Passive pre, what potentiometer to use

[dogmamann]

I want to connect a passive potentiometer between my dac Topping e30ii and a power amp Arcam P80. What should I look for while selecting the potentiometer ? For example: alps rk27 100k, 50k and so on..

 

[Shorty]

I want to connect a passive potentiometer between my dac Topping e30ii and a power amp Arcam P80. What should I look for while selecting the potentiometer ? For example: alps rk27 100k, 50k and so on..

Elma? https://www.elma.com/en/products/ro...tions?q&sortBy=relevance&sortOrder=asc&page=1

 

[mhardy6647]

Use a TVC (or an AVC).

intact audio

 

[raindance]

You want the lowest usable impedance. Typically I would start with 10K. Audio taper. My preference is Alps Blue from Parts Express, but they don't always have good channel matching (you can buy a couple and measure them and pick the best). Or you can just buy a Schiit Sys (although it uses a lower quality pot).

 

[dogmamann]

Should it match the input impedance of the power amp somehow ?

 

[DVDdoug]

Typically I would start with 10K. Audio taper.

I'll 2nd that. 10K is about right and audio taper is a requirement. I don't know if you'll find a spec for "channel" tracking/matching and that's the main thing I'd be concerned with. I've had pots where you could hear the mismatch and pots where there was "play" between the front and back pots.

 

[raindance]

Should it match the input impedance of the power amp somehow ?

It should be at least 10x less, typically, but in this case will be a compromise because you don't want to load the source too much and under normal listening conditions your amp will probably see about a 5K source impedance using a 10K pot.

 

[dogmamann]

It should be at least 10x less, typically, but in this case will be a compromise because you don't want to load the source too much and under normal listening conditions your amp will probably see about a 5K source impedance using a 10K pot.

when we connect a DAC to an integrated amp, theoretically the source is loaded this way,right?

 

[dogmamann]

Use a TVC (or an AVC).

intact audio

this costs more than my power amp

 

[JeffS7444]

Could be as simple as this:
https://www.digikey.com/en/products/detail/bourns-inc/PDB182-E420K-103A/3780709
Have tried cheapo ganged pots which actually had pretty decent tracking. Can't say that I've ever noticed a sonic difference between something like this, Goldpoint step attenuators built with bulk-foil resistors ($$$) or other exotics. Maybe spending a couple more bucks for conductive plastic type would be a worthwhile upgrade.

When using a passive "pre", keep cable capacitance low, give preference to sources with low output impedance. In this sense, using an active volume control makes life a lot simpler! And if you opt for an active solution, then you have the option to try circuits designed to use linear potentiometers which typically track very well.

 

[egellings]

Should it match the input impedance of the power amp somehow ?

No.

 

[DSJR]

A cheapo Omeg 10k log film pot will do just fine (the £2.50 or so green colour one). The maker I know who used them did an 'upgrade' to a stepped attenuator shunt type with I believe, a 47k inline resistor and different shunt resistors across the load to cut the levels down, this meaning that eacxh volume 'step' alters th eloading seen by both the source and the power amp the thing is feeding. Maybe it doesn't matter, but I hate variables like this...

 

[mhardy6647]

For best results: the attenuator should not alter the impedance as a function of attenuation.

 

[Blumlein 88]

It should be at least 10x less, typically, but in this case will be a compromise because you don't want to load the source too much and under normal listening conditions your amp will probably see about a 5K source impedance using a 10K pot.

It will see a maximum of a 5 kohm source impedance, which will occur at -6 db. At higher and lower volume settings source impedance is less.

If you have a choice, put the passive pre very close to the power amp. Half meter interconnect maybe, and it reduces how much the source impedance matters to the power amp.

At different times I've used lots of variations. The inexpensive Bourne pot someone posted a link to is quite fine.

 

[Blumlein 88]

For best results: the attenuator should not alter the impedance as a function of attenuation.

It won't alter the input impedance, but output impedance will vary in a pot. A switched resistor unit can be made that keeps both ends under more control.

The P80 amp has an input impedance of 22k ohms so keeping the pot output impedance low and keeping the interconnect length to the amp short is a good idea.

 

[mhardy6647]

It won't alter the input impedance, but output impedance will vary in a pot. A switched resistor unit can be made that keeps both ends under more control.

Thanks. I was a bit too elliptical.
(which isn't like me, is it?)

 

[Blumlein 88]

One method I've used is to have a metal film resistor in series usually 4700 ohms. Use a 100 kohm log taper pot to vary the resistance between ground and the output side of the series resistor. This way max output impedance is not more than 4700 ohms and that only occurs at max volume. All other settings are lower. This means the input impedance seen by the DAC varies, but if 4700 is okay then it will always be that or higher.

 

[solderdude]

I want to connect a passive potentiometer between my dac Topping e30ii and a power amp Arcam P80. What should I look for while selecting the potentiometer ? For example: alps rk27 100k, 50k and so on..

Alps RK27 10kA will be fine. The ones I use have good tracking and have never given me problems such as scratch and feel nice when adjusting.

It will load the DAC with 6.8k (at full volume) to 10k (volume at 0) which is perfectly fine for E30-II and the source impedance of the DAC is not raised too much (input capacitance and interlink cable capacitance) can start to play a role.

 

[Jim Shaw]

Instead of rolling your own, you might consider this: Schiit SYS passive 'preamp' $49.

 

[pma]

This is my best "passive pre ever" , confirmed by measurements and listening, completely immune to EMI in the environment.