Blog e página pessoal de Tiago Charters de Azevedo (Blog and personal webpage of Tiago Charters de Azevedo)

L-Pad attenuator (15W)


Sometimes the simplest thing is the the most useful one! A L-Pad attenuator (15W):

It changes the output response of the amp after the 12 o'clock position, but works nicely.

Etiquetas/Tags: DIY, amplifier, attenuator, guitar



Com projectos interessantes para o DIY: http://www.bloguetronica.com/

Etiquetas/Tags: electrónica, DIY, PT

Tim Escobedo's Circuit Snippets


Etiquetas/Tags: Tribute page to Tim Escobedo's Circuit Snippets

John Mclaughlin, U Srinivas,Zakir Hussain, V Selvaganesh,Mahadevan -- Jazz a Vienne



Etiquetas/Tags: guitar, Indian, mclaughlin

The 4ft Voigt Loudspeaker


Etiquetas/Tags: Voigt, horn, tractix




I've been planning, for quite some time now, on building an audio amplifier, and after reading Pass's articles on audio amplification decided to desgin one for myself.

I found this topology in "Design of VMOS Ciruits" book from the 80's (the same book that Jack's mentions on his BS170 booster webpage) but Pass's patent for a very similar topology is dated from 1998. Go figure?!?

Quoting Pass on Dick Olsher:

Dick Olsher famously remarked that “The first watt is the most important watt.”

and looking for "the personal amplifier" reviewed by Olsher (made by http://davidberning.com/) I decided that a 1W per channel amp would be a good amp to aim.

Enough talk here is the schematic (one channel)

I call it nez amplifier,

Etiquetas/Tags: hifi, amplifier, nelson pass, zen, nez, 1W

Birdman in Lisbon



Etiquetas/Tags: art, music, Lisboa, Portugal



Pop quiz. What was the fastest-adopted gadget of the last 50 years? The Color TV? The mobile phone? The DVD player? No, believe it or not, it was the boombox. — Sprite

Etiquetas/Tags: hifi, audio, boombox, diy

Reproduction sonore a haute fidélite


Reproduction sonore a haute fidélite, G. A. Briggs, Editions Radio Paris, Deuxiéme Édition, 1948

Etiquetas/Tags: hifi, audio, speaker, voigt, briggs, west

Voight pipe enclosures


Pipe enclosures were design in the 30's by Paul G.A.H. Voigt, it was subject to a patent (GB447749 (A) ― 1936-05-18). The principle is quite simple

Probably inspired by pipe organ tubes.

The image below shows the Herbert Jeschke's Voigt Pipe for a build the pipes for a undetermined 8" driver: the classical way of building the Voigt pipe.

The angle is given by

(atan (/ (+ 8 (/ 3.0 4.0)) 71.0));0.12262114279484264

(/ (* (atan (/ (+ 8 (/ 3.0 4.0)) 71.0)) 180) pi);7.025673961215487

Position of the driver: latex2png equation

Length of the pipe:

latex2png equation

Actually it should be latex2png equation removing the area of the speaker at the bottom, latex2png equation is the speaker resonant frequency.

Here is my hack on it with a Fonestar 3inch=7.5cm speaker (20-14.000 Hz, 8 Ω, 89 dB - 1 W/1 m)

Not really a full-driver, but for 10Eurs, who can complain.

(atan (/ 15.0 108));0.13800602365751946

(/ (* (atan (/ 15.0 108)) 180) pi);7.907162702958458

Top area:

(* 7.0 7.5);52.5

Bottom area:

(* 7.0 15.5);108.5

Speaker position:

(/ 108.0 (+ 2 (pow (/ (* 7.0 7.5)
                      (* 7.0 15.5)) .5)));40.06516757332509

Further reading:

Some more thoughts soon.

Etiquetas/Tags: voigt, speaker, hifi, audio

Cab for a 1W amplifier



Etiquetas/Tags: guitar, amplifier, cab, speaker

Was Wittgenstein Right?



Ref.: http://opinionator.blogs.nytimes.com/2013/03/03/was-wittgenstein-right/?_r=0


Etiquetas/Tags: Wittgenstein, philosophy

Dragon booster


This is a series of one transistor circuits, a simple design exercise. It will contain:

Etiquetas/Tags: diy, booster, guitar

Diode function generator


Since I've started to play with guitar circuits I wanted to try a non linear resistor diode network device. The circuit is base in an old paper "Design of a diode generator using the diode equation and iteration" by Vincent G. Bello (1971). It uses the following

This is a quite general synthesis procedure. Given a convex monotonically increasing function the resistors can be chosen such that a set of voltage points can be obtained (Vin,Vout). The controls are highly interactive and, as the simulation shows, the breakpoints are hard to set by hand.

Here is the circuit

I've added a sum/difference opamp at the output.

Here are some typical output wave forms (sum on the left, difference on the right)

It needs, in this form, 10 pots. If the control of negative part is include it will need a total of 14 pots!!

My idea is to build something like this variable diode function generator

but I can not find on-line any of these function generator used in analog computers. Any links? Refs? Some other diode/resistors networks?

Are there any stompbox that uses such a function shaper? Is it feasible?

BTW this variable diode function generator is a Comdyna (http://www.comdyna.com/) module.

Etiquetas/Tags: guitar, diy, diode function generator, analog computer

The TRANSFET: latest DIY experience


Here is my latest experience which I dubbed TRANSFET

It has a good compression and distorts very well under overdrive (I've used a mini-booster to do it).

