Beginner's Gainclone, Safety and, The Power Supply Board (please contribute)

[danielwritesbac]

This is for the purpose of an accessable hifi gainclone amplifier power supply board, it is in reference to http://www.diyaudio.com/forums/showt...9#post1515609, and it is by request.

After some experience with the confusion that can result from rectifiers and layout, I'm somewhat prepared to present a design that's not so confusing. And, I hope that the photographic format can overcome my lacks in writing skills.

However, I'll need some help from the guru's--especially on Earth Grounding needs for the U.K. and international requirements.

Before presenting a design, I'd like to cover safety. And, I'll need some help with that too.

Main topics for safety:
1). Wooden enclosure (safety at the workbench)
2). Safety Earth Grounding (safety during operation)
3). Drainer/bleeder resistors (safety at the workbench)
4). Light bulb operated test unit (safety for components)
5). Power LED (safety at the workbench)

[danielwritesbac]

Wooden enclosure:

Due to conflict in international safety, I can only discuss this topic in terms of using a wooden enclosure. And, personally, I'm clumsy enough that I need a wooden enclosure.

Advantages:
Low cost
Any size
Variety of appearance

One disadvantage is that a wooden enclosure doesn't shield from RF. Therefore we may want a 330 picofared capacitor from + to - of the input at the amplifier board, so that it can block the RF. That isn't vital, but can be helpful.

There's no problem in putting the entire amplifier and power supply together in the same box. An established practice is to put the transformer on the opposite side of the heatsink, so that the heatsink becomes a shield. Ground the heatsink.

Although the wooden enclosure does decrease voltage reference for fingers, etc. . ., it doesn't do a complete job.
Since audio components are all grounded together via the RCA cables, we do need safety earth grounding.

[ibmeris]

http://sound.westhost.com/earthing.htm

[danielwritesbac]

Originally posted by ibmeris
http://sound.westhost.com/earthing.htm

Thanks!!

One of the schematics shows that even if the amplifier is wooden, perhaps the interconnect cable (RCA) goes right to a metal-cased tuner. Reference Figure 1 on that link above.

For a more-complete presentation, I'd sure like a photograph of the 35A ground loop breaker. Reference Figure 3 on that link above.

[danielwritesbac]

The reason that I want a photograph is that the Faston connector of the typical 35a bridge rectifier. . . doesn't match that schematic at all.

On the Faston connector, the + is marked, leaving one to assume that the - is located in the opposite diagonal corner (farthest distance away from the +).

Therefore, the schematic doesn't show a "real" unit. We need to show the real thing.

[danielwritesbac]

Here (click photo) is an example of a heavy duty bridge rectifier.

These are super-strong and long lasting. Some are even shielded, which is a nice bonus if you enjoy listening to your radio.

We're going to use a few, so here's a photo indicating the polarity of the larger models.

Notice: The one connector at a different angle is the +

[AndrewT]

connect + to -
connect ~ to ~
connect ~ to audio ground
connect + to Safety Earth

This gives a continuous 70A rating using a 35A bridge rectifier.
It survives longer (undamaged) than it takes a T8A fuse to rupture and the arc to extinguish on 240Vac mains supply.

The optional components: 10nF to 100nF cap, 2r2 to 10r power resistor and/or power thermistor, can be soldered between any pair of adjacent spades connectors. Since one has 4 spade connectors that leaves four locations for the optional components. I use the 4th location for a low inductance/low power 10r to ensure that the impedance of the network stays fairly low at all frequencies.

[danielwritesbac]

So, if I have understood correctly, the ground loop breaker module (disconnecting network) for the UK has:

A 35a rectifier bloc
A 100nF (code 104) capacitor
A 10 ohm, 5w (or 10w) resistor

And its wired like this photo:

[danielwritesbac]

Here's the United States version for out 10 to 15 amp home circuit breakers. This can be built from parts available at Radio Shack.

Four of 6A (or better) diodes*
*Folks with fuses need the stronger UK version (above post).

A 10 ohm, 5 watt (or 10 watt) resistor

A 100nF (probably printed with "104") capacitor**
**That vendor sells the cap as 0.1uF.

And here's the photo. . .
This version is for use only if your house has 10a or 15a circuit breakers--spec for U.S. houses. Otherwise, please DO use the stronger UK model in the previous post. This weaker model was posted, because its a clear illustration.
(Click photo).

[danielwritesbac]

Originally posted by AndrewT
connect + to -
connect ~ to ~
connect ~ to audio ground
connect + to Safety Earth

This gives a continuous 70A rating using a 35A bridge rectifier.
It survives longer (undamaged) than it takes a T8A fuse to rupture and the arc to extinguish on 240Vac mains supply.

The optional components: 10nF to 100nF cap, 2r2 to 10r power resistor and/or power thermistor, can be soldered between any pair of adjacent spades connectors. Since one has 4 spade connectors that leaves four locations for the optional components. I use the 4th location for a low inductance/low power 10r to ensure that the impedance of the network stays fairly low at all frequencies.

Okay, I think I got the message on where to connect everything except. . . the amplifier side. Considering the big UK power, I came up with this:

The most likely spot to connect, seems to be the Power Star Ground / Chassis Ground, CG, because those examples are the strongest point for connection.