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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, 08:25 PM   #11
maxmix69 is offline maxmix69  Italy
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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.
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scrivi pure in italiano che facciamo prima!
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Old 3rd April 2020, 11:42 PM   #12
Mark Tillotson is offline Mark Tillotson
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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?!
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Old 4th April 2020, 09:44 AM   #13
rozzilla is offline rozzilla  Italy
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@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)
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Old 4th April 2020, 09:47 AM   #14
rozzilla is offline rozzilla  Italy
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I also found a used DCP100 supply, which supply +-15V instead of +-17V
What kind of differences i would notice with less voltages but a lot more current on rails ?
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Old 4th April 2020, 03:44 PM   #15
maxmix69 is offline maxmix69  Italy
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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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Old 4th April 2020, 04:42 PM   #16
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Check you have +-17volts on the rails to the op amps. If you have that is it, it is working and not the power supply.
Simple to do and effective.
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Old 5th April 2020, 09:24 AM   #17
turk 182 is offline turk 182  Canada
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if using headphones affects the master output i would start there, somethings wrong!


as to input problems are you correctly gain structuring things in your mix?
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Old 5th April 2020, 11:54 AM   #18
rozzilla is offline rozzilla  Italy
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@turk I do my best for gain staging, but I "feel" I cannot get much regulation to work with.
my cans as my ears have low impendance, so I suppose a step increase of power consumption when they are in.
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Old 5th April 2020, 12:07 PM   #19
turk 182 is offline turk 182  Canada
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are B+ voltages fluctuating under signal conditions?


what sort of test equipment do you have access to?
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Old 5th April 2020, 12:26 PM   #20
turk 182 is offline turk 182  Canada
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is the snippet of schematic in your first post an authentic scan of a Soundcraft schematic?
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