What is the voltage necessary to turn on Q1 and Q2? I looked at the charts and I think that it's 10V, am I correct? What is the symbol for voltage at which a MOSFET turns on and off?
So far I'm thinking that the voltage to switch off Q1 and/or Q2 is lower than the voltage needed to turn it on, and that it might be the cause for why I can force turn on the amp to keep it running.
The issue that I have described in my earlier post occurs when the batteries are at about 8.30V.
So far I'm thinking that the voltage to switch off Q1 and/or Q2 is lower than the voltage needed to turn it on, and that it might be the cause for why I can force turn on the amp to keep it running.
The issue that I have described in my earlier post occurs when the batteries are at about 8.30V.
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Vgs(th), the gate-to-source threshold voltage. 2Vdc to 4Vdc for the N-channel device and -2Vdc to -4Vdc for the P-channel device. The higher (lower, p-ch) the voltage goes from there the more "on" the device goes, up to the gate to source maximum (Vgss) of 30Vdc (-30Vdc p-ch), although things level off pretty quickly. At 8.3Vdc x 2 = 16.6Vdc (rail to rail voltage across the gate to source) both devices will be fully "on" from graphs 1 and 2 in the respective data sheets:
http://www.fairchildsemi.com/ds/FQ/FQPF10N20C.pdf
http://www.fairchildsemi.com/ds/FQ/FQU11P06.pdf
The problem isn't the mosfets. RocketScientist included a hysteresis circuit around the comparator (R25 and C1) that works by making the "trip on" voltage a tad higher than the "trip off" voltage. That is a common thing to do in comparator circuits to prevent oscillations around the trip point. The "8.4Vdc" NiMH batteries actually run closer to 8.5Vdc - 8.7Vdc through their useful charge range, from here:
http://support.radioshack.com/support_tutorials/batteries/Images/nimh-9v-lodis.gif
NiMH 9-Volt Battery Engineering Data Sheet
By the time one of the batteries is down to 8.3Vdc is is pretty well shot and in need of a recharge. So the circuit is working as it should - it is just saying "recharge me", essentially.
Would have been handy if RS had included a LED to indicate when the power management circuit had tripped, for diagnostic purposes if nothing else.One suggestion is try a different brand of batteries. It is common for batteries to "self-recharge" a few fractions of a volt once the load is removed, another reason RocketScientist put in that hysteresis circuit, and the reason he had to change the values in that circuit once when the recharge voltages turned out to be a bit more than he expected. It sounds like your particular batteries are not recharging at all when the load is removed. Given the battery recharge phenomenon, the low battery behaviour most people seem to get is off/on osciallation as the battery load is cut, then recharges past that hysteresis trip point, turning the amp on again, then dragging the voltage back down below the "off" trip point. Since your batteries don't seem to be doing the load-off-recharge thing, your amp just goes off and stays off with the battery voltage drops below the hysteresis point. A different brand of battery may get you the low battery oscillation behavoir, which at least is more indicative of "recharge me" time.
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Hey one correction to what I posted. Working through the math on RocketScientist's power management circuit the per-battery "off" voltage is about 7.07Vdc per battery and the "turn on" voltage is around 8.33Vdc. So it probably isn't the case that your batteries are not doing the "recharge voltage rise" thing once the O2 is off, but rather they are not quite recharging enough, 8.30 vs. around 8.33Vdc. But a solution is still trying different batteries. Another thing to try would be going back to RocketScientist's original values of R25 = 2.7M and R9 = 40.2k. That would lower the upper trip point (power management circuit "on") to 7.0Vdc and the lower trip point (PM circuit "off") to 6.3Vdc. He made the change to prevent the power management circuit from oscillating when the battery got low, but it wound up doing that anyway due to the battery voltage rise behavior when the load is removed. He eventually decided the oscillation was a good "recharge the batteries" signal.
Also, if you happen to be using the bass boost modification I posted in the mod thread, I just posted a warning that it won't work if the O2 gain is set to 1 (R17 and R21 clipped out in the low gain position). Been meaning to do that for awhile. The details are here: http://www.diyaudio.com/forums/head...rc-diode-cap-heatsink-mods-3.html#post3193906
Also, if you happen to be using the bass boost modification I posted in the mod thread, I just posted a warning that it won't work if the O2 gain is set to 1 (R17 and R21 clipped out in the low gain position). Been meaning to do that for awhile. The details are here: http://www.diyaudio.com/forums/head...rc-diode-cap-heatsink-mods-3.html#post3193906
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Hi all and sorry for being a bit late into the post... Is anyone planning any group buys for the o2 amp in the near future?
