Constant impedance relay-resistor logarithmic attenuator - Page 8

Alain Dupont · 27th April 2005, 01:28 PM

guido,

One solution is to put 1 more relay used as a "Mute relay"
it makes a short cut at the output during the volume adjust, and opens a few millisecond after the volume change...

Regards.

Alain.

Kermit · 27th April 2005, 08:36 PM

If you can spare some gain you can also put a fixed L-pad after the last relay. I have a 2dB L-pad in my setup and can hardly notice any clikcs.

Henry Pootel · 2nd May 2005, 05:27 AM

Help... I got confused along the way!

If I was using x-pro's circuit between a pre-amp and amplifier, do I put a 10K resistor in parallel with the amplifier input? Or, if I had an amplifier with a 10k input impedance, do I simply connect the last attenuation stage of the circuit to the amplifier (and not have the 10k resistor)?

In other words: if I have a 10k input impedance amplifier, is that the 10k load on the right hand side of x-pro's diagram?

Thanks!

x-pro · 2nd May 2005, 08:02 AM

Quote:

Originally posted by Henry Pootel
In other words: if I have a 10k input impedance amplifier, is that the 10k load on the right hand side of x-pro's diagram?

Yes, and if the input impedance is more than 10K you'll need an additional resistor - i.e. if the amp input impedance is 20K than you need another 20K in parallel to the input to get 10K load.

Cheers

x-pro

Analoghorn · 27th June 2005, 11:03 AM

Hi,

Been lurking for a long time here...

Fist, a great thank you to X-pro for posting this attenuator topology.

I have used another topology for years, but it has never worked that well. This weekend I tried this one, and it works great.

I changed it to 1,25dB/step and 50kOhms, and produced a spreadsheet to calculate the values, based on the L-pad formulas in Dickasons Loudspeaker Cookbook.

Re the clicks, I use dual coil latching relays (one coil for 'on' and one for 'off') and delay the 'on' pulse. The relays need to open before the others close. This works pretty well. If you use a µC-based control, first switch the relays that are turning off, then the ones that are turning on. Then it will work without dual coil relays.

I attach the spread sheetI did for this, it allows you to choose the step attenuation, attenuator impedance and number of bits. You can also try standard values and see how they work out in practice.

Regards,

Bjørn

Analoghorn · 27th June 2005, 12:12 PM

Seems I can't attach anything yet, so I've uploaded the spread sheet to http://www.geocities.com/la1zka/diverse/Attenuator.zip

Bjørn

27th April 2005, 08:36 PM	#72
Kermit diyAudio Member Join Date: Jun 2002 Location: Oslo - Norway	If you can spare some gain you can also put a fixed L-pad after the last relay. I have a 2dB L-pad in my setup and can hardly notice any clikcs. __________________ Sven Sødem

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27th April 2005, 01:28 PM	#71
Alain Dupont diyAudio Member Join Date: Sep 2003 Location: Paris - France	guido, One solution is to put 1 more relay used as a "Mute relay" it makes a short cut at the output during the volume adjust, and opens a few millisecond after the volume change... Regards. Alain.

2nd May 2005, 05:27 AM	#73
Henry Pootel diyAudio Member Join Date: Nov 2003 Location: Sacramento, CA	Help... I got confused along the way! If I was using x-pro's circuit between a pre-amp and amplifier, do I put a 10K resistor in parallel with the amplifier input? Or, if I had an amplifier with a 10k input impedance, do I simply connect the last attenuation stage of the circuit to the amplifier (and not have the 10k resistor)? In other words: if I have a 10k input impedance amplifier, is that the 10k load on the right hand side of x-pro's diagram? Thanks!

27th June 2005, 11:03 AM	#75
Analoghorn Account disabled at member's request Join Date: Jan 2005	Hi, Been lurking for a long time here... Fist, a great thank you to X-pro for posting this attenuator topology. I have used another topology for years, but it has never worked that well. This weekend I tried this one, and it works great. I changed it to 1,25dB/step and 50kOhms, and produced a spreadsheet to calculate the values, based on the L-pad formulas in Dickasons Loudspeaker Cookbook. Re the clicks, I use dual coil latching relays (one coil for 'on' and one for 'off') and delay the 'on' pulse. The relays need to open before the others close. This works pretty well. If you use a µC-based control, first switch the relays that are turning off, then the ones that are turning on. Then it will work without dual coil relays. I attach the spread sheetI did for this, it allows you to choose the step attenuation, attenuator impedance and number of bits. You can also try standard values and see how they work out in practice. Regards, Bjørn

27th June 2005, 12:12 PM	#76
Analoghorn Account disabled at member's request Join Date: Jan 2005	Seems I can't attach anything yet, so I've uploaded the spread sheet to http://www.geocities.com/la1zka/diverse/Attenuator.zip Bjørn

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