Inline Attenuator Help

Haoleb · 8th February 2006, 06:48 PM

Im looking to make some inline attenuators like the Rothwell's But i am unsure of what resistor values to use. I have some electronics experience but not so in depth to design this myself.

I am planning on using it between my preamp and poweramp because as it stands i have too much gain to use the two together. The Preamp is a Audire Diffet 2, im not sure of the output impedance of this unit but perhaps someone else knows?

The poweramp is a NAD C370 and im using it directly into the poweramp input (therefore bypassing preamp) the input impedance listed on NAD's site is 20k.

Im not sure how much attenuation i need but i think starting off with a -10db like the rothwell's would be a good place to start. If anyone would be willing to help me with this that would be great because id really rather build my own parts than spend the 60 bucks to buy the rothwell's I think it would also be good for others because i wasnt able to find much searching. I was only able to find one thread and i tried the schematic included but they didnt work well.

AndrewT · 9th February 2006, 06:54 PM

Hi,
fit the two resistors inside the RCA plug that goes onto the NAD poweramp input. No cable to help avoid the hf rolloff that would ensue due to capacitance between attenuator and input stage.

use a 10k in line and then choose a grounding resistor from the list.
Interconnect core to 10k to RCA centre pin.
and
RCA centre pin to grounding resistor to ground.

grounding resistor
4k7 => -9.9db these low atten give more risk of HF roll off
3k9=>-11db
3k0=> -12.7db
2k0=>-15.6db
1k5=>-17.7db
1k0=>-20.8db
750r=>-23db at this atten HF roll off almost zero @ 20kHz.

should be enough options to get you going.

BTW attenuation = 20 times [inv log (grnd res/10k+grnd res)]
This formula is not accurate because it does not account for the source impedance nor the poweramp input impedance but again it is close enough.

Haoleb · 9th February 2006, 11:38 PM

Thanks for the response. I think i will try a couple different combinations first before i built the set to see which matches my needs the best.

rabbitz · 10th February 2006, 12:07 PM

Did some a while back and gave 6dB reduction using the same value resistor for hot and ground.

http://www.diyaudio.com/forums/showt...614#post547614

dimdom · 21st June 2011, 03:03 PM

attenuation = 20 times [ log (grnd res/10k+grnd res)]

carz · 9th August 2011, 08:50 AM

what are best types of cost-no-object resistors to use ? Brand and type?

8th February 2006, 06:48 PM	#1
Haoleb diyAudio Member Join Date: May 2004 Location: Hawaii	Inline Attenuator Help Im looking to make some inline attenuators like the Rothwell's But i am unsure of what resistor values to use. I have some electronics experience but not so in depth to design this myself. I am planning on using it between my preamp and poweramp because as it stands i have too much gain to use the two together. The Preamp is a Audire Diffet 2, im not sure of the output impedance of this unit but perhaps someone else knows? The poweramp is a NAD C370 and im using it directly into the poweramp input (therefore bypassing preamp) the input impedance listed on NAD's site is 20k. Im not sure how much attenuation i need but i think starting off with a -10db like the rothwell's would be a good place to start. If anyone would be willing to help me with this that would be great because id really rather build my own parts than spend the 60 bucks to buy the rothwell's I think it would also be good for others because i wasnt able to find much searching. I was only able to find one thread and i tried the schematic included but they didnt work well.

9th February 2006, 06:54 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, fit the two resistors inside the RCA plug that goes onto the NAD poweramp input. No cable to help avoid the hf rolloff that would ensue due to capacitance between attenuator and input stage. use a 10k in line and then choose a grounding resistor from the list. Interconnect core to 10k to RCA centre pin. and RCA centre pin to grounding resistor to ground. grounding resistor 4k7 => -9.9db these low atten give more risk of HF roll off 3k9=>-11db 3k0=> -12.7db 2k0=>-15.6db 1k5=>-17.7db 1k0=>-20.8db 750r=>-23db at this atten HF roll off almost zero @ 20kHz. should be enough options to get you going. BTW attenuation = 20 times [inv log (grnd res/10k+grnd res)] This formula is not accurate because it does not account for the source impedance nor the poweramp input impedance but again it is close enough. __________________ regards Andrew T.

10th February 2006, 12:07 PM	#4
rabbitz diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	Did some a while back and gave 6dB reduction using the same value resistor for hot and ground. http://www.diyaudio.com/forums/showt...614#post547614 __________________ No longer DIY active

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9th February 2006, 11:38 PM	#3
Haoleb diyAudio Member Join Date: May 2004 Location: Hawaii	Thanks for the response. I think i will try a couple different combinations first before i built the set to see which matches my needs the best.

21st June 2011, 03:03 PM	#5
dimdom diyAudio Member Join Date: Jun 2011	attenuation = 20 times [ log (grnd res/10k+grnd res)]

9th August 2011, 08:50 AM	#6
carz diyAudio Member Join Date: Dec 2009	what are best types of cost-no-object resistors to use ? Brand and type?

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