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Old 25th February 2012, 08:30 AM   #2501
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Default Humming along nicely

Has anyone got any ideas why my DCB1 has an almost inaudible hum ?

It does vary with volume and does not goo away with the interconnects disconnected.

My thoughts are:-

1. The 0V to the transformer could be a bit heavier gauge.
2. The 0V for the volume control is attached to J3.
3. The input 0V arrangement.

(3) Due to the lack of 0V connections for the inputs I have commoned them at the input sockets and then connected them to the PCB with heavy gauge wire.

I'm discounting pickup as this is the same box that I used for the B1 and that had no pickup problems with unshielded wiring.
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Old 25th February 2012, 09:36 AM   #2502
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Its your groundin scheme. My cb1 is dead quiet. Pcb needs to be star point. Fyi, i dont have my case grounded, whol thing is floating. I see you like Mundorfs the best. Nice neat work, btw
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Old 25th February 2012, 09:42 AM   #2503
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I've still got the Obbligatos attached to the B1, they will go in eventually.

I've just noticed that I've got 100mV ripple at the input to the regs, ie after 2 x 4700uF, that seems a bit high to me with such low current draw.

I'm just going to piggy bank some 10000uFs across each rail at the inputs.
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Old 25th February 2012, 09:59 AM   #2504
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I would recommend running the input ground wire to the ground tag on the pot and from there to the centre connection of the input on the pcb.Thats how mine was done and I had no hum;perfectly silent.
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Old 25th February 2012, 10:05 AM   #2505
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Hi KatieandDad, you might want to check out my blog post linked below to get an idea of ripple and how CRC can reduce it. here is an excerpt (the pictures in the post really show the effect though).

Quote:
The reduction in ripple from directly after the bridge to the input to the regulator is basically from ~110mV / div to less than 2mV/div. Load for these tests was approximately 125mA
http://www.diyaudio.com/forums/blogs...-progress.html

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Last edited by wintermute; 25th February 2012 at 10:38 AM. Reason: spelling
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Old 25th February 2012, 10:08 AM   #2506
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Well the extra main reservoirs brought the input ripple down to 50mV.

I guess I'll now have a go at re-routing all the 0Vs.

What a pain.
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Old 25th February 2012, 10:43 AM   #2507
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Default All gone quiet over here

Thank you all for your comments and help.

Re-routing the 0Vs ALL to the point between the reservoirs has cured the humming and all is now silence.

Beggars the question why are there 0V connections on the PCB for inputs and outputs ?

Case is connected to Mains Earth. There is NO connection between 0V and Case Earth.
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Last edited by KatieandDad; 25th February 2012 at 10:48 AM.
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Old 25th February 2012, 10:59 AM   #2508
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Just to make sure that everything is as it should be.

I'm currently running 22R's which give me about 63mA.

No heatsinking as you can see.

The circled MOS-FET is running warm, the others are all cool. (SORRY - I've drawn that wrong it should be the one to the left of it that is running hottest.) But the -ve reg is running hotter than the +ve. After 40 mins without sinks they were at about 40 Degrees. I'm going to put a small sink on each to help them out.


I presume that is the timing circuit that is helping the +ve rail to run a bit cooler as the shunt has less to do ?
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Last edited by KatieandDad; 25th February 2012 at 11:09 AM.
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Old 25th February 2012, 11:35 AM   #2509
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This is so frustrating, the distortion is back again and the thump on "Turn On" but on the other channel.

I think I'll just opt for the basic B1, I can't hear the difference and my B1 PCB is of better quality than the DCB1.

NOTE - BOTH PCBs are Home Brew and in NO WAY reflect the quality of boards being offerred by other members of this forum.
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Old 25th February 2012, 11:38 AM   #2510
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I run all ground connections to the center of PCB (like your pic), on this type of board on between the four caps.
From there I run a CL60 to earth IEC, and a IEC then connects to chassis.
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