line level mics

[ioaudio]

i think about making a pair of tube large diaphragm condernsers, as well as a stereo mic pre.
if i would lets say combine g7 and g9, could i get rid of the mic-out/pre-in transformers?

im aware of the fact that i cannot plug in various mic pres any more and that the two missing transformers in the audio-path would sound different.

 

[ioaudio]

pump

maybe someone could point out the mein disadvantages

 

[rodabod]

Do you mean put the mic and the preamp in the same body?

Would it fit?

Well, I suppose you could. You would be stuck with the same preamp though.

I would not do this just to save money - it is not worth the savings.

 

[ioaudio]

same body- good question.what should be the maximum length of a cable between the capsule and the grid of the first input tube?

 

[Gus]

A "standard" cathode bias triode gain stage can have a good amount of gain.

LuLu the space cat had a nice microphone circuit

Look at the levels a a U47 can put out.

Also look at the levels a ATT4060 or even a TLM103 can put out The AT and 103 are a unity gain amp as best I can tell.

The u47 has a stepdown transformer at the output

Now take say a 12at7 set the first section up as a cathode biased stage then to a vol control then to a CF made from the other triode no output transformer. Hint the UM57 tube is like 1/2 of a 12at7.

You could wire the CF direct to the first stage and control the vol with a control on the power supply box unbalanced you could add more stuff in the power supply box.

One could place a servo from a RC car or plane etc on the pot to turn it remotely(270 degrees if IRCC), mute the output from the microphone durning the 1 to 2 ms pulse stream on time to turn the motor. 5VDC 1ms is one side 1.5 ms center and 2ms other side at about 50hertz IIRC. You could do this with a micro but a 555 and pot work well

There are other way of doing this

 

[ioaudio]

lets say i would build all the electronics into an external case. how long could the lead be capsule<->preamp?

 

[rodabod]

[quote author="Gus"]
LuLu the space cat had a nice microphone circuit

One could place a servo from a RC car or plane etc on the pot to turn it remotely(270 degrees if IRCC), mute the output from the microphone durning the 1 to 2 ms pulse stream on time to turn the motor. 5VDC 1ms is one side 1.5 ms center and 2ms other side at about 50hertz IIRC. You could do this with a micro but a 555 and pot work well
[/quote]

I've asked this before, but is LuLu the space cat still around? I loved that website.

That servo idea sounds crazy - where did you get that idea from?

lets say i would build all the electronics into an external case. how long could the lead be capsule<->preamp?

You couldn't really just connect a capsule straight to an external box via a cable - that's just not a good idea. The electronics need to be in close proximity.

What's wrong with putting the electronics inside the mic body?

You could compromise and have some amplifier circuitry in the mic, and the rest in a box - seems like a bit of a waste of effort though.

 

[ioaudio]

i would love to have smaller mics...thats the main reason for this approach...
if i already have a case for psu, why not stuff in the preamp, saving two transformers...
but anyhow i somehow knew there was a reason for not doing so...

 

[Gus]

I raced RC cars years ago. Ace made a nice servo tester that used a 555 that you could plug a servo into with out having to turn on the radio control. This allowed one to set things up on the car plane boat etc.. That was 20+ years ago so things might be different

Capsule to gate or grid should be short as possable a few inches max IMO.

I don't know what happened to the LuLu site.

Say a microphone has a 10:1 output transformer that is a gain reduction of about 20Db

But remember some of what a tube microphone is about sometimes is the gain stage distortion and the transformer distortion and the type of bias. If you don't want clean maybe you want a "standard" microphone preamp setup.

The G9 with oeps I heard is not what I call clean preamp even with Lundals it has it sound and the G7 has it own sound. So what do you want?