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Old 18th December 2006, 05:52 AM   #1
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Default A new Aikido is born - and kicking butt!

Following my scare with too many volts, and a phone call with Bruce Anderson, I decided to go ahead with my current configuration. By the end of the day, I managed to finish all wiring and plug the new Aikido in.

No flames, fizzles, no smoke.....wow! So I connect it to a cheap amp and walkman CD-player with volume control and wire my cheap speakers.

The Aikido works, with next to no hum, in fact when the volume pot on the Aikido is turned up, the slightest trace of hum disappears and the music really shines.....Phew.

Well, I should have left things there for the night, but no, I had to take things further and wired the bouncing baby Aikido to my main system.

Again, no flames, fizzles or smoke (much to my relief)....BUT.....the hum is overwhelming.

So, the circuit-board is not connected to the chassis, or the GND to chassis/Earth. The signal GNDS are not connected to chassis or Earth, although they are connected to the circuit-board GND via the board's star GND.

Maybe I need to go from circuit-board GND (also PSU GND point) to the chassis/Earth bolt????

What should be my first plan of attack with dealing with this hum?????

Thanks,
Charlie
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Old 18th December 2006, 05:59 AM   #2
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Default further note

I forgot to mention, that I referenced the 6.3VAC heaters to 25% of B+ as in John Broskie's instructions.

I am using a separate mains transformer for the heater voltage. I did just read in Morgan Jones that AC heater wiring needs to have a DC path to HT (B+) 0V. It suggests that I can use the center tap of the AC transformer and connect it to main ground.

Do I need to do this?
Would I connect it to the circuit-board / B+ GND?
Or would I connect it to chassis / Earth?

In the Morgan Jones book, the diagram shows the center-tap going to chassis/Earth as shown by:

|
|
--------
////////

Thanks,

Charlie
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Old 18th December 2006, 11:43 AM   #3
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Way to go Charlie!!
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Old 18th December 2006, 06:56 PM   #4
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Default Aikido Hum

Hi Charlie,

This system is used in the UK/Europe but there is no reason why it will not work in the US but TAKE LOCAL ADVICE. Can't stress this too strongly!
Electricity NEVER misses a chance to bite you

A pretty common way to earth (ground ) the system is as folllows.
All exposed metalwork, chassis etc is connected to power line ground or, if you have no ground as in some parts of US and Europe , to the ground stake or whatever.
Then the star point for signal etc is taken to chassis ground above via a network of a 10 - 100R/2Watt in parallel with a 0.1F 250v capacitor. This acts as an "earth lift" to avoid hum loops.
The fact that you have a loud hum when all is connected in your system means you possibly have a ground loop. You will need to experiment with methods of grounding to get the best results and minimum hum but it will depend very much on whether you are using the "star" or "daisy chain" principle

Star = each item has its own ground to a common point (power line ground?) and the interconnects hve only one end grounded.
Daisy chain = all items except the power amp have their power line ground lifted and ground connections are through he interconnects in, say, the following way.
phono stage > pre amp > main amp.

Regards

John Caswell
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Old 18th December 2006, 07:15 PM   #5
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John,

Thank-you for the reply. I already have the chassis connected to IEC Earth via a braided strap. I felt that this should be the first thing done.

The Broskie PCB has a star ground built into it, and I believe that signal and B+ converge at that point. So my HT is connected to the PCB via 2 pads, one labelled B+, the other labelled GND. There is a second pad directly connected to the GND pad, which can be jumpered to a bolt-hole for connection to the chassis via mounting bolt. When I did the jumpering, there was no difference.

So, one option would be to take a single wire from the second pad (connected directly to GND) and run it to the bolt in the chassis that I use to connect the chassis to IEC Earth. This would form another star ground.

Does the above sound reasonable?

Regards,
Charlie
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Old 18th December 2006, 07:23 PM   #6
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Are the input jacks isolated from the chassis? And where do their commons connect?

Same question for the volume control.
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Old 18th December 2006, 07:45 PM   #7
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Sy,

I isolated all jacks from the chassis. In fact, they are on extended lengths of cable and not attached to the chassis at all as I want to get the Aikido working before I dismantle my passive preamp for good quality jacks and selector switch.

The volume pot is wired similarly with input jacks connected to pot directly. Signal + from jack to common leg of pot. The +ve side of pot (ie the one that decreases in resistance when pot turned clockwise) to signal input on PCB. The jack signal -ve to the third leg of pot, which is also connected to signal gnd of PCB.

I suppose that I could try using my passive preamp to test the Aikido. It uses a bussed jack gnd to a star-earth that is chassis coupled. However, it is only a 50K pot wired in shunt.

My plan has been to use the Aikido as preamp and for source selection and volume control. I want to get a stepped attenuator, once I confirm that the Aikido works without hum.

Maybe, I need to rewire the jacks without the 100K pot, check for hum using a source with built-in volume.

Regards,
Charlie
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Old 18th December 2006, 07:49 PM   #8
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I think your pot is wired incorrectly. External input to the "top" of the pot, input common and "bottom" of the pot to the star ground on the board, and middle (wiper) to the preamp input on the board.
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And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
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Old 18th December 2006, 07:59 PM   #9
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Sy,

Thank-you for the reply. I wish I could remember how I wired the pot. The volume goes up and down correctly, but I may simply have got the PCB signal and jack signals switched. I will check this when I get back home.

Regards,
Charlie
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