Guitar and Bass Effect Pedals

Archive for March, 2011

Name: Tone Zipper Comp

Type: Compression

Power supply: 9v Dc – Center Negative

About: Modifyed Ross compressor with vintage (NOS) CA3080

Artists: Cristi Donos

Name: 10-12 Cabsim

Type: Cabinet Simulation

Power supply: 9v Dc – Center Negative

About: Cabinet Simulator with 2 notch filter mode – Vintage & Modern and Direct output

Artists: Vlad Radoi

Name: Sfc Overdrive

Type: Medium gain Overdrive

Power supply: 9v-Dc Negative center

About: A standard Sfc with a custom made artwork.

Artists: Pierre Picho

About guitar boosters  What’s a booster, what’s its role soundwise? I’ve decided to write this after a long discussion with Peter Welsh on Facebook. I shall try to be punctual and stay on the subject (I’m an engineer not a book writer ). First, you will find there’re quite a lot of booster pedals: Fet Booster, IC Booster, Vacuum Tube booster, Treble booster and so on. The difference? How they sound (in terms of tone) and what you need them to do. However, there are a few aspects to consider: input impedance, the order in FX chain and last but not least buwhat you want it to do (for this i will try to explain the functionality of a booster in terms of the order in FX chain). Moreover, I shall try to provide some help with DOs and DON’Ts. Booster-wise. First: a booster is a piece of equipment that raises you signal level with a certain selectable amount (this amount could be fixed or variable). Take the simplest chain possible: Guitar -> Tube amp -> Speaker Cabinet. And I shall explain the behaviour of a booster in different positions into this chain.
1. We shall modify the chain like this: Guitar -> Booster -> Tube amp -> Speaker Cabinet. This topology is used with a very clean or a mild overdriven amp to get distortion. One could say: ok, but I used a Booster in front of an amp and I still had a clean signal. That is half true, you had a pseudo-clean signal – imagine that an average guitar has an output of about … 200-250mV at the buffer’s output you will have at least 300-350mV at the lowest setting, with this signal you will have a richer harmonic content when the signal will hit your first amplification stage – it’s still a clean signal but it’s on the edge – the more you push this chain the more you will go over the top; at this border between the clean and overdrive signal you will notice a richer sound (more treble and mid-treble content). That is because of the harmonic content. At this point the end of clean signal is near: more boosted signal – more distortion. With the volume control at half you will have an overdriven sound, not too over the top but it will not be a clean signal anymore: it’s a good sound for blues, jazz and things like that, that do require a little bit of bite (not too much; we do not want to play hard rock, we will stay in the clean/mild crunch zone). Over the half setting of the booster you will have (depending on the amp – remember we’re talking about a clean amp or a clean channel of an amp) more harmonic content, more distortion and more clipped signal – a good tone for blues solo and small interventions. Remember that at any given time you can roll-back you guitar volume and change the character of the sound / distortion – you can even go from a distorted sound to a pseudo-clean one only by backing off the guitar volume – and this is THE professional way to do it (you have all the controls you need to shape your sound – guitar volume, booster volume and guitar tone knobs – if any) a basic setup that will sound better then any digital processor or amp-simulation. And keep this in mind – the tone is something personal – there are some general rules but in the end your sound is something that should please you first and then the others.

2. The 2nd scenario assumes that your amp has an FX loop. The chain: Guitar -> Amp FXloop Send -> Booster Input -> Booster Output -> Amp FXreturn -> Speaker cabinet. Some may say that it’s a more complex topology as it involves more cables and more adjustments (you will find out that it’s nothing likes this). You will also wonder – why the hell would I want a booster in my FX loop. Here’s the answer: because I love my amp tone characteristics, but I would like to have a volume boost in which I can find the same sound, but with a higher volume. So as a final sentence: use this if you only want a VOLUME boost and nothing more.
But now, at this point you will have more things to take care of. One of them is the way in which your amplifier’s FX loop is built; is it a buffered or unbuffered one? If it’s buffered then you don’t have any problems (use good cables and good jack connectors and you’re done). But what if my FX loop is not buffered? Well, then you do have a problem. Usually the FX loop is placed between your tone stack and phase splitter stage. On a vast majority the final amplification stage that drives the tone stack is made by a triode that drives the TS from its anode – and here is the problem: collecting the signal from a tube anode results in a signal with a high impedance, high impedance means: NO log cables, NO EMI(electromagnetic interference), NO low impedance in the next chain and a lot of other things that have smaller NO’s. So to use a booster in an unbuffered FXloop you will need: short cables, a high input impedance on the booster input, a good quality cables – if one of those things are not applied … well let’s say bad things could happen: tone loss, high noise floor, volume drop etc. So as a final conclusion: use Boosters in unbuffered FX loops but take care of some “little” things. And use boosters in FX loops if you like to have a volume boost with no tonal modifications.  3. This is the last point of this article and will contain only one sentence: DO NO USE BOOSTERS IN FRONT OF MODULATION PEDALS LIKE: delay, chorus, phasers etc. you will result in a bad tone and you will overdrive the input stage of the effects. If you do use a pedal board use boosters only at the end of the FX chain (it doesn’t matter if it’s in front of the amp or in the FXloop) or in front of OD / Distortion pedals if you need to overdrive them harder (remember that plenty of gain doesn’t necessarily mean good tone).  This is my opinion regarding the use of a booster. It’s not universally accepted knowledge.

