On my bench today is an old ca. 1993-95 Akai hardware sampler. This runs on both a linear and Smps supply. Both are getting on in age and ripple seems fairly high. My guess is simply tired caps but I'd like to post here so someone experienced can help me troubleshoot in order to isolate the problem and of course learn.
I havent looked at the the smps that drives the digital side of the sampler. This gives me some 150mv ripple on average which I guess is high but rather alarmingly the linear AC to DC supply that feeds the samplers sensitive DAC and output stage carries 22odd volts under load complete with a nice juicy 700+mv ripple. This dirty power goes to two LDO + - -15v regs that run the analogue output stage and in turn feed the dac (an old PCM63p) through a couple of 78/7905s
By this point ripple is down to 34mv but that's probably still high for a DAC opamp I/V stage so I'd like to minimise what the main supply feeds this circuit and get on top of this rather loud ripple.
The sampler isn’t playing well either. I see ringing peaks on square and saw wave edges so there are other issues but i figure start with the supply.
I’ve attached a shot of the psu board. this is fed by a separate smps which appears ok given its age. These were expensive devices back in the day and Akai specd them quite well. The SMPS looks medical grade. I’ll recap that too.
I’ve done a quick in circuit cap esr test with a ‘peak’ meter and most including the main filter caps look good. The only suspect is the small .47 next to the rectifier which I’ll desolder for test later today.
I’ll also measure all voltages under load and update the image with these printed in case that helps the process.
So I’d be most grateful for suggestions on what could be amiss here. Is 700mv ripple normal ?
Thanks in advance
I havent looked at the the smps that drives the digital side of the sampler. This gives me some 150mv ripple on average which I guess is high but rather alarmingly the linear AC to DC supply that feeds the samplers sensitive DAC and output stage carries 22odd volts under load complete with a nice juicy 700+mv ripple. This dirty power goes to two LDO + - -15v regs that run the analogue output stage and in turn feed the dac (an old PCM63p) through a couple of 78/7905s
By this point ripple is down to 34mv but that's probably still high for a DAC opamp I/V stage so I'd like to minimise what the main supply feeds this circuit and get on top of this rather loud ripple.
The sampler isn’t playing well either. I see ringing peaks on square and saw wave edges so there are other issues but i figure start with the supply.
I’ve attached a shot of the psu board. this is fed by a separate smps which appears ok given its age. These were expensive devices back in the day and Akai specd them quite well. The SMPS looks medical grade. I’ll recap that too.
I’ve done a quick in circuit cap esr test with a ‘peak’ meter and most including the main filter caps look good. The only suspect is the small .47 next to the rectifier which I’ll desolder for test later today.
I’ll also measure all voltages under load and update the image with these printed in case that helps the process.
So I’d be most grateful for suggestions on what could be amiss here. Is 700mv ripple normal ?
Thanks in advance
