A aula prevista para amanhã, devido aos seminários, será transferida para 5ª ou 6ªf da parte da manhã (voltar aqui amanhã para ler a confirmação).
Etiquetas/Tags: aviso, alunos, ISEL
Setar r is one of the Iranian plectrum-type string instruments, which is plucked by the player's forefinger's nail. Sehtar or Setouyeh is a three-cord instrument, which was converted into a four-cord instrument under the reign of the Qajars. It is, in general, an ancient and gnostic instrument usually played at the gathering of dervishes most often held at Khaneqahs (monasteries or houses of dervishes), which makes the listener feel high. In view of its special vocal features, Sehtar is known as the instrument appealing to the listener's heart and the Iranian musical instrument ranking second among Iranian musicians. It is simpler than other instruments both in appearance and the method of playing. Its low tune, compactness and tenderness are the main reason for its great appeal in the course of the past centuries. It is made in various types and sizes including large, small, flat and zir-abai. Tars are made in two methods: Turkish (in many pieces) and scraped kasdani (in one piece). Sehtar is generally made from berry wood, while at some occasions that of pear or walnut tree might be used as well. Its bowel is a pear-shaped semi-sphere, while its thin and delicate handle is tenderer than that of other instruments. (http://www.orientalinstruments.com/oriental/joomla/index.php?option=com_content&view=article&id=49)
(click to enlarge)
Etiquetas/Tags: Setar, Sehtar
Etiquetas/Tags: instrument, musica, iran
Etiquetas/Tags: electronics, diy, voltmeter
Etiquetas/Tags: clip, signal
Este é dos meus preferidos! Gosto muito da abordagem da construção do amplificador, especialmente o último botão "Power". Controla o bias do estágio de output. Very clever!
Etiquetas/Tags: guitar, amplifier, class a
Não custa fazer a experiência.
Etiquetas/Tags: flop, water, experiment
Symmetry breaking describes a phenomenon where (infinitesimally) small fluctuations acting on a system which is crossing a critical point decide the system's fate, by determining which branch of a cable is plugged into the guitar. To an outside observer unaware of this, the choice will appear arbitrary. This process is called symmetry "breaking", because such transitions usually bring the system from a symmetric state into one definite state. Symmetry breaking is supposed to play a major role in guitar playing[clarification needed].
Etiquetas/Tags: guitar, cable, amplifier
Etiquetas/Tags: music, moondog
Etiquetas/Tags: speakers, audio
Etiquetas/Tags: amplifier, guitar, preamp, mosfet, IRF
Etiquetas/Tags: amplifier, guitar, preamp, mosfet, IRF
Can we do this using solid state devices? ;)
Etiquetas/Tags: guitar, dumble, solid state, question, tube, amplifier
I've build a simple cab for a cheap Skytronic Kevlar cone speaker
|Skytronic: 5 1/4'' Kevlar cone speaker|
Although it sounded ok, a bit of math would benefit the sound that it produces. Note that this is not a typical guitar speaker. In what follows I will try to convince you that regular speakers (namely woofers) can be used to make great guitar cabs!
The specs for this speaker are these.
|B x L||8.7|
The quantity that really one should look, because I'm doing a synthesis, is total Q; this value is a combination of the properties of the speaker taken conjointly with the cab.
The best reference to learn how to design speaker enclosures is still the papers by Richard H. Small and Neville Thiele. So the relevant equations are the electrical Q (taken into account the output impedance of the amplifier , the total Qts, combines Qe and Qms, like two resistors in parallel and the volume of the enclosure where is the total Q of the enclosure and speaker system.
The predicted Fc frequency of the system is then
The design process can be simplified by using a dimensionless parameter called the system compliance ratio, that can be written as
A simple GNU/Octave script will allow us to get a more clear view about the choices we are about to make.
#1; Rg=8; Re=7; Fs=55 Qms=5 Qes=.44 Qts=.41; Sd=81; Vas=5.6; Cms=605; Mms=14.5; BxL=8.7; Qe=Qes*(Rg+Re)/Re Qts=1./(1./Qe + 1/Qms) eta=4*pi^2/344^3*Fs^3*Vas/Qes*1e-3 alpha=[1:.01:4]; Qtc=Qts*(1+alpha).^.5; Vb=Vas./alpha; Fc=Fs*(1+alpha).^.5; clf subplot(3,1,1) plot(alpha,Fc,'r') ylabel('F (Hz)') grid title(sprintf('Rg = %i',Rg)) subplot(3,1,2) plot(alpha,Qtc,'r') ylabel('Qtc') grid subplot(3,1,3) plot(alpha,Vb,'r') ylabel('Vb (l)') xlabel('alpha') grid
Before choosing the dimensions of the enclosure let us look at some graphs.
The next figure shows the values of Fc, Qtc and Vb as a function of alpha.
|Left:Amplifier output impedance Rg=0, high damping factor (infinite).Right: Amplifier output impedance Rg=8, damping factor equals 1.|
The next plot shows the frequency response of a typical high damping output amplifier (not for this particular speaker).
|Left plot: Rg=8. Right plot: Rg=0.|
We see that a non-null output impedance permits the speaker to shine through, and also gives us a clear separation of bass and treble regions. This feature somewhat tames the distortion and gives the a good spectrum that we all like in guitar amplifiers (that can be found in tube/valve guitar amplifiers). This fact is one of the main reasons that a typical solid state hi-fi amplifier is found to sound terrible when fed with a distorted guitar signal.
So I'm aiming at a Rg=8 amplifier and a Fc around 80Hz (low E string), this gives and for which will give a warm and dark tone (for smaller Qtc the Fc will be smaller and although it gives a clearer tone, due to the low Fs of this speaker, the final tone would be somewhat a bit mushy).
(to be continued)
Etiquetas/Tags: DIY, guitar, speaker, kevlar
Etiquetas/Tags: electricidade, DIY
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
Etiquetas/Tags: Tribute page to Tim Escobedo's Circuit Snippets
Etiquetas/Tags: guitar, Indian, mclaughlin
Última actualização/Last updated: 2014-10-21 [23:11]
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