Showing posts with label Theory. Show all posts
Showing posts with label Theory. Show all posts

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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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.

Tonebender MKIII clone (Aion Electronics Phobos)

Here is my last build: a Tonebender MKIII clone! The tonebender was initially a derivative of the Fuzz Face, a bit closer to an amp distorsion than a fuzz. (read my post about the different types of fuzz) It became quickly famous thanks to a lot of guitarists like Jimmy Page or Jeff Beck.

The MK2 version used two germanium transistors to get fuzzy tones. However, due to the nature of the circuit, the quality of the fuzz was very dependent on the transistor's gain and characteristics, just like in the Fuzz Face. In order to avoid the selection of transistors, the Mk3 version used 3 transistors, so that the quality of the sound is less dependent on the germanium transistors used. Here is my version:

Tonebender MKIII clone Aion Electronics Phobos

Relay bypass with anti pop system: noiseless and clickless true bypass

Did you like my post about relay bypass? At least I did, and now I use it in almost all my pedals! Thus, they are longer lasting, and we avoid the mechanical noises of a 3PDT. However, I noticed something annoying: the relay bypass makes more "pop" noises than the 3PDT, especially with high gain circuits...

Indeed, relays tend to switch from one state to another much quicker than big mechanical 3PDT switches, which causes the "pop" noises to appear. The gainier the pedal, the more it will amplify the pop and make it louder.

So I adapted a system that I have found on Stompville that suppresses all these noises. Here is the result, with a (very) simple "before and after" video:

Tap tempo tremolo DIY: a complex project!

I am currently prototyping a tap tempo tremolo that I conceived. It is quite a big project, and I have been working on it since nearly 6 months now! Like many guitarists, I really like the warm vintage sounds that you can achieve using tremolo (like in "Bang Bang" from Nancy Sinatra), but also the choppy madness that you can get with square waves, like in "Know your enemy" from Rage Against The Machine, or even weird stuff with high speed tremolos... A really cool effect!

I play regularly in a band, and my point of view is that tap tempo is just absolutely needed for rhythmic effects like delays for instance. Thus, I decided to add one in my tremolo. It is not easy to implement a tap tempo, as you have to use digital circuitry, as we will see later... Here is my current prototype:
DIY tremolo with tap tempo
That is a lot of knobs! You can already notice that there are two footswitches: tap tempo (right side), and the true bypass footswitch that is a clickless relay bypass system! I used the relay bypass system that I conceived, which is completely silent, and more reliable than classic 3PDT true bypass. Indeed, 3PDT footswitches are the main reason for guitar pedal failure. The little switch in the middle of the two LED (bypass LED, and tempo LED) allows you to switch the pedal temporarily. This is nice to add some choppy stuffs while you play!