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April 07, 2020, 12:03:29 AM

Author Topic: single attenuator for Two Quiet upgrade  (Read 272 times)

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Offline Rory

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single attenuator for Two Quiet upgrade
« on: March 03, 2020, 05:55:42 AM »
Hi All,

The time has come to install the Two Quiet upgrade on my C2A.  I only have one source, a Bluesound Node 2i and I generally just set the volume of my C2A at ~2/3rds and adjust the volume through the Bluesound app. Since I almost never touch the volume on the C2A, I think I only need one attenuator, the Coarse. I would only do this if removing a few solder joints and a resistor or two from the signal path would improve the sound. I suspect it won't. Thoughts?

Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #1 on: March 03, 2020, 05:58:50 AM »
If you turn the fine control all the way up, it's out of the signal path.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rory

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Re: single attenuator for Two Quiet upgrade
« Reply #2 on: March 03, 2020, 06:05:59 AM »
Is the same true of the stock attenuator on there now? 

Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #3 on: March 03, 2020, 06:27:02 AM »
With the stock volume/balance pots, turning the volume pot all the way up just turns it into a pair of 100K resistors that you'd need anyway, but there's still the balance pot and associated resistors providing some additional shunt and series impedance.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rory

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Re: single attenuator for Two Quiet upgrade
« Reply #4 on: March 03, 2020, 06:37:48 AM »
Thanks Paul. I don't adjust the Balance either. It sounds like I couldn't just bypass the Bal though, correct? I'd need to add some resistance, or at least keep the two resistors that are between Bal and Vol in the signal path?

Regarding the 100k resistance when the volume pot is at max, would I be better off replacing that with a pair of 100K resistors? Or perhaps adding to that whatever resistance the balance pot section provides, so i just have a single resistor? It would be essentially turning the C2A into a power amp, using my Bluesound as the preamp. I'm thinking I'd rewire the input selector to select between stock mode and amp mode, since I only have 1 input.

Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #5 on: March 03, 2020, 06:53:29 AM »
I would just leave it stock.  Mods like this decrease functionality and resale value and offer very little in return for that sacrifice. 

The lesser of all evils for doing what you want to do would be to add a set of RCA jacks on the wood that are direct input jacks.  You can install a pair of RCA jacks with wires presoldered to them, then glue the washers to your wood base and wire those RCA jacks in directly to the circuit after the volume pot.  (The volume pot will still need to be turned up all the way though so it doesn't short the direct input signal)
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rory

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Re: single attenuator for Two Quiet upgrade
« Reply #6 on: March 03, 2020, 07:00:09 AM »
That'll do it. If this is the route I'm going I'll install the Two Quiet as-is and still be able to have my straight-path amp only config. Do I need and resistors in the bypass circuit?


Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #7 on: March 03, 2020, 07:48:31 AM »
Nope, just be sure the coarse attenuator is turned up all the way when you use it.  You do not need to switch this input since you don't have a bunch of different sources.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rory

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Re: single attenuator for Two Quiet upgrade
« Reply #8 on: March 06, 2020, 05:51:48 AM »
I set up the direct input and at the same time swapped the electrolytic output capacitors for Dayton Audio film capacitors. The capacitors have made a big difference: soundstage, clarity, bass, and just the overall sense of presence that I was missing. The direct input made a difference as well. When I switch the input back to the volume+balance path there's definitely something different though hard to put into words, maybe less air or presence or realism, but it's subtle. Question: why does the balance control still have an effect even though I connected the new inputs into the circuit after the Bal pot? Is it because the pot shunts voltage to the ground to achieve the balance attenuation? Could it have any impact on the sound in this configuration?

Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #9 on: March 06, 2020, 06:19:03 AM »
Yes, the volume pot and balance pot are still in the signal path with the direct input. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rory

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Re: single attenuator for Two Quiet upgrade
« Reply #10 on: March 06, 2020, 10:23:26 AM »
If I wanted to remove them from the signal path with, say, a switch, is it as simple as it seems or would I need to add some resistance for input loading?

Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #11 on: March 06, 2020, 10:27:58 AM »
Yes, you would need to add resistance back in.  You would be trading the resistance of the pots for the same resistance just in a resistor.   
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Rory

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Re: single attenuator for Two Quiet upgrade
« Reply #12 on: March 07, 2020, 01:04:56 AM »
OK, looking at the 2Q instructions, to recreate max fine and coarse volume I would need to put a 34.8K resistor in the direct path, plus a 57.8K shunt resistor to ground. The calc for the shunt resistance is 1/R(t)=1/137K + 1/(.562K+1.02K+2.87K+8.06K+22.6K+64.9K). Is this correct?

Offline Paul Birkeland

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Re: single attenuator for Two Quiet upgrade
« Reply #13 on: March 07, 2020, 06:20:05 AM »
You would only need shunt resistance.  47K-500K is fine for that.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man