Black Hole : Sunn Model T preamp

This is my last pedal I made : a Sunn Model T preamp in a box! For those who do not know the Sunn Model T, a bit of history...

Sunn Model T preamp

I was introduced to the Sunn o))) band by a friend a few years ago. At first, I was quite amused by their druid look and fan of the Les Paul of the lead guitarist. However, when I listened to them, I was not really found of it.... Until I saw them live!

It was in a festival in June at the begining of the night. We waited for nearly one hour before the show started, first by envelopping the crowd in a thick mist of smoke.

There was a full row of amps on the stage, and we could distinguish the red warm lights of overheating tubes and standby indicators in the dark.

Then a sound.

Sunn o))) concert

And what a sound! I think I have never heard a band play that loud. It make the whole crowd's chest vibrate in rythm with the heavy Nâzgul music played in this mystic mist in the night of June... What an experience! I think the only way to understand this is to see them live, it is a crazy experience that almost looks like a ritual...

Since then, I have becomed quite obsessive with the amp they used to achieved that heavy sound: the Sunn Model T.

History of the Sunn Model T

Originally, the first Sunn amplifier was created in the late 60s by a bass player who thought his amp was not powerful enough for large stages.

The first model T was marketed as an amp that could suit both guitar and bass, a 150 Watt beast with four 6550 tubes, inspired by the Fender Bassman 5F6A amp.

Sunn Model T head

There are two channels, a bright and a normal channel. It is possible to use both for maximum gain and power... Guess which is stoner's favorite setting! :)

It has lots of bass and is super loud! No wonder why stoner rock bands like it so much. It is also very rare and quite expensive nowadays, easily reaching a 3,000$ tag price.

A reissue was released in 2008 by Fender, and is also quite rare. Sunn did also issued solid state amplifiers that are quite hyped today as well like the Sunn beta bass.

My version

So I tried to reproduce this killer sound in a box. To do that, I basically reproduced the preamp circuit of the Sunn Model T and replaced the tubes by JFET transistors.

It is very different from the Earthquacker Devices Accapulco God that is completely different and simply use a LM1458. The circuit has nothing to do with a Sunn model T, even if it sounds very good.

I made the layout myself, and added a few modifications to have more gain. There is a LPB1 boost before the preamp, that you can switch on or off with a DPDT switch, and tweaked a bit the circuit to make it a bit more gainy,

Sunn Model T preamp

The preamp is wired with both channels added for more gain. Turning a dial up makes this channel louder, but it is also possible to cut a channel by putting the pot to zero. So you can choose easily between

Good news is: I made the PCB available if you want to build one for yourself:

 Make one yourself

Through-hole JFET are very hard to come by these days, so I made the layout compatible with SMD JFET. Most of the through hole JFET that are available online are not legit, so I used Fairchield SMD J201 instead. It is however totally possible to use through hole transistors as well.

Sunn Model T preamp JFET inside circuit

Even if I made it gainier, it is still very usable as a clean preamp, or as a light drive. It is possible to use it as an overdrive, the JFET are sounding very well for this, there is a nice warm crunch which is quite different from diodes clipping.

The three band EQ is very nice to switch from a heavy bassy drive to a light crunchy drive with more mids and trebles.

When the LPB1 is activated, you go directly in "beast mode", super heavy, almost fuzzy drive that sounds actually quite like Sleep Dopesmoker album

How does it sound?

Here is a short video I recorded to give you an idea of the sound of this little beast!

Circuit Analysis

This circuit is basically the original preamp circuit plus the three band EQ and a few tweaks to have more gain, pretty much like the Supreaux Deux I made before.

Here is the original schematic:
Sunn Model T original schematic

Basically, I took the top-left part of it and replaced tubes with JFET, with minor tweaks to have more gain, and added a volume stage at the end to have plenty of volume on top.

Here is my schematic:
Sunn Model T preamp JFET schematic

Let's delimit it in several parts:
Sunn Model T preamp JFET schematic

First, the signal goes through the LPB1, which is a clean boost in order to have more gain. There is a switch first to choose whether you want it or not, depending on how much gain you need. For a more detailed analysis of the LPB1 circuit, please check this post.

