diyAudio

diyAudio (https://www.diyaudio.com/forums/index.php)
-   Pass Labs (https://www.diyaudio.com/forums/pass-labs/)
-   -   VFET amp Bourns trimmer exchange (https://www.diyaudio.com/forums/pass-labs/373208-vfet-amp-bourns-trimmer-exchange.html)

MEPER 5th June 2021 04:05 PM

VFET amp Bourns trimmer exchange
 
2 Attachment(s)
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? :-)

Zen Mod 5th June 2021 04:12 PM

well, you can proudly say that your OCD outgrown eve mine OCD :rofl:

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

:devily:

MEPER 5th June 2021 04:50 PM

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).

Soundhappy 5th June 2021 05:29 PM

Quote:

Originally Posted by MEPER (https://www.diyaudio.com/forums/pass-labs/373208-vfet-amp-bourns-trimmer-exchange-post6681128.html#post6681128)
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 ?

MEPER 5th June 2021 05:41 PM

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?

Zen Mod 5th June 2021 05:47 PM

no

MEPER 5th June 2021 05:58 PM

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.

TungstenAudio 5th June 2021 06:09 PM

A worthy sidebar discussion for those of us with OCD for these things.

:up:

chromenuts 5th June 2021 06:43 PM

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!

tombo56 5th June 2021 06:55 PM

Don’t we call our OCD “attention to detail” or “strive for perfection”?


All times are GMT. The time now is 05:47 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 17.65%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio

Wiki