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Low cost, high performance headphone amp using OPA1656 and LMH6321
Low cost, high performance headphone amp using OPA1656 and LMH6321
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Old 29th November 2020, 09:48 AM   #61
levistubby is offline levistubby  United Kingdom
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Old 30th November 2020, 07:44 PM   #62
wynpalmer2 is offline wynpalmer2  United States
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Wiring for headphone board input
Dropbox - HP-input-wiring.jpg - Simplify your life
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Old 3rd December 2020, 06:51 PM   #63
wynpalmer2 is offline wynpalmer2  United States
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Three boards remain from the latest batch.
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Old 3rd December 2020, 08:48 PM   #64
chris719 is offline chris719  United States
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Low cost, high performance headphone amp using OPA1656 and LMH6321
Is it truly stable into any capacitive load without any isolation? The datasheet indicates a decent amount of overshoot at 1 nF.
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Old 3rd December 2020, 09:22 PM   #65
wynpalmer2 is offline wynpalmer2  United States
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I'm not certain what you mean by truly stable. Yes, it is stable in the usual sense- even if the phase margin drops and there's significant peaking and overshoot in the >1MHz region.
I tested all of the loads 15, 30 and 200-300 ohms with zero and 1000pF, and sometimes in between values as those are the most likely to show the worst phase margin.
I was unable to make the design be unstable (i.e. break into oscillation) either in simulation, using TIs models, or on the bench, but there are combinations of load Rs and Cs that cause the margin to drop.
I have attached simulation results for the 15ohm/1nf and 300 ohm/1nf cases.
If the 10k bypass 1nF is removed then the composite amp IS unstable, both in simulation and on the bench- there is visible oscillation using a 70MHz scope.
Attached Images
File Type: png step10k15 300 1000p.PNG (68.0 KB, 237 views)
File Type: png 15 300 1000p freq.PNG (96.8 KB, 238 views)

Last edited by wynpalmer2; 3rd December 2020 at 09:43 PM.
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Old 3rd December 2020, 10:34 PM   #66
GKTAUDIO is offline GKTAUDIO  United States
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Just finished another headphone amp - this one will go into a line/MC preamp with warp filter, lower right portion of chassis, which will have relay input switching, and a separator panel for the power supply section.
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File Type: jpg DSCN6716a.jpg (655.5 KB, 219 views)
File Type: jpg DSCN6715a.jpg (566.4 KB, 214 views)
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Old 12th December 2020, 11:49 AM   #67
levistubby is offline levistubby  United Kingdom
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Mouser don't have any OPA1656 op amps in stock. Does anyone have a lead on a reliable supplier in the UK/EU? Or does anyone have one that they would be willing to sell me?
Thanks.
Tony
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Old 12th December 2020, 01:28 PM   #68
wynpalmer2 is offline wynpalmer2  United States
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Mouser UK has the OPA 1656ID in stock. Same part- just not in "reel" form like the slightly cheaper OPA1656IDR that is specified.
Mouser part # 595-OPA1656ID.
Just modify the cart accordingly.
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Old 12th December 2020, 02:14 PM   #69
wynpalmer2 is offline wynpalmer2  United States
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The last headphone board in the second run has been sold.
Presently six boards, that I know of, have been successfully built with no problems.
If anyone is interested in an amp, please post your interest in this thread then PM me.
The boards will continue to be sold at cost plus shipping.
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Old 15th December 2020, 10:13 PM   #70
schiirrn is offline schiirrn  Germany
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I just finished mine. The board layout is well done and makes soldering easy. My current hack/test wire up hums in various ways depending on how I wiggle the wires, so a subjective description will have to wait. I am using a Didden Silent Switcher set to +/-12V.


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