1. Bright channel

The bright channel reproduce exactly the amp chanel 1, replacing the tube by a J201 JFET.
Sunn model T bright channel schematic
The signal first gets through a 68k resistor, and a 1M resistor is used to increase the input impedance of the circuit. It also avoid "pop" noises when you activate the effect.

The signal is then amplified with a first JFET transistor, that simply replace the tube in the orginal schematic. The trimpot is used to bias it correctly, the 220uF capacitor increases a bit the gain of it.

There is then a coupling capacitor that prevents any parasitic DC current to get through the circuit, and a Bright pot allows you to set the gain of this stage. The lower its value is, the bigger the signal will be, resulting in more gain later on.

The 470pF removes a bit of trebles as well, increasing the value will result in more trebles in the bright channel.

2. Normal Channel

This is basically the same layout with some minor changes:
Sunn model T preamp normal channel schematic
The only change is the presence of a low pass filter with R7 et C4. It removes some trebles to have a bassier sound. Well, it is the "normal" channel after all!

I also removed the resistor that bias the JFET, in order to have more gain on this channel. This way, I can achieve a very bassy, saturated sound that is very close to stoner rock standard "Dopesmoker" by Sleep

3.Gain and volume stage

This part of the circuit is where the magic operates!
Sunn model T preamp gain and volume stage
The JFET Q3 is smashed with the amplified signals of both channels, and start to saturate. It is this transistor which create the gain of the pedal.

Then, another transistor re-amplify the signal before it goes through the tonestack.

4. Three band EQ

It is a classic passive tonestack that you will find in many other pedal. This schematic was made popular by Marshall amps:
Three band EQ schematic
It is basically three low pass RC filters that will cut bass, mids and trebles respectively

There it is! I hope that you like this blog post! You can follow Coda Effects on the Coda Effects facebook page or on Instagram for more news and infos.

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Enclosure art: how to make good looking DIY pedals

One of the nicest parts of making guitar pedals is having a personalized design. However, it is quite hard to make good looking guitar pedals.

Here are a few techniques to make guitar enclosures pretty! You can of course combine these techniques to get the best looking pedal possible!

I will present you a lot of techniques, from the most basic ones to the most professional looking ones.

1. Bare aluminum enclosure

It is the simplest way to do: just let the enclosure in bare aluminum.

Please don't do that.
DIY guitar pedal bare aluminum
Bare aluminum enclosure guitar pedals simply do not look good. They really look like something cheap and dirty that you have done quickly in your garage, whereas you have probably spent a lot of hours on it!

It can be nice for prototyping though, you can improve the design later on if you are satisfied with the result. (practically speaking, it is very rare to improve the design... and I like good looking prototypes so not for me!)
  • A circuit in a box is better than a circuit without a box... 
  • Cheap
  • Quickest possible method

  • Not really good looking
  • Do not really reflect your hard work and dedication

2. Polished / Brushed aluminum enclosure

This already look waaaaay better than the bare aluminum enclosure, and good news: it only take a few minutes to do!

Here is an example of a Big Muff I have made this way:

Polished guitar pedal

Just grab some sandpaper (I recommend to use different grit, 150 for the beginning and 400 for final polishing), and start polishing your enclosure under running water. Finally, apply a varnish layer to protect it!

Beware: I noticed that the maximum quality of the polishing that you can get highly depends on the quality of the aluminum used. For instance, a "mirror" finish can be really difficult to achieve with low grade aluminum. 
If you want to go for the "mirror finish", be prepared to spend some time on it. Use really fine grit sandpaper and a polishing spray for the last Polish.  Here is a good tutorial
  • Good looking!
  • Easy to do
  • Cheap

  • Can be time consuming
  • Depends on the quality of the aluminum of the enclosure

3. Spray painting

I would not recommend spray painting guitar pedals enclosures. Read my post about it for more detail.

If you still want to go this way, apply really thin layers, at least three times. Wait between each spray for the paint to be dry enough. Finally apply a layer a varnish. For your health, please do it outside and wearing a mask!
  • Easy to do
  • Cheap

  • Time consuming: 3 layers is a long way to go
  • Toxic: wear a mask and do it outside!
  • Wears off easily

4. Hammertone finish

This is a special kind of spray painting that will give an amazing vintage feel to your pedals. You can create really beautiful textures with this kind of paint and it also does not wear off as easily as spray paint.

