SMPS and Linear PS together

Thread Starter

ACK303

Joined Mar 13, 2020
24
Hello everyone, hope someone can offer advice.

I have built a hifi preamp, ESP P97 to be exact and very good it is too. The preamp itself runs from a dual linear power supply and there are no issues.

However, I have also placed a SMPS into the case to power a 5v LED strip and although it works (LED's power on), I have a massive, and I mean massive, buzz through the preamp.

The incoming mains is via chassis IEC which then goes to a switch, then a terminal block where I have connected both the linear power supply for the pre amp and also the SMPS for the LED strip together.

Maybe something simple I am doing wrong, maybe you cannot do this, but the way I have wired them together is not any different than having them both connected, albeit individually, into a mains extension block.

Any ideas would be greatly appreciated. A couple of photos of the preamp plus a sketch of the mains wiring.

Regards

Adam.
 

Attachments

OBW0549

Joined Mar 2, 2015
3,300
However, I have also placed a SMPS into the case to power a 5v LED strip and although it works (LED's power on), I have a massive, and I mean massive, buzz through the preamp.
A high-quality, sensitive audio preamp and a SMPS in the same case is a prescription for absolute disaster. You've no choice but to separate them-- as far apart as possible.
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
Thank you both for your replies.

I'll take the SMPS out, place on the floor and run the 5v output into the preamp with a seperate cable. That may work, albeit it means I'll have another cable coming into the preamp.
 

nsaspook

Joined Aug 27, 2009
7,181
Thank you both for your replies.

I'll take the SMPS out, place on the floor and run the 5v output into the preamp with a seperate cable. That may work, albeit it means I'll have another cable coming into the preamp.
I need to ask this.

Why in the world do you need lights inside a pre-amp?
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
Well, that's a very good point nsaspook, as it's a DIY pre amp, as with my power amp, I feel that if you make something yourself it is worth trying to make it look good too. Of course, what looks good is a matter of opinion. The electronics was easy as they are pcb based but the metalwork took an age. The lights, to me, are a nice finishing touch that make a diy project look professional. Superfluous, but nice nevertheless.
 

Attachments

nsaspook

Joined Aug 27, 2009
7,181
Well, that's a very good point nsaspook, as it's a DIY pre amp, as with my power amp, I feel that if you make something yourself it is worth trying to make it look good too. Of course, what looks good is a matter of opinion. The electronics was easy as they are pcb based but the metalwork took an age. The lights, to me, are a nice finishing touch that make a diy project look professional. Superfluous, but nice nevertheless.
They look very nice.

Second question, why did it need to be BLUE.
https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
Thanks for that, a very interesting read.

The photos are a little deceptive though the LED's are actually cyan/green colour.

The pre amp also has UV ones which I presume are worse than blue?
 

schmitt trigger

Joined Jul 12, 2010
198
First of all: CONGRATULATIONS (yes, with capital letters) on a beautifully made project.

I understand the reason for you putting the LEDs inside: it showcases a gorgeous project.

To your question: power the LEDs from a linear supply, It appears that you have enough room inside to fit an additional supply.
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
Thanks Schmitt, very kind!

I do have a separate linear shop in there already but it is an ln317 regulated supply and using the 5v, 1m LED strip at 14.4w or 2.88a/m plus a voltage drop from 18v input down to 5v the regulator got very hot. The lights on in this picture is powered that way but was worried and then tried the SMPS option. Maybe if I change to a 12v led strip? these have a current rating of 0.6amp/m with less of a drop from 18v to 12v, plus a bigger heatsink, maybe this would be OK?

Few more pictures added...

Maxheadroom, sorry I'm bit of a novice I'm not too sur
 

Attachments

Thread Starter

ACK303

Joined Mar 13, 2020
24
Hi Scmitt,

Here is the, currently, spare linear supply at the top, with the digital read out at 5.2v. Powers the lights but the lm317 with its little heatsink is finger burning hot on the right. The bottom supply is for the preamp. Both have ac 18v incoming

(Looks a bit messy but this was testing stage)
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
20,414
Maxheadroom, sorry I'm bit of a novice I'm not too sure
It is very easy to place an overwind on a toroidal, you just need a small qty of coil wire, just size it for the anticipated current that you expect to draw.
A trial test with a few known No. of turns will give you the turns/volt number, I would assume you don't really need a regulated supply for LEDs?
Which in that case you would just need a small bridge and a capacitor.
I have modified several and it is usually quite simple.
Max.
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
Thanks for the reply Max.

