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PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

soundcraft spirit folio SX Psu improvememnt
soundcraft spirit folio SX Psu improvememnt
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Old 3rd April 2020, 01:38 PM   #1
rozzilla is offline rozzilla  Italy
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Default soundcraft spirit folio SX Psu improvememnt

this is a good sounding unit but it is vey easy to clip, wonder why such a large desk can run on a tiny 18-0-18 AC 600mA transformer.
Would does the worth to improve somehow PSU ?
any suggestions to easiest route to get a tangible result ? Iw would be possible to feed +-20 DC to rectifiers ?

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Old 3rd April 2020, 02:01 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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18 X 1.414 is the amount of DC feeding each regulator. That is 25 volts so 20volts would degrade it slightly.
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Old 3rd April 2020, 02:35 PM   #3
maxmix69 is offline maxmix69  Italy
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Good morning. I also answer in English because if I remember correctly I remember in this forum it is mandatory.
The original circuit is made like this because by duplicating the voltage of 18-0-18 AC you get about 64V ​​DC used to make the 48 V phantom power through another stabilizer that is not seen in your partial scheme. This is used to power condenser microphones, if connected to the mixer. What exactly would you like to improve? What would you like to achieve?

Buongiorno. Ti rispondo pure in inglese perchè se non ricordo male ricordo in questo forum è obbligatorio.
Il circuito originale è fatto così perchè duplicando la tensione di 18-0-18 AC si ottengono circa 64V DC utilizzati per fare l'alimentazione fantasma a 48 V attraverso un altro stabilizzatore che non si vede nel tuo schema parziale. Questa serve per alimentare i microfoni a condensatore, se connessi al mixer. Precisamente cosa vorresti migliorare? Cosa vorresti ottenere?
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Old 3rd April 2020, 04:42 PM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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The Phantom power works happily on 20volts or more.
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Old 3rd April 2020, 05:07 PM   #5
rozzilla is offline rozzilla  Italy
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grazie max
my issue is about channels clipping which occurs quite easily, I noticed also how master signals degrades when phones are used... I suppose both of these symptons might be related to weak Psu.
in the short term i dont care about phantom.. but more in down time of this unit, so for me would be great to build a new external DC psu than proceed with swap. suggestions ?
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Old 3rd April 2020, 05:33 PM   #6
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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You are limited to the op amps in use which is +-17volts absolute maximum.
Turn the gains down and then there will be no more clipping.
It is difficult to polish a turd.

I see it uses a double bridge capacitor fed as voltage doubler for the Phantom power. Cheap and cheerful plus it works well.
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Last edited by JonSnell Electronic; 3rd April 2020 at 05:36 PM. Reason: More information.
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Old 3rd April 2020, 05:37 PM   #7
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Have you got +-17 volts?
If yes, there is nothing to do, you cannot 'improve' it.
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Old 3rd April 2020, 06:12 PM   #8
maxmix69 is offline maxmix69  Italy
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If it distorts something, it is NOT the fault of the poorly designed mixer. Other professional mixers are even powered at lower voltages, + 15V and -15V. First check if the capacitors of the power supply are still good. Then I didn't understand what phones have to do with it. Can you be clearer? Make a long, well-written post and explain everything, not a piece at a time.

Se distorce qualcosa NON è per colpa del mixer progettato male. Altri mixer professionali sono alimentati addirittura a tensioni inferiori, +15V e -15V. Controlla innanzitutto se i condensatori dell'alimentatore sono ancora buoni. Poi non ho capito cosa c'entrano i telefoni. Puoi essere più chiaro? Fai un post lungo scritto bene e spiega tutto, non un pezzetto alla volta.

Last edited by maxmix69; 3rd April 2020 at 06:14 PM.
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Old 3rd April 2020, 07:06 PM   #9
rozzilla is offline rozzilla  Italy
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i see +-21 from the transformer with no load, wonder if with more current juice it would works better, a 24ch delta come with 200w psu....
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Old 3rd April 2020, 07:38 PM   #10
rozzilla is offline rozzilla  Italy
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I apologize for being cryptic and fedding incomplete informations. I actually have 2 concerns.
First one regards to dimensioning of the power supply for a 24ch 4 bus desk, I actual wonder how 22w can suffice proper operations, to validate my suspicion I can reckon the lack of power when I connect my headphones on the desk, this cause lowering of amplitude and clarity on master signal output
Second concern is about channels behaviours which are very prone to clip. Meaning if input gain is far below clipping edge, it is hard to push them to 0db on master, wonder if low power figure is involved in this too.
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