Hi,
i would like to get some kind advice about a possible external supply for a preamp
I read that the original is not very silent
I have a question ... it is better transfer voltage through the umbilical power cord as AC or DC ?
I would say AC ... but it is just a feeling
Thanks a lot, gino
i would like to get some kind advice about a possible external supply for a preamp
I read that the original is not very silent
I have a question ... it is better transfer voltage through the umbilical power cord as AC or DC ?
I would say AC ... but it is just a feeling
Thanks a lot, gino
Keep the high voltage AC out of the preamp circuit box, where EMI will induce stray current in your audio circuit. This is the main purpose of having a separate power supply box, to isolate the noisy AC components.
If it is a tube preamp the DC will be very high voltage, so suitable safety measures should be employed for the umbilical, like tough insulation, strain relief and mechanically fastened ends that can't unplug with just a tug.
If it is a tube preamp the DC will be very high voltage, so suitable safety measures should be employed for the umbilical, like tough insulation, strain relief and mechanically fastened ends that can't unplug with just a tug.
Never put the rectifier remote from the transformer - the loop between the two is the greatest source of noise in any system. Extending that loop area into a separate chassis via an umbilical is a noise nightmare.
So transformer, rectifier(s), main reservoirs in one box and smoothed DC on the umbilical as a minimum.
So transformer, rectifier(s), main reservoirs in one box and smoothed DC on the umbilical as a minimum.
Hi and thank you all very very much indeed
I am considering to modify one of two preamps in the power supply section taking out the transformer ... now i know that i have to put at least transformers and diodes bridge in the same box
Would it be really that bad to put reservoir caps in the preamp box instead ?
Thanks a lot again, ginetto
I am considering to modify one of two preamps in the power supply section taking out the transformer ... now i know that i have to put at least transformers and diodes bridge in the same box
Would it be really that bad to put reservoir caps in the preamp box instead ?
Thanks a lot again, ginetto
Yes. Read post 3, then remember that the noisy loop carrying charging pulses runs from the transformer via the rectifier to the reservoir cap. If careful, you could put smoothing caps in the preamp box but not reservoirs.ginetto61 said:
Hi and thank you very much indeed again. No more question on this.
Instead ... if i have two identical single voltage power supply in order to get a dual power supply can i use the schema here below without problem ?
Because i have nice schematics for single 0-30 V power supply ... but i need a dual +/- 30VDC power supply (let's say from 24 to 30)
I was thinking to buy one of those chinese lab power supply ... but i wonder if it is really needed. Maybe using LM317 can give a nice low noise as well at a fraction of the cost.
Thanks a lot, gino
Hi and thank you very much indeed again. No more question on this.
Instead ... if i have two identical single voltage power supply in order to get a dual power supply can i use the schema here below without problem ?
Because i have nice schematics for single 0-30 V power supply ... but i need a dual +/- 30VDC power supply (let's say from 24 to 30)
I was thinking to buy one of those chinese lab power supply ... but i wonder if it is really needed. Maybe using LM317 can give a nice low noise as well at a fraction of the cost.
Thanks a lot, gino
EDIT : Brainfart. Nevermind.
Hi and thanks for the reply but which output are you referring at ?
In the preamp there will be an DC input V+/0/V-
I like the idea to take out the transformer.
For instance i have an old Bryston preamp that i use as a workbench
I see that the better and more expensive models have external transformer like the one here depicted (this is balanced instead mine is unbalanced)
An externally hosted image should be here but it was not working when we last tested it.
So my idea is to have and additional external regulation stage (the internal one is performed with 24V fixed regulators
Thanks a lot again, gino
The output of your packaged PSU. In some cases the negative rail will be tied to incoming mains ground. If so, sometimes this can be safely undone.
Hi and thanks for the explanation.
Maybe a mains transformer also able to provide isolation could be a solution ?
i still noticed that many totl preamps from audio brands have separate power supply units from the actual preamp circuits.
It could be beneficial probably.
Thanks again, gino
No, simply adding mains transformer will make no difference - and I am concerned that you think it might as this shows you have not understood the issue.
The basic point is that a PSU cannot have an output rail simultaneously at -30V and 0V. If the negative rail is grounded then you can't also ground the positive rail. Think about it.
The basic point is that a PSU cannot have an output rail simultaneously at -30V and 0V. If the negative rail is grounded then you can't also ground the positive rail. Think about it.
