Hi
Today I found something pretty surprising for me. I have this ELAM inspired circuit with a MBHO CK12 like capsule and a Haufe T14 transformer. Until a few years ago I used an ECC81 as the tube and I really liked that mic a lot.
The tube got noisy so I thought, well, The original ELAM was also build with an ac701 so I can install a 6s6b tube and enjoy the ultralow noise floor and good sound of this tube as well. I used a 100k plate resistor and 2,2k cathode resistance. The tube sounded clean and the noise floor was really low, but somehow I used that mic only rarely after the tube change. I found it too bright a lot of the times.
So a few days ago I thought I could try a deemphasis network like in this thread https://groupdiy.com/threads/u67-ish-microphone.75162/ to make the mic more usable.
I used a 10k trimmer as R10 and 100p as C9 and found I like the sound much better with 2dB less at 10kHz.
So I measured the circuit at the test input and found out that I simply linearised/repaired it with that network
Look at that:
The transformer is badly ringing going into my fireface400 Micpre. No wonder the mic sounded kind of wrong most of the times I tried it.
I guess the higher source impedance of the ecc81 linearised the transformer before, at least that is the only way I can explain my observation. The T14 was made to interact with the 6072 and this tube has a pretty high output impedance also.
All the years I was wondering if my taste in sound had changed, or something, I never connected the tube change to be responsible for that, because the 6s6b worked great in other microphones of mine. But they all have a 7:1 bv107 transformer and I guess that one is better suited to the 6s6b.
From now on I am going to measure more thorough, that is for sure.
What do you recommend as the best solution?
I could try to change the plate resistor from 100K to 200k and bias the mic colder.
Or change the tube to something like the the 6s7b with its higher plate resistance. I would love to keep the ultralow noise floor of the 6s6b, maybe the 6s7b has the same quality in that regard?
Or simply keep the tube and the feedback network as is now, since it works?
Edit:
I just tried the 200k Plate 3,6k cathode resistor mod (AC701 like) and it does not work out at all... That tube needs more current to work right, I guess.
Today I found something pretty surprising for me. I have this ELAM inspired circuit with a MBHO CK12 like capsule and a Haufe T14 transformer. Until a few years ago I used an ECC81 as the tube and I really liked that mic a lot.
The tube got noisy so I thought, well, The original ELAM was also build with an ac701 so I can install a 6s6b tube and enjoy the ultralow noise floor and good sound of this tube as well. I used a 100k plate resistor and 2,2k cathode resistance. The tube sounded clean and the noise floor was really low, but somehow I used that mic only rarely after the tube change. I found it too bright a lot of the times.
So a few days ago I thought I could try a deemphasis network like in this thread https://groupdiy.com/threads/u67-ish-microphone.75162/ to make the mic more usable.
I used a 10k trimmer as R10 and 100p as C9 and found I like the sound much better with 2dB less at 10kHz.
So I measured the circuit at the test input and found out that I simply linearised/repaired it with that network
Look at that:
The transformer is badly ringing going into my fireface400 Micpre. No wonder the mic sounded kind of wrong most of the times I tried it.
I guess the higher source impedance of the ecc81 linearised the transformer before, at least that is the only way I can explain my observation. The T14 was made to interact with the 6072 and this tube has a pretty high output impedance also.
All the years I was wondering if my taste in sound had changed, or something, I never connected the tube change to be responsible for that, because the 6s6b worked great in other microphones of mine. But they all have a 7:1 bv107 transformer and I guess that one is better suited to the 6s6b.
From now on I am going to measure more thorough, that is for sure.
What do you recommend as the best solution?
I could try to change the plate resistor from 100K to 200k and bias the mic colder.
Or change the tube to something like the the 6s7b with its higher plate resistance. I would love to keep the ultralow noise floor of the 6s6b, maybe the 6s7b has the same quality in that regard?
Or simply keep the tube and the feedback network as is now, since it works?
Edit:
I just tried the 200k Plate 3,6k cathode resistor mod (AC701 like) and it does not work out at all... That tube needs more current to work right, I guess.
Last edited:
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