Here is an amazing example done by Basic Audio:

hamertone guitar pedal

Here is a very good step by step tutorial about how to use it.
  • Easy to do
  • Cheap
  • Looks great!

  • Time consuming
  • Toxic: wear a mask and do it outside!

5. Powder coating 

Powder coat is the kind of paint used on cars, and the one used on most guitar pedals as well. It looks very professional and there is a wide variety of colors available.

Here is an example of a commercially powder-coated enclosure:
prepainting guitar pedals

You can either buy pre-painted enclosures, or make it yourself. Making it yourself would require some space and equipment, but it is not that hard.
  • Really good looking
  • Nothing to do
  • Professional standard

  • Expensive
  • No writings

6. Aluminum etching

Aluminum etching is an easy way to have a custom design without spending too much time and money. It requires a bit of practice though.

Here is a beautiful example:

Aluminium etching guitar pedal
You can find a nice tutorial here. It is not an easy technique to master (requires a bit of practice before managing to have a precise etch), but it can give really good results. Moreover, you get a fully custom design with anything you want on it.
  • Can be good looking...
  • Cheap
  • Fun! You get a fully custom design

  • Hard to make it as sharp and neat as above
  • Beware of acid!
  • Time consuming

7. Reverse etching

It is very similar to the technique above, except that the etching is reversed, so the non-engraved parts sticks out of the paint that you can apply afterwards.

I tried this technique once on one of my first pedals (+spray painting):

Reverse etching guitar pedal

Cody of "They Remained Silent" is an absolute expert with this technique and has written up a really good tutorial about it. LIke etching, it can be a bit long before your perfectly master this technique, but it really worth it.
  • Good looking
  • Cheap
  • Fun! You get a fully custom design

  • Hard to make it as sharp and neat
  • Beware of acid!
  • Time consuming
  •  Requires spray painting...

8. Decal

Decals are a good way to have a fully personalized design. 
Here is a good tutorial about it. Another nice one here on the Big Muff page.

If you are good with Photoshop or Illustrator, you can make your own design on your computer and use it for your guitar pedals. Print it on a decal paper, then apply it on your guitar pedals. You can use prepainting guitar pedals as well.

However, this technique is quite hard to master and to have good results. Most of the times, you will need to apply varnish layers. You can use Envirotex for a professional look,
  • Easy to do
  • Cheap
  • Personalized design

  • Time consuming
  • Not always so good looking

9. Laser engraving

Some folks use a laser etching maching to remove the paint and engraved their design.

The graphics are thus very sharp and neat looking: a laser cutting machine can be as precise as 0.1mm! Here is an amazing example by function f(x) Third Rail:

Laser engraving guitar pedal

However, it does not work very well with dark colors scheme because of the color of the aluminum (dark grey). One other problem is that you will have to have access to a laser cutting machine, or find a supplier that would accept low volumes, and this can be difficult or expensive...
  • Looks amazing
  • Custom design
  • Very precise

  • Requires design of the pedal
  • Can be expensive
  • Requires access to a laser cutting machine

10. Laser etched plate

More and more common on commercial effects these days. All the Greer amps pedals are made this way for instance. 

In France, Anasounds makes its pedals with a similar process, on wooden plates, they look great!

Anasounds Guitar pedals
This is a nice way to avoid painting the enclosure, or having to use expensive techniques like UV printing, and still have very professional looking guitar pedals.

You can combine it with powder coating to get even more pro looking DIY pedals. Like with laser engraved pedals, finding the right supplier can be difficult or expensive. However, it is generally easier than laser cutting the whole enclosure.
  • Good looking
  • Easy to do
  • Custom design

  • Expensive
  • Difficult to find the righ supplier for low volumes

11. Silkscreening

This technique is used by many professional pedal builders. It looks great and you can make hundred of enclosures in a few hours. Walrus used it for their pedals for instance:

Silkscreening guitar pedals

It consists of a fine mesh that will let a special acrylic paint goes through only in specific parts of it (like a pochoir). With a râteau, you can pass the paint over this mesh on a powder coated enclosure, and directly print your graphics on the enclosure. Here is a video of how it is done:

It is a great technique if you have many many similar pedals to make in a row

Making this mesh is quite a complicated process involving projecting UV light on a light sensitive plate, but fortunately, you can order these meshes to specific suppliers. Applying the paint is quite a messy process, which requires both space and practice. 

