g7 tube mic 2nd trial

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nashkato

Well-known member
Joined
May 3, 2007
Messages
872
Location
Europe/Austria
built up the mic a second time cause the first wouldn´t work.
guess what: the problems got worth.
got highmid cracking and scratching.
and very low bass rumble.
the disturbancesounds got even louder.
i think the build is quite ok ,much better than the first time.
changed the polystyrol caps and 1G resistors nothinng changed.

nobody got the same problems.?

is there a necessarity to isolate the sensitive part around the 1n cap and the 1G resistors?

could it be the capsule ? (though it´s a new one from akg).
or could it be the ps? (unclean supportvoltages) how can i check that.?
thanks a lot in advance.
david
 
[quote author="nashkato"]is there a necessarity to isolate the sensitive part around the 1n cap and the 1G resistors?[/quote]
Yes. Finger oils or grease will make LOTS of noise.

Also, decent shielding is crucial.

PS where are you? There may be someone local who you can team up with to beat the problems...

Keith
 
[quote author="SSLtech"]
Also, decent shielding is crucial.[/quote]
sounds like the problem here is something else, highmid cracking and scratching doesnt fit to insuffiecient shielding. but, of course, in general, decent shielding is crucial (if you experience any hum)

david, can you post a mp3 with the noise? and pics? voltages?
we need some more information in order to help.

the high-z part in the circuit (1n&1G) is very sensitive for anything that could cause leakage, gus points this out about once a week.

some days ago i helped somebody trouble-shooting his tube microphone via skype&webcam + high res pictures taken with a normal digicam, worked out very good.
 
ah, ein kärntner :green: (turns out we are from the same location)
did you already contact me via email some time ago?
filling out the location is always a good idea.

voltages: look OK, but in order to find out if the circuit runs ok check the plate, cathode and polarisation voltages.
see here for reference :

http://www.omnipressor.com/Other/G7mics/Comments.html
 
i just recognized you made another thread about your mic problem in the past, in which i also answered.

people, please: keep your information together!
 
Dokument1-1.jpg



i ain´t got 0 V at the output at the trafo
of course that´s the noise ?

sometimes it´s dc with 0,3 V and then display changes quickly undefineable.
ac says : 0,03 V

i´ll rember the next time when i think about a new topic.

yes max: we mailed a time ago .
 
i just remember i got such an indication at an earlier project:
a pushpull hifitubeamp with EL34 A-class.
it was nearly ready until i came to the point where i should bias the symmetry which was impossible because i didn´t get correct data.
i used to long cables to the grids so the amp began to swing at a very low frequency.
 
ok, now we still need two values (the rest looks fine)
the "80v" on the schematics between the two 470k resistors (you should read the half of your 141,9 , b+ after the 10k) EDIT ok you were faster

and "k" on the tube, the cathode. check out the pins+connections in this area again, and that g3 is connected to k.

you said you build the mic a second time - did you use new caps and resistors?
did you replace the tube?
 
k is connected to g3 ,
i checked the whole connections and the schematic now several times.
that doesn´t mean there´s not a mistake (wood and trees)

i tried 3 different ef86

a new EH / 2 older siemens or phillips / and an used (1 year old from an amp) svetlana or something ,don´t know now exactly

at first i built it with the same parts ,and then changed the 1 and 10n polys,
and the 1G´s
 
voltages read ok.
hm. don´t know right now...
audio signal at the mp3 comes through only at a certain point, is it recorded while the tube heats up?
do all three tubes lead to the same sonic result (noise)?
which (audio) transformer do you use, is it connected properly?
can you rule out ck12 capsule problems?
if you want to get deeper into building stuff, troubleshooting can be a very good/intense way to learn.

-max

p.s. if trees are overwhelming you, just send me the thing.
 
hi max,

audio signal at the mp3 comes through only at a certain point, is it recorded while the tube heats up?

what do you mean with audio signal? i didnt record a signal or so ,tried to be calm ,once you
can hear a seat cracking very quiet.
is that what you mean.
and yes ,the tube really wasn´t long heated up ,but i recorded at least 5 minutes and cut out the specific parts.


do all three tubes lead to the same sonic result (noise)?

yes.

which (audio) transformer do you use, is it connected properly?

use the lundahl 1538 , and yes as far as i can say it´should be correct.
(there isn´t really that many ways to connect it wrong ?)

can you rule out ck12 capsule problems?

no , definitly i can´t ,bought it new from akg ,but ain´t got another mic at hand in which i could test it.
don´t really want to destroy my 414EB.
really also got that thought , shit ,worst case scenario.

p.s. if trees are overwhelming you, just send me the thing.

if really all ropes tear , it would be very nice if you could have a look at it.
i´m sure you are able to test the capsule and mic for a defect or missbuilt.
i consider visiting vienna anyway the next several weeks.
i´d write you a mail some days before.
electronical design : mmh , i find it the most heaviest thing to find mistakes .though everything seems to be right , the hum could appear cause of square circuits.
 
well , it took the whole day to do the third built.(but not the 3rd mic,it´s still the first)
got still a problem : on cardiodid it works as eight
on 8 it´s omni
omni quite nothin´
think i got something wrong with the patternvoltages (may capsule wrong wired)???
sure i´ll get that tomorrow (it´s nearly 2 o´clock in the morning ,tired)

ok : what did i change : etched a pcb instead of floating/free building
used 5% coal(?) resistors instead of 1% metalfilm
no grey mkt´s ,but fkp and mkp (wima) and blue phillips mkt caps.

no disturbing sound anymore .
gonna have a cleaning again and finish it up with laquer to isolate( saw that at an rode)

for sure i´ll built a second one as soon as i ´m able to finance another capsule and try some versions of caps and resistors to see if really my building is that worse.
:oops:
good nite
 
what a great piece of gear !!
didn´t have much time to check and compare it to an 414EB , but what i could hear was really great.
i´m looking forward to some recording sessions

thanx a lot to all from gyraf for sharing this and of course all the other stuff(G9 ,....)
thanx to the people in this forum who try to help.

bye
 
hi max ,
now i understood what you meant by that:
audio signal at the mp3 comes through only at a certain point, is it recorded while the tube heats up?
if you listen to the mp3 on your built in speakers of your laptop or computer it´s impossible to hear those low frequencies which are there.
i think thats what you meant that you can´t hear something.
my book is mostly connected to bigger speakers ,so sorry.
maybe using a headphone ?
 
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