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Old 15th October 2013, 02:11 PM   #1731
AndrewT is offline AndrewT  Scotland
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yes.
Look at the datasheet for explanations.
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Old 17th October 2013, 10:22 PM   #1732
Kreisky is offline Kreisky  Italy
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Hello,

I am sorry if I am off topic ... but I have soldered the components to change My-ref A in My-ref C in that way:

Click the image to open in full size.

Click the image to open in full size.

I don't have yet turn on the amp, do you think it is right ?

I have used SMD where it was possible to solder them, here is a picture:

Click the image to open in full size.

Click the image to open in full size.
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Cairn FOG2 - My_ref C - DIY speakers

Last edited by Kreisky; 17th October 2013 at 10:33 PM.
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Old 17th October 2013, 10:44 PM   #1733
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Quote:
Originally Posted by Kreisky View Post
I don't have yet turn on the amp, do you think it is right ?
At first glance, yes, it seem right.
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Old 18th October 2013, 08:42 PM   #1734
Kreisky is offline Kreisky  Italy
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Originally Posted by ClaveFremen View Post
At first glance, yes, it seem right.
It's now playing
I don't know if I prefer the A or C version... but, ok, I've listen only 2 songs The high frequencies are more defined...


Thanks Dario !
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Old 18th October 2013, 08:46 PM   #1735
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Thanks Dario !
You're welcome
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Old 21st October 2013, 08:23 AM   #1736
Kreisky is offline Kreisky  Italy
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There is a problem, I have a hum
The first time I turn on the amp I didn't hear any noise, I listen to music for about an hour.
The day after when I power on the amp, I hear the hum. I am not sure that the first time the the amp was silent... but I didn't notice any noise.
Anyway, the the "A" version has run for two years without any noise, totally silent.
The amp is not in a metal box, it just lay in a wood table...
The body of the pot is connected to the cold (signal).
The GND (PCB) is connected to the GND (IEC) by a 47 ohm resistor.
The body of the selector is not connected to the cold pole.

If I move the wires there is no change in hum noise.
I know that a metal box is better... but it has run silently for more than two years

I have also change C29 and C13, the new capacitor (SCR MKP) is a bit bigger than the old one and now C13 is touching C9 and C15...
Here is a pic :

Click the image to open in full size.

Any ideas to solve this hum ??
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Cairn FOG2 - My_ref C - DIY speakers

Last edited by Kreisky; 21st October 2013 at 08:29 AM.
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Old 21st October 2013, 09:13 AM   #1737
AndrewT is offline AndrewT  Scotland
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You have quite large AREAs of loops at all the In/Out sockets.
Tighten these up, a lot.
The speaker outputs at the PCB have enormous loop AREAs.
You should look at using longer wiring and ensure the twist is kept for as long as possible right up until the twist reaches the PCB. Then make very short wires to the two tapping points. Keep the two untwisted wires very close to the PCB to minimise the loop areas between the PCB current and the wire current.

I somehow doubt this will cure the hum, but it might reduce it.

I suspect you have changed something else.
What did you change? See the brown wire of the right hand pair and that it passes directly along the top of the left hand white capacitor ! That is really asking the current in that speaker wire to affect the current in the capacitor.
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Old 21st October 2013, 04:28 PM   #1738
Kreisky is offline Kreisky  Italy
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Quote:
Originally Posted by AndrewT View Post
You have quite large AREAs of loops at all the In/Out sockets.
Tighten these up, a lot.
The speaker outputs at the PCB have enormous loop AREAs.
You should look at using longer wiring and ensure the twist is kept for as long as possible right up until the twist reaches the PCB. Then make very short wires to the two tapping points. Keep the two untwisted wires very close to the PCB to minimise the loop areas between the PCB current and the wire current.

I somehow doubt this will cure the hum, but it might reduce it.

I suspect you have changed something else.
What did you change? See the brown wire of the right hand pair and that it passes directly along the top of the left hand white capacitor ! That is really asking the current in that speaker wire to affect the current in the capacitor.
Thank you Andrew,

I have tried to rewire the IN/OUT and roll-back C13-29 to original capacitor but the noise is still there. I can "feel" the hum if I touch with my hand the woofer, it's quite loud and annoying

I have also bypassed the input selector but no improvement.

The original and silent version was: My-ref A + passive pot (10k). Then I have modified the circuit as you can see in photos above, replaced C13-29 with new cap and added input selector.

So... I suspect that I should roll back to A version The PCB is intended for A version, maybe there is something wrong in new components placement. Any idea ?

marco
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Old 21st October 2013, 06:51 PM   #1739
Kreisky is offline Kreisky  Italy
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I roll back to A version and it is terribly silent. That's nice but...

Does it make sens to try to use normal metal film resistor instead of SMD ? juste to keep the "track" more distant from PCB tracks?
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Last edited by Kreisky; 21st October 2013 at 06:54 PM.
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Old 22nd October 2013, 12:38 PM   #1740
Kreisky is offline Kreisky  Italy
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Yeees

I soldered, once again, the components for rev C (with film resistor instead of SMD) but without R42 (47ohm) and I had again the hum...

Then I tried R42 = 270ohm and... no noise at all
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