my question, as electrolytic caps have life expectancy of thousands of hours, as that life expectancy decreases with heat, what can be an expected recap schedule for these modules?
Maybe 30 years, don't know but I'm concerned about a slowly fading SQ as caps degrades. Maybe 10 years (soon!), maybe I should take my medication... ;)
 
B

Baka

Member
Joined 2005
Look at the datasheets.
Caps which are declared at 105C very often have a specification of life expectancy at 85C.
Then try to assume what would be the temperature inside the enclosure.
After that ask yourself how often do you listen to the music and how long are your sessions.
Most likely you should be fine with much more than 10 years.
Besides that recaping can be beneficial for UcD modules.
I recommend Panasonic FC.
 
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