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EuroRack PSU Design Questions
Old 30th March 2021
  #1
Here for the gear
 
EuroRack PSU Design Questions

I intend to built a power supply to run Eurorack synth modules, one for bench with a single output (to test new modules that I will build next) and one to power the rack used for production, which I intend to have eight outputs (for eight modules) per rail.

The goal is to provide up to one amp of equipment per PSU module.

Some sample equipment specs:
Hermod: 310mA from the +12V rail and 30mA from the -12V rail
Rings: (2x5 pin connector), 120mA on +12V rail, 5mA on -12V
Plaits: 50mA from the +12V rail, and 5mA from the -12V rail

This seems like a good representation of module power requirements.

I intend to 3D print a case for the PSU, and print a set of Eurorack format to 19" rack adapters to mount it all on 19" racking rails.

I've found several PSU schematics online that I've been studying, and I believe I understand the theory of how it works. I've drawn my own schematic from scratch based on other designs, particularly the design used by Moritz Klein in his excellent YouTube videos.

I've added a few features, and I also have some questions based on differences I've found in other designs, and I'm looking for feedback or suggestions for improvements before I order parts.

I'm attaching both the schematic and a spreadsheet of the components that I've located and am proposing to use with links and prices. It's about $45 without the case and transformer.

Please let me know if you have any suggestions for improvements.

Aside from that, I also have some specific questions:

1. Moritz used 4700uF capacitors, but states in his video that he doesn't know the formula for determining them, but that size "seems to work". Another design (AI Synthesis) calls for 3300uF capacitors in this same role. How much does cap size matter here, and what difference will it make? Is there a formula for picking the ideal size?

Both designs agree on 1uF for the buffers. I'm opting for tantalum here because ceramic can (supposedly) introduce noise.

2. Moritz calls for 1N4007 rectifier diodes while AI Synthesis calls for 1N4004. What effect does this have?

3. Moritz uses three rectifier diodes while AI Synthesis uses six. In the AI Synthesis build video, he says the extra diodes are to conform to US safety standards, but it's unclear how they are being used electronically to do that. Where would the extra diodes go in the attached schematic? In series with the first two? After the voltage regulators?

4. Can we confirm that the 7912 does not need a safety diode (please see D3 on the schematic) while the 7812 does?

5. Should we add a fuse?

6. Is there any case where a component failure (bad cap, bad diode) can cause damage to the connected synth modules? If so, what modifications can be made to mitigate or eliminate any potential for over/under voltage/current damage due to component failure?

7. Are the blue LED's with the 410 ohm resistors on each rail a sufficient ghost load to prevent damage to the PSU if powered on with no synth modules attached?

8. Suggestions on a transformer to use? I drew it with a mains voltage transformer because I thought it would be easier to modify the design to add a +5v rail for digital modules by having a half tap on the transformer going to a 7805 regulator. (While you can supposedly run 12 volts into a 7805, it sounds like that is a bad idea, because it would essentially be a space heater.) So I thought a transformer with a 12 volt and 6 volt tap would be a better choice. If wall warts are used, you would need two wall warts, 12v and 5v, and I don't know if there would be any "weirdness" from using two separate transformers. Thoughts?

9. Is unbalanced load on the rails a concern? It seems that most modules have a much greater draw on the +12v rail than the -12v rail.

10. Heat sinks. Can someone recommend the right (specific) heat sink for the voltage regulators? It's a TO-220 package, but they range from pennies to lots of money each. And I can't figure out the specs on them or how much heat dissipation is needed. Something that runs cool without a case fan, even if physically larger, is preferred.

Thanks,
Nick


Resources:
https://www.youtube.com/watch?v=pQKN30Mzi2g
https://aisynthesis.com/diy-eurorack...y-build-guide/
Attached Thumbnails
EuroRack PSU Design Questions-modularsynthpsu.r0.1.jpg  
Attached Files
Old 1st April 2021
  #2
Lives for gear
That is a lot of questions, and I can see a pattern that a lot of them can be cleared up by consulting component datasheets. So my first advice would be just this - make a habit of reading datasheets for stuff. They often contain typical applications as well.

Heres my take:

1. As a general rule, the more capacity you put in, the less ripple voltage you get, but it has diminishing returns. Also, you should check the datasheet for your regulator and follow its recommendations on stability.
Cannot imagine ceramic caps actually introducing noticeable noise. I'd avoid tantalums for their parasitics and just go straight to metal film.

