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Stuart R · 11th Aug 2020, 4:50 pm

I was in a bit of a hurry to build mine. The recent repair of a Strad PW461 for a friend was nearly complete, but the sounds coming from it didn't make for relaxing, everyday listening. The deadline for delivery was approaching – fast.

Gary's amplifier PCBs have been made very meticulously on Manhattan style 'tiles' and David has improved the design further with a custom PCB. I didn't have the time, nor the facilities, but further web-searches found the article by George Smart who is also mentioned in the 2018 article. George's website has the complete solution; he has produced a PCB and had a limited number for sale, along with the 'binocular' ferrite cores. The website also includes a full parts list, with other components sourced from RS. Interesting to note that the commercially-made Loop that started George's project off is built on Veroboard, so maybe it wouldn't be a disaster to resort to a more readily available construction technique?

I usually buy from CPC and Farnell, but the RS prices aren't too bad and the quantity/price of copper wire for the transformers gave an instant £15 saving with RS. That, plus my laziness made me open an RS account an order from them. Connectors, cases and accessories came from CPC, mainly as I wasn't convinced the RS BNC socket came with a fixing nut and washer and they were encouraging me to buy a pack of 25 fitting kits, costing £11. In the end, I opted for bulkhead mounting BNC connectors, rather than PCB mount.

Making the Outdoor Loop

A trip to B&Q sourced some 20mm diameter electrical conduit, 3.1m long and a round, 'T-piece' junction round box. I'd watched a YouTube demonstration of someone using a heat gun to bend this into loops, it seemed worth a go.

I made a rough former with wood screws on chip board for the first loop. There are a few pitfalls with this method:

When heated, the conduit stays solid for quite some time then suddenly becomes flexible. At which point the cross-section can accidentally be distorted with light finger pressure.
The weight of any hot conduit hanging over your work surface will cause it to droop. For the second loop, I worked within a smaller circumference of my former so the warmed conduit was always supported. A nearby sawing horse also helped.
The second loop was made during warmer weather, the conduit became pliable much more quickly.
The former's screws make indentations on the conduit as it is bent around them. I reduced the radius of the 'screw circle' and added a strip of cardboard to stop this.
Whilst bending the conduit into the circle, the centre of this bend tries to move outwards, creating another kink. It's a constant game of spotting these and putting another screw in on the outside of the curve to stop this happening. I wrapped the screws in gaffa tape or wedged the tube in place with a rounded cardboard tube to stop more 'notches' appearing.

Pictures:

Materials gathered
Circle sketched out on chipboard, not enough screws in position
Adding more screws, but still get a 'stepped' finish with notches
Cardboard Jacket around screws to reduce notches in heated conduit

11th Aug 2020, 4:50 pm	#2
Stuart R Heptode Join Date: May 2011 Location: Letchworth Garden City, Hertfordshire, UK. Posts: 693	Re: Lockdown Loop Aerials I was in a bit of a hurry to build mine. The recent repair of a Strad PW461 for a friend was nearly complete, but the sounds coming from it didn't make for relaxing, everyday listening. The deadline for delivery was approaching – fast. Gary's amplifier PCBs have been made very meticulously on Manhattan style 'tiles' and David has improved the design further with a custom PCB. I didn't have the time, nor the facilities, but further web-searches found the article by George Smart who is also mentioned in the 2018 article. George's website has the complete solution; he has produced a PCB and had a limited number for sale, along with the 'binocular' ferrite cores. The website also includes a full parts list, with other components sourced from RS. Interesting to note that the commercially-made Loop that started George's project off is built on Veroboard, so maybe it wouldn't be a disaster to resort to a more readily available construction technique? I usually buy from CPC and Farnell, but the RS prices aren't too bad and the quantity/price of copper wire for the transformers gave an instant £15 saving with RS. That, plus my laziness made me open an RS account an order from them. Connectors, cases and accessories came from CPC, mainly as I wasn't convinced the RS BNC socket came with a fixing nut and washer and they were encouraging me to buy a pack of 25 fitting kits, costing £11. In the end, I opted for bulkhead mounting BNC connectors, rather than PCB mount. Making the Outdoor Loop A trip to B&Q sourced some 20mm diameter electrical conduit, 3.1m long and a round, 'T-piece' junction round box. I'd watched a YouTube demonstration of someone using a heat gun to bend this into loops, it seemed worth a go. I made a rough former with wood screws on chip board for the first loop. There are a few pitfalls with this method: When heated, the conduit stays solid for quite some time then suddenly becomes flexible. At which point the cross-section can accidentally be distorted with light finger pressure. The weight of any hot conduit hanging over your work surface will cause it to droop. For the second loop, I worked within a smaller circumference of my former so the warmed conduit was always supported. A nearby sawing horse also helped. The second loop was made during warmer weather, the conduit became pliable much more quickly. The former's screws make indentations on the conduit as it is bent around them. I reduced the radius of the 'screw circle' and added a strip of cardboard to stop this. Whilst bending the conduit into the circle, the centre of this bend tries to move outwards, creating another kink. It's a constant game of spotting these and putting another screw in on the outside of the curve to stop this happening. I wrapped the screws in gaffa tape or wedged the tube in place with a rounded cardboard tube to stop more 'notches' appearing. Pictures: Materials gathered Circle sketched out on chipboard, not enough screws in position Adding more screws, but still get a 'stepped' finish with notches Cardboard Jacket around screws to reduce notches in heated conduit Attached Thumbnails Last edited by Stuart R; 11th Aug 2020 at 4:58 pm.