Interrupt AHEQ-3 active on-board bass EQ
Posted: 19 Aug 2014, 22:48
Not exactly sure if this is exactly the correct place for this post, but i thought i'd share it here anyway. (Admins/Mods are welcome to move this if there's a better suited subforum...)
Friend of mine had some grounding issues with his bass and i promised to take a look. The bass is Aria Pro II XRB Series JP/modern-styled bass with active on-board EQ. Late eighties or early nineties instrument. First i checked the basic stuff and everything seemed to be in order. Except for massive buzz coming from electronics being lifted off from grounds. There was one bad fix in there. The battery snap was replaced and the new snap was simply soldered to the old wires - and the one who had done this had left the new solder joints bare and visible. The shell of the battery was acting as a short for it.. Anyway. After putting some heatshrink tube over those joints i resoldered all the ground joints. Nothing. The buzz was still there. Then i started to take all the different parts of the wiring out to see what's wrong. The volume pot had a switch on it for battery + lead. That was leaking voltage and there was ~250mV being passed to the bridge grounds. Soldered a new pot in, but still nothing. After having a new jack hooked up to a new master ground wire and the pickups with 470k resistor posing as volume pot - the buzz was still there. Yup. The pickups are dead. Sort-of working, but the inductance seems totally gone. The coils seem to act as a 10k and 14k resistors and not much else. To confirm, i tried couple of my old guitar pickups in the place of the original ones and with those, the buzz was finally gone. Grabbed used set from musicians market on the web and those should arrive torrow, so i had some time with bass doing all the wiring from scratch with new pots, switches and a jack. The active EQ board was working flawlessly though. Snapped a few shots and traced it. This may be of interest to some folks.
All the markings on the PCB are "Interrupt" and "AHEQ-3". The dual gang pot has a center detent and the EQ is flat in the center position, just boosting the overall tone a bit. CCW boosts lows and CW highs. It's not a bad sounding circuit.
Friend of mine had some grounding issues with his bass and i promised to take a look. The bass is Aria Pro II XRB Series JP/modern-styled bass with active on-board EQ. Late eighties or early nineties instrument. First i checked the basic stuff and everything seemed to be in order. Except for massive buzz coming from electronics being lifted off from grounds. There was one bad fix in there. The battery snap was replaced and the new snap was simply soldered to the old wires - and the one who had done this had left the new solder joints bare and visible. The shell of the battery was acting as a short for it.. Anyway. After putting some heatshrink tube over those joints i resoldered all the ground joints. Nothing. The buzz was still there. Then i started to take all the different parts of the wiring out to see what's wrong. The volume pot had a switch on it for battery + lead. That was leaking voltage and there was ~250mV being passed to the bridge grounds. Soldered a new pot in, but still nothing. After having a new jack hooked up to a new master ground wire and the pickups with 470k resistor posing as volume pot - the buzz was still there. Yup. The pickups are dead. Sort-of working, but the inductance seems totally gone. The coils seem to act as a 10k and 14k resistors and not much else. To confirm, i tried couple of my old guitar pickups in the place of the original ones and with those, the buzz was finally gone. Grabbed used set from musicians market on the web and those should arrive torrow, so i had some time with bass doing all the wiring from scratch with new pots, switches and a jack. The active EQ board was working flawlessly though. Snapped a few shots and traced it. This may be of interest to some folks.
All the markings on the PCB are "Interrupt" and "AHEQ-3". The dual gang pot has a center detent and the EQ is flat in the center position, just boosting the overall tone a bit. CCW boosts lows and CW highs. It's not a bad sounding circuit.
