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High-quality potentiometer or attenuator for DIY passive pre-amp?

T

Tumeni Notes

pfm Member
Thinking of building my own passive pre-amp, anyone got any recommendations for high-quality pots or attenuators, or examples of previous builds that have been discussed here?

I did a quick forum search, but most passive discussions relate to crossovers...
 
Hificollective have quite a big range of vòlume pots and stepped attenuators. You can even buy the switch and put whatever resistors you like in it. I think SA's sound better than pots so would be going that way personally.

I intend to put my own SA's together using my own choice of resistor values. As the loudest settings are never used I thought I would work out what resistor was needed for the loudest volume I would require and then use more rsistors in the range I need so the volume difference between steps is reduced. This will be especially useful for low level listening.

And I get to limit the volume so when my kids get older they can't crank it up and destroy my speakers and/or amplifiers. :)

Good luck
 
I have had little success with potentiometers: the channel imbalance is unacceptable in my view. I have measured the channel difference to be up to 25% even in £75 pots.
People say the attenuators sound better.
Cheers Andy.
 
Try to find an Alps as used by Quad on their 34 and later 44 preamps. Those are really great items.

Alps blue pots I also use are fine really but slightly inferior, as regards track matching.

Last time I saw one was on eBay @ Sithnamara (what has become of him?) at £ 40.

No differences in sound quality to speak of.

Also, your having have imbalance worries may be caused by a wrong resistive value. Or use a log pot!
 
andrewsutton said:
I have had little success with potentiometers: the channel imbalance is unacceptable in my view. I have measured the channel difference to be up to 25% even in £75 pots.
People say the attenuators sound better.
Cheers Andy.
Click to expand...

Are you talking about the value of the "full" track for each channel?
What matters is the attenuation.

I recently used a very cheap pot for <100Hz in an active crossover. The poor channel balanced was fixed by an external "frigging" resistor in series with one channel. I achieved <<1% tracking between channels at all the mid-travel settings, which means 99.9% of all use in this application.

Method: Apply 10V to both channels (100K pot) and read the wiper voltages using 2 DVMs.
 
My first recommendation would be to get a buffer in the preamp. I've never settled with what I perceive as the lack of drive with Passive Preamps and with a buffer things like impedance matching have less of an effect.

Secondly, I would never use a potentiometer, from Any manufacturer, and would recommend you build a custom stepped attenuator or buy a Khozmo, which I have always found to be great vfm.
 
Honestly that TKD (and the smaller one) are so good that they will probably better any stepped, they also have a really beautiful / quality action and are infinately adjustabe. TVC? - Don't go there either

Agree with BM regards buffers/ cathode followers.
 
sideshowbob said:
This is a build I did a couple of months ago using a Khozmo 48 stepped stereo attenuator:

https://www.hificollective.co.uk/blog/Glasshouse-Passive-Pre-amplifier-Kit-No-1.html

It's a really nice thing, recommended. I liked it enough to build a second preamp, using a pair of mono Khozmo attenuators. I like that even more.
Click to expand...

Been there, done that. Wasn't impressed

My strong recomendation would be to get a Croft Micro 25R, keep the PSU and phono and strip out the LS. Drop a John Broskie Aikido follower in. Maybe use TKD pots as well.

http://www.tubecad.com/2006/06/blog0071.htm
 
I've never found any lack of drive or dynamics with a passive and in fact it is not technically possible. I would not use a follower/buffer unless the power amp is a real awkward load as it will cause a slight degradation in transparency.
 
Dan K said:
Honestly that TKD (and the smaller one) are so good that they will probably better any stepped, they also have a really beautiful / quality action and are infinately adjustabe. TVC? - Don't go there either

Agree with BM regards buffers/ cathode followers.
Click to expand...

I haven't tried a TKD, so I will.

If that doesn't match up to my soon to be built custom stepped attenuator, then I'll report back separately in a comparison thread.
 
TKD pots are superb IMHO.

29704793576_ca13e22b1b_b.jpg


My simple little Tupperware DIY job uses the smaller TKD type and sounds superb. More dynamic and coherent to my ears than the Valab or Tisbury type of stepped attenuators that stack up resistors at each step rather than switching. It is a remarkably good sounding thing (the wiring is HiFiCollective’s cloth-covered solid-core stuff, can’t remember the brand)!
 
Tony L said:
TKD pots are superb IMHO.
My simple little Tupperware DIY job uses the smaller TKD type and sounds superb. More dynamic and coherent to my ears than the Valab or Tisbury type of stepped attenuators that stack up resistors at each step rather than switching. It is a remarkably good sounding thing (the wiring is HiFiCollective’s cloth-covered solid-core stuff, can’t remember the brand)!
Click to expand...
You should have it filled with an exotic noble gas and then sell it at a remarkably high price. You should be able to sell it through the same dealers that sell the wood boxes filled with cat litter and copper bars.
 
booja30 said:
You should have it filled with an exotic noble gas and then sell it at a remarkably high price. You should be able to sell it through the same dealers that sell the wood boxes filled with cat litter and copper bars.
Click to expand...

I can fart into it if that would help, though I may subcontract that to the cat.
 
I've owned a Goldpoint stepped pot, owned a khozmo stepped pot and their relay driven optical encoded attenuator ive used all the usual suspect pots from Noble, Alps, Penny and Giles.

The TKD tcp 601 is what I currently use. While it might not have the absolute level matching of a stepped resistor unit, any imbalance is below my hearing ability and its step-free, fluid action and attenuation range make it easier to live with. Sound quality is no different to the Khozmo I last had, its usability far beyond.

A buffer stage can be useful if you have issues with impedance matching, if you don't they only add complexity and a little noise. My pre amp has/is one.
 
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