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Old 27th October 2010, 11:49 AM   #571
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sorry

constant Input Impedance

Last edited by samoloko; 27th October 2010 at 11:52 AM.
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Old 27th October 2010, 11:55 AM   #572
AndrewT is offline AndrewT  Scotland
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Hi Sam,
which arguments have swayed you towards an attenuator with a varying output impedance?
What makes that version attractive to you?
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Old 27th October 2010, 12:34 PM   #573
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constant Zin Is good for source
the signal In showed attenuator goes only through 2 resistors / relay
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Old 27th October 2010, 12:42 PM   #574
AndrewT is offline AndrewT  Scotland
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what is the effect on the source if the load impedance varies?
How much can it vary for no audible effect. Must the load impedance stay exactly the same for
Quote:
constant Zin Is good for source
to hold true.

Let's take an example.
Rin =100k for power amp
R of pot = 20k
Rs = 200r
Capacitance of cables 100pF

At maximum volume (minimum attenuation) the load is 16k667
At minimum volume (maximum attenuation = -60dB to -100dB) the load is ~20k

What effect does this change in load impedance have on the source?
Is it audible?

Quote:
which arguments have swayed you towards an attenuator with a varying output impedance?
What makes that version attractive to you?
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Old 28th October 2010, 04:05 PM   #575
qusp is offline qusp  Australia
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Quote:
Originally Posted by Tea-Bag View Post
Vishay Z-Foils. TX2575. I dont think you'll regret the investment, especially if there is something else in their first to try.

Direct from texas instruments I get them for for about 10.00 each before shipping and handling. That may be another $10.00 for that. Maybe more for asia shipping. Anyone can order from there I think, even just 1 resistor.

Use caddock for 220k, 1M anything else IMO.
yep excellent resistors, but I would also let the circuit settle a bit before trying them, although you really cant go wrong with them IMO. they are 10 each for their plain vanilla 0.1% overall value match but also go up in price as the value goes up, for a 500k will cost more, for 0.05% is about 14 and for 0.005% is like 19. then you can pay for them to be matched to the same degree as a relative match to each other in pairs or quads. they also sell the Zfoil power resistors at up to 5W rating and numerous other exotic types of precision R's.

another vote for PRP here tho, fantastic resistors at a great value plus they look sweet in red

caps on the other hand I would definitely wait to see if the system needs tuning one way or another.
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Old 29th October 2010, 03:40 AM   #576
Salas is offline Salas  Greece
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Matching is irrelevant here, its for instrumentation applications and fighter jets. Don't pay for such in the DCB1. It does not have differential ultra low noise sensors or something. The audio part resistors just terminate impedances and buffer cables. Influential but for material properties, not value accuracy. Ask for their worse tolerance possible and best quote.
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Old 29th October 2010, 04:18 AM   #577
qusp is offline qusp  Australia
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Haha, of course its irrelevant Saias; I mentioned it more out of interest. I wasnt suggesting the highest degree, even if we could get the components and signal from before this point perfectly matched, it would be overwhelmed by a touch more solder in a joint here, or a couple cm of wire in the cable there. but since when has it been totally about audio quality, if I get them i'll get the 0.01% global and relative in quads because I can and because it makes me feel better the highest degree match global and relative in quads is insanely priced, but i'll go the next one down because I have a mental problem. 0.1% is the lowest
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Old 29th October 2010, 08:05 AM   #578
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0.1% accuracy to an arbitrary and subjective value is in the "Mundorf unobtanium plated fairy wings in virgin's blood capacitor" league. You might as well have you're circuit board remade in Gold. Silly.

Experimenting with different values of PRPs might give you more mileage. Sorry, I'm in the PRP fan club now. So good! So cheap!
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Old 29th October 2010, 08:42 AM   #579
qusp is offline qusp  Australia
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Quote:
Originally Posted by LucasAdamson View Post
0.1% accuracy to an arbitrary and subjective value is in the "Mundorf unobtanium plated fairy wings in virgin's blood capacitor" league. You might as well have you're circuit board remade in Gold. Silly.

Experimenting with different values of PRPs might give you more mileage. Sorry, I'm in the PRP fan club now. So good! So cheap!
i'm wondering if you read my post at all, it seems to be your native tongue. in order to get less than 0.1% Zfoils, I would have to pay them a custom fee, do you suggest that I do this? paying them more to give me less seems a bit strange does it not? 0.1% is the lowest and cheapest matching they come with. now THAT would be silly. also you might be able to see my recommendation for and love of PRP a couple posts up.

I doubt that their tooling is even capable of it, they are laser trimmed. I suppose I could put 220 through a random number generator and specify 219.7, 220.8, 219.2 and 220.3 in order to simulate a 1% degree of matching

Last edited by qusp; 29th October 2010 at 08:46 AM.
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Old 29th October 2010, 12:21 PM   #580
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Sorry Qusp, I wasn't referring to you at all - I read already that you agreed with Salas, so I knew that you were not personally chasing that degree of tolerance. There are people, however, that build a circuit without trying to understand it much, and then just throw money at it's shortcomings.

I'm a novice, but it has become quite clear to me that there is a lot of snake-oil around, and boutique parts are often a big part of that - not always, but often. Most of what we hear is design and implementation anyway. Experimenting with resistor values, as opposed to "value" is really the wise form of modding, in my opinion.

Anyway, no offence intended whatsoever.
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