Who is using passive preamps and why?

Is it safe to assume that the Goldpoint is shunt-type?

No, they are series types. From the Goldpoint website:

Goldpoint Level Controls used to offer Ladder and Shunt type stepped attenuators too. The fact is that with the very low noise, 0.1%, thin film resistors we are now using, we believe that there is no real advantage to Ladders and Shunts - and so have ceased offering them.

And a schematic of their Mini-V series attenuator:

http://www.goldpt.com/schm_ser.html

Best regards,
-- Al

I know it is a good thread when I understand half of it. On the issue of impedance matches and best pot ratings, I see the theoretical, and perhaps measureable difference, but are they audible (to most people)? I suspect that in my setup, whether the pot is 10, 25, or 50 I would ne hear the difference, though my test equipment might.

Hi Clio,

I took a look at it. I see that several different transformer ratios are offered. 1:1 and 1:2 will certainly be no problem for low impedance sources. The other two ratios, 1:8 and 1:13, will, as I speculated earlier, result in an overall input impedance that is extremely low. 1:8 will divide the 10K attenuator impedance down to 156 ohms. 1:13 will divide it down to 59 ohms. Addition of a 100K amplifier load may reduce those numbers slightly further, depending on the volume control setting.

Whether or not that heavy a load will result in good sound is dependent, of course, on how well the source component can handle having to supply relatively high currents, and on how flat its output impedance vs. frequency curve is. But in general I don't think that those two ratios can be counted on to perform well.

Also, I don't understand the statement about output impedance remaining constant as a function of attenuation setting. If the attenuation is set for minimum volume, the output impedance looking back from the amplifier into the pva will be zero or very close to it. If the attenuator is set fully clockwise (max volume), the output impedance will be 10K in parallel with the source component's output impedance times the square of the transformer's step-up ratio. As I indicated in one of my earlier posts, if the attenuator is set to the middle of its resistance range, the output impedance will be around 2.5K (the worst case), assuming the source component's output impedance and the transformer's step-up ratio are small.

BTW, moving the transformer to the output side of the pot, as you may realize, would most likely not be helpful, because it would probably raise the pvc's output impedance to levels that would be too high relative to the amp's input impedance. Also, it would increase the range of amplitudes over which the transformer would have to operate, which MIGHT compromise its performance to some small degree (I'm not knowledgeable enough in that area to be able to say).

The bottom line, imo: Assuming (as I do) that parts quality is good, it looks like an excellent product at 1:1 or 1:2 transformer ratios, but performance at 1:8 or 1:13 will be highly dependent on the characteristics of the source component, and good performance at those ratios cannot be counted on.

Best regards,
-- Al

big caveat, I've never tried this but those who's ears I trust, like Dave Slagle and Jeffrey Jackson tell me performance is compromised when you go with transformer ratios in TVCs that exceed 1:1. In other words trying to get voltage gain from a transformer volume control deteriorates the sound. No proof from my end but these guys have yet to steer me wrong.

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