In the pursuit of Impedance

[ALL212]

This is a follow up to the passive preamp I built with a 100k pot in it. Sounds like I put the wrong one in.  I've taken that pre and made an impedance listening test bed out of it.  I need to hear it!!   

My difficulty initially was that I was not going to buy more Gold Point attenuators as they are too expensive.  I didn't want to pick up something I wouldn't use later so the Blue Alps hits a sweet spot at about $20.  Next issue - how to mount these and make it easy to switch in and out.  The Blue Alps is a nice pot but designed to be used on a circuit board.  Soldering to those small pins is more than a pain. 

Bring in the magic.  AMB Audio Shop has the Epsilon 27 volume control mounting board. 

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_3837_zpsccpusrgp.jpg&hash=06a9822e97b214aa0067fd253107c0ff1da6e09c)

You can use Molex connectors on it for easy on/off mounting.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_3838_zpseesyeet2.jpg&hash=0be63a82c8d9dd0413d9f25581c84f0aaebed5cb)

The Blue Alps solders directly to the board.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_3840_zpslb5f3dkw.jpg&hash=b90803d99b86e1d11ecbe4376fa42550ab569061)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_3839_zpsvucrvjzi.jpg&hash=724c9b3e97994228b6473466e96f73f501888041)

The test units.  10k, 20k, 50k and 100k.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_3842_zpsfhuuos6y.jpg&hash=962467dcebb613f27b85cdede4baf1fa977644b5)

Mounted in the pre plate.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi905.photobucket.com%2Falbums%2Fac253%2Fall212212%2FDSC_3843_zpsswximdyp.jpg&hash=12ddfc75e8ecd5b83c3371e1cf2074839c457d5b)

Tonight I'll start with the 10k.  I'll keep you posted.  Molex mounting is not required.  You can solder directly to the mounting points.  All connection points are clearly labeled.

[JamieMcC]

This looks a interesting experiment I'm looking forward following your progress.

[Deluk]

There is a correctly rated ALPS pot that has ring connections for the wires which does make the job easier. I've seen it pictured here somewhere so someone should have the ALPS part number.

[ALL212]

Testing units:

Input #1:  Analog - TT, Music Hall MMF 5 to Reduction
Input #2:  Digital - Stello DA 220

Output #1: the BA Crack with Senn HD 650's
Output #2: S.E.X with MrSpeakers Alpha Prime
Output #3: TT back to the main rig

This might take a bit to complete.  There's quite a few variations on input/output but nothing too crazy.

[Paul Birkeland]

Bravo on your efforts!  This is a very well designed experiment, and you're almost certain to land on a pot value that suits your system best.

-PB

[ALL212]

I've been traveling and not much time to play so I put the 100k's in (10k's were in before this).  Figured if I can't hear something different I might as well give up.

I don't like the sound and I'm not sure why.  It's very fatiguing. 

[ALL212]

Had the 20k in - it's ok.  Decided that I wanted to get some serious listening in so popped the 10k back in.  Wonderful!
Something definitely not good about the 100k.

So I thought I'd drop back even further and put in the original switcher - no volume.  Same selectors, wiring and RCA's.  I'm not so sure I like it!    The Crack has a 50k in it.  It's as if the sweet spot is 60k.  10k in the preamp and 50k in the Crack.

That make any sense at all?

[Doc B.]

Yes, you have ended up with the classic impedance for a passive preamp. It's not 60K. It's 10K driving 50K. The next logical step would be to try 100K in the Crack. Well actually the most logical step would be to loose the passive since the Crack has a volume control, but that wouldbe the next logical step in terms of experimentation