Low impedance stepped attenuator...

[Roscoe Primrose]

As some of you already know, I've recently switched from using inductive volume controls to using low impedance (500-600ohms) pots or stepped attenuators. However, I didn't have anything that would fit the bill that was stereo, and the 500ohm Daven stepped attenuators I've been using lately are linear rather than audio taper, which even with the very low gain of my screen drive amps have too large a change in volume for the lower steps. With loud source material, volume goes from off to too loud for background music at dinner time in the first step. Turns out I had a stereo 23 position switch that I'd never used for another project, so off to the races. This attenuator is not linear taper, but not a standard audio taper either. Resistance values are as follows:
72, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 37.5, 8.45, 8.45, 8.45, 8.45, 8.45, 6.81, 6.81, 6.81, 6.81 for a total of 591.49ohms. Resistance values determined by what I had on hand, not calculated for audio taper... Sometimes the best parts for the job are the ones in the parts bin Haven't put it in anything yet, but it ought to give a lot more fine control at low volume settings. Here's what the completed unit looks like:




Roscoe

[pboser]

Roscoe, can you please tell us more? Are these series attenuators? Are you planning to use these passive, or as part of an active linestage? Or input on your amps? Related next question is, how does the source deal with that low impedance? And I don't recall- what inductive volume controls are you replacing.
Thanks!

[TubeDriver]

Roscoe, this is an improvement over the Slagle AF? Even the big boy version?

[SoundMods]

Rather than agonize over switched attenuators and switch and resistor quality, why not do what Victor Khomenko did at Balanced Audio Technology (aka. BAT)?

A simple shunt attenuator where you can have a simple audio-taper (log) pot or digitally-controlled resistor array as in a BAT pre-amp. You have only one resistor in the signal-path ever and that can be of the highest quality that one can afford because you only need one per channel.

I also did the same thing decades ago when I had a PS Audio pre-amp. The level of improvement in sound quality was not expected, but appreciated.

You can have an el-cheapo pot but still have superb sound quality.

Attachments

[Roscoe Primrose]

Roscoe, can you please tell us more? Are these series attenuators? Are you planning to use these passive, or as part of an active linestage? Or input on your amps? Related next question is, how does the source deal with that low impedance? And I don't recall- what inductive volume controls are you replacing.
Thanks!

Yes, standard series attenuator. Passive linestage, I may, at some point, add a single buffered input to handle anything that can't drive 600ohms. All of my DACs are fine with the low impedance, I had to make some changes to the phone stage Replacing the low & middle end Slagle autoformers.

Roscoe

[Roscoe Primrose]

Rather than agonize over switched attenuators and switch and resistor quality, why not do what Victor Khomenko did at Balanced Audio Technology (aka. BAT)?

A simple shunt attenuator where you can have a simple audio-taper (log) pot or digitally-controlled resistor array as in a BAT pre-amp. You have only one resistor in the signal-path ever and that can be of the highest quality that one can afford because you only need one per channel.

I also did the same thing decades ago when I had a PS Audio pre-amp. The level of improvement in sound quality was not expected, but appreciated.

You can have an el-cheapo pot but still have superb sound quality.

In that circuit the pots are still in the signal path.

Roscoe

[pboser]

Roscoe, can you please tell us more? Are these series attenuators? Are you planning to use these passive, or as part of an active linestage? Or input on your amps? Related next question is, how does the source deal with that low impedance? And I don't recall- what inductive volume controls are you replacing.
Thanks!

Yes, standard series attenuator. Passive linestage, I may, at some point, add a single buffered input to handle anything that can't drive 600ohms. All of my DACs are fine with the low impedance, I had to make some changes to the phone stage Replacing the low & middle end Slagle autoformers.

Roscoe

Thanks for the reply and the details. Please let us know what you think of the differences. (and let us know if you're looking to unload Slagleformers - experimenters need to change things!)

[SoundMods]

Rather than agonize over switched attenuators and switch and resistor quality, why not do what Victor Khomenko did at Balanced Audio Technology (aka. BAT)?

A simple shunt attenuator where you can have a simple audio-taper (log) pot or digitally-controlled resistor array as in a BAT pre-amp. You have only one resistor in the signal-path ever and that can be of the highest quality that one can afford because you only need one per channel.

I also did the same thing decades ago when I had a PS Audio pre-amp. The level of improvement in sound quality was not expected, but appreciated.

You can have an el-cheapo pot but still have superb sound quality.

In that circuit the pots are still in the signal path.

Roscoe

NOPE! You could say it's "under the signal path." The path to the pot is tied to ground and bypassed by a dead short across the pot to the output. The voltage divider is actually formed by the grid load and the shunted pot.

COOL!

Attachments

[Roscoe Primrose]

The bottom half of the pot is still in the signal path no matter how you look at it.

Roscoe