linear VS switching power supply for D-Amp?

[ijason]

good evening,

my appologies if this question has already been answered, i was unable to find an appropriate-sounding thread on the forum.

i am just beginning to look into building a "receiver", as a birthday gift. luckily the birthday is not until august... so i have time to plan. i say receiver because in addition to the amplifier function, it will also serve as an input selector, including a DAC. but to the point of my question :

i have seen a lot of people lauding the advantages of using (building) a linear power supply, VS a switching power supply. i have no doubts that using a nice beefy toroidal transformer and a rectifier with huge caps will deliver cleaner DC than a switching supply will... but it will also nearly double the cost of my build.

in the case of a small D-amp (https://www.parts-express.com/2x100w-tda7498-class-d-amplifier-board--320-303, for example), is there any advantage to be gained in using a linear supply? the amp itself will be doing some very high frequency switching.

i specifically mention that i'll be including a DAC within the same housing as my amp. so perhaps the sensitivity of that equipment will warrant spending on a linear power supply.

thanks for any advice!

 

[Julf]

My experience with the high-end hypex nc400 amp modules and SMPS600 power supplies has been that a *well-designed* SMPS is superior to a linear PS.

 

[ijason]

My experience with the high-end hypex nc400 amp modules and SMPS600 power supplies has been that a *well-designed* SMPS is superior to a linear PS.

thanks for your reply

after a bit of looking, it appears that the Hypex SMPS600 you are referring to has a retail price of over €150. considering the amp I am planning on using is only €30, I'm afraid that this particular SMPS is out of the price range I am looking for.

Do you have any experience with good results from cheaper SMPS, or is the Hypex basically the price point you need to get better performance from a SMPS than a linear power supply?

Do you have suggestions for features to look for in a SMPS that would indicate better design? or is there a "go-to" method for modifying or post processing the output from a mediocre SMPS?

thanks.

 

[Julf]

Do you have any experience with good results from cheaper SMPS, or is the Hypex basically the price point you need to get better performance from a SMPS than a linear power supply?

The Hypex one is definitely overkill. Cheaper SMPSs can definitely do the job.

Do you have suggestions for features to look for in a SMPS that would indicate better design?

Peak current capacity is a pretty important criteria when driving a class D amp.

is there a "go-to" method for modifying or post processing the output from a mediocre SMPS?

Not really - additional chokes etc. only limit the current capability. The best way is to use an amp that has good power supply noise rejection.

 

[SGK]

Julf, what linear power supplies did you try with the NC400?

 

[Julf]

Julf, what linear power supplies did you try with the NC400?

A simple, unregulated toroidal-transformer-rectifiers-and-caps one, and a regulated, adjustable lab supply.

 

[cats squirrel]

I have bought a stereo pair of class D amplifiers, based on the IRS2092 chip and IRFI4019H Fet's. I understand the reluctance to overspend on the power supply, and I, too, am looking at the simple linear variety. However, I understand that it is important to have lots of capacitance, to soak up the excess voltage from the amplifier.

 

[ijason]

good afternoon,

thank you everyone for your replies.

the impression that i'm getting is that for the digital amps, it does not matter greatly whether you use a linear power supply, or a switching supply. as long as it is of decent quality, and has the needed power.

to phrase it another way: there's less risk of getting noise from the power supply on a D-amp... so there is no explicit advantage of using a linear supply verses a switching.

correct?

that being said, i still might build a linear supply. it's looking like i can get a single toroidal transformer that can drive the D-amp from the 30v rails, AND drive the DAC from 15v rails. to get a switching power supply that can drive 5amps of 30v and 2amps of 15v is three times the price of the transformer.

i haven't searched the forum for this information yet, but i might as well ask here and now - is the rating for a transformer (0.25kW for example) the combined capacity of all output rails? i asked a few electricians i work with, and in their experience the transformer should be rated for total capacity.

thanks

 

[Bare]

n/a

 

[gychang]

Is looking like i can get a single toroidal transformer that can drive the D-amp from the 30v rails, AND drive the DAC from 15v rails.

thanks

I also have a similar question.

I like to have a 30 DCV output to drive a d-amp and 15DCV out, and want to use a torroidal transformer. Since torroidal output is AC what do I need in addition, I realize this is a very basic question.

 

[ijason]

I also have a similar question.

I like to have a 30 DCV output to drive a d-amp and 15DCV out, and want to use a torroidal transformer. Since torroidal output is AC what do I need in addition, I realize this is a very basic question.

good afternoon,

to convert AC to DC requires rectification. this is performed by a Bridge Rectifier. for best DC sinewave, you will want to use a full wave, single phase model.

for example : https://www.amazon.com/BRIDGE-RECTIFIER-SINGLE-PHASE-PROFILE/dp/B007Z7LXVQ/

you will want to add a heat sink to the bridge rectifier.
-

this will produce DC current, but it will not be continuous, it will pulse at the cycling rate of your mains power. to even this pulse into a steady "stream" of current you need to add capacitance.

for example : https://www.amazon.com/10000uf-Electrolytic-Capacitor-35x51mm-105ºC/dp/B00K87I3PO/

you need two caps of equal rating, and they should be rated at twice the AC current they are exposed to. the more capacitance the less ripple in your DC output.
-

you also want to add a heavy resistor across the terminals of each capacitor to safely drain their charge when the amplifier is turned off.
-

please refer to more educated guides than this one on the assembly of these components into a bridge rectifier
-

possibly a more reliable option is to buy a AC to DC Bridge Rectifier.

for example : https://www.amazon.com/RioRand-Converter-Rectifier-TDA8920-Amplifier/dp/B00J1E3FMG/ i have not used this board, and cannot vouch for quality.

another example : Connexelectronic i have ordered from this company, so can at least vouch somewhat

personally, i decided to go with a SMPS for four reasons :

1. after exhaustive research i drew the conclusion that any "noise" added to the amplifier by the switching function on the power supply would be at a frequency far above 20kHz, and thus ignored by D amps.
2. transformer power supplies can add "noise" at the 50/60hz cycling rate of the mains supply, which is right in the middle of audible frequency.
3. i needed a power supply that worked at either 220v or 110v mains supply, and this could not be accomplished by a transformer solution.
4. portability is a priority, SMPS is a fraction of the size and weight of transformers.
5. cost is equivalent between the two designs.

cheers!