brightening up a U47 clone

Hello,

A few years ago I built myself a U47 replica/clone from micandmod.com.  My mic uses two 408a tubes.  I really like the microphone and am happy with it.  It has been used against an actual telefunken u47 and my microphone was chosen over it in the studio. I know mine is not an exact replica but it's close enough for me.

I have a friend who was so impressed with my microphone that he decided to order one just like mine.  Only thing is, his microphone uses a Telefunken ef800 tube.  It sounds dull and lifeless compared to my microphone. He is asking me if I can modify his microphone to increase the brightness or presence.  It is of no use to him the way it is.

I told him it may not be as easy as just changing out a capacitor or component.  It could be the differences in capsules, transformers, tubes etc.

My questions is:  Is there a capacitor in the u47 circuit that determines the amount of high frequency response?  I am no expert on microphones.  I haven't studied them in depth yet but in a guitar amp , which i do build regularly, there are capacitors that can be selected for more or less high frequencies.  Does the U47 work this way? 

I would measure frequency response of the circuit first. Could be he has some HF roll off going on somewhere.

Check all the high-ohm resistors, and compare between the two mics.

My guess, yours are 100-150 MΩ
His are 1GΩ
Big difference in highs and 'liveliness' of the microphone.

Then check coupling capacitor: is yours 0.5uf or 1uf? Is it different from his?

what kind of capsule does you pals mic have? it's likely the culprit, the capsule is the biggest deal in these or any mics for that matter.

What capsules were used in each build?

Did you use the same transformer and other parts except the tubes with both microphones? If so that could be what you are hearing

As other guys mentioned. You have to check every single part inside, but generally sound is in Capsule-tube-transformer. But hey, resistors and capacitors has some influence, also PSU design and PSU parts.
Don't get me wrong, but building microphone with cheap parts is always gamble.  Guys who sell those kits doesn't pay too much attention about the sound.

Glacier

anything?  You asked questions and people posted.

I'm sorry for the silence.  I had a death in my family and am not working on any equipment for the time being (its my hyper-hobby so I don't have to do it).  I still have my friend's microphone and will get to it soon. When I do, I will update with my findings. Thank you for taking the time to comment. I'll be back.

Update:

I opened both microphone's up tonight and inspected them side by side.

I discovered that my microphone has 100M  r1 and r2 and my friend's mic has 1G r1 and r2.

So...I am going to begin with swapping those resistors out and see what happens.  I didn't have any 100M on hand so I ordered a few from Mouser.

Banzai said:

Check all the high-ohm resistors, and compare between the two mics.

My guess, yours are 100-150 MΩ
His are 1GΩ
Big difference in highs and 'liveliness' of the microphone.

Then check coupling capacitor: is yours 0.5uf or 1uf? Is it different from his?

Click to expand...

I think you may be correct.  Both of our microphone coupling caps are 1uF.

tonycamp said:

what kind of capsule does you pals mic have? it's likely the culprit, the capsule is the biggest deal in these or any mics for that matter.

Click to expand...

I do not know what brand the capsule's are.  They came with the mic kit. I am sure they are not the deluxe capsule like from Peluso or the like. I would guess they may be Chinese capsules.  Or possibly they were assembled in France where the kit came from?

Inspecting the two side by side, they look identical in construction.  The specs only say that they are a K47/M7 style.

Gus said:

What capsules were used in each build?

Did you use the same transformer and other parts except the tubes with both microphones? If so that could be what you are hearing

Click to expand...

Same transformers in both mic's.  Different tubes (2x408a vs. 1x ef80).  Resistors and capacitors were identical between mic's, except for the grid resistors r1 and r2.  Capsules also look the same to me. 

Glacier said:

Same transformers in both mic's.  Different tubes (2x408a vs. 1x ef80).  Resistors and capacitors were identical between mic's, except for the grid resistors r1 and r2.  Capsules also look the same to me.

Click to expand...

Now, if I double think I think that you have to try to change the tube. Not because Ef80 sucks, but because you like 2x408a.  Of course, you will have to change much more because of  the PSU heater but then you will have something close enough to compare.