UcD400, in summary.

[ivigueras]

Yes, I know. There are some complete threads for this question, but these have so many messages that have become impossible to follow them.

I think that it would be good that somebody made a summary of the best mods of the Hypex Ucd400.

And, why not?, the same about NCD and ColdAmp.

Thanks.

Ignacio.

[Code]

same thing for charlize would be nice too..

[pinkmouse]

Thats why we have a Wiki.

As you find stuff copy it there, we really don't need yet another tweaking thread.

[Code]

the wiki page only includes input caps and a bit on psu upgrades, i was looking for more detail in the psu buffer caps specifically.

[ivigueras]

True. But in the Wiki there are not so concrete.

I am thinking in a very concrete thread with very few messages with only the most recommendable mods. Directly.

Otherways would be in the wiki: "The very best cookbook for the Hypex's mods".

[lucpes]

Here's what I did to my UcD 400 AD's:

UcD400 (AD)

1) Coupling caps. 22uf. They are between the opamps and the input modulator stage. Removing really clears up things. If you really need DC protection you can use a 2.2 uf quality cap before the input connector. With the 100k input impedance it forms a more than enough highpass filter (2-3Hz).

2) Current protection. Remove R13 (SMD on the bottom). I wouldn't encourage that as there seems to be not much of a difference. Don't blame me for your modules go poof if you accidentally short the output.

3) Low voltage caps (22uf/50V I believe). Replaced with 47uf/16V Rubycon ZA's. Tighter bass and overall clarity improved.

4) Main voltage caps (470uf/100V). Replaced with 2x680uf Panasonic FC (soldered another pair on the bottom of the boards). Result is deeper bass and more 'sparkle' in the highs.

5) Output filter capacitor. Replaced with .68uf/250V EPCOS polypropylene from Farnell. Opens up things quite a bit.

6) Bootstrap cap (220/16 I think). Replaced with 180uf/16V OSCON SEP. Low impedance is key here.

7) Power supply: dual mono, +/-60VDC, 1000VA, dual bridge, 18000uf, choke, 18000uf, 250uf/160V polyprops per rail/amp. (The 250uf polyprops are huge but they take care of most noise in the supply and seem to help provide a lot of details I was missing before). Adding chokes in the supply really makes things sound 'musical'. Wired with 12Ga teflon silver plated wire.

8) Separate supply for the front-end (+-12V). Used 2x12Vac 25VA trafos, with 4700uf 25V panasonic FC/dual rectifier/7812/7912 regs, CLC filtering with 82uf 16V Panasonic FC- common mode choke - 47uf/16V rubycon ZAs. Current draw is very low, you may use other types of regs such as TL431's. (Attached pdf from hypex for where to connect the supply)

And most important tweak for difficult loads, direct soldering of the power/output wires on the board (have screw-type main capacitors, I can remove the connectors from there), also added a thick solid copper wire on the module where the ground connections are (measured a tiny drop there during heavy bass passages with my speakers).

[ivigueras]

Thank you, lucpes.

[motto]

Lucpes,

Could you please post a some pictures of your modified UCD400 module?

Thanks,

motto

[felixx]

@lucpes
How is the sound after tweak,comparing with a clasic AB class design?...and maybe a few words comparing with similar topology AB class.

[deandob]

You could also save some money and purchase the standard edition of the UCD400 and swap out the OPA2143 opamp with a LM4562 op amp which is getting all the rave reviews at the moment. While you are there, you can wire a CRD across the output for biasing the output stage in class A, but you can't use the CRD pads on the UCD as the LM4562 needs the bias on the -ve supply.

I have a couple of points about using an auxillary supply, I dont think its a worthwhile tweak especially when using the LM4562 and you can save the expense of another power supply because:
- The PSRR of the LM4562 around 100db, which is excellent, especially if you use the CRD.
- The power regulator circuit used in the UCD400 is superior to the UCD180 and according to TNT audio has pretty good performance. TNT regulator articles
- As the regulator significantly drops the voltage from the main rails and the current draw of the opamp is low, variations in the main supply due to current draw from the UCD output will not impact the regulated supply.
- Use a CRD instead of a resistor to better regulate the zener diode voltage reference improves the regulation of the supply. There is a good thread on pinkfishmedia if you want to learn more.

Also, do use two 4.7uF tantalum capacitors wired to the power supply pins of the opamp, for decoupling and improved bass.

Regards,
Dean