Long cables from PSU to power amp OK?

[tcpip]

I am building an active speaker with Gainclones, and I don't have space within the speaker enclosure for the transformer (it's a large E+I thing). So I was thinking of building a separate box with the transformer, bridge(s), and cap banks. I'll pull long, thick three-core copper cables from this box to the speakers. Inside each speaker enclosure, I'll put all my Gainclones, and I'll also put a star ground. The cables will probably be about two to three metres long, going from the central PSU box to each speaker.

The main cap banks, as I've mentioned already, will be very close to the bridge rectifiers. There will be a common transformer, but two separate bridge rectifiers and two separate cap banks, one for each speaker. In addition, each Gainclone PCB will have a pair of electrolytic caps for supply decoupling, maybe of 470uF or 1000uF.

The ground line from the PSU will terminate on the star ground plate inside the speaker enclosure. All the power grounds from the Gainclone PCBs will also be connected to this star ground plate.

I am new to amp building. I've just built chip amps in the past. Will this sort of long cable from PSU to power amp work? Will there be any oscillation problems?

[richie00boy]

With 1000uF local decoupling I suspect you will be OK, but how long leads do you intend to use?

[jackinnj]

if you pull AWG #12 (I suppose you folks use the British standards, however) you shouldn't have too much in the way of I^2R losses.

fwiw, there are those of us who use power cable from Home Depot for loudspeakers --

[gni]

I would make the run in the AC realm and convert and rectify as
close to the amp as possible. You don't want long leads of DC
running around your room. The field set up by AC is canceled each
cycle ( 50Hz or 60Hz) The DC current will set up a permanent
field and create noise that will get into anything not shielded 100%.

I think it was RANE who subscribes to this philosophy and they
might have a tech note on the subject. Keep the transformer
as far away from the circuit as possible.

Sounds like a worthy project.

Chris

[jackinnj]

Originally posted by gni
I would make the run in the AC realm and convert and rectify as
close to the amp as possible. You don't want long leads of DC
running around your room. The field set up by AC is canceled each
cycle ( 50Hz or 60Hz) The DC current will set up a permanent
field and create noise that will get into anything not shielded 100%.

I think it was RANE who subscribes to this philosophy and they
might have a tech note on the subject. Keep the transformer
as far away from the circuit as possible.

Sounds like a worthy project.

Chris

Are we revisiting the argument between Westinghouse and Edison ???

[poobah]

We are not allowed to do those kinds of things to sheep anymore.

[mrshow4u]

I would make the run in the AC realm and convert and rectify as
close to the amp as possible. You don't want long leads of DC
running around your room. The field set up by AC is canceled each
cycle ( 50Hz or 60Hz) The DC current will set up a permanent
field and create noise that will get into anything not shielded 100%.

For the electromagnetic field, it's the current through the conductor that's going to create your interferrence. If you rectify near your speaker, you still have the power amp currents and your rectifier current modulating your EM field. Shielded wire wouldn't hurt here. I think twisting the wires will make the biggest improvement assuming the currents are complementary down the wire. They should be. I'd keep the filters (additional) close to the amps. .....you don't wan't that inductive run back to the power supply to cause oscillation.

I see a DC permanent field causing noise only when the DC field is modulated by currents. A stable DC field (by definition) can't be noisey. There would be no mechanism to couple. Capacitive = DC block. Inductive DC block, as well as no AC component in the DC to even create the noise.

I think your big plus here is moving the transformer away from the amp (due to stray fields), not how the current is fed to it.

[jackinnj]

Originally posted by poobah
We are not allowed to do those kinds of things to sheep anymore.

sounds like you're running for Congress

[AndrewT]

Hi,
I think your idea would work.
Look up the previous threads and you will find many contradictory views.
Here's another:-

I would make the run in the AC realm and convert and rectify as close to the amp as possible

I think the exact opposite. Keep the power AC out of the speaker/amplifier box.

The cables have resistance, you cannot eliminate that.
So, use it to your advantage.
Build a RCRC PSU.
The filters of the Rs combined with the Cs reduces the hum at the amplifier substantially more than removing the R and combining all the Cs into one big bank.

The first R is the resistance of the transformer. The first C is the main smoothing bank and supplies the DC requirement of the amplifier. The second R is the resistance of the connecting cables and these do not need to be thick IF you can supply the AC (dynamic) demands from the local decoupling. The final C is the local decoupling.

Taking some guessed figures for your chipamp as an example.
The first R is about 0r1, the first C is made up from two or three 4m7F capacitors in parallel and repeated for each polarity. The ripple in these first capacitors is very high and paralleling small cheap capacitors is an economic way to keep the temperatures down and the life up.
The cables could be 0.75sqmm or 1sqmm, an R of about 0r1 to 0r5 would be perfectly acceptable, If you are prepared to increase the size of the local decoupling you can increase R2 upto about 1r0. The final C would be a high quality 6m8F upto about 10mF if you have space. Both these sizes will probably not fit on board thus necessitating further decoupling on board, 470uF would probably do here.

go and read my recomendations on grounding and safety earthing.

[peufeu]

Seems to me like a recipe for ground loops.

Draw a current flow schematic of your grounds. Now draw it when the rectifiers are conducting (replace them with wires).

You get a huge ground loop modulated by the rectifier currents.

If you send filtered DC to the amps, you'll probably just get extra distortion from ground noise. If you send AC, I guess it will hum.