UCD180 questions

[Bruno Putzeys]

Originally posted by SEIJI
what in the right amount of capacitance to serve the 6 module of UCD180 via double bridge 500VA transformer. I would like to try some BlackGate, Elna Cerafine & Nichicon GoldTune.

For 6 modules in a real 6-channel project I would use around 30000uF per side. On the other hand, you are making an active speaker. Because of this, only the LF channels draw significant amounts of power. So, in this application it would be OK to use much less than that (2x20000 or even 2x10000)

I'm not very impressed about the very large BG's for buffer storage. Cerafines sound nice (a touch "euphonic" to my taste though). I haven't tested the Nichicons yet. High time I try them somewhere.

[Bruno Putzeys]

Originally posted by stef1777
My plan is to use 4 MUR1520 + snubber caps across the diodes per transformer wiring.

OR

4 MBR1100 without snubber caps across the diodes per transformer wiring.

Difficult choice!

What to you think of each solution?

If the schottkys survive the inrush I would prefer them slightly over the ultrafast diodes+caps.
Only slightly though

[Pasi P]

Originally posted by Bruno Putzeys


The 2 large elcaps and the output film cap are the prime candidates for tweaking (unfortunately you can't use larger MKP's for the output cap. Any replacement should fit in the alotted space and be mounted flush to the PCB, to prevent stray inductance).

Thanks for the information.

You mean these biggest 470uF caps?
Output film cap is this white one marked .68J63 (=0,68u/63V)?

In general, can all other elcaps change to lower ESR ones, without being afraid some problems and/or decreasing sound quality?

[Bruno Putzeys]

Originally posted by Pasi P
You mean these biggest 470uF caps?
Output film cap is this white one marked .68J63 (=0,68u/63V)?

In general, can all other elcaps change to lower ESR ones, without being afraid some problems and/or decreasing sound quality?

Apart from those, C23/C24 (input coupling caps) and C28/C29 (regulator decoupling) are also nice places to experiment. The remaining 3 have fairly little influence on sound (insignificant compared to the rest).

Most low ESR caps sound dreadful, but let that not stop you. As they say, all generalisations are wrong.

[Pasi P]

Originally posted by Bruno Putzeys


Apart from those, C23/C24 (input coupling caps) and C28/C29 (regulator decoupling) are also nice places to experiment.
The remaining 3 have fairly little influence on sound (insignificant compared to the rest).

Sorry, i maybe miss something.

I just want to ensure that we are talking about UCD180 Rev2.
C23/C24 and C28/C29 are all SMD:s.

There are 7 (non SMD) elcaps total. You say that two 470uF elcaps are are the prime candidates for tweaking, 5 elcaps still remains. So do you mean these 5 elcaps are not worth of tweaking?

[Jan-Peter]

Tweaking of the UcD modules;
two 470F capacitors (UcD180-63V/UcD400-100V)
two 22F capacitors (UcD180-63V/UcD400-100V)
These are mounted very close to the heatsink.

Two 22uF coupling caps between op amp stage and modulator.

The 680nF MKT output capacitor (white) mounted very near to the coil.

These are the to tweak components........

Jan-Peter

[Zodiac]

My power supply is at around 51V when unloaded. Is this safe for the modules?

[Hans L]

Originally posted by Zodiac
My power supply is at around 51V when unloaded. Is this safe for the modules?

You need not worry for the modules: they have overvoltage protection. If I'm not mistaken the voltage drops when you load the psu. Measure it when it's connected so you're sure that the voltage is not too close to 52V, the voltage where the protection is triggered.

[Hans L]

Originally posted by Bruno Putzeys
Most low ESR caps sound dreadful, but let that not stop you. As they say, all generalisations are wrong.

Does this apply to all caps, including psu reservoir, or just the caps in the amp circuitry? Do you have an explenation for this general rule?

You have spoken very highly of Sikerol caps (which are bleeding expensive, I'm chosing parts for 6 ucd180) and also of Slit-Foil (like ALC 10 S 1080 DF) which are very reasonably priced.

The Sikerol is about three times as expensive. Will it be worth it (I know, impossible to answer, but please give it a shot)? I'm using the ucd's in an active system. The drivers are topnotch (Seas M15, Acuton C23). Could one or the other capacitor perhaps be better suited for a particular frequency range (bas/mid/treble)? For instance, I can imagin a 'better' cap being only better in the higher frequencies, which could make it a waste of money used in a sub amp.

Thanks!

[ghemink]

Originally posted by Bruno Putzeys
Annoyingly, things that matter to the sound, while often measurable, go hidden among a bunch of other equally measurable effects that do not matter very much.

The most interesting look at capacitor performance in this circuit comes from the switching alone - no need to modulate the amplifier. Looking at the rail you will see things change when you change caps (amplitude of the ripple, any ringing? etc).

You will find that certain things do correlate well with the listening results, but that often you'll hear things that are not at all obviously linked to visible changes.

Hi Bruno,

By modulating the amp, I wanted to force more current so that voltage drops during switching increase.

I agree that it is annoying that some measurable things have no effect on sound and others do have an effect. So the solution is simple: just find the right measurements :-) Which is obviously the difficult part. On the other hand, are measurementes useless on these caps? I would say the job of a cap on the DC rail close to the switching stage is quite simply defined: keep the rail voltage as stable as possible whatever happens. So if cap x does that better than cap y, then ....... better sound??????

The caps you have now are 470uF and almost exactly same height at the heatsink. What if I don`t care that they stick out a bit, then I could for example put 100V 1000uF in there, may give that a try. Have a few lying around that need to go in the 2nd SMPS sometime (next year or so:-)).

But at least, when playing with the caps, I do not only want to depend on listening tests since how objective am I when I just installed a so-called supercap??? Of course it sounds good since these modules sound already good in unmodded versions. The coupling caps are going to be removed (on UcD400) since my preamp has no DC at the output (DC servo). On My UcD180 those caps have been replaced by BG HQ caps (small ones since only used for mids and highs).

When I have my UcD400 finally installed (still working on the power supplies, you know the SMPS, and too busy at my regular work) I will try some measurements and tweaks on the 470uF caps and some others. Maybe by the time I have my UcD400s hooked up, you guys have come out with something new that I need to have :-)

Best regards

Gertjan