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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

shunt type attenuator
shunt type attenuator
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Old 8th February 2018, 01:07 PM   #1
glennjarrett is offline glennjarrett  United Kingdom
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Default shunt type attenuator

looking to make a shunt type attenuator 23 step 10k
will be using Z foils for the 2x input/output resistors 10K
what effect has the resistors that go to ground have on the sound if any ?
goldpoint website says that the ROA Speer mouser stock are the best through hole they have tried and for pennies ( pity mouser charge so much for posting a few bits ) cant seem to find them anywhere else

Click the image to open in full size.shunt by glenn jarrett, on Flickr
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Old 8th February 2018, 01:26 PM   #2
Mooly is offline Mooly  United Kingdom
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shunt type attenuator
In principle they have as much effect as the other fixed resistor because the two together are simply a series pair forming an attenuator. In practice, and at higher levels of attenuation as the switched shunt value becomes lower and lower then any of its 'problem contributions become less. At lower levels of attenuation any 'problem' effects start to predominate.
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Old 8th February 2018, 01:37 PM   #3
scottjoplin is offline scottjoplin  Wales
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A "selling point" of shunt attenuators is that the resistor to ground is not in the "signal path" . Since they are in series, I take it that any noise generated by the resistor is present equally at both ends?
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Old 8th February 2018, 03:05 PM   #4
nashbap is offline nashbap  United States
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I have used the KOA Speer in the shunt position and TX2575 as you plan and found the combo harsh. Switched to Takman metal film and found an improvement. Switched the TX to Shinkoh 1 watt for the series and it sounds wonderful. All this for classical music.

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Old 8th February 2018, 05:13 PM   #5
KCHANG is offline KCHANG  United States
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Quote:
Originally Posted by scottjoplin View Post
A "selling point" of shunt attenuators is that the resistor to ground is not in the "signal path"
Unfortunately, this "selling point" is one of the audiophiles' myths that are not technically correct. It is in conflict with Kirchhoff's law and Thevenin's theorem. The resistor to ground contributes to the "equivalent resistance" of the simple voltage divider network (including the amp input impedance), so it is never out of the equation (pun intended), and the voltage to the amp will be affected by the visually "out of the signal path" shunt resistor. In other words, it is not electrically "out of the signal path."

Cheers,

Kurt
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Old 8th February 2018, 05:51 PM   #6
scottjoplin is offline scottjoplin  Wales
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Yes, I get that, and this helps Shunt Attenuator Myth
Is my assumption about the noise heading in the right direction at all?
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Old 8th February 2018, 06:20 PM   #7
rayma is offline rayma  United States
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Quote:
Originally Posted by scottjoplin View Post
Is my assumption about the noise heading in the right direction at all?
The noise is determined by the Thevenin equivalent circuit, which here is the two resistors
(series and shunt), in parallel.
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Old 8th February 2018, 06:44 PM   #8
scottjoplin is offline scottjoplin  Wales
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Got it, thanks Ray
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Old 9th February 2018, 02:16 AM   #9
madisonears is offline madisonears  United States
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Vishay/Dale and TX2575 make a nice combination. Those KOA's do not make good sound anywhere I've tried them.

Peace,
Tom E
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Old 9th February 2018, 09:29 AM   #10
DF96 is offline DF96  England
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The popularity of shunt attenuators is a good sign that electricity is poorly taught in school science lessons.

Resistors are the second most perfect/ideal components used in electronics. (The first most perfect components are wires.) Why get worked up about near perfection when much worse problems come from nasty things like transistors and valves?

Anyway, someone who is worried about resistors and knows anything about resistors would use the same resistor technology for the shunt and series elements. This will minimise errors. Ideally, use the same value too - but this makes changing the volume rather difficult unless you use strings of resistors. It makes absolutely no sense whatsoever to use an expensve resistor for the series element and something different for the shunt element.
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