PAIA Stak In A Box Tube Preamp Kit Build.

Hey Everyone,

I've got a new diy project to work on over the next few weeks, recently, I ordered online a new PAIA Stak In A Box Tube Preamp kit from PAIA in the US, it arrived in the post this afternoon.

Okay, so, what is the PAIA Stak In A Box Tube Preamp?

It's a preamp that uses a single 12AX7 tube, plus some extra solid-state circuitry to get that "Tube Stack" sound, but here's the interesting part, it gets the "Tube Stack" sound by deliberately running a 12AX7 Tube at lower voltages than what a 12AX7 would typically be run at in, say an old Fender Twin, or a Marshall amp, according to the kit's manual, the 12AX7 is run at +42V DC at low current, it uses a special circuit based on a CD4049 Hex Inverter IC and a "Voltage Multiplier" made up of some diodes and capacitors to generate the +42V DC, it runs off a standard 12V AC plugpack adaptor, so, no need for dangerous 240V AC wiring.

The PAIA Stak In A Box includes an FX loop, as well as two built-in speaker simulation circuits which can be bypassed, there's also a Crunch, Drive, and Output control as well as a balanced XLR out which you can connect up to a studio or PA mixer.

The kit comes with all the necessary parts and mounting hardware and etc, but the 12V AC plugpack adaptor and front panel are not included, for some reason the front panels for a lot of the kits PAIA sell aren't currently available, so, I have two choices, either make a front panel using a 3U 19-inch rackmount front panel, or a case, both bought from my local Jaycar Electronics store.

The Tube that PAIA supply in the Stak In A Box kit is a brand-new Sovtek 12AX7WA high mu (100) twin triode tube.

The kit looks easy enough to build, and since it doesn't use dangerous voltages, I'd recommend building one for those wanting to get started in building Valve/Tube amplifiers.

I decided to start this thread so I could document the build-process just in case others may be interested in building one for themselves.

Will include some pics and scope screenshots.....stay tuned.

Here's a link to the PAIA Stak In A Box Tube Preamp kit on the PAIA website for those interested in building one: https://paia.com/dp/9210KP_Stack-In-...%29%3C%2Fa%3E/

This looks really cool. I love the idea that it works off 12 V.

Quote:

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Originally Posted by DrNomis_44

The kit looks easy enough to build, and since it doesn't use dangerous voltages, I'd recommend building one for those wanting to get started in building Valve/Tube amplifiers.

I decided to start this thread so I could document the build-process just in case others may be interested in building one for themselves.

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This is a big part of the reason I have never attempted things with amps...and the reason I sold my old Sunn head to a collector. I am afraid of those voltages. Will look forward watching this build!

I have no idea of how to do this - and the acronyms are a puzzle in themselves....

..but I'd love to build my own amp/speaker....

Quote:

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Originally Posted by fender3x

This is a big part of the reason I have never attempted things with amps...and the reason I sold my old Sunn head to a collector. I am afraid of those voltages. Will look forward watching this build!

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.... In my forays into the interwebs.....I've come across the option of creating a tube amp from old tube radios....... (as well as making amps from transistor radios).

I imagine the result would be a straight forward,"punkish" direct amplification of the guitar......

The Stak In A Box I'm building is basically a clean booster amp going into a couple of low-voltage/low current tube gain stages, with the output being fed into two op-amp based cab simulator circuits designed to simulate what a speaker cab does to the output signal of a tube amp, the two tube gain stages are deliberately run at a low current and low voltage HT supply (about +42V DC), the idea is to get the two tube gain stages operating in the non-linear part of their transfer curves to generate a caricature of the "Tube" sound.

I'm going to be popping into Jaycar Electronics tomorrow to buy the rest of the bits and pieces I'll need to build it, I will be taking pics to document the build process, and will also include some scope screenshots so you can see what the preamp does to a signal being fed into it, I'll also post links to sound demos so you can hear what it sounds like.

As part of the build, I've managed to re-design the power supply circuit so that it generates regulated +/- 15V DC to run the op-amps, and the +42V HT supply, as well as +12.6V DC to run the 12AX7 tube's heater, it only needs 12.6V DC at 150ma, I elected to use a toroidal mains transformer with two 12V AC/800ma secondary windings, the original power supply design required a 12V AC/200ma plugpack, reason why I decided to re-design the power supply was to reduce hum/noise levels to a minimum, so I can use the preamp for recording into a Daw (Digital Audio Workstation) like Ableton Live, Reaper, or FL Studio.

Update:

I managed to buy most of the bits and pieces I need to finally start work on building the Stak In A Box kit, including the metal case, so, I will be working on it this week.

Update:

Here's a pic of the finished and fully-populated Stak-In-A-Box Tube Preamp PCB, I had a pic I took just after I started soldering parts on it, but the simcard it was on got corrupted:

Attachment 45851

Yes, that's a real Sovtek 12AX7WA/7025 tube on the Stak-In-A-Box PCB, it is used a lot in tube guitar amplifiers, like old Fenders, old Marshalls, and etc.

That larger IC on the left is part of the circuitry that generates the +42V DC for the tube, the other two smaller ICs on the right form part of the clean booster amp and the two cab simulator circuits.

I elected to use IC sockets to avoid any damage to the three ICs.