Murata regs + Caiman = Problem??

[pixel]

I have replaced the ST L7805 reg with the Murata, mainly because I did not like the heat dissipation of the linear reg and series resistor at its input. Also the input resistor modulates the variations in current consumed from the 5v into unnecessary ripple at the input of the reg.
A side bonus with the 5v Murata, is less current counsumed from the 15v supply, which might in turn, make it less noisy. In order to reduce switching HF ripple, I have added more capacitance on the 5v.

The L7812C does not dissipate hit, as the current is moderate and the voltage drop is low. A linear reg seemd to be better choice than a switched one for that case. It was replaced with the L7812A which has 7.5X lower noise, and also better line regulation and load regulation. All that at a negligible price.
78xx data sheet: http://www.st.com/stonline/products/...re/ds/2143.pdf pages 14 Vs. 23.

Have also added protection diodes between the output and input of the regulators. As adviced at Fig 28 of the data sheet, not needed in the Caiman, but just in case.

As for the sound, it was good before and it is at list as good after the modifications. (Do not have two Caimans to do the comparison at the same time). I am happy with the end result.

[HighFidelityGuy]

Did anyone manage to solve this issue?

I installed a Gator board a couple of weeks ago and have just noticed that I now get a slight background hiss and whistle. I'm using a SuperTeddyReg linear supply, Gator board, Murata regs and every other Caiman mod including film reservoir caps.

[Gazjam]

Depends on what the internal voltage reference of those regulators is like. If it's zener-like, it will regulate well but be noisy. Have you tried a Dexa in the 12V position? I don't get noise at any sensible volume level at all.

Another guy (Canetoad) put in the Dexa's instead of the Murata's with his gator and has zero background noise.

[Canetoad]

That's right. I had Muratas to go in but read a few posts about noise. I went with Dexas instead and I have zero noise. They are excellent! Cost a bit more but sound great with the Silmic IIs and the Gator board. I'm very happy!

If I had stayed with the passive mod I would have used the Muratas without a problem. Anybody who'd like a set of Murata regs for use with the passive mod, PM me.

[HighFidelityGuy]

Another guy (Canetoad) put in the Dexa's instead of the Murata's with his gator and has zero background noise.

Thanks.

That's right. I had Muratas to go in but read a few posts about noise. I went with Dexas instead and I have zero noise. They are excellent! Cost a bit more but sound great with the Silmic IIs and the Gator board. I'm very happy!

If I had stayed with the passive mod I would have used the Muratas without a problem. Anybody who'd like a set of Murata regs for use with the passive mod, PM me.

Ok thanks. That gives me some confidence but the possibility remains that you may not have had the problem even with the Murata regs, as from what I've read not everyone encounters the problem. What power supply do you use?

I was thinking about the issue today and I started to wonder if the problem could be due to the Caiman not being optimised to work with these super regulators. Reading through the application notes for the Murata regs I noticed that it says that if you put filtering caps in parallel with the input or output they should be low esr. I haven't had chance to trace the tracks around the regs in the Caiman but it looks like there is a 220uF lytic and a small tant cap near both regs. In my Caiman the lytic caps have been swapped for Elna Silmic II. I can't find any info on the esr ratings of the Silmic II caps, so I'm wondering if their esr is a bit too high? I'm guessing the tant caps are bypassing the lytics to reduce the esr but perhaps it's not quite enough. Does anyone think this is likely to cause the issue and would swapping the Silmic II's with lower esr caps be of any benefit.

[Canetoad]

I'm currently using a Maplins CBR linear supply but am working on a replacement of my own construction based on info gained here on AOS.

[MartinT]

My Caiman with Dexas is fed from a SuperTeddy PSU set to 16V.

[Canetoad]

Hi Martin, That's what I am going to do with my PSU. I have the STR and will be using a hexfred rectifier and 80VA tx.

How much capacitance should I use? I have a Panasonic 22000uF TSUP but it's a bit big to fit in the Maplins case. Can you explain what different values would achieve?

[MartinT]

I have much less than that, Bernie, primarily because I had to fit the thing into my case! The Caiman's current draw is not great (in my case, I have removed the op-amp board) and 3300uF cap of high quality (low ESR) should be fine. The STR does amazingly good regulation so you just need to ensure that the resrvoir voltage does not sag to below about 22V.

[HighFidelityGuy]

Thanks Martin and Bernie.

Martin, have you swapped the 220uF caps near the regs with Elna Silmic II's or anything else?