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VFET amp Bourns trimmer exchange
VFET amp Bourns trimmer exchange
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Old 5th June 2021, 04:05 PM   #1
MEPER is offline MEPER  Denmark
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Default VFET amp Bourns trimmer exchange

I have started the small academic exercise to verify if the 25k Bourns trimmer is the root cause of a very small amount of on/off noise in R-channel. It is academic because it is only audible with ear very close to tweeter. But L-channel is almost 100% "dead" and could be nice to achieve this also for R-channel. While new 25k trimmers are on the way I did the removal of the old and also I measured a value for a R1 and R2 resistor if I should want to try this out and use fixed resistors insted.

The removal went very smooth. I used a smd hot air gun I got long time ago. A hobby version (Velleman brand). But it worked perfect. I adjusted the temperature to 390 C and set airflow to medium. After 10 sec. or so heat up I could pull out the trimmer.

I measured 3 resistor values (R1: 10k80, R2: 12k52 and R3: 23k30 (check value). I miss 20 ohm somewhere.....

I guess if I had a 12k5 and a 10k8 resistor I was good to go but I don't have these values. But it looks very close to some standard values.

I suspect the trimmer is the problem as it creates noise by just the slightest touch of the trimmer screw. But time will show......

23k3 is quite far away from 25k but within the 10% tolerance. So maybe you guys out there has a 23k in one channel and 27k in other channel? :-)
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Old 5th June 2021, 04:12 PM   #2
Zen Mod is offline Zen Mod  Serbia
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VFET amp Bourns trimmer exchange
well, you can proudly say that your OCD outgrown eve mine OCD

though, there are other things at my side,so you're reaching just 100 mZM with this

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Old 5th June 2021, 04:50 PM   #3
MEPER is offline MEPER  Denmark
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OCD = Obsessive-Compulsive Disorder?
I think this is "spot-on" :-)
But I don't feel alone with this in this forum :-)

My mono block ACA's are in service now and they can certainly still deliver nice sound!
I had them out to a friend last week driving Snell C speakers.....and that was a bit of a surprise what they could do (4 ohm speakers as far as I know).
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Old 5th June 2021, 05:29 PM   #4
Soundhappy is offline Soundhappy  France
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Quote:
Originally Posted by MEPER View Post
I have started the small academic exercise to verify if the 25k Bourns trimmer is the root cause of a very small amount of on/off noise in R-channel....23k3 is quite far away from 25k but within the 10% tolerance.
So maybe you guys out there has a 23k in one channel and 27k in other channel? :-)
So how much Ohm's difference in another channel ?
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Old 5th June 2021, 05:41 PM   #5
MEPER is offline MEPER  Denmark
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Trimmer is in place in other channel. It seems to work perfect so I plan to just insert another trimmer in R-channel.

If C3 was not there......then I could probably measure trimmer "in-circuit"?

But maybe not knowing if there could be 2k difference in trimmer values......could cause bad sleep for many nights?
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Old 5th June 2021, 05:47 PM   #6
Zen Mod is offline Zen Mod  Serbia
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VFET amp Bourns trimmer exchange
no
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Old 5th June 2021, 05:58 PM   #7
MEPER is offline MEPER  Denmark
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Ok, but while VFET is out of service for a while until new trimmers arrive the ACAs has just played:

Brad Mehldau: Mon Chien Stupide
Brad Mehldau was a band I discovered by accident but I like their music and recordings very good.....and ACA did it very well.
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Old 5th June 2021, 06:09 PM   #8
TungstenAudio is offline TungstenAudio  United States
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A worthy sidebar discussion for those of us with OCD for these things.

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Old 5th June 2021, 06:43 PM   #9
chromenuts is offline chromenuts  United States
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VFET amp Bourns trimmer exchange
Maybe we need a thread about OCD...I know that it prevents me from accomplishing a lot more of what I’d like to.

Good luck with your trimmer issues!
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Old 5th June 2021, 06:55 PM   #10
tombo56 is offline tombo56  Croatia
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VFET amp Bourns trimmer exchange
Don’t we call our OCD “attention to detail” or “strive for perfection”?
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