MATTI

G7 alive and beautiful!!!
« Reply #40 on: July 27, 2008, 02:30:31 AM »
Your mic looks good and once the problem is found / cured
I bet it sounds good aswell  :thumb:

Matti


karloff70

G7 alive and beautiful!!!
« Reply #41 on: July 27, 2008, 03:59:31 AM »
Thanks guys. I just took the Nady 1050 and cut the framing rods inside and lenghtend them with a couple of metal strips that I cut. Then I got a 2 1/4" 16swg coppertube and had it cut to the right length and spun into on the ends so the endpiece would still fit. Screws together like the original. :green:

Starting to think I might get a piece of matrix board and redo the entire inside point to point....loosing trust in those traces......would like to avoid it though, as I've got a project to record asap.

HEEEEELP.....

Gus

G7 alive and beautiful!!!
« Reply #42 on: July 27, 2008, 09:37:29 AM »
Tube microphone like this are simple things to trace.  One gain stage

Do you or your tech know how to use a signal generator and a scope and also know how to work safely around tube voltages?  Don't work on it powered up if you don't. Your questions are why I am asking

BASIC troubleshooting, break it up into sections to start, capsule to input, plate to cap and transformer,

Can you test the tube in another known good circuit?

The voltages posted look OK

Now disconnect the capsule  and use a signal generator to drive the circuit.  If this works it is the capsule.  If the capsule section is the problem try the stock capsule and mount also check the capsule charge voltages.  Also check the capsule backplate to metal mount with a DMM set to the highest resistance setting no power and microphone disconnected from the cable in ohms this will help check if your mount has problems

IF that does not work disconnect the transformer connection to the plate and cap.  Solder in say a 47k to 100K cap to ground as a crude transformer sim(plate to cap to 47k/100k).  Feed a signal in and look at the output at the cap load resistor.  If you don't get a good signal at the 100K check at the plate as a test if the cap is bad


Are the wires to the capsule the ones that came with it?  Do you know how to test the transformer out of circuit with a signal generator for ratio?  How clean are the solder connection of flux around the capsule to tube area?  Have you read the microphone metas?

karloff70

G7 alive and beautiful!!!
« Reply #43 on: July 27, 2008, 10:26:39 AM »
Hi Gus, thanks for chiming in!!

My tech definitely knows (very good tech!), but I'm out of funds for this, so I'm on my own for now....

I, as you will have noticed from my questions do not know to much, but am careful to definitely not touch anything powered up other than the chassis with one hand or something I've had the meter on first. I'm guessing the tube and the little electrolytic are the main contenders for shockage??

The tubes are most probably good, but I have tried it with an EF86 (as I can crank the voltage to 6.3V with the pot) which is definitely good, same result.

I do not have a signal generator or a scope unfortunately....will check the backplate to mount with DMM.

Wires are the ones that Dale's M7 arrived with, bar the one soldered to the outside of the mount of course(backplate).

I have repeatedly cleaned the whole board, including the capsule to tube area with 100% isopropyl....no difference, and yes there is literally nothing in the diy microphone meta's which I haven't read at least once (the 'on-topic' stuff more like 2-4 times....)

One thing I just noticed this morning when trying again is that now (since I refitted the capsulemount with electrical tape around the screwstem for isolation) I have a random crackling in there, aswell as the same miniscule signal. Also, the cable (original chinese 7-pin) seems to be somewhat unhappy, as it creates interference when moving it. This happens even when the PSU is not connected.......??

As I can't do most of what you suggested without a signal generator, I'm off to put the DMM on the mount/backplate......will report back.

Thanks again!

karloff70

G7 alive and beautiful!!!
« Reply #44 on: July 27, 2008, 10:36:37 AM »
Just measured the mount's brassring to the backplate at 2000kOhm setting. It jumps around between 000, 025, 050-ish and 300-ish.....??

karloff70

G7 alive and beautiful!!!
« Reply #45 on: July 27, 2008, 10:54:23 AM »
Just had another clean around the 3 capsule solderpoints on the pcb and resoldered a not so nice joint elsewhere and am now back to 'no more random crackle but still miniscule/superskinny signal'......

rodabod

G7 alive and beautiful!!!
« Reply #46 on: July 27, 2008, 01:39:18 PM »
Quote from: "karloff70"
Just measured the mount's brassring to the backplate at 2000kOhm setting. It jumps around between 000, 025, 050-ish and 300-ish.....??


