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Old 24th October 2012, 06:42 PM   #31
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Originally Posted by audio mind View Post
I looked up "optical" resistors and there was not much info. Apparently they are also called "photo" resistors and there was quite a bit more info.

In the recording studio an optical compressor is one type of audio compression device that uses a photo sensor to reduce level. They are noted for a very smooth level change. I never closely studied the optical design so I didn't realize the optical device was a resistor.

Well how do the optical's sound or don't sound in a conventional audio circuit as a fixed resistor?

I was having trouble finding values under 2k where do you get yours?

and it the specs were a little strange compared to conventional resistors, do they all change resistance or something when light is applied? Do you need a light to operated them?

Wiki definition:photoresistor or light dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits photoconductivity.

Thanks for the input.
I understand that optical resistors have been around for a long time. They do not however seem to have been used very much. They have mainly been used as volume attenuators. Within the last few years they have become popular as volume controls (mainly diy) for HiFi. Search Lightspeed Attenuator. This Lightspeed Attenuator and it's derivatives have been very successful. I use one and it is certainly the best volume control I have heard.
All these attenuators have been variable. Uriah Dailey however designed a circuit to enable these attenuators to be of fixed resistance. They are based on the Silonex NSL-32SR2. This optocoupler has four connections, two are the LDR part and the other two the resistive part. It is a sealed unit. Simply put the resistance part varies with the amount of current that is applied to the LDR part. It is therefore possible to apply a certain fixed amount of current to obtain a fixed resistance.
Uriah Dailey explains his circuit here. All credit to him. https://picasaweb.google.com/udailey...at=directlink#
I have had mixed success using these resistor replacers in the signal path of various circuits. When first set up they provide a definite sonic improvement over metal film resistors. I have however had drifting problems, the resistance would change from the original fixed value over time. This is something that requires further investigation. They are also limited to values below 10k, above this they are unstable. It is also neccessary to check the voltage drop across the resistor to be replaced is below 2.5 volts, over this voltage and you introduce distortion.
I hope this helps.

Paul.
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Old 27th October 2012, 11:53 PM   #32
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A wire-wound resistor...is...
...er...
...WIRE !!!

Listen to THAT !!!

Si.

Welwyn is OK wire holmes !
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Old 28th October 2012, 05:40 AM   #33
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Yes I plan on testing several different wire wounds.

Space Egg, Welwyn W21 versus Mills wire wounds, have you compared?
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Old 29th October 2012, 12:37 AM   #34
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Hi AM

I dunno...I try to avoid 'listening to wire' !

I have used 5% Welwyn ( never shifts from original match ! ).
&
Also 0.1% type from RS Components, for more precise apps.
Not sure who makes it...would have to check...they are costly due to the 0.1% spec.

Not sure about Mills...
...I hear them mentioned here alot...I'm sure they are just as good as any others.
Is Mills an American company ?

It's hard to resist a good resistor !!!

Cheers

Si.

Irresistable !!!
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Old 29th October 2012, 02:21 AM   #35
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Yes, I believe Mills is an American company that was absorbed by the juggernaut Vishay. Mills wire wounds are sound nice, smooth, clear and classy sounding to me and they take away the harsh edge of a those rectangular sand cast resistors.

Some like the bite of sand cast resistor in low end system to cover up the flaws and give a dull system some zing but I will never use a sand cast resistor anywhere in any system that I listen to if I can help it.

Although Mills costs a bit more than your average resistor I have never been disappointed with the sound in any circuit I have used them in so far....

Now, I have not heard the cast Dueland graphite resistors at around $50 a pop yet. I will try at least a few of the cheaper $25 Dueland resistors on my next high end project.

Price on Dueland resistors and caps and coils is sky high compared to everything else but I suppose if you are trying to build equipment to compete with the finest commercial audio gear out there, I think the price is a mere drop in the bucket price wise compared to the "shock" marketing "you could buy a nice Italian sports car" prices we have these days on some high end audio equipment.

Overwhelming consensus I have seen so far is that the Deuland "cast" components are the finest and most natural sounding caps, resistors and coils out there second to none and in the lead by a nice margin.

Wow, now back to reality....It is fun to dream though.

Last edited by audio mind; 29th October 2012 at 02:24 AM. Reason: typo
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Old 29th October 2012, 02:32 AM   #36
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You could wind your own !

( like the legendary wire-wound products in Tokyo audiophiles garages ! )

I'm not winding you up either !

Used to wind my own coils...why not resistors !

Si.
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Old 29th October 2012, 02:49 AM   #37
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AM

I trully believe people more often than not, confuse MONEY with QUALITY...
...I do generally also believe you get what you pay for.

But hey...a coil of wire...is a coil of wire...is a coil of wire...

BTW I'm not sure why exactly William put opticals in positions 1 & 9 ( I think it was, 100 Ohms ).
R1 & R9 are not even needed in my opinion.

I would avoid ANY kind of resistance between the cartridge and the JFET gate...
...in fact I would go as far as to solder the JFET's gate DIRECTLY to the RCA phono input socket.
No kiddin'...
...my current phono pre will get that treatment.

Better to have good layout & quality soldering, than a bunch of $$$ wasted on over-hyped components.

OK a challenge...
...build a good preamp, just using parts busted down from a scrap TV set etc...
...totaly & entirely possible.

Gimmie a couple of crap scrap TV's...
...I bet I could make a preamp that you would think cost a GOOD few $'s
( blind test of course, no demolished TV's laying about to spoil the 'High-End' ambience either !!! )

Cheers

Si.
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Old 29th October 2012, 04:37 AM   #38
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Coil winding has been on my mind, winders on ebay start at about $60 for a manual winder without an electric motor (I would get a motor for sure for what I want to do).

I could finally build the 8 mono tube amps with 16+ trannies for a four way all horn system with electronic tube crossover and pre I had in mind. I would need several more transformers for the tube pre amp, crossover, filaments, driver stages, maybe some chokes. Probably 25-30 transformers total!?!!.

This is a lot of transformers and I could control the quality, high purity soft silver wire, etc. best core materials, my choice of bobbin,etc. Being that a silver output transformer is a few thousand bucks or so, this coil winder would be an amazing investment.

Yes a coil winding machine would pay for itself winding one or two trannies, resistors would be icing on the cake.
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Old 6th November 2012, 08:33 AM   #39
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Default Optical resistors

Further to my drifting problems using Silonex NSL-32SR2 (thread 31), these are affected by the ambient temperature. The drifting problems I experienced were when the phono stage was not in an enclosure. Once in an enclosure the Silonex NSL-32SR2 are much more stable.

Paul.
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Old 28th March 2013, 10:19 PM   #40
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Please swap the 33(34)nF caps before any resistor...it does change the sound a lot!

Arne K
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