Etiquetas/Tags: guitar, Indian, mclaughlin
Etiquetas/Tags: Voigt, horn, tractix
Etiquetas/Tags: hifi, voigt, Visaton, frs 8
- High fidelity loud speaker enclosure: US 2834423 A
- Espacenet patent
Etiquetas/Tags: hifi, bradford, baffle, audio, diy
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:
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.
Dick Olsher famously remarked that “The first watt is the most important watt.”
Enough talk here is the schematic (one channel)
I call it nez amplifier,
Etiquetas/Tags: hifi, amplifier, nelson pass, zen, nez, 1W
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, G. A. Briggs, Editions Radio Paris, Deuxiéme Édition, 1948
Etiquetas/Tags: hifi, audio, speaker, voigt, briggs, west
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:
Length of the pipe:
Actually it should be removing the area of the speaker at the bottom, 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
(* 7.0 7.5);52.5
(* 7.0 15.5);108.5
(/ 108.0 (+ 2 (pow (/ (* 7.0 7.5) (* 7.0 15.5)) .5)));40.06516757332509
- EXPERIMENTS WITH TAPERED PIPES BY DAVID B. WEEMS
- The Voigt Pipe: The world's most easy-to-build High End Loudspeaker
- Voigt Pipes -- the simplest hi end loudspeakers you can do-it-yourself!
Some more thoughts soon.
Etiquetas/Tags: voigt, speaker, hifi, audio
Etiquetas/Tags: guitar, amplifier, cab, speaker
Etiquetas/Tags: Wittgenstein, philosophy
This is a series of one transistor circuits, a simple design exercise. It will contain:
- a booster
- tone booster
Etiquetas/Tags: diy, booster, guitar
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?
Etiquetas/Tags: guitar, diy, diode function generator, analog computer
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).
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.
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 Norwich — A 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.
Dito isto aqui ficam mais alguns detalhes técnicos da montagem do amplificador:
- é necessário montar o IRF510 num dissipador de calor, assim como a resistência R4 de 10W
- o valor da tensão em A deve ser posta em 4.5V através da resistência R3; talvez no futuro se possa usar também um depletion-mode mosfet para o amplificador, por exemplo IXTH20N50, como vem no De-Lite Amplifier de Nelson Pass
- provavelmente o valor de C2=47n deve ter de ser aumentado de modo a garantir uma melhor resposta nos graves; aliás o valor de C3 também.
Etiquetas/Tags: amplificador, guitarra, 1/2W
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 .
The basic circuit of a class A JFET amplifier is given in the following figure.
|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 Where is the threshold voltage (pin-off voltage) and is the drain current with . Then we can write the drain current as a function of the input voltage as In order to simplify the analysis let us define the variables (normalized current and voltage, respectively) and the constant, which determine the value of the source resistor, We also need the normalized input voltage The relation between the normalized current and voltage can be put into the form
We want to obtain a power law relation between normalized current and the normalized input voltage and, in particular, the exponent 3/2 for the triode emulation. So, in order to get that, let us assume that one has that is Taking the logarithm derivative of the last expression and solving it in order of one gets or
The next figure shows the value of the exponent as a function of the normalized input voltage
|The exponent n as a function of the normalized input voltage z.|
The value of the constant that determines the value of the source resistor is given by For and one gets 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 permits to obtain for any working voltage and exponent the value of the parameter 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
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
It is easy to see why?
Here is Arsenios explanation:
The operation of the circuit more closely resembles a vacuum tube than a diode clipper does because of the strong square law characteristic. This is due to the negative feedback around both base-emitter pairs. This feedback accentuates the junction non-linear behaviour manyfold. Thus each transitor drives the other even harder so that the transfer curve ends up more logarithmic than is typical of a single transistor. In other words: the clipping is gradual and not abrupt like it is in the case of a silicon diode. Typically a lot more 2nd harmonic is produced as well. As a bonus the waveform folds over on itself when the circuit is overdriven!
