F5 power amplifier

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#2,202
jameshillj said:
Yeah, Phresh,

Now, if you take this a step further, you seperate the power rails (supply) and amp speaker wires (output) - this is just better power distribution and returns - obvious, really.

This results in the 3 seperate and distinct groups/types of earth wiring, okay?

When you have a seperate p/supply case, add another one that keeps both cases tied directly to the mains earth connection, not the "star"earth on the supply, with everything else.

The same thing applies with preamps, Xovers, etc, even tho there isn't large currents - the "ground plane" needs to be much cleaner.

The idea of using balanced line level signals can be quite useful but also produces it's own problems and even more connections!
Click to expand...

Thanks, I knocked up a couple of diagrams to try and show the schemes i'm working on.

The first is fairly standard with audio grounds tied in he amp and the power supply grounds tied in the power supply. These are then connected through the power cable. The chassis grounds are connected through an external banana plug so that they are both 'behind' the disconnecting network.

EDIT: Deleted second image due to it being completely wrong!


An externally hosted image should be here but it was not working when we last tested it.
 
#2,203
Nichoh46: thanks for the suggestion - I had looked at RS, but they didn't come up in the search. I looked at farnell, but as it turns out now RS are cheaper for the transformer too so now I will build a dual mono one with 2 x 160VA transformers and bigger heatsinks for the same $$.


Thanks,

Fran
 
#2,204
The power supply is the place for your "Star Earth" and is okay, but the second star earth in the amp case combines all the speaker return currents with the amp 0volt reference points plus adding noise to the input shields - this (IMO!) is where it's better to run them seperately back to the p/ supply star earth [the chassis earth is okay].
Mind you, many amps do exactly as you have drawn and it works just fine - in fact, the original F3 (for example) has a very similar setup to your schematic but all in the one case and there's no problems at all.

Suggest you just assemble both cases and if there's problems, split the earth returns then. If you want to do the multi wire method, there are some excellent mutlipin plugs but none of them are cheap!
 
#2,205
I have thought that this way is also acceptable.

Seasons Greetings,

🙂
 

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#2,209
Ground loops are one of the problems that you will tend to enjoy with
10 channels. I recommend 10 little transformers making 10 isolated supplies
that share a common chassis earth ground through resistors. This way
you can make it pretty quiet without special effort.

😎
 
#2,212
I started on the casework tonight and I almost cried. I'm recycling a worn out fostex rack mount 8 channel digital tape recorder as the case for the F5. Although the thing came from a studio and the heads were worn out, it was a real shame to gut the thing out. It was a lovely piece of engineering. You wouldn't believe the number of screws and crossbraces in this thing. It must have cost a fortune to make!!

Anyway, it will make for a nice case. Depending on how hot this thing gets I may add a fan... so I will be leaving provision for that. Adding even a small fan on my mini-aleph made a fair difference, dropping the internal case temp by 10 degC and dropping the heatsinks by about 5 deg C. Brings them back from 60 to 55. Nelsons controller circuit worked a treat (thanks)


Fran
 
#2,214
I hve visited that website loads of times intending to buy a case there but it just never worked out, or I recycled something else to suit.

They seem very fair in their prices both for the cases and shipping...

I might just fit a wooden front to the amp but am a little concerned as to how it would hold up to the heat. Maybe a little spacer would help a bit with that.

Fran
 
#2,216
kierownik said:
hello
i planning to build a 10 channel amp, and i was wondering if i could stuff 5 F5 boards in to single case (how big the transformer would have to be?) or should i do 5 dual mono blocks?
Click to expand...


I don't know how you'll fit ten chanels in one case. That will be one large amplifer. Maybe you could make ten monoblock modules each with it's own transformer.
 
#2,217
Jeez, 10 channels! and i'm worrying about the heat that 2 will throw out!

Maybe you should consider going to forced cooling - might simplify the build and make it a bit smaller.

Fran

edit: nichoh - nice, I like that carbon fibre. Maybe as a front on its own. Right now though I think I'm gonna get some figured wood and maybe inlay it with some metals.


Does anybody know where I might get a latching push/push off type switch that will handle the current draw of this amp. Looks not really important, just that it works and is preferably 2 pole?
 
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