Hi everyone.
I'm designing a preamp that will contain opamp gain stages, a minidsp (2x4 balanced, 12v supply required) and pic controlled input relays, motorized pot etc etc.
I need a +/-15v supply for the opamps (ESP project P05), +12v for the Minidsp and +5v for the pics and relays etc. I'd like the 15v and 12v supplies to be switched and the 5v supply always on (to maintain power to the pics which will operate the power on relay).
I'd like to run it all off a single 16vac wallwart transformer.
Question is, can I have 3 seperate supplies, each a standard circuit with its own rectifier and voltage regulator(s), each taking AC from the same wall wart? Obviously the wall wart would have to be able to supply ample total current for everything connected.
Are there any issues with this?
Am I better just dropping the +15v rail down to 12v then to 5v? I'm not sure about powering pics and relays from the same supply as the preamp.
thanks, Jon
I'm designing a preamp that will contain opamp gain stages, a minidsp (2x4 balanced, 12v supply required) and pic controlled input relays, motorized pot etc etc.
I need a +/-15v supply for the opamps (ESP project P05), +12v for the Minidsp and +5v for the pics and relays etc. I'd like the 15v and 12v supplies to be switched and the 5v supply always on (to maintain power to the pics which will operate the power on relay).
I'd like to run it all off a single 16vac wallwart transformer.
Question is, can I have 3 seperate supplies, each a standard circuit with its own rectifier and voltage regulator(s), each taking AC from the same wall wart? Obviously the wall wart would have to be able to supply ample total current for everything connected.
Are there any issues with this?
Am I better just dropping the +15v rail down to 12v then to 5v? I'm not sure about powering pics and relays from the same supply as the preamp.
thanks, Jon
> can I have ....
Yes.
> Are there any issues with this?
Probably.
Why are the relays 5V? 12V relays take <half the current, less waste less spike. This may need buffers from the 5V logic, of course.
16VAC wallwart may be slim for +/-15V rails. Why not +/-12V? The opamps work the same and you rarely need that last 2dB of clipping headroom.
Yes.
> Are there any issues with this?
Probably.
Why are the relays 5V? 12V relays take <half the current, less waste less spike. This may need buffers from the 5V logic, of course.
16VAC wallwart may be slim for +/-15V rails. Why not +/-12V? The opamps work the same and you rarely need that last 2dB of clipping headroom.
What's the amperage on your supply ? You'll get about 21VDC from it, if the load is light vs its capacity.
I would create one 21VDC single supply, then use two switching regs, one to 12VDC, one to 5VDC. Use a DC to DC converter to create the dual 15V supply from the 12V supply.
Some CLC filtering might be needed to clean up the outputs of the switchers.
I would create one 21VDC single supply, then use two switching regs, one to 12VDC, one to 5VDC. Use a DC to DC converter to create the dual 15V supply from the 12V supply.
Some CLC filtering might be needed to clean up the outputs of the switchers.
PRR - fair point, no reason not to use 12v relays, they would use less current.
The 16v ac wall wart is as recommended for Rod Elliotts P05 power supply (which I have for the preamp supply). I like the idea of using this instead of a transformer in the preamp case. Agreed I could use +/- 12v with no problems.
00940 - I'll be using a transformer that can supply about 1A, so it should be plenty to run the opamps, Minidsp and a few relays and so on. I was going to base it all around 78XX regulators (because I already have these lying around).
I was considering half-wave rectifiers using a single diode for the +12v and +5v supplies. I know ripple is high but with a big enough smoothing cap, I would have thought the dc coming out of the regulators would be smooth enough for the Minidsp and the microcontrollers etc, and I dont need loads of current.
Any thoughts on this plan? I've read something about "dc saturation of the transformer core" with half wave rectifiers, but I dont really know what this means or if I should worry about it.
The 16v ac wall wart is as recommended for Rod Elliotts P05 power supply (which I have for the preamp supply). I like the idea of using this instead of a transformer in the preamp case. Agreed I could use +/- 12v with no problems.
00940 - I'll be using a transformer that can supply about 1A, so it should be plenty to run the opamps, Minidsp and a few relays and so on. I was going to base it all around 78XX regulators (because I already have these lying around).
I was considering half-wave rectifiers using a single diode for the +12v and +5v supplies. I know ripple is high but with a big enough smoothing cap, I would have thought the dc coming out of the regulators would be smooth enough for the Minidsp and the microcontrollers etc, and I dont need loads of current.
