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[zerofly]

Hello Klaus and people,

I have a Flea-f47 u47 clone and i have a strange, allways the same midrange resonance and not so much of a bass weight.

It has a vf12 tube and a Flea f7 capsule.

My thinking on trying to solve this myself is changing capacitors first and maybe the capsule.

The c3 capacitors is a Russian k42 pio, not the worst nor the better but i would like your input on that.

The c2 capacitor, strangely, is a 100nf capacitor instead of the standard 0.5 or 1uf capacitor?? why could this be? how can i upgrade that?

also the C1 capacitor does not make me that calm, it looks like the old siemens stacked polyester capacitors. How can i improve this??

here are some photos:
http://s1098.photobucket.com/user/zeroestudios/library/flea%20F47%20inside

Please hep me out!!

Thank you.

Kind regards.

[klaus]

If FLEA's copy of the U47 follows the Neumann schematic exactly, the values for C2 would be 0.5mfd or 1.0 mfd, and C3 would be 1.0 mfd.

Measure the capacitors found in the mic with a capacitor tester (you did not state the Russian Paper In Oil cap's value), and replace, if necessary, with the afore mentioned values.

For the time being don't fret about the material of these caps, but first verify that their value is the same as in original Neumann U47, THEN start experimenting with the more subtle effects of capacitor material.

[zerofly]

Hello Klaus,
i sincerely thank you for the response.

Sorry, the russian cap is 1uf, K42 type. what can i put in there? MP? Pio?

C2 is 100nf,  bugs me!! i never saw any u47 schematics in which C2 is lower than , 0.5uf.what do you think? should i place a 1uf or 0.5uf capacitor in there?

C1 is 10nf, correct value, but, can the type of capacitor be an issue?

It is supposed that they followed a U47 schematic, but.. the only difference should be the FV12as well as the heater´s voltage.

i have a ringing around 800Hz, independently of the vocal or instrument i always have to correct it there.

Many thanks.

Kind regards,
Pedro.



 

[klaus]

I mentioned in my earlier response the specific capacitor values I would put in this mic AFTER confirming with a meter that the values currently installed are indeed off. I also mentioned that considerations of what capacitor material to choose rank down the ladder from value considerations.

In my opinion, you will never get a genuine U47 sound out of this mic, given that at minimum the tube, capsule and transformer are non-original, and, in the case of the capsule and tube, are very far from the original design.

But with my recommendations, you will at least get closer to an aurally pleasing result.

[zerofly]

Ok, got it!!

Thank you very much, will try that.

Kind regards,
Pedro.

[Kai]

cap (c3) is 1uf, K42 type.
C2 is 100nf
C1 is 10nf, correct value, but, can the type of capacitor be an issue?
i have a ringing around 800Hz

C2 together with the transformer inductance, forms a 12dB/Okt low cut that can even build up a resonance at the mentioned frequency if C1 is too small.
C2 has to be tuned to give a low cut in the range of 30Hz if you want to follow the original.
Start with 0.5uF and measure the amps frequency response (feed a freq. variable sinewave ca 30mV via a small cap ca. 1nF into the capsule connection, capsule can stay connected if done in a not too noisy environment).
C1 and C3 are not responsible for any sound changes, as long as they do their job filtering any hum and noise to GND.
I would avoid ceramic at C1, use a foil type, e.g styroflex.
C1 needs to be low DC loss, else you get LF noise.


What remains is the sound of the capsule - get yourself a genuine new Neumann K47 to make this a highclass mic (probably, if the transformer holds the quality).

[zerofly]

Hello Kai,

Ok, that makes sense!

I was thinking about replacing C1 with Styroflex or polyester but you just cleared my doubt, ill try Styroflex.
Also i was gonna jump into replacing C2 With 1uf but i will try first 0.5 and measure it´s frequency response to see where the LC is , thank you, just learned something valuable today, never came to me injecting a sweep into the capsule to measure the amps response.

there is something else strange, R1 is 200M, and R2 is 100M metal film, i don´t know if the Ef12 needs that much of a change in the circuit besides heater voltage but it is strange to my limited knowledge.


Yes, it came to me aiming at a K47, i don´t know if the capsule that came in is good or bad nor the transformer but it surely does not sound like a U47, it´s not a neumann, i know, but i have heard some great copies.

I highly appreciate your help, thank you!!

Kind regards,
Pedro.

[gtoledo3]

Doesn't changing values in the circuit presume that this is 100% similar to the U47 circuit? Not saying it isn't, I just find that an interesting place to start jumping in, especially if that's a mistaken presumption. Especially when the values you're finding are so far from expectation... maybe there is a rhyme and reason to it that is being glossed over by asking third parties on it instead of the source (FLEA). The EF12 is substantially different, and I would think that the circuit has been amply changed to work with it, if it's the same at all.

While I think there are some pretty good k47 "copies", usually from sources that really have vast experience with the real deal and have manually selected them... my experiences would lead me to think that this would be the first thing to consider upgrading on the FLEA. At least you won't blow anything up.

[klaus]

Doesn't changing values in the circuit presume that this is 100% similar to the U47 circuit? Not saying it isn't, I just find that an interesting place to start jumping in, especially if that's a mistaken presumption. Especially when the values you're finding are so far from expectation...

Excellent point which I did not consider in my original response. I was assuming all along that your mic is an attempt at a genuine copy, rather than possibly an alternate take on a theme (the EF12 should have clued me in)!

[Kai]

Doesn't changing values in the circuit presume that this is 100% similar to the U47 circuit?

This is why I suggest to measure the amplifier.
If the frequency response is down to 30 Hz there is no need to change anything.

