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Old 25th November 2009, 05:59 AM   #231
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Some more explanation:
BL is the magnet strength and very often does not have a maximum in the rest position.
Le is inductance. it varies over the movement of the coil.
Cms is the stiffness of the suspension and should be minimal in rest position. that is often not the case and that yellow "spider" you see is a big problem.
what happens is the following: the cone like to be where BL is maximum, Le is maximum and stiffness is minimum. so what happens in a real speaker that a DC shift is happening that is frequency dependent around the resonace Fs. Asymmetric problems produce 2nd harmonic and symmetric problems produce 3rd harmonic. that are the main sources of distortion in loudspeakers not considering rubb and buzz that create much higher harmonics. i whould not call that crossover distortion but it is a dynamic problem with hysteresis that creates all kinds of frequency and volume dependent intermodulation products. you can learn how to measure that on the Klippel GmbH - Home Page website. we tried to get a handle on that problems with DSP for 20 years have succeded so far more with low tech mechanical improvements. a good modern speaker
at medium volume ( 85-95dB) has about -50dB distortion over a 60dB dynamic range to put that in perspective.
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Old 25th November 2009, 05:32 PM   #232
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I just confirmed with a simple sim that the circuit in #217 or one very similar to it yields a null of both offset and second harmonic with two trims for very unmatched JFET's.

On speakers I was only stating that in my experience the DC transfer function of displacement vs current is continuous and fairly smooth. Systems with second order nonlinearities will typically exhibit DC shift when excited.
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Old 25th November 2009, 06:23 PM   #233
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hi scott!
what circuit are yot refering too? in post 217 i made a link to another guys stage that has no fets. i asume it was one of my circuits and i whould like to know which. what was the dissimilarity to mine you mention ?
Anyway, thank you very much for simulating the circuit. i just start to learn that and have not much experience. of cause i do a lot of simulation with loudspeakers.
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Old 25th November 2009, 07:16 PM   #234
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Sorry meant #201. I just used resistive loads to the rails not current sources and only two FET's with 50 Ohm source resistors to ground through 10 Ohms so there are only 4 active devices. -100db @ 2v p-p out

A few Ohms unbalance in the 50 Ohm resistors cancels most of the second and a few 10's of Ohms in the other resistors balances the offset.

Matching j74's to k170's is a thankless task anyway.
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Old 25th November 2009, 07:43 PM   #235
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thank you, i will build the circuit and try it out in praxis. what simulation programm are you using ? microcap ?
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Old 25th November 2009, 07:49 PM   #236
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In house but should not matter. One could use pencil and paper on this one.
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Old 25th November 2009, 09:05 PM   #237
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understood
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Old 26th November 2009, 07:32 AM   #238
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was that approximately the circuit you simulated ? i reduced source degeneration by half to get somewhat lower noise, so distortion will be a bit higher i assume.
Attached Files
File Type: pdf MPP Fet Headamp SW.TSC - TINA.pdf (46.9 KB, 172 views)
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Old 27th November 2009, 09:27 AM   #239
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I saw an interesting RIAA stage in the december 2009 issue of Audioxpress. because we have discussed the possibility to use coils for equalization in this thread and for compleetness



i publish the circuit here with default values (eccept the coil) because i do not know if i am allowed to publish the circuit with the correct values. the author makes a good point for using a coil in the first stage and it has a resonable value of 25mH and some ohms so it should be possible to find that coil or make one yourself. the design does the second breakpoint (500Hz) passive and the third breakpoint (2122Hz) active in the output stage. i whould try it also the other way around with 75usec passive and the 500Hz active but one would end up with a higher value capacitor in the feedback loop of the output opamp. i can recommend that Issue because it also has an interesting interview with Professor Malkolm Hawsford in it. I worked with Malkolm a lot in the 90th and he is one of my most important influences. i do not know if the digital version of Audioxpress is yet available but i know from the editorial that they are working on it.
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File Type: pdf Phonostage 50Hz breakpoint with coil.TSC - TINA.pdf (36.9 KB, 123 views)
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Old 27th November 2009, 10:00 AM   #240
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here is one way to implement inductive RIAA into the MPP structure. i have not build it yet so take the values with a grain of salt.
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File Type: pdf MPP SE RIAA Inductive EQ.TSC - TINA.pdf (77.8 KB, 136 views)
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