You just need to make sure that there is no path of low resistance (eg. less than say 1G Ohms) between the backplate and earth (eg. the chassis of the mic). You can have the mount electrically connected to the backplate, but then the mount must obviously be insulated from earth.


Quote from: "karloff70"
Also, the cable (original chinese 7-pin) seems to be somewhat unhappy, as it creates interference when moving it. This happens even when the PSU is not connected.......??


Start by looking here. Sounds like you clearly have an issue with the cable/psu combination. Check the Apex PSU thread here, the G7 psu schematic, and compare to your own PSU.
Quote from: tv
punchy fat bastard chip

zebra50

G7 alive and beautiful!!!
« Reply #47 on: July 27, 2008, 02:52:04 PM »
Hi!

Just had a quick skim through this - really busy with 14 days straight work so sorry for not chiming in before, and apologies if any suggestions have been covered already

I agree with Gus's prompt to go back to basics. Please remeasure the voltages at all the tube pins and post them up. Also measure volts on all XLR pins and post. That will help us track it down.

Also, double check the transformer. I read this in your earlier post....

Quote
In:

Yellow from pin 5
blue from pin 6

Out:

pink to pin 4 (200 Ohm out)
brown to pin 3 (common)


What do pins 5 and 6 refer to? In this photo, it looks like the blue and yellow go to the XLR connector, which would be wrong - kind of hard to tell.

http://img508.imageshack.us/my.php?image=gutsbackdw7.jpg

Cheers!
Stewart
Ribbon microphone services
http://www.xaudia.com
Microphone blog

karloff70

G7 alive and beautiful!!!
« Reply #48 on: July 27, 2008, 05:55:05 PM »
Hi Stewart,

Thanks for joining the help-posse.... :green:

Here are the measurements:

XLR pins:

1: 0V
2: 169V
3: 0V
4: 0V
5: 56.8V
6: 4.55V
7: 0V

Tube pins:

1. G2     : 0V
2. Shield: 0.02V
3. K       : 1.65V
4. Heater: 0.02V
5. Heater: 4.55V
6. Anode: 71V
7. Shield: 0.02V
8. G3     : 1.65V
9. G1     : 0V

The transformer is wired correctly I think:

yellow from 2.2uf blocking cap
blue from plate

pink to XLR pin 3
brown to XLR pin 4


Hope this gives away the problem......

Thanks again   :thumb:

Boris

zebra50

G7 alive and beautiful!!!
« Reply #49 on: July 28, 2008, 03:19:16 AM »
Quote
yellow from 2.2uf blocking cap
blue from plate


Presumably you mean blue to ground? Not the tube plate?

One of the grids (G2, pin 1) should have the same voltage as the anode.
Ribbon microphone services
http://www.xaudia.com
Microphone blog


karloff70

G7 alive and beautiful!!!
« Reply #50 on: July 28, 2008, 05:04:27 AM »
Yep, sorry, blue goes to the XLR pin 1 rail (ground). Transformer pinhole 6 on `Gustav's pcb.

Must have got the voltage on G2 wrong yesterday, as today it does have the same as the anode (68,9V)......

karloff70

G7 alive and beautiful!!!
« Reply #51 on: July 28, 2008, 02:26:07 PM »
Still no joy.... :oops:

zebra50

G7 alive and beautiful!!!
« Reply #52 on: July 29, 2008, 03:16:02 AM »
OK.

Test the amplifier circuit by disconnecting the capsule and putting some kind of signal on the input instead. I know you don't have a generator so use some kind of signal - iPod, walkman, whatever - via a resistor or pot (about 1 meg will be OK ).

