The new "My Ref" Rev C thread

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#1,721
Thanks Troy, the mu metal band is a little bit cheaper than copper wrap so if there's no advantage in using copper screening, i'll probably go for the mu banded version.

Mu metal band sounds like the sort of name a German hard rock group might go for 😀
 
#1,724
Just finished chasing down a hum problem. It turned out to be a combination of the terminal blocks I was using and the fact that the signal pin inside the RCA could break contact. Part of the solution was to solder the input leads directly to the board - something I had planned to do eventually.

So to Dario - those holes are quit small IMHO, so I'm sure you have experimented with several wire types and sizes. Do you have a suggestion for the beat of the best at that location - RCA to PCB?
 
#1,728
bcmbob said:
That's what I have. Been using his silver coated Teflon stuff for all my builds. Just thought D might have something he likes a lot 😉

P.S. His multi-color multi-size heat shrink package really comes in handy.
Click to expand...

What I like best is in fact the multisize heat shrink package...

Also really nice is the "TFT Teflon 6N Copper Wire Cable" you can find on ebay.

This long grain copper cable has different strand sizes like Kimber cables.

Sadly both are directional and for optimal results you should test them for direction... 😉
 
#1,732
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:

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


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:

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
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#1,736
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 :scratch:

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 :

An externally hosted image should be here but it was not working when we last tested it.


Any ideas to solve this hum ??
 
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#1,737
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.
 
#1,738
AndrewT said:
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.
Click to expand...

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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