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Class A Headphone Amp; OPA827 and IRF610/9610
Class A Headphone Amp; OPA827 and IRF610/9610
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Old 22nd March 2019, 09:57 AM   #21
knauf1919 is offline knauf1919  Romania
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Hello, I'll try in my spare time. I would need a list of components from a European distributor, TME, Mouser, and final schematics.

Last edited by knauf1919; 22nd March 2019 at 10:00 AM.
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Old 28th March 2019, 10:11 PM   #22
knauf1919 is offline knauf1919  Romania
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Interesting. Nobody says anything ...
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Old 7th April 2019, 07:40 AM   #23
John Luckins is online now John Luckins  Europe
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I have just knocked up a version of the circuit in post 9 with OPA1641's and 2SC5171's on Veroboard. Each channel runs at 200mA and with 18v supplies you need a good heatsink. Sounds excellent just off lab supply.

John
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Old 14th June 2019, 09:08 AM   #24
lineup is offline lineup  Sweden
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I wonder if anyone has built this amplifier?
I am sure the performance is very good.
Better than most headphone amp suggestions
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Old 8th July 2019, 09:19 PM   #25
Carl_Huff is offline Carl_Huff  United States
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Quote:
Originally Posted by lineup View Post
I wonder if anyone has built this amplifier?
I am sure the performance is very good.
Better than most headphone amp suggestions
I just finished a version. I used a LM4562 op amp. In my case I used FQP3N30/FQP3P20 output devices rather than IRFs. I had no good reason to do that, other than the fact I had some on hand. I also bumped up the circuit gain to 16dB. In use that might prove to be too much and I'll end up dropping it back a bit.

Using FQP3N30/FQP3P20 output devices caused me to add a pair of 10 ohm resistors in series with their source outputs.

I've just started listening to it. So far it sounds to be very good!
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Old 9th July 2019, 11:57 AM   #26
xrk971 is offline xrk971  United States
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Class A Headphone Amp; OPA827 and IRF610/9610
Nice work, Carl Huff! Very neat layout. I bet it sounds great. Few questions: what is the bias current running at and what is the DC offset? Sometimes a bipolar electrolytic (220uF or so) between R11 and ground can keep the offset centered at 0mV.
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Old 9th July 2019, 03:30 PM   #27
Carl_Huff is offline Carl_Huff  United States
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Originally Posted by xrk971 View Post
Nice work, Carl Huff! Very neat layout. I bet it sounds great. Few questions: what is the bias current running at and what is the DC offset? Sometimes a bipolar electrolytic (220uF or so) between R11 and ground can keep the offset centered at 0mV.
Thank you for your comments XRK,

The offset is very low, less than a millivolt. I haven't had the opportunity to measure anything beyond that. I checked it briefly with a scope and PC spectrum analyser to verify that it was working and then just plugged it in. I confess, I built it quickly from 'familiar' parts. I am certain that it can be improved upon. In any case it is a very nice circuit that sounds very good! And now I am off traveling on holiday with my wife. I will revisit this project in a couple of weeks and let you know my findings.
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Old 9th July 2019, 05:16 PM   #28
DontHertzMe is offline DontHertzMe  South Africa
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Class A Headphone Amp; OPA827 and IRF610/9610
That looks great, Carl . Do you recall the part number of the heat sinks you used?
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Old 9th July 2019, 05:28 PM   #29
Carl_Huff is offline Carl_Huff  United States
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Originally Posted by DontHertzMe View Post
That looks great, Carl . Do you recall the part number of the heat sinks you used?
Those heatsinks are made by Ohmite and are perfect for these kind of projects.

Mouser stocks them as part #588-CSM221-40AE
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Old 9th July 2019, 06:45 PM   #30
EUVL is offline EUVL  Europe
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> I used FQP3N30/FQP3P20 output devices rather than IRFs. I had no good reason to do that

I have. The FQPs are truer complementary devices than the IRFs.
Check out the F5 Headamp thread at the Pass forum.
F5 Headamp ?
Posts #195, 196, 205

> Using FQP3N30/FQP3P20 output devices caused me to add a pair of 10 ohm resistors in series with their source outputs.

For fear of thermal run-away ?
They wont when you have enough heatsink.
I have used 3.3R with no issues.

> The offset is very low, less than a millivolt.

Comes with the opamp. Any output stage offset will be corrected by the NFB loop of the opamp.

> I am certain that it can be improved upon.

Replacing R1 with a current source (e.g. E252) will improve PSRR.
And you can simplify the circuit a lot by replacing the Vbe multipliers with 2 resistors.
See :
DIYForums.org • View topic - discrete diamond buffers
https://www.amb.org/ti/audio/mosfet_buffer_sch.png

> Those heatsinks are made by Ohmite and are perfect for these kind of projects.
> Mouser stocks them as part #588-CSM221-40AE

Thermal resistance is 12C/W.
Assuming +/-15V supplies and 100mA bias per channel (per heatsink), temperature rise is 36C above ambient. So HOT !
And the vertical MOSFETs (whether FQP or IRF) have positive tempco.
Which means bias will increase with temperature which in turn will increase bias further.
That is why a large heatsink is advantageous, so as lateral MOSFETs because of negative tempco.
The XEN XELF Headphone Buffer


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Patrick
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