Any thoughts on this plan? I've read something about "dc saturation of the transformer core" with half wave rectifiers, but I dont really know what this means or if I should worry about it.
Rod's P05 shows two connections. CT AC with full-wave bridge, and single AC with +/- voltage doubler.
With sufficient C the doubler works very well. With balanced loading, there is no DC strain on the transformer. So you get +/-21V DC. Barely enough for regulating to +/-15VDC. If there are no other odd loads.
Now you have odd and unspecified loads. How hungry are the relays? miniDSP? PICs? Few-mA? Hundreds-mA?? With the plan so far, these are unbalanced and will cause DC strain the transformer. Few-mA, no big deal. 100mA could hurt, even with a 1,000mA winding.
With sufficient C the doubler works very well. With balanced loading, there is no DC strain on the transformer. So you get +/-21V DC. Barely enough for regulating to +/-15VDC. If there are no other odd loads.
Now you have odd and unspecified loads. How hungry are the relays? miniDSP? PICs? Few-mA? Hundreds-mA?? With the plan so far, these are unbalanced and will cause DC strain the transformer. Few-mA, no big deal. 100mA could hurt, even with a 1,000mA winding.
Just use transformer at half of its rated power (1.41 less actually, if I remember right).
A MiniDSP 2x4 works fine from 4.5 to 24 V, so you could run it on +15 V.
Note that ac wall warts consume more power when lightly loaded than energy star V or VI dc wall warts. You could use a separate 5 V supply to reduce power consumption as this will always be on. Another option is to build the power supply of Project 158. See figure 5. Project 158
Note that ac wall warts consume more power when lightly loaded than energy star V or VI dc wall warts. You could use a separate 5 V supply to reduce power consumption as this will always be on. Another option is to build the power supply of Project 158. See figure 5. Project 158
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> ...odd and unspecified loads. How hungry are the relays?
Call it <150mA for the Minidsp, <100mA total for relays and PICs, plus 100mA for short periods for the motorized pot. So typically around 250mA. Plus <100mA for the preamp via the P05.
If I forget the half wave and use bridge rectifiers instead, will my transformer be happier? Any issues with multiple bridge rectifiers and a voltage doubler all off one transformer (rated for about twice the max current draw)?
> A MiniDSP 2x4 works fine from 4.5 to 24 V, so you could run it on +15 V
I have a Minidsp balanced, v1.5. As far as I know it needs a 12v supply.
> You could use a separate 5 V supply...
I considered a separate wall wart for the 5v, but it would be neater to run it all off one wart. When the unit is in "standby" everything but one picaxe chip will be de-energised, so it should consume very little power.
Call it <150mA for the Minidsp, <100mA total for relays and PICs, plus 100mA for short periods for the motorized pot. So typically around 250mA. Plus <100mA for the preamp via the P05.
If I forget the half wave and use bridge rectifiers instead, will my transformer be happier? Any issues with multiple bridge rectifiers and a voltage doubler all off one transformer (rated for about twice the max current draw)?
> A MiniDSP 2x4 works fine from 4.5 to 24 V, so you could run it on +15 V
I have a Minidsp balanced, v1.5. As far as I know it needs a 12v supply.
> You could use a separate 5 V supply...
I considered a separate wall wart for the 5v, but it would be neater to run it all off one wart. When the unit is in "standby" everything but one picaxe chip will be de-energised, so it should consume very little power.
If your transformer can supply 16VAC/1A, that means it can supply roughly 21VDC/550mA max with a full wave bridge setup (see). If you use a switching reg like the lm2596 for example, you can get about 12VDC/850mA from that, with very little heat. Add a little dc-dc converter for your opamps and you're good, without overtaxing nor unbalancing your transformer (a bit of an expense but you save on regulators and caps).
If you play with half wave rectifiers and stick to linear regulators, you will seriously unbalance your transformer and may not have enough mA on hand for your 12V rail.
The minidsp balanced is specced at 12VDC, 200mA max btw.
If you play with half wave rectifiers and stick to linear regulators, you will seriously unbalance your transformer and may not have enough mA on hand for your 12V rail.
The minidsp balanced is specced at 12VDC, 200mA max btw.
