What to do to increase the output?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Slava

Member
Joined
Mar 19, 2019
Messages
10
Hello, could you please answer my question about the microphone with Tim Campbell capsule CT12 and a valve Telefunken EF 86. We made the voltage 60V on a capsule. Appeared such things: the volume became quiter, a valve Telefunken EF 86 has made the harshness of sibilants. Here is the question. How much can i increase the voltage on a capsule? Does it need to increase? Will it change the dynamics of high frequencies with an increasing the voltage on a capsule. How will the signal volume change? What to do to increase the output? 
 
I was starting to wonder if the measurement point (or the wiring) was correct.
There's a chance the B+ might've been adjusted to 60v(?) or something, which might drop the capsule bias below optimal.

That's why i asked about the circuit.

RuudNL said:
Don't go higher than 60 V. on a CT12!
 
Khron said:
What sort of circuit is in that microphone?

At first it was U47 circuit but then the man who did that began  to make changes in it. Till this moment there was a Russian tube 6ж32п (analogue EF86), which needed 6.3 V of heater voltage. Then he decresed the heater voltage for  Telefunken EF 86.
 
Referring to the attached schematic, were you measuring that 60v at the point between R7 (2Meg) and R8 (3Meg)?

Also, what are you measuring as the B+ voltage (on "St1/5", 105v in the original schematic), and across C3?
 

Attachments

  • u47.gif~original.gif
    u47.gif~original.gif
    126.6 KB · Views: 11
Here are the samples of 2 tests with different tubes.
https://vocaroo.com/i/s17spFGuBeIA - Test microphone+Russian tube 6ж32п - on a capsule 85V
https://vocaroo.com/i/s0UpRzFAV9el - Test microphone + Telefunken tube  EF 86  - on a capsule 60V 

What you can say about the mic sound? They are processed a lil bit different but the compresion is the same and reverb preset is the same. 
Vocal Processing: Rvox waves, LA 2A IK Multimedia, Q Hi Pass filter, Liquidsonics reverb. 
 
Khron said:
Referring to the attached schematic, were you measuring that 60v at the point between R7 (2Meg) and R8 (3Meg)?

Also, what are you measuring as the B+ voltage (on "St1/5", 105v in the original schematic), and across C3?

I will ask the master about your question and get back to you.
 
I have a problem with "harsh" definition in general. I never really found out what it means, as it seems to vary from person to person.

Is it just bright, or do you hear/measure some type of distortion/phasing/smearing in high end?

I've made several circuit options with several diferent tubes and ct12, but never found that certain tube makes a mic harsher. I used various russian tubes.

One thing to have in mind is that ct12 is pretty bright capsule. It should be, c12 is a bright mic. However that high end is very, very nice. And very different compared to bright k67 capsules. Both boosted and attenuated it has silky character, it's never abrasive, pointy for lack of better term. It's centered at abouk 8k which i find to be very musical point.

I remember trying it for the first time on vocals, without any backing track. I thought it was waaaay too bright. I was a bit puzzled. But then i introduced backing track, and found out the vocal didn't need any eq treatment at all. It has just the perfect amount of everything. Sometimes i just use hpf, and that's it.

People like u87s and u47s for their "warmth", but then end up boosting hell lot of high end to make those work in mix, not the case with ck12 mics.

Could it be the same thing you are experiencing?
 
Absolutely true.  I agree with you that this capsule doesn't need the eq, and i used HPF too.  When it had a russian tube, the high frequencies sounded restrained and not so dynamically. I liked that but the sounding did not have a  high end breath . This high end breath appeared when we inserted Telefunken EF86.  But now the range approximately 8-10 khz became a lil bit shooting.
I know Telefunken EF86 is very dynamic tube. The man that was making our microphone asked me not to hurry with my opinion and to wait about a week until all components work together well.  May be he is right.  Tomorrow i want to buy Valvo EF 86 which is sounding very good too but a lil bit different.  What do you think about it?

kingkorg said:
I have a problem with "harsh" definition in general. I never really found out what it means, as it seems to vary from person to person.

Is it just bright, or do you hear/measure some type of distortion/phasing/smearing in high end?

I've made several circuit options with several diferent tubes and ct12, but never found that certain tube makes a mic harsher. I used various russian tubes.

