UcD400 Q & A

[BWRX]

Originally posted by DSP_Geek
The regulators are specified for 18 volts. I have a preamp running on 15 volts; would the regulators be happy with that input?

The regulator's performance was measured with an input voltage of 18V but the regulators are specified to have a max dropout voltage of 3V (assuming that's with a load current of 100mA but that is not specified). With an output voltage of 12V, 15V is the minimum input voltage you should use.

Two specs I wanted to see that are missing are the line and load regulation. Not sure why those weren't included as they are important to know since these are voltage regulators.

[ghemink]

Originally posted by BWRX


....

Two specs I wanted to see that are missing are the line and load regulation. Not sure why those weren't included as they are important to know since these are voltage regulators.

Aren't those spec there (in an indirect form)?

There is a graph for ripple rejection versus frequency, stating 110dB rejection for a wide frequency range, I would say that is equivalent to line regulation in a sense.

There is also a graph for output impedance versus frequency, showing about 50mOhm over a wide frequency range.

Isn't that saying enough?

Gertjan

[Bruno Putzeys]

Line regulation corresponds to ripple rejection at DC, expressed in %. Load regulation corresponds to output impedance at DC multiplied by load current divided by output voltage. Clearly ripple rejection and output impedance vs frequency plots tell quite a bit more. It's not very useful to have a fantastic load regulation figure (i.e. DC output impedance) if you can't have the same value at audio frequencies.

[BWRX]

Thank you guys for pointing that out. I didn't realize you could derive those directly from the graphs.

Were any line and load transient tests performed? Those tests may not be terribly important considering the intended application of the regulators but it would be interesting to know.

[Bruno Putzeys]

The tests were done but I still need to process the graphs so as to fit the document lay-out. That'll happen "as time allows".

[a007udio]

Hello.

Im just finishing my UCD400 amps and i have some questions.

1. I didnt twist the wires from power supply to the amps. They are about 15cm long. Is this bad?

2.Do i need to bypass bridge diodes with caps? What if i dont?

3. Any simple mods for better sound (not on the modules)?

4. I use transformer with 2x 40v sec. and dual bridge with ground in the middle of the caps. Is this ok?

5. Is anything wrong if the AC cable goes near to the modules?


thank you for help.

[Portlandmike]

Originally posted by a007udio
Hello.

Im just finishing my UCD400 amps and i have some questions.

1. I didnt twist the wires from power supply to the amps. They are about 15cm long. Is this bad?

2.Do i need to bypass bridge diodes with caps? What if i dont?

3. Any simple mods for better sound (not on the modules)?

4. I use transformer with 2x 40v sec. and dual bridge with ground in the middle of the caps. Is this ok?

5. Is anything wrong if the AC cable goes near to the modules?


thank you for help.

1) Best to twist those to minimize radiation.
2) You'll get different responses from different folks on this.
I wouldn't bypass the bridge diodes.
The bridge also matters. i.e. FRED's better than standard.
If you want to do something, you put a series RC on the leg of the output secondaries (before the bridge.)
You may search around. I don't recall the values and I did once actually measure a transformer. It is transformer dependent, but something on the order of 100n, 47ohms is a very dusty guess.
Bottom line. You need not do anything. It will be fine, but there is always room for improvement. IMO snubbers best done with a scope to optimize, or measure the transformer properties. i.e. A lab more than most DYIers don't have.
3) #4 for sure. Good clean wiring. Good PS caps. FRED bridges. I'll stop there for others to add.
4) That's good.
5) That depends on how close, but bottom line is that's not great, but the UCD is less dependant on EMI than most amps I think.
You might make sure you have a tight twist in the wires, and also shield them. I'd worry most about keeping them away from the input wires I think. Make sure your inputs are shielded for sure though!

Good luck and good listening!

Portland Mike

[tawn10]

my knowledge is limited but im trying to understand the use of differential signal or more rather what I stand to gain, from what I can gather i might be wrong is that a differential amplifier will "push and pull" where a single ended amplifies whole + and half - signal ???? so would there be an ultimate reason to bridge ucd modules and what in terms of loudspeaker control this may gain (or not)

i understand that the use of differential signal rejects common mode noise in the signal but what im pondering on is having the difference stage working all the way to the loudspeaker (bridging two ucd modules)

so if the ucd modules have a damping facter which controls the emf of the speaker would that be a different scenario for a full-bridge configuration?

these questions have probably been answered on another forum but like so many others looking for a needle in a haystack isnt my first choice!

please help my limited knowledge and others! any help greatly appreciated thanks...

[Portlandmike]

Originally posted by tawn10
my knowledge is limited but im trying to understand the use of differential signal or more rather what I stand to gain, from what I can gather i might be wrong is that a differential amplifier will "push and pull" where a single ended amplifies whole + and half - signal ???? so would there be an ultimate reason to bridge ucd modules and what in terms of loudspeaker control this may gain (or not)

i understand that the use of differential signal rejects common mode noise in the signal but what im pondering on is having the difference stage working all the way to the loudspeaker (bridging two ucd modules)

so if the ucd modules have a damping facter which controls the emf of the speaker would that be a different scenario for a full-bridge configuration?

these questions have probably been answered on another forum but like so many others looking for a needle in a haystack isnt my first choice!

please help my limited knowledge and others! any help greatly appreciated thanks...

The input of the UCD is differential. That means that it amplifies the difference. You can ground one side if that makes life easier, say from a single ended preamp. The advantage of differential input is that you get some benifit in CMR, which for the UCD isn't bad, but not stellar. I believe its 45dB, but its likely better than that over most of the audio band.
Bridging two UCD's would be most benifitial if you wanted more power. That would be the main, and perhaps the only reason if you were using hypex UCD's.
The damping factor would be half, as in any bridge, but likely would not be an issue.
The more talked about issue is pumping. That is when a ucd is sourcing current to the speaker, it actually is sucking current from the negative rail, i.e. making it more negative. This really isn't an issue though, even with minimalistic supply caps, and I think is only an issue is Lab amp applicatoins where one might actually wish to drive something at 5Hz -10 Hz at high power.
The less talked about issue is that when you bridge, the noise or ripple induced by the load becomes primarly 2nd harmonic. When single ended, the induced ripple from the load is a mirror of the fundimental times the impedance of the supply caps.
One theory is this is preferred. The PSSR of the UCD's, like hte CMR, is not stellar, unless one considers its flat over the audio band, which is very good. Thus given the DS spec for PSSR of 45dB (i think i recall) one could conclude that single ended may be better.
Bottom line though, if you need more power, maybe do it, or just up the ucd to the next bigger one.

Best Regards,
Portlandmike

[a007udio]

Thanks Mike for help.

Ok, the amp is ready for use. Its dead quiet.
I have some more questions.
I cant ground chasis and XLR conector. Anything wrom with this?
When the amp is playing and i swich on solder station it makes pops in speaker. Way?
When i put amp off after 2, 3 seconds meke some kind of sweep in twetter????

Thats all.

Thanks.