The Meatsphere

I hate that name. Then again it’s a play on the name Meatball. The Meatball, if you are not familiar, is an envelope filter based on the Mutron III. The Meatball was made by Lovetone who went out of business in the early to mid 2000s. Lovetone seems to be coming back. Hard to tell from their site. The Mutron III was made by Musitronics.

The Mutron III is a envelope controlled filter produced by Musitronics in the 1970s. An envelope filter is a filter effect controlled by the dynamics of the input signal. The volume of the input signal determines how much sweep is applied to the filter effect. Think of it like a wah where the action of the treadle is controlled by the dynamics of the input. Some would refer to this as an auto-wah. The Mustron III had three filter modes  High Pass, Band Pass and Low Pass. It had an input Gain control and a peak control which set the resonance of the filter. It also included a Low and High Range switch and a sweep switch to set the direction of the filter sweep to either Up or Down.

The Meatball added several controls the original Mutron. With six knobs and four multi position switches the Meatball has a lot of options. Besides the original options in the Mutron III the Meatball adds Attack and Decay to control the filter sweep, Intensity controls the range of the sweep, Blend blends the original signal with the effected signal. A Bandwidth control which sets the range of input signal is used to control the envelope. One of the bandwidth settings disables the envelope sweep. The Meatball also adds an Effects loops. This is an important option with the envelope filter since many effects placed before the effect may compress the signal flattening dynamics which confound the envelope generator.

The Meatsphere is essentially PCB that can be used to make a clone of the Meatball. I suppose you could use it to make a Mutron III also. The PCB is available at MusicPCB.com.

I had started a Meatball on perfboard some years ago. I put the thing on a shelf due to not finding an enclosure I was happy with and lacking enthusiasm for the copious amount of wiring required. Hmm let’s see, thats 6 pots, 3 * 6 = 18, plus 4 3 pole 4 position switches, that another 3 * 4 * 4 = 48 wires. Then there’s the four jacks. Two of which are switching, include power jack, LED and foot switch and there’s more wires than I can count. The original Meatball I started has remained on the shelf.

The Meatsphere is a brilliantly conceived PCB. All of the pots and switches (excluding the foot switch) mount to the PCB. This reduces the amount of wiring to a minimum. The PCB neatly fits a 1790NS enclosure available at smallbearelec.com. This enclosure is slightly larger than the common 1590BB boxes used by many DIY stompbox builders.

After thinking about this new PCB and how easy it would make the whole project I ordered two boards and parts to build a pair. The PCBs were $17 each and the enclosures were another $11.25. With switches parts and shipping on everything I figure the cost to be about $60 each. Fairly steep for a DIY project. This is a large project but looks to be a more simple build than most thanks to the MusicPCB Meatsphere PCB.

Here’s a link to a discussion of the Meatsphere on DIYStompboxes.com.

The Meatsphere PCB

The PCB looks great. The production quality is amazing. The board itself is well thought out with pads for external parts well placed. The is two sided and planned so the pots and rotary switches mount on the backside. All of the off board wiring is neatly arranged near the edges of the board.

The board is well labeled. I could easily read all of the part values and soldered everything up without referring to the PDF instructions. I made sure to read the discussion and the notes before starting in case there were any errors.

The Box

I started with the box. Using the drilling template provided by Vince b on the Stompbox forum. The template made things simple and easy. I printed the template taped it to the box and marked each hole with a punch before drilling.

After drilling I checked all of the hole sizes against the parts they would fit, resizing holes with my trusty reamer as needed. From here I assembled the rotary switches and pots. Then I aligned the switches with the PCB. Discussion on the forum seems to say that the rotary switches can fit in any orientation. At this point I wanted to make sure that everything aligned. The drilling template seems to be spot on. Everything aligned perfectly.

On closer inspection I noticed that the height of the rotary switches is taller than the pots. This leave the legs of the pots a little too short to reach the PCB. I tried bending the legs of a pot to make it reach the PCB. This might have worked, but I didn’t like the idea of the extra stress it might place on the solder connection. I decided to solder some wire extensions on to the legs of the pots. I tinned the pots first then soldered a short approximately 3/4″ length of solid copper wire to the leg. A small heat sink work well to hold them in place while I soldered.

I tested one pot in the box after I was done. This looks like it will work well. At this point I figured I’d assemble the whole things and make sure everything fit. I tested out a few different knobs and decided on plain black with points for the pots and some chickenhead pointers for the rotary switches.

Soldering the PCB

I started soldering with all of the resistors. Then followed with the diodes and caps. After the resistors I soldered all of the non-polar caps followed by the polarized caps. Next I soldered the ICs. The Meatsphere uses two ICs a TL074 a quad op-amp in the DIP 14 pin package and a LM1458 in a DIP 8. There was some talk on the forum about the LM1458. The claim is that this chip is a must and should not be subbed with another variety. This seems odd but credible. I decided to use socket.

LED and LDRs

The Meatsphere uses two LED and LDRs to affect it’s filter sweep. These parts are notoriously varied. The board shows VTL5C3 as the part value. These parts are well made and easy to use, but cost more than discrete parts. I used the VTL5C3 for the first board. I think I might use a socket for the next build and test out some of the other LED/LDR parts to see what the difference might be.

Box and test

Once I had everything in the box the first test failed. The envelope did not seem to function. I remember the notes about the LM1458. I had used an MC1458. I tested a few chips from my parts bin and found one that worked. Turns out this chip is also labeled MC1458N, though it appears to be different from the other chips labeled MC1458.

A box with ten controls, six knobs and four multi-position switches, is pretty confusing to operate. I had to label everything. I chose to point the two outer rotary switches straight down in the center position and point the two inner rotary switches to the  inside. I just marked everything with a sharpie and placed a big dot at each position to make the choices clear.