Salas hotrodded blue DCB1 build

[df_genius]

hi all I have a problem with my dc-b1 in that the relay isn't clicking in. I am using a 12v g6h2 relay and measure 12v at the wire jumper. Reg voltages are a stable +11.5 -11v. Are there any other checks I can do?

 

[AndrewT]

Check the voltage across the relay diode.

 

[Salas]

Ah, i was looking around every part of the PCB to make sure i didn't miss out anything. Turns out one of the transformer wire wasn't secured properly to the terminal and it was loose.

The whistle/high frequency hash is gone - but the hum's back.

I've tried every conceivable way of wiring up the GND but i can't just get rid of the hum; the hum gets louder as i turn up the attenuator volume. This is even without any source plugged in.

Is it possible that i overheated any of the parts during soldering? Are the FETs particularly susceptible to overheating? But if that were the case, then wouldn't my measured values of the voltage, offset etc be weird/wrong?

The whistle has gone is positive. Does it get warm on all sinks the same now also? Fets are sensitive, but they would just cease if soldered too hot, just getting to hum bcs of that is quite unlikely. Do you have an alternative system to check it out also, even very small one, to see if there is hum there too? Any other source than the computer card? Even an Ipod, whatever.

 

[cersepn]

The whistle has gone is positive. Does it get warm on all sinks the same now also? Fets are sensitive, but they would just cease if soldered too hot, just getting to hum bcs of that is quite unlikely. Do you have an alternative system to check it out also, even very small one, to see if there is hum there too? Any other source than the computer card? Even an Ipod, whatever.

Yea the sinks are all equally warm. You're absolutely right - it was the wind draft that caused some to be cooler than the rest.

Actually the strange thing is i've been testing the dcb1 out with a cd player all this while and the hum's there. But when i tested it with the computer sound card, it was dead quiet despite the lack of attention to wiring detail. Because of the nasty sudden hum that triggered out of the blue, i stopped testing it using the PC.

 

[Salas]

Are all relevant equipment powered from same mains outlet off a strip on same ground?

 

[cersepn]

Yea, same power strip

 

[Salas]

Where does the middle (mains earth) pin of your IEC receptacle goes connecting, talking about the one on that wooden board build.

 

[cersepn]

it's not connected anywhere, will that be a problem other than safety?

btw, i tried connecting the CDP directly to the speakers without the dcb1 and the hum is much much louder than with the dcb1. Can i say then, that it's the cd player with the problem? It's an el cheapo dvd player

 

[Salas]

It looks like a system grounding thing relative to the actives. You probably got no problematic component per se. Two things to try are: 1. Link the mains earth IEC prong to DCB1 earth (middle transformer wire screw terminal will do, or whatever handy near there point on same line). 2. Wire the DVD's chassis to DCB1 earth. See if one of those actions, or both, can help.

 

[cersepn]

Doh! After all that work.. it was really my mistake - the rca plugs were not properly inserted at the CDP, somehow causing the hum and weird noise.

The preamp is whisper quiet now. Zero hum/buzz at all Thank you for all your help!

Now i will get to mounting it inside a proper chassis. Fingers crossed it will be as quiet as it was when mounted on the wood panel

 

[df_genius]

Check the voltage across the relay diode.

Hi, It is 0V

 

[AndrewT]

Then the relay has no trigger signal.
That could be the transistor switch that is not working or some other faulty component.

You need to now measure back through the relay drive circuit to find where the error starts.

 

[parodielin]

10W Sandcast Resistor

I have some of these left around:

Dayton DNR-10 10 Ohm 10W Precision Audio Grade Resistor

10 ohm 10 W sandcast. Would it OK to replace the parallel 68 ohm so I can bring the current to 200 mA?

 

[Tea-Bag]

Yes, that's fine.

 

[Salas]

Hi, It is 0V

Then the relay has no trigger signal.
That could be the transistor switch that is not working or some other faulty component.

You need to now measure back through the relay drive circuit to find where the error starts.

Surely the ''note'' jumper for a 12V relay is installed?

 

[AndrewT]

You are referring to the relay circuit ground return link, located elsewhere on the PCB.

 

[df_genius]

Thanks for the help guys, turns out it was the BC550. All working fine now thanks. David

 

[Salas]

You are referring to the relay circuit ground return link, located elsewhere on the PCB.

The jumper at ''note'' resistor position Is linking the 12V line to the relay.

 

[Salas]

Thanks for the help guys, turns out it was the BC550. All working fine now thanks. David

Nice.

 

[AndrewT]

both those resistors are in parallel. Only one is needed to supply the relay coil.

I have split those resistors in a MEZ build, one feeds the mute/unmute relay with 15Vdc from a 7815 using 2k as the dropping resistor.
The other feeds the selector relays. I use 1k here, but without the current boost at start up sometimes the relay does not fire. All I do is turn the selector and then the (or any) relay always triggers on re-selection.

In my Hyp build I used one resistor to feed the relays and the other resistor to feed the current boost. Again that was 15Vdc into a resistor fed 12V relay.