Any chance your capsule could be touching the grill ?
Ribbon microphone services
http://www.xaudia.com
Microphone blog

karloff70

G7 alive and beautiful!!!
« Reply #53 on: July 29, 2008, 04:11:04 AM »
I'll see if I can do that tonight. Don't know if I can rustle up a 1meg resistor....so I disconnect the capsule and put the resistor on , say the front input and then connect a CD player to the resistor and the backplate point?

Recording today.

The capsule is definitely not touching the grill.

Thanks, and I'll report back tonight!

ioaudio

G7 alive and beautiful!!!
« Reply #54 on: July 29, 2008, 08:04:50 AM »
yes, and connetc the - from the cd player to ground. again, be careful with HT. if you leave the mic housing open you will have LOTS of hum.
another, quicker test: if you disconnect the capsule and leave the mic open: it should hum like hell (strong signal)
if it hums, but at the same weak level like the signal you had with the capsule connected, your problem is behind the plate/coupling cap/transformer/wiring&leads, as i suggested already.

edit: i just re-read what i´ve written: of course you can make the open hum mic test without disconnecting the capsule, it will hum as well.

rodabod

G7 alive and beautiful!!!
« Reply #55 on: July 29, 2008, 02:30:23 PM »
Quote from: "karloff70"

pink to XLR pin 3
brown to XLR pin 4


On the standard Nady PSU, I believe the XLR output from the PSU (ie. XLR3 pins 2 and 3) are taken from the input socket's pins 5 and 6. Have you modded your PSU to accomodate this? Or the cable?

Check the continuity between the socket in the mic and the output XLR (and also the continuity for each pin in the mic to the input socket at the PSU) to confirm that the connections are correct.
Quote from: tv
punchy fat bastard chip

karloff70

G7 alive and beautiful!!!
« Reply #56 on: July 29, 2008, 04:20:54 PM »
Couldn't find a suitable resistor so I did the hum test (with capsule disconnected) without the body. Turns out it doesn't give any more than the hiss I got with the skinny signal before, only due to cranking the mic in. No big hum at all.......so I guess the problem is not near the capsule but with the amplification. Will have another look around the areas you suggested ioaudio!!

Rod, the psu has been modded by a pucker tech (Pom) to fit for G7 (to schemo), so is no longer Nady-wired (I duoblechecked aswell) and the lead has been checked and now only goes pin to pin as opposed to pin 4 going to ground as before.

Starting to think my soldering skills may have been detrimental to the pcb's reliability......if I can't find anything soon I'm seriously tempted to start again on a matrixboard, point to point.....

karloff70

G7 alive and beautiful!!!
« Reply #57 on: July 30, 2008, 06:28:34 AM »
Just a thought....before I throw caution to the wind and abandon the pcb for a fresh matrix board point to point, it occurs to me that it would be worth finding out if all my components are healthy first. Maybe I've cooked something soldering on the same side......

How do I check the health of caps? Resistors seem easy enough to measure across, although I'm not getting a reading on any DMM setting for the 1G's and the 33M.....the little resistors check out. Does this mean my bigger resistors could be shot?

steppenwolf

G7 alive and beautiful!!!
« Reply #58 on: July 30, 2008, 09:20:43 AM »
Hi!

The styro caps seem to be a bit sensitive to heat.

I noticed, you are using gustav's board.
I had a little issue with my G7 board that I had to fix but noticed it before powering it up, so I can't confirm it is the problem you encountered.

On my board, near the cathode resistor and cap of the EF86, there was an eyelett touching the ground trace behind it that shouldn't. (look on the schem). I scratched away that tiny connection and my G7 has been working day after day.
Just trace the groundplane and look for an eyelett near the area I told you that is bearely touching it.
I don't know, if only my board had that fault...
Try it!
Best,
Stefan

karloff70

G7 alive and beautiful!!!
« Reply #59 on: July 30, 2008, 09:26:11 AM »
Hi Stefan,

I guess you must mean the 1K6....indeed it looks like it's touching and shouldn't be (at least not befor the 220R).....I'll scratch that and see....hopefully like a winning scratchcard... :green:

Vielen Dank, der Herr!

Gruss,

Boris


 

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