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Old 13th November 2013, 02:03 AM   #3571
bob711 is offline bob711  United Kingdom
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Hi there i have had a few pcb's of the o2 amp for like a couple of years now just sat in a drawer never got round to doing anything with them but recently decided to build one of them however having the problem that it powers on but doesnt produce any sound through headphones was wondering what the main cause of this is? just wondering what i should be looking for in troubleshooting this problem.
thanks
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Old 13th November 2013, 03:26 AM   #3572
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Make sure you have the correct voltages at the correct points on the board. After checking the in/out jacks with an ohmmeter.
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Old 13th November 2013, 07:05 PM   #3573
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Before I take my O2 apart, I'd like confirmation that it will work perfectly OK without the batteries installed, and there is no need to do any other alterations without batteries installed. I am finding that I am using it 100% with the power adapter. Rather than leave the batteries in and risk leaking or whatever, I'd remove them, but I'd like some reassurance before I go through the bother of taking the thing apart.
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Old 14th November 2013, 01:12 AM   #3574
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It is just four screws to remove and replace, but the O2 will work just fine with the batteries removed.
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Old 14th November 2013, 01:51 AM   #3575
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Sofaspud,
Thank you.
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Old 15th November 2013, 10:51 AM   #3576
lhalha is offline lhalha  Australia
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Default Search for FQPF10N20C brings back FQPF19N20C. Ok to use?

For the N Ch MOSFET Q2, a search on Element 14 for this...

FQPF10N20C (as per the BOM)

is hard wired to bring back this:

FQPF19N20

Can I use this part? (In Q1 I have the FQU11P06TU as per the BOM)

Comparing the parameters on the data sheets for each, there are many differences.

Interestingly, removing the "C" and searching for FQPF10N20 returns the following message, suggesting it is a "replacement"

FQPF19N20 (NOTE-Suggested replacement for: FQPF10N20)

Thanks!!!

lhalha
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Old 16th November 2013, 04:38 PM   #3577
agdr is offline agdr  United States
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Quote:
Originally Posted by lhalha View Post
Can I use this part?
Well.... from a DC standpoint the answer is yes, but from an AC/step-response standpoint it is probably more like "who knows". You would be best off just trying it and see what happens as per turn-on and turn-off thumps, which is the thing that would be affected.

I see that RS Components has the BOM mosfet in stock. Do you have access to them?

Details:

As for DC parameters, the "on" resistance of the 19N20 is smaller (a good thing). The threshold voltage is a volt higher, but in the O2's particular usage that shouldn't matter. The mosfet is being fed from a fast-switching comparator that pretty much goes from 0V directly to either 16V [on batt] or 24V [on AC]) as far as the mosfet gate is concerned. One biggee is that the maximum gate voltage of the 19N20 is still +/-30V, like the 10N20. I actually talked NwAvGuy into changing that on his final BOM as the other mosfets he lists have +/-25V gates and the rail-to-rail is 24Vdc, cutting it a bit close.

As for AC parameters, NwAvGuy is relying on the mosfets being closely matched enough to switch at more-or-less the same instant to avoid turn-on/turn-off thumps in the headphones. I never really could get that to simulate with any degree of accuracy. He was using the actual ocilloscope captures of the turn-on/turn-off ramps in circuit. I see the gate charge is a bit higher on the replacement part. The turn-on delay time of the 19N20 is 10nS or so slower, but the turn-off delay is around 10nS faster. The turn-on ramp time of the 19N20 is about double the 10N20C. Then there is that threshold voltage difference and the associated shift in the Id vs. Vgs curves during switching. But have no idea if those parameter differences would affect thumps in the actual circuit. NwAvGuy is already "slowing down" the transfer with those gate-to-rail capacitors, acting as a turn-on-delay. So all I could say here is try it, and you either get turn-on and/or turn-off thumps or you don't. That would be the only negative effect if the replacement's switching properties don't match up as well as the original.

Good luck!

Last edited by agdr; 16th November 2013 at 05:01 PM.
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Old 17th November 2013, 09:06 AM   #3578
lhalha is offline lhalha  Australia
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Quote:
Originally Posted by agdr View Post
Well.... from a DC standpoint the answer is yes, but from an AC/step-response standpoint it is probably more like "who knows"
Thanks for all this great info - I had for some reason not checked that one on RS which I was doing for every other part on the shopping list. So I now have both parts and can experiment with each. Will report back with any findings...
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Old 22nd November 2013, 03:00 AM   #3579
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Location: Wisconsin....what did you expect?
Send a message via AIM to Spasticteapot
Is there a single vendor with a complete BOM?
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Old 22nd November 2013, 03:07 AM   #3580
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You mean a complete kit of parts?
My understanding was that there was at least a few. I don't recall any USA based, but I thought there was a Canadian, and you're next door.
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