FET Audio | Hi-End Audio & Electronics DIY Electronics & Repair

I acquired this set (total 3 sets and other 2 sold) from Singapore Cinema of 80 people as it need to upgrade the system and move to a bigger place. Changes as below:

1. Add heatsink on those hot chips as seen in the photos. Reduce temperature and increase life time!
2. Changed all power supply capacitors to Good brand like Nichicon and 105C long life type at the output sections. This supply is a standard stocked unit but use normal grade capacitors and become swelled after prolong use.
3. I changed from two analogy IN and two analog Out card to 1 Digital IN, 1 Analogy IN, 1 Digital OUT & 1 analogy Out cards.
4. Design a digital crossover for subwoofer below 100Hz and let the 100 to 20K Hz channel handle by FDA-1B and power amp. Subwoofer channel go to another Yamaha DA2X DAC and power amplifier DSi4000 to drive JBL 4642A (also acquired together with the BSS unit in special sales).
5. My system is driven either by Raspberry PI + HIFI berry digital Pro or CD pro drive.
6. Software is both Foobar or Volumio with Harman Motion Control Apps in PC, iPhone or iPad. All songs is kept in NAS Synology DS212J old unit. Volumio is more easy to use than Foobar but each has its good and bad! Of course the Rasberry Pi also allow Apply play from any device in the same network!
7. The Raspberry Pi case cover cannot fit with the HiFiberry board and thus I need to drill, file and odd shape hole to make it fit so that it can protect the inside part to further corrosion by the Humid weather.

Related Images:

The problem is noisy and sometime signal weak. Open up (screw from bottom) the mic see nothing wrong with parts but after some searching around, found one yellow wire was broken, then the next one wire. As you can see the wire strand all oxidized and become poor connection! This is probably mic is not used in Studio environment and humidity weather cause the problem after 10 years use!

Related Images:

The symptom is can power on, display show LOW RAIL but no sound.  LED on main board not flash.  +rail at heat sink at 89V (normal at +30V with no signal) and -rail at heatsink -30V (normal).  The cause of defect is due to probe around fan control circuit and suddenly power off and then show defect symptom above.  The fan noise is really too loud for home use and but if not set the fan on, the drop down resistors are too hot and also the +/- 15 regulator is also hot and cause the pcb to be brownish color.

The failure is due to U17 LM358 defective (body very hot) and thus replace a similar op-amp M5238.  Reboot the set and it is working again.  The +rail voltage will only drop to +30V after the set is fully boot up.  Tested for 2 hrs output and confirm the set is fully functional again.  See some AP measurement.

Note that with no input, the output is quite noisy, may be due to the switch mode supply.  Also at 1kHz, the harmonics distortion is quite a lot.  S/N is about 95dB, while the spec quoted for 100dB.  Thus this amp does not sound very quiet at background but good for high power drive for PA and Cinema use.

[Show as slideshow]

1 2 ►

Related Images:

Got these all at very good price back in March 2016!  The amp and the subwoofer is used in one of a 70 seat cinema locally by government for film screening.  All equipment are on auction due to relocation.  Hope to hear more!

[Show as slideshow]

1 2 ►

Related Images: