Sound signature differences between IRF510, 520, 530, and 540s? - diyAudio
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Old 3rd August 2010, 10:36 PM   #1
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Default Sound signature differences between IRF510, 520, 530, and 540s?

Are there generalizations about the sound signature that can be made between the IRF510PBF, IRF520PBF, IRF530PBF, and IRF540PBF along with their IRF9xxxPBF complements?

I've searched and it looks like the gate capacitance effects the treble extension and the trans conductance effects the slew rate, but is it really that easy and clear cut?

I have all four, but before I go through the efforts of swapping them out, I wanted to have a theoretical idea of what to expect.
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Old 3rd August 2010, 11:11 PM   #2
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Sounds like a job for a white noise generator and a spectrum analyser.

Unless your doing something silly with them they should all give a good sound.
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Old 3rd August 2010, 11:17 PM   #3
lineup is offline lineup  Sweden
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If you just use one of those as a follower, just for buffering,
without any feedback
then it might be diffences in sound.
Especially between 510 and 530, 540.

Such a follower 'amplifier' is for example Szekeres HeadPhoneAmp:
HeadWize - Project: A Class A MOSFET Headphone Driver by Greg J. Szekeres

When using MOSFET or any other power transistor
inside an amplifier with plenty of Feedback
then there is a correction taking place.
This will overrun most any quality of single components.
The 'sound' is here often dependant on the input stage
where the feedback comes in and is used to reduce distortion from the rest of Amp.
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Old 3rd August 2010, 11:17 PM   #4
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You may find only the 540 can support the levels of current/power you need without paralleling.
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Old 3rd August 2010, 11:45 PM   #5
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Thanks guys. It's for a lower power P-P amp. A pair of complements per channel in SE for about 7W bias around 200mA on 30V rails. All DC coupled. With better heat sinking I can crank it up later.
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Old 4th August 2010, 03:35 AM   #6
CBS240 is offline CBS240  United States
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Hi

Lineup has a point about the feedback. A feedback/feedforward drive circuit will 'adjust' Vgs as needed for adequate conductance. This Vgs vs Id value will not be the same for the different devices. Without any fb/ff, the distortion components will not be be the same. I think the driving circuitry will have greater influence on sound than the transistors by themselves.
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Old 4th August 2010, 02:38 PM   #7
DF96 is offline DF96  England
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I believe a 520 is just two 510 chips in the same package etc. - so everything more or less just halves or doubles as the case may be. If it is your own amp design then you can work out the likely effects of this.
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Old 4th August 2010, 03:25 PM   #8
ervinl is offline ervinl  Indonesia
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Quote:
Originally Posted by CBS240 View Post
Hi

Lineup has a point about the feedback. A feedback/feedforward drive circuit will 'adjust' Vgs as needed for adequate conductance. This Vgs vs Id value will not be the same for the different devices. Without any fb/ff, the distortion components will not be be the same. I think the driving circuitry will have greater influence on sound than the transistors by themselves.
Should it be current feedback only, or both with voltage feedback? And how many feedback (what gain) is needed (what maximum gain is needed)? Will this feedback auto adjust / correct DC offset too (e.g. due tome small miss match of complement)?

Thx,

Ervin L
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Old 5th August 2010, 05:13 AM   #9
CBS240 is offline CBS240  United States
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Well, there is more than one way to skin that cat. CFA is one way but it works a bit differently than VCA. I've never tried local Vfb within a Cfb loop. Could be an interesting concept.
You can use local fb around the output stage, but that will not affect the DC offset or so much the rest of the amplifier. It will help to linearize the output transistors though. If you use vertical cellular type switching mosfets such as the IRFs or similar, there will be a significant amount of distortion components generated by this type of device due to non-linear Gm and quite a bit of it at very high frequencies. This is one reason they are not popular as linear output stages. Global fb will not be sufficient to reduce these components because of the many stages and time delay within the loop, and the BW of the amplifer gain stage limit how much 'correction' can be obtained. But then they were designed for switching after all, eh? One type of gate drive circuit I find works quite well is HEC (Hawksford error correction) adapted for use with these mosfets. Bob Cordell's EC mosfet pwr amp paper is a good reference for this. It is based on Malcolm Hawksford's paper, EC for Darlington output stage. One major advantage of this fb/ff EC topology aside from linearization is the amplifier output becomes much less load dependent as changes in the gate drive signal related to the variable load Z, as speakers are, is included in the error signal. Damping factor is significantly improved.

As for DC offset, I prefer a DC servo.
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Last edited by CBS240; 5th August 2010 at 05:22 AM.
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Old 5th August 2010, 01:12 PM   #10
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Wow, thanks CBS240. That's a lot of info for a newbie to digest.

Perhaps you could shed a little theoretical light on a given scenario:

If the local feedback was optimized for IRF540s, such that they are as linear as they can be, what is the effect on the sound signature when IRF510s are inserted in the circuit with no other changes? I understand that the THD will be higher, but does it skew the sound towards a bass emphasis or treble emphasis, or is there simply not enough information to draw any useful conclusions?

Of course, this leads to the next level of questions, what happens if the IRF540s are replaced by IRFZ24s or 2SK2013s...
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