PC stereo speakers - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: November 09, 2020, 04:30:14 pm
content: Hello, regarding the Microlab B77 Bluetooth stereo speakers, I would like to ask if it is worth to replace the SMPS which has +15V, 0V and -15V, with a toroidal transformer, a rectifier and some filter capacitors ? I was thinking about a 2x12V/100VA transformer, 2x4700uF/25V or 2x6800uF/25V filter capacitors and some 100nF/50V ceramic ones in parallel with the electrolytic capacitors...Also, I am interested in replacing all of the electrolytic and non polarised capacitors with some new ones, better quality than the original capacitors.I don't have the schematic of the product, I will only open the case and find the capacitors and then order some new ones with same specs...Many thanks in advance !LE: I don't know for sure if there is needed a voltage regulator for some components in the internal circuit ...

author: Zero999
author_rank: Super Contributor
timestamp: November 09, 2020, 06:42:06 pm
content: Just one question: why? It will most likely result in poorer performance and increased power consumption.

author: Manul
author_rank: Super Contributor
timestamp: November 09, 2020, 06:45:41 pm
content: In my opinion it is not worth, because it will not make it a (much) better sound system. In fact, it may even make it worse. SMPS has very little low frequency noise, and your rectifier will have some at 50Hz. Will it be audible depends on the amplifier circuit (its PSRR). It may or it may not be a problem. I would probably just make additional filtering for existing SMPS if there is some noise you want to reduce. Also I hardly imagine, how you will fit transformer power supply inside that small space.Electrolytics, which experience high ripple and/or high temperature, mainly SMPS capacitors may benefit from replacing if the speakers were used a lot, but most of other capacitors should be just fine for many more years.

author: wraper
author_rank: Unknown
timestamp: November 09, 2020, 07:01:28 pm
content: It won't improve anything since this system is crap to begin with. Quite likely will also add mains frequency hum. Not to say you will need to add voltage regulators since it's not designed to run from unregulated voltages. Power section probably could be powered from unregulated voltages but the rest certainly not. Worthless waste of money and effort if saying it short. Also don't forget that your signal source (supposedly PC) is most likely powered from SMPS to begin with if you don't run it from BT (which sucks even more).

author: Zero999
author_rank: Super Contributor
timestamp: November 09, 2020, 08:00:05 pm
content: Quote from: mike_mike on November 09, 2020, 04:30:14 pmTo expand more. Modern switched mode power supplies, with propper filtering, are much less noisy than old linear power suppliesQuoteWhy do you think replacing the existing parts, with new ones with the same specification will improve the design? If the new parts have the same specification, be it crap, or good, then it will have exactly the same performance!If the filter capacitors in the switched mode power supply are underspecified (too higher ESR/lower value) then you want to replace them with better ones, although they're probably fine, so it won't make any difference. Caution should also be exercised, as often using lower ESR/higher value, filter capacitors can create more problems, than it solves.QuoteIt's quite likely it will be designed to work off a regulated power supply. Using an unregulated power supply, will definitely result in poorer performance.

author: mike_mike
author_rank: Super Contributor
timestamp: November 12, 2020, 01:29:34 pm
content: Thank you @Zero999.One more question: if I will set the soundcard software equalizer to a preset for more bass (or if I will set more bass from the pot on the back of the speakers) then it is possible to destroy my speakers ?

author: Zero999
author_rank: Super Contributor
timestamp: November 12, 2020, 04:36:54 pm
content: Quote from: mike_mike on November 12, 2020, 01:29:34 pmThat depends on whether or not the amplifier can drive them with more power, than they can handle? Probably not. What's more likely is the amplifier will go into clipping and it will sound really distorted.

author: Simon
author_rank: Unknown
timestamp: November 12, 2020, 04:55:10 pm
content: SMPS operate at 100kHz and up, your hearing tops out at 22kHz or less. It is therefore physically impossible to hear that 100+kHz. Forget what the audio fools tell you.

author: Zero999
author_rank: Super Contributor
timestamp: November 12, 2020, 08:22:46 pm
content: Quote from: Simon on November 12, 2020, 04:55:10 pmThat's true, but it doesn't mean that a switched mode power supply won't cause audiable interferance. Non-lineararities in the amplifier can cause higher frequencies to be demodulated, so that 100kHz can become audiable, especially if the amplitude or frequency is changing, with the load on the power supply. To prevent this, the power supply will be fitted with a filter, which will block the high frequency components and the amplifier can be designed, so it doesn't demoduate high frequencies.

author: Simon
author_rank: Unknown
timestamp: November 12, 2020, 08:26:28 pm
content: The first phone switch mode chargers were not great but modern ones not a problem. Unless the OP can actually hear interference I can't see any benefit and the bluetooth receiver could also be as much to blame if the unit is that bad.

author: Zero999
author_rank: Super Contributor
timestamp: November 12, 2020, 11:22:38 pm
content: Quote from: Simon on November 12, 2020, 08:26:28 pmTrue. I've used a switched mode power supply for an intercom system, which uses dynamic microphones with mV level signals. The only issue I had with noise was due to leakage through the class-Y capacitors and it was solved by connecting the secondary to earth, via some 10µF capacitors. I could have directly earthed the secondary, but decided against it, for reliability reasons.It's also a myth that old linear supplies are completely free from high frequency noise. The diodes in the bridge rectifier produce significant high frequency harmonics, as they switch on and off, as the mains cycle reverses.