Attenuator for Rod Elliott's Bi-amped projects - diyAudio
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Old 2nd October 2010, 06:40 AM   #1
ialpha is offline ialpha  Australia
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Default Attenuator for Rod Elliott's Bi-amped projects

I am looking at building a bi-amped system using

2x 20w class A amp for tweeters 20 Watt Class-A Amplifier
2x 60w power Amp (project 3a) for mid/lows 60-80W Power Amplifier.
1x 24 dB/Octave 2/3-Way Linkwitz-Riley Electronic Crossover Linkwitz-Riley Electronic Crossover

I am bit overwhelmed with choice of pre amps on the net and trying to work out what the best match would be for this.

I have decided to stay away from the traditional potentiometer type attenuator so i'm thinking of trying one of the following, has anyone ever built any of them before? I have never heard any of these attenuators and have no idea how good they sound. Would any of these be a good match for this arrangement ?

Audio Volume Relay Attenuator with IR Control

Audio Volume Relay Attenuator with IR Control

The light speed Attenuator

DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)

PGA 2310

I also would love to build a preamp based on Mark Hennessy design Hi-Fi Preamp but maybe this is little ambitious for a first time builder.

Any advice and suggestions would be greatly appreciated.

thanks
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Old 2nd October 2010, 08:17 AM   #2
col is offline col  Australia
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I use a modified version of Rod's P88 preamp with an extra output. My mains and subs are sealed so I use a p09b to cross between tweeter, mid then just overlap the bottom end of the mains with the top end of the subs using a P48A EAS bass controller. Sounds awesome.

Click the image to open in full size.

For a good quality pot search these forums for the "jaycar pot".

Another good aussie kit maker is SKA audio. They have something similar to the lightspeed:

http://www.ska-audio.com/diy/optivol.html

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Last edited by col; 2nd October 2010 at 08:19 AM.
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Old 2nd October 2010, 09:26 PM   #3
maxw is offline maxw  United Kingdom
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The Lightspeed is very popular but lacks digital control because it is only controlled via a pot. Don't know if that's important to you.

The "Audio Volume Relay Attenuator" you link to is a popular design, also the same as the Twisted Pair Joshua Tree (also very popular):
Joshua Tree - A Twisted Log Attenuator
I also used this design and made my own PCBs to use with an Arduino for control, you can see here:
My Preamp Project: Arduino, I2C, relay selector+attenuator, tube stage

The PGA2310 is another popular choice, has very low distortion. I haven't seen many popular projects using this chip though. Twisted Pear made one but no longer offer it. You can get cheap kits on eBay though. I think I will design a PGA2310 PCB to compare to my relay attenuator and see what I prefer.

This site has some kits too:
Dantimax - Remote control audio kits
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Old 3rd October 2010, 08:40 AM   #4
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With the light speed you could have remote control by using a microprocessor use pwm you have to design in carefully as to not inject any noise into the system. Its the cost of matched Ldr that puts me off the light speed but iam a cheap skate.

Last edited by Mankysteve; 3rd October 2010 at 08:55 AM.
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Old 3rd October 2010, 08:55 AM   #5
maxw is offline maxw  United Kingdom
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Quote:
Originally Posted by Mankysteve View Post
With the light speed you could have remove control by using a microprocessor instead of the 555 and use pwm. Its the cost of matched Ldr that puts me off the light speed but iam a cheap skate.
I don't think many people used PWM as its thought that the PWM frequency will affect the audio signal!
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Old 3rd October 2010, 09:25 AM   #6
ialpha is offline ialpha  Australia
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Quote:
Originally Posted by maxw View Post
The Lightspeed is very popular but lacks digital control because it is only controlled via a pot. Don't know if that's important to you.

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Just a thought but how well would the lightspeed work with a motorised pot and remote control kit. That shouldnt affect the sound quality should it??
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Old 3rd October 2010, 11:15 AM   #7
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I did see a design some where that used a 555 timer but cant find it at the moh.
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Old 3rd October 2010, 11:32 AM   #8
AndrewT is online now AndrewT  Scotland
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try search 555.
I found this one for you,
I think I have a neat, simple and easily implemented idea for a soft start circuit
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Old 3rd October 2010, 11:37 AM   #9
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Yeah that not a attenuator. that a soft start circuit.
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Old 3rd October 2010, 11:39 AM   #10
AndrewT is online now AndrewT  Scotland
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555 is a timer chip.
There are many schematics in that referenced thread of 555 chips used as timers.

If you don't like any of those then search further for other 555 posts.
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