I didn't challenge the stability problem..others did...so I'm not talking for everybody here.
It was just an advice...I know people doing very high end proffessional audio which never enter forums disclosing real names, private emails, etc...they tackle the problems professionally in private.It's the right way to go in my opinion...That's if you want 4... 5 figure contracts and sign NDAs every 3...6 months...If not...it's your choice.It's not a bad thing if you get rich...you know that, don't you?
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I had a power amp do the “snick”, then silent on one channel thing after replacing the ceramic input filter caps with film.
Not sure if that’s what actually caused it with my situation, but it definitely made me wonder…
Either way, a single failure shouldn’t put the entire product line in question.
Maybe if there was a monitored test where things go awry way before they have been advertised, indicating some sort of defect.
Not sure if that’s what actually caused it with my situation, but it definitely made me wonder…
Either way, a single failure shouldn’t put the entire product line in question.
Maybe if there was a monitored test where things go awry way before they have been advertised, indicating some sort of defect.
In this context, this idea came to my mind: Simply use the phono input as an output and connect it to a line input from an integrated amplifier.
Then observe which noises are audible to what extent when switching on and off (initially with a low volume setting, of course). Additional the same without loudspeakers and with an oscilloscope - volume control now at full power.
A division by the gain factor (usually 30-50, as long as only a passive preamp and a power amp is present) provide the value that is present at the cartridge coils.
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post 2 under
https://www.diyaudio.com/community/threads/monticelli-ultra-efficient-ultra-low-distortion.401389/
show the internal schematic from OPA1611 - unfortunately as simplified schematic.
Are there discrete OP-Amps in the kind from those under
https://www.diyaudio.com/community/...able-discrete-op-amps-overview-wanted.263440/
where the internal topology from OPA1611 is in use ?
Thanks for an advice.
You can simply use a series capacitor after the load network and before the opamp, with a DC bias resistor of quite large value so the capacitor can be relatively small - then the maximum energy the chip can dump into the cartridge is severely restricted. And of course there should be an RF suppression cap directly on the input jack, which for MC can be quite large (1nF ceramic) as the impedances are low.
My theory is that strong RF got into the input wiring (some of which looks like it would make a good magnetic antenna not being shielded or twisted pair), causing the opamp to burn out, possibly with poor rail decoupling contributing. These days mobile phones are everywhere, able to push 30dBm or more in the UHF and/or microwave bands. Without good protection from this input stages can get burned.
Note for MC inputs a ground-plane is a great idea as the impedances are low enough not to be loaded by the plane.
Yes, that would work to protect the cartridge and with no real noise penalty no matter what the actual cause was.
What problem is solved by inserting a cap after the load, unless a single power supply is used ?
Hans
Hans
And with magical non coupled stages.
Eventually you find out why DC is a issue.
As shown 33n across 100k is far more distortion
than coupling
Eventually you find out why DC is a issue.
As shown 33n across 100k is far more distortion
than coupling
The cartridge is connected directly to the non-inverting input of the OPA1611. That's a high-impedance node ... during normal operation. So where did the current come from? Never mind enough current to fry a piece of wire?
ESD damage from the MC input... Yeah, I suppose. But if the MC load resistors were enabled that charge would quickly have been drained to ground. And if one of those resistors was not enabled the ESD structures within the OPA1611 should have taken care of it. After all, we're talking about a slow buildup of charge rather than a huge zap here.
Latchup? That's something that's looked for (by software) before the part even undergoes its first prototype run. So I find it unlikely that the internal protection diodes across the input would cause latch-up. It's pretty easy to avoid the parasitic SCR structure that causes latch-up in the layout. I find it unlikely that you'll find a modern day IC that'll latch up during normal operation within its spec limits - in particular a "high-voltage" IC like the OPA1611.
The only way I can see getting enough current to flow into or out of the non-inverting input of an opamp is to turn on the ESD structures on the pin. So you need to forward-bias one of the PN junction diodes connected from VCC and VEE to the input. Unless the power supply does something funky I just don't see how that'll happen. OP said the issue occurred during playback so unless the supply did something funky I think we can rule out power-up/down issues.
I'm curious if OP reached a conclusion on this.
Tom
ESD damage from the MC input... Yeah, I suppose. But if the MC load resistors were enabled that charge would quickly have been drained to ground. And if one of those resistors was not enabled the ESD structures within the OPA1611 should have taken care of it. After all, we're talking about a slow buildup of charge rather than a huge zap here.
Latchup? That's something that's looked for (by software) before the part even undergoes its first prototype run. So I find it unlikely that the internal protection diodes across the input would cause latch-up. It's pretty easy to avoid the parasitic SCR structure that causes latch-up in the layout. I find it unlikely that you'll find a modern day IC that'll latch up during normal operation within its spec limits - in particular a "high-voltage" IC like the OPA1611.
The only way I can see getting enough current to flow into or out of the non-inverting input of an opamp is to turn on the ESD structures on the pin. So you need to forward-bias one of the PN junction diodes connected from VCC and VEE to the input. Unless the power supply does something funky I just don't see how that'll happen. OP said the issue occurred during playback so unless the supply did something funky I think we can rule out power-up/down issues.
I'm curious if OP reached a conclusion on this.
Tom
Tom, I fully agree with your analysis and as mentioned in #38, put a set of antiparallel diodes across the inputs and you will never experience a problem with the 1611/1612.
Not with a MM and not with a MC.
A capacitor in line with the input can only stop slow changes, but a “huge zap”, unlikely to ever happen, won’t be stopped by a cap and will just as much damage the Cart.
Hans
Not with a MM and not with a MC.
A capacitor in line with the input can only stop slow changes, but a “huge zap”, unlikely to ever happen, won’t be stopped by a cap and will just as much damage the Cart.
Hans
The coupling cap is not intended to protect the chip but to protect the cartridge in case of chip failure.
@Hans Polak , this is actually the most important reply of this thread, as you appear to be the only one here besides the thread starter who has experience with unintendedly blowing up OPA1611s. How many OPA1611s did you blow up before adding the diodes and what type of diodes do you use?
Hi Marcel,
I blew one Opa1612 without any clear cause and decided to place anti parallel diodes across the input which made that the problem didn’t repeat.
But then a Moon 110LP came on my way and I noticed a bit to my surprise that this MC/MM preamp without input cap also had two anti parallel diodes across its OPA1612 input opamp.
This preamp must have been made in quantities, and reading the positive reviews, I can’t imagine they had serious problems with blown inputs.
Hans
I blew one Opa1612 without any clear cause and decided to place anti parallel diodes across the input which made that the problem didn’t repeat.
But then a Moon 110LP came on my way and I noticed a bit to my surprise that this MC/MM preamp without input cap also had two anti parallel diodes across its OPA1612 input opamp.
This preamp must have been made in quantities, and reading the positive reviews, I can’t imagine they had serious problems with blown inputs.
Hans
I’ve not ever had an opamp (OPA16xx or other) blow on any type of input over stress, but it seems 2 anti-parallel diodes on MC or MM inputs is s neat solution.
Some hot MM outputs might clip a diode pair, and for a 10 ohm MC for instance diodes allow 0.7V x 70mA = 50mW dissipation in the coil, perhaps too much continuous.
Hans recommended anti-parallel diodes between the op-amp inputs, if I understood him correctly.