Category Archives: techno

Germanium transistors for Fuzz – 4

Switching transistors
ex : 2N404 (the american classic)

The first transistorized circuits for automation and computing required specific components that were straightforward in their response but without extreme bandwidth. Rather close to radio frequency transistors, they are distinguished by their reliability and deliberately moderate maximum frequency. Some models may produce a vintage sound grain, suitable for Fuzz Face. They could make as much reference as the ubiquitous small power audio transistors : American do-it-yourselfers have not been mistaken, and have since a long time embraced the classic 2N404 …

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Germanium transistors for fuzz -3

High Frequency Transistors
ex : OC44 (Rangemaster, 1966)

High frequency germanium transistors have appeared as a second generation. Their elaborate technology made it possible to obtain a consequent gain even at radio frequencies : 30MHz, then 100MHz or more.
More expensive, and fragile at the beginnings, they have not been much used by pedal manufacturers, before all concerned by economy and robustness.

The OC44 was however exploited by Arbiter in the first Treble Booster, the Rangemaster, where its gain and bandwidth yet modest worked perfectly.
With the contemporary recoil, we rediscover the quality of these transistors, the fineness of their sonic grain, and their real interest in designing modern boosters and fuzz …

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Germanium transistors for Fuzz -2

Audio preamplification transistors
ex : NKT275 (Fuzz Face, 1966-67)

These are the most common germanium transistors. They were designed for audio pre-amplification circuits in consumer and mid-range equipment, where they quickly replaced the tubes. They are distinguished by a gain which can reach 200, and a maximum frequency of the order of 1MHz.

Pedals made in 1966-68 first operated with black glass models like OC75 and then encapsulated glass like OC76 and OC81 … As the AC125 and AC126 by Philips / Mullard were a bit expensive, cheap versions like the NKT275, and some SFTxxx had their hour of glory before being forgotten, then rediscovered around 1990 …

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Germanium transistors for fuzz -1

Output audio transistors
ex : AC128 (Fuzz Face, 1966-69)

These transistors were at first designed to drive the loudspeakers of radios and consumer audio products. They are distinct from other families by their dissipable power and their maximum collector current.
In 1967, some models have been known as bringing a so called “creamy” sound texture to Fuzzboxes. Therefore, they gained a reputation that made this family of components enter the guitar effects culture.

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Germanium transistors : Sonic properties

There is a “germanium sound”. It is especially suitable for guitar amplification, and can apply to harp and some keyboards. The sound of germanium has a warmth and a granulity as pleasant to the ear as the tube sound, without being the same : The sensation of warmth is about equivalent (for analog reasons, in particular the Miller effect that dynamically attenuates the high frequencies). The sonic  grain of germanium is generally a bit rougher than the tube grain, and especially less flat and plain than silicon …
In all domains of audio, germanium transistors and their “good defects” are opposed to the cold pharmaceutical perfection of integrated circuits.

After years spent in tests and development, I feel able to specify some characteristic parameters… And happy to share this knowledge that I apply in the products shown on this site ; stuffs just to please the guitars.

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Germanium transistors : TO1 case models

The TO1 standard was the first all-metal case used for germanium transistors when the black glass models were abandoned around 1964. This concerns European series like ACs, industrial series ACYs, ASYs, ASZs, the british NKTs and the japanese 2SAs…
Transistors manufactured in Eastern Europe used an elongated version of the TO1 case : some ACs, SFTs manufactured under license, and the national productions of these countries.

The TO1 standard was not strictly followed by all manufacturers, which can nowadays seem surprising. From another point of view, this can help identify the origin and sometimes the quality of the transistors. This article is here to share some pointers and background information.

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Germanium transistors : Black Glass models

 They were thus nicknamed in allusion of their very particular black glass case. Glass technology had been selected because at that time plastics were still unable to ensure a perfect seal between case and terminals. They have been the first transistors widely available, and the aged electronic techs have fond memories of them. It must be said they are found in the earliest fuzz, the first solid state professional audio systems and computers.

This is an opportunity to discuss the properties of the main types and identify their ability to be used in circuits devolved to guitars .
NB: I will only talk about transistors that I actually had in hand.

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Stompbox power supply : An overview

Stompboxes power supply is both a trivial issue and a relevant subject. There are some basic points behind banality that can help make a good choice — and avoid troubles — when organizing a pedalboard. This overview on the current situation will bring some classic issues, such as polarity of old pedals, consumption orders of magnitude according to types of stompboxes. The big issue remains choosing between traditional transformer power supplies and switching power supplies, that nowadays begin to impose their technology, but are not always appropriate to analog circuits…

A second article will expose points on which ensure personal choices … A third will be devoted to the system that equips my Guitar Poppa pedals, in order to power them silently through any types of DC power supply respecting the negative to ground standard.

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Stompbox Power Supply : Poppa’s tricks

Early stompboxes were exclusively powered by batteries. Their low consumption made it possible. When most demanding stompboxes came around 1978, external power supplies, less or more stabilized, were necessary. Today, current switching power supplies are widespread because they are cheap for the manufacturer and reliable for the user. The problem is they are often noisy when used on analog equipment.

So I had to integrate the issue of power supply in my Guitar Poppa project : My products had to operate as silently as possible with any negative grounded DC power supply, and providing 7 to 12V in charge. As I moreover use both silicon NPN and germanium PNP transistors, the question of polarity was added to the problem.

From these objectives came a specific supply circuit that is in all my effects pedals. It uses an active noise filtering and decoupling cells.

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Biasing a fuzzbox

Biasing is to set the DC potential of some critical points in the circuit so that the AC signal which will be superimposed can be held wholy and without deformations. This issue is evident in the case of HiFi or mixing equipment. It is the same in an Overdrive or a Fuzz : even if their output signal is saturated, it has a specific shape and must not be damaged.

This article should help fuzz users to bias or rebias their equipments more accurately than common use. It is specially devoted to owners of my LikeYourFace and Hi-GeFuzz


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Stompboxes : True Bypass

This article is devoted to one of the best known switching system : the True Bypass, which is generaly said to be the best, although it has some not so known limits … We shall see that the big question is that TrueBypass keeps a high impedance bypass routing, which makes this circuit not so efficient as usually said when many pedals are chained.

This introduces to a classical quarrel among guitarists : Pro and cons buffering…
Input buffering will be the subject of a second article.

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Input buffers

Buffers are devices that are interposed between a signal source and an active circuit. The most simple ones do not provide signal amplification but operate impedance matching. This prevents from signal losses, espacially concerning the level and the bandwith.
They are technically very useful but little known, and sometimes badly regarded by vintage electronics purists under the pretext that historical circuits do not have any of them — and that Japanese equipment is stuffed with.

Guitar Poppa could not stay indifferent to this electronico-aesthetic quarrel…

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