Background
This pedal always intrigued me and was on my Reverb "watch" list. Recently, the prices have SKYROCKETED to $2,000 USD+! Incredible! This is instantly out of my range for buying one out of pocket. Luckily, I have some amazing friends to whom I am forever grateful, and he let me borrow his.... FOR SCIENCE!
Reverse Engineering
This was difficult at first because the circuit board is 4 layers and the traces were hidden between the top and the bottom layers (which are also copper pours).
I used my digital multimeter (DMM) and poked around until I identified each connection. I can confirm that this circuit is unique and does not share too much with the Timmy/Jan Ray. At this time, I am not going to share the schematic but I will share with you two very important things.
The diodes measure ~.61vF which can be your typical 1N914, 1N4148, or 1S1588 if you want to go the NOS route.
The opamp is blacked out however using my scope I was able to determine with a level of confidence that the opamp is a OPA2134PA.
Creating the Above Top Secret (ATS808)
I really wanted to try making my first 4 layer circuit board because conceptually, it would create a pseudo-coax connection between each component and lower the noise floor theoretically. I also wanted to stick with 1:1 component types as the original. The result is truly something I'm happy with and I'll be doing more this way too!
"The Tone Geek Touch"
One of my goals with this circuit board is to make it easy to adjust the saturation, bass, and clipping options so I made the adjustable from the top. The only other opportunity for an optional modification is changing the reverse polarity protection diode to a 1N5817 (forward voltage drop of .2v) vs the stock 1N4148 (forward voltage drop of .72v). This optional change will give a slightly better headroom from the opamp especially since there is an additional 100ohm power supply smoothing resistor in the original design. If you plan on building one of these, it's completely optional to change the diode to a 1N5817. When I did a test on my scope, the only difference between the two diodes is I was able to get slightly more output of the pedal. Clipping/gain remained exactly the same.
For the power supply, I prefer solid polymer "electrolytic" capacitors as used in high-end graphics cards and the automotive industry. The service life and performance of these capacitors will far exceed the original type of electrolytic that is rated for 2,000 hours.
The pictures on the scope are a comparison between a real TSV808 (channel 2) with my ATS808 (channel 3). After auditioning a few opamps, I determined OPA2134PA must be the one used on the original pedal because of the clipping response as well as the apparent rail-to-rail opamp performance. Using a JRC4588, JRC4580, LT072, NE5532, and others would not reach the same output peak-to-peak on the scope but plugging in an OPA2134PA was almost perfect. Please do try different opamps as you may prefer the nature of the other types!
The Above Top Secret name ties in with my personal interest in highly advanced technologies that might be out of this world. 👽
Some photos
Build your own ATS808!
I'm very proud to be the first to market a TSV808-style PCB! Here are some build resources that will expand over time.
BOM Spreadsheet: https://docs.google.com/spreadsheets/d/1pVJ02BixP1Bysd5rCMhDHq2_Vn1_FWQ2Udkb8QfVFTE/edit?usp=sharing
Note on the BOM: Component selection can easily be done with Tayda if you're not picky on component selection being exact as the original. I'm sure it will be 99.8% the same tone as the original. Order the Mouser components if you want the exact original component selection. Jacks and knobs are your personal preference and might need to be sourced elsewhere. I tried to keep the vendors narrowed down to a few to ease the cost of shipping.
1:1 PDF outline and faceplate/drill template
My preferred tools and supplies
PCB Holder | http://amzn.to/2eFxEfj |
Resistor/Capacitor Lead Forming Tool | https://amzn.to/3tkivE0 |
Flush Cut Pliers | https://amzn.to/2Sr8wb8 |
Cardas Soldering Wire Quad Eutectic Silver Solder | https://amzn.to/3tkiGPG |
Solder Tip Cleaner | http://amzn.to/2upj6Ez |
Hakko FX888D-23BY Digital Soldering Station | https://amzn.to/3Mw8kmg |
Klein Wire Stripper | https://amzn.to/3MAeUbw |
22 Ga. Stranded, Tin Plated, Aerospace Grade, Tefzel Wire | https://tubedepot.com/products/22-ga-tin-plated-aerospace-grade-tefzel-wire |
The Tone Geek Touch
The PCB will absolutely allow you to build 1:1 the original circuit. After building a bunch of these, changing two pots (no change to the PCB) will yield bass that goes down closer to a traditional Tube Screamer and still has the TSV808 bass sweep, as well as more natural level control by simply changing the pot to an audio taper.
Specifically, change the bass to a B100k trim pot and the level pot to A10k. You will find this information in the Google Sheet BOM above.
Just in case there are some components out of stock on Mouser
Video coming soon!
