madbeanpedals::forum

Hello! My first post.
I recently bought the Archibald PCB and I'm about to start building it. I see that the build document lists 1 470pf electrolytic cap as 25v and 2 that are 16v. These are C16, C24 & C25.  I don't see any indication in the document or on the PCB as to which one needs to be the 25v.

Welcome!  That info is on the schematic: C16 is the 25V, C24/C25 are the 16V. 

As long as they will tolerate the 12V bus voltage, anything would be fine - they could all be 16V, or 25V, or 50V.  Higher voltage caps may last a few years longer, or be slightly better in other ways, but they're also usually larger and cost a bit more. 

Ohh d'oh! Of course. Well there's my first post, a complete noob question.

Thank you for answering!

And with the 1mH inductor, there is no polarity? First time I've used this part.

Quote from: joelorigo on January 30, 2023, 09:19:16 PM
And with the 1mH inductor, there is no polarity? First time I've used this part.

No inductors do not have polarity.

Thank you!

Not about capacitors, but I just realized that the power supply I was going to use with the Archibald is center +. Eek! good thing I thought of this in advance. What is a good 12v power supply out there?


EDIT: I'm finding many of the 12v ones are center positive. I did see this:
https://www.sweetwater.com/store/detail/1SpotCYR--truetone-1-spot-reverse-polarity-converter

Is that something I can use with my 12v 750mA center positive supply to power the Archibald. Actually, I think I actually have one from a Godlyke Power All that I bought a long time ago.

Seems like the ma needed are in the build doc, you may need more than that, I can't remember right off, or it may be the other tube drive.


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Yep, it suggests a 500mA. I'm questioning polarity, assuming that it is center negative like most pedals.


EDIT: I now see in the schematic it says center negative.

Quote from: joelorigo on January 31, 2023, 09:31:48 PM
Yep, it suggests a 500mA. I'm questioning polarity, assuming that it is center negative like most pedals.


EDIT: I now see in the schematic it says center negative.

Sorry about that. You can pretty much assume everything is center negative unless it's a fuzz or a deluxe memory man.


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No worries. I'm having trouble finding a center negative 12v supply.  I have an unused 12v 750mA center POSITIVE.

Do you know if I can use the polarity coverer above?

Or this one?
https://www.amazon.com/Voodoo-Lab-Reverse-Polarity-Barrel/dp/B00ADWTYWU/ref=sr_1_3?crid=T8TREUYK7E4M&keywords=voodoo+lab+polarity&qid=1675201352&sprefix=voodoolab+polaity%2Caps%2C108&sr=8-3

Yes, either one of the polarity converter cables you linked to will work.  And you couldn't make one yourself for less than $2.99...

Thanks guys. It turns out I have 2 of the red adapters from the Godlyke Power All I have, and a one with a red end that came with my Pedal Power 2+. I never used them and I'm glad I saved them.

Any opinions on using this for the Archibald? It has 12v and a way for either polarity.

https://www.amazon.com/gp/product/B08SQ8NZ21/ref=ox_sc_act_title_1?smid=A2WETDVOSZN7JY&psc=1

That will work, but you're gonna want to eventually get a decent power supply for yourself. Those universal adapter can sometimes act a little wonky and introduce artifacts into your sound. Someone was troubleshooting theirs because of that very thing, turned out to be a similar power supply.


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

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

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.

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.

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

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?

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.

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.

Quote from: mauman on February 04, 2023, 10:43:47 PM
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.

Nice

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

I use a Voodoo Lab Pedal Power Digital

Quote from: EBK on February 05, 2023, 10:04:56 PM
I use a Voodoo Lab Pedal Power Digital

One of the 12v outputs?

Quote from: joelorigo on February 05, 2023, 10:35:48 PM

Quote from: EBK on February 05, 2023, 10:04:56 PM
I use a Voodoo Lab Pedal Power Digital

One of the 12v outputs?

Yep.

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?

Quote from: joelorigo on February 09, 2023, 01:06:42 AM
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?

No special precautions are needed here, other than being careful around that LM317 voltage regulator.  It gets mighty hot.  And once you get the heater voltage adjusted, it will work for 9V or 12V without needing further adjustment.

Yes, black lead to ground and red to the test point.  Set your DMM to DC voltage measurement mode.

Thank you! Getting close to that point in this build.

Should it be 6.3 exactly? the trimmer I used is very sensitive and it's easy to barely touch it and go over and under. Closest I have gotten is 6.28.

Quote from: joelorigo on February 09, 2023, 10:16:18 PM
Should it be 6.3 exactly? the trimmer I used is very sensitive and it's easy to barely touch it and go over and under. Closest I have gotten is 6.28.

Nah, 6.28 is fine.


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Great, thanks!

Ok, hopefully my last questions on the Archibald before I make post my first build report on this forum!

I finished it and it seems to work. All the knobs and switches do what they are supposed to. And it does sound really good. There is a certain characteristic about the overdrive that is spongy like an amp but also like a drive pedal. It seems to have it's own thing. Thanks for all the advice on this project already.

But, is it normal, that when I have it in Hi-Lo mode, with the Gain at about 9 o'clock, the Hi & Lo knobs at about noon, Bias full CCW, that even with the Level all the way up it is just under unity volume? This has just been at 9v. Have not tried 12v yet.

Quote from: joelorigo on February 10, 2023, 03:28:52 PM
But, is it normal, that when I have it in Hi-Lo mode, with the Gain at about 9 o'clock, the Hi & Lo knobs at about noon, Bias full CCW, that even with the Level all the way up it is just under unity volume? This has just been at 9v. Have not tried 12v yet.

I just tested mine at those settings.  I am at unity with Level just a hair past noon, and it definitely gets louder as I move the Level up from there.

Hmmmm. Let me try it again. It's possible I had the gain all the way down and was getting that result.  Also, I will try it at 12v.

Yea, I misspoke in my Feb 10 post.

What I have is - with Gain full CCW, the Hi & Lo knobs at about noon, Bias full CCW, with the Level all the way up, it is just under unity volume? This is at 9v.

I did try it with 12v and it just over unity with those settings. The only reason I asked is because I even line the sound of the pedal with the Gain full CCW. Just want to see if that is normal.

For anyone following this now or in the future, I switched 12AX7s and the output was significantly greater. One of the tubes I am trying was causing noise in an amp a couple of years ago but instead of isolating which one it was I just replaced both v1 & v2 in the amp. So I had 2 sitting around and I'm assuming I put the problem one in the Archibald first. Unless a bad tube would cause more output.

Well, that sucks but glad it was sorted.