tidbits diy/electronics questions

[doors666]

I often have these small small electronics/diy related questions that I am too lazy to start a new thread about. I guess a single consolidated thread for these is a good idea.

1. I am finally making myref. Was looking at the schematic, do I need a 12v supply also or is the zener used for generating that.

2. I need a metal plate for the trafo, where can i get that. Any jugaad ideas will also do. This needs to be non-magnetic right? I found a plastic one, but that doesnt seem to be damping all that well.

3. How does one determine the size for a heatsink requirement. I can figure out the power wasted in a heatsink, but how does that tell me which heatsink to go for.

4. Does the following circuit has protection against reversal of polarity. what about the cap bank. Are they going to explode or are they safe.



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[linuxguru]

1. I am finally making myref. Was looking at the schematic, do I need a 12v supply also or is the zener used for generating that.

The zeners are used to generate the +/- 12V supplies for the opamp, so there's no need for an additional 12v supply. However, you may still need additional supplies if you plan to use additional boards like a Pass B1 or Lightspeed attenuator later in the same cabinet, so it helps to get a trafo with additional secondaries, even if you don't need it for the initial build.
A typical generic EI for audio use would be 24-0-24, 5A; 2x 0-12, 500 mA.

2. I need a metal plate for the trafo, where can i get that. Any jugaad ideas will also do. This needs to be non-magnetic right? I found a plastic one, but that doesnt seem to be damping all that well.

If you have an EI-core trafo, no additional metal piece is needed, but a Copper-foil belt-band is mandatory (to reduce hum) if not already supplied with the trafo.

If you have a Toroidal trafo, it helps to have a circular rubber mat/isolator with a central hole, to mount the trafo. This can be cut in a jugaad way from one or two layers of a discarded bicycle tube, or just ask around in HW stores for a thin flat bushing.

3. How does one determine the size for a heatsink requirement. I can figure out the power wasted in a heatsink, but how does that tell me which heatsink to go for.

Not the answer you're looking for, but for a 2x MyRef stereo setup I've used generic extruded heatsinks with 4 or 6 parallel fins which have pre-drilled holes for 4 or 6 TO3 transistors, and they work fine.

4. Does the following circuit has protection against reversal of polarity. what about the cap bank. Are they going to explode or are they safe.

Not sure about the context, but a MyRef doesn't need additional regulators or protection against reversal of polarity. You do, however, have to take care with the transformer connections to the board - i.e., 24-0-24 has to be connected to AC1-PGND-AC2. Most blown MyRef boards are caused by accidental interchange of one the AC connections and PGND.

 

[doors666]

If you have a Toroidal trafo, it helps to have a circular rubber mat/isolator with a central hole, to mount the trafo. This can be cut in a jugaad way from one or two layers of a discarded bicycle tube, or just ask around in HW stores for a thin flat bushing.

i have a torroidal, rubber is not an issue, i have a sheet. I have seen a metal plate on the top on which the nut goes. some thing like in this image

Not the answer you're looking for, but for a 2x MyRef stereo setup I've used generic extruded heatsinks with 4 or 6 parallel fins which have pre-drilled holes for 4 or 6 TO3 transistors, and they work fine.

this is more of a generic question, not with respect to myref. say while using a 20v supply on a 7812, drawing 1A will dissipaate about 8W. How do i know the heatsink requirement. or say while making an F5, how do I know the minimum heatsink requirement if I know the power dissipated. Want to take the guesswork out of it.

Not sure about the context, but a MyRef doesn't need additional regulators or protection against reversal of polarity. You do, however, have to take care with the transformer connections to the board - i.e., 24-0-24 has to be connected to AC1-PGND-AC2. Most blown MyRef boards are caused by accidental interchange of one the AC connections and PGND.

This is not for myref but some other experimental stuff i was trying. the input goes to output through a diode, with some assistance from the bulk capacitance in case of high current requirement. the input and output on the circuit is dc. how to protect the caps from reverse voltage.

 

[linuxguru]

i have a torroidal, rubber is not an issue, i have a sheet. I have seen a metal plate on the top on which the nut goes. some thing like in this

In my case, that circular metal piece came with the toroidal trafo from the supplier. You can perhaps check in hardware stores for a suitable large washer with small inner diameter and large outer diameter - I think it's OK if it is mild-steel or galvanized steel (magnetic) material. It's outside the magnetic circuit of the toroid, so it only interacts with stray and leakage flux and has no impact on the primary and secondary windings.