Anyone ever put a 9v pedal supply in an amp?

[chrisd]

Hi! I've got a Fender Blues Junior I'm planning to gut and put something nicer/less buzzy in. I kind of fancy something cathode biased though, and as a result I won't need the bias/SS reverb PT secondary.

As far as I can tell from the schematic (https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Blues-Junior-III-Schematic-Rev-D.pdf), it's 20VAC - so I'm thinking I could convert this to a 9v supply for a small pedal board.

I can't find any other examples on the forum or elsewhere, but looking at things like Belton Brick 5v supplies, or relay supplies, it seems to be as simple as:

PT bias secondary -> rectifier (maybe half wave to drop a few extra volts early on?) -> big old filter capacitor -> LM7809 voltage regulator -> barrel socket and out to a pedal.

Does that sound right, or have I missed something? And does anyone have any thoughts on grounding? My first thought would have been to ground the negative leg of the rectifier, but presumably that would create a massive ground loop - there would be two paths to the chassis ground, one via the power cable and one via the signal ground. Can I safely leave it floating until it's plugged into a pedal and grounded via the guitar cable?

Thanks!

[vampwizzard]

Id recreate the +/- 15V secondary circuit and swap D7 and D8 with 9.1 or 10V Zeners to get +/- 9V

[JB]

We discussed this just a few weeks ago:
https://el34world.com/Forum/index.php?topic=26789.0
If all that bias winding is doing is supplying the reverb stage then it might not be capable of supplying much current.  What pedal load are you wanting to put on it?  Might be okay for analog stompboxes but not digital pedals.  Dropping from approx 30V to 9V might make the regulator a bit warm too, must be near the limit for that device. 

When I did it I put in a dedicated toroid and a PSU board.  I left it floating in the amp, took it to an isolated multipin connector on the rear panel that took audio, power and midi out via a stage cable to the pedal board.

[vampwizzard]

that winding is 2VA.. 20V at 0.1A. so, you are indeed limited on what pedals will work in circuit.

[chrisd]

We discussed this just a few weeks ago:

Aaargh, apologies for not finding that one.

Thanks for digging up that spec @vampwizzard, that's a shame though - for some reason I was thinking that because it was powering the reverb it must be quite beefy, but I guess two op-amps is nothing compared to a digital pedal.

I usually have a NuX Cerberus multi-effects pedal in my guitar bag, but it's a tight fit with power adaptors etc as well so I was hoping to eliminate one. The spec claims it draws 275mA so I think that's out :(

A separate transformer might still be worth it though, I'll have to see how much space I end up with when I start laying stuff out.

Thanks!

[vampwizzard]

you mightve been SOL on that particular pedal but folks like benson and peavey have put solid state chorus and phaser and compression circuits in the amps directly.. think Peavey VTX which used +/- 15V. Milkman does a SS trem circuit. That sort of what I thought you were trying to do.