PGA2311 pre-amp static discharge problem

I've built a PGA2311 based pre-amp like this one on eBay.

Works very well and sounds good but is extremely sensitive to static discharge which causes the pre-amp to "crash" and make the most appalling speaker destroying loud noise. It's like hum and buzz at full volume.

The "crash" can be triggered occasionally simply by touching the volume knob and more frequently by the static discharge from vinyl LP's :eek:

I've tried earthing the case but it hasn't made any difference.

Any suggestions to fix this problem are most welcome!!
 
If the case is correctly grounded it should not be a problem as it is then I would suggest that the grounding scheme has a high impedance connection, probably a star point, run large seperate ground wires between points to improve and lower the ground impedance.

A schematic of the grounding would help give a more qualified answer.
 
Thanks for the reply Marce. Here's a schematic for the board:

$(KGrHqFHJ!sE9BV0EYNBBPWi1dCKlw~~60_57.JPG


And here's my pre-amp:

[IMGDEAD]https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-ash3/581866_10151824767329832_1072807795_n.jpg[/IMGDEAD]



There's no obvious grounding point on the board. In fact the commercial assembled versions of the pre-amp on eBay do not appear to have any grounding. :confused:
 
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I've had similar problems in similar circumstances. Check the grounding between the PGA digital ground connection, and the digital ground of your ucontroller and rotary encoder setup.

If there's an issue there, static discharge can look to the controller as a digital input stream. The fact that it happens when you touch the knob points that way. This can send all kinds of random commands to the PGA with the results that you see - random levels, quickly changing, sounding like hell breaking loose ;)

jan
 
Yes anodising is a good insulator.
What concerns me is the damage that the discharges are doing to the actual devices, it can destroy chips.
I would affix a nice thick wire from the front panel to the safety earth at the mains input, also a thick GND wire to connect the two boards together, minimising the GND (0V) impedance, the aim is to create a low impedance path for the ESD energy to discharge down.
I would be interested to any links to the PCBs used as this problem is probably down to far from optimal PCB layout, and or things lacking in the circuit layout such as protection devices for ESD. It is srtrange to hear of these problems these days, they were more common in early to mid 80's!
 
Yes anodising is a good insulator.
What concerns me is the damage that the discharges are doing to the actual devices, it can destroy chips.
I would affix a nice thick wire from the front panel to the safety earth at the mains input, also a thick GND wire to connect the two boards together, minimising the GND (0V) impedance, the aim is to create a low impedance path for the ESD energy to discharge down.
I would be interested to any links to the PCBs used as this problem is probably down to far from optimal PCB layout, and or things lacking in the circuit layout such as protection devices for ESD. It is srtrange to hear of these problems these days, they were more common in early to mid 80's!

Will give it a try, thanks for the suggestion :)

During my 50 odd years tinkering with audio gear, I recall RF breakthrough being an issue way back when, a lot less dangerous than chip-killing static discharge.
 
No it may give a ground loop problem, but ground loops are solvable.
What do you mean do not connect the earth wire to the unit, dangerous and under no circumstances should it be ommited from ANY DIY gear.
And while I am on a roll, we have a major proble to solve ESD, no point worrying about possible ground loops.
Ground loops are caused by some high impedance point in the 0V (GND) scheme of a system, Henry Ott, Tony Waldron etc have plenty of info on interference grounding of audio systems.
 
Looks like you have not used an amp with 2pin mains connector.
Class II is perfectly safe, BUT IS NOT SOMETHING A DIYER CAN USUALLY BE RELIED UPON TO PULL OFF SAFELY....

There is nothing inherently wrong with a class II (double insulated) amp, but the engineering to ensure safety in the event of a fault is subtle enough that this site quite rightly takes a 'if you have to ask' view on the subject and bans discussion of building class II mains power supplies. Class I is very much easier to make safe, and if implemented sanely does not cause ground loops.

The circuit does however generally seem to be missing anything much in the way of ESD protection and anti RFI measures, AND WHERE IS THE DECOUPLING??!
Those 100uf cans are fine at audio frequency, but the digital side will be running more then a little bit faster that, a scattering of 100n ceramics around the +-5V rails really would not go amis.

Check continuity between the mains earth and the PCB mounting screw in the lower left of the picture (That seems to be the PCB earth terminal), and check that the logic board earth is connected correctly.

73, Dan.
 
Check continuity between the mains earth and the PCB mounting screw in the lower left of the picture (That seems to be the PCB earth terminal), and check that the logic board earth is connected correctly.

73, Dan.

Continuity between mains earth, PCB mounting, logic board and control knob checks out fine. Any other ideas?

Regards,
Steve
 
As was said previously, anodizing is an insulator, if you want to make the chassis completely at earth ground you have to add some bite through the oxide into the aluminium itself, use some lock washers!!


Continuity is good. The mounting screws go through drilled holes and are in direct contact with raw aluminium but I'll give lock washers a try.

Regards,
Steve