...there is something else strange, R1 is 200M, and R2 is 100M metal film, i don´t know if the Ef12 needs that much of a change in the circuit besides heater voltage but it is strange to my limited knowledge.

R1 is uncritical, it just feeds in the bias voltage and is bypassed by C1. Higher values don't hurt here.
A higher value of R2 means a tiny bit more sub-bass. If this one gets too high the tube might not work correct any more, but keep in mind it's a EF12, not a VF14.
I would guess it's in a reasonable range.
What is the anode voltage of the tube? Should be about 34V +/- some.

[zerofly]

Hello people,

Doesn't changing values in the circuit presume that this is 100% similar to the U47 circuit? Not saying it isn't, I just find that an interesting place to start jumping in, especially if that's a mistaken presumption. Especially when the values you're finding are so far from expectation... maybe there is a rhyme and reason to it that is being glossed over by asking third parties on it instead of the source (FLEA). The EF12 is substantially different, and I would think that the circuit has been amply changed to work with it, if it's the same at all.

While I think there are some pretty good k47 "copies", usually from sources that really have vast experience with the real deal and have manually selected them... my experiences would lead me to think that this would be the first thing to consider upgrading on the FLEA. At least you won't blow anything up.

Yes, allot of things differ from the U47 circuit, probably a different one around the EF12 that it is not what Flea informed me when choosing the tube to come with it, but, that doesn't bother me at all if the mic sounds good, at least that's my goal.

I decided to try and fix what has been bothering me for a wile, the ringing that makes me use EQ
every time,  bass response and  having other mics has a reference to a U47 kinda sound that is what i am after.

Not exposing this question to Flea is probably the same reason as many people don't go to Neumann for troubleshooting and probably is the reason why this forum exists.
I have learned many things from reading in forums, this one specially, where people like Klaus Heyne ,  Oliver Archut(RIP), Kai ( allready lerned alot), chime in with their great knowledge to help others. Even in the Neumann forum, i had question about my U67, looked up for answers that already were there where Klaus Heyne and Oliver Archut cleared them up for other people as well as for me. So why not come here?

Im am not stating, at all, that Flea is not a good microphone manufacturer, in fact i have heard many great microphones from them, this issue alone bugs me and in my much limited knowledge i am willing to try and make it work. and i really hope this question does not degrade Flea's reputation in any way, great microphones!!

This is why I suggest to measure the amplifier.
If the frequency response is down to 30 Hz there is no need to change anything.R1 is uncritical, it just feeds in the bias voltage and is bypassed by C1. Higher values don't hurt here.
A higher value of R2 means a tiny bit more sub-bass. If this one gets too high the tube might not work correct any more, but keep in mind it's a EF12, not a VF14.
I would guess it's in a reasonable range.
What is the anode voltage of the tube? Should be about 34V +/- some.

At the anode,i get a 120v peak at startup and in around 15 minutes backed down to 56.1V, measured at pin 8 of the tube ( please correct me if i'm wrong)
I am trying to find someone with an audio precision analyser to try and measure the amps FR, if not i will try and use some software analyser.

Thank you all,

Kind regards,
Pedro.

[Kai]

At the anode,i get a 120v peak at startup and in around 15 minutes backed down to 56.1V, measured at pin 8 of the tube ( please correct me if i'm wrong)
I am trying to find someone with an audio precision analyser to try and measure the amps FR, if not i will try and use some software analyser.

120V at start is OK, the tube is not active, no current is flowing.
56V sounds a bit hot to me, but I'm not familiar with the EF12.
 You don't need special equipment to measure the frequency response.
 Just do it old-school: tune a sine wave generator and read out the results on any meter you have.
 Any sine wave generator software or phone app will do.
For metering you can use the normal recording path you have for the microphone.

[klaus]

You don't need special equipment to measure the frequency response.

I'll do you one better: You don't even have to plug in a mic whose de-coupling capacitor is 0.1mfd!  There is no way that low value could allow for full frequency in the bass, however you define "full frequency".

No one has ever used that low a value in a traditional plate loaded tube mic circuit, as far as I know. With 01.mfd, your mic is probably down a good 6-10dB @ 50Hz.  Install a 1.0 mfd, and listen. if the sound is a bit tubby, go down to 0.5. If it is a bit lean and honky with 1.0. go to 1.5 or 2mdf.
There. Done!

[zerofly]

Hi people,

120V at start is OK, the tube is not active, no current is flowing.
56V sounds a bit hot to me, but I'm not familiar with the EF12.

Humm!!! i´m gonna check all of the voltages and tube specs and tame them down if necessary.

 You don't need special equipment to measure the frequency response.
 Just do it old-school: tune a sine wave generator and read out the results on any meter you have.
 Any sine wave generator software or phone app will do.
For metering you can use the normal recording path you have for the microphone.

I have "REW" and "Electroacoustic Toolbox" , gonna check with these.

I'll do you one better: You don't even have to plug in a mic whose de-coupling capacitor is 0.1mfd!  There is no way that low value could allow for full frequency in the bass, however you define "full frequency".

No one has ever used that low a value in a traditional plate loaded tube mic circuit, as far as I know. With 01.mfd, your mic is probably down a good 6-10dB @ 50Hz.  Install a 1.0 mfd, and listen. if the sound is a bit tubby, go down to 0.5. If it is a bit lean and honky with 1.0. go to 1.5 or 2mdf.
There. Done!

Ok, sounds good, i´m going to order some capacitors values, try them there, listen, plot the FR and listen again.

Also swap C1 with Styroflex , and probably end up changing the capsule.


I sincerely thank you all for the great help.

I´ll let you know how it work´s out as soon has i get it solved.

Again, thank you very much.

Kind regards,
Pedro.