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Pots in a box

Paul's Posts — 04 May 2012

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Pots in a box

In the early 70′s Stan (The “S” in PS) and I only made phono preamplifiers. They had no controls, just a turntable input and a set of RCA outputs. Designed to go into the auxiliary inputs of the user’s preamplifier. But that was never how we used it.

It was impossible for us to design good phono preamplifiers with another manufacturer’s preamp – because we’d be tuning the sound of the phono stage to work perfectly with one preamp – and that preamp wasn’t ours. Pretty tough to tell customers they’d have to buy an Audio Research SP3 to get full benefit of the PS phono stage. We used only a potentiometer (called a Pot) into the power amp because our phono stage had plenty of gain – but most importantly it didn’t color the sound of the phono stage.

When it came time to acquiesce to customer demands for a full PS preamplifier, which traditionally consisted of a phono preamp a pot and a line stage, Stan and I started to design one – only to discover we couldn’t make a line stage that didn’t both add and subtract from the sound of just the pot into the amp. We tried every circuit we knew how to make but they all colored the sound somewhat. Neither of us were willing to give up the purity of the pot going straight into the amp. We were stumped.

Stan came up with the answer. “Let’s do both!” He said.

“Both?” I asked what he meant.

“Just add a switch on the front panel. In one mode you’d have just the output of the pot into the amp like we have now. In the other mode you’d get the output of the line amp for the guys that need the extra gain.”

And thus the switchable concept we pioneered of “pots in a box” or not – later called “Straightwire” was born – all because we were unwilling to compromise the sound.

I wonder how many concepts we take for granted were born out of this very same process?

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About Author

Paul McGowan

Paul McGowan is the CEO and co-founder of PS Audio Inc. a Boulder Colorado design and manufacturing company of high-end audio products and services. McGowan has been designing and building high-end products for nearly 40 years. Hobbies include skiing, music, hiking, artisan bread baking, kick boxing and cooking. He lives in Boulder Colorado with his wife Terri and his 4 sons.

(1) Reader Comment

  1. Soundminded

    May 4, 2012 at 5:36 pm

    I for one am not a fan of so called “passive preamplifiers.” (They don’t pre- amplify anything so why are they even called pre-amplifiers, because they come before the power amplfier? So do other components.) First of all, you have a circuit presenting a variable load which might affect the performance of the system. In a true preamplifier, the potentiometers are between gain stages that buffer the input and output presenting a constant load to the signal source and a constant source load to the power amplifier. This means the effect the pots will have on the rest of the system are isolated and within the preamplifier design engineer’s control.

    Then there’s the cost. For every one I’ve seen, it seems to me that the box, the screws, the non functoinal hardware to “sex it up” cost far more than the functional parts inside. I’m sure I’ll hear a lot about what great quality those switches, jacks, and pots are. So if they’re so great why don’t high end manufacturers use them in their power amplifiers and then you can do without a preamp passive or active altogether?

    Personally I like to have as much control over the signal as I can get. That’s the exact opposite of what seems to be the current trend in high end audio. But don’t fool yourself. That so called room correction device is nothing more than a glorified multiband self adjusting equalizer and noise generator you have little or no control over. If you don’t like it’s effect, you might just as well chuck it for all the good it does.

    The argument against fully equipped preamplifiers and signal processors is that they “pollute” the audio signal distorting it. You wouldn’t care to guess how many transistors and/or vacuum tubes the signals on the recordings you buy have gone through before they get to you, would you?

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