Once the technique mastered, you can make lots of pedals very quickly. The graphics will be very precisely printed on the pedal, and will last for a very long time. It looks really professional. However, the only problem with silkscreening is that you can only print one color at a time. You have to make one mesh per color and it can become quite time consuming if you want to use more than 3 colors... So adapt your graphics!
Good news is: you can apply this technique to many other usages like making t-shirts or posters for your next gig.
  • Professional looking
  • Custom design
  • Do not wear off

  • Difficult to make it yourself
  • Requires high volumes
  • Difficult to find a supplier
  • Requires some practice

12. UV printing

The nice part about UV printing is that you can print litteraly anything you like on your enclosures :)
This is the technique I use for my commercial projects like the Dolmen Fuzz or Montagne Tremolo:

Coda Effects Montagne Tremolo

UV printing machine are highly expensive, however it is possible possible to lease it. That is what is done by many professional like Kelley Electronics. A solution easily accessible to hobbyist is to use Pedal Parts Plus services.
They can UV printing pedals for a reasonable price. However they are based in the US so you  can unfortunately expect some shipping delays and customs issues... Anyway the people there are great and really helpful so I highly recommend it.
  • Really good looking
  • Custom design
  • Durable and professional

  • Expensive
  • Minimal volumes necessary

There you go! I hope that you liked this post! Show me your best guitar pedal and let's share our ideas on the Coda Effects Facebook page. You can also follow Coda Effects on Instagram.

Relay Bypass: final code

After the crowdfunding campaign, I decided to update the relay bypass code.

Indeed, this first version was nice, but one main drawback that was feedbacked to me is that the switch was activated on release, which was not always very intuitive or easy to handle. Moreover, I wanted to add a "temporary" bypass option in the Montagne Tremolo.

Montange Tremolo Relay Bypass

In this post, I am going to explain a bit the new code and to show you how I did it.

If you have not read my post about Relay Bypass, I highly recommend you to read it before reading this post. All the basics of microcontrollers are presented there.

  Tip! The full code is available on Github. With the relayonpress.c and header.h files, you will have everything needed to code or burn chips.

If you already have a GitHub account, you can Star the project for updates, or Fork it to modify it and make your own Relay Bypass code.

Lets go!

Ground loops and guitar pedals

Yesterday, I received an email from a beginner that decided to make his first guitar pedal. I always enjoy this kind of emails and answering questions is part of the game. This time, he asked me a question that I had several times: "my circuit is noisy, could it be a ground loop?"

Ground loops are part of the legends and myths around DIY guitar pedals. When asking about noise in a setup, it is the most common answer, and is supposed to be the main cause for hum, hiss or other noises that you can have on your first circuits.

Montagne Tremolo PCB

So I decided to write a post about it, starting from the begining:

What is the ground?

The ground connection is the reference point of the circuit, with a 0V potential. On schematics, it is represented by these symbols:

Ground schematic

It is very important that the reference point is the same in all the circuit, so all the ground connections should be connected together!

To make it easier, lazy PCB designers like me usually add what is called a "ground plane". It is a large conductive surface that is connected to ground and allows easy connections of grounds together.

On this picture, you can see the ground plane between the components and the tracks. I circled a pad of R21 that is connected to the ground plane:
Ground plane connection

You can clearly see the cross-shaped pad that connect it to the ground plane.

So what happens if you do not connect the ground connections together? By doing that, the reference point is not the same in every ground connection: you create a potential difference that is to say a voltage! Most of the times your circuits will not work, so pay attention to it!

So, what is a ground loop then?

Most of the times, ground is connected to "earth". This is the third plug that is usually on your power outlets. It avoid electrocutions by connecting metallic parts of the device to ground.

