Attenuator for Rod Elliott's Bi-amped projects

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ialpha

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Joined 2009
#1
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 🙂
 
#2
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.

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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

col.
 
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#3
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:
http://www.diyaudio.com/forums/anal...i2c-relay-selector-attenuator-tube-stage.html

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
 
#4
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.
 
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#11
maxw said:
I don't think many people used PWM as its thought that the PWM frequency will affect the audio signal!
Click to expand...

As there no electronic coupling between the Led side and the Resistor side of things. If one was to suitable smooth the PWM on the led so that all the Led see is an increase or decrease in voltage and non of the PWM signal. I suspect there would be virtually no interference.
 
#15
ialpha,
I built a PG2310 volume control that was featured in Silicon Chip a few years ago that I use with my active 3 way speakers. Since you are in Melbourne, I'd be happy for you to have a look and a listen. It is on at the moment, but since it is daylight, that is a given. 🙂

Frank
 
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