Archibald Capacitor Question

[joelorigo]

Thanks. I won't bother then. I just can't find a 12v center negative unit!

[jwin615]

Can't vouch for it but
https://www.sweetwater.com/store/detail/GTRPWR1--gator-gtr-pwr-1-pedalboard-power-supply-wall-wart-1700ma

[jwin615]

Some of the issues with this circuit and power supplies may be inrush current.
It may draw a nominal 500mA once running, but what's the peak inrush and can the PSU handle it?
Some PSUs will trip a (resettable) fuse and or have other over current protections that cause them to fail to power it if only rates for 509mA.
Most hobby DMMs and even low-mid flukes won't accurately measure inrush.
Don't be afraid to over rate the supply. It's absolutely safe and often recommended in other parts of electronics. If you are only pulling half the potential of the supply, it will run cooler and last longer.
The circuit will only consume the current it needs unless it's a rare constant current/variable voltage deal which -never- happens in audio except some class D amps IIRC.

[joelorigo]

Thanks! That seems like a good 9v with high mA. But the Archibald build doc says it is highly recommended to run at 12v so that's what I'm having trouble finding.

[jwin615]

Appears I copied the wrong tab

https://www.sweetwater.com/store/detail/PowerPlug12--tc-helicon-12v-power-supply

But here's a jameco for less
https://www.jameco.com/z/DDU120150H4530-Jameco-ReliaPro-AC-to-DC-Wall-Adapter-Transformer-Single-Output-12-Volt-1-5-Amp-18-Watt_203036.html

Unfortunately they don't a regulated one that is center negative.
If decide to mod to center positive, you can get a regulated PSU for $14

[joelorigo]

Oh thank you. They both look like what I was looking for. But what are you referring to about "regulated?" I'm assuming that regulated is better and that the sweetwater one is and the jameco one isn't.

And do you mean modify the Archibald to be center positive?

[jwin615]

Regulated is better but not always necessary but is generally recommended. I don't know how the Archibald handles it's power so can't comment on how much effect it would have.
The one at Sweetwater doesn't denote if it's regulated but if I had to guess, it's a regulated switch mode supply. Switching supplies used to be terrible for audio but they've improved greatly over the last 10 years.
I'm old school so go linear regulated when able, efficiency be damned.
If you live somewhere where the mains fluctuate a lot, stick to regulated for sure.
I don't think swapping the pedal connector to center positive would be an issue but maybe someone here that's familiar with the circuit could chime in.

[mauman]

An unregulated power supply puts out a voltage that varies with the load.  Unloaded, a 12V supply may read 24V, but drops to 12V with a 100 mA load (or a 500 mA load, depending on the design.)  You need to match an unregulated power supply to the expected load current in order to hit the right supply voltage for your pedal.

[jwin615]

An unregulated power supply puts out a voltage that varies with the load.  Unloaded, a 12V supply may read 24V, but drops to 12V with a 100 mA load (or a 500 mA load, depending on the design.)  You need to match an unregulated power supply to the expected load current in order to hit the right supply voltage for your pedal.

Crap. I forgot about that. Was just thinking of the ripple and swing with mains.
Looks like there's quite a bit of filtering and regulation going on in that circuit as is so even a cheapo Amazon supply may work without too much issue. Was looking for one related to a music company at least.(jameco supplies shipped with a lot of stuff back when)

Maybe this guy?
https://www.amazon.com/Accessory-USA-Negative-Adapter-Charger/dp/B01LQ23ZJS/ref=mp_s_a_1_12?crid=ZSFC6SONTHIJ&keywords=linear+regulated+12v+power+supply+center+negative&qid=1675551970&s=electronics&sprefix=linear+regulated+12v+power+supply+center+negative+%2Caps%2C121&sr=1-12
Think this is center neg.

[jimilee]

Nice

[joelorigo]

Thanks for the one on Amazon. I looked at so many 12v ones and they were all center +.

[EBK]

I use a Voodoo Lab Pedal Power Digital

[joelorigo]

I use a Voodoo Lab Pedal Power Digital

One of the 12v outputs?

[EBK]

I use a Voodoo Lab Pedal Power Digital

One of the 12v outputs?

Yep.

[joelorigo]

I have another Archibald question. The build doc says:

Before powering up for the first time, set the T1 trimmer to 50%. After powering up, use your DMM to measure the voltage at the test point. Adjust T1 until you read about 6.3v for the heater voltage. With the trimmer in the middle, it will already be very close to that.

I have only had to bias a pedal couple of times so I want to be clear on how to do this. With my DMM put the black lead on a ground point on the pedal and the red lead on the pad that is labeled "63.v TEST"? Because of the higher voltage in this pedal (my first tube one) do I need to be careful of touching anything while doing this??? And do you have to re-do this bias if you move form 9v to 12v and back?