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Old 11th March 2008, 11:03 AM   #1
oshifis is offline oshifis  Hungary
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Default Vishay Audio Resistors

I would like to share my experiences with the new Z-foil Vishay Audio Resistors (VAR):

http://www.vishay.com/product?docid=63140&query=VAR

I built in six resistors at the most critical location in my home-made tube preamplifier. The circuit where I tested the VARs is a two-stage passive RIAA equalizing circuit with three SRPP tube stages. The equalizer between the first and second stage realizes the bass boost: 95.4k series between the stages, 10.6k + 30nF shunt to GND. The equalizer between the second and third stage is for treble cut: 75k series between the stages, 1nF shunt to GND. I used Russian vacuum-sealed 0.5% silver-mica SGM-3 capacitors in the equalizer (in combination with the VAR resistors). I got the exact corner frequencies with the resistors as below:

Output impedance of each tube stage = 1.2k

(1.2k + 94.2k + 10.6k) x (4 x 7500pF) = 3180us
10.6k x (4 x 7500pF) = 318us
(1.2k + 73.8k) x 1000pF = 75us

I used Yageo 2W metal-film resistors at these positions before and at all other positions. The system: turntable Thorens TD160 Super, arm Mayware Formula 4, pickup Denon DL103, MC-pre: Dynavector PE-2, preamplifier: home-made SRPP stages with E88CC as above, power amp: home-made push-pull with Russian G-807s without negative feedback, loadspeakers: Quad ESL (aka ESL-57). The coupling capacitors in the preamplifier are Russian K40-U9 1uF/400V PIO types, and Russian FT-3 teflon types in the power amplifier. All the other resistors are 2W Yageo (RSF2WS) and the volume pot is a plain Piher (shame, I know...).

I listened to these randomly selected LPs:

Pal Esterhazy: Harmonia Caelestis (Hungaroton, http://www.hungaroton.hu/hu/node/2314)
Sara Marie Anderson: Bergen Havn (Opus 3, http://www.rauna.com/slides/covers/18.gif)
Dire Straits: Communiqué (Vertigo)
Miles Davies: Sketches of Spain (Columbia)
and some more.

My impressions after the first listening:

- The dynamics of the music increased. There is more "air". Before I observed that the fortissimos are a bit annoying, one want to turn down the volume. Now I can listen to high volume without feeling it "too loud".
- The bass notes can be separately heard (especially at contrabass, bass guitar), they are not melting together like they did before.
- The female voice is very clean, transparent, nature-like. I can feel her presence in the room.
- It is possible to chat while load rock music is played.

I did not believe that so big improvement can be caused by just replacing a few resistors, before I actually heard it. Now I have no rest until I throw out the remaining metal-oxide resistors...
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Old 7th June 2008, 12:19 PM   #2
oshifis is offline oshifis  Hungary
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Finally I replaced all 1k5 resistors in the SRPP cathodes to Vishay Audio Resistors. I expected a great improvement, and there is a big difference indeed. My initial impressions are quite mixed. The sound became a bit harsh (or was it too smeared before?). On the other hand I can hear much more low level details that were before masked by the high level signal. The preamplifier has run ony for a few hours now, and the sound is getting more and more smooth, the harshness is going away gradually. I expect it will be smooth and detailed at the end. I am "rediscovering" my LP and CD collection, as it used to happen...
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Old 7th June 2008, 12:28 PM   #3
Zen Mod is offline Zen Mod  Serbia
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glad to read about improvements

where you purchased these resistors ?
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Old 7th June 2008, 01:12 PM   #4
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Default Re: Vishay Audio Resistors

Quote:
Originally posted by oshifis
Now I have no rest until I throw out the remaining metal-oxide resistors...

You may find much less improvement with the remaining resistors.
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Old 7th June 2008, 02:11 PM   #5
BC is offline BC  United States
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Hi ZenMod,

This is the company for the resistors. They will sell just one!


http://www.texascomponents.com/


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Old 7th June 2008, 09:38 PM   #6
BrianL is offline BrianL  United States
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Note that these "VAR" resistors are just "naked" versions of the standard packaged Vishay resistors. I find it hard to believe that the naked version has any audible advantage over the standard version, but whatever...
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Old 7th June 2008, 10:28 PM   #7
trodas is offline trodas  Czech Republic
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This is very interesting. So, just the input resistors can make such change? Wow.


oshifis -
Quote:
10.6k + 30nF shunt to GND... 75k series between the stages, 1nF shunt to GND...
Excuse my lame question, but... why placing into the audio signal path a capacitors that are "shutting the signal to the ground"?

I just did not understand.
As soon as the signal reach the capacitor... I think this is completely unnecessary blurring of the sound, as capacitor in general act to prevent voltage changes, so it has to "blur" a little the amplitude to prevent fast and rapid changes of it.

Don't I get it right?
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Old 7th June 2008, 10:49 PM   #8
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by trodas
......
Excuse my lame question, but... .........

phono section
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Old 10th June 2008, 10:10 PM   #9
trodas is offline trodas  Czech Republic
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Pardon me, but what section of forum do you mean?

I think tha this is about Electronics and Parts, it is well suitable there... nope?

I just have no idea what you mean.
Regardless it looks like no-one want even touch my complex questions there: Genius SW-5.1 HT mod - are my ideas good?

So looks like I need to chop them down to more managable parts...
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Old 10th June 2008, 10:22 PM   #10
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by trodas
Pardon me, but what section of forum do you mean?
......

I wrote that original poster use them in phono section of preamp ........ so - that's why caps are shunted to gnd - passive RIAA EQ
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