Some of the features are:

• Stereo in & out
• Two tremoloes (one of which can pan between left and right)
• Tap tempo
• MIDI PC’s and CC’s
• Multiple in- and outputs so the tremolo can be placed before or after the preamp
• Speed, volume, depth etc. can be controlled real-time through MIDI CC’s or expression pedal
• Various waves: sine, triangle, ramp up/down, square, patterns, random…

This will be a huge improvement on the pedal tremolo but it’s also a very big project. At the moment there are only ideas, some schematics, a bit of software pseudo-code and an idea about the design:

Next week I’ll probably start with the power supply, the PWM filters and the voltage-controlled amplifiers.

The video shows an older version. Recently I started to rewrite the software because the old software was too unreliable (tap tempo problems, rotary encoders issues, noise).

Some features so far:

- Sine, triangle, ramp-up, ramp-down, square, pattern modulation;
- Tap-tempo with subdivisions (including triplets)
- Very low and very high speeds for weird effects
- Three user-programmable patterns (a la BOSS Slicer)
- Duty-cycle control for square wave modulation
- Fade-in with tap-tempo switch (in ‘special mode’)

Future add-ons:

- Stereo input/output for panning options
- Additional ‘special mode’ features such as compressor, expander, random on/off…

A while ago I decided it was time for something to replace my Peavey Bandit amp. I was looking for a three-channel amp so I could have a separate channel for solo’s. Most three-channel amps however are pretty expensive so I started looking for a DIY-amp that suited my needs. I remembered a three-channel preamp kit that was sold at Musikding.de, and I noticed that they’d added another preamp kit called the Anvil.

The Anvil was designed by Andreas Hoppe (or Andy) and is now being sold as a kit. It’s a high-gain three-channel rack preamp with five JJ 12AX7 tubes, MIDI switching, effects loop, two inputs et cetera. More info is available at Andy’s website (in German).

I decided to write this article to share my experiences and tips concerning the building of this kit for those of you who are interested in building this kit too. Apart from Andy’s site and a couple of forum threads here and there there is not a lot of info on the web regarding the Anvil so that’s why I wrote this post. I’ve also made some modifications to my preamp which I will describe here as well.

Before you start

First of all, this is nothing like building Tubescreamer clone #2352135 on a rainy sunday afternoon! I think I’ve spent about 50 hours on this thing so far and it’s still not completely finished (although I can use it, but I still need to paint the enclosure and apply the decals). Populating the PCB took me about ten hours although I have quite some experience in soldering et cetera. You’ll spent most of the time on the enclosure (drilling all the holes, mounting everything, measuring out all the knobs…) and that’s also the most boring part. You will also need some experience in soldering and high voltage safety, since this preamp uses voltages of over 300VDC. Therefore you need to isolate all the high voltage wires, connect all sides of the enclosure to protective earth (PE), carefully test the board for the first time. Luckily Andy has written a build manual in English (available from his website) which is a step-by-step guide on how to put it all together. All in all this is a big project but if you think you have the experience needed and want to build a good-sounding preamp with plenty of features you might consider ordering the kit!

About the kit

The kit costs 269 euro and contains everything you need: the enclosure, tubes, circuit board, connectors, resistors, transformer and so on. The only thing you need to buy extra are the knobs which you have to choose yourself. Fortunately, Musikding has a lot of knobs to choose from.

Kit contents

Building the preamp

Populating the board is pretty straightforward as all the component values are shown on the PCB’s silk screen. You might have a couple of components left at the end. Carefully check the PCB though for any overlooked components!

When soldering the small output board (where the jacks are mounted on), replace R2003 with a jumper. This is also written in the build manual, but it is easily overlooked so I will notice it here again. If R2003 is not replaced with a jumper the output of the preamp will be very low because of the output relay not switching properly!

As everything concerning the further assembly and testing of the kit is described in the build manual I will proceed with the modifications I did. Just follow the instructions and you can’t go wrong.

Modifications

In the original design all the channels have a bright switch. Personally I don’t like a bright switch for high gain channels so I decided to remove them from the rhythm and lead channels. The lead channel has an additional Presence control which controls the amount of top high (higher than the treble control) is passed to the output. This is a very useful feature, especially for rhythm/lead channels. It is really easy to add an extra Presence control to the rhythm channel, you can just copy it from the lead channel. If you take a look at the schematic you can see that all you need to do is connect a 1n capacitor in series with a 500k logarithmic pot across the rhythm channel’s volume pot!

Another modification I did is the master volume. This lets you control the total output volume of the preamp which is useful when you want to quickly adjust the total volume of your rig. The master volume is a 25k linear pot which basically replaces R405. Be careful to use shielded wire here!

I also recommend to replace all the jacks and midi connectors with better quality ones. The connectors supplied with the kit are not that great I have to say (although the mains connector is pretty solid). For the jacks I used Neutrik NYS216 jacks, they are sturdy, directly replaceable and inexpensive (about 0,50 euro a piece). For the midi connectors I used Procab VCD20 connectors.

I’m still experimenting a bit with this preamp and perhaps I will add some tweaks to the tonestacks later on and post them here. Stay tuned, and good luck!

The preamp in my rack

You can also use it to get some more gain out of an amp or distortion pedal. The circuit is a very common amplifier circuit built around a TL071-opamp. Other opamps can be used as well, but the TL071 is cheap and produces very little noise.

The ‘Boost’-knob controls the amount of boost, but can also attenuate the signal so you can use it as a sort of pre-settable volume knob.

Here’s the schematic:

Notes:

• The maximum gain of this circuit is about 10 dB. If you need more (which I doubt), increase R2 (or decrease R1).  The gain A = 20*log(1+(R2/R1))
• Rp is optional, it’s a pulldown-resistor to avoid ‘switch-popping’ when the effect is turned on.
• The circuit also acts as a buffer since it has a high input impedance (about 1 MOhm). This will give you more overall ‘clarity’ (high frequencies) when you’re using long cables.
• The booster is preferably used at the very end of the effect chain, just before the signal goes into the amp-input (or FX-return when using your amp’s effect loop).

Update: andre has provided a PCB layout for the booster: