Not thrilled with sound of 4562 in active xovers - diyAudio
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Old 28th June 2011, 06:59 AM   #1
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Default Not thrilled with sound of 4562 in active xovers

After two years of design and build, my speakers are mostly finished, using active xover between mids/highs and bass, with passive between mids and highs. I am using the ESP 24db/octave boards, populated with quality parts, including LM4562.

Although I'm quite happy with the dynamics and detail this arrangement affords, I don't entirely like how things have turned out. When run full-range, the mid/high speakers are open and clear, with delicate, extended, spacious highs and tonally truthful mids. With the same amps and xovers in the circuit, there is plenty of detail (almost too much), but the midrange seems fake, with kind of a shallow or hollow tonality. Some of that may be due to xover point/slope issues, and I think I can fix that. But the highs seem "flat" and somehow truncated, with no sign of life or openness, and that is NOT a slope or xover point problem.

In addition to the designed bypass caps, I have added ceramic caps soldered right across the power pins of each opamp. I don't think that's an issue.

I have read all the threads, here and elsewhere (spending many hours), that discuss opamp sonic characteristics, and I know there are lots of different opinions with no clear consensus. I wonder if anyone has found an ideal combination of opamps in this or a similar application. I am on a limited budget, so I can't just buy 8 OPA627's or discrete opamps, unless that is absolutely the only alternative to achieve good sound.

If I were to try a couple 627's, would they yield the best results as input buffer, output buffer, or in the filter section?

Any other opinions or suggestions? I'm more than a little frustrated after all this work and expense, and I would appreciate your help.

Peace,
Tom E
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Old 28th June 2011, 07:07 AM   #2
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Old 28th June 2011, 07:12 AM   #3
nmiljac is offline nmiljac  Germany
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What does your power supply look like?

If you're using 78xx/79xx you may try e.g. AD826 which seems to work well even with these crappy regulators.
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Old 28th June 2011, 07:13 AM   #4
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well switch it back to a tl072 and see the difference, also I would wait for burn in..

usually esp designs work rather well with the suggested chip, I would try the 72 and the humble 4558 (*powers most of the cheap HT equipment*)..

I know they are not good but really worth a try..
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Old 28th June 2011, 07:40 AM   #5
nmiljac is offline nmiljac  Germany
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You may even try NJM 2068 if you have some at hand.
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Old 28th June 2011, 07:59 AM   #6
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Tom, this may not be what you want to hear, but I speak from personal experience. I suspect that what you are hearing as spacious highs, etc. are actually cone breakup modes that are adding pleasing colour to the sound when the drivers are run full range. I've been there, and been fooled too, and only realised what was going on when I ran distortion tests. So my advice, double check your measurements before starting to obsess on op-amp sound.
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Old 28th June 2011, 08:44 AM   #7
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I had a problem with the high pass XO on my bought actives - they'd fitted LM4562s, did not like the highs at all. Fixed it with a 'downgrade' to NE5532. Worth a try at least seeing as 5532s are dirt-cheap.
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Old 28th June 2011, 09:10 AM   #8
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Have you measured the overall frequency response? Messing about with opamp and capacitor types is not the thing to be doing if you have not got your various filter turnovers and gains just right.
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Old 29th June 2011, 04:42 AM   #9
Bonsai is offline Bonsai  Taiwan
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Stop blaming the opamps guys! Have scoped the outputs?
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Old 29th June 2011, 03:38 PM   #10
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Thanks for your responses so far. I don't have any measuring equipment. The xovers are thoroughly broken in, as they have been playing for a month or so. I have been listening to music and a CD with steady test tones to try to set the levels. I know that is not ideal, but it's all I've got.

The level of mids to highs is fixed by a passive xover, designed by Madisound. I am completely satisfied with it. The mid/high sections sound excellent without the active xovers in the circuit, and it's not because of cone break-up!

The active xover is between bass and mids/highs. There are pots on board to adjust gain. I am also considering using fixed or stepped resistors to get rid of the pots in case they are a factor in the aspect of the sound I don't like.

These speakers do lots of good things, but I know they can be better. I have ordered some of the NE5532 to try out. I also ordered parts to try different turnover point and slope.

Peace,
Tom E
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