soundcraft spirit folio SX Psu improvememnt

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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 ?

An externally hosted image should be here but it was not working when we last tested it.


thank you
 

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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?
 
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 ?
 
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.
 
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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.
 
Could it be that the power supply is that of the smaller mixer? However if it is underpowered you see it immediately because it adds hum to the sound when you request power, for example with the volume of the headphones at maximum. Check the capacitors, it wouldn't be the first time they run out.

Può essere che l'alimentatore è quello del mixer più piccolo? Comunque se è sottodimensionato lo vedi subito perchè si aggiunge ronzio al suono quando richiedi potenza, per esempio con il volume della cuffia al massimo. Controlla i condensatori, non sarebbe la prima volta che si esauriscono.
PS:
scrivi pure in italiano che facciamo prima!
 
One possible improvement is adding a protection circuit that will disconnect both rails if one of them drops out - having only one rail working is one of the few ways to take out opamps wholesale in a mixer.

You can do this a bit like a loudspeaker protection circuit - use a 1:1 voltage divider between the rails and if that average voltage strays too far from 0V for too long, open the relays. Some time constant is needed to allow power up to happen without interruption I think.


Most opamps consume <= 150mW quiescent, and a full 11V rms signal at 5k load is another 50mW or so. 600mA supply is producing 22W at +/-18V, enough for 110 opamps running full whack.

So how many opamps and other active stages are there? Perhaps there are a lot of micropower opamps?!
 
@max my psu seems the stock one. At first service time i will look at capacitors and regulators too if there is a chance (space) to improve them.
@mark i can count 108 opamp and 56 npn, my desk is well fullfilled (i.e. every channel used, no direct out or insert connection yet)
 
With less voltage and more current available nothing will change, on the contrary you will probably have too little voltage at the inputs of the integrated stabilizers and consequent production of hum on all the outputs of the mixer.
If the power supply is original, check the capacitors !!!!

Con meno tensione e più corrente disponibile non cambierà nulla, anzi avrai probabilmente troppa poca tensione agli ingressi degli integrati stabilizzatori e conseguente produzione di ronzio su tutte le uscite del mixer.
Se l'alimentatore è originale controlla i condensatori!!!!
 
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