DBX FS900 Power supply

[thomasdf]

When no connector is plugged in the input (TRS jack in my case) the LEDs are off, as they should be since no GR is happening.
When I plug my TRS jack in the input, they light up depending on the range knob position (no LED when the know is CCW and all LEDs when CW).
When there's audio playing thru the unit, the LEDs are just blinking and displaying random informations. When silence : LEDs are on, and they turn off when there's sound.
Maybe my best chance to solve this is getting in touch with an exorcist now

 

[abbey road d enfer]

When no connector is plugged in the input (TRS jack in my case) the LEDs are off, as they should be since no GR is happening.
When I plug my TRS jack in the input, they light up depending on the range knob position (no LED when the know is CCW and all LEDs when CW).
When there's audio playing thru the unit, the LEDs are just blinking and displaying random informations. When silence : LEDs are on, and they turn off when there's sound.

that suggests a huge oscillation...

 

[Brinxter]

If I were you, I would use a pair of 24V Meanwell smps and LM317/337 for the regulated rails. That would take care of the magnetic radiation issue.
The 24V rails would need additional CLC filtering. See attachment.
I have PCB's for that. PM me if interested.

Hi what inductors are you using/recommend for the filtering?

 

[abbey road d enfer]

I use the 10mm Panasonic 100uH

 

[thomasdf]

ah wait, I didnt filter the 24v rails, they are straight out of the Meanwell PSUs... Maybe that's my problem ? I assumed that since it needed unregulated +/- 24v, taking it out of the PSU would be more than good enough.

 

[thomasdf]

After some testing with 100uH and all sorts of other attempts, Abbey suggested me to test with an analog source, which I did... and magic... the LEDs behave perfectly.
We came to the conclusion that my converters produced a heavy amount of ultra sonics frequencies. I'll put a bypassable LPF (35Khz) on the audio path of the 902s and will report back !

 

[trashcanman]

Just a general note about these modules. I've been racking up a couple of the Noise Gates that had a few problems which were all due to bad switches on the front panel so anyone with problems should take a look at those first imo, at least on the older models. They were fairly easy to take apart and clean/fix but replacing them would probably be better in the long run.

 

[thomasdf]

Thanks for your input !
I ended up changing C1 and C2 at the input of the 902, for 4.7nF, making a 33.8Khz low pass filter with the 1K resistors, and solving my problem.

 

[GavinO]

Hello all. I realize this was more than a year ago, so hopefully one of the clever folks on this thread will see this. I have an F900A chassis and whilst it was literally still in its box in an audio warehouse sale, some bright spark had replaced the toroidal and swapped wiring on the voltage selector so when I powered up it fried both the toroidal and the PSU board. Nothing that can’t be fixed I’m sure, but I was wondering if would be better to build an external PSU using either linear or SMPS. What caused me to doubt is that somebody told me an SMPS may change the characteristic of the analog audio and/or introduce some sort of high frequency interference into the analog modules. This thread suggests not, but I’m aware that @thomasdf had to jump thru some hoops to get this method to work.

I’d really appreciate any advice that is on offer about the best way to approach this.

 

[abbey road d enfer]

somebody told me an SMPS may change the characteristic of the analog audio and/or introduce some sort of high frequency interference into the analog modules.

I have made a PSU for a 6-way 500 lunch box, which is in essence the same as an FS900. I used 4 X-power 15W enclosed smps, connected to a battery of filters constituted each by a 12uH 10mm inductor and a 470uF capacitor paralleled with a 0.1uF ceramic. Never had any issue with interference.

 

[chilidawg]

I have made a PSU for a 6-way 500 lunch box, which is in essence the same as an FS900. I used 4 X-power 15W enclosed smps, connected to a battery of filters constituted each by a 12uH 10mm inductor and a 470uF capacitor paralleled with a 0.1uF ceramic. Never had any issue with interference.

Did something similar a few years ago. I used a pair of Mean Well EPS-65-24 SMPS, and a couple of DC-to-DC converters using XLSemi XL4005E1 and XL6009E1 IC which I designed the PCB based on the application circuit schematic they provided in the datasheet, to get +/-16V and +48V regulated rails. No issue with interference either. Very quiet.

 

[abbey road d enfer]

I used a pair of Mean Well EPS-65-24 SMPS, and a couple of DC-to-DC converters using XLSemi XL4005E1 and XL6009E1 IC which I designed the PCB based on the application circuit schematic they provided in the datasheet, to get +/-16V and +48V regulated rails.

So you used the 6009 for 48V, yes? How does it behave in a no-load situation? Did you have to provide minimum load?

 

[chilidawg]

So you used the 6009 for 48V, yes?

Yes.

How does it behave in a no-load situation? Did you have to provide minimum load?

It's doing just fine without a minimum load. I used the IC a lot in the custom order mic preamp units that I built to provide the phantom power, and I also use it for converting single supply source like a cheap 5V phone charger or the computer USB port to a symmetrical supply +/-15V for powering op-amps.

 

[abbey road d enfer]

Thanks! Good to know.

 

[chilidawg]

Thanks! Good to know.

Here it is.

U1 is XL6009.
Ignore R3, R4, R5 (they are for the LED indicators on the front panel).
L3 is Sumida CDRH127 47uH. Probably could have used a smaller inductor, but I like having a part that is sorta unified in all the stuff I build. I calculated 37.4K for the voltage output adjustment resistor to get 48V, so that's what I put in.


* well whaddaya know, I DID put LC filters on the +/-16V rails after all, haha. It's such a long time ago I totally forgot.

 

[thomasdf]

Thanks for your input !
I ended up changing C1 and C2 at the input of the 902, for 4.7nF, making a 33.8Khz low pass filter with the 1K resistors, and solving my problem.

Well, after a few years I must say the deesser with such a mod takes out a little too much highs / air for my taste, and they still behave weirdly sometimes. I am a bit puzzled !