John Curl's Blowtorch preamplifier part II

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#79,045
I've done very careful listening tests with ferrite beads in the inputs of a preamp.

The ferrites are designed to attenuate RF ingress above 20 MHz. Below 1 MHz, the insertion loss is low, and at audio (i.e. under 100kHz) it's in low single ohms.

There is NO audible difference with the ferrites in place, other than a complete absence of RFI.

Better still, when I look at the response with a signal generator and scope, I see no anomalies that could possibly point to anything detrimental happening with the sound
 
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#79,049
john curl said:
I have always hated Ferrite beads, based on early experience with them in the early 70's. I could not measure much then, but I just did NOT like the overall sound effect. This paper might be an eye opener.
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Ferrite is ok, the problem is how it's used. I've heard awful effects nearly every time I've applied certain types. However I have no objections to transformers and CMC's, etc... there's a reason that I've noted.
 
#79,050
john curl said:
Many here, who use their ears, and trust their personal judgements often come up with what really works, and what sort of works, you might say. Class D amps have always been problematic with me, for example, except to bass, (maybe). Others have heard the same thing. At the moment I am working on a Class D amp, so any input from you all would be appreciated. No, not the digital, just the analog part, but I am now focusing on Class D as a design. Thanks in advance. Hear no difference people, need not apply. '-)
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I could probably tell you numerous things that make a big difference... You're welcome to PM me.
 
#79,051
Bonsai said:
I've done very careful listening tests with ferrite beads in the inputs of a preamp.

The ferrites are designed to attenuate RF ingress above 20 MHz. Below 1 MHz, the insertion loss is low, and at audio (i.e. under 100kHz) it's in low single ohms.

There is NO audible difference with the ferrites in place, other than a complete absence of RFI.

Better still, when I look at the response with a signal generator and scope, I see no anomalies that could possibly point to anything detrimental happening with the sound
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You were warned...

Hear no difference people, need not apply. '-)
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John what about those that honestly hear no difference?
 
#79,053
jneutron said:
In this specific discussion, I've pointed out concerns with the generalized engineering models used; specifically how the transient use of a system engineered for steady state may not be sufficient.

John
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In general the models I've seen correctly predict complex impedances and their implications, the problem in usually the user.

A good place to look might be the difference between the impulse response measured with an impulse vs. any of the techniques that spread the energy over a broad range of frequencies.
 
#79,055
Waly said:
Why would anyone volunteer to support your business endeavours for free, only to be insulted three pages later?
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When a designer is not competent enough for a particular task, and has to ask for free help at a diy forum, the crazy one isn't the designer, it's the person who's willing to pay him and the person who teaches him how to do the design properly and does so without sharing in the paycheck. 😀
 
#79,057
Class D suggestion: If you're going to use MOSFETs in common source switching configuration to produce the high current square waves, spend a bit of time considering the idea of inserting a low-value noninductive resistor in series with each drain. External resistances on the order of RdsONmax and/or on the order of 2-3 times RdsONtyp. Why? So that your risetime, and your final flat-top voltage level, is repeatable from one MOSFET to the next, from one batch of MOSFETs to the next, and from one finished Class-D amplifier to the next.

Another suggestion: when designing your nonoverlap generators, focus on fast output risetime more than you focus on getting a complete and total nonoverlap where the waveforms cross literally at the rail. You've got Vth of safety margin to play with: exploit it!
 
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#79,058
Just Class D problems, not how to design Class D. Others will design the digital part, and they have done very well, so far as I know. I doubt that any here could or would tell me anything useful knowingly. I am not personally going into Class D design, I will leave that to Bruno and others.
 
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