UCD180 questions

[Hans L]

Originally posted by Jan-Peter
Hans,

What you hear in your tweeter when you switch the amp on is a VERY small thick. Switching the amp off, doesn't create any noise........

When the customs has FINALLY gives our transformer free we will have a 160VA o-shape toroidel transformer.

Cheers,

Jan-Peter

www.hypex.nl

Hi Jan-Peter,

do you already know the pricing of these transformers? What voltage are they (... - 0 - ...) and what kind of advantage does the round shape give?

I'm thinking about using one UCD180 per woofer on a stereo dual 15" TCSound dipole as part of a 4-way (already have amps for the other 3-way main panel, namely AKSA)

Thanks,
Hans.

[Bruno Putzeys]

The reason why I generally avoid parallelling ceramic caps with something else (e.g. another ceramic cap!) is because circuit inductances are liable to form a resonant circuit together with the ceramic cap.

You can parallel a ceramic and an elcap if the ESR of the elcap is greater than sqrt(Lcircuit/Cceramic). BG caps have lowish ESR so this requirement is unlikely to be met.

Other tricks are to use another, smaller elcap as a "damper" or "snubber". Should you ever have wondered what the 22uF small elcaps are doing on the UcD rails, there you are.

Now, if you consider that elcaps have hardly more inductance than their own pins (contrary to popular belief), additional ceramics are unnecessary if the elcaps are small and close enough to the op amp you're trying to decouple. Their ESR and high capacitance will insure that they will never enter into any sort of resonance with other caps located elsewhere. Thus, consistently using only elcaps to decouple opamps is a no-brainer.

The point brought forward by Peranders is a different one.
Regulators are a control loop and the decoupling capacitors are actually a part of this. The highest performance circuits (such as jung etc) rely on this heavily. The ESR on elcaps placed across the regulator will act as a form of lead compensation, allowing better loop gain than would be available if the cap were perfect.

[ghemink]

Originally posted by Jan-Peter
Bruno,

The two 100nF capacitors are in the UcD180 revision 2!!

Cheers,

Jan-Peter


www.hypex.nl

Hi Jan-Peter, Bruno and others,

I have revision one, I already saw that there are no decoupling caps after the regulators (well transistors like emitter followers with a zener defining the base voltage).

I have modified two of my UCD modules. Besides replacing and adding BG caps at different positions I also put decoupling after those regulators. I have put one 22uF 50V BG cap between the + rail and the - rail after the regulator, so not 2 caps to GND but one cap between the + and - rail. Besides that, I have added a 0.1uF BG-NX cap directly over pin 4 and 8 of the NE5532 opamp for decoupling close to the opamp. So I`m not decoupling to GND but between + and - rail. I think that should be OK and I think I read somewhere that that way of decoupling prevents GND noise to be transferred to the rails which could be beneficial? So I have done that mod but no listening yet.

I have also replaced the 22uF caps that are parrallel to the zener diodes with BG types. Replaced the 22uF coupling caps between NE5532 and UCD with 4.7uF BG-N types (this gives a cut-off frequency at 16Hz or so which is far lower than that of my speakers, so no problem). I did not remove the 22uF caps that are power supply decooupling caps close to the switching transistors. I wanted to replace them with 22uF BG caps, but there is not enough space. So I added 22uF BG caps in parallel on the underside of the PCB. I was also thinking of replacing the 470uF caps with 100uF BG caps (about the same size), but instead, I just added 100uF BG caps by mounting those also on the underside of the PCB.

See the attached picture for what I have done to the underside of the PCB.

If you have any comments/advice, please let me know.

I`ll add another picture in a seperate post

[Bruno Putzeys]

Originally posted by Hans L
do you already know the pricing of these transformers?

Hi,

JP already got scolded for having "done commerce" in this forum (we believe it was unintentional and in good faith). It's best to ask financial and other sales-related matters by private email. That saves him any further embarrassment.

