Best way to balance control to the crack

phatfish · 1819

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Offline phatfish

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on: August 18, 2024, 06:08:01 PM
Greetings!  I recently finished adding the speedball to my crack and I'm loving the sound and the building experience. :)  I'd be buying a Crackatwoa if the kit was available. 

I currently have balance control on my solid-state phono preamp which I use.  I'm planning on building up an Eros2 which I would like to run directly to the crack and fear I would miss the balance control. 

Why:
My ears themselves seem to be a bit unbalanced and I prefer to have some degree of balance control even when using a stepped attenuator on my solid-state streaming system.  This isn't simply to overcome low volume issues with the stock pot. 

The plan: 
Add a 100k Balance Pot in series between the RCA inputs and the existing 100k volume pot.  Mount it roughly to the left of the vents. 

Questions:
Is this a good/sane plan?  If not, what is the optimal way to add some form of balance control (within or outside the crack).

I read in the FAQ that the resistance of the pot isn't really important (25k-250k).  I'd love to know more about why that's the case.  Would adding the balance pot as described make this similar to a single 200k pot?

Any gotchas I should look out for?

Many thanks for any answers and assistance!


« Last Edit: August 18, 2024, 06:12:06 PM by phatfish »



Offline Paul Birkeland

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Reply #1 on: August 18, 2024, 07:07:40 PM
Man, this is such a simple sounding question with a lot of viable answers.  There's some good reading here:
https://sound-au.com/pots.htm
Our kits with balance controls use figure 9 on that page, and I would recommend starting with that.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline phatfish

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Reply #2 on: August 19, 2024, 04:44:32 PM
Thank you Paul.  That link perfectly explains how to wire a normal volume pot for balance control, something I didn’t even know was an option.  I was planning on getting a 100k audio note balance pot specifically for this purpose…still might buy great to know there is a much more reasonable option!

I still feel lost about the impact of putting more pots and/or resistance in the signal path tbh.  I’m confident it’s a non issue based on other bottlehead products doing this, but I’d like to know what something extreme like adding 10 pots (nothing I would actually do of course) would do?  High frequency roll off?

Edit: I suppose at the center position the balance pot wouldn't be adding any resistance, and not much to one channel when slightly off center.  I'm still confused why a pot resistance of 25k-250k wouldn't make much difference.  Wouldn't the 25k pot offer less resistance at the same position compared to a 250k pot?  Wouldn't that affect the audio signal in some appreciable way? 
« Last Edit: August 20, 2024, 04:16:45 AM by phatfish »



Offline Paul Birkeland

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Reply #3 on: August 20, 2024, 05:13:49 AM
Lower resistance potentiometers decrease the input impedance of the amp and can load down your sources.  Higher resistance potentiometers are more susceptible to picking up noise.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline 2wo

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Reply #4 on: August 20, 2024, 06:09:47 PM
Have you considered using separate pots/attinulators for each channel? Like the early Foreplay.

John S.


Offline phatfish

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Reply #5 on: August 21, 2024, 03:55:46 PM
Appreciate the explanation Paul! 

2wo: I did briefly consider, but I tend to adjust the volume frequently and the balance infrequently, so I’m quite set on the balance control. 

I’m ordering parts and will update here on the results.   8)  I appreciate the help.



Offline phatfish

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Reply #6 on: August 30, 2024, 06:51:49 PM
Success!  Thanks y'all.  8)

The audio note balance pot ain't cheap, but I gotta say I really like the center position feature it has compared to using a regular pot for this purpose.  Parts Connexion was also quick to provide a wiring diagram specific to this pot.