AndrewT said:
Sorry, but I'm not sure how to calculate an RF filter value in uS?
The schematic is pretty simple, with only a 1K resistor in series, and a 22K to ground on the input. The output has only a 2R7 and 0.1uF zobel. I opted to leave out the 47uF to ground on the feedback loop, but the notes said this was optional, and better sound might be had with it left out, at the cost of more DC offset. I'm getting <20mV of DC.
(Using the boards from chipamp.com)
I will try lifting all the grounds except safety and see what happens. Thanks.
Ok, I removed all grounds attached to the star point, except the transformer CT and the AC line in ground. Lots of hum.
I then removed the CT ground, leaving only the safety - dead silence. So what does this mean? I assume running it this way is not a good idea...
I had a C+R parallel filter on the ground line from PS grd to star - should I have this on the CT ground instead (or in addition), since the hum seems to be from there?
I then removed the CT ground, leaving only the safety - dead silence. So what does this mean? I assume running it this way is not a good idea...
I had a C+R parallel filter on the ground line from PS grd to star - should I have this on the CT ground instead (or in addition), since the hum seems to be from there?
Tried adding a 2ohm resistor + .22uF poly cap in parallel on the CT ground (with other grounds left off), and no change.
I've seen mention of a diode isolating network - is this what I need here? I've seen them placed between the Signal ground and the chassis ground point, but since my hum is present even with the SG left hanging, doesn't this mean I should have the diode network at the source of the hum, ie: the CT ground line?
Ok, this is one of the places I saw the diode bridge used, so I will try this next:
http://sound.westhost.com/earthing.htm
I've seen mention of a diode isolating network - is this what I need here? I've seen them placed between the Signal ground and the chassis ground point, but since my hum is present even with the SG left hanging, doesn't this mean I should have the diode network at the source of the hum, ie: the CT ground line?
Ok, this is one of the places I saw the diode bridge used, so I will try this next:
http://sound.westhost.com/earthing.htm
Hi Tdw,
you need to do more research before you start mucking about with mains powered equipment.
Rule 1. always make a permanent connection from all exposed conductive parts to safety earth.
Rule 2, 3, ... 101 do the same!!!!
For example,
the RCA ground barrel is an exposed conductive part. It must be connected to safety earth with a wire or trace that can carry enough fault current to rupture the mains fuse before the connection melts.
you need to do more research before you start mucking about with mains powered equipment.
Rule 1. always make a permanent connection from all exposed conductive parts to safety earth.
Rule 2, 3, ... 101 do the same!!!!
For example,
the RCA ground barrel is an exposed conductive part. It must be connected to safety earth with a wire or trace that can carry enough fault current to rupture the mains fuse before the connection melts.
TDWesty said:
And how long do you think this will last before combusting during a fault condition... ?
You need to parallel those with 2 high current rated (8A) diodes, with the 2 diodes in oposite polarity config.
Failing to do so can let your earth go open circuit... leaving your chasis etc not connected to ground, but potentialy connected to whatever caused the fualt condition... without tripping the mains circuit breaker.
This is totaly out of context of any of the other posts, its just something unsafe I noticed in your post.
Nordic said:
Point taken. I had only used this C/R on the ground from PS board ground (neg leads of big caps) to chassis, not on either the ground from transformer CT to chassis, or the mains earth to chassis. I understand the latter must be a permanent connection. I do plan on using the diode method, either with a bridge, or two diodes as you suggest. I have lots of nice big diodes from laser printers and monitors I can recycle.
AndrewT: I take your point about many correct ways to solve this. The hum is actually acceptablly low when connected to a 3020 pre amp; it is only noisy when connected to my PC sound card, which is via about 15' of cheap mini-phono extension cable. But the same setup is free of hum on other amps, so my chipamp grounding does need refinement.
Hi,
the Thiele network is just a L//R in series with the load.
Then a R+C in parallel with the load.
The R+C can be attached before or after the L//R.
The Leach amp shows the R+C after the L//R.
A very few amps show a pair of R+C one fitted before the L//R and one after. This forms a Pi circuit before the load.
the Thiele network is just a L//R in series with the load.
Then a R+C in parallel with the load.
The R+C can be attached before or after the L//R.
The Leach amp shows the R+C after the L//R.
A very few amps show a pair of R+C one fitted before the L//R and one after. This forms a Pi circuit before the load.
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