Typical Royer 5840 Mod Tube Noise?

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Michael_Joly

Active member
Joined
Nov 11, 2004
Messages
42
Years ago I built Dave's MXL/5840 mod. Love the sound but have never done much recording with it because of the noise. Here's some figures for S/N. What are you guys getting?

Test source: Tongue / teeth "click" (that fast transient sound made by pullling the flat surface of your tongue quicly away from the top of your front teeth) and normal level speaking voice.

I'm using a peak reading LED meter. Mic warmed up for 12 hours (more on this later)

I set the gain of the mic pre to read 0dB on the peak of the tongue click 2" from the capsule. My normal speaking voice comes in at -24dB at the same distance. Noise floor measures -56dB. I was recording a quiet singer yesterday, a 32dB S/N is just not going to be acceptable.

Noise is very LF and MF weighted - not hiss, a real rumble and crackle. My engineering notes from several years ago state "...this mic takes several days to warm up and settle down to a level that aproaches a solid state circuit".

I'm going to let it continue to sputter away for a couple of days and check it again to see how valid my old lab note is and if all the bad electrons have boiled off and the thing has settled down.

Should I swap tubes? Bad resistor noise? What have you guys found for this circuit? I noticed Mojave doesn't publish a noise spec for their 5840-based MA-200 mic.
 
make sure the membrane to grid connection is clean. It´s very high impedance, and moist or dust may cause problems...

My friend had two ELAM-251 mics that didn´t sounded the same. Number one had an old ceramic tube socket and number two had a newer plastic one. Number one sounded way better. I mean very noticiable. No audiophoolish. He tried to swap parts, including capsule, to find out what was going on, but it kept the same. Number one nice, number two bad. So he bought an old ceramic socket for number two. That solved the problem. :shock: Well, you can´t point one or another now. They sound identical and nice!
 
Is the grid wire soldered to the PCB? If so lift it in the air and connect it to the capsule wire also in the air. Also make sure the capsule is clean. One of the 2001s I bought was noisey out of the box and needed the capsule cleaned, this was a few years the newer MXLs I have have not had this problem.
 
I built it point-to-point with connections as short as I could manage. I think I'll try resoldering the capsule / grid connection and cleaning the capsule.

While I'm in there maybe I'll short the grid to ground and just listen to the tube noise.
 
Grounded the grid - nice and quiet. Just the normal type of tube circuit hiss, mostly 1kHz and above.

Swapped in a known good 34mm capsule from a Studio Projects C1. LF-MF crackles and pops come back.

Maybe this particular 5840's grid doesn't like the source impedance of the capsule?
 
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