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Old 13th January 2003, 01:28 PM   #1
diyAudio Member
Join Date: Sep 2002
Location: Milton Ontario
Default Boz

I notice that a lot of DIYer's put higher resistance volume controls on the input of the BOZ. I was wondering why? If someone was to use a 100K pot. for the volume control (could not find a 5K) would it be better to place it at the input?
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Old 13th January 2003, 02:17 PM   #2
diyAudio Member
Join Date: Feb 2001
Location: Columbia, SC
There's a lot of latitude in the values. I come from a background of messing with tubes, so values of 100k look normal to me (most all resistance values in tube gear are an order of magnitude higher than what you see in solid state).
The case for higher values is that you don't load down the outputs of your source pieces, i.e. you're not trying to draw a lot of current from them. Yes, it's only in the micro-to-milliamp range, but hey, if it's all they've got to give then you're making them work hard. Distortion will be somewhat lower. Depending on about twenty other factors, you may see a slight reduction in high frequency response. 100k at the input should do a good job.
Lower values seem to make some people happier. As long as your source has sufficient drive--and most do--you'll be just fine. Distortion slightly higher. Less chance that your 100kHz response will droop.

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Old 13th January 2003, 02:22 PM   #3
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Join Date: Sep 2002
Location: Milton Ontario
Great response, thanks very much grey.

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Old 13th January 2003, 05:28 PM   #4
Join Date: Jan 2003
Location: Texas
Default volume controls on the input of the BOZ

The worst case resistance for a 100K pot is 25K assumeing it is driven by a low impedance. This gives -3dB of about 50KHz or about -0.6dB at 20 KHz with my BOZ Spice model. Roll off from the cable capacitance and the output resistance will also effect high frequency roll off by would require a pretty capacitive cable load. A pot on the output will attenuate circuit and power supply noise is why that attenuator configuration was most likely chosen.

I am perplexed at the other 18 factors that influence high frequency response of this circuit topology and a 100K input potentiometer. Oh leave out R107 out of Mr. Pass's schematic when an input pot is used.

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