Good day all,

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I am new to the group but learning much from digging through old posts and files.? Microphones, specifically, is a relatively new area of interest. I have tinkered with electronic and electro mechanical devices for many years, mostly related to RF communications.

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What brought me here is an interest in what is often referred to as "natural radio" - listening to and recording the sferics, tweaks, whistlers and chorus of? extremely low frequency (ELF) radio waves emitted by charged particles in the Earth's atmosphere and magnetosphere in the range of 10kHz to 25kHz ( plus and minus ).?

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It occurred to me that the likes of electret and condenser microphones and their circuits are not that much different to something suitable for monitoring "natural radio" - the need to interface a very high impedance transducer, the electret or condenser capsule in the case of the microphone and the electrically very short antenna in the case of the receiver, to the much lower impedance electronic amplifier circuits which follow.

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As is often the case, my interest in a specific application area developed into a much broader interest in the very interesting and much broader subject area of microphones.

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In my tinkering with various types of microphones I have a need to boost the output of a dynamic microphone. Easy enough to do - just plug in one of those generic inline phantom powered microphone preamp/boosters - job done.

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However, plug and play just does not cut it with respect to learning and understanding. Opening up a couple of these inline preamps plus many hours of searching and reading online has helped in the learning and understanding but has also left many more questions.

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What brings me to my post today was prompted by my recent comparison of a Klark Technique CM-1 inline preamp and the Rodyweil AC-1 inline preamp. Certainly not high end devices but suitable for my current needs.

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On comparing the PCB's from these two devices it quickly became apparent that the designs of these two devices were exactly the same - same components ( 2x PNP BJT, 2x NPN BJT, same number of capacitors and resistors of same value) and similar PCB layout, almost as if these two devices used the same "common" or "reference design" circuit.? I have yet to fully sketch out the circuit diagrams of these two devices but that will come with time.

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That was a long way around to the crux of my posting - Is there somewhere ( that I've not yet stumbled upon) a circuit diagram of these or similar devices ( i.e. phantom powered 4x BJT inline microphone booster/preamp). Is it or are they in fact some "common" or "reference design" of some older origin and now often copied and duplicated in these low cost Asian sourced implementations??

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cheers, Graham

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On Thu, Aug 1, 2024 at 01:25 PM, Jerry Lee Marcel wrote:

Actually, most of the in-line boosters use JFET's. Typically 2SK170 or its dual version LSK389.

This subject has been discussed to death in a few threads in the GDIY group.

Yes, I have found many references to the inline boosters using JFETs including the Cloudlifter which uses the? the LSK389.

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However, the Klark Technik, at least the one I have, and Rodyweil to which I referred both have four sot-23 style SMD transistors two each marked CBL and 2GM which decode to the best of my knowledge as 2SC3324 (NPN) and MMBTA56 (PNP) BJT transistors respectively.

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I use this website to help decode SMD markings: ? There was another I had a link to but it seems to have disappeared.

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I have been finding some details on the and forums but nothing (so far) which help answer my questions BUT there is much information and these online forums are not always the easiest to search. Just a matter of continuing to look under rocks to see what can be found.

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cheers, Graham

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Still no luck in finding references or schematics of a phantom powered balanced microphone preamplifier using two pairs of PNP/NPN BJTs.
It seems that since these two preamplifiers from two different manufacturers that each have the exact same components, layout, and presumably the same circuit, leads me to think that the underlying circuit should be quite common but I have yet to stumble across the same or similar in the various online groups. Perhaps just overshadowed by the popularity of the FET types.

On Fri, Aug 2, 2024 at 11:15 PM, kennjava wrote:

On Fri, Aug 2, 2024 at 01:08 PM, Jules Ryckebusch wrote:

I use a 32 bit float All the time. Game changer?for me.

Digression, but would you consider writing up your experiences with 32 bit, and what post rebalancing workflow you follow? There's still a lot of hype around 32 bit, and good articles are welcome.

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My 24-bit recorders still satisfy my 12-bit ears, but some year, maybe I'll take the plunge. That will be approximately when everyone else is going 48 or 64 bit.

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Appreciate that your post is addressed to Jules, but the nature of 32 bit float tends to make the concept of 48 or 64 bit A/Ds rather redundant! ....?

As Jules says, it's real game changer. It is almost counter intuitive not to worry about setting gain levels for optimum performance, but with 32 bit float you really don't need to.?

Although the higher resolution A/D converters make the problem less critical, they do still lose some resolution at very low signal levels, and will clip hard at 0dBFS.

Neither of those two things happen with 32 bit Float!? I found this page from Sound Devices quite useful :

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Note that the advantages of 32-bit float apply to the recording process, not to the converters. Most converters are 24-bit and do not actually achieve the theoretical dynamic range of 146.26dB, just because of the limitations of the analog path.