top of page
  • Writer's pictureRyan

Above Top Secret | Reverse Engineering the Vemuram TSV808

Updated: Nov 6, 2022




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.




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

ATS808 PCB Outline
.pdf
Download PDF • 456KB

ABOVE_TOP_SECRET_ATS808 Wiring Diagram
.pdf
Download PDF • 178KB

ATS808 Faceplate and Drill Template
.pdf
Download PDF • 161KB

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!

7,814 views

4件のコメント


Dorin Pitariu
Dorin Pitariu
3月09日

a fantastic project! Thank you very much Ryan!



いいね!

Old geezer in So Cal
Old geezer in So Cal
2023年7月17日

Just curious, why the high voltage capacitors?

Thanks,

Rick

いいね!

Clement Cochois
Clement Cochois
2022年6月23日

Hi man,

thanks for all your work and your helpful advices.

Don’t want to hurry you but do you plan to share the schematic someday ? I’m very curious about this one. I’m used to build my one TS with Timmy/JR mods and that would be cool to compare.

thanks anyway ;)

Clement

いいね!

fingolfen01
fingolfen01
2022年5月26日

Nice detective work! I can't wait to get this one built! :D

いいね!
Featured Posts
Recent Posts
Archive
Search By Tags
Follow Us
  • Facebook Basic Square
  • Twitter Basic Square
  • Google+ Basic Square
bottom of page