Synthrotek Crossfader (CF) and 2hp Buff Mult - DIY Builds

In December 2021, we highlighted a few smaller modules produced by Synthrotek. These modules included the Power Pak, Adapt 1/4 and a Stereo Buffered Mult. The new Crossfader Module (CF) and the new Buffered Mult from Synthrotek are two new modules that join their line of utility modules and we had the opportunity to put them on the build table. 

Just like the previous utility modules, the Crossfader module is a quick and easy build. There are very few hole-through components to complete the module. The Buffered Mult on the other hand, has SMD components and requires finesse when assembling. A novice builder would want to steer away from the SMD soldering until they have had some practice. 

One thing remains true about both of these modules though. Being that both of these modules have a very small footprint in your rack, it is a no-brainer on why they both are“must haves”. Let’s get on with the builds. 

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Module 1: The Crossfader or CF Module

The CF is a passive crossfader module and it doesn’t have the bleed at the extremes like other passive crossfaders. It is ideal for attenuating, mixing or crossfading audio signals (not as ideal for precision voltages). One thing to be aware of is when using unbuffered audio sources, there can be a slight dip in amplitude at the extremes. You can even group several of the CF modules together to bring movement to your modular performances or recording gigs.

Synthrotek Crossfader (CF) - Time Lapse Build

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The CF kit consists of a couple resistors, a slide pot, 3 jacks, a standoff and a slider knob. These parts along with the front panel, PCB and visual BOM are what is included in the kit provided by Synthrotek. Starting with the resistors, place them onto the PCB and flip the board over to tack them down. You can place them in any direction because they are non-polarized. 

Crossfader (CF) - Build Gallery

Completing the Modular Build

Next, attach the slide potentiometer and flip the board over to tack it down. While you are here, install the standoff and then place the jacks one at a time. We like to solder the ground pin to the PCB one at a time as the jacks are being placed. This keeps the jacks in place but doesn’t permanently tack them down.

Once you have the jacks seated, gently place the panel onto the front side of the module. Then set the black screw into the standoff and lastly attach the slider knob to the fader pot. Pat yourself on the back, because you have just completed the Synthrotek Crossfader module. Now go get your fader on! 

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Module 2: 2hp Buff Mult (Buffered Multiple)

The buffered multiple comes in as contender for one of the most used modules in a modular system. This and the non-powered version (aka. passive multiple), allow you to copy one signal and paste it in multiple signals. The Buff Mult from Synthrotek comes in multiple versions and is their second module that utilizes SMD components (MIXIV being the first).

Since this build is a more advanced build, we do not recommend novice builders trying to take this one without some practice first. We used our digital microscope for the build, as well as soldering paste, normal solder and a very pointed tip on our iron to complete the build. 

Builders Tip: Make sure you haven’t had a lot of caffeine prior to taking on an SMD module. You will find yourself very frustrated and your work could get a little messy. 

Diodes and Resistors

Just like other modules, we usually start with these types of components. Even though these are SMD parts, it doesn’t matter. The two diodes need to match the outline on the PCB (two pads on one side and one on the other). Dab a little solder paste or solder on one of the pads and then using tweezers, set the diode onto the pad while heating it back up. It will click and stick to the board. If you need to adjust the placement, heat up the pad and move the part with your tweezers. (This soldering/setting tactic will be the same for all of the parts we discuss in the build). 

Resistors are next and you can place these in either direction on the PCB pads. Since polarity doesn’t matter, just place some solder and then heat, click and stick the resistor as stated previously. Here again, you can use solder paste or regular solder to tack down the parts… it is totally up to you. 

Synthrotek 2hp Buff Mult - Time Lapse Build

IC’s (the chubby bugs)

The ICs or OP Amps are up next. These are the little rectangles with 8 legs (4 per side) around them. ICs are finicky and they require  great care when soldering or handling. One thing to remember is that the dot on the PCB indicates pin “1” of the IC and it needs to be placed toward the notch on the silkscreen.

If you mount these incorrectly, you might as well toss the module in the trash. Be careful not to cause any solder bridges when you are tacking these down. 

We like to use solder paste here and drag a line of it across the 8 pads. Next, place the part in its final resting place and then quickly drag the soldering iron across the legs of the IC. This will suck up the paste and meld the part to the PCB. You can then go back and clean up or remove any bridges if they occurred. After the ICs are done and everything looks good, move onto the capacitors. 

Ceramic and Electrolytic Caps

The Buff Mult has only two electrolytic caps and you want to pay attention to the orientation when placing these parts onto the PCB. You want to make sure that the longer lead goes into the square pad, which has the “+” next to it on the PCB silkscreen. Set the parts, trim the leads and move forward. Again, if you mess this up, toss the module and call it quits. 

Ceramic caps are brown little rectangles and being that we are building the audio version of the Buff Mult, there are only two. Since they are non-polarized, you can place them in any direction as long

Synthrotek 2hp Buff Mult Build Gallery

Power Header, LED and Jacks

As for the power header, most modules use the 2×5 headers. This module uses one row of pin headers that will need to be trimmed very close to the control side of the board to allow the jacks to mount flush with the PCB. After completing the header, set the LEDs into their relative position. You want to make sure the long leg of the LED goes into the circular pad and not the square pad. Do not solder these yet as we will come back to them later. 

Next up are the jacks. You will want to place all of the jacks into the PCB and bend over the ground leave on the two jacks nearest to the LEDs. As you can see from the photo below, it becomes very close quarters moving forward.  

Before soldering everything into place, the front panel will need to be placed onto the jacks. If you have tacked down the ground pin on each jack prior to panel placement, everything should stay in place as you place the panel. You might need to wiggle a jack around but rest easy that they are not just going to fall off when you are placing the panel on. 

After the panel is lined up, hand tighten a few of the nuts onto the jacks. This will keep the panel and jacks in place so you can flip the board over and solder the leads. As for the LEDs, you will want to push the LEDs up to the backside of the front panel prior to tacking them down.

Once this has been completed, tighten down the jack nuts with your Synth DIY Tools and trim any excess leads. The Synthrotek Buff Mult has been completed and its time to rack it up, power it on and start patching! (make sure you plug your power cable in the correct way!!)

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Synthrotek 2hp Buff Mult Introduction

Where do you get these wonderful toys?

Synthrotek has a couple different options when it comes to purchasing the the Power Pak, Adapt and the Stereo Buffered Mult modules. The prices are excellent and the quality of this build is way worth it!

If you are interested in buying the kits or the assembled modules, click on the links below and you will be redirected to their site to purchase! Make sure and tell the gang at SR that we sent you!

Purchasing Links (click to expand)

Our Final Thoughts

Both of these modules, the Crossfader and the Buff Mult are utility modules that play an important role in modular synthesis. These kits are inexpensive and the Buff Mult brings a varying degree of difficulty that many builders admire.

If you are thinking thinking about getting into the DIY world, we recommend the Crossfader module as this is a really easy module to build. The Buff Mult on the other hand takes a little more skill and patience to conquer.

In the end, Synthrotek saw a need for a new module and they filled that gap with these two releases. Head on over to the store and pick a couple up today… and tell them we sent ya!

Comments or Suggestions?

If you have questions about the build process or suggestions/feedback about this article, feel free to let us know by contacting us  We look forward to hearing from you!

Until the next build … 

~ f i N

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