Here is the transformer for the TRANSFET.

I've also tested Escobedo's Ultra Class A Superdrive Power Amp has a preamp. It sounded good! Very Fender-ish with a lot of gain.

Have fun!


Etiquetas/Tags: jfet, transformer, class a, preamo



Um dos próximos projectos que vou executar é este pequeno amplificador de 1/2W e corresponde à junção de vários esquemas que se podem encontrar por aí.

É constituído por um pré-amplificador (aliás, um buffer de ganho unitário) com o MPF102, um depletion-mode mosfet, cuja ideia foi retirada do Ruby, já montado anteriormente. De modo a evitar confusões sobre a autoria da utilização deste tipo de topologia, facto que perturba o sono da malta (ver aviso no início da página), a verdade é que a ideia de colocar um mosfet à entrada do amplificador foi usada em 1969 por Linsley Hood num famoso artigo da Wireless World sobre um "Simple Class A Amplifier: A 10-W design giving subjectively better results than class B transistor amplifiers". Uma colectânea de artigos relacionados um este amplificador pode ser consultada em: The JLH Class-A Amplifier.

A segunda parte consiste no amplificador que usa um IRF510, circuito retirado da página do The Radio Amateur Society of NorwichA Potpourri of Audio Amplifiers. Note-se que este amplificador foi já testado como amplificador para guitarra (http://www.beavisaudio.com), no entanto, e segundo o construtor "Sounds ok, but not great". Veremos!

Nelson Pass, autor da mais expressiva forma de amplificadores de classe A, o Zen amplifier, expressa muito bem a vantagem de se usar uma configuração em classe A para amplificação de áudio.

Simplicity is not the only reason for the use of the single-ended topology. The characteristic of a single-ended gain stage is the most musically natural. Its asymmetry is similar to the compression / rarefaction characteristic of air, where for a given displacement slightly higher pressure is observed on a positive (compression) than on a negative (rarefaction). Air itself is observed to be a single-ended medium, where the pressure can become very high, but never go below 0. The harmonic distortion of such a medium is second harmonic, the least offensive variety.

Ref.: Zen Amplifier, by Nelson Pass

Dito isto aqui ficam mais alguns detalhes técnicos da montagem do amplificador:

Etiquetas/Tags: amplificador, guitarra, 1/2W

The "triode" emulator revisited


After reading the excellent page at http://www.runoffgroove.com about the Fetzer Valve circuit and the paper that supports it (Dimitri Danyuk, "Triode Emulator", 116th Audio Engineering Society Convention, May 2004 in Berlin, Germany), I wonder how the results in that paper could be obtained analytically. This page contains my impressions on it. I've found that the exact value of the magic constant is latex2png equation.

The basic circuit of a class A JFET amplifier is given in the following figure.
Plain circuit of a class A JFET amplifier.
Plain circuit of a class A JFET amplifier.

The basic equations that governs the behavior of a JFET, in the saturated regime, are given by latex2png equation Where latex2png equation is the threshold voltage (pin-off voltage) and latex2png equation is the drain current with latex2png equation. Then we can write the drain current as a function of the input voltage as latex2png equation In order to simplify the analysis let us define the variables (normalized current and voltage, respectively) latex2png equation and the constant, which determine the value of the source resistor, latex2png equation We also need the normalized input voltage latex2png equation The relation between the normalized current latex2png equation and voltage latex2png equation can be put into the form latex2png equation

We want to obtain a power law relation between normalized current latex2png equation and the normalized input voltage latex2png equation and, in particular, the exponent 3/2 for the triode emulation. So, in order to get that, let us assume that one has latex2png equation that is latex2png equation Taking the logarithm derivative of the last expression and solving it in order oflatex2png equation one gets latex2png equation or latex2png equation

The next figure shows the value of the exponent latex2png equation as a function of the normalized input voltage latex2png equation
The exponent n as a function of the normalized input voltage z.
The exponent n as a function of the normalized input voltage z.

The value of the constant latex2png equation that determines the value of the source resistor is given by latex2png equation For latex2png equation andlatex2png equation one gets latex2png equation which is closed to the value obtained by Dimitri, 0.83, but not exactly the same. This is the exact value of the constant that determines the value of the source resistor.

One can also see that the expression latex2png equation permits to obtain for any working voltage latex2png equation and exponent latex2png equation the value of the parameter latex2png equation that emulates a super-triode, a "triode" with a exponent between one and two.

Who says that math doesn't pay off?

Fetzer Valve - A mu-amp variation

You could also make a mu-amp variation

by biasing the upper jfet in a different way!

If you have any comments about this page, please fell free to send me an email:


Etiquetas/Tags: DIY, triode valve, fet, electronics

Triode emulator - from a pentode to a triode


In 1938 Schade proposed a mechanism to transform a pentode tube into a triode by connecting the plate to the grid using a resistor network. Here is the graphs from is work "Beam Power tubes" by O. H. Schade, March 1938.

So I've simulated a few circuits to try to understand a bit more what is going on. All of you know the triodizer. Here are the simulations. The version described in the text with a battery at the gate:

and the circuit from a MIT lab course

Wonderful graphs don't you think!

I've also simulated the Fetzer valve circuit and as suspected the characteristic curves are not of that type... although it sounds good

This graphs and simulations does put things into perspective. ç

Etiquetas/Tags: tube, diy, triode, pentode

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Última actualização/Last updated: 2014-04-08 [11:56]

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