DIY Tube Mic project

[Emmathom]

What is a “hoops”?

the tube support circuit is not glued, but it stands as a rock !

 

[rock soderstrom]

The 1uF MKP is what I got in stock...

I always have to smile about the term “Audiophiler”.

They've changed the design a bit, but I often use the original Audiophiler caps. Nice and cheap, I haven't noticed anything negative yet. I particularly like the 10uF type because it's not that big.

 

[Emmathom]

I always have to smile about the term “Audiophiler”.

They've changed the design a bit, but I often use the original Audiophiler caps. Nice and cheap, I haven't noticed anything negative yet. I particularly like the 10uF type because it's not that big.

I'm sure you're impatient to know about sound tests @rock soderstrom ...
are you gonna build one for you too ?

 

[rock soderstrom]

the tube support circuit is not glued, but it stands as a rock !

Ahh, I see. "cross struts" maybe?

 

[rock soderstrom]

I'm sure you're impatient to know about sound tests @rock soderstrom ...
are you gonna build one for you too ?

Yes, I will build one, just to see what the mods will do to this circuit. I have just ordered the CRD E352s...

 

[Emmathom]

Yes, I will build one, just to see what the mods will do to this circuit. I have just ordered the CRD E352s...

I've oredred 10 x E-352 (and a 10th of E-562) on Ali Express and they seem to work (10€ shipping included for 10 pieces)
At Mouser's I would have been charged +20€ for shipping...

 

[Emmathom]

Hum... Plate voltage has changed from 56v to 77v now... ? The other voltages are the same as before

The plate voltage goes down -2v / -3v when I hold the mic (and so add my body (?) to ground)

 

[rock soderstrom]

Hum... Plate voltage has changed from 56v to 77v now... ? The other voltages are the same as before

The plate voltage goes down -2v / -3v when I hold the mic (and so add my body (?) to ground)

But this must not happen, check your connections and solder joints. This sounds like a contact problem, possibly to ground. Also make sure that your body does not accidentally touch any unwanted connection/contact point in the mic. I've had that too...

 

[Emmathom]

Which plate voltage should I get ?
The shield is connected to ground on PSU side and to the mic body at thé mic side (but not to mic ground side)

 

[rock soderstrom]

Which plate voltage should I get ?

If I have understood Thor correctly, then around 60V. But much more important than the exact value is that this voltage is stable. Over 20V DC fluctuation is not ok.

The shield is connected to ground on PSU side and to the mic body at thé mic side (but not to mic ground side)

Hmm, is there a dedicated ground wire in your 5pin (or 7pin) XLR cable?

 

[Emmathom]

A drawing is sometimes more explicite...

PSU side : 0v connected to aluminium box & cable shield
Mic side : 0v connected to 0v (but not to shield) / shield connected to mic body
This to avoid ground loop... (well I thought so...)
So the "minus" (or 0v) on mic side is not connected to the body (and nor to the shield : is it clear ?)

Yes there is a dedicated ground wire in my 5 wires cable (1 for Hv / 1 for heater / 1 for ground / 1 for signal out + / 1 for signal out -) and last the shield

 

[rock soderstrom]

looks good to me so far

 

[Emmathom]

I pay a lot of attention to my connexion and soldering, above all when voltage are up to 50v and more...
I think (but I'll check one more time) that everything is well soldered and there's no false contacts or errors

 

[thor.zmt]

B+ = 90v
Polarisation caps. = 58,28v
Anode volt. = 56,25v (thru E-352)
Cathode volt. = 830mV (thru 235Ω to ground)

I haven't put 1GΩ from grid to ground... capsule is connected straight to grid

Biases fine, innit?

Voltages look more or less on the map. Change out a tube and you get different voltages.

Thor

 

[thor.zmt]

Hum... Plate voltage has changed from 56v to 77v now... ? The other voltages are the same as before

The plate voltage goes down -2v / -3v when I hold the mic (and so add my body (?) to ground)

Like the Hong Kong guy who's GF had a black baby 9 Month after the USS Hancock made a port call in '66 said: "Sum Ting Wong!"

Is all "loose metal" tied to Audio ground, nothing but audio ground and nothing else?

Thor

 

[Emmathom]

Like the Hong Kong guy who's GF had a black baby 9 Month after the USS Hancock made a port call in '66 said: "Sum Ting Wong!"

Is all "loose metal" tied to Audio ground, nothing but audio ground and nothing else?

Thor

My english is not strong enough to understand the joke, sorry...
Don't understand too about "loose metal"
The mic body is not connected to 0v but the shield is (see my drawing please)

 

[thor.zmt]

My english is not strong enough to understand the joke, sorry...

Sum Ting Wong is mock Cantonese - Some Thing Wrong

Don't understand too about "loose metal"

Loose Metal is any piece of metal that is not explicitly connected to something. Floating would be a more technical term.

The mic body is not connected to 0v but the shield is (see my drawing please)

So where is it connected to?
Attach files
Thor

 

[Emmathom]

Sum Ting Wong is mock Cantonese - Some Thing Wrong

Loose Metal is any piece of metal that is not explicitly connected to something. Floating would be a more technical term.

So where is it connected to?
Attach files
Thor

See attached please : 0v is connected to PSU enclosure AND cable shield > (mic side) 0v is connected only to 0v mic and shield is only connected to mic body

 

[thor.zmt]

See attached please : 0v is connected to PSU enclosure AND cable shield > (mic side) 0v is connected only to 0v mic and shield is only connected to mic body

So Mic-body = Shield and Shield = PSU Case = Earth?

How do you link Audio GND and Earth?

Thor

 

[Emmathom]

So Mic-body = Shield and Shield = PSU Case = Earth?

How do you link Audio GND and Earth?

Thor

Earth is not yet linked...
Audio ground is linked to the PSU chassis
The SMPS is connected to earth from "outlet" but since it's mounted on a bread-board (and so isolated from chassis) only the SMPS is connected to earth (for the moment...)