Bride of Zen output impedence

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5K at the output, 10k at the input. I had a quality 100k pot so I gave it a try (it's placed at the input). Why not? It seems to work fine, but, the preamp is not mine (but my brother's in law) and it supposed to be done "on a shoestring" If I would be building it for myself, I would use 3k or less pot at the output. But sourcing such a pot is not easy and custom switched unit should probably be implemented.

Here's such an example, 3K stereo, ladder type attenuator, made out of Grayhill switch. It's only 16 steps, but it's enough in most applications. Used in my other BOZ.;)


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Have you used your BOZ to drive many different power amps? If so do you run into problems with volume sensitivity when driving a power amp that requires 1V for max output?
I know you can control the gain by adjusting certain resistors. However, Nelson Pass suggested a pot. on the input and on the output. Does this mean that by adjusting the input pot. you effectively change the maximum gain the output pot. will let thru?
The input pot lets you optimize the signal level so that the output can run with the lowest distortion and lowest noise. (The "sweet spot" was right around 1 to 2 volts output, if memory serves me right.)

The output pot would then serve as your volume adjustment, taking the signal from that 1 - 2 volts to whatever input would make for a comfortable listening level with your amp of choice.

RobPhill33 said:
Thanks Erik.

How high of quality should the input pot. be? an enclosed trim pot?


It is a matter of preference, really. If you like to adjust things frequently, you might choose a regular audio-taper pot for the input side and then adjust it by ear each time you change to a different source.

If you're like me -- and I know I am -- I don't like to mess with things once I get it set up right. Well, not on a daily basis anyway. Maybe once in awhile, though. :) To that end I was planning to install trimpots at each input so that I can set them and (mostly) forget them. I'd have to readjust them when I change gear, though... so maybe I'll leave them so I can adjust them through holes on the top or rear panel.

I my BoSoZ I use 10 K pot at input and 5 K attenuator at output.
R15 is 430R giving approximately 10 db gain.
After having used this amp for some time now my experience is that I tend to turn up the input pots to around 2 o'clock using CD and a bit higher using weak sources like tuner and tape and then adjusting the master vol with the attenuator.
However if I turn the input pots down to say 9 o'clock I have to turn the output attenuator all the way up to get a reasonable volume.
So I'm beginning to wonder if I should raise the overall gain at R15 a tiny bit, in order to get a wider operation range of these input pots...or would more gain not affect this at all?
The negative side of more gain is higher distortion as far as Nelsons article is concerned, but I'll give it try some day to see if it works out fine.
regards Jan
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