Building a symmetrical PSU B1 buffer

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.
 

Attachments

  • DSIR9366.JPG
    DSIR9366.JPG
    188.6 KB · Views: 561
  • DSIR9330.JPG
    DSIR9330.JPG
    229.8 KB · Views: 549
Just another Moderator
Joined 2003
Paid Member
Last edited:
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.
 

Attachments

  • DSIR9368.JPG
    DSIR9368.JPG
    216 KB · Views: 525
Last edited:
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 ?
 

Attachments

  • DSIR9368.JPG
    DSIR9368.JPG
    222.9 KB · Views: 510
Last edited:
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.
 
I've put the DCB1 on SWAPMEET.

I personally can't hear any difference between the DCB1 and my B1, but that might be my old ears or choice of components or anything else you might like to speculate upon.

As my B1 is slightly better built than the DCB1 I am opting for the more reliable one of the two.
 
I might still try my B1 with the SALAS Shunt Reg.

I've got to use caps anyway because my power amp is DC coupled so I might as well use the more reliable circuit board.

As the DCB1 is only problematic around the relay (cos the tracks are too close together), I might just chop it short to leave me with the wrking PSU.

With 22R I'm running 63mA.

I did read that someone was running at over 600mA. That's going to get WARM.
 
Watch out for Noise

Hi guys, and congratulations on a great forum.

I would like to share what I have learnt from building and testing your DCB1.
I have recently completed a preamp which uses the DCB1, an LDR attenuator and remote volume control. The unit replaces an passive preamp with ALPS pot.

I am very happy now with this new preamp, but I did have an interesting hickup! On connecting the new preamp to my system I was happy to hear immediate improvements in detail, definition and clarity but..... something sounded wrong. The midrange sounded rather strangled and un-natural.:( A friend was adamant that I should leave it to "run-in", but after a week things weren't much better.

I resisted the urge to change components and instead started looking around with my scope. I found no problems with the DCB1 itself. The only thing I could find was some ringing on a transformer winding supplying the LDR, and some very minor ringing on the DCB1 windings. (There are 3 seperate windings, one for the LDR, one for volume control circuit and two for DCB1).

Does this ringing matter?

I placed a temporary snubber on the offending supply, adjusting the values to get a smoother waveform. This seemed to stabilise the waveforms on ALL windings. Then I hooked it all back up and had a listen.

....WOW! A different preamp, with natural blooming vocals. A big improvement.:D

So I went back in and replaced the LDR supply rectifier diodes with schottkies and fine tuned my snubber again.

Another improvement in smoothness, reaching into the treble this time.

So what was being affected? I am guessing that noise was coupling across windings and onto the DCB1 supplies, upsetting stability. Your thoughts might vary. One thing is for sure, BEWARE of power supply switching noise and ringing, (even on other windings). It seems to have a nasty effect on fidelity, even at low levels.

Jeremy