Members moody Posted October 13, 2007 Members Share Posted October 13, 2007 Set up the M12 for the first time tonight. Due to the size of the room and crowd (lots less than expected) I ran a lot less than I had originally intended, I could have done the same gig with the spirit E8 that I have as my backup. One thing that was good though was having the third monitor mix (something I haven't had available before). I think it will take time before I'm quick with setting it up though. Good sounds, easy control of each aux etc. Really easy to see if any channels are peaking. I'm very happy with it. Link to comment Share on other sites More sharing options...
Members Mr Blues Posted December 10, 2012 Members Share Posted December 10, 2012 Hi Guys I am now a big fan of the soundcraft M series. I brought used M4 about a year ago but hardly used it until recently . The clarity and the depth of the mic pre's are very smooth and sweet sounding. Plus the EQ wow . Quality. Are the Soudcraft spirit E series similar and I am wondering why the m series are being discontinued? I know they are quite bulky in size but I love my M4 to bits and glad i brought it when I did. Dave Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 10, 2012 Members Share Posted December 10, 2012 Originally Posted by Mr Blues Hi GuysI am now a big fan of the soundcraft M series. I brought used M4 about a year ago but hardly used it until recently . The clarity and the depth of the mic pre's are very smooth and sweet sounding. Dave So Dave... how do you know this is because of the mic pre's? Link to comment Share on other sites More sharing options...
Members OneEng Posted December 10, 2012 Members Share Posted December 10, 2012 Hey Andy,Thanks for the diagram!I was wondering a few things. First, it looks like the front of the circuit is a decoupling cap. I was wondering why one wouldn't use a dual zener diode to clamp the voltage before the cap was exposed to it. Also, I thought that zeners were able to isolate transients faster than the setup they have (simple diode clamp to + and - VCC.Second, I tried to look up the bjt being used and it was some Chinese thing I couldn't read. I would think that this would be an important component since it will effect the linearity of the circuit (as will the op amps, but those are generally pretty linear by design if you use an op amp designed for audio applications).Third, while there were a few questions in my mind about how the circuit was designed (and I am far from an analog design engineer .... more of a micro guy), it seemed like a reasonable approach. What could you possibly do to put $100.00 worth of parts into a preamp?To the OP, I have nothing but good things to say about the Soundcraft boards I have used (borrowed ). Nice stuff. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 10, 2012 Members Share Posted December 10, 2012 Originally Posted by OneEng Hey Andy,Thanks for the diagram!I was wondering a few things. First, it looks like the front of the circuit is a decoupling cap. I was wondering why one wouldn't use a dual zener diode to clamp the voltage before the cap was exposed to it. Also, I thought that zeners were able to isolate transients faster than the setup they have (simple diode clamp to + and - VCC. Because of the switching that goes on at the input (mic/line and tape return), the diff amp input uses coupling caps for DC blocking. IF you direct couple this circuit, differences in (DC) input resistance to ground due to switching of functions such as pads, or shorting one of the inputs to ground, at the bases of the input transistors could change the bias currents resulting in large offsets (same occurs if there were to be a small DC offset voltage present).The reason for using the diode clamps to +/-Vcc is because strange things can happen at power up and down so this way, regardless of the supply voltage, the input can not go more than 0.7V above or below the supply. 1N4148's are very fast too. Originally Posted by OneEng Second, I tried to look up the bjt being used and it was some Chinese thing I couldn't read. I would think that this would be an important component since it will effect the linearity of the circuit (as will the op amps, but those are generally pretty linear by design if you use an op amp designed for audio applications). These input transistors are generally picked for their noise performance, in the case of a mic preamp with low input impedance the noise current is generally as important as the noise voltage (disclaimer, I am rusty on the calculations and deep theory these days). If you notice, along with the "massive open loop gain" is global feedback that goes around the transistors. This is essential to maintaining linearity. Biasing this circuit is pretty tricky though, notice the + inputs of the op-amps at +8V, this offsets the output (independant of AC gain) to draw currenbt through the bass-emitter junction via the 100k bias resistor. Not my favorite way to do a mic pre but the concept is the same as many of the others. Originally Posted by OneEng Third, while there were a few questions in my mind about how the circuit was designed (and I am far from an analog design engineer .... more of a micro guy), it seemed like a reasonable approach. What could you possibly do to put $100.00 worth of parts into a preamp? Good question grasshopper... this is an example of a well designed $2.50 preamp. It is a question that I have no good answer to, other than some very pretty sheet metal and often an overly complicated circuit that usually performs worst than the simplest execution of a quality approach. I think it's kimd of a crap shoot, I don't think most folks could tell the differentce between the variations on this theme. Originally Posted by OneEng To the OP, I have nothing but good things to say about the Soundcraft boards I have used (borrowed ). Nice stuff. When they work... Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted December 10, 2012 CMS Author Share Posted December 10, 2012 Five-year-old thread necromancy...... wow! Link to comment Share on other sites More sharing options...
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