Styroflex Capacitors - capacitance value options - U87 clone

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zaraxisof

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Hi there to all of you, been reading forum a long time ago, first post here.
I have recently discovered an old box with NOS Polysterene capacitors inside, there are plenty of 680pF 630V and some other 220 or 330pF 630V i think (maybe other capacitance values also, all at 630V).

Can i use these 680pF caps instead of 470,820,220,560 ones in each cap? 

C1,C4: 470pF 630V                  -----> 680pF 630V
C3:        820pF 500V    ------>680pF 630V
C6:        220pF 630V                  ------>680pF 630V
C15:    560pF 630V                  ------>680pF 630V

... what is the range value for capacitance and volts (approx.) someone could use instead of the original ones? I mean for example, volts of C3 needs to be at 500V?  What are the options if we could say we want to be more closer to its original built/sound?

I know this may has already been said here and that values may range depends on what someone want to get and forgive my ignorance as i am a bit begginer in electronics theory (my first job is pharmacist and second musician  :D), but due to all of you i have learnt a lot of useful things and really thank you for this.  :) :)

Every answer appreciated.
Regards from Greece, peace.
 

zaraxisof

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Ok  TillM, thanks for your reply.  As for pF  values,  i will be OK if i use 680pF instead of 220,470,560 and 820pF in each cap?
 

zaraxisof

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TillM said:
As I knew in the Original Neumann schematic they use 160v, so 500v should be no problem

You may didn't understand exactly my question and is my fault because i thought that it was 500V in the Neumann schem.
I asked if i could use 600V instead of 500V.  The caps i ve found are all at 600V.
 

ln76d

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In that way you can even use 10kV, if you will fit it inside  ;)
None of these caps have to be styroflex.
For better performance you can not install C4 and R6 at all.
For C7 you can use film capacitor instead of any electrolytic.
C5 - higher value more low end.
Rest especially low values caps need to be same value.
C6 - you can try different values from 150pF-300pF - mostly 220pF is optimal, it control amount of HF attenuation.
 

zaraxisof

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thank you very much for your reply ln76d.  About C5 by saying higher value you mean the value of capacitance (e.g. 0.05uF) or volts? (again forgive my ignorance in case of becoming silly  :p)
 

ln76d

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Yes, for example with 100nF you should get full low end response.
For the voltage rating always you should look on schematic as for minimal value, you can always install cap with higher rating.
Voltage rating doesn't change anything with response or circuit properties.
It give you only information what is maximum voltage with can be used that capacitor.
It is good to keep at least 20% tolerance (for higher current even more) - for example voltage in the part of the circuit is 20V so you should use capacitor with at least 35V rating.
 

RuudNL

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Some time ago I had a problem with a couple of 'thin' sounding U87ai microphones.
I suggested to increase the value of C5. I also put this question on the forum of Klaus Heyne.
This was his answer:
"You increase the measured low end at the mic's output when you increase the value of C104 (corresponding to C5 in U87) through which the calibration tone is fed. But it affects only calibration audio going through this cap. The mic's audio signal from the capsule is not processed through this cap. "
Does this 'microphone guru' even understand how the circuit works?... (C5 is in the feedback loop, also affecting the sound from the microphone capsule!)

 

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Khron

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The test that might clear that up would be to feed a signal where the capsule goes (ie. FET gate), not the calibration input. Wouldn't it?
 

zaraxisof

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haha  :) trust your ears only and gooo
Nice replies here, glad for this conversation, really helpful  :)
Ah, as we talk about ears etc. , i m thinking of doing the fet biasing by the method of putting 1k sine wave via my daw and may need also some advice more, when time comes... Do you think it can be a good alternative way, as  i dont own and dont know how to use an osciloscope?

And somthing else: Do you think a 3U Audio GZT-87 transformer (9.5: 1) could be a good cheap choice instead of Cine and AMI?
http://3uaudio.com/Show.asp?id=660

Again, thank you mates! :D :
 

Khron

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There are plenty of oscilloscope VST's as well ;) Not sure about other DAWs, but Studio One definitely comes with one stock.
 

zaraxisof

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i am a bit afraid of using one as i am beginner  :p
As for the transformer? (see again my post, i edit it asking for a trans while you were replying)
 

ln76d

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For DAW as an oscillator, use highest sampling rate as possible.
GZT-87 is an excellent choice, you shouldn't notice difference, in U87 circuit, between it and ami or cinemag.
 

zaraxisof

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Ok guys thanks for all these useful infos, great you are here so for us to learn!
I ll check the video later as i m at work right now.
I have spoken to other musicians and people and inform them about the forum and the amazin diy built of U87 and are excited too, so i hope the ''diy U87 etc.'' community here in Greece to get bigger and bigger day by day !

Peace to all of you.
 

rockinrob86

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The cinemag transformer is only $50 if you call them and order it.  Not sure on shipping outside of US though, but they are great and very helpful on the phone.


An oscilloscope is very simple - just think that it graphically displays sound waves.  If you inject a square wave into a circuit, it should show up square on the scope.  If it doesn't, you have distortion!  If you inject a sine wave, but the top is flat - distortion!

I use a signal generator app on my phone.  Made a couple cables to connect my phone's headphone jack to different circuits.

Voltage in a capacitor means how much voltage the capacitor can handle.  nothing else.  More voltage handling means bigger size, so often if only 6v is going to be going through that part of the circuit, you can put a 12v capacitor to save space. 

But if 300v is going through, I recommend not using a 12v cap!

In audio circuits, typically capacitor's farad value is used to carve frequency response.  The actual number matters depending on where it is in the circuit and what it is doing.

If for instance, a 500pf capacitor is called for, and you use a 470, maybe instead of impacting the highs above 8k, it now impacts the highs above 7.9k - as you can see, this doesn't really matter. 

But if you use a 680, maybe now it would affect the highs above 10K - and that's a pretty big difference.

In guitar amps, coupling capacitors block DC voltage from one stage while allowing the signal to flow to the next as AC.  You can change the frequency response by changing the value - a larger UF value allows more bass to pass.


 

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