Salas hotrodded blue DCB1 build

470r carbon resistor

The carbon film , just like metal film, is usually cut to form a helix. Both will have the same inductance if the number of turns in the helix is the same and the diameter of the helix is the same.
Carbon composition does not have a helical form.

Confused now. The BOM says carbon FILM, but if I interpret what Andrew said above and Salas said in post #900 it should be carbon COMPOSITION. Is the BOM right or wrong?
 
I am working on heat sinking for a stage 2, 600mA version.

  • Option 1) Use the case bottom as the heatsink, assuming a roughly 12x12x1/4" plate of aluminum with the MOSFETs bolted to them from the bottom of the PCB
  • Option 2) a single 140x190x32mm horizontal finned plate, mounted fins down in the case, with the PCB mounted on the back.
  • Option 3) A pair of 140x81x44mm vertical finned plates on each side of the PCB, MOSFETS mounted above board and bolted to the heatsink.
  • Option 4) As above, 250x100x55mm
Anybody successful at 600mA with any of these approaches?
 
I fired everything up last night and it was working wonderfully!! Much more 3D, sound is more organic and alive than my previous pre. But after about 30 odd minutes and no music was playing, my speakers suddenly started humming real loudly and the overheat/protect red LEDs were flashing (i'm using active monitors).

I immediately turned off the speakers - the amp's heatsink at the back was really hot. I turned it back on and tried playing some music using my old preamp. Seems to work fine. But the volume output seems to be much lower. I left it for the night and got back to it today again. The volume output is still quite low. I'm wondering if any permanent damage was done to my speakers?

More importantly, i'm not sure what happened to the dcb1 and why it happened. I re-measured the voltage levels, dc offset and resistor voltage levels and they are all same as before, which is fine. Any help on what troubleshooting i should be doing now?
 
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Does not sound like you had DC, but you may had an oscillation between the two components? Long cables? Is the speakers amp AC coupled by the way? Leave the DCB1 on but not connected for an hour and check if for some reason develops DC offset also. If your actives don't sound as loud, there is damage done to them most possibly.
 
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More importantly, i'm not sure what happened to the dcb1 and why it happened. I re-measured the voltage levels, dc offset and resistor voltage levels and they are all same as before, which is fine. Any help on what troubleshooting i should be doing now?

Its highly possible nothing happened to the DCB1 itself. If all offset sampling will measure OK after long in power, then its OK. Tell us more about your source and active speakers, also type and length of interconnects.
 
Its highly possible nothing happened to the DCB1 itself. If all offset sampling will measure OK after long in power, then its OK. Tell us more about your source and active speakers, also type and length of interconnects.
Source is motherboard onboard sound for now . 3.5mm -> 2 x rca to DCB1. Speakers are dynaudio bm5a. They accept only xlr, so i made a rca -> xlr cable using an existing balanced cable. I have no idea if they are AC coupled. I tried looking it up but i found no information regarding that...

I have a feeling i mucked up the wiring inside and one of the joints came loose, causing a short or something.

Also, i realized something strange. When i leave the dcb1 turned on at the workbench, all 4 heatsinks get warm and toasty. But when i'm using the dcb1 to play music, one of the 4 heatsinks is really abnormally cool. Not sure if it's the room fan being the cause of it... but the temperature seems too low to be true.
 
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The signal part has nothing to do with the sinks part. That is the PSU. If its not some draft cooling it, its a very weird thing that I first time hear in the threads. Measure PSU voltage the cool sink's side when it does it, with volume down, and see if its OK still.

Can there be weird sounds erratically coming out of the computer audio card, due to CPU halts, drivers etc.? Remember DCB1 will pass down to 0 Hz.

Also how long are the connections from audio card to input and from DCB1 to the actives? It may be important.

But check all your connections are well done firstly.

P.S. I read in your speakers manual that pin 3 of its XLR input is normally expected grounded when unbalanced to balanced is used. Is it? Did you use the same wring when checked with your other pre and the sound was still low? Says it has several limiting circuits for overload. Are their power plate sinks just warm when its low volume with the other pre now?
 
Cables are approximately 1.5m (max) for each connection.

Hmm i guess the pin 3 works that way? I have the rca->xlr wired in http://www.diyaudio.com/forums/atta...able-where-connect-sleeve-rca-xlr_cablex3.gifthis way (#2):
39966d1109259390-rca-xlr-cable-where-connect-sleeve-rca-xlr_cablex3.gif


Yes the power sinks are the usual warmness when used with other pres. I'm just wondering what could have caused the overload. Could it be caused by any solder joints coming loose and touching each other in the rca->xlr cable? Then what damage could have been done?
 
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I would have been worried if you had said something like 5m to the actives about it may had needed higher value interfacing resistors than 220R not to oscillate on cabling capacitance, but 1.5m is very near to what all people use with DCB1 in home systems.

Both 1 & 2 on the graph ground pin 3 fully. So you had it grounded as your speaker's manual usually expects.

I am suspicious of possible bad joints, the computer's output as a source and what it may give out erratically through a DC preamp as the operating system does stuff, possible peculiarities in the unknown Dynaudio active plate amp, its preamp, filters, on board protection and limiters. As for what it may had happened to it and is lower but still has voice...don't know, from a tripped and stack limiter to burned stuff in a Class D power circuit. Check it with a balanced source with XLR output and XLR ready made cables first.
 
The DCB1 is six circuits tied together.
The common PSU for all power.
The negative shunt regulator.
The positive shunt regulator.
The left B1 buffer.
The right B1 buffer.
The regulated relay mute.

Once the shunt regulators are tested and proved to be working it becomes impossible to damage the PSU and the shunts by outside loading. Even shorting the shunt outputs cannot damage the shunts and the PSU.
The Shunts by design are short circuit proof.

No matter what loading you put on the B1s, you cannot damage the shunts.
No matter what loading you put on the relay, you cannot damage the PSU, there is a protected regulator in between.

If one of the shunt sinks operates at varying temperatures then that points to a shunt regulator build error.
Did you test the shunts for open circuit loading when mains is at highest voltage?
Did you test the shunts for short circuit loading at highest mains voltage?
Did you test the shunts on maximum "normal current" draw when mains is at lowest voltage?

Disconnect the B1s from the Shunts.
Test the shunts properly.
 
Salas: My other preamp is balanced so i run xlr direct from it, so maybe it's the rca->xlr cables with the problem. I shall check and revert back

AndrewT: Thanks for the detailed, technical help. Your advice is flying past my head though - i'm too much of a newbie and i don't know how to do the tests you speak of. Any more specific help please? Thanks!
 
You need a voltmeter that reads DC and AC.
start up the shunt regs.
Let them run for half an hour.
Measure:
the Mains AC voltage.
the secondary AC voltages.
the rectified voltages.
the regulated voltages.
the voltage drop across the CCS resistors.
the temperature of each heatsink.

Now short the regulator outputs to ground.

Repeat all those measurements.

The CCS mosFET will be very hot and even hotter when the mains voltage is at it's highest. The circuit should not be damaged by this test. If it does not recover and operate properly after removing the output short then you have built your HotRod wrong.
When the CCS FET is "hot" the output (shunt) FET is cold during the "shorted" test.
 
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