Must be, I know what the “Karaoke Amplifier” means. Because everybody is drunk at karaoke time, the sound quality doesn’t matter much. The shop price for such a bestia is 69 EUR (in .EE).
Here you see the hidden marks of the metalwork:
One thing is clear – this bestia yells loud – at all your 69EUR. It should be a sin to expect more for this money. However, the issues:
1. Nasty periodical clicks 1,2Hz at any time when the USB block is reading the memory card. Even selecting the mute position will not make that click disappear. Of course, no filtering near the digital USB module. Power caps have no 0,1uF satellites as assumed in Hi-Fi technology. With an 16GB SD card (a Goodram P/N SDU16GHCAGRR10), an approx 1 sec long cracking noise is heared in front of every song (some -25dB level) – what we hear is the tiny controller solving the VFAT puzzle 😉 That noise is much shorter with smaller SD cards. [Added 2014-01-01]
2. Knobs are – uh! – really cheap. So cheap as a knob could ever be.
3. Treble pot comes before (on the left compared to) the bass one – in no way is it a western style. The volume can be regulated either “DOW” or “UP”.
4. The Volume pot is so cheap …, without any loudness compensation, and the regulation characteristic is wrong. First 5 degrees suck as with any cheap pot. In addition to that sin, at the low volume, something is wrong with basses. Could be, someone has miscalculated the impedance and thus the matching is crying for an 47KOhm resistor.
5. The transformer is so cheap as a few coins ever can buy. This is the reason why it gets relatively hot (some 42 degrees C).
6. I have a strong suspicion that the mains transformer is probably calculated for Chinese 220V (despite what the marking says), while at the West , der Spannung is at sure ~237V. On the mains transformer, it is written: 2×21.5V. The actual voltage measured, is some 2x ~25V. Likewise is hot the +5V stabililizer. The evergreen classics for any “Made in CN” production.
7. For a 2x50W amplifier, the main capacitors are as cheap a money can buy: 3300uFx50V.
8. Some very weird modifications are visible – like the +5V line to the USB PCB which is cut straight – most probably done to avoid some interference or ground loop.
9. Blue blinking LEDs in a living room are certainly not kosher.
Nii. Ja nüüd vaatame, mis on karul kõhus.
Do you see any initials above? Are initials possible at all with the hieroglyph writing? 😉
In my particular location (not exactly a Faraday cage but inbetween of 1m thick limestone walls) I did not yet succeed to hear a single FM station. Saying it otherwise, probably the same solution is in use as in extremely cheap MP3 players. It helps you within a 10 km circle from a powerful FM transmitter … While an ancient Sony Walkman Sports receives tens of stations in the same location.
The positive side: the device does work indeed and it is relatively cheap! At loud volumes, the highs-bass balance is satisfactory. Highs are relatively blurred from Hi-Fi standpoint… but hey – what did you expect when playing MP3 tracks? I am not sure about advertised 50Watts, but 2×20-35W are relatively clean. The subjective quality is the best at approx 50% loudness (some 2x20W) while listening to spectrally unsaturated disco&trance pieces. Spectrally more filled songs (with a singer present) are not OK – a trained ear can hear intermodulations long before the highs-bass balance achieved. As said above, a pair of coupling resistors could improve the sound. For comparison: my normal listening environment is – Peavy PV-4c amplifier with various speakers and M-Audio BX8a monitors – not the highest grade of an equipment, but nevertheless.
The 103.131 amplifier is accompanied by a quality coupon. While it means nothing technically, the gesture itself is relatively friendly. Unable to buy your ears, they buy you by a bow.
The verdict – Buy!! in any of these 5 situations:
- you are a masochist;
- you are a mad repairman (like me) planning to modify the barebones;
- you mostly listen to music in a high condition;
- you are financially somewhat limited.
- you need a reliable unmanned “ownsource” of a music collection to amplify – feeding a pirate FM station or whatever.
The device is very good as an automated MP3 player. [added 2014-01-01] – The system works well even with a 16GB SD card (tested). You put the USB stick in and there it is … very stable and lasting several days. And imagine – the device has the consumer grade Line Out !!! Your mood will be considerably better, if you do not understand, which particular PCB of which size is actually responsible for that little miracle 😉 Most probably the device is usable as a source of the background noise in a small bar, in a classroom or for a tiny open air event (like child birthday). The only condition – use speakers with good bass elements and, try to keep the volume no lower than 50%.
The first candidates for mods are: the Volume pot (substitute it for a real Alps), mains transformer (by a toroid… while there are stringent space constraints), main U+ U- capacitors (from 3,3 to at least 10 mF) altogether with 0.01 uF HF shunts to these. An absolute necessity is to find the USB clicking source and damp this phenomena via e.g. Tantal capacitors. The second round of modifications could include throwing out the PA PCB altogether and substituting it e.g. to two LM3886 based channels. The heatsink is of relatively good design and permits modifications.
Here is the English part of the manual. With typical Sino errors (both language- and culturewise), but still usable.
Other sources:
1. www.tronios.com – Here lives the manufuckturer.
karu sisemus 
Hey, i just go one of this super amps with burned transformer can u help me to peek right one to replace it? Thanks
I have no idea where to get the replacement. However, that’s written on the transformer: “EI66X40, 230V/50Hz, 21.5V .. 0 .. 21.5V”. While measuring the transformer, the output was 2×21.7V AC indeed. Thus you need a ~42-44V AC transformer with a center tap. On the PCB connector, the center tap pin stands a little apart from other 2 pins. It seems like any 80mm-90 wide toroid will do the the electrical substitution. However, the toroid is to be fastened in a DIY way.
A loose suggestion: http://uk.farnell.com/block/rk40-22/transformer-40va-2-x-22v/dp/1419543?ost=toroid&selectedCategoryId=&categoryId=700000005694