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Old 13th November 2009, 11:27 PM   #1
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Default What's the differences among trimmers?

There are so many brands and types of trimmers and price various between 50 cents to $30 each. Did anyone try and compare differences among trimmers?

Bourns 3266W costs less than $1 (From anywhere)
Copal RJ5W costs $3 (Digikey at $2 for 200 pcs)
Vishay 1280G costs $8.5 (From Percy Audios)
Vishay 1260W costs $22 (From Texas Components)
Vishay 1240W costs $34! (From Texas Components)
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Old 14th November 2009, 01:40 AM   #2
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The first two are cermet (thick film); the last three are bulk metal foil and of substantially higher quality: very low Tc, noise and voltage coefficient. Too bad they're so expensive.
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Old 15th November 2009, 12:32 PM   #3
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Then is it worthwhile to try these expensive trimmers?
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Old 15th November 2009, 06:51 PM   #4
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If you >need< that level of quality, perhaps. Exactly how would they be used?
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Old 16th November 2009, 01:40 AM   #5
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I am building the Erno Borbely 320 phono. There is a trimpot (P1) in his circuit to balance the output offset between 8 pairs of JFET in the input section. This is a critical stage that requires very low noise components. Erno is supplying his kit with Copal trimpot which is already very good but I am thinking should I change it to bulk metal foil trimpot? I am already using his 432 (low cost) phono that blows away all my phono preamps (including ASR Basis Plus) therefore I am thinking should I do a bit extra for the 320 kit.

You can have a look of his 320 circuit in his website
http://www.borbelyaudio.com/products.asp

Last edited by Sunsun22; 16th November 2009 at 01:44 AM.
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Old 16th November 2009, 01:49 AM   #6
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Genuine Bourns aren't that inexpensive -- there are a lot of trimmers with the same product numbers which aren't of the Bourns quality.

It shouldn't be surprising, but trimpots fail even when they aren't adjusted. The current is always heating the junction of the resistive element and the contactor. I had a bum Krohn-Hite analyzer with exactly one bad trimpot, another Tektronix PS5010 with failed trimpots. But this isn't exactly going on the Mars Rover...
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Old 16th November 2009, 01:59 AM   #7
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While I think the Vishay is still overkill even in this application, it won't hurt to use it if you can afford it. The bulk metal foil is probably the best technology for this application.

Being more engineering oriented, I rate resistors based on their demonstrated specifications, especially temperature and voltage coefficient as well as noise. The lower the better, so I prefer 50ppm and 25ppm Tc .1% when in the critical parts of a circuit. Bulk metal foil easily beats those requirements, whereas a typical trimmer is doing very well to give 200ppm or higher because of the cermet resistive element.
(Carbon film is always much worse, and carbon composition worse still, but some like the 'sound'.)

Alas, the best technology also tends to be the most expensive by a wide margin.

(Boggling over the schematic; my Hafler SE-100 preamp is all-JFET and much simpler in parts count and design.)
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Old 16th November 2009, 02:08 AM   #8
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damon:

just curious, how do you like your hafler phono stage? i always thought the riaa preamp in the se100 and 915 preamps was pretty neat and wondered why more people didn't try to "clone" it, in spite of the rare jfets.

sorry, didn't mean to hijack the thread ...

Quote:
Originally Posted by Damon Hill View Post
...
(Boggling over the schematic; my Hafler SE-100 preamp is all-JFET and much simpler in parts count and design.)

Last edited by mlloyd1; 16th November 2009 at 02:08 AM. Reason: spelling error
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Old 16th November 2009, 02:30 AM   #9
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mlloyd: hate to disappoint you, but I so rarely listened to my record collection that I finally sold my turntable and vinyl to another audiophile. I couldn't fault the sound quality, just that getting the arm to track well and the general fiddlyness of vinyl wasn't my cuppa. (after listening to some of those records on his very high-end system, I may come to regret that decision)

My Hafler is pretty well hacked with a Jung superregulator supply and Black Gates, and soon some of those bulk metal foil resistors, too. The phono board is now surplus and I may put it up on the marketplace. Otherwise I'm very happy with it, to the point of thinking about acquiring another one so I can do a proper A/B comparison of the mods.
I bought it precisely because of the JFET design and never once regretted that.
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Old 16th November 2009, 02:41 AM   #10
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Quote:
Originally Posted by mlloyd1 View Post
damon:

just curious, how do you like your hafler phono stage? i always thought the riaa preamp in the se100 and 915 preamps was pretty neat and wondered why more people didn't try to "clone" it, in spite of the rare jfets.

sorry, didn't mean to hijack the thread ...

Erno is doing a good job on his kits, although I also admit it is a bit expensive. If you want to clone his design, it is possible because he shows all his design, circuit explanation etc. on his website. Yet, if you would consider the followings: -

1. His original design
2. Expensive parts - 0.1% Dale, Copal trimpots, PS caps, Elna caps etc.
3. JFETs are difficult to find - yes, you can find a lot of fake J74, perhaps 10 times in the market are fake.
4. Erno is living in Germany - do you know how much is the cost of a burger there?
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