(orGreetings.
I've acquired a Studiomaster Trilogy 206 Mixing Board which has a PSU that is designed to be able to work both 240V and 120V. I have no intention of ever going to non-US locations where 240V would be used--so I'm looking to streamline the PSU--it is bulky, heats up considerably, has flimsy wiring and introduces noise when within 3 feet of the mixer itself.
To be up front, I have really no electrical training--so I'm at square one. In my head, I'd like to have a simple AC to DC converter (I think these are called rectifiers?)--as part of a simple PSU--the kind we get with our laptop computers.
The board requires 48V (for phantom power) and +/- 17V lines, along with a ground. It has a 5 pin input/output to the back of the board--which runs to the external PSU (heavy/bulky) where the actual power switch is located. I've looked for a 5 pin adaptor with a rectifier for AC to the required DC voltages--but no luck. I already contacted Studiomaster and they no longer sell these old PSU. I've asked a local engineering school and separate electronics shop but they said they had no interest in working on this. Makes me wonder if there is something really difficult or unusual about my request. I love the mixing boards--I actually have another I picked up which has no PSU--hence my idea to create one (or better yet, be able to simply purchase one).
I've attached a schematic if it might help. My preferred solution would be to simply have a three prong insert and on/off right at the back of the board >>rectifier (like the laptop cable/box) >> standard US AC outlet. Thanks in advance for suggestions!
I've acquired a Studiomaster Trilogy 206 Mixing Board which has a PSU that is designed to be able to work both 240V and 120V. I have no intention of ever going to non-US locations where 240V would be used--so I'm looking to streamline the PSU--it is bulky, heats up considerably, has flimsy wiring and introduces noise when within 3 feet of the mixer itself.
To be up front, I have really no electrical training--so I'm at square one. In my head, I'd like to have a simple AC to DC converter (I think these are called rectifiers?)--as part of a simple PSU--the kind we get with our laptop computers.
The board requires 48V (for phantom power) and +/- 17V lines, along with a ground. It has a 5 pin input/output to the back of the board--which runs to the external PSU (heavy/bulky) where the actual power switch is located. I've looked for a 5 pin adaptor with a rectifier for AC to the required DC voltages--but no luck. I already contacted Studiomaster and they no longer sell these old PSU. I've asked a local engineering school and separate electronics shop but they said they had no interest in working on this. Makes me wonder if there is something really difficult or unusual about my request. I love the mixing boards--I actually have another I picked up which has no PSU--hence my idea to create one (or better yet, be able to simply purchase one).
I've attached a schematic if it might help. My preferred solution would be to simply have a three prong insert and on/off right at the back of the board >>rectifier (like the laptop cable/box) >> standard US AC outlet. Thanks in advance for suggestions!
What you have here is a good old linear power supply with a little quirk.
The fact that this one is designed for 120 and 240 V doesn't make it any bulkier than if it was designed for 120 V only.
The PSU is external from the mixing board for a reason, and you found out already why.
You might consider using modern SMPS PSUs, but they too would probably need to stay outside of the mixing board, so in that respect I don't really see much benefit from not keeping the original PSU.
The fact that this one is designed for 120 and 240 V doesn't make it any bulkier than if it was designed for 120 V only.
The PSU is external from the mixing board for a reason, and you found out already why.
You might consider using modern SMPS PSUs, but they too would probably need to stay outside of the mixing board, so in that respect I don't really see much benefit from not keeping the original PSU.
Thanks for your thoughts Jitter! I've attached a file with an image this time.
So to follow up then, I'm assuming there is one single transformer in the unit (I've labeled that "B")--but correct me if I'm wrong. And since it's already doing the job for both 240 and 120, I see why you'd say that I may as well just leave it alone. But would a 120V transformer even be required if I was only using this in the US? Sorry if that seems like a stupid question--but 120V AC is coming from a US wall--so if the remainder of the PSU expects 120V, is a transformer even required? I'm curious about that, because clearly, not everything requires a transformer, right (like my lamp, my radio, a hair curling device, etc.). And if a transformer is not required (if I only plan on using it in the US), then can't I just offload (what I believe is) the bulky component in the PSU?
And the "Rectifier"...if someone doesn't mind telling me, is the rectifier visible in my attached image)? I'm trying to learn here...my understanding is that it is the rectifier which will take the 120V, and specify that the system deliver 48V and +/- 17V along the different wires which lead to the mixer itself.
