Passive Volume Control for DACs/Sources

Would you recommend the 10k or 50k version of the khozmo between a Yggdrasil and a tube amp? The 10k has input impedance 10-110k and output impedance 0-100k and the 50k has output impedance 0-500k.

 

Very roughly, you want the pot value somewhere in between the source and amp (log scale), leaning closer towards the amp side if you don't have wiggle room because you don't want to overload the output stage of the dac.

If your amp has a very low input impedance, then consider a transformer type preamp or something active.

 

To clear up a bit of the confusion:

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

 

Thank you! This is very useful. Since my tube amp has 100K from input signal to ground, it means that if I have a shunt style attenuator with in-out resistor = 10K and range 0-100K, then the maximum Vout seen at the grid of the first tube I will get = 50/60 Vin = 0.83Vin. This is because I will have two 100K in parallel at the highest attenuator setting.

With a smaller in-out resistor, Vout : Vin goes up. But then the page says that a larger value minimizes the varying impedance as seen by the signal source. So for the Yggdrasil, what would be a good value for the in-out resistor taking all the above into consideration? 1K? 5K? Or is 10K sufficiently good?

Thanks!

 

I would save myself a lot of headache and stay away from any questionable shunt attenuators. You can easily get away with a 10k-50k pot. Load seen by the source will be a constant value. Easy peezy

 

Just because I like playing with spreadsheets, I messed around and plotted 3 regular pots 10/50/100k. The deviations from the straight line are due to the parallel load with the amp input impedance (100k) mucking with the voltage division. Overall, not what you would call a big honking deal.

Granted, this is looking ONLY at impedance values and ignoring whatever witchcraft comes from impedance and capacitance and low pass high pass lube passing cockamamy you want to worry about.

 

This is awesome, thank you! I followed your lead and created a graph of Delta Vout/Vin for the series pot values 10K/20K/50K/100K assuming the 100K parallel resistor in the amp and 24 linear resistor steps. The results emphasize the differences between the pot values. The ideal is a constant horizontal line. In reality, the pot will be a log pot so the differences will be exaggerated more.

Given this the 20K pot seems to strike the right balance between high impedance and change close to the ideal. Thoughts?

@Armaegis Please see if you get the same results with the Deltas to double-check my work.

 

Er... did you graph past 100% there? it doesn't make sense for the lines to cross. But yeah, I think you essentially have the same graph that I do. A 10k or 20k pot is just fine.

 

This is basically the derivative of your graph so it shouldn't be strange that they cross (I don't go beyond 100%).

Edit: In your graph, Vout/Vin is the mirror image (using x=y as the reflection line). So then you can see that e.g. 100K goes up slowly and then its rate increases to meet the ideal at 1. The derivative graph shows exactly this behavior. But you're right, it is strange they all cross at one point. The discrete points in my sheet are not exactly the same. I'll look into why there exists an intersection point.

 

Eh?? Not sure if we're saying the same thing or not in different words. Such things do not translate well. In any event, just pick a 10 or 20 or be done with it.

 

LOL

 

don't forget low capacitance cables between the passive preamp and the amp and as short as possible so there's no high end rolloff

 

Thanks! The cables I'm intending the use are 1m long. 1m from DAC to passive, and 1m from passive to amp. They have the following characteristics:
Z: 55Ω, capacitance: 98pF, R Signal: 0.065Ω, R Ground: 0.008Ω
What do you think?

I've decided to order the passive pre from Khozmo with their 25K series pot (they don't have 20K for the series attenuator version). So it'll be this:
http://www.audiophonics.fr/en/compo...ereo-48-positions-shunt-cms-50k-1-p-8686.html
inside this: http://www.khozmo.com/stereo_selector.html

 

For kicks, I repurposed an enclosure for something I will never use, put in a new Alps pot I had ordered a while back + some wire, and built a passive.

 

oh no! not an Alps RK27! The audiophiles will eat you alive!

 

omg so common like a fleet street tart charging tuppence a go.

 

Nagra Jazz. MSRP: 12 500$

Uses Alps 50KAX2.

 

At least the signal wires aren't covered in teflon tubing so they won't rattle

 

OMG, my non-audiophile approved (or audiophile non-approved) passive is f'ing great. More details, more resolution, clearer, more details. Did I mention more details?