Lightspeed Attenuator a new passive preamp - Page 43

Panelhead · 21st February 2007, 02:42 AM

Looking at it, looks like it should work fine. Guess I spent all those hours digging through surplus bins for dual linear 100K pots for nothing. Single pots are much easier to source.
Everyone but me seems to have used log pots. I find the taper works fine with linear. The reason is because the shunt and series move in opposite directions, so the result is a second order function. If a fixed shunt and variable series element was used the taper would require a log pot.
Just picked up new pots today, passed up a BUNCH of high quality cheap single pots. Guess it is back to surplus soon.

George

georgehifi · 21st February 2007, 03:29 AM

This looks good, though I think you would have to use a 200k log pot as the entry of the 5vdc is now at the centre of the rseistance track.
Keep it up guys this is good thinking.
As for using a linear in my setup it comes on too quick, a log is just right, but with this single setup who knows you'll just have to suck it and see.
BTW. I think the sound will not change at all, but the feel of the volume control's advance will, and also it would make it a dollar or two cheaper to build.

Cheers George

Blues · 21st February 2007, 04:51 AM

Thanks, George (Panelhead).

George(hifi), attached is a schematic of the LSA...let me know if I missed something...Thanks for sharing!

Blues · 21st February 2007, 05:00 AM

Here's the one with a Single Pot...

georgehifi · 21st February 2007, 05:07 AM

Quote:

Originally posted by Blues
Here's the one with a Single Pot...

The only thing is you have your 5vdc coming in on the wiper and one end of the resistance track on each section, where I only had it coming in on one end of the resistance track of each section and not the wiper as well. and you'll only need the 1k trimmer on the channel with the highest gain.

Cheers George (Nice drawing BTW).

ackcheng · 21st February 2007, 07:39 AM

would this schematic work for balanced input?

ackcheng · 21st February 2007, 07:43 AM

Quote:

The only thing is you have your 5vdc coming in on the wiper and one end of the resistance track on each section, where I only had it coming in on one end of the resistance track of each section and not the wiper as well.

Dear George,

Can I ask what is the advantage with this arrangement "I only had it coming in on one end of the resistance track of each section and not the wiper as well"?

georgehifi · 21st February 2007, 07:55 AM

You posted a different zipped one 3 posts back, I think you made a booboo.
And this last one I think you may have to use a 200klog pot

Cheers George

georgehifi · 21st February 2007, 08:01 AM

This single pot balanced version should work nicely, again with a 200klog pot, wish you all the luck on the matching of the LDR's double the work.

Cheers George

georgehifi · 21st February 2007, 09:05 AM

Disregard my thinking about the 200k pot for the single version, my head wouldn't think straight about it, I think now as you it should be 100k as well.

Cheers George

21st February 2007, 02:42 AM	#421
Panelhead diyAudio Member Join Date: Dec 2002 Location: Houston	Single pot Looking at it, looks like it should work fine. Guess I spent all those hours digging through surplus bins for dual linear 100K pots for nothing. Single pots are much easier to source. Everyone but me seems to have used log pots. I find the taper works fine with linear. The reason is because the shunt and series move in opposite directions, so the result is a second order function. If a fixed shunt and variable series element was used the taper would require a log pot. Just picked up new pots today, passed up a BUNCH of high quality cheap single pots. Guess it is back to surplus soon. George __________________ Cheapest is bestest

21st February 2007, 03:29 AM	#422
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	This looks good, though I think you would have to use a 200k log pot as the entry of the 5vdc is now at the centre of the rseistance track. Keep it up guys this is good thinking. As for using a linear in my setup it comes on too quick, a log is just right, but with this single setup who knows you'll just have to suck it and see. BTW. I think the sound will not change at all, but the feel of the volume control's advance will, and also it would make it a dollar or two cheaper to build. Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com

21st February 2007, 07:55 AM	#428
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	You posted a different zipped one 3 posts back, I think you made a booboo. And this last one I think you may have to use a 200klog pot Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com

21st February 2007, 08:01 AM	#429
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	This single pot balanced version should work nicely, again with a 200klog pot, wish you all the luck on the matching of the LDR's double the work. Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com

21st February 2007, 09:05 AM	#430
georgehifi diyAudio Member Join Date: Sep 2003 Location: Manly Australia (Jewel of the Pacific)	Disregard my thinking about the 200k pot for the single version, my head wouldn't think straight about it, I think now as you it should be 100k as well. Cheers George __________________ Avatar : Production Lightspeed Attenuator www.lightspeedattenuator.com


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