Etiquetas/Tags: guitar, diy, arsenio novo, Tube Sound Overdrive
As you see it shares with the Ruby the same topology: a buffer and a chip amp. It uses a JFET buffer with a MPF102 and the 1W TDA7052 chip. It is a clean amp and it reacts very well with any pedal in front of it. I don't use a lot of distortion so this little amp suits all my needs. It doesn't have a volume and tone control because I wanted a plug-in-and-play amp. If you want an amp with a volume control try the TDA7052A, it has a volume voltage control pin that works perfectly (simple pot), this chip has the advantage that the volume pot is not on the signal path.
Of course the PUNCH also works with batteries, a 9v battery or with six 1.5V batteries in series. For small voltages and currents the sound could become distorted or to muddy, if so decrease the 1u cap to 470n or smaller.
What about the speaker? The guys from ROG say
What speakers do you recommend for use with your mini-amp circuits? While the Ruby, Little Gem, and Little Gem MkII practice amps can be used with any speakers, best results are achieved with full-size speakers intended for use with guitar amps. The amps will work well with an total impedance of 4, 8, or 16 ohms. We've tried hi-fi speakers, clock-radio speakers, and auto speakers - they just can't cut it. For me, using anything other than a speaker designed for the frequencies of an electric guitar produced sounds more like a toy than an actual amp. However, you may want to ask at Aron's Stompbox Forum. Many of the members have built one of the aforementioned amps and may be able to suggest a decent-sounding small speaker.
This is only in part true. One thing they are right is that clock-radio speakers and small radio speakers won't work! But the same is not true for hi-fi speakers and auto speakers. Let me be more precise about it.
I've tested the PUNCH and the Ruby with some 6'' auto speakers and they work great, specially with the PUNCH. This Fonestar UT528 speaker of 5.25''=13.3cm with a frequency response of 50-12.000 Hz and a sensitivity of 90 dB - 1 W/1 m works great.
I've also test it with a smaller one, the Fonestar 3''=7.5cm speaker (20-14.000 Hz, 8 Ω, 89 dB - 1 W/1 m)
and also has a great sound.
Here is the PCB pdf file.
Here is a cabinet for the PUNCH with a 3'' Fonestar speaker and using a IKEA wooden box. The rear photo shows the 9V battery enclosure.
As always comments, questions or suggestions to my email.
Etiquetas/Tags: guitar, amplifier, 1W, DIY
I'm planning on building a simple 5 band EQ using the BA3812L chip but changing the frequencies to more suitable values. The frequencies that I'll be using are the ones from Mesa Boogie DC-5 amp. Here is the schematic:
And here is a copy of the Mesa Boogie DC-5 owner's manual about a similar EQ.
The capacitor values were obtained using a simple GNU/Octave script:
#1; # Calculations for a simple EQ: BA3812L # All resistors in Ohm and capacitors in F R0=1.2e3; R1=68e3; Q=.7; f=[80 240 750 2200 6600]; C0=1./(2*pi*R0*Q*f); C=Q./(2*pi*R1*f); Q=1; C0=1./(2*pi*R0*Q*f); C=Q./(2*pi*R1*f); disp("Q=1") disp(" Freq C0 (uF) C (uF)") disp([f' floor(C0'*10^12)/10^6 floor(C'*10^12)/10^6])
One can relate the octave bandwidth N to quality factor Q by the expression or inversely This is important because one would like to be able to control the complete frequency range of the guitar signal.
For the EQ frequencies 80, 240, 750, 2200 and 6600, roughly a factor of 3 for consecutive frequencies, and a Q factor of order 1 one gets a 1.5 band width in octaves, so because of the ratio of the EQ frequencies one can, with this Q=1, control the full interval of frequencies between 40Hz to 10kHz.
I think I'm getting it right?!
Here are the capacitors values fitted to the standard values
freq real_freq real_Q C*1 C*2
f f Q C*2 C*1 80 83 1.1 1.5u .030u 240 257 1.1 .47u .01u 750 830 1.1 .15u 3n 2200 2137 .9 .068u 1n 6600 6260 1 .022u .36n
Etiquetas/Tags: EQ, guitar, BA3812L
Última actualização/Last updated: 2014-02-20 [14:38]
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