Best regards,

Gabriel Tudoran

From time to time i get a lot of questions about Output Transformers for tube amplifiers. I will try to explain inthis article the main difference between 2 types of output transformers (from now on i will refer them as OTP). There is a lot of folklore about this subject … a lot of secrets and a lot a lot of empty words. We will not focus out discussion on how OTP are made or what is the best solution to build one, i will try a more general approach on the subject. And we will start our discussion from the output stage of a tube amplifier, which can be: single ended (SE) or push-pull (PP). You could also have parallel SE and parallel PP but those are just variations from the original configurations.The main difference between them is this (in a more or less trivial way): on a SE output stage there is a constant flow of voltage (and current) trough the OTP, so we can say that the output tube is always open, even more, the output tube is always open at about 70% of it’s maximum power, the result is that: there is always a DC component that flows through OTP.On a PP output stage there are 2 tubes that are functioning like this: when one is open the other one is closed, so for a given period of time through the OTP we don’t have any DC component (in practice there is a small DC component that flows through but we can ignore that… i told ya.. we ain’t going to discuss any level below basic.

Another question that i answer frequently is this: why do you need an output transformer? Well there are quite of few reasons: first is to isolate the high voltage from the tube anode (you wouldn’t like to have 400-500v in your speakers), the second reason is that you will need a impedance adapting between the output tube and speakers (the tube output impedance is at least 4kohm, speaks impedance is no more then 16ohm… so for a optimum power transfer you need to adapt those), another reason is that a tube will not function in parameters if the impedance load is so low, the level of distortion will be high and the tube will be way out of his parameters.So … as we see WE need OTP (at least if we don’t want to make a giant amplifier). So from this point of view the OPT for SE and PP are very different and you should not attempt to use a PP OTP on a SE amplifier, the result will be… let’s’ say hot and smokey. You could use a SE OTP on a PP amplifier … but there is no reason to do that because the PP OTP’s are more easy to get and to build (if you feel so inclined). So remember the main difference between SE OTP and PP OTP is this: SE OTP needs an air gap in it’s core so that the core won’t saturate because of the DC component that flow trough it all the time. This air gap it’s made very simple if you use a E + I core: you take the E core on one side and I core on the other side and put them one above the other, like this EI. Before you put them into place, you put a little sheet of paper between the E core and I core, so you will have a distance of 0.1mm between them and this way the core will not be saturated by DC component. For a PP transformer you don’t need this precaution so the OTP core will be interlaced: one E core, one I core and so on.There is also a little trick you can do for small PP and SE amps, that is not the best practice to do but at least you could use it for testing and why not … for live environment. The trick is this; you can use any transformer as an OTP as long as you respect some guidelines:

- power rating should be larger then the output you expect with at least 10-15%

- for SE output stages you need to do an air gap as explained above

- for PP output stages you need a center tap on your primary winding

If you have all the variable above on OK then you can proceed to the next step: choosing the transformer. You have to keep in mind that the output impedance is reflected in the primary winding by the impedance ratio. To calculate the impedance ratio you need the voltage ratio (you can calculate this very easy): Vprimay / Vsecondary. Ex: if you have a transformer that with a 220v input voltage will put 9v on the secondary, then the ratio will be: 220/9 = 24.44 (this is your voltage ratio). Now we need to calculate the impedance ratio, which is voltage ratio^2, so our impedance ratio will be 24.44 ^ 2 = 597.42, so we will have this: for 1ohm output load in the secondary we will have 597.42ohm reflected in the primary. Remember that the input and output impedance are proportional, so we can say that if we have 8ohm load in the secondary then in the primary winding we will have 597.42 x 8 = 4779.37ohm. So this transformer will be excellent for a SE output stage with:el84, 6n6p (ecc99), ecc81 and other tubes that have a plate resistance 3-4 times smaller then our primary impedance (you could use with other output tubes but you will suffer from power loss). Remember: ALWAYS USE AN AIR-GAP IN A SE OUTPUT STAGE.For a PP output stage we will need a transformer that have a CT (for our example if the transformer is rated for 220v in the primary then we will need a CT for 110v), and keep in mind that an air-gap is not necessary. For a PP output stage you will connect the anode voltage on the center tap and the other to ends each one to the tubes anodes.

Hope this will help you with the experiments that you like to do, but remember this: a small power transformer will not be the same in terms of quality with a special designed OTP.Any comments and questions will be appreciated.
Best regards,

Gabriel Tudoran

Analog Sound

PS: IN TUBE AMPS, THE ANODE VOLTAGE CAN AND WILL KILL YOU IF YOU DON’T PAY ATTENTION !!

Name: THC-OD

Type: Medium Gain Overdrive

Name: Plexi In a Box

Type: Medium Gain Overdrive

Power supply: 9v Dc – Center Negative

About: Medium gain overdrive pedal custom made for Peter Kolscar. The main features are: tone stack bypass and 3 clipping types selected trough a toggle switch and also an integrated cabinet simulation.

Artists: Peter Kolscar

Name: The Boogie Man Distortion

Type: High Gain Distortion

Power supply: 9v Dc – Center Negative

About: A high-gain distortion pedal with a full tonestack 0 works very well connected either in an amp or in a power amp. There are 2 models: with or without cabinet simulation.

Artists: Calin Rotuna

Name: The OptoComp

Type: Optical Compressor/Limiter

Power Supply: 9V-DC Center Negatiive

About: Vintage optical compressor, nice transparent sound, good compression ratio and very dynamic. If you are looking for a vintage compressor sound, then look no more.

Name: The Re-Peter

Type: Custom Boost & Delay

Power supply: 9V-Dc Center Negative

About: A custom made pedal for Peter Welsh. A delay and a boost in the same pedal, with the particular characteristic that the delay will be available only when the boost is engaged.

Artists: Peter Welsh