What output capacitor value for BOSOZ - diyAudio
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Old 4th April 2002, 10:11 AM   #1
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Default What output capacitor value for BOSOZ

My question is probably generic as a number of us are building the BOSOZ to drive the Aleph 2, 4 etc in balanced mode.

I am buying parts at the moment and are considering the trade offs of quality, price and value for the output capacitor.

I am wondering how small a value I can select, as this will enable me to purchase a capacitor of good quality that I can afford!

Given there are (4) capacitors there is a reasonable cost involved and it is difficult to obtain large values and friendly prices!

So I have tried to consider the operating impediance of the circuit.

In the article Nelson lists a value of 10uf for the output which he indicates will give a worst case - 3 at 4hertz for a 10K ohm load with a 5Kohm value of P3 & P4.

(ie total load of 3.33Kohms with the wiper fully open)

Running balanced input on the Aleph gives about 25k input impediance so this implies about a 4.16 Kohm load impediance ie 25% lower -3 db point of 3 hertz.

I assume these computations are correct.

Given this is it reasonable to consider a small value of output capacitor ?

Say 3.3 uf or even 2.2uf capacitor without ill effects?

This would be good as it would enable use of a true film and foil device which are superior to metalised varieties

ie REL Capacitors PPFX 3.0 uf 100 volt in the last Parts Connection catalogue for $18.04 or Holvand 2.2 uf 100 volt for $18.56

But there may be other reasons for using 10 uf ie phase shift etc.

Some ideas and input from everyone would be most appreciated.

Best regards

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Old 4th April 2002, 04:51 PM   #2
FBJ is offline FBJ  United States
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I paralleled a expensive PP cap in my BOZ per channel. And even though I like the sound (much smoother in the midrange). I have to question does real muisc sound that nice? And I think this is the idea that Mr. Pass has been trying to get across to us.
But since we are DIYers, we can do anything we want to.
I would suggest that maybe, just maybe, build the preamp as designed, listen for a few months and then parallel a small value high quailty PP cap. Listen for a few more months and if you want to experiment some more then buy the expensive PP caps.
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Old 4th April 2002, 09:54 PM   #3
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One of the things I enjoy most about DIY is that even the
most heinously expensive tweaks are cheap compared to
retail goods, and failure of a project results in only the loss
of a couple bucks, with lots of usable parts left over.

Building your own equipment is like making your own wine,
even when the result is not world class, it still tastes good.
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Old 4th April 2002, 10:57 PM   #4
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Default What capacitor value for BOSOZ

Nelson and FBJ,

I appreciate your humour!

And your probably right, I remember the last concert I went to was definately not HIFI.

But can I get away with say 3.3uf (in lieu of 10.00uf) in balanced mode. ie 25Kohm input impediance as per my calculations in my last post.

best regards

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Old 4th April 2002, 11:52 PM   #5
FBJ is offline FBJ  United States
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Sorry I thought you were looking to refine the sound of the preamp to your liking by cap-swaping.
But technically I am not sure if the smaller value caps will work, as Mr. Pass designed the circuit, cause in the instructions for the BOSOZ (on passdiy web page) page 8 and 9 talks about the frequency rolloff dependent on the output impedance which would include the 10uf in series with what ever value of P3 and P4.
But looking at other projects on the passdiy where difference values of other parts are used. I don't think the smaller cap will hurt.
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Old 12th May 2004, 06:33 PM   #6
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Default 4.7mf instead of 10.0mf output cap for BOZ.


I read in a french site that using 10K output pot (Alps blackmetal in my case) you can replace 10.0MF to 4.7MF.

Any thoughs?


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Old 12th May 2004, 06:57 PM   #7
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Default Macka

You could just use the metallized polyester 10uf cap NP suggests and bypass it with a high quality - not so expensive 0.01uf MKP cap (or one of those old Siemens styroflex 1% tolerance caps, if you can find one).
I think the result will be the same as if you were using a single 10uf MKP cap.

Is this phase one of Lumpy Gravy?
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Old 12th May 2004, 08:00 PM   #8
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Nickolas K.

I used 2 BlackGates Type: N 10 microF with good results in my CCS-X-Bosoz
Henrik used 47 micro BG N in his X-Bosoz

Make your choice...

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