External 9v power for electro-acoustic guitar

erky32

Has anybody tried capacitor decoupling to run 9v to an electroacoustic?

My Godin is fairly heavy on 9v batteries, and I was wondering if I was to rig a decent sized electrolytic cap to filter out ac from dc at each end, I could supply the guitar from the amp end using a conventional cable and pedal 9v PSU,  a) without risk, b) without induced noise, & c) without compromise to guitar signal.

The way I see it would be to add an inline low voltage hi-C (say 2200µF 16v) at each end , then add the 9v at the amp end direct to cable core, and strip it off at guitar end.

ICBM

I doubt it would work without messing up the guitar signal - the filtering in the DC supply should be effective enough that it will kill the AC in even a buffered signal, and you'll probably at least lose top-end response. Much easier to use a stereo cable - most very power-hungry guitars (eg Line6 Variax) do it like that.

Even that is a lot of a faff for an electro-acoustic though - personally I would just use rechargeable batteries if it's eating them too often. Batteries are much better for not picking up and transmitting noise too.

Danny1969

You don't need a cap that big, your only blocking DC not using the cap as a reservoir ..... there's a few other things to consider but in theory you can do what you want.

The size of the cap will limit the amount of low end that can pass through it, now that also depends on the impedance of the load but in general assuming the input impedance is somewhere between 10 and 50K ish about 220N to 400N non polarized polyester cap would be fine, the higher the value of cap the lower the low end slope off will be. For acoustic guitar you don't generally need to pass anything lower than around 80Hz. So aim for around -3dB ish at 80Hz

Quality of the power supply
A lot of pedal supplies and generic mains adapters generally only contain a bridge rectifier and one smoothing cap, relying on the device that's to be powered to have it's own regulation and further smoothing. You want the DC smooth and noise free before it reaches your guitar so I would generally use something like an L78XXCV regulator and some ceramic decoupling caps in the supply, choosing an input voltage around 3V higher than I want the regulated voltage.

I would mod the guitar internally so V+ appears on the ring of a stereo lead and guitar jack when plugged in, that would do the same job with less hassle

olafgarten

If it uses a standard 9 volt battery, can you not just get a battery clip and rig that to a PSU seperate from the guitar cable?

erky32

Thanks guys for the advice, yes I like @ICBM and @Danny1969 thoughts, the stereo lead is the better way ahead, BTW I wrote to Godin asking about replacing with rechargeables, but they said forget it, they will only last 2-3 hrs!! ....must have a high threshold voltage?? .....but I'm also interested in the point about regulation quality, maybe the el-cheapo Thomann 9v supplies could push a load of noise into the system. I must admit theres a little man inside my head now saying, 6€ every couple of months isn't a lot to pay for a hassle free life!! But at least I've learnt a bit from sharing the idea with you guys, many thanks!