2. Probably what they had on hand. 1N4007 has higher reverse voltage rating. Both are perfectly fine, but I'd choose 1n4007s just out of habit. Again, evident from the datasheet.

3. Hard to say without the schematic, but I don't think this is strictly necessary unless you want to sell these units to customers, in which case, this requirement would not be your biggest concern.

4. This sounds strange to me. The reverse diode is supposed to help the device in a situation when there is a failure on its input or a transient somewhere, and so the output somehow becomes more positive than the input for the positive rail and more negative for the negative. In these cases the current stored in the capacitors will tend to flow through an internal junction diode of the device possibly damaging it in the process. I'd say both devices can benefit from reverse current protection, but I don't think this schematic accomplishes this goal on the positive rail. D3 is connected in parallel to the internal diode of the regulator, but since it is an ordinary silicon device, it won't actually conduct in case of the failure described above. You want a Schottky diode for that because it will start conducting before the internal diode in the regulator. See here for details.

5. Yes! Add 3. Not joking - fuse mains then fuse both rails.

6. Caps and diodes usually have an open circuit mode of failure. The only real concern that redaily comes to my mind is overvoltage of the connected device due to some transient voltage event at the instant of something failing brought on by parasitic reactances of the system. If it makes you sleep better at night, you can include simple overvoltage protection to each rail using for example a couple of 15V zener diodes.

7. Fairchild for example states the that the chip already has a quiescent current of about 5mA and also does not include the minimum load in the typical applications schematic in the datasheet. From this I'd conclude that you actually don't need any and therefore the LEDs are fine. But If you are in doubt - just monitor the device's temperature under no load conditions to be sure.

8. In order for the regulator to do its job, it requires that its input voltage is at least one internal dropout higher (flip for negative). If we take a look at the datasheet (), we can conclude that it is 2V. Therefore your input should be at least 14V at all times. From this we can see what the secondary AC voltage of the transformer should be:
Code:
Vac = (Vreg + Vdrop + Vfwd) / sqrt(2) = (12V + 2V + 0.7V) / 1.41 = 10.4V
Everything above that will be dissipated as heat in the regulator. But since there are all kinds of component tolerances and mains voltage fluctuations, I'd throw in another 10-20% and call it 12VAC.
And yes, you need a separate winding for 5V due to the same considerations.

Since your schematic is basically two half wave rectifiers with a capacitive load, I'd also go for 3.6A rating on the secondary. Or make it a round 4A.

9. I cannot see how it can be if both branches are rated properly for the load.

10. The bigger the better . Seriously though, the datasheet states that the juction to case thermal resistance is 5C/W and junction to air is 65C/W. Next we can choose a moderate junction temperature (since we're so nice to our components) of 80C, then see how hot would it get by itself. Taking the maximum 1A regulated current to be the norm:
Code:
Pdissipated = Vdrop * Ireg = (12V * 1.41 * 1.1 - 0.7V - 12V) * 1A = 6W
Note that I take 12 + 10% to illustrate ascenario where your mains voltage stays at the upper edge of its tolerance for a significant amount of time.
That in turn should mean that the temperature of the junction would rise above the ambient air by:
Code:
Pdissipaded * Rt = 6W * 65C/W = WAY TOO MUCH


If we want to stay within our limits of 80C, and we conclude that ambient air inside the enclosure can rise up to 50 or even 60C (depending on construction), we can see that the required thermal resistance of the heatsink should be:
Code:
(80C - 60C) / 6W = 3.3C/W
Which is a bit of a pain, but manageable, and can also be relaxed with better enclosure construction and less safe temperature margins.

As for the general notes, since this is a PSU of audio equipment, I'd certainly add some common mode rejection filtering on the mains side, as well as a fat NTC thermistor to limit inrush currents that would inevitably happen because of those big capacitors and that would stress the transformer and diodes.
You can take a look at the attached schematic for some inspiration about mains filtering and protectionю A good practice also would be to look for a tranny with a middle point in the secondary.
Attached Files
File Type: pdf Yellowjacket_rev12e.pdf (392.3 KB, 4 views)

Last edited by Orson Maxwell; 1st April 2021 at 02:53 PM..
Old 4 weeks ago
  #3
Here for the gear
 
Thanks for the feedback and suggestions!

