Looks heaps better, much easier to follow now - are you still using the original opamp? There's some chance that it was damaged.
6V to the capsule is plenty, that's not your problem. You should also have enough gain that speaking loudly at arms length should give plenty of signal.
Are you using OPA2132 or 2134? I've found that *2 will generally tolerate lower supply voltages better than *4, and that *4 will sometimes misbehave until it gets more voltage.
6V to the capsule is plenty, that's not your problem. You should also have enough gain that speaking loudly at arms length should give plenty of signal.
Are you using OPA2132 or 2134? I've found that *2 will generally tolerate lower supply voltages better than *4, and that *4 will sometimes misbehave until it gets more voltage.
Following somebody's advice to check the input and output voltages, I played a long 440 Hz tone from my PC's line-out and fed that into the input of the circuit.
I hope my motherboard's line-out had output caps on it, because I just gave one channel the mic cartridge's DC bias by feeding it to the regular mic-in on the circuit. The line-out seems to be working ok now, though.
Anyway, at the given volume output, VAC of the line-out was about 81 mV. The VAC of the output from the circuit was 56 mV.
Wonder of wonders.
I hope my motherboard's line-out had output caps on it, because I just gave one channel the mic cartridge's DC bias by feeding it to the regular mic-in on the circuit. The line-out seems to be working ok now, though.
Anyway, at the given volume output, VAC of the line-out was about 81 mV. The VAC of the output from the circuit was 56 mV.
Wonder of wonders.
"So using a OPA2134 would be ~8mA and a OPA134 would lower that by 4mA."
You know, this seems to be something that nobody cares about....I see battery-operated boxes all the time with one op amp in a dual package totally unconnected, and drawing power from the battery just to sit there.....
For those beginners who aren't following this, the OPA 2134 is two op amps and the OPA 134 is just one. If you only need one but you install two, they both run down the battery even though you're only using one....
You know, this seems to be something that nobody cares about....I see battery-operated boxes all the time with one op amp in a dual package totally unconnected, and drawing power from the battery just to sit there.....
For those beginners who aren't following this, the OPA 2134 is two op amps and the OPA 134 is just one. If you only need one but you install two, they both run down the battery even though you're only using one....
Figured out the problem. The output cap that I had wasn't passing any AC. Now the output VAC is 3 times the input VAC, which is about right.
I need more gain, though. I'm thinking of switching the 5K res to a 100 ohm res. I'd like to speak normally with the cartridge about 1 foot away and have the output be pretty loud. Actually, how much gain could I get by playing with the Rf/R ratio before the noise from the circuit becomes significant?
An SPDT switch could be used to convert from recording to testing, I think.
I need more gain, though. I'm thinking of switching the 5K res to a 100 ohm res. I'd like to speak normally with the cartridge about 1 foot away and have the output be pretty loud. Actually, how much gain could I get by playing with the Rf/R ratio before the noise from the circuit becomes significant?
An SPDT switch could be used to convert from recording to testing, I think.
Get yourself a 5kohm multiturn trimmer - that way, you can wind that resistance up to where it is now, then wind down until you reach an appropriate point. Then you can replace it with a fixed res, if you want.
http://jaycar.com.au/productView.asp?ID=RT4612&keywords=multiturn&form=KEYWORD
Is the sort of thing I mean, should be readily available everywhere. A regular 5kohm linear pot would be fine, too, just won't be as adjustable as a 10 turn trimmer.
The self noise of the capsule may become an issue before the noise of the opamp does. May I ask why you want to mic from a whole foot away? For speaking purposes, that's a long way, typical vocal mics are designed to be used around 1-2 inches away. However, I've heard of the WM-61A being used by birdwatchers and whatnot, so I gather their self-noise is quite low, unlike the cheap capsules I have here for testing.
http://jaycar.com.au/productView.asp?ID=RT4612&keywords=multiturn&form=KEYWORD
Is the sort of thing I mean, should be readily available everywhere. A regular 5kohm linear pot would be fine, too, just won't be as adjustable as a 10 turn trimmer.
The self noise of the capsule may become an issue before the noise of the opamp does. May I ask why you want to mic from a whole foot away? For speaking purposes, that's a long way, typical vocal mics are designed to be used around 1-2 inches away. However, I've heard of the WM-61A being used by birdwatchers and whatnot, so I gather their self-noise is quite low, unlike the cheap capsules I have here for testing.
I think you deserve at least that much.TheSeekerr said:
It's because I also want to use this to replace my headset when I'm using my computer. Keeping it far away will reduce the variation in volume w.r.t. to head position, and I want to reduce the pickup from my speakers as much as possible.
Rightio. That's gonna make minimising speaker pickup a little tricky, but I'm sure you've thought about that already.
Given that you're not exactly aiming for hifi, I think you'll find it's fine to just wind up the gain until it all gets loud enough. Sure, for minimising noise there's all sorts of fancier topologies, but I've got INA217 based mic preamps which can still sound OK with the gain wound all the way up to 1000, so taking yours up from whatever it's at now (I don't recall, but I think that as shown it's only got a gain of something like 3 times?) to whatever is required should be fine, so long as it's below about 200 times the noise level should be acceptable - if I had to guess, I'd say you'll probably find it needs to be about 50ish.
If it isn't, well, you'll have to start looking into fancier chips, like TI's INA range.
Given that you're not exactly aiming for hifi, I think you'll find it's fine to just wind up the gain until it all gets loud enough. Sure, for minimising noise there's all sorts of fancier topologies, but I've got INA217 based mic preamps which can still sound OK with the gain wound all the way up to 1000, so taking yours up from whatever it's at now (I don't recall, but I think that as shown it's only got a gain of something like 3 times?) to whatever is required should be fine, so long as it's below about 200 times the noise level should be acceptable - if I had to guess, I'd say you'll probably find it needs to be about 50ish.
If it isn't, well, you'll have to start looking into fancier chips, like TI's INA range.
You know, this seems to be something that nobody cares about....I see battery-operated boxes all the time with one op amp in a dual package totally unconnected, and drawing power from the battery just to sit there.....
Sure, but I'm going to want to hook up 2 cartridges at times.
No offense, I was really just waxing philosophical....
B
Sure, but I'm going to want to hook up 2 cartridges at times.
No offense, I was really just waxing philosophical....
B
http://leonli.com/howard/IMG_0717.JPG
New build (OPA227) for Altoids tin. I wish the opamp output was on the same side as the inputs.
New build (OPA227) for Altoids tin. I wish the opamp output was on the same side as the inputs.
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