Modifying Amp Highpass (resistors) - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-07-07, 09:51 AM Thread Starter
Senior Shackster
tom

Join Date: Jan 2007
Location: Ohio
Posts: 85
Modifying Amp Highpass (resistors)

I have been looking into modifying a highpass on a sub plate amp by changing the resistors.

I recently contacted the manufacturer of my amp to get the correct resistor values since they weren't listed on the chart. However I cannot find resistors to match the values I was given.

I was told: "In order to reach 15Hz highpass you can try R17 = 26k1 and R18= 90k9"

I think it is weird he used the word "try", like these may not be the correct values. Anyway, I cannot find any 26100 Ohm or 90900 Ohm resistors. Are resistors meant to be combined to achieve the correct values? For example, will 3 30k resistors equal 1 90k resistor?

If not, can someone tell me where to find 26k1 and 90k9 resistors? Thanks
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Old 02-07-07, 12:39 PM
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brucek

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Re: Modifying Amp Highpass (resistors)

Quote:
Anyway, I cannot find any 26100 Ohm or 90900 Ohm resistors. Are resistors meant to be combined to achieve the correct values?
Those value are exact 1% resistor values. Resistors come in 1%, 5% and 10% variety.
For 26100ohms and 90900 ohms the closest values for the three types and the errors involved are:
1%(26100 @0% error), 5%(27000 @3.4% error), 10%(27000 @3.4% error)
1%(90900 @0% error), 5%(91000 @.11% error), 10%(100000 @10% error).

Quote:
For example, will 3 30k resistors equal 1 90k resistor?
Yes.

brucek
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Old 02-07-07, 01:13 PM Thread Starter
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tom

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Re: Modifying Amp Highpass (resistors)

I don't see any 1% resistors on Radio Shacks or PE's sites. Does anyone know where to get 1% resistors? Or should I just use 5%?

I would like to be as precise as possible, while not spending an arm and leg to ship these little things.
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Old 02-07-07, 01:32 PM
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brucek

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Re: Modifying Amp Highpass (resistors)

Quote:
Or should I just use 5%?
Just use 5%. They're readily available.
Use standard [5% 91K] and [5% 24K in series with (2.2K or 2.0K)]

bruck
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Old 02-07-07, 01:58 PM Thread Starter
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tom

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Re: Modifying Amp Highpass (resistors)

Quote:
brucek wrote: View Post
Just use 5%. They're readily available.
Use standard [5% 91K] and [5% 24K in series with (2.2K or 2.0K)]

bruck
Boy am I glad you said in series, because I didn't even think about that. How would you reccomend I attach the EDIT:resistors to each other?

Last edited by letzleta; 02-07-07 at 02:49 PM. Reason: Mistyped
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Old 02-07-07, 02:06 PM
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brucek

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Re: Modifying Amp Highpass (resistors)

capacitors?
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Old 02-07-07, 02:48 PM Thread Starter
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tom

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Re: Modifying Amp Highpass (resistors)

Sorry, I mistyped... Meant resistors.
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Old 02-07-07, 03:07 PM
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brucek

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Re: Modifying Amp Highpass (resistors)

Quote:
How would you reccomend I attach the EDIT:resistors to each other?
Ahhh, OK.
Well, if the single resistor is on a printed circuit board, remove it and just solder one end of each new series resistor into the spot where the single resistor was located and solder the tails together by bringing them together in a teepee shape...

brucek
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Old 02-07-07, 03:49 PM Thread Starter
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tom

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Re: Modifying Amp Highpass (resistors)

Sounds good.

Thanks for all your help Bruce.
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Old 02-09-07, 08:54 AM Thread Starter
Senior Shackster
tom

Join Date: Jan 2007
Location: Ohio
Posts: 85
Re: Modifying Amp Highpass (resistors)

Does using 2 resistors in series cause any issues?

If I am correct in assuming 5% tolerance means a 100k resistor is within 5% of 100k (95k-105k), then 2 5% resistors in series would create a 10% tolerance series, right?

The reason I ask is I cannot find 91k resistors or 24k, the closest I have found is 2x47k=94k and 22k+4.7k=26.7k. I found 1/2 watt 22k+3.9k=25.9k and 47k.

So, my options right now are:
1/4 watt 5%:
2x47k=94k and 22k+4.7k=26.7k
or
1/2 watt 5%:
2x47k=94k22k and 22k+3.9k=25.9k

What would you do Bruce?
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