However, it sometimes happens that earth connections are not connected to each other. This can cause a slight difference between the two grounds reference point, creating a small voltage between the two grounds!
Ground Loop

Even if this difference is generally quite low, it is sufficient to generate a current if you connect these two grounds with a jack! This current will generate noise, usually modulated by the frequency of your outlets (50 or 60Hz depending where you live): it is a ground loop!

Ground loop guitar pedals

In this case, the ground loop would be caused by your electrical setup. This happens quite on lot on crowded pedalboards in houses with old electricity installations.

However, the same thing can happen between your effects pedals! Sometimes, each pedal can have a reference point that is slightly different and create current in the ground! This is why it is generally better to use power supplies with isolated outputs.
Ground loop guitar pedals
However, even with the best power supply available, ground loops can still happen between the grounds of the jacks. You understand that it is no simple solution! 

This is why it is important in to design pedals that do not have this kind of problem.
But how to do it?

Ground loop and star wiring

Ideally, multiple path to connect two different grounds should be avoided. If many paths connect ground together, it can create potential differences that will generate noise! That is why a ground plane should not be divided in several parts.

A good practice that I always recommend for your DIY pedals is the "star wiring": connect all ground connections in one point, most of the times at the negative pin of the power supply jack.
This is what I recommend in my post about guitar pedal wiring.

Ground and antenna

As you see, everything is very simple... So let's add one more level of complexity: did you know that the ground connection can behave like an antenna?

That is why it is very important to connect the enclosure to ground. By doing so, you create a Faraday cage that prevents the circuit from being parasited by outside electromagnetic fields. A metallic enclosure is thus a must to make guitar pedals. Avoid plastic enclosure and use aluminum enclosures like Hammond enclosures for instance.

This can also be a huge problem when mixing analog and digital circuits. Indeed, the high frequencies used by digital chips can be received by the analog ground and create noise. It is thus very important to separate analog ground from digital ground physically and connect them only in one point.

This was one of the main difficulty that I encountered when I designed the Montagne Tremolo circuit board. It was quite a lot of work to solve it out!

There it is, I hope that everything is clear for you now! If not, post a comment!

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Icons used to desig the diagrams in this post are from the Noun Project and are protecte under the Creative Commons License.

Development Hell: multiple fuzz pedal

Today, I am going to introduce the concept of Development Hell: it is a special place where projects stay when they need a lot of fine tuning before properly work. Unfortunately, I have a few projects that are still burning there, like the one I am going to present today.

It is a multi-fuzz machine! I always felt that a lot of Fuzz are quite a "one trick pony", they have a very characteristic sound that can be modulated by mods, but still sounds "like a fuzz face", "like a big muff"...etc. Moreover, fuzz are usually quite simple circuits, and I find that allowing one spot per fuzz on a pedalboard can quickly be space-inefficient.

So I decided to create a multi fuzz pedal, with no more than 3 different fuzz inside : a germanium Fuzz Face, a Muff Fuzz and a Companion Fuzz, which should provide the 3 main "flavors" of fuzz in this world: a classic warm, soft fuzz face, a "chainsaw", very raspy Companion Fuzz, and a compressed and heavy Muff Fuzz.

On top of that, I added an upper octave generator that allows to combine it with any fuzz, with a potentiometer to adjust the amount of octave. It is based on the Green Ringer circuit, which is a small, but efficient analog octaver circuit.

And of course, I made it fit in a 125B enclosure...

Here it is in its current form:

Hakko FX888D: a $100 high quality soldering station

Let's face it: your good old soldering iron is not always the best pal to work with.

I had some troubles with mine: no support to put it when I busy doing something else than soldering, which can be quite dangerous if it falls or burn something. Moreover, the power cord was quite short and not very flexible, so it was not always easy to find a good "spot" for it in order to be perfectly comfortable. Finally, it takes a long time before getting hot enough to solder, and 30W is sometimes a bit low to solder big potentiometer or jack legs.

So I decided to invest a bit in a soldering station.

After reading a lot on the web, I have found this little gem: the Hakko FX888D, a Japanese soldering station that you can find for $96 on Amazon

Here is mine:
Hakko FX888D