U47 multi pattern build

[Spencerleehorton]

have tested the caps and they test ok?
all connections are correct to schematic?
seem to get omni but the mic cuts out again for about 30 seconds when the B+ voltage goes up then slowly the voltage comes down and i turn the mic all the way round and it sounds like omni on headphones.
cardioid and fig 8 sound identical?
no noise at all on all patterns, so the PSU is doing its job, my heater is about 5.34v with the EF800, ive tested with the EF80 as well and same problems, just lower voltages because of the extra current.
going between cardioid and fig8 it cuts out when going back to cardioid? should it do this?
the back capsule does sound like it gets more treble when going to fig8, so maybe it is working its just the cutting out of the mic for 30 seconds im worried about?
B+ voltage settles at about 118v but goes up to 132v then comes back down?

front capsule on fig8 defo sounds like it has more top end than rear, should it be the same? or is this normal?

 

[Spencerleehorton]

im going to go with case closed now and just put up with the long tie it takes to get between patterns.

 

[Spencerleehorton]

I put a light on the front as it annoyed me on the back!!

 

[rock soderstrom]

front capsule on fig8 defo sounds like it has more top end than rear, should it be the same? or is this normal?

If you only test this on the headphones, phase cancellations (in your head) may occur if you listen to it in real time. Make a test recording and then compare the front with the back capsule. Still different?

 

[rock soderstrom]

no noise at all on all patterns, so the PSU is doing its job, my heater is about 5.34v with the EF800,

I am a proud designer

 

[Spencerleehorton]

Yeah I think Ive had this before I just wanted to know about the time delay between patterns? Is this normal for the mic to stop working for 30+ seconds?

 

[rock soderstrom]

Yeah I think Ive had this before I just wanted to know about the time delay between patterns? Is this normal for the mic to stop working for 30+ seconds?

I can't say much about this, as I hardly ever build with switchable polar patterns. I think a certain switching time is normal until the new polarization voltage has become established. But 30+ seconds seems a bit too long, doesn't it? If everything else works, I probably wouldn't care, as I would very rarely switch.

 

[Spencerleehorton]

Yeah I’ve never had a mic with 11 switchable patterns be like this, maybe it’s the config?
I’ll do some recording with it and hear how the patterns sound.
The odd thing about this is I can’t really set the correct voltages as the B+ rises differently depending on what pattern your on!!!

 

[pasarski]

Seems weird. Changing polar patterns should not affect B+ if I understand anything. There no current involved so no voltage drop either. Voltage divider of 100M and 1G will result about 118V with 130V input. Maybe there's a clue?

 

[Spencerleehorton]

I thought to Maybe try changing the polypropylene caps to polystyrene? But like you say there seems to be a current drop that’s why the voltage is changing?
Confused?

 

[volker]

Yeah I think Ive had this before I just wanted to know about the time delay between patterns? Is this normal for the mic to stop working for 30+ seconds?

Calculate the time constant, then you know what is to be expected.

 

[Spencerleehorton]

Calculate the time constant, then you know what is to be expected.

Could you explain further maybe?

 

[rock soderstrom]

Could you explain further maybe?

Thanks @volker.

I also had to look it up again, it's been a long time since I calculated that.

Check the link, in the examples you will find RC filters, which is your topic.

https://en.wikipedia.org/wiki/Time_constant

 

[Spencerleehorton]

I hate to say it but this is well over my head!


My poor little brain doesn’t get it?

 

[Spencerleehorton]

Well after some help from Rick we thought we had found the problem!
May have been the actual switch not being make before break and the caps having to recharge, and that taking a while to do would explain why the voltage would change then settle after 30 seconds or so!! Sounded plausible so I changed the switch for a lorlin make before break and put some 150k resistors on it.
Powered it up and the same problem, so it’s not the switch!!
Must be the mic, so I will take some photos of the guts and label and explain how it’s all connected.

 

[Spencerleehorton]

Here is a picture and a label below!!


Spot the mistake!

 

[Bonnie1]

At a quick glance, looks like your B+ voltage divider is connected to ground, instead of backplate.

-dmax

 

[Spencerleehorton]

At a quick glance, looks like your B+ voltage divider is connected to ground, instead of backplate.

-dmax

Are you talking about the 3m to gnd?

 

[Bonnie1]

Are you talking about the 3m to gnd?

Oops, apologize Spencer. I glanced at that too quickly this morning.

Reading though your thread, I would suggest bypassing the pattern switch, disconnecting the rear diaphragm and confirming you have approx. 60vdc at the voltage divider, at least 45vdc on the plate, and approx. 1vdc bias. Confirm the mic works in cardioid only. If that all checks out connect the rear diaphragm (with pattern switch still bypassed) and confirm you have approx. 120vdc at the 100meg resistor and then Confirm you have Fig. 8 pattern. If all the above checks out, your issue is not inside the mic.

-dmax

 

[Spencerleehorton]

Well these are my findings so far today:

Cardioid only:
B+ = 118.7v
H+ = 5.3v
2M/3M = 60.5v
Plate (pins 7,8,9) = 52.4v
Kathode = 1.226v
30k/100k = 103.7v

so all seems normal

Omni only:
B+ = 118.5v
H+ = 5.3v
2M/3M = 60.5v
Plate (pins 7,8,9) = 53.9v
Kathode = 1.226v
30k/100k = 103.7v

so all seems normal

Fig 8:
B+ = 118.7v B+ rises to 130v when going from fig8 to omni
H+ = 5.3v patterns have no effect
2M/3M = 60.5v rises to 65.5v when changing pattern
Plate (pins 7,8,9) = goes from 34v to 128v when changing pattern
Kathode = 1.226v patterns have no effect
30k/100k =

have changed 1uf caps to 0.47uf caps 630v and still the same?
will change all 10nf caps just in case as i have spares!!! totally clutching at straws here!!!!
will also swap out transformer to at least discount these.