I know you are in love with your 16V 1A wallwart, but I think it's right on the edge of not-working. Either not enough raw DC for even 12V regulated; or smoke. Depending on my assumptions, either transformer current exceeds 1A (and you do NOT want to push the rating of a cheap transformer fulltime), or the raw DC sags to under +14V leaving no headroom for a regulator. That's before allowing for wall-voltage variation (+/-7% in my house; most are better).
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The 16vac transformer is as recommended by Rod Elliott for his P05 power supply, which I have a PCB for. I believe its a tried and tested circuit so I assume the ac voltage recommended is capable, albeit for a limited current.
Granted I'm trying to push more current out of the transformer than the P05 would typically be asked to provide on its own, but I figured (probably naively - i'm new to this) that if the total current draw from all the seperate circuits (+/-15, +12, +5) was well within the current capability of the transformer, I would be ok.
> it can supply roughly 21VDC/550mA max with a full wave bridge setup (see)
Thanks for the link - useful info. For normal long term operation (i.e. when no relays are being switched and no motors are running) I should be well below 550mA total. The half-wave rectifier idea is out the window by the way.
> use a switching reg like the lm2596...
I didn't know much about switching regs, but looking into it it does seem like a good option.
For audio purposes, such as a preamp, is a supply with switching regs inferior in terms of noise to a supply with linear regs?
Am I better using the P05 supply for the preamp and switchers for the rest? Or does this offer no benefit to supplying +/-15v with a dc-dc converter?
The 16vac transformer is as recommended by Rod Elliott for his P05 power supply, which I have a PCB for. I believe its a tried and tested circuit so I assume the ac voltage recommended is capable, albeit for a limited current.
Granted I'm trying to push more current out of the transformer than the P05 would typically be asked to provide on its own, but I figured (probably naively - i'm new to this) that if the total current draw from all the seperate circuits (+/-15, +12, +5) was well within the current capability of the transformer, I would be ok.
> it can supply roughly 21VDC/550mA max with a full wave bridge setup (see)
Thanks for the link - useful info. For normal long term operation (i.e. when no relays are being switched and no motors are running) I should be well below 550mA total. The half-wave rectifier idea is out the window by the way.
> use a switching reg like the lm2596...
I didn't know much about switching regs, but looking into it it does seem like a good option.
For audio purposes, such as a preamp, is a supply with switching regs inferior in terms of noise to a supply with linear regs?
Am I better using the P05 supply for the preamp and switchers for the rest? Or does this offer no benefit to supplying +/-15v with a dc-dc converter?
> is as recommended by Rod Elliott
For some opamps (which I don't recall specs for).
I used default 1k resistors to simulate a ~~16mA opamp current; this eats about 0.7 Watts.
Using the latest number (200mA), there's 300mA(!!) of digi-stuff, which you propose to take from one 20V rail through regulator. The transformer sees 21V*0.3A which is over 6 Watts of DC. So you are 9 times hungrier than the circuit Rod was feeding. Even if not all the parts are clacked all the time, you are far past what Rod proposed.
And there's 5 Watts of plain heat in sag and regulator, which can be significant in a small box.
For some opamps (which I don't recall specs for).
I used default 1k resistors to simulate a ~~16mA opamp current; this eats about 0.7 Watts.
Using the latest number (200mA), there's 300mA(!!) of digi-stuff, which you propose to take from one 20V rail through regulator. The transformer sees 21V*0.3A which is over 6 Watts of DC. So you are 9 times hungrier than the circuit Rod was feeding. Even if not all the parts are clacked all the time, you are far past what Rod proposed.
And there's 5 Watts of plain heat in sag and regulator, which can be significant in a small box.
ok, so i'm out of luck with my 16vac wall wart. So what are my options?
I'm trying to achieve a fully featured preamp in a compact box. This was the benefit of using a wall wart to keep the transformer out of the box. The preamp will contain a phono stage as well so having a transformer very close is maybe an issue.
How do people normally achieve the different voltages in a preamp like this? It must be done all the time.
Some possible options:
Multiple 'normal' transformers in a seperate box (i.e. one for the +/-15v, and a seperate one for the +12v & +5v), or squeezed into the preamp box.
A 16vac wall wart for the P05 supply and a 12vdc wart for the rest.
Any other ideas?
I'm trying to achieve a fully featured preamp in a compact box. This was the benefit of using a wall wart to keep the transformer out of the box. The preamp will contain a phono stage as well so having a transformer very close is maybe an issue.
How do people normally achieve the different voltages in a preamp like this? It must be done all the time.
