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Minion 1st November 2006 07:24 PM

How to star ground to Chassis without a Chassis??
Hi Folks, I am building a Guitar amp useing a OPA2134 for the pre stage and a LM3886 for the power amp stage but the Enclosure(Chassis) I am useing is 100% wood so I am wondering what the proper grounding would be for a Wooden chassis.....

So far i am not useing a Chassis ground so I have just been running all of the DC Grounds to a Common Point (Star ground) and connecting AC ground to DC ground useing a Couple 4007 Diodes on Opposite directions.....

Is this an appropriate grounding scheme for this type of application??


PS: I am useing a 100vA 18v,0v,18v Toroid with about 8000uF of filtering on each rail.....

Jan Dupont 1st November 2006 08:51 PM

Your star ground should always start (or end if you like) at a point at the center of the ground between your 8000uF PSU caps ;)

Minion 1st November 2006 10:07 PM

Well that is pretty much how I have it ......


pinkmouse 1st November 2006 10:14 PM

Just make sure that any exposed conductive surfaces, such as metal control panels, are firmly attached to safety ground.

Minion 2nd November 2006 12:04 AM

Hi, actually there is absolutly no metal at all accept for what is inside the Case so there is no chance of touching any metal and all Pots are grounded so even touching an exposed pot should not cause a problem......

I actually just Finnished Raching the whole thing up in the case and am about to test it accept that I think I will probably blow the fuse as it only has a 1 amp fuse in it but maybe I can test it at Low volume and if it works fine I can replace it with a Bigger one.....

I"ll post some pics of it later is it is pretty nice looking , It has a 12in Woofer and a 6in Midrange/Tweeter and has a High quality adjustable JBL Crossover which I haven"t ever seen in a Guitar amp but I thought I would try it.....


PS: I just tried the amp and it doesn"t work....I get absolutly no sound out of the speakers accept after a minute I get a sort of sound like a heart beat which goes away if I click the Mute button...I tested the PSU and get the proper Voltages off of it and I went over the whole circuit to see if it is Right and it seems OK so I don"t have a Clue were the problem is.....

Anyone have any suggestions were to look for the problem???


pinkmouse 2nd November 2006 08:05 AM


Minion 2nd November 2006 04:28 PM

it"s OK...The amp works now...


AndrewT 5th November 2006 10:07 AM

sorry ACD, but never do this

Originally posted by ACD
Your star ground should always start (or end if you like) at a point at the center of the ground between your 8000uF PSU caps ;)
The ground on the RCAs could become live if a mains connection broke off and touched the PCB or internal wiring.

ALL exposed conductive parts MUST have a permanent safety earth.

The audio ground (including the RCA) must not be connected to the safety earth for best sound.

That leaves a problem, how do you satisfy both requirements?

Use a disconnecting network to connect the safety earth to the audio ground. The disconnecting network can consist of some or all of the following wired in parallel:-
Power diode wired in inverse parallel.
Power resistor.
High frequency capacitor.
Power Thermistor.

The audio ground should float and using wires connect it to the following:-
Signal ground
RCA ground
Power ground on PCB
Decoupling ground on PCB
Thiel network (or Zobel)
Speaker return
0volt to PSU.
Transformer 0v
Ancilliaries returns (relays etc)
Disconnecting network.
I hope I've not missed too many.

If you want/need more detail read through my previous posts.

forr 5th November 2006 10:39 AM

---Your star ground should always start (or end if you like) at a point at the center of the ground between your 8000uF PSU caps---

Exactly what is recommanded to avoid by Doug Self, with some very good reasons.

Jan Dupont 5th November 2006 03:11 PM


However recommanded by many others ;)

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