Green Pre capacitors - signal path

[Guest]

[quote author="clintrubber"]

So there's no way to increase the voltage handling of a capacitor by using double parts.

Sure there is. To make a higher voltage part from caps with smaller ratings simply put them in series, but you need to use caps with double the uF's each.

Or as an example: you find a bag with 47uF/50V caps but need a 100V rating. Just use four to get one cap of 47uF/100V: put two times two in // and put these two pairs in series.

BTW: coils behave like resistors w.r.t. the series & // thing:
(value of) L_total = L_1 +L_2[/quote]
And the downside is that it is going to cost you an arm and a leg for the Elnas
BTW - I spent a 100 euros at Audio Cube on Silmics and Cerafines
You can get carried away sometimes

 

[clintrubber]

True, we've been forgetting about cost.

I used other Elna's for the big gain-switch-cap, cheap from
www.easymeasure.nl

More specific:
http://www.easymeasure.nl/elcos.html

 

[muadgil]

Hi
i have the same problem for the 9k : looking for a 2u2/63V good cap, but i can't find it.

To make a higher voltage part from caps with smaller ratings simply put them in series, but you need to use caps with double the uF's each.

That could be the solution to my problem, but one question : is the high voltage doubling is still here if i use polarised capas?
Meaning two polarised 4u7/35v in serie should give one unpolarised 2u35/70V, is that right?

Gilles

 

[clintrubber]

[quote author="muadgil"]Hi
i have the same problem for the 9k : looking for a 2u2/63V good cap, but i can't find it.

To make a higher voltage part from caps with smaller ratings simply put them in series, but you need to use caps with double the uF's each.

That could be the solution to my problem, but one question : is the high voltage doubling is still here if i use polarised capas?
Meaning two polarised 4u7/35v in serie should give one unpolarised 2u35/70V, is that right?

Gilles[/quote]
Yes, that's right. But I wouldn't do it like that, since it isn't guaranteed that the voltage is 'spread evenly'.

In tube-gtr-amps you can see stacked capacitors since say 600V parts are unavailable or even more expensive than using two of a lower voltage (& double value). So they do it and put high valued resisitors in parallel to divide the volts evenly.

For values & voltages you have I simply would get the right cap and don't do any series-connection and the resistors in parallel..

So yes, it's like you said, but no, don't do it like that (unless you have to travel half the country for the right cap.)

 

[muadgil]

Thank you for your answer, it saves me many euros.
So i'll continue my quest for the perfect phantom blocking cap.

Can I use a polarised cap at this place? it's noted unpolarised on the 9k schema, but does it make a difference if i wire it correctly (+ to the input), no current should run in the other way?

 

[clintrubber]

[quote author="muadgil"]Thank you for your answer, it saves me many euros.
So i'll continue my quest for the perfect phantom blocking cap.

Can I use a polarised cap at this place? it's noted unpolarised on the 9k schema, but does it make a difference if i wire it correctly (+ to the input), no current should run in the other way?[/quote]

Polarized is fine. Unpolarized ('bipolar') is less common, harder to find, more expensive - but often looks more pretty....

Keep in mind though (but sorry for stating the obvious) that if you happen to use this mic-pre with dynamic mics only, then simply skip all things phantom for now and toy around with your new mic-pre. Meanwhile you can look for the missing parts.

 

[muadgil]

:thumb: Thanks again clintrubber.

If i can use polarised ones, i think i have a solution : Blackgate, but they are only 50V, hope it'll be ok.

 

[clintrubber]

I guess 50V will be OK, but check if your phantom is indeed around 48V and not higher by accident. Or have a look around here, it's an 'universal' question you have.

Good luck

 

[soundguy]

I dont know about phantom blocking caps, but I would bring a larger "world view" to what makes up the "audio path" in the circuit. Ive gotten some of my biggest audible changes from swapping filter caps in the power supply and power decoupling caps in the circuit. These days I tend to go with one type for the power related stuff and another for the audio coupling. If you can hear a diference in the audio coupling between the two channels you built Id look at the power supply next. For years I would just throw any old cap in there and buy the more expensive caps for audio. That was real bad thinking.

dave

 

[Freq Band]

So, what would it take , to use poly (phantom blocking) caps in the Green (they would need to be 10u to 20u)....I read somewhere (quoted below, from a different preamp project) some resistance is added to one side the caps?

