Low cost, high performance headphone amp using OPA1656 and LMH6321 - Page 7

levistubby · 29th November 2020, 09:48 AM

PM sent.

wynpalmer2 · 30th November 2020, 07:44 PM

Wiring for headphone board input
Dropbox - HP-input-wiring.jpg - Simplify your life

wynpalmer2 · 3rd December 2020, 06:51 PM

Three boards remain from the latest batch.

chris719 · 3rd December 2020, 08:48 PM

Is it truly stable into any capacitive load without any isolation? The datasheet indicates a decent amount of overshoot at 1 nF.

wynpalmer2 · 09:43 PM

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.

GKTAUDIO · 3rd December 2020, 10:34 PM

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.

levistubby · 12th December 2020, 11:49 AM

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

wynpalmer2 · 12th December 2020, 01:28 PM

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.

wynpalmer2 · 12th December 2020, 02:14 PM

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.

schiirrn · 15th December 2020, 10:13 PM

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.

IMG_8945.jpg

15th December 2020, 10:13 PM	#70
schiirrn diyAudio Member Join Date: Nov 2018	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. IMG_8945.jpg __________________ Preferred BSC? Just using a wide enough baffle.

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29th November 2020, 09:48 AM	#61
levistubby diyAudio Member Join Date: May 2011 Location: Hampshire coast UK	PM sent.

30th November 2020, 07:44 PM	#62
wynpalmer2 diyAudio Member Join Date: Oct 2016 Location: Greensboro NC	Wiring for headphone board input Dropbox - HP-input-wiring.jpg - Simplify your life

3rd December 2020, 06:51 PM	#63
wynpalmer2 diyAudio Member Join Date: Oct 2016 Location: Greensboro NC	Three boards remain from the latest batch.

3rd December 2020, 08:48 PM	#64
chris719 diyAudio Member Join Date: Jun 2004 Location: Connecticut	Is it truly stable into any capacitive load without any isolation? The datasheet indicates a decent amount of overshoot at 1 nF.

12th December 2020, 11:49 AM	#67
levistubby diyAudio Member Join Date: May 2011 Location: Hampshire coast UK	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

12th December 2020, 01:28 PM	#68
wynpalmer2 diyAudio Member Join Date: Oct 2016 Location: Greensboro NC	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.

12th December 2020, 02:14 PM	#69
wynpalmer2 diyAudio Member Join Date: Oct 2016 Location: Greensboro NC	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.