Gentlevoice's comments. (I could open the doc and paste them in, but had to get rid of the accented e's!)
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I note that meanwhile PRR has posted again (thanks
) - I have considered your reply in my comments below, although have not yet commented on your high current suggestion as it seems that some of the other aspects already discussed may mean a possible "go" or not. Please see below.
@ PRR
Thanks for your detailed comments. They inspired more thoughts and a couple more comments:
The common-grid connection is _NOT_ low noise in audio systems. Either it loads the source so bad you lose half the source Power (3dB NF), or it mis-matches and emitter resistance noise exceeds source noise.
Hmm.. I have used it with audible success (to my preferences) in an A/D converter's I/V stage. Also, I know that such a stage was used in L'Audiophile's le Prepre back in the eighties (?) - a design intended for MC cartridge amplification (impedance 2-3 ohms, though). I used to have one of these (with the extra transistor you mention - which BTW in Spice makes for a low frequency hump < 2 Hz which is one reason I chose not to use this configuration) and in my opinion it had some qualities. I do read your other comments, however, about noise. And I remember that used with a moving coil cartridge it was not entirely noise-free (hiss only) which is a must in this application.
I reckon there may be another reason for using it, though:
- Due to it's very low input impedance the overall impedance of the ribbon + input circuitry is low. If I'm not too mistaken (I may be
) airborne hum & other electromagnetic noise has relatively low power, yet may have "high" voltage, meaning that in low impedance circuitry hum induction would be lower.
I don't know, however, if loading the ribbon with a low impedance will choke the LF response as Marik noted in one of his thread - links. Also, if an additional 40 dB amplification relative to a dynamic mic (and another 3 dB to the KM184's 15 mV) is needed - that is some ....
I have not dinked with naked ribbons, but I thought they liked to be wired symmetrical to cancel hum fields. That seems to require a balanced input.
If that is so it would indeed be an issue as a balanced input is not an option. No way to work around this?
In considering your other comments I agree with your thoughts on currents going through the membrane & a DC servo. I didn't include it in the schematic to keep focus on the amplifying part. I'll be using the system off-grid and the voltages correspond with typical lead-acid battery voltages some hours after charging (most likely will be lithium - haven't decided on that yet. I first would like to know if the basic ribbon design will work).
Very low noise in this design is however crucial so if it cannot be done ......?? I'm also open to using a condenser or another superb microphone technology, but need it to go down to ~1 Hz and up to ~40 kHz - again with low noise. And a loose membrane is very much preferred.
@zebra50
The only commercial active ribbon mic i've seen without a transformer is the Oktava ML51. I haven't used one, but Marik gives his opinion on the noise level. Here's a link to the circuit.
Hi
I've taken a look at the microphone and without knowing I guess it would use a less powerful magnet system than the Neodym magnets? I also looked at the schematic and noticed that the supply voltage is 3 VDC meaning that the current through the transistor necessarily will be very low. With the 2SC3329, going from 0.1 mA to 5 mA means a 6 dB NF improvement.
Do you mean 0.6 micrometers for the aluminium thickness? You may be up to around 0.5 ohms for the ribbon resistance depending on length & width. But good luck with that - it will be very tricky to cut & handle at that thickness.
Actually I'll be using an appr. 0.4 mymeter (0.4*10-6 meter) thickness which I hope to attach to an ultra thin mesh - sort of like a spider's web. And no, I wouldn't like to tinker with the 0.4 mymeter membrane on its own :-\ I don't yet know what the resistance will be but probably about 15% lower than a similar thickness aluminum membrane.
@ Samuel Groner
Hi- thanks, Samuel. What I'm looking for, though, is the "raw" (unaltered=unamplified) output of the ribbon + magnet motor itself. I would also be interested in knowing the "raw" output of a typical 3/4" condenser capsule.
Wauw - many words ... so maybe I should sum up. I'd appreciate to know more about:
Is it possible to make a naked ribbon feed into a single ended amplification stage - no transformer - without hum (e.g. with a low impedance input amplifier)? Is it an option to split the conducting foil of a ribbon microphone into e.g. 5 paths thereby raising the resistance and matching better to the input of the amplifier AND maintaining superb sound?
And if not, do you have a suggestion for a condenser microphone/other microphone design going from ~1 Hz to ~40 kHz with a loose membrane?
Other suggestions/comments?
If you got this far then thanks for reading & best wishes for your evening (it is so here in Denmark)
Jesper
