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Old 4th December 2008, 01:32 PM   #111
Brit01 is offline Brit01  United Kingdom
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Will the placement of the tranny's have any effect on the psu and main board?

I mean if they are close to the tube and other components could there be any unwanted side effects?

I'm thinking I could build a base for the tranny's totally separate from the main board and psu to isolate them otherwise they will be very close to the circuitry.
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Old 4th December 2008, 02:29 PM   #112
Renron is offline Renron  United States
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Brit,

Quote:
Originally posted by Brit01
Will the placement of the tranny's have any effect on the psu and main board?

I mean if they are close to the tube and other components could there be any unwanted side effects?

I'm thinking I could build a base for the tranny's totally separate from the main board and psu to isolate them otherwise they will be very close to the circuitry.

Xformer placement won't have much effect on the Mobo or PSU board. Not likely to affect the rectifier tube either.
With the Xformers exposed (up top) that should be enough to mediate their flux effect on the Mobo.
If you are using a choke input on the PS board it will effect the choke dramaticly. Here's how I figured my Xformer / choke layout:
Being cautious not to short the secondaries, apply power to the primary side of both Xformers, set them approximatly where you would want them to live. Clip the leads of your Ohm meter to the choke's two wires and move it around the Xformers.....watch the meter move magicly. When you have found the location that effects the least and your happy with the look, bingo, your done.
Make sure to set Xformer windings at 90* to each other if they are close. A great explaination of this procedure can be found in "Building Valve Amplifiers" by Morgan Jones.

Very nice looking Xformers BTW.
Ron
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Old 4th December 2008, 02:49 PM   #113
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Yes, twin the wires! Heaters too! In fact, twin all wires with AC
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Old 7th December 2008, 09:43 PM   #114
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Today I have been working on the hum problem.
There is most hum in my right channel, and much less in left!

First I removed my old heater-wires, and made new better ones using a proper method. Always follow corners, and far away from the components...
The hum didn't change.

I tried DC-heaters. I have a 13,5V stabilised power supply.
I made a voltage divider between the heaters and some power resistors, and calculated the value of the resistors using Ohm:s law.
My voltmeter measured 6,6 VDC over the heaters, and I thought it was close enough just for a short test.

The hum still didn't change.

Then I made woodturner-fran:s ground breaker circuit.
Didn't help either, but it might be good anyway...

So I switched places of the tubes, just to make sure the tubes are ok.
No change, so I think they are good.

Then I connected my oscilloscope on the output:
Left channel:
Click the image to open in full size.
Right channel:
Click the image to open in full size.
The input is my Squeezebox music-player and it was paused, so this is only the hum, no other signal!
I have a triangle-shaped waveform on the output This is very strange!

I have no idea why this is happening, but I will take a look at the power supply tomorrow.
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Old 8th December 2008, 07:49 AM   #115
Brit01 is offline Brit01  United Kingdom
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Interesting find Olle. Maybe a faulty component on that channel. Very strange. Let me know what you discover.

I'm still trying to figure out what I need to do with the heater bias point on Bas's psu. In cases I've seen they have attached the CT to this but I have no center tap on my tranny's.


Also what do I use as a ground point if I am not using a metal chassis? Just a thick copper rod maybe?
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Old 8th December 2008, 11:18 AM   #116
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About the grounding: This is a good method!
Click the image to open in full size.
A copper bar will work fine!
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Old 8th December 2008, 11:48 AM   #117
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Default Hummm elimination

Stixx wrote:

Quote:
I was struggling with a bit of hum in my first headphone amp for 6 months, until I found out that I had connected the shield of the input wires on both sides...
I too have some hum on a combined phono & line preamp I built. The hum is coming from the phono section, because it's not there from the line preamp. I tried a number of modifications but it's still there.

I was wondering what you mean by: "I had connected the shield of the input wires on both sides." Isn't this how it should be?

In my system I have separate earths for each channel. The shield of the input wires (from the input jacks) goes to the corresponding channel earth point. The two earth points are then connected together and wired to a common earth point.

Could this be what is causing the hum in my system. I know I could try it out and see but there's no harm in asking first.

Regards,
Joe A
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Old 8th December 2008, 11:52 AM   #118
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Quote:

I'm still trying to figure out what I need to do with the heater bias point on Bas's psu. In cases I've seen they have attached the CT to this but I have no center tap on my tranny's.

No center tap on your heater supply? No problem ...attach a 100 ohm resistor to each leg. attach the ends of the resistors together and inject your 1/4 of the power supply there. Instant CT and a place to raise your heater supply and poof no more noise.

I had the same problem with the 2) transformers I used on my dual mono Aikido. One minute I had noise and the next it was gone.

Go thru your grounding. I used microphone wire on the input jacks to the boards and also to the 2) VC's I have.
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Old 8th December 2008, 11:54 AM   #119
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"I had connected the shield of the input wires on both sides." Isn't this how it should be?
No! You should only connect one side of the shield!

Brit01: This is a way to lock the heaters if you don't have a centre-tap!

Click the image to open in full size.
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Old 8th December 2008, 12:50 PM   #120
Brit01 is offline Brit01  United Kingdom
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Thks for that.

So if I understand correctly, also trying to visualize my JB Aikido board and Bas's psu,
I would connect the Hot and Neutral cables from the secondary with 2 resistors and ground the mid point?

Sounds a bit dangerous.

What would happen if I just connect the + and - cables from the secondary to the board without a center tap or this mod?

Thks
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