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Old 22nd December 2010, 12:56 PM   #1
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Default EL34 Triode Mode Resistors

Hi. About 2 months ago I converted my Cary Audio SLA 70A Signature EL34-based amp to triode mode tying back the UL tap and adding 100 ohm 1/2W metal films and I like what I heard in the conversion very much.

But to play it safe, I decided to replace these resistors with Radio Shack 100 ohm 1W metal oxide resistors. The problem is that the resultant sound changed. There's now a slight tilt in the upper mids and a grain in vocals that wasn't there previously. After about a month of listening, I decided to convert back to UL and the symptoms disappeared.

Could the resistors cause the change in sound that I heard? Also, what resistors would you recommend for this conversion? Thanks.
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Old 22nd December 2010, 01:51 PM   #2
kevinkr is offline kevinkr  United States
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I'm not a fan of metal oxide resistors in the signal path - what you describe sounds a lot like what I hear. Subjectively to me they sound brighter and harsher, perhaps they generate distortions that other types don't since there is no such thing as a perfect passive component, but some are much better than others. I have never bothered to measure one, but below is the story of a distortion generating metal film that caused me some grief.

Something over 20yrs ago I had a problem with the subjective and measured performance of a solid state pre-amplifier design I was working on at the time. It sounded quite bad and seemed to have unexpectedly high levels of distortion, and I was very puzzled. It turned out that the feedback resistor in one of several compound complementary amplifier stages was generating significant amounts of odd order distortion - these resistors were made by Mepco Electra and were MF types. Unused samples drawn from my inventory all generated > 0.15% in a series connection, know good reference resistors gave results very close to the generator residual which was around 0.01%.. Replacing those resistors solved the problem.
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Old 22nd December 2010, 01:55 PM   #3
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Originally Posted by kevinkr View Post
I'm not a fan of metal oxide resistors in the signal path - what you describe sounds a lot like what I hear. Subjectively to me they sound brighter and harsher, perhaps they generate distortions that other types don't since there is no such thing as a perfect passive component, but some are much better than others. I have never bothered to measure one, but below is the story of a distortion generating metal film that caused me some grief.

Something over 20yrs ago I had a problem with the subjective and measured performance of a solid state pre-amplifier design I was working on at the time. It sounded quite bad and seemed to have unexpectedly high levels of distortion, and I was very puzzled. It turned out that the feedback resistor in one of several compound complementary amplifier stages was generating significant amounts of odd order distortion - these resistors were made by Mepco Electra and were MF types. Unused samples drawn from my inventory all generated > 0.15% in a series connection, know good reference resistors gave results very close to the generator residual which was around 0.01%.. Replacing those resistors solved the problem.
Thanks Kev. What resistors brands should I look for? Vishay's maybe? The shipping will probably cost more than the resistors, lol.
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Old 22nd December 2010, 01:58 PM   #4
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Mills, Kiwame or better Shinkoh.
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Old 22nd December 2010, 02:09 PM   #5
kevinkr is offline kevinkr  United States
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Vishay, Dale, Roederstein, Draloric, etc..
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Old 22nd December 2010, 02:18 PM   #6
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Originally Posted by merlin el mago View Post
Mills, Kiwame or better Shinkoh.
What design though? Carbon comp, metal film or metal oxide? CC's get rather noisey quickly don't they?

It's a shame because I have a bunch of NOS CC's from Allen-Bradley and Wirt from back in the 60's but with resistive values that I can't use.

But I did find some RShack 1/2W metal film 150 and 220 ohm resistors. Will these suffice or should I seek out better resistors at the 100 ohm value?
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Old 22nd December 2010, 03:36 PM   #7
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Originally Posted by Monjul View Post
What design though? Carbon comp, metal film or metal oxide? CC's get rather noisey quickly don't they?

It's a shame because I have a bunch of NOS CC's from Allen-Bradley and Wirt from back in the 60's but with resistive values that I can't use.

But I did find some RShack 1/2W metal film 150 and 220 ohm resistors. Will these suffice or should I seek out better resistors at the 100 ohm value?
Mills: non inductive, non magnetics, Nickel-chromium or nickel-copper
alloys used

Kiwame: carbon film

Shinkoh: tantalum

If possible avoid, metal oxide, metal film, generic ceramics, etc
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Old 22nd December 2010, 04:03 PM   #8
jrenkin is offline jrenkin  United States
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Originally Posted by merlin el mago View Post
Mills: non inductive, non magnetics, Nickel-chromium or nickel-copper
alloys used

Kiwame: carbon film

Shinkoh: tantalum

If possible avoid, metal oxide, metal film, generic ceramics, etc
Some say to use metal film, you say avoid it. Can you elaborate?
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Old 22nd December 2010, 05:07 PM   #9
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Originally Posted by jrenkin View Post
Some say to use metal film, you say avoid it. Can you elaborate?
It's my subjective opinion a question of personal taste, it's easy try metal film & after try non inductive, non magnetic & you can hear the difference.
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Old 14th January 2011, 12:39 PM   #10
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Originally Posted by merlin el mago View Post
It's my subjective opinion a question of personal taste, it's easy try metal film & after try non inductive, non magnetic & you can hear the difference.
I might have to agree with you.

I didn't even like what I heard in triode mode using 100 ohm 1/2 RShack metal film resistors let alone the metal oxides. After speaking with Jim McShane, he thought the amp might be oscillating. So upon his recommendation I bought some 272 ohm Vishay/Dale's and amazingly, all the problems I heard disappeared and it's now obvious that this Cary amp in triode mode is the way to go. The sound is smooth, sweet, open and less electronic sounding although the added warmth from 2nd harmonic distortion can make some recordings sound slightly heavy.

So the advice here is if you don't like the way your EL34 amp sounds in triode mode, give it another chance by trying better manufactured resistors with an increased resistance (>100 ohms), to be on the safe side.
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