Got 2 boards from a kind member and would like to do one using the cheapest components and the other using "the best" components. I dont want to measure or analyse the output, i just want to hear if there is any difference. If there is... the wife can have the cheap one
Got 2 boards from a kind member and would like to do one using the cheapest components and the other using "the best" components. I dont want to measure or analyse the output, i just want to hear if there is any difference. If there is... the wife can have the cheap one
So I successfully built my O2 when it was first released and it's been a long time since my last DIY project. I'm a bit rusty and I don't know what to do to fix the issue I'm having.
I was sitting listening to music when a random burst of DC went through the right channel of my headphones. It sounded like pulsing distortion. I measured it with the multimeter today and it measured something crazy like 1.5 volts (it might not have been 1.5 volts, but it was absurdly high)
What's weird is that it doesn't do it on startup, but it takes about a minute or two for it to kick in.
Does anyone know where I should start? My guess would be the ICs, but what do I know.
thank you.
I was sitting listening to music when a random burst of DC went through the right channel of my headphones. It sounded like pulsing distortion. I measured it with the multimeter today and it measured something crazy like 1.5 volts (it might not have been 1.5 volts, but it was absurdly high)
What's weird is that it doesn't do it on startup, but it takes about a minute or two for it to kick in.
Does anyone know where I should start? My guess would be the ICs, but what do I know.
thank you.
I must say, I've been concerned too. He hasn't approved any comments since Aug. 28th, and apparently people haven't gotten hold of him via email either.
It'd be a shame if the community lost him.
Poof... and my amp just turned off.
I am sitting at a coffee house enjoying music on my O2 and all of a sudden I fear a poof and no sound comes out. The headphones are fine. Thank god. I assembled the amp about a month ago. Did all the initial testing and every number was spot on. I didn't drop the amp, didn't even touch it and I stopped working. The LED is still on but completely no sound comes on.
Any of this ever happen to anyone? How do I even start to troubleshoot?
I am sitting at a coffee house enjoying music on my O2 and all of a sudden I fear a poof and no sound comes out. The headphones are fine. Thank god. I assembled the amp about a month ago. Did all the initial testing and every number was spot on. I didn't drop the amp, didn't even touch it and I stopped working. The LED is still on but completely no sound comes on.
Any of this ever happen to anyone? How do I even start to troubleshoot?
According to the JDS Labs blog, his commercial partners seem to have had no better luck getting hold of him, and have arrived at the conclusion that he's taking an extended break from everything.
The way his comment updates tailed off gradually would seem to suggest that, along with his repeated allusions to a very heavy workload - I just hope he comes back again!
I don't know if this is the appropriate part of the forum, but I've got a question regarding my O2 amp. I've participated in the group buy but only recently started to assemble the amp, and;
C 16 is missing and I need to replace it somehow.
It's got a value of 22nf or 0.022µf.
Data sheet says it's supposed to be spec'd at 50V (ceramic cap.)
How critical are the volts in the application the cap sits in?
Can I buy a 100V spec'd variant? I know that it affects how much charge the cap can hold, but is it a critical spec?
I only need on part of the cap and so I thought about ordering on ebay, only thing is they don't have 50V spec'd caps.
I'd appreciate input
All the best guys.
C 16 is missing and I need to replace it somehow.
It's got a value of 22nf or 0.022µf.
Data sheet says it's supposed to be spec'd at 50V (ceramic cap.)
How critical are the volts in the application the cap sits in?
Can I buy a 100V spec'd variant? I know that it affects how much charge the cap can hold, but is it a critical spec?
I only need on part of the cap and so I thought about ordering on ebay, only thing is they don't have 50V spec'd caps.
I'd appreciate input
All the best guys.
Thank you very much
One 22nF was included the other one wasn't so I really only need 1.
They come bundled in 10 on ebay though, so I'm stocked I guess.
I haven't read the remark about "non critical part", sorry
But, better be safe than sorry, right?
All the best.