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Old 7th May 2009, 08:02 PM   #1611
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Default Re: Using B1 with an amp requiring balanced inputs

Quote:
Originally posted by timothyshields
I'm not quite sure where I choose to use the preamp. In one set up I can utilize the unbalanced RCA outputs, but in another the amplifier requires balanced XLR inputs.
To use the B1 in a balanced application, you'd need four "channels" of B1 - two each for the left and right balanced channels. To do this you'd probably want to use matched quads of jfets. If that's not what you've built, you may as well use it in your unbalanced setup.

-j
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Old 7th May 2009, 10:05 PM   #1612
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Quad match is nice, but really not essential at all. If you don't have
matched devices, don't let that deter you, just use the lower Idss part
as the current source.

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Old 8th May 2009, 07:24 AM   #1613
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Hi Nelson
I just wanted to say I finished my B1 yesterday. I took it into work today and got a friend (electrical engineer) to do some measurements.
I didn't say too much about the design.
The first thing he said was, where are all the active devices?
I don't know what his initial impressions were before testing, but after testing he said, it is better than good, it is amazingly good.

So I felt pretty good with myself since this is my first complete diy project.
I hope that you also take this as a compliment Nelson.

Anyway I can't actually listen to it yet because I am still finishing my amps.

Just out of curiosity I was wondering if anyone here had built both the B1 and BOZ and could elaborate on which one they preferred sound wise, or describe any differences if any?
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Old 8th May 2009, 01:10 PM   #1614
jacq. is offline jacq.  Canada
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Default Re: Re: cap tolerance

Quote:
Originally posted by Diomedian


+/- 25% should do. :-)

-j
Thank you Diomedian, but how would a + - 25% variance influence sound or performance?

Also, perhaps someone could sort out what cw, w and ccw stand for with regards to pot. input, output and ground on the B1?

Jacq.
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Old 8th May 2009, 01:46 PM   #1615
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Default Re: Re: Re: cap tolerance

Quote:
Originally posted by jacq.




Also, perhaps someone could sort out what cw, w and ccw stand for with regards to pot. input, output and ground on the B1?

Jacq.

CW (in) W(out) CCW (ground)
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Old 8th May 2009, 02:49 PM   #1616
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Yeah . . .

It seems like CW=Clockwise W=Wiper CCW=Counterclockwise . . .
If we turn the volume to the CW, the sound should go lounder so that CW should go to the input side. In opposite way, it we turn the volume to the CCW, the sound goes lower so that CCW should go to the ground. Then, the wiper should go to the output.

Just my positive guess . . . based on Tea-bag's reply . . .

><
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Old 8th May 2009, 03:20 PM   #1617
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Quote:
Originally posted by Babowana
Yeah . . .

It seems like CW=Clockwise W=Wiper CCW=Counterclockwise . . .
If we turn the volume to the CW, the sound should go lounder so that CW should go to the input side. In opposite way, it we turn the volume to the CCW, the sound goes lower so that CCW should go to the ground. Then, the wiper should go to the output.

Just my positive guess . . . based on Tea-bag's reply . . .

><

I hooked it up that way, and it seems to act like a normal volume pot, and doesn't work counter-clock wise. of course I only did that cause I referenced your picture earlier

I still need to put the board into box with some connectors and really listen to it.
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Old 8th May 2009, 03:26 PM   #1618
AndrewT is online now AndrewT  Scotland
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it should work (badly) when connected the wrong way (output is always wiper).
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Old 8th May 2009, 03:36 PM   #1619
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Default Re: Re: Re: cap tolerance

Quote:
Originally posted by jacq.
how would a + - 25% variance influence sound or performance?
The purpose of the input cap is block and DC on the signal from your source. For this purpose, I think any old cap would do.

However, the input impedance and the input cap together form a high-pass filter. At the "corner frequency", the signal is diminished by 3dB (just barely audible). Above this frequency, the attenuation diminishes asymptotically to 0, and below it, the attenuation increases. In the case of a 25% tolerance part and a 25K pot, the corner frequency would be anywhere from 8.5Hz (-25%) to 5.1Hz (+25%) (ie. you shouldn't be able to hear the difference).

The higher the corner frequency too, the more (possibly) audible phase shift you'll see in the bass region, below say, 80Hz (guesstimate). Even with a -25% 1uF cap though, it shouldn't trouble you. In fact, thinking about it will trouble you a lot more than listening to it. :-)

-j
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Old 8th May 2009, 03:47 PM   #1620
AndrewT is online now AndrewT  Scotland
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Default Re: Re: Re: Re: cap tolerance

Quote:
Originally posted by Diomedian
The purpose of the input cap is block and DC on the signal from your source. .................
However, the input impedance and the input cap together form a high-pass filter.....................
the corner frequency would be anywhere from 8.5Hz (-25%) to 5.1Hz (+25%) (ie. you shouldn't be able to hear the difference).
and I recommend ~ 2octaves lower, for a power amplifier, i.e. cap value 3 to 4times higher.
For a pre-amp or buffer I'd go another half to 1octave lower again.
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