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Old 9th October 2012, 01:57 PM   #1
maouna is offline maouna  Greece
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Default NE5532 Tone Control

This is a tone control circuit with NE5532 which i am planning to build. It uses 10K pots (R4-R5 , R8-R9 ).
I would like your comments...
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Old 10th October 2012, 01:26 AM   #2
Bare is offline Bare  Canada
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Have (had :-) a 5532 Tone control in My Amp.
Bypassing the contraption entirely, made a HUGE improvement.
Are you Sure you want this gizmo??
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Old 10th October 2012, 06:39 AM   #3
maouna is offline maouna  Greece
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I have all the parts sitting in a box so i desided to make one.
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Old 10th October 2012, 07:15 AM   #4
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Is R12 necessary? You'll have a high input impedance at the next stage, so I can't see 100 ohms making much difference. And unless DC offset is a problem, C10 & C11 aren't needed.
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Old 10th October 2012, 01:09 PM   #5
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Quote:
Originally Posted by sofaspud View Post
Is R12 necessary? You'll have a high input impedance at the next stage, so I can't see 100 ohms making much difference. And unless DC offset is a problem, C10 & C11 aren't needed.
C10 is the DC block for the bass cut lowpass though, yeah, it could also be implemented as a shelving filter. It's common to AC couple guitar gear on both input and output just in case the next gizmo in the chain doesn't adhere to the AC coupling convention. So C11 is optional but conventional. R12 is the usual source impedance pad to move the capacitive load pole far enough down in frequency that the op amp remains stable.

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Originally Posted by Bare View Post
Bypassing the contraption entirely, made a HUGE improvement.
Sounds like tone suck. The 5532's a perfectly fine audio op amp when used appropriately but at 30k min, 300k typ it has an unusually wide input impedance range. Check the impedance matching; wouldn't surprise me if you got a 5532 on the low corner and the circuit's dragging. If so, a quick fix may be to switch from bipolar (the 5532's built using BJTs) to a process with higher input impedance. The Jfet TL072 is a common choice for its teraohm input inpedance, low cost, and decent performance.

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Originally Posted by maouna View Post
I would like your comments...
Looks fine to me (though I didn't sim the circuit and do a noise analysis ). The second order ~450kHz lowpass around U1 is arguably overkill---first order and using U1 as a buffer would be fine too. Either way I'd probably corner it more like 50-100kHz; no need for the extra bandwidth so it's just more noise susceptibility.

As an aside, I think this thread should be in the instruments and amps forum.
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Old 11th October 2012, 05:53 AM   #6
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twest820, the only post in this thread mentioning guitars is yours.
I'm reserving further comments.
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Old 11th October 2012, 07:14 AM   #7
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But it's still in the wrong place so I'm moving it to Line Level.
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Old 11th October 2012, 10:52 AM   #8
AndrewT is offline AndrewT  Scotland
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Having started re-reading Cordell's book, I think Cordell will argue very strongly that R12 @ 100r is very necessary to interface with the following cable/interconnect.

There may be good logic for reducing the value to 75r, or 50r, if coax, of those characteristic impedances, were to be used for interconnect, but the 100r value would be good for a twisted pair interconnect.
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Old 11th October 2012, 11:06 AM   #9
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Quote:
I think Cordell will argue very strongly that R12 @ 100r is very necessary to interface with the following cable/interconnect
I would, too. [Originally] Being in the Chip Amp forum made me answer in an integrated amp context. I'm still holding to my C10-C11 comments. What are your thoughts on R11? Would a smaller value matter at all, yet still provide isolation?
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Old 11th October 2012, 11:18 AM   #10
Bonsai is offline Bonsai  Taiwan
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I'd fit R12 unless you can be sure the capacitive load is well known and controlled. 100 may be a bit on the high side, but not so much that it is cause for any concern.
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