Unfortunately a 100 uF dc blocking cap in polypropylene is about the size
of a Mack truck.
----------------------
Yeah, but if you're designing the thing yourself you can do it so as not to
need 100uF. Make the resistance on the right-hand side of the cap 10k and
you can get away with 10uF. That's doable in polypropylene.
--------------------------
That's where the rub is. You want a low input impedance on your preamp,
so that it properly loads dynamic microphones. BUT, you want a high input
impedance, so your phantom blocking caps aren't enormous.
With a 600 ohm input Z, 10 uF gives you a -3dB point at 20 Hz or so, which
is kind of high, I think. But not insane.
--scott dorsey

And also in the text and second schematic, here (using the Phantom I'm building):
http://sound.westhost.com/project96.htm

??

=FB=

 

[Freq Band]

Also, is there a better (best) value here at the input, when tweaking the mic-pre to your favorite condenser microphone.....one that you use all the time?

=FB=

 

[DaxLiniere]

Hey hey! Another parts revelation.

I spoke to WES components in Sydney about possible incorrect information on their Elna Cerafine range.
The catalog says "All values 100v," but according to information I'd found online, this was not possible.

Here's the reply:

Hi Dax,
We have checked our stock, and they were all 100v.
Regards,

Luke Martinelli
Wes Components A/Asia

Hooray! 4x 47uF 100v caps for the phantom blockers and Elna Stargets from RS at low prices for the rest! Yay!

 

[muadgil]

Hello
Another question about the phantom blocking cap value.
For example, in the 9k, it should be 2u2 according to the schema. What would happen if i put there 4u7, or even 10uF?

The resistor after the caps going to ground determines which cap size you need. Together they form a high pass filter, so you adjust the size in order for the filter to only work far below 20Hz. The formula to calculate the frequency is: f = 1/(2*Pi*R*C)

So, with this maths, I guess that, with a fixed R value, the higher is the cap value, the lower will be the frequency cutoff of filter no?
I ask this because i found good 10uF/63V (ELNA) capas that could fit the PCB, but no 2u2 ones, or only 50V (and the polypropylène ones are huge!)

Thanks
Gilles

 

[Freq Band]

The formula to calculate the frequency is: f = 1/(2*Pi*R*C)

Thanks olafmatt.
Unfortunatly I have neatly avoided understanding math written like that...but I need to learn, especially here in this forum. If you would be so kind and spell it out this one time....( plus minus equals multiplied divided).....??please??

BTW, I have (four) 15uf AEON caps that might go there.
I am also using Cerefine caps on the boards..... 63v for most caps...cause it's all Welborne had!!

EDIT:they are 25v caps, not 63v.


Thx
=FB=

 

[Guest]

[quote author="muadgil"]Hello
Another question about the phantom blocking cap value.
For example, in the 9k, it should be 2u2 according to the schema. What would happen if i put there 4u7, or even 10uF?
Thanks
Gilles[/quote]
If you want
2U2 - Wima - that fit 63v from Farnell
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=1006054&N=401
You mayl need to drill the holes a bit wider to fit the thicker wires

 

[muadgil]

Thanks for that ref uk03878. It's right that it would perfectly fit the PCB. I'll probably use it if i find nothing else.

But in fact, I read in many places that polyester capas were not recommanded for audio.
So I was looking for Polypropylène, or good electrolytics, like BlackGate or ELNA.
You know something about the problem wich could appear if I use a 10u instead of 2u2?

Thanks

 

[Guest]

muadgil
Unfortunately my knowledge in this matter is as lacking as my beer belly is large
Sorry..

 

[muadgil]

Thanks anyway, at least i learnt a good british expression :grin: