How to replace trimmer pot with fixed resistor? - diyAudio
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Old 7th August 2008, 08:47 AM   #1
kptseng is offline kptseng  Singapore
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Default How to replace trimmer pot with fixed resistor?

I intend to replace the 2 trimmer pots in my amp with fixed resistors.

I looked at the datasheet of the trimmer pot and the 3 legs are labeled 1, 2 and 3.

Question is do I connect 1 and 2 with the fixed resistor and leave 3 unconnected?

Many thanks in advance
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Old 7th August 2008, 09:15 AM   #2
burbeck is offline burbeck  United Kingdom
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hi,
are all three pins 1,2 and3 used in the circuit?
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Old 7th August 2008, 09:25 AM   #3
kptseng is offline kptseng  Singapore
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What I can see is that pin 3 is connected to the ground. Can I leave the ground unconnected then?

The trimmer pots are for setting the bias after the emitter resistors.
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Old 7th August 2008, 09:29 AM   #4
AndrewT is offline AndrewT  Scotland
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the output bias pot is unlikely to be connected to ground.
Look again, or post a close up pic of both sides of the PCB.
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Old 7th August 2008, 09:58 AM   #5
burbeck is offline burbeck  United Kingdom
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hi
it is important that you are sure that all three pins are connected because it is possible to damage the amp if you get this wrong.
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Old 7th August 2008, 08:54 PM   #6
jaycee is offline jaycee  United Kingdom
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Why use fixed resistors at all?
If you're going to replace with anything, replace them with good quality trimmers instead of the cheap rubbish thats normally used
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Old 8th August 2008, 06:46 AM   #7
kptseng is offline kptseng  Singapore
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Quote:
Originally posted by jaycee
Why use fixed resistors at all?
If you're going to replace with anything, replace them with good quality trimmers instead of the cheap rubbish thats normally used
But isn't a good fixed resistor anytime better than a good trimmer? Say on the same price level.

The trimmers value is to provide option to vary the resistance conveniently but if the "optimal" reistance value can be established maybe a fixed resistor would be better?

Well these are just my thoughts, as you can see I know very little about electronics and I could be very wrong.
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Old 8th August 2008, 07:31 AM   #8
AndrewT is offline AndrewT  Scotland
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but you must find out what the trimmer is doing before you can change it to one or two fixed resistors.
Investigate and report back.
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Old 8th August 2008, 04:10 PM   #9
kptseng is offline kptseng  Singapore
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Hi Andrew,

Looked at the bottom of the board and realised that 1 (A) and 2 (S) are actually connected to the same point (nothing in between).

Hence I suppose it is ok to use a fixed resistor and connect the either 1 (A) or 2 (S) to 3 (E).

Thanks.
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Old 8th August 2008, 04:29 PM   #10
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Default come down to earth .....

there is not possible to replace the bias trimmer of the amplifier to fixed resistors .....if you decide to do so this a hard thing to do it will require acurate resistors with minimum tolerance and also a very sofisticated procedure to do that ......

you need to warm the amp set the idle in the desired level and then after all is ok remove the trimer measure it and then replace it with a resistor or a network of resistors ......depending on the application

totally not needed .....

if you want to make things better do your shelf a favour and buy a 10 turn trimmer of BB trimmer replace the old one ,set the idle very carefully ( i trully have second thoughts about if you know how to do that ) and then considering this issue your amp will be extremelly happy

don sakoulis
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