While we are on the subject of half-brained ideas on how to reduce AC voltage, what about a capacitive voltage divider on the secondaries? In this case the current would likely be low, which would hopefully mean that heating of the caps would also be low...
For those not familiar with this concept, see:
Capacitive Voltage Divider Circuit an AC Voltage Divider
I'm surprised no one suggested this approach, since it's an AC application.
Now here's my follow up question: Could this be used in a "power" application? For instance, let's say you want both a voltage for the output rails and a slightly higher voltage (at low current) for the VAS stage in a power amp. Specifically this would ONLY be used after the transformer and before rectification - I am NOT advocating a transformerless supply, which is unsafe. Could you get both of these voltages from a single transformer using a capacitive divider?
For those not familiar with this concept, see:
Capacitive Voltage Divider Circuit an AC Voltage Divider
I'm surprised no one suggested this approach, since it's an AC application.
Now here's my follow up question: Could this be used in a "power" application? For instance, let's say you want both a voltage for the output rails and a slightly higher voltage (at low current) for the VAS stage in a power amp. Specifically this would ONLY be used after the transformer and before rectification - I am NOT advocating a transformerless supply, which is unsafe. Could you get both of these voltages from a single transformer using a capacitive divider?
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Ignoring the phase of the load impedance, (What's the impedance of AC-DC, capacitor-smoothed power supplies anyway), to get 20V 1A out of 40V with 10% regulation would required 4x 800uF capacitors from my calcs
Sounds reasonable, but why not get a voltage multiplier for the VAS instead
Sounds reasonable, but why not get a voltage multiplier for the VAS instead
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In nearly every case you can supply an LV PCB with DC in place of the recommended AC. You might need to adjust the voltage slightly to allow for the now redundant diodes on the PCB.
£1.85 with FREE P&P.
In nearly every case you can supply an LV PCB with DC in place of the recommended AC. You might need to adjust the voltage slightly to allow for the now redundant diodes on the PCB.
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STOP POSTING STUPID RECOMMENDATIONS. THE RIGHT SOLUTIONS HAVE ALREADY BEEN SUGGESTED.
You can't supply regulated 9VDC to something with an onboard 9VDC regulator and have it work properly. Your 9VDC will be well inside the dropout range of the internal regulator.
You can't supply regulated 9VDC to something with an onboard 9VDC regulator and have it work properly. Your 9VDC will be well inside the dropout range of the internal regulator.
Many tube powered Preamps/pedals/distortion boxes/etc. ask for 12VAC wall warts.
You can NOT repeat NOT again NOT feed them 12V DC (neither 13 or 14V DC to compensate for "now redundant rectifier diodes" and/or "internal regulators".
One famous example is Mesa Boogie V-Twin
https://www.youtube.com/watch?v=h3hz4BxjOio
Which is powered by 12VAC ONLY.
Why?
Because out of 12VAC they get:
1) +12VDC , rectified and filtered to feed tube filaments with no hum.
FWIW they might feed it 12VAC if they wished, which is the standard way to feed filaments.
2) using a back mounted transformer (which of course works on AC only 😉 ) they get some +260V rectified for tube plates.
3) they get raw +16VDC , which become +12V regulated for Op Amps positive rail.
4) they get raw -16VDC , which become regulated -12V for Op Amps negative rail.
I'd LOVE to hear how somebody can plug a single 12VDC (or any other DC voltage, by the way) wall wart and get such a variety of voltage and polarity.
To boot, DC would be shorted by the transformer primary impedance (which would become a low value resistor) .
Obviously, if the Preamp mentioned asks for 6 to 9VAC ... there must be a reason for that 😉
It would have been easier to offer a DC supply if that were not the case.
The V-Twin power supply:
You can NOT repeat NOT again NOT feed them 12V DC (neither 13 or 14V DC to compensate for "now redundant rectifier diodes" and/or "internal regulators".
One famous example is Mesa Boogie V-Twin
https://www.youtube.com/watch?v=h3hz4BxjOio
Which is powered by 12VAC ONLY.
Why?
Because out of 12VAC they get:
1) +12VDC , rectified and filtered to feed tube filaments with no hum.
FWIW they might feed it 12VAC if they wished, which is the standard way to feed filaments.
2) using a back mounted transformer (which of course works on AC only 😉 ) they get some +260V rectified for tube plates.
3) they get raw +16VDC , which become +12V regulated for Op Amps positive rail.
4) they get raw -16VDC , which become regulated -12V for Op Amps negative rail.
I'd LOVE to hear how somebody can plug a single 12VDC (or any other DC voltage, by the way) wall wart and get such a variety of voltage and polarity.
To boot, DC would be shorted by the transformer primary impedance (which would become a low value resistor) .
Obviously, if the Preamp mentioned asks for 6 to 9VAC ... there must be a reason for that 😉
It would have been easier to offer a DC supply if that were not the case.
The V-Twin power supply:
Attachments
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Agree.
Most rude, of course, is suggesting solutions which will burn, damage or at least be non functional for the OP needs.
IF the device in question asks, both in its user manual and printed by the power jack, for "6 to 9 VAC" then so be it.
Suggesting anything else without having seen the schematic is arrogance.
Most rude, of course, is suggesting solutions which will burn, damage or at least be non functional for the OP needs.
IF the device in question asks, both in its user manual and printed by the power jack, for "6 to 9 VAC" then so be it.
Suggesting anything else without having seen the schematic is arrogance.
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