One thing to have in mind is that ct12 is pretty bright capsule. It should be, c12 is a bright mic. However that high end is very, very nice. And very different compared to bright k67 capsules. Both boosted and attenuated it has silky character, it's never abrasive, pointy for lack of better term. It's centered at abouk 8k which i find to be very musical point.

I remember trying it for the first time on vocals, without any backing track. I thought it was waaaay too bright. I was a bit puzzled. But then i introduced backing track, and found out the vocal didn't need any eq treatment at all. It has just the perfect amount of everything. Sometimes i just use hpf, and that's it.

People like u87s and u47s for their "warmth", but then end up boosting hell lot of high end to make those work in mix, not the case with ck12 mics.

Could it be the same thing you are experiencing?
 
I'm sorry, but that just triggered my "BS alarm" :eek: Let me guess, components now need to "burn in"?  ???

Sure, 'cause it's always the components / devices that (need to) "burn in", and never our hearing or our perception of them...  ::)

Slava said:
The man that was making our microphone asked me not to hurry with my opinion and to wait about a week until all components work together well.  May be he is right.
 
Tubes do need to burn in, specially in microphones.

Don't expect a single tube from a brand to have any kind of predictable characteristics - for EF86's it is about trying a handful of different ones until you find one you like.

Even in same-batches (which is very rare now for NOS EF86), there is wild variation between tubes when it comes to suitability for mic frontend use. This because in a mic, it's used outside the specifications that factory aims at.

Which also means that even though you tried one russian tube, this dosen't tell you anything in general about a "sound" of this russian tube type. This is a common misunderstanding that generates a lot of imagined differences between tube brands: The only safe thing you can say about differences between brands is HOW MANY of a batch that can be predicted to be suitable for microphones.

And this even only applies if you have tubes that was not previously de-selected in someone else's selection process. Ebay is full of tubes of all sorts that has been through similar selection processes many, many times before - but that still fulfills manufacturers specs despite being unusable for audio purposes...

Jakob E.
 
I agree with Jakob, I would try a few EF86's and a few of your russian tubes before I would decide on what sounds best. The same model tubes from the same manufacturer sound very different from each other, some brighter , some darker, some with hotter output. I would also let the mic stand when turned on for at least 10 min so you are sure the tube is working optimally.  You may find that 55v on the capsule sounds a bit smoother.
What transformer are you using?
 
I can't answer your question about transformer because the man who made the circuit doesnt want to tell about it.  He's odd.

Tim Campbell said:
I agree with Jakob, I would try a few EF86's and a few of your russian tubes before I would decide on what sounds best. The same model tubes from the same manufacturer sound very different from each other, some brighter , some darker, some with hotter output. I would also let the mic stand when turned on for at least 10 min so you are sure the tube is working optimally.  You may find that 55v on the capsule sounds a bit smoother.
What transformer are you using?
 
Is it btw. possible that reducing bias voltage on some capsules will shift the resonant frequency downwards so that it will move towards the sibilant area?  It is possible in theory, isn't it? At least if the diaphragm has been treated with almost overvoltage like in this case?
 
Now the output is ok. The voltage on a capsule - 55V.  But the sound has  a such dryness especially in high mid and high frequencies.
Samples enclosed. Vocal test without processing  and vocals in the mix.
Also the man who did the circuit said that it was a scheme U47 with some corrections.  Here are the photos of the components.
What you can say about capacitors?  Why do you think the sounding has dryness?
https://vocaroo.com/i/s1PV2Fnhz7k0
https://vocaroo.com/i/s1E9i9AKlKFj 

Here are the photos. 
What can you say about the sounding of these capacitors used in this circuit?
Vishay/BC X2 Suppression Film Metallized Capacitor MKP
Rifa phe 830 м 250v sh x2 40/100/56 E7
1.0uF-250V MATSUSHITA ECQ-UV POLYPROPYLENE 10% MKT GPF












 
Any chance you could measure frequency response of the circuit, and the microphone itself acoustically? At least circuit response.

It is pretty straightforward process, revealing, and might tell you if there is anything wrong with the mic. It also helps with abstract adjectives, and might show you if different random capacitors do anything for the sound.
 
Back
Top