Oscillation issue DQ LP1's "upgraded" op amps

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Posted by jk (A) on June 17, 2016 at 07:50:58

I sure hope you can help me here. I am running into oscillation issues with my Dahlquist DQ LP1 low pass crossover. Apparently the OPA2601 op amps I recently put in are not compensated. Unfortunately I love the way these op amps sound so I'd like to fix the problem.

There are 5 of these op amps in the unit. I've read about using small capacitors to aleviate this issue, but I need to check with experts to ensure I get it right. The articles say one should put the capactitor on each of the +15 volt and -15volt power rails to ground.

1) wanted to check my interpritation (it's not one cap between these 2 pins right? Gosh that would be easier)

2) I have a large supply of capacitors on my work bench. There are formulas to calculate the proper value but honestely they are beyond my abilities. Does using a 0.01uf cap sound like a good value?

3) Do I really have to solder in 10 capactitors (2 for each opamp) to tame the oscillation? Could I get away with using one on each leg of the power trace on the circuit board, or 3 inches away at the power supply? (I am trying to simplify things and reduce the number of capacitors needed space can be tight)

Thank you for looking and I appreciate any thoughts you can share.

Let me share something back for any DQ LP1 owners: I found out that modifying one of the resistors allows you to modify gain. I realized, after years of trying to figure out why I don't have good bass, that the gain on the LP1 couldn't match the gain of the amps I use. Spoke someone who worked at Dahlquist with these units and was taught that changing this resistor will increase gain by 3db. Works wonderfully. Let me know if I can help. The reason I am not listing it here is that I am not next to the schematic and I don't remember the resistor number for sure, not trying to hide something. If anyone is interested, just let me know.

Thanks,

John

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Topic - Oscillation issue DQ LP1's "upgraded" op amps - jk 07:50:58 06/17/16 (16)

RE: Oscillation issue DQ LP1's "upgraded" op amps - KanedaK 04:34:11 06/19/16 (0)

Found this on a search..... - Cougar 07:02:53 06/18/16 (1)

RE: Found this on a search..... - jk 04:00:56 06/19/16 (0)

C15, C16 - djk 22:54:45 06/17/16 (1)

RE: C15, C16 - jk 04:04:18 06/19/16 (0)

iIs that the correct p/n for that I.C.? - Cougar 20:59:01 06/17/16 (0)

RE: Oscillation issue DQ LP1's "upgraded" op amps - jk 20:17:01 06/17/16 (4)

Schematic above (no text this post) - jk 20:19:11 06/17/16 (3)

How do you even know it's oscillating? - Cougar 20:48:49 06/17/16 (2)

RE: How do you even know it's oscillating? - jk 23:03:24 06/17/16 (1)

Make sure you got the ICs in the right way. - Michael Samra 19:38:09 06/18/16 (0)

some opamps don't like driving high capacitance loads directly off the .... - Cougar 19:01:39 06/17/16 (0)

RE: Oscillation issue DQ LP1's "upgraded" op amps - adam@denderapartners.com 18:10:34 06/17/16 (0)

RE: Oscillation issue DQ LP1's "upgraded" op amps - Lee of Omaha 15:14:12 06/17/16 (0)

RE: Oscillation issue DQ LP1's "upgraded" op amps - Hornlover 08:37:58 06/17/16 (1)

RE: Oscillation issue DQ LP1's "upgraded" op amps - jk 09:02:50 06/17/16 (0)

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