Quick check RE: Murata regulator replacement for Caiman?

[Gazjam]

On the subject of the 12V Murata reg possibly not getting enough head room; I've swapped the Caiman's reservoir cap for a 35V film version, removed the input diode, removed the resistor behind the 5V reg and set my linear supply's output voltage to 16V with the load attached. So I know that both regs are getting 16V, which is well above their drop-out voltage. Despite all that I still get hiss and whistling. So we can safely rule out the theory of the Murata regs not getting enough voltage.

The issue seems to be caused by the way the PSU, Murrata regs and Gator board interact with each other.

Is anyone having the noise issues with the Murata regs and Gator while using the original 15V Caiman supply?

Good info Dave, cheers.
Only ever used my Gator/Caiman with my 16V linear so cant help out there.
I know that theres no whistling with film caps in place (passive mod) regardless of what PSU I used?

[Canetoad]

Hey Bernie...

what I've had from them is an email Titled "Your Receipt Order Number: xxxxx" which breaks down the cost showing both regs at $39.95 each + Tax@ $10.39, totalling $90.29

I'm guessing this is just to acknowledge the order and not the final invoice?
Sure it wont be a problem though

*EDIT*
Recent email: "The discount will be applied once we enter the order in and then you will receive an order confirmation from one of our sales administrators. "

Speaking of which,
we should compare dacs at some point - always nice to say howdy.

Gaz, when I ordered mine the full price was charged on their site but I received an invoice via e-mail as a PDF attachment with the discount applied. If the guy said you'd get a 20% discount you should get it. Get back to him if you don't. Wait a day or so till you get the PDF.

[Gazjam]

cheers Bernie,


Got that confirmation PDF from them, 2 Dexa regulators for the princely sum of 43 squid delivered.

Thats a big whack cheaper than UK based sellers have to say...£30 each plus delivery.
Brings out the happy scotsman (i.e. tightwad) in me!

[Canetoad]

Yup! I though it was great value too. Watch your carbon footprint though!

[maniac]

On the subject of the 12V Murata reg possibly not getting enough head room; I've swapped the Caiman's reservoir cap for a 35V film version, removed the input diode, removed the resistor behind the 5V reg and set my linear supply's output voltage to 16V with the load attached. So I know that both regs are getting 16V, which is well above their drop-out voltage. Despite all that I still get hiss and whistling. So we can safely rule out the theory of the Murata regs not getting enough voltage.

The issue seems to be caused by the way the PSU, Murrata regs and Gator board interact with each other.

Is anyone having the noise issues with the Murata regs and Gator while using the original 15V Caiman supply?

Hi Dave, yes, the whistling is there also with Caiman 15V supply. It's also there when cable from Caiman psu to Caiman itself is shortened to about 20cm - i've tried even that

[Reid Malenfant]

These regulators that are causing problems... You do realise that the problem is downstream of the regulator?

All or should i say just about every regulator that has negative feedback (which covers any i can think of) shouldn't oscillate unless there is something connected after the regulator that is seriously affecting the feedback loop that stabilises it's output.

SMPS can become unstable if too much external capacitance is connected following the PSU, a cure is to place an inductor after the PSU so the SMPS doesn't see the extra capacitance.

I'm not saying that is what is going on here, but it does sound like the regulator is becoming unstable & causing a low level oscillation at a certain frequency

[maniac]

SMPS can become unstable if too much external capacitance is connected following the PSU, a cure is to place an inductor after the PSU so the SMPS doesn't see the extra capacitance.

I'm not saying that is what is going on here, but it does sound like the regulator is becoming unstable & causing a low level oscillation at a certain frequency

Hi Mark,

sounds interesting, but would it apply also when whistling is there with Caiman 15V SMPS but also with linear laboratory PSU? Whistling disappears when I turn down the voltage to 12.9V on linear PSU (lower voltage than 13.0V will put regulator to just pass-thru and not regulate).

In Murata data sheet there is recommended to put some capacitor to Vin+gnd of regulator if there is long path from PSU to regulator. I've tried to shorten the PSU-Caiman power cable but without any success. I've also tried putting caps to Vin+gnd on both muratas - there was change - the whistling tone disappeared, but the sound on all outputs was grainy (like there would be error at DAC output for let's say least significant 4 bits).


By using inductor you mean to put ferrite bead around cable going out from PSU?

Tomas

[Reid Malenfant]

Yes, if the regulator can't regulate at the proper output voltage then it'll have an open feedback loop (it'll be trying to turn on harder to get the correct voltage but it can't as the input is too low) & there won't be any oscillation. The output will be hard on, it won't actually be regulating at all, but acting like a pass transistor as you mentioned.

This just reinforces my thoughts that it is something on the output that is loading the regulator in such a way as to cause it to go unstable

[HighFidelityGuy]

What voltage are you reading at the 12v regulator (pin in) with the DAC powered up?

Regards

Chris

16V

Good info Dave, cheers.
Only ever used my Gator/Caiman with my 16V linear so cant help out there.
I know that theres no whistling with film caps in place (passive mod) regardless of what PSU I used?

No probs. I too had no problem with whistling or hissing with the passive mod when everything else was the same. It only started after installing the Gator.

Hi Dave, yes, the whistling is there also with Caiman 15V supply. It's also there when cable from Caiman psu to Caiman itself is shortened to about 20cm - i've tried even that

Thanks. So it seems to me that the supply isn't the cause as the symptom is still there with different supply types and voltages. This also tallies with what Mark is saying.

This just reinforces my thoughts that it is something on the output that is loading the regulator in such a way as to cause it to go unstable

Thanks Mark. This takes things back to a suggestion I made earlier that the Elna caps near the regs may have too much ESR or may be too big. That is if they are connected to the reg output and not the input. Can anyone confirm if they are connected to the output?

If so there could be multiple possible cures:

1. Swap the Elna caps to something to a different type that doesn't cause oscillation.
2. Remove the Elna caps if they aren't needed with the Murata regs.
3. Swap the Murata regs to Dexa's as the the Elna caps may not cause them to oscillate.
4. Perhaps it's the tant caps causing the oscillation rather than the Elna lytics? So maybe swap or remove them?

What do you think Mark?

[chrism]

Or a solution that removes the two levels of regulation i.e two PSU's one to deliver 5v and the other 12v. That's where I ended up and it works a treat. I don't use a Gator though so not certain if this would eliminate the whine.

Regards