[CornellAlum]

I know a lot of folks have had a lot of success modding the ucd modules.  I have 2 X 400ad modules that I would like to turn into something special.  Is there anything besides improving the actual components on the board that I should be aware of?  I saw the thread over at diyaudio.com, but good god, it's like 600 pages and I would appreciate something a little more concise.  Are you guys using the hypex power supply or something a little more esoteric?  Switching perhaps?

Thanks!

[shokunin]

I went the DIYcable route to save time making a chassis and punchouts for connectors etc.  Modding the module is quite easy if you’re comfortable de-soldering as well as soldering.  Here’s a list of mods I’ve done to my 5 channel UCD400AD amp kit I bought from DIYcable.

Input bypass, you can short two small caps or remove them and jumper them to improve the overall clarity and definition.  The caps are there to protect against DC from entering into the amps.  If you are sure your preamp is DC free then go ahead with this.

Changing the PSU caps on the module themselves, these are the 100v 470uf Yageo caps (on revision 6.1), I changed these with Rubycon ZL’s.

+12v, -12v, 0 dedicated power for the AD opamp, this requires the removal of the 2 transistors as indicated by the Hypex PDF file that outlines what is needed and hardwiring supply for +/- 12v supply.

Output filter cap.  Of the 5 modules I have I just recently changed 2 of them from the stock red dipped cap to Auricap that Kevin sells on diycable.  Expensive for a small cap, but I’m still burning that cap in to make a definitive statement to it’s benefit.  Since the cap is in the output signal it should be beneficial to upgrade it to a better capacitor.

The power supply design and cap will make a difference as well but I stuck with the diycable version since I need it to power all 5 channels.  It would have been nice to be able to use some Jensen 4-poles, but the PCB is designed for standard 2 terminal caps.  If you roll your own I’m sure using a good supply of 4-poles would be great, expensive, but great.

[Gordy]

I've done some limited moding to the modules and found the most significant change was to remove and jumper the two 22uf input caps.  I left them dc coupled but, most would want the protection and use a favorite 2.2uF poly, I really like the Sonicap Gen. I there.

Hypex improved the output cap since I bought mine, though they're still electrolic I believe, replacing them with a mkp type works very well, I've used two Wima .33uf there, placed top and bottom on the board.  Several people here at AC have also used Sonicap Gen II's (.47 or.68) there as well and that's what I used on my amps.  The Sonicaps are about 2/3 the diam. of a Auricap, which makes for an easier fit and shorter leads. 

I replaced the 480uf Yageo's with 680 muse caps but, if I were to do it again I'd go with the ZL's too.

Depending on your taste, playing around with opamps could reap rewards, the new LM4562 is getting raves... HTH!

[CornellAlum]

Let's say I like fast and detailed with a big midrange, and op-amp that fits that bill (might be asking a lot, I know).  I found the below on diyaudio.com, and this seems to be kind of what you guys are talking about.  Any comments?

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.

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).

[Gordy]

Dang, it's been awhile    I used the 680 FC's not Muse and used 22/50 Blackgate for the low power caps...

The 2107 (or the 4562) opamp might be to your liking, Occam and Tianguis both love the 2107's for their mids in dac mods.  I never heard them in my system or a/b'd as original, only in a Zhaolu dac Tiangius moded.

[shokunin]

Of that list on diyaudio, I did 1, 4, 5, and 8 translated into

IMO, all of these changes are small, minor improvements or refinements in the sound.  To my ears they were not drastic, awe dropping changes, but better definition and clarity.   There's not a whole lot more left for me to mod on these modules, except change out the power supply, which will play a rather key role in it's overall sound. 

If you want to extract the best possible sound, then go all out, dual-monoblocks, separate supply for the modules, separate transformer for the 12v Opamp supply,  Jensen 4poles, for both module powersupply and 12v power supply, hardwired direct, etc...  takes some time but that would be one approach to make the ultimate UCD amp. 

[CornellAlum]

If I am going to spend the time, I am going all out.  Could I use the same design for the power supply as I used for my sb3 (jensens, hexfreds, etc), just modifying for voltage?  It is basically a DIY version of Wayne's ultimate with a few changes.

Thanks guys!

[Kevin Haskins]

I've played with these things a lot over the last few years and here are my general recommendations.   

On the modules:

#1.  Bypass the DC blocking cap (only if your sure you have a DC free source)

#2.  Use the regulated 12V supply for the opamp buffer. 

#3.  I know this is hard for some people but the rest of my advice is to LEAVE EVERYTHING ELSE ALONE.   

For the power supply:

#1.  Use the appropriate sized supply.

#2.  I actually prefer the Panasonics to the more expensive caps I've tried (Jenson, United Chem-con, Elna, Slit-foils).   I use Panasonic TSHAs in all the Exodus power supplies and they are my favorite cap at this point.   This is a taste thing to some degree.    I've used both the soft recovery and standard bridge rectifiers and I hear little difference between the two.  There is no benefit in bypassing the caps on the power supply.   They are shunted at the module.   

#3.  The rest of my advice is to use good layout and grounding practice.   Grounding & layout are more important than anything else.   If you use poor layout and grounding all other improvements are for naught. 

YMMV and IMHO etc.....

[PaulHilgeman]

Hey Kevin!

Happy New Year!

What do you mean by:

There is no benefit in bypassing the caps on the power supply.   They are shunted at the module.   

I have found that some large value Metalized Poly caps work great in the supply.

As to your recommendations, I totally agree.  If you do not have DC, get rid of the caps, that is the biggest improvement to be had.  The power supply is the other most important area to address.  With a few simple tweaks, these can be as good sounding as some of the best SS amps out there (especially below $4000), with plenty of power for most applications, no huge heatsinks, low power consumption, and great reliability. 

-Paul

[Kevin Haskins]

Per either Bruno or Jan-Peter.   It is from an old thread on DIYAudio.  Please don't ask me to find the original thread.   

I've tried small value MKPs but it had a negative rather than positive effect in my system.

[CornellAlum]

This may be a really dumb question...but how do you know if you have DC?

[PaulHilgeman]

I know the threads, they are worthlessly large.

It just does not make sense to say that they are shunted at the module.  I think they just mean that there is another electrolytic per rail on the module side of things.  I too found that small value MKP's were detrimental, say less than 10uF. 

This may be a really dumb question...but how do you know if you have DC? Embarassed

The best way is with a multi-meter:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=391-015

Something along these lines.  You should have one anyways!!! .

In almost any case you do not, but every once in a while you will find a preamp that passes DC, or has a DC offset, or a source with a DC offset.

Be sure to play with the volume knob and try all sources with each source turned on.

-Paul

[CornellAlum]

Thank you sir...fwiw, I think I have four!