Thanks so much. I'm sure this is pretty basic for the experienced crew here...but this is the first help I've gotten in trying to understand what I'm working with. Again, if there were a way for me to simply purchase a 5 pin power adaptor to deliver the above-mentioned voltages--without having to do any wiring--that's what I'd prefer. But I just can't seem to find that.
So to follow up then, I'm assuming there is one single transformer in the unit (I've labeled that "B")--but correct me if I'm wrong. And since it's already doing the job for both 240 and 120, I see why you'd say that I may as well just leave it alone. But would a 120V transformer even be required if I was only using this in the US? Sorry if that seems like a stupid question--but 120V AC is coming from a US wall--so if the remainder of the PSU expects 120V, is a transformer even required? I'm curious about that, because clearly, not everything requires a transformer, right (like my lamp, my radio, a hair curling device, etc.). And if a transformer is not required (if I only plan on using it in the US), then can't I just offload (what I believe is) the bulky component in the PSU?
And the "Rectifier"...if someone doesn't mind telling me, is the rectifier visible in my attached image)? I'm trying to learn here...my understanding is that it is the rectifier which will take the 120V, and specify that the system deliver 48V and +/- 17V along the different wires which lead to the mixer itself.
Thanks so much. I'm sure this is pretty basic for the experienced crew here...but this is the first help I've gotten in trying to understand what I'm working with. Again, if there were a way for me to simply purchase a 5 pin power adaptor to deliver the above-mentioned voltages--without having to do any wiring--that's what I'd prefer. But I just can't seem to find that.
OK, so before we continue forum rules demand a warning about the dangers of working on mains powered devices in which category this PSU belongs.
Even if the forum rules did not demand such a warning, I would have given it anyway as, by your own admission, you do not have any electrical training. And because of ignorance and/or complacency, I myself had a potentially lethal current pass through my body once, and I consider it now as one of life's valuable lessons. It was just luck I walked away unharmed.
⚠️Do not work on mains voltage powered equipment if you are unaware of the dangers, have someone who does help and/or supervise you.
If you do decide to go on, at least educate yourself on the dangers and the precautions needed to mitigate them.
But whatever you do, you do so at your own risk.⚠️
It is not meant to scare you or anyone else following this thread, but worth a quarter of an hour of your life is this video of Mr Carlson from Mr Carlson's Lab telling us about his worst electric shock. I'm glad my worst shock wasn't anywhere near as bad as his.
So, if you're intent on modifying or replacing the PSU, please be very careful, especially with the mains side of wiring. In this particular case, the secondary side of the transformer is not only low voltage, it has been galvanically isolated from the mains. The manufacturer did a good job shielding exposed mains carrying parts (which in older equipment isn't there) but still stay alert at all times when the PSU is connected to the mains.
Even if the forum rules did not demand such a warning, I would have given it anyway as, by your own admission, you do not have any electrical training. And because of ignorance and/or complacency, I myself had a potentially lethal current pass through my body once, and I consider it now as one of life's valuable lessons. It was just luck I walked away unharmed.
⚠️Do not work on mains voltage powered equipment if you are unaware of the dangers, have someone who does help and/or supervise you.
If you do decide to go on, at least educate yourself on the dangers and the precautions needed to mitigate them.
But whatever you do, you do so at your own risk.⚠️
It is not meant to scare you or anyone else following this thread, but worth a quarter of an hour of your life is this video of Mr Carlson from Mr Carlson's Lab telling us about his worst electric shock. I'm glad my worst shock wasn't anywhere near as bad as his.
So, if you're intent on modifying or replacing the PSU, please be very careful, especially with the mains side of wiring. In this particular case, the secondary side of the transformer is not only low voltage, it has been galvanically isolated from the mains. The manufacturer did a good job shielding exposed mains carrying parts (which in older equipment isn't there) but still stay alert at all times when the PSU is connected to the mains.
I will come back later for some more explanation but for now some quick answers to your questions:
B is indeed the transformer, however C is probably not an output but an input.
Yes, when dropping down from mains voltage and galvanically isolating it from it, a transformer is always required. There are non isolated power supply topologies but they are not safe to be used in this case.
Devices can work straight off mains voltage if designed to do so, your hairdryer is a good example.
A LED lamp will usually have a built in PSU enabling it to work from mains voltage and (e.g.) an amp with a 120 V input will have a PSU inside, I'm pretty sure there will be mixing boards with integrated PSUs as well.
Your mixing board's PSU cannot do away with a transformer, even at 120 V.
