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Old 27th June 2004, 07:59 PM   #1
Odysei is offline Odysei  Lithuania
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Default Avoid static charge at the input

I want to avoid static charge at the input in Zen Var 4 in order to keep P mosfet safe (lets say I'm using IRF9610 instead of ZVP3310, like in Aleph3). What should I do?

Can I use method like in Aleph 3 ? Two 9,1V Zener diodes connected like this --|>[----]<|-- to the input and to the ground.
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Old 27th June 2004, 08:39 PM   #2
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Odysei,

Yes, 2 * 9.1 volt zeners in opposition.

I have soldered them right on the XLR connectors on my A75.

regards.

Alain.
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Old 28th June 2004, 03:40 AM   #3
jwb is offline jwb  United States
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I always wondered why people do that, actually. The critical rating is Vgs, Voltage from Gate to Source, and it's &plusmn;20V usually. The rating isn't from the gate to ground, or from gate to the gate of some other transistor, it's Vgs. So I like to put the zeners directly from the gate to the source of the transistor to be protected. Any other method seems needlessly indirect.
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Old 28th June 2004, 12:47 PM   #4
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jwb,

You have to consider the hole circuit, not only the differential pair at the input, the pick can travel all over your circuit ; using power supply cables, chassis, etc. and be able to do a lot of damage.
So its wiser to put protection right at the input of the signal.

Regards.

Alain.
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Old 28th June 2004, 05:24 PM   #5
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Since the input Gates on ZV7 are held at ground potential,
you can actually use quite low zener voltages, even diodes
in reverse parallel.
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Old 25th October 2005, 11:12 AM   #6
Rixsta is offline Rixsta  United Kingdom
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Thanks for this idea ..i have the problem where the input buffers seem to go bad after a while. in the zen 4
The problem comes ..from my computer sound card connected directly to the amp
If we have a power cut ..the pc turning off ..creates a thump on the speakers ..i can presume this is bad for my amp ..lol
The same if i turn on my computer when the amp is on..or still has power left in the capacitors.
I have however noticed a diferance in the sound between the

zvp3310
(sounds better in the mid's and trebble)
and the
zvp3306a
(seems to give tighter bass ..but other freaquancys a bit dull) but both sound good tho

I prefer to stick to the zvp3310 ..and use another amp for the lower bass

The transistors have goon bad about 6 times .lol
there becomes a humm and the bad channel is quite a bit quiter

please exuse my spelling ..lol
anyways cheers to all who helped me ..and to Mr. Pass
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Old 26th October 2005, 07:26 PM   #7
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It's worth noting that Zeners should be outside any
Gate resistor (those resistors on the Gates of Mosfets
which prevent parasitic oscillation) as connecting the
Zener directly to the Gate can cause oscillation.

Also, as an aside, I put the protection zeners on my
public circuits, but at home I don't bother with them
- I just make a marginal effort not to zap the input,
and I've never lost one.

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Old 31st October 2005, 01:04 PM   #8
Rixsta is offline Rixsta  United Kingdom
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Thanks
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Old 2nd November 2005, 03:05 PM   #9
df is offline df  Switzerland
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For months I did not lose one, but since I have connected a soundcard to one input of my enlightened boz it's the third IRF510 I have to solder

Is there a solution with LEDs to protect the FETs?

Daniel
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Old 30th January 2007, 03:50 PM   #10
Vix is offline Vix  Yugoslavia
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Hi,

Iím resurrecting this old thread cause I didnít want to start a new one. I have a question (maybe silly to some of you, but Iím curious):

If you damage a mosfet with a static charge at the input, what will it sound like? I mean, for example, if you damage a BOZ (assume there is no zener protection) will it continue to produce any sound, or will it continue to work, but just sound muddy?

I have an impression that my BOZ is sounding muddy lately, so Iím wondering if Mosfets could be damaged by a static? (I disconnected Zener protection a while ago)

Thanks

Vix
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