OK to use 200R pot on preamp output?

leadbelly · 4th February 2006, 04:45 PM

I already have a 200R quad pot I would like to make use of in a preamp I am building since quad pots are not trivial to source. The op amp driving aginst the pot is an OPA1632. I don't see a problem, as the OPA should be able to drive this load and the amp should work fine with a lower-Z input. Is this acceptable? I do have room to increase the gain on the OPA, and I was considering doing that and maybe putting 400R in series with the pot to bring it up to a nominal 600R. Is that worth the effort?

anatech · 4th February 2006, 06:24 PM

Hi leadbelly,
I was waiting for someone to give you a reply. I don't believe this is a good idea for the simple reason that you are making life hard for the op amp. Just because they can handle, say, a 600 ohm load does not mean you should. Distortion almost always increases with decreasing load impedance. You are increasing the dynamic impedance seen by the amplifier.

You would be further ahead to use your quad 200 ohm control for something else.

-Chris

leadbelly · 4th February 2006, 07:28 PM

Thanks Chris. I think I'll concentrate on rigging up multiple pots to do the job. A lot of effort but you get a payback of better signal separation too.

anatech · 4th February 2006, 07:49 PM

Hi leadbelly,
Four channel preamp? Just wondering.

4 gang pots are not cheap and easy, you lucked into it?

-Chris

leadbelly · 4th February 2006, 08:11 PM

Quote:

Originally posted by anatech
Hi leadbelly,
Four channel preamp? Just wondering.

4 gang pots are not cheap and easy, you lucked into it?

-Chris

I need it for a balanced phono stage: Would this work (simple OPA1632 phono preamp)?
I can make do with a dual gang but prefer not to compromise. I'm handy enough to cobble up something that should track well, at least I hope I am

A couple of quad gang pots came my way in a mess of goodies that a gentleman moving out of the country gave me. All low grade electronics, lots of stuff from India, but occasionally I find something useful in there.

anatech · 4th February 2006, 08:32 PM

Hi leadbelly,
I understand now. You may want to go with a DAC or relay switched resistor network (the balanced lightstar preamp does it that way).

Good luck with your project!

-Chris

4th February 2006, 04:45 PM	#1
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	OK to use 200R pot on preamp output? I already have a 200R quad pot I would like to make use of in a preamp I am building since quad pots are not trivial to source. The op amp driving aginst the pot is an OPA1632. I don't see a problem, as the OPA should be able to drive this load and the amp should work fine with a lower-Z input. Is this acceptable? I do have room to increase the gain on the OPA, and I was considering doing that and maybe putting 400R in series with the pot to bring it up to a nominal 600R. Is that worth the effort? __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

4th February 2006, 07:28 PM	#3
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Thanks Chris. I think I'll concentrate on rigging up multiple pots to do the job. A lot of effort but you get a payback of better signal separation too. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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4th February 2006, 06:24 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi leadbelly, I was waiting for someone to give you a reply. I don't believe this is a good idea for the simple reason that you are making life hard for the op amp. Just because they can handle, say, a 600 ohm load does not mean you should. Distortion almost always increases with decreasing load impedance. You are increasing the dynamic impedance seen by the amplifier. You would be further ahead to use your quad 200 ohm control for something else. -Chris

4th February 2006, 07:49 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi leadbelly, Four channel preamp? Just wondering. 4 gang pots are not cheap and easy, you lucked into it? -Chris

4th February 2006, 08:32 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi leadbelly, I understand now. You may want to go with a DAC or relay switched resistor network (the balanced lightstar preamp does it that way). Good luck with your project! -Chris

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