Hi and i am concerned me too ... i do not want to get hurt.
The power cord has L, N and G
The transformer will have 2 secondaries 0 and V
I would connect the L and N to the transformer leaving the G floating, or connected to the case if i use a metallic case
Then i will connect each secondary to a regulating circuit and then connect the outputs like in the picture already attached
So you mean that the arrangement here above will not work ...
I have to find a circuit to make a dual power supply out of two identical single supply.
As i said circuits for very good single supply are very common. Not so for dual supply.
And i do not know why sincerely. They seem very much more tricky to me.
Thanks again, gino
L, N and E
E is the third wire in the Mains Power cord/cable.
Always connect E to Safety Ground in your equipment. It is your Protective Earth (PE).
Always fuse the Live (L).
If there is no metal case then attach it to the largest metal component inside the insulating Chassis.
Then connect ALL exposed conductive parts to this Safety Ground.
It is this rigorous following of "normal safety" practice that helps prevent you killing/injuring yourself.
E is the third wire in the Mains Power cord/cable.
Always connect E to Safety Ground in your equipment. It is your Protective Earth (PE).
Always fuse the Live (L).
If there is no metal case then attach it to the largest metal component inside the insulating Chassis.
Then connect ALL exposed conductive parts to this Safety Ground.
It is this rigorous following of "normal safety" practice that helps prevent you killing/injuring yourself.
The isolation between Primary and Secondary leaves the WHOLE Secondary side "floating".
So you mean that the arrangement here above will not work ...
I have to find a circuit to make a dual power supply out of two identical single supply.
As i said circuits for very good single supply are very common. Not so for dual supply.
And i do not know why sincerely. They seem very much more tricky to me.
Thanks again, gino
If both Secondary sides are floating and you connect them together at one point in each, then the two secondaries and all the circuits will "float".
You touch one point in any of the isolated circuits and the WHOLE "floating" side will move in voltage to match your "body voltage"
Your body and the secondary side are still isolated from Mains by the isolating transformers.
Since you are standing on the "earth" your body voltage and the secondary circuits are at "earth" voltage and you are still isolated from Mains voltage.
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If the two identical PSUs have floating output (i.e. not grounded) then you can put them in series to make a bipolar CT supply. If you are making these PSUs yourself then of course you can ensure that they are floating, so you are then free to ground the CT in an appropriate way. However, I always get twitchy when someone planning to build a mains powered PSU asks very simple questions as it gives me the impression that he does not know enough to design, build and test safely.
I get worried too, about the abilities of our Members to assess the risks involved in working with Mains powered equipment.
It's the quality of the questions that often alerts us to inability to assess risk.
It's the quality of the questions that often alerts us to inability to assess risk.
Hi and thanks again and let me explain better.
Of nice single power supply is full the universe. Not so for dual power supply.
I have already built some kits of single power suplies without problem.
From this my idea of connecting two together to make one dual.
I did this with batteries and it worked.
Yes the idea is to connect the mains ground only to the case of the power supply an using each secondary of the transformer to supply the regulation circuits.
I have seen already basic circuits based on LT1083 regulator that should be work just fine as a first regulator stage
Another one, the final one, will be in the preamp
The hope is that cascading two regulation stages the noise will be reduced more. This is more or less the rationale behind the project.
I will also use a EI type transformer that i know provides a better isolation from the mains for its nature.
You are right and actually i would like to put a safety upstream the power strip i will use to connect the prototype just to have another protection stage. I have to study this seriously.
Thanks a lot again, gino
Hi and thanks. You mean tha i should connect the metallic chassis to E ?
Ok. By the way i see sometimes that only L and N are connected in some equipment.
This is fine. Ok !
Like the transformer frame ? ok !
I understand. But i was thinking why not to use a protective isolation tape ?
I could wrap the conductive parts with this
For instance some transformers come with plastic covers to put on the terminals ... that is very convenient i think.
Anyway i understand the danger playing with AC.
This is difficult ... i will try not to touch anything when it is connected to the mains
My main concern is about ground loops ... but the only way is to try and listen for noise.
To end my main goal is to use two identical single supplies of which i can find anything in every shape to make a dual power supply instead of having a positive and a negative regulator ... this i do not like at all.
Thanks again, gino
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