I've put together a working prototype based on the schematic from the original post and it seems to work. I would like to implement some of your suggestions, though, and I have some questions and "discoveries" to share.

I am using a 12VAC wall wart, specifically this one:

https://www.digikey.com/en/products/...AtSByAREAugL5A

The attached picture shows the oscilloscope readout of the prototype with a Rings (120mA) and a Hermod (310mA) module connected. The teal line is the +12v rail, the purple is the -12v rail and the yellow is the AC after the step down transformer and before the rectifier diodes. It's referenced to AC neutral (which is circuit ground).

The noise on the +12 rail appears when the modules are connected, but not when they are disconnected. With just the LED's, the rails look cleaner.

How much "dirty" on the rail is acceptable? Or perhaps I should ask, can anything be done to fix this? I added a fourth 4700uf cap on that rail, and I think it smoothed a little more, but still noticeable noise (on the scope) under load.

It also seems odd that the AC is squaring off at the top (clipping). But it's possible that I don't have the scope set up right. It didn't come with a manual.


Questions:

1. Is there a reason to use a different AC step-down transformer? Or an internal instead of a wallwart? What specs should I look for when purchasing a transformer for audio use? Are there factors that contribute to noise?

2. Before the voltage regulator, with the caps installed, the DC rails measure (with a multi-meter) +20 and -20 volts. It's about 14VAC coming out of the transformer, so it looks like the caps are stepping it up to 20VDC. Its back to 12VDC after the regulators. But it's normal for the caps to increase the voltage?

3. When you say, "this requirement would not be your biggest concern", are there other major safety or quality issues that need addressed that weren't called out in your original reply? I would like it to conform to best practices and safety standards.

4. Will any Schottky diode do for the reverse current protection? Or how do I calculate what values are needed?

5. AC Fuse: Do we fuse just the hot, or put a fuse on both hot and neutral? If the PSU is 1 amp @ 120 v, do we want 1 amp @ 120v? Or do we divide the amperage or use some other formula due to the power being split into two rails?

6. Same question for DC: if the AC coming in is rated at 1amp, do both DC rails get a a 1 amp fuse, or are they each 0.5 amp?

7. Is there such thing as "AC" and "DC" fuses?

8. I let it run all day with two modules attached. The AC wall wart got very hot. But the caps and regulators weren't even warm (there was a very slight amount of radiant heat, but only slightly above room temperature. The heat sink I used was a HS352-ND.

https://www.digikey.com/en/products/...MBaAcgERAXQF8g

9. Is there any protection necessary to protect the PSU itself from a problem in a connected module? ie. if a module reverses the + and - pins on a trigger inverter, will the caps in the PSU be damaged?

10. At what point do we get concerned about wire gauge? The ribbon cable uses 28 AWG. I'm having a hard time finding information/calculators for low voltage DC. Can I pull 1 amp of 12VDC though one 28AWG ribbon cable? For example, if I wanted one ribbon cable to go from the PSU to a distribution bus bar (that all modules pulled through) would it be OK? Or would I need to split it up? How do I calculate this?

I used this to make my own cables:
https://www.digikey.com/en/products/...BmwDkAREAXQF8g

11. "Since your schematic is basically two half wave rectifiers" - is this not an good or optimal way of doing this?

12. How do you size a NTC thermistor? And does it go before or after the step down transformer?


Thanks,
Nick
Attached Thumbnails
EuroRack PSU Design Questions-ds1z_quickprint3.png  
Old 4 weeks ago
  #4
Here for the gear
 
You mentioned NTC Thermistors in your post, but the "Inrush Current Limiter" category on Digi Key lists PTC Thermistors instead. The NTC Thermistors are listed as being for temperature measurement.

Here is one of the PTC Thermistors:

https://www.digikey.com/en/products/...30A020/7364726

According to it's Spec Sheet () it's listed as "Inrush current limiter for smoothing and
DC link capacitors" and "To replace high-power fixed resistors for capacitor charging".

So it seems like this may be the part I want to order? The lowest voltage on the spec sheet is 280, so that should be fine. Not sure on the resistance values. And was there a reason to go with an NTC over a PTC?