I wouldn't know where to start and to be honest I'm not going anywhere near mains transformers
 

ElectricSpidey

Joined Dec 2, 2017
1,058
Yea, I think going to 12 volt LEDs is a good idea, but stick to using a regulator because I have a feeling that *360 degree radiator will still give you problems.

* The LED strip.

Of course you could always switch to a COB type LED, center it in the case, and better match the voltages.

https://www.ebay.com/itm/High-Power-10W-20W-30W-50W-100W-SMD-COB-LED-Chip-White-UV-Red-Blue-RGB-Lights/322503112476?var=&hash=item4b16aef71c

Use the 10 watt.

A blue in series with a green would probably get you real close, and create a cool effect. (blue and green = cyan)

Mount them directly to the case to heat sink them.

And believe me, those things are plenty bright well below their rated wattage.

Power them with a bridge and cap, place a dropping resistor and you are good to go.


They actually make cyan, but I don’t see them in that listing. (which is only an example)
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
20,414
Thanks for the reply Max.
I wouldn't know where to start and to be honest I'm not going anywhere near mains transformers
That is unfortunate in light of how easy and relatively safe it is, the main input winding is wound on first, so any slight mod such as the overwind, is very simple and safe.
When you said you had built the amp, I figured you might have tackled it.
But that OK if not comfortable.
Max.
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
Yea, I think going to 12 volt LEDs is a good idea, but stick to using a regulator because I have a feeling that *360 degree radiator will still give you problems.
Would that be ok with the current linear supply I have which is shown in the picture?

By '360deg' radiator you mean even with a massive heatsink I'll still have problems? (Sorry to ask)

The COB ones look great but they have a forward current of 900mA each, which means the existing supply will be no good again. Wouldn't it be easier to use a proper led driver?
 

Thread Starter

ACK303

Joined Mar 13, 2020
24
When you said you had built the amp, I figured you might have tackled it.
But that OK if not comfortable.
I know only a little about electronics I'm afraid, as I mentioned the electronics side of the amp is pcb based, which is like painting by numbers.

Bit scary messing with mains transformers, I would be comfortable with some basic education rather than just having rudimentary self teaching.
 

ElectricSpidey

Joined Dec 2, 2017
1,058
I'm not sure what supply you are referring to, but any linear with a clean output should do.

By 360 degree radiator I mean the LED strip can radiate any ripple into your amp.

Those COB LEDs can be run at whatever current you want, as long as you don't exceed 10 watts. I would think 200mA would be plenty to light up that enclosure.

What are the stats on that regulator module in post #12? That may be perfect for running a couple of COBs in series with a dropping resistor. (or 12volt strips)
 
Last edited:

Thread Starter

ACK303

Joined Mar 13, 2020
24
What are the stats on that regulator module in post #12? That may be perfect for running a couple of COBs in series with a dropping resistor. (or 12volt strips)
This is the item ElectricSpidey:-

https://www.ebay.com/itm/371580598599

Notice:
The minimum differential between input and output is 3V; the input must be higher than the output voltage above 3V to be regulated.
Buck, not boost, when input 5V output 1.25-2V, not 6V.

Specifications:
Input Voltage: DC: 0-30V; AC: 0-22V
Output Voltage: DC 1.25-28V
Output Current: 2A(Max.)
Size: 62 * 59 * 27mm / 2.44 * 2.32 * 1.06in (L * W * H)
Weight: 42g / 1.5oz
Package Weight: 47g / 1.66oz
Included:

I've looked into a dropping resistor using an online calculator but the forward voltage is questioned.

Thank you for your help with this by the way.
 
Top