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December 06, 2022, 10:05:27 AM

Author Topic: Eliminating volume and balance pots & selector switch  (Read 226 times)

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Offline Skipperrik

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Eliminating volume and balance pots & selector switch
« on: June 22, 2022, 05:25:31 AM »
I have a DAC that has an excellent remote volume control. Since my furniture arrangement requires me to sit 15 feet away from the stereo I take full advantage of the remote and seldom touch the volume control on the amp. After contemplating many changes to the stock volume control in my Crack-a-two-a I've decided that the most efficient solution from both sound quality and cost perspectives would be to eliminate the volume control and balance pots. Since I only have one source, I may as well eliminate the selector switch too and remove all three devices from the signal path.

Here's the proposed change:

The combined resistance of the volume, balance and input switch is 100k + 30k + 30k = 160k. Is that correct? I also want to reduce the volume to a more controllable level so 200k resistors in each channel might be the appropriate amount. One end of each resistor would be soldered to the signal terminal of each input jack. The red and white signal wires would be soldered to the other end of the resistors. The red (right channel) signal wire would be soldered to terminal 4 and the white (left channel) signal wire would be soldered to terminal 12. The ground wires from the RCA inputs would be combined and soldered to terminal 1.

Does this sound feasible? Am I missing anything?

Thanks for any comments!

Offline Paul Birkeland

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Re: Eliminating volume and balance pots & selector switch
« Reply #1 on: June 22, 2022, 05:54:32 AM »
The value of the resistor across the input of the amp will not change its gain (unless you set this resistor to be way, way too low in value, which will cause problems with your source).

If you turn the volume pot up all the way, it's out of the signal path. 

On the balance pot, move the middle white wire to the outer lug with the other white wire.  Also move the middle red wire to the outer lug with the other red wire.  This will take the balance pot mostly out of the signal path.

You can temporarily solder in jumpers across the selector switch if you wish to disable that function.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: Eliminating volume and balance pots & selector switch
« Reply #2 on: June 22, 2022, 06:22:57 AM »
I'm not sure I follow your first comment. In this thread https://forum.bottlehead.com/index.php?topic=4295.0, Item #3, resistors were inserted into the signal path to reduce the volume. Is what I proposed different?

Offline Paul Birkeland

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Re: Eliminating volume and balance pots & selector switch
« Reply #3 on: June 22, 2022, 06:32:50 AM »
You could pad the inputs, yes, but you would want to do that much closer to the 12AU7 if possible to reduce the possibility of noise issues. 

(It would also be an equivalent fix to just turn down the volume pot on the stock circuit)
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Skipperrik

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Re: Eliminating volume and balance pots & selector switch
« Reply #4 on: June 22, 2022, 06:35:30 AM »
Okay. I'll mull it over some more. Thanks for the input.

Offline Skipperrik

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Re: Eliminating volume and balance pots & selector switch
« Reply #5 on: July 06, 2022, 03:44:22 AM »
Just a follow up - I removed all three of the devices from the signal path and decided to omit the installation of any resistors to attenuate the signal. It was a good call as they were not needed. I also ordered a couple of feet of black, white and red Teflon coated wire from Eileen to use instead of Cat 6 and twisted the signal and ground wire together for each channel to help reject interference.

The elimination of the devices made a huge improvement in the sound quality. Detail retrieval was greatly improved and the decay of notes and voices was extended. I can hear details in bass frequencies that were just a blur before. The difference was quite amazing.

I imagine the improvement would be similar to installing the TwoQuiet stepped attenuator for those whose source doesn't have a volume control. It really brought the amp to a new level of clarity and refinement.