EDIT:
Quote:
Cannot imagine ceramic caps actually introducing noticeable noise. I'd avoid tantalums for their parasitics and just go straight to metal film.
I'm new to electronics so I'm trying to learn as a much as I can. I used the tantalums in the prototype. I tried looking up parasitics for capacitors, but didn't find anything that explains it in plain English. I would note for anyone else interested in building a power supply, that ceramic caps might be a bad idea, since supposedly they fail closed, and can start fires inside a power supply.

Based on this video, where the host (an electrical engineer) says this isn't the first time he's had a ceramic cap cause a catastrophic failure in a PSU: https://www.youtube.com/watch?v=Q2rvAoO-MIA

Do metal film capacitors suffer from the same problem? I'm also wondering if a fuse would have stopped the fire or not. I'm also thinking that I should acquire or build a metal case instead of 3D printing a case for the PSU, for fire safety.
Old 2 weeks ago | Show parent
  #5
Lives for gear
Hey, you're welcome.

Lets continue tackling this point by point:
Quote:
Originally Posted by lightnb ➡️
The noise on the +12 rail appears when the modules are connected, but not when they are disconnected. With just the LED's, the rails look cleaner.
I'd say that is expected - it is the effect of loading things down.

Quote:
Originally Posted by lightnb ➡️
How much "dirty" on the rail is acceptable? Or perhaps I should ask, can anything be done to fix this? I added a fourth 4700uf cap on that rail, and I think it smoothed a little more, but still noticeable noise (on the scope) under load.
Well, usually PSUs are designed with specific ripple voltage magnitudes in mind. For starters, I'd consult any available documentation for the modules themselves - it might contain PSU requirements.
Also I'd AC couple the rail channels so I could magnify their traces and see the amplitude of those ripples better. Then you can consult the regulator's documentation to see if that ripple is within spec.
Lastly, if you cannot detect any hum in the audio you're producing, than it's ok

Quote:
Originally Posted by lightnb ➡️
It also seems odd that the AC is squaring off at the top (clipping). But it's possible that I don't have the scope set up right. It didn't come with a manual.
This has nothing to do with the scope - power transformer cores are usually designed to work in the saturation region for effeciency. If you have a variac you can try lowering the input voltage and see if the clipping goes away. You can also observe the mains waveform itself - some electrical companies are known to nudge effective voltage of the mains supply by clipping it off and therefore increasing the area under the not-so-sine curve without changing the maximum amplitude to stay in spec.
All in all this is pretty normal.

Quote:
Originally Posted by lightnb ➡️
1. Is there a reason to use a different AC step-down transformer? Or an internal instead of a wallwart? What specs should I look for when purchasing a transformer for audio use? Are there factors that contribute to noise?
If this one doesn't melt down, I'd say no. Main factors contributing to noisiness are leakage inductance (how much energy the core releases into surrounding space) and the core magnetisation operating point, and the presence of a screen between the primary and the secondary windings.
Tighter manufacturing tolerances and better core construction yeld less leakage. Electrical screen that can be grounded externally can help with all kinds of interference finding its way into your device via capacitative coupling between the windings. Magnetisation point is something designed into the transformer for cost efficiency - the more magnetic flux you're trying to push through the core, the more power you can put through it up to the saturation point. All that yields worse leakage and heat losses.
But frankly it doesn't really matter if you're not intending to physically place the tranny right next to some high-gain input stages.

Quote:
Originally Posted by lightnb ➡️
2. Before the voltage regulator, with the caps installed, the DC rails measure (with a multi-meter) +20 and -20 volts. It's about 14VAC coming out of the transformer, so it looks like the caps are stepping it up to 20VDC. Its back to 12VDC after the regulators. But it's normal for the caps to increase the voltage?
They do not really increase the voltage - they are just being charged to the peak amplitude of the AC voltage which is 1.41 times higher than the effective voltage in case of pure sine. So 14 * 1.41 = 19.8 is quite expected.

Quote:
Originally Posted by lightnb ➡️
3. When you say, "this requirement would not be your biggest concern", are there other major safety or quality issues that need addressed that weren't called out in your original reply? I would like it to conform to best practices and safety standards.
I was referring to the 1001 demands any respectable country would impose on anything electrical sold to customers, so it is more of a legal question, which I'm not qualified to answer.

On a more technical note, you might want to invest into snubbing the secondary winding circuit. That means suppressing any oscillations that might rise from the diode switching by placing a capacitor across the secondary winding. That might not be necessary at all in your design, but it is useful to look for sudden sharp bursts on the secondary sine waveform since you have a proper oscilloscope.

