AMB Laboratories DIY Audio

[median]

Hi, I'm not sure of the appropriate forum to post this but here it goes.

I am in the first power on stage of my beta24, however the mechanical relay to the unregulated power supply refuses to trip. I have replaced the relay to see if it was duff, but to no avail. I have also checked polarity and even put the mechanical relay in series with the solid relay (the solid relay does trigger).

The only deviation from the specified build is the transformer, as the correct one wasnt in stock. The transformer im using is:

http://uk.rs-online.com/web/p/toroidal- ... 4E4F4E4526

Has anyone had a similar problem or know of what is likely going wrong?

[amb]

Sounds like your issues are with the ε24 switch circuit rather than the β24...
Which mechanical relay are you using and how is its coil wired?

[median]

The solid state relay is:

http://www.digikey.co.uk/product-search ... =cc1003-nd

and the mechanical relay is:

http://www.digikey.co.uk/scripts/DkSear ... 12&x=0&y=0

both components work as I tested them without the E24 circuit, however im seeing a voltage decay over the mechanical relay.

definately should have posted this in the other forum, but i imagine when i actually get the B24 boards going, there will be another host of problems!

[amb]

OK, what are you using as power transformer to power the ε24? Maybe it's not rated high enough. Measure its secondary voltage when both relays are in the circuit.

Also, the solid state relay you purchased is rated to 120V AC. Is your mains voltage 240V? If so you should use the D2440 instead.

[median]

You are quite right, I am using 240V and have picked up a new D2440

The transformer I am using is:

http://uk.rs-online.com/web/p/toroidal- ... 4E4F4E4526

With both the relays in parallel, the voltage across the transformer is 14.0Vac.

[amb]

With 14V AC, the rectified But pre-regulated voltage should be around 18V. Measure the DC voltage across C1 and see if you get something around that. Also measure the voltage across C2 to see if it's 12V.

[median]

C1 has 16.74V across it and C2 has 11.9V.

I have just picked up a few more bits which will allow me to add a third solid state relay in between the sigma board and the mechanical relay. Its not pretty but it works.

I have "tested" my B24 boards and I can see 4 happy LED's on each, which is a miracle given my track history with a soldering iron.

Unfortunately, the 10,000uF capacitors in the power supply started to smoke, further more, the 22ohm 10W resistors (initial set up only ones) also heated up until they melted the varnish on my desk.

I imagine there is a daft mistake hiding in their somewhere, I will root it out eventually.

[amb]

Smoking electrolytic capacitors probably means reversed polarity.

As for heating of the 22 ohm resistors, make sure you pre-set the trimpots as instructed before powering up! Also check the output MOSFETs to make sure they are all the correct ones in each position (i.e. you didn't mix up the IRFP140N with IRFP9140N).

[median]

Found I had wired the mechanical relay to be closed when the amp was on Any way, I have replaced the 10,000uF capacitors and the 25watt 30ohm resistors (which popped).

However, approximately 60% of the time, when I turn the amp on, I get a continuous arc across the mechanical relay terminals (link below).

http://i.imgur.com/Jl1Zp.jpg

Secondly, you do mention that the 22ohm resistors get hot, however mine seem to smoke and melt electrical tape, is that normal?

Finally the V+ and V- relative to ground are only 5.1 volts so something is seriously wrong here. I will pre-emptively accept blame

[amb]

Are your trimpots installed in the correct orientations? Are they pre-set according to the instructions before powering up?
With all the trimpots in that initial state, do the 22 ohm resistors get significantly hot?