samgraysound
Well-known member
Hello,
I've been working on fixing a mummy face Bad Stone Phaser. It is not the standard mummy phase it's a more obscure version that uses two triple op amps and two single op amps instead of two quad op amps as discussed here.
The original triple op amps have all markings sanded off. The problem was the op amps so I needed to replace them.
I first got SMD triple op amps and DIP 14 adaptors. Unfortunately the pinouts were significantly different, so that didn't work.
I next rewired the PCB to match a standard 14 pin quad op amp pinout, not using one of the amps. I tried TL074s. They passed signal and phased, but had high frequency oscillation.
I next tried op amps with slower slew rates. Both NJM2058 and LM324s acted the same. The passed through the first phase shift stage fine, then all the other stages outputed +9vDC with little to no signal.
The op amps are getting a bipolar supply, +/-9v off two 9v batteries.
I don't understand why the NJM2058 and LM324 are not working. Any advice?
Schematic of the current phase shift stages attached
I've been working on fixing a mummy face Bad Stone Phaser. It is not the standard mummy phase it's a more obscure version that uses two triple op amps and two single op amps instead of two quad op amps as discussed here.
The original triple op amps have all markings sanded off. The problem was the op amps so I needed to replace them.
I first got SMD triple op amps and DIP 14 adaptors. Unfortunately the pinouts were significantly different, so that didn't work.
I next rewired the PCB to match a standard 14 pin quad op amp pinout, not using one of the amps. I tried TL074s. They passed signal and phased, but had high frequency oscillation.
I next tried op amps with slower slew rates. Both NJM2058 and LM324s acted the same. The passed through the first phase shift stage fine, then all the other stages outputed +9vDC with little to no signal.
The op amps are getting a bipolar supply, +/-9v off two 9v batteries.
I don't understand why the NJM2058 and LM324 are not working. Any advice?
Schematic of the current phase shift stages attached
