Nicerizer 16 --- 100 Hz hum [SOLVED]

Hi,
I have an "old" Nicerizer 16 [SN 0053] thats humming [more than -70dB, no input signals at all, all knobs set in the middle, output level at 3/4] at 100 Hz.
Found that there is indeed a ripple [-66 dbV] after the L78S24CV regulator of the onboard PSU.
Supply Voltage Rejection is rated at 80dB for 100Hz on L78S00 series datasheet [but for only vi=10V vout=5V, while on nicerizer there are 24V],
so I assume that maybe there is something wrong here.
My plan is to try to change regulator, bridge, capacitors, or to move and maybe improve the PSU on a veroboard.
Curious to know if someone else has the same issue.

I'll update of course this thread when I'll have the problem solved.

Your regulator works as it should; 80dB regulation, that's the attenuation between the input hum and the output hum. I suspect the hum level on the unreg side is ca.2-3Vac (+10dBu), so on the regulated side you should get -70dBu. -66 is close enough.
And anyway, the active electronics in your box are supposed to "filter out" the power supply noise; a typical IC (5534, TL0) has at least 80dB PSRR, which would leave ca. -150dBu noise.
No, I suspect there is something else, maybe magnetic induction from a transformer (perhaps the unit's mains transformer). Very difficult to say, since -70dBu was once considered a good performance, and not knowing either the unit itself neither its schematics, it is impossible to give more advice.

Thanks!
No its not transformer magnetic induction, tried moving/shielding the mains transformer, something changes yes but only at 50/150 etc Hz,
100 Hz hum is always steady.

Just doubly [Fluke meter and an Advantest spectrum analyzer] measured now, ripple [clear peak at 100Hz] is 0.17 Vac on unregulated side [just after the bridge],
so I still hope moving/improving the PSU [= bridge, 2 caps & the regulator for now] will lower the noise.
I still think/hope something is wrong with the regulator itself or the way its used, or anyway that there is room to improve it.

btw all the line amps of the mixer are potted "class A" opamps, I like a lot how they sounds but dont think PSRR is their point of force.

You said you measured -66dBu noise on the reg output and -70 at the unit's output. If it was due to poor PSRR of the modules, that measure at only between -4 to -15dB. Any DOA is capable of much more than this, so I suspect noise comes from somewhere else.
100Hz is typical of wrong layout of the PSU. You may find that reinforcing the ground connection between center-tap of mains xfmr, junction of smoothing caps, reference point of regs, and output stage ground is beneficial.

Thanks again for your input.
Checked the ground connections, it seems to me that there arent noticeable parasitic currents.
Meantime, I've found in my super-old junkbox an unused MC7824CT  ;D, I've seen this has better overall specs and precisely  better ripple rejection than L78S24CV ,
so I'll give it a try.
Dont want to cut pins, so I'll go with dismanteling-desoldering.

Abbey road d enfer, you was right.  :

To resume:

Swapped in the MC7824CT, and the ripples went from -66dBu to -75dBu, as I was hoping.
But the 100 Hz hum was still here.

So I've tried with an external PSU [ripple = both -66dBu and -77dBu, same results].
All the 100Hz hum completely gone, less than -85dBu with the 2 busses amp knob cranked all the way.  ;D ;D ;D
[before, it was some -58dBu]
That, and the sheets from member hotbaby for the 50/150Hz hum, has made the nicerizer dead quiet.

While I was here with hands on knobs of the external PSU, I've discovered also that with 20V instead of 24V, the sound becomes a little distorted, but in a pleasant way.
So, I'll add, in the external veroboard PSU I'll build, a switch for this control.
On the back there is just room for it.

P.S. It was really a breeze to dismantel/reassemble this thing.
I love when gear is made with user's improvements/repairs/etc in mind.


[btw, and slightly OT, in dismanteling the unit I've discovered (I think..) that someone (previous owner?) tried to do an absurd attempt to mark/saw (all except one!) the pots shafts,
thus breaking the 50% of the "bodies" of the pots (see the missing "top caps" of white plastic on 2nd pic).
anyway, with some loctite I've been able to perfectly fix them all,
so I'm documenting it here if someone will be in a similar boat.]

I'm glad you pound a solution. Now you can build external PSU's and sell them as improvements for this apparently not completely developped piece of gear.

Just an update.. there was a blown op-amp on a channel input
[I wonder how the previous owner has used the Nicerizer.. sawn shafts, burnt inputs..]
Mailed Phoenix Audio about availability, they've just sent me 2 new op-amps  for free