Quote:
Originally Posted by lightnb ➡️
4. Will any Schottky diode do for the reverse current protection? Or how do I calculate what values are needed?
Usually those voltage reversal cases are rare and short in duration, so I'd say any Schottky diode would do.

Quote:
Originally Posted by lightnb ➡️
5. AC Fuse: Do we fuse just the hot, or put a fuse on both hot and neutral? If the PSU is 1 amp @ 120 v, do we want 1 amp @ 120v? Or do we divide the amperage or use some other formula due to the power being split into two rails?
If you want to fuse the primary, you need to know your operating current first. 1 Ampere is what your PSU spits out at 12V. Since there will be inevitable heating of the regulators, you can go with that [email protected] as the overall power that the PSU supplies. But since you're using a 120V mains, your current demand from this higher voltage will be proportionally less because your device cannot consume more power than it supplies and dissipates itself.
So in this case you supply 20W therefore you must consume 20W which translates to 20/120 = 166mA. That is your average current from mains.
If you intend to use an off-the-shelf wall wart, you are fusing on the secondary side, so you choose fuses in accordance to that 1A capability, which means taking a slightly higher current rating so the fuse doesn't blow during normal operation. like 2A for example.
See here for the proper fuse placement though:
http://www.valvewizard.co.uk/fuses.html

Quote:
Originally Posted by lightnb ➡️
6. Same question for DC: if the AC coming in is rated at 1amp, do both DC rails get a a 1 amp fuse, or are they each 0.5 amp?
So in your schematic half the time current flows out of the secondary winding through the diode, past the filters, through the regulator, into the load, then into the 'ground' therefore returns into the secondary winding. The other half of the time it does the same for the negative rail, but never at the same time.
So in my understanding, you want to fuse the outputs right near the output connectors to protect your circuit from the load and connecting cable failures, and then place another one right at the secondary winding before the rectifier diodes.

Quote:
Originally Posted by lightnb ➡️
7. Is there such thing as "AC" and "DC" fuses?
Its a complicated subject, but for most intents and purposes, no.


Quote:
Originally Posted by lightnb ➡️
8. I let it run all day with two modules attached. The AC wall wart got very hot. But the caps and regulators weren't even warm (there was a very slight amount of radiant heat, but only slightly above room temperature. The heat sink I used was a HS352-ND.

https://www.digikey.com/en/products/...MBaAcgERAXQF8g
That is a good sign. Also related to that clipped sine question.

Quote:
Originally Posted by lightnb ➡️
9. Is there any protection necessary to protect the PSU itself from a problem in a connected module? ie. if a module reverses the + and - pins on a trigger inverter, will the caps in the PSU be damaged?
Can you elaborate on this please? What do you mean by this reversal?

Quote:
Originally Posted by lightnb ➡️
10. At what point do we get concerned about wire gauge? The ribbon cable uses 28 AWG. I'm having a hard time finding information/calculators for low voltage DC. Can I pull 1 amp of 12VDC though one 28AWG ribbon cable? For example, if I wanted one ribbon cable to go from the PSU to a distribution bus bar (that all modules pulled through) would it be OK? Or would I need to split it up? How do I calculate this?

I used this to make my own cables:
https://www.digikey.com/en/products/...BmwDkAREAXQF8g
It's all about the length of the cable. Cable is basically a resistor, and its resustance gets larger the longer it is and the thinner it is.
You can use this calculator to see how much voltage would your cable drop and then decide if this is a problem or not.
Last time I designed low voltage DC was for my truck's wiring harness, and I went for 2% voltage loss as a threshold.

Quote:
Originally Posted by lightnb ➡️
11. "Since your schematic is basically two half wave rectifiers" - is this not an good or optimal way of doing this?
It is not, but it depends on your transformer design. A better way would be to go with a centre-tapped secondary and use a bridge rectifier.
See this tutorial.

Quote:
Originally Posted by lightnb ➡️
12. How do you size a NTC thermistor? And does it go before or after the step down transformer?
It goes before the transformer because the transformer itself has an inrush magnetisation current as well.