There are two rectifiers visible in your image, the black round discs with a flat side. These are so-called full wave bridge rectifiers.
The PSU for this device looks pretty proprietary, but that is not to say there are no other options, they are just harder to find.
B is indeed the transformer, however C is probably not an output but an input.
Yes, when dropping down from mains voltage and galvanically isolating it from it, a transformer is always required. There are non isolated power supply topologies but they are not safe to be used in this case.
Devices can work straight off mains voltage if designed to do so, your hairdryer is a good example.
A LED lamp will usually have a built in PSU enabling it to work from mains voltage and (e.g.) an amp with a 120 V input will have a PSU inside, I'm pretty sure there will be mixing boards with integrated PSUs as well.
Your mixing board's PSU cannot do away with a transformer, even at 120 V.
There are two rectifiers visible in your image, the black round discs with a flat side. These are so-called full wave bridge rectifiers.
The PSU for this device looks pretty proprietary, but that is not to say there are no other options, they are just harder to find.
Last edited:
Thank you Jitter! I appreciate the warning--can't ever be too careful. I'm feeling pretty health and so, no need to change that! 🙂
So each device is "different" in terms of how it might be designed (some to work direct with 120V; some which require a transformer). I didn't' know that--but in thinking about that, it makes sense. And as far as my mixer goes, it makes sense to say I can't do away with the transformer--it's obviously there for a reason.
Referring back to my schematic then, I can see that after the transformer, we have a "20-0-20 Off Load" (orange and green wires). Would that be because the number of windings on the transformer's secondary side are fewer--such that the input voltage (either 230 or 115) is stepped down to 20V? And I'm assuming that would be 20V AC until it passes through the rectifier, which would convert the full range (the plus and minus side of the AC) signal to DC, correct?
In this same concept, there must be another "secondary" portion of the transformer to step the load down (yellow wires) 46V. So it's kind of a complicated transformer--or not so much but I haven't come across a transformer type in my research that will produce two different voltages simultaneously. Are these called something specific so I can read about them more?
One final thought for this post...how do we have a 46V off load end up resulting in 48V on the DC output side (after the rectifier)? Unless I'm totally misunderstanding, that doesn't make sense at this point.
Thank you for sharing your time with me on this Jitter. I really appreciate it and feel like I'm learning a lot about what I've got here! And you are correct--these PSU for the Trilogy series are hard to find. The boards are often sold without the PSU. But then that makes me think that I'm not the only one trying to figure out how to build something that would work (or more appropriately, in my case, have someone else--who truly knows what they are doing--build one for me).
So each device is "different" in terms of how it might be designed (some to work direct with 120V; some which require a transformer). I didn't' know that--but in thinking about that, it makes sense. And as far as my mixer goes, it makes sense to say I can't do away with the transformer--it's obviously there for a reason.
Referring back to my schematic then, I can see that after the transformer, we have a "20-0-20 Off Load" (orange and green wires). Would that be because the number of windings on the transformer's secondary side are fewer--such that the input voltage (either 230 or 115) is stepped down to 20V? And I'm assuming that would be 20V AC until it passes through the rectifier, which would convert the full range (the plus and minus side of the AC) signal to DC, correct?
In this same concept, there must be another "secondary" portion of the transformer to step the load down (yellow wires) 46V. So it's kind of a complicated transformer--or not so much but I haven't come across a transformer type in my research that will produce two different voltages simultaneously. Are these called something specific so I can read about them more?
One final thought for this post...how do we have a 46V off load end up resulting in 48V on the DC output side (after the rectifier)? Unless I'm totally misunderstanding, that doesn't make sense at this point.
Thank you for sharing your time with me on this Jitter. I really appreciate it and feel like I'm learning a lot about what I've got here! And you are correct--these PSU for the Trilogy series are hard to find. The boards are often sold without the PSU. But then that makes me think that I'm not the only one trying to figure out how to build something that would work (or more appropriately, in my case, have someone else--who truly knows what they are doing--build one for me).
Given your questions, I know you are missing basic knowledge. Those basics are required for understanding the concept of electricity, so I would suggest you try to find some tutorials. There's lots out there on the web, and as an example here is one about transformers, AC, DC, voltage, current, power, etc., explained in a way that's easy to understand.
That's a good questtion about how you can get 48 Vdc from 46 Vac and that has to do with the way AC works. You're probably familiar with the shape of a sinewave which swings up and down from a centre line, half the period the value is positive, the other half of the period, it's negative. And unlike DC, which is constant at a single value all the time, the momentary value of a sinewave changes all the time.
