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?
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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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).
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).
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 ?
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?
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?
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?
for 10.8 parallel 15:39
for 12.5 parallel 15:75
That is also a way to do it. I could probably find values I already have and parallel them to get close to the values.
So some builders have already installed fixed resistors.....
It will probably not work if I calculated other values but with the same ratio between the two resistors as this would require more knowledge of the impedance around the trimmer.
So some builders have already installed fixed resistors.....
It will probably not work if I calculated other values but with the same ratio between the two resistors as this would require more knowledge of the impedance around the trimmer.
If it is not the trimmer I think I will just "live" with amp "as is".....maybe exchange the zeners. But of course a new trimmer could also have troubles so fixed resistors would make the final conclusion if it was trimmer or not.
But just to try fixed resistors before new trimmer then I could just use 10k and 12k1 I already have? ....and if it was the same issue.....I could even put in the old trimmer again
But just to try fixed resistors before new trimmer then I could just use 10k and 12k1 I already have? ....and if it was the same issue.....I could even put in the old trimmer again
I got new 25k trimmers today (10 pcs).
They measured from 22k9 to 24k2.
I selected a 23k3 trimmer like the one I pulled out and installed the new trimmer.
Until now I have same constant very low noise level in both tweeters. So until now it behaves as I hoped. Amp can also play nice music.
I will check over several days if it still "behaves".....or I should just relax now and enjoy some music.....
If anyone would like to try the old 25k trimmer I will be happy to ship it.....to someone.....it looks very nice with thin straight trimmed legs.....
They measured from 22k9 to 24k2.
I selected a 23k3 trimmer like the one I pulled out and installed the new trimmer.
Until now I have same constant very low noise level in both tweeters. So until now it behaves as I hoped. Amp can also play nice music.
I will check over several days if it still "behaves".....or I should just relax now and enjoy some music.....
If anyone would like to try the old 25k trimmer I will be happy to ship it.....to someone.....it looks very nice with thin straight trimmed legs.....
