hex sustainer Q's

[alecacca]

Hello!

Over the lockdown I've decided to make a hex sustainer built into an Marlin guitar, without any means of it looking nice but just to get the thing working. And spend the furlough money in a better way than in boxes of Peroni.

Anyway it works better than I thought, but there's two small issues though.

1- The coils heat up quite a bit after a few minutes and I'd like to calculate how much each coil can withstand in terms of Watts per amount of time. The only data I have now is coil resistance around 6ohm, 38awg wire for about 170 turns. The output of the lm386 has spikes around 10vpp but the oscilloscope measures 3.7Vrms when it's full on.

2- this is the most important. All the happiness of the whole thing working got erased as I plugged the guitar in the amp. Whenever I turn the sustainer on the driver coils induce a massive amount of distorted sound in the normal pickup. Stupidly I didn't think about that. the middle pickup, closer to the driver is somewhat impossible to use and the neck pickup is about half clean pickup sound and half distorted interference coming from the driver. Even being quite far from it. I tried isolating guitar and sustainer ground but didn't change much.

I tried using a cage of kitchen foil connected to ground to isolate the guitar pickups from the driver but that didn't change much. I used then a 1mm thick metal plate and that somehow reduces it but still not a good amount.

Do you think I just need to properly encapsulate the non sustainer related pickups in a 5mm steel cage? does thickness have more effect than type of material?

I attached a couple of pictures to horrify you and to show how's the layout.
The hex pickup on the left is the driver and the one closest to the bridge is the listen pickup. On the back there's the 6 preamp/amp, on top 18650's with usb charger and dc-dc converter.

I'll be grateful if anyone had any suggestions so I can finally play this guitar as it's meant to.. through an amp!

Cheers,
Alex

[PRR]

> The coils heat up

When "sustaining"? Or sitting there silent? Should be zero power when zero signal. Heat suggests mis-wire. Possibly no blocking capacitor to the coils.

> a better way than in boxes of Peroni

Miller beer in Italy?? 

[alecacca]

Hi PRR,

They heat up only when sustaining, at rest the output is quiet and current absorption is very minimal.

Is Peroni under Miller?? Not sure cause I'm in the UK atm!

A

[PRR]

You have an implied 2+ Watts in coils but the '386 won't really make a whole Watt of square-wave so the impedance is higher than the DC resistance. It will heat up in 1 or two minutes. It may get too hot to touch, but modern enamel wire can stand that. Mounting and PVC covered wire may be at risk.

[alecacca]

I see. I was thinking to measure how high the temperature actually gets to cause it might stabilise at some point with the ambient temperature.. It seems the enamelled wire I've used keeps together up to 220 celsius. The plastic pickup case probably less! 

I've also just read magnetic metal should be used to isolate the pickups. I'll give it a go.