Cheers,

Bruno

[ghemink]

And here from the other side

[Bruno Putzeys]

Originally posted by ghemink
I think that should be OK and I think I read somewhere that that way of decoupling prevents GND noise to be transferred to the rails which could be beneficial?

Depends on the application

In single-ended (ground-referenced) circuits this can be a good thing, although it reduces the phase margin of the op amp.

In the UcD pre gain stage, ground is not used as a signal reference so the advantage of decoupling only across +/- is gone. The disadvantage (phase margin) remains, however.

[ghemink]

Originally posted by Bruno Putzeys
The reason why I generally avoid parallelling ceramic caps with something else (e.g. another ceramic cap!) is because circuit inductances are liable to form a resonant circuit together with the ceramic cap.

You can parallel a ceramic and an elcap if the ESR of the elcap is greater than sqrt(Lcircuit/Cceramic). BG caps have lowish ESR so this requirement is unlikely to be met.

Other tricks are to use another, smaller elcap as a "damper" or "snubber". Should you ever have wondered what the 22uF small elcaps are doing on the UcD rails, there you are.

Now, if you consider that elcaps have hardly more inductance than their own pins (contrary to popular belief), additional ceramics are unnecessary if the elcaps are small and close enough to the op amp you're trying to decouple. Their ESR and high capacitance will insure that they will never enter into any sort of resonance with other caps located elsewhere. Thus, consistently using only elcaps to decouple opamps is a no-brainer.

The point brought forward by Peranders is a different one.
Regulators are a control loop and the decoupling capacitors are actually a part of this. The highest performance circuits (such as jung etc) rely on this heavily. The ESR on elcaps placed across the regulator will act as a form of lead compensation, allowing better loop gain than would be available if the cap were perfect.

Hi Bruno,

Based on this statement in your above post:

You can parallel a ceramic and an elcap if the ESR of the elcap is greater than sqrt(Lcircuit/Cceramic). BG caps have lowish ESR so this requirement is unlikely to be met.

It seems like a bad idea to use BG caps in parallel with the 22uF normal elcaps that also have ceramic chip caps in parallel with them on the underside of the PCB. Is that true? If so, I`d better remove the BG caps at that point.

I had slight worries about the BG caps after the regulators (regulator stability) what do you think about that? Should I get rid off that 22uF cap and leave the 0.1uF that I placed directly over the opamp?

Best regards

Gertjan

[ghemink]

Originally posted by Bruno Putzeys

Depends on the application

In single-ended (ground-referenced) circuits this can be a good thing, although it reduces the phase margin of the op amp.

In the UcD pre gain stage, ground is not used as a signal reference so the advantage of decoupling only across +/- is gone. The disadvantage (phase margin) remains, however.

Hi Bruno,

Thanks for the advice. I may reconsider this act and place a 22uF after the regulator between + rail and GND and - rail and GND. Using the GND connection that is also used by the zener. Then for the 0.1uF cap directly over the opamp. I don`t see any GND pin/pad in the direct neighborhood of the opamp so that is another reason why I placed that cap directly over pin 4 and 8.

Any advice appreciated.

Best regards

Gertjan

[Bruno Putzeys]

Originally posted by ghemink

It seems like a bad idea to use BG caps in parallel with the 22uF normal elcaps that also have ceramic chip caps in parallel with them on the underside of the PCB. Is that true? If so, I`d better remove the BG caps at that point.

I had slight worries about the BG caps after the regulators (regulator stability) what do you think about that? Should I get rid off that 22uF cap and leave the 0.1uF that I placed directly over the opamp?

Well in any case if you want to place BGs at the position where the 22uF caps are in the power stage you would do good to remove the original caps first. If you're into placing components on the bottom side, the ideal place to have the "damper cap" is straight across the 100nF caps.

As for the op amp, make your life easy and have only two 22uF elcaps to ground.

[Hans L]

Originally posted by Bruno Putzeys

Hi,

JP already got scolded for having "done commerce" in this forum (we believe it was unintentional and in good faith). It's best to ask financial and other sales-related matters by private email. That saves him any further embarrassment.

No problemo,

Hans.