Some possible options:
Multiple 'normal' transformers in a seperate box (i.e. one for the +/-15v, and a seperate one for the +12v & +5v), or squeezed into the preamp box.
A 16vac wall wart for the P05 supply and a 12vdc wart for the rest.
Any other ideas?
- Preamp is ESP P88 - 2 opamps, probably OPA2134
- Phono stage is ESP P06 - 2 more OPA2134s
- Minidsp Balanced
- A couple of Picaxe microcontrollers plus oled display
- Relays for input selection, power and possibly power amp switching.
- An led or two.
- Alps motorized pot which has a 5v motor (burns about 100mA when turning I think)
- Phono stage is ESP P06 - 2 more OPA2134s
- Minidsp Balanced
- A couple of Picaxe microcontrollers plus oled display
- Relays for input selection, power and possibly power amp switching.
- An led or two.
- Alps motorized pot which has a 5v motor (burns about 100mA when turning I think)
Allright.
Now, let's see if we can power all that from your transformer, using it to create a conventional +21VDC rail.
- analog section: about 50ma continuous for the preamp and phono, at +/-15V. That's 1.5W. With a Meanwell DCWN03A-15 converter, we can get that from a 18-36V rail at 87% efficiency, let's say 80% to be safe. Which means we draw about 90ma from the 21V supply at all times, a bit more under dynamic conditions, let's say 100mA.
- pics, relay, pot: About 100ma continuous @5V, with peaks at twice that, in between 0.5W and 1W. Using a lm2596, also considering about 80% efficiency, we're drawing in between 30 and 60ma from the 21V.
- minidsp: max 200ma @12V, that's 2.4W worst case. Using another lm2596, we're drawing about 150mA from the 21V supply.
Let's summarize: we're taking 100mA+60mA+150mA = 310mA worst case, 90+30+100=220mA at rest. As the transformer can supply about 550mA (dc), we're pretty good, with some margin.
LM2596 are dirt cheap on ebay on small pcb, buy from a reliable vendor though. You might want to but an inductor after the one feeding the minidsp.
The DCWN03A-15 isn't cheap but you don't need regulators afterwards. A clc filter after it to remove the HF switching noise isn't a bad idea (it's switching at 100khz).
Now, let's see if we can power all that from your transformer, using it to create a conventional +21VDC rail.
- analog section: about 50ma continuous for the preamp and phono, at +/-15V. That's 1.5W. With a Meanwell DCWN03A-15 converter, we can get that from a 18-36V rail at 87% efficiency, let's say 80% to be safe. Which means we draw about 90ma from the 21V supply at all times, a bit more under dynamic conditions, let's say 100mA.
- pics, relay, pot: About 100ma continuous @5V, with peaks at twice that, in between 0.5W and 1W. Using a lm2596, also considering about 80% efficiency, we're drawing in between 30 and 60ma from the 21V.
- minidsp: max 200ma @12V, that's 2.4W worst case. Using another lm2596, we're drawing about 150mA from the 21V supply.
Let's summarize: we're taking 100mA+60mA+150mA = 310mA worst case, 90+30+100=220mA at rest. As the transformer can supply about 550mA (dc), we're pretty good, with some margin.
LM2596 are dirt cheap on ebay on small pcb, buy from a reliable vendor though. You might want to but an inductor after the one feeding the minidsp.
The DCWN03A-15 isn't cheap but you don't need regulators afterwards. A clc filter after it to remove the HF switching noise isn't a bad idea (it's switching at 100khz).
Brilliant, thanks. I really appreciate your help.
Can I ask a few more questions?
How do I calculate the current draw from the ESP P05 circuit which, when fed with a single AC rail, is a full-wave voltage doubler?
How do I calculate the values for the CLC filter? Can you point me to any good sites where I can learn the theory?
Most lm2596 converter modules (and the typical application circuit on the datasheet) seem to include an inductor around 33uH. Is this the inductor you are referring to for the Minidsp supply, or does it need something extra?
Thanks
Can I ask a few more questions?
How do I calculate the current draw from the ESP P05 circuit which, when fed with a single AC rail, is a full-wave voltage doubler?
How do I calculate the values for the CLC filter? Can you point me to any good sites where I can learn the theory?
Most lm2596 converter modules (and the typical application circuit on the datasheet) seem to include an inductor around 33uH. Is this the inductor you are referring to for the Minidsp supply, or does it need something extra?
Thanks
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