I'll skip over the mathematical bit for now just telling you that a sinewave's RMS value is what we usually mention and is what a multimeter displays.
So when saying 46 V, we actually mean 46 Vrms. The peaks of the sinewave are a factor of √2 higher than the RMS value. So when rectifying and smoothing this AC to DC, the value of 46 V is multiplied by √2 (~1.41) and so becomes 65 Vdc minus what the rectifier diodes drop (about 1.4 V), resulting in approx 63.6 Vdc.
This voltage is then regulated by REG1 (see schematic below) to the desired 48 V.
If you look at this schematic, you'll see I made a small correction to the original.
Way on the left is the mains input which feeds the transformer's primary windings through the voltage selector. On the other side of the core, are the secondary windings.
You can see there are two secondary windings, the upper 46 V and the lower 20 - 0 - 20 V one (0 is the centre tap which lies in the middle of that winding).
That centre tap is needed to be able to make a symmetrical power supply of (in this case) +17 V and - 17 V.
"Off load" is a strange way of saying "no load". A transformer's output always sags a bit when there's a load connected, this will be the no load output spec.
If you then look further to the right you'll find the rectifiers and smoothing caps followed by voltage regulators with the necessary periferal components and output capacitors.
That's a good questtion about how you can get 48 Vdc from 46 Vac and that has to do with the way AC works. You're probably familiar with the shape of a sinewave which swings up and down from a centre line, half the period the value is positive, the other half of the period, it's negative. And unlike DC, which is constant at a single value all the time, the momentary value of a sinewave changes all the time.
I'll skip over the mathematical bit for now just telling you that a sinewave's RMS value is what we usually mention and is what a multimeter displays.
So when saying 46 V, we actually mean 46 Vrms. The peaks of the sinewave are a factor of √2 higher than the RMS value. So when rectifying and smoothing this AC to DC, the value of 46 V is multiplied by √2 (~1.41) and so becomes 65 Vdc minus what the rectifier diodes drop (about 1.4 V), resulting in approx 63.6 Vdc.
This voltage is then regulated by REG1 (see schematic below) to the desired 48 V.
If you look at this schematic, you'll see I made a small correction to the original.
Way on the left is the mains input which feeds the transformer's primary windings through the voltage selector. On the other side of the core, are the secondary windings.
You can see there are two secondary windings, the upper 46 V and the lower 20 - 0 - 20 V one (0 is the centre tap which lies in the middle of that winding).
That centre tap is needed to be able to make a symmetrical power supply of (in this case) +17 V and - 17 V.
"Off load" is a strange way of saying "no load". A transformer's output always sags a bit when there's a load connected, this will be the no load output spec.
If you then look further to the right you'll find the rectifiers and smoothing caps followed by voltage regulators with the necessary periferal components and output capacitors.
Last edited:
Hi Mark,
If that's something I need to physically measure, I don't know how to do that.
If it's in the schematic that is attached above...there is a note that the maximum DC load for +/- 17V is 900mA. If that's not what you were looking for, feel free to elaborate/direct me.
Those are probably max. ratings in this particular product.
If you look at the specs of the TL783, it should be capable of 700 mA, and the LM7815 and 7915 are capable of 1.5 A, so I think the limiting factor here is the transformer.
But these values are a good starting point should you decide to modify things.
For measuring the actual current drawn by the mixing board, you'll need a multimeter that can measure DC current (A=) and you'll need to wire the leads of the multimeter in series with the supply to be measured (which means you'll need to disconnect the lead to be measured and reconnect it with your DMM in series and the leads plugged into the COM and A sockets).
When finished measuring, IMMEDIATELY remove the red lead from the A socket to prevent shorting stuff inadvertently later (don't aske me how I know).
If you look at the specs of the TL783, it should be capable of 700 mA, and the LM7815 and 7915 are capable of 1.5 A, so I think the limiting factor here is the transformer.
But these values are a good starting point should you decide to modify things.
For measuring the actual current drawn by the mixing board, you'll need a multimeter that can measure DC current (A=) and you'll need to wire the leads of the multimeter in series with the supply to be measured (which means you'll need to disconnect the lead to be measured and reconnect it with your DMM in series and the leads plugged into the COM and A sockets).
When finished measuring, IMMEDIATELY remove the red lead from the A socket to prevent shorting stuff inadvertently later (don't aske me how I know).