Quote:
Originally Posted by lightnb ➡️
You mentioned NTC Thermistors in your post, but the "Inrush Current Limiter" category on Digi Key lists PTC Thermistors instead. The NTC Thermistors are listed as being for temperature measurement. Not sure on the resistance values. And was there a reason to go with an NTC over a PTC?
NTC means negative temperature coefficient, so they conduct better when hot. So they limit the inrush current by having high resistance just as you start the device up, then they warm up and present less resistance to the circuit.
You must chose the NTCs for their operating current. If you're putting one in front of the tranny, than your current is about 170mA. For linear supplies more cold resistance is better - means softer start.
You can get some info here as well.

Quote:
Originally Posted by lightnb ➡️
I'm new to electronics so I'm trying to learn as a much as I can. I used the tantalums in the prototype. I tried looking up parasitics for capacitors, but didn't find anything that explains it in plain English. I would note for anyone else interested in building a power supply, that ceramic caps might be a bad idea, since supposedly they fail closed, and can start fires inside a power supply.

Based on this video, where the host (an electrical engineer) says this isn't the first time he's had a ceramic cap cause a catastrophic failure in a PSU: https://www.youtube.com/watch?v=Q2rvAoO-MIA

Do metal film capacitors suffer from the same problem? I'm also wondering if a fuse would have stopped the fire or not. I'm also thinking that I should acquire or build a metal case instead of 3D printing a case for the PSU, for fire safety.
Tantalum and other electrolyte capacitors have weird properties besides the ones we use them for. For example they may have hysteresis and act differently on different frequencies. Also tantalums are not considered reliable in the long run.
Ceramics can in fact fail short therefore my general advise was to go for metal films if the capacitance does not cost you an arm and a leg. There are a lot of things to consider if you get into the whole fail modes territory, but there are special ratings for those as well - like the X and Y caps that are supposed to go in mains circuits.
Properly fused circuits are indeed more well-behaved, but I cannot say just from the video.
Any metal case is conduictive to the touch, so it is another can of worms entirely, but since you do not have mains power inside your case, it might not be a problem. But frankly, I don't see a problem with a plastic case as well.

Cheers.
Old 2 weeks ago
  #6
Here for the gear
 
Thanks,

That's a lot to go through and experiment with.

One other issue I've observed: one of my modules in particular won't start if it's plugged into the Power supply when I plug the power supply into the wall. Unplugging and re-plugging the ribbon cable going to the module with the power supply on, causes it to "boot" correctly. It is a digital/micro-controller based module. I'm thinking that it takes a while for the capacitors to charge and not enough power is available at first, which causes the module to fail to power on.

Is there any type of device that can go at the output side that doesn't let any power out at all until the power supply is warmed up and ready?



UPDATE:

Going back to the bridge rectifier with center tap which you linked to above (picture attached), is this transformer a good choice:

https://www.digikey.com/en/products/.../166L14/270130

It's 14VAC output, center tapped, with a 2 amp rating. I've read that toroidal is better for audio, but I can't find any center-tapped toroidals.

The schematic is showing 1N4002 diodes. Is there any reason not to use 1N4007's everywhere instead (since I already have them and 1N4002 says "obsolete" on digikey?)

And that schematic isn't using Schottky diodes for the reverse, they're just 1N4002's. So should I substitute in Schottky's there?

With the center tapped transformer, will I be able to get +6 volts from a tap configuration as well? And will it unbalance the power supply?

And what is the purpose of D6 and D8 in that schematic?


UPDATE 2:

The thermistors I ordered arrived and I was able to test them. They do a good job limiting the current, so when the power supply gets plugged in, it takes about 5 seconds instead of 1 second for the caps to charge up. The problem is, once you put a load on the power supply, the voltage drops by a lot. With a 160 mA load, I'm getting about 5 volts(!) on the "12 volt" rail. Remove the thermistors and it works fine at 12 volts. It's also 12 volts with the thermistor connected and no load (just the LEDs).

The thermistor is:

https://www.digikey.com/en/products/...mSeq=362527967

It seems like there should be a way to bypass the thermistor once the caps are charged.

I also checked the AC on the scope: the wave is not clipped when metering the output of the AC transformer, until the diodes, capacitors and voltage regulators are connected. Then it gets clipped. In both cases, I'm metering after the AC transformer and before the rectifier diodes.





Thanks again,
Nick
Attached Thumbnails
EuroRack PSU Design Questions-78xx_bipolar.gif  
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