New PassDIY Headphone Amp (now available)

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xrk971

xrk971

Founder of XSA-Labs
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I'm late to this thread and somehow missed why this amp uses an opamp to drive the class A MOSFETs? Given that the title says PassDIY HA, I am surprised there is an IC opamp in the audio signal path.

I have built a variant of the F5 HA (Prasi mod) and I have to say that the F5 inspired 2SK170 and 2SJ74 inputs are all you need to drive the MOSFETs. I have actually made a version with 2SK2013 and 2SJ313's and it sounds great. Absolutely silent amp with very fast clean sound. Also, it is a DC coupled design all the way through.

Here it is in stereo with a cap multiplier downstream of two 19v laptop SMPS bricks in series as easy to use external PSU's.

580132d1479202840-f5-headamp-small-f5ha-2sk2013-2sj33-cap-multiplier.jpg


So just trying to understand why opamps were used here.
 
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blackdod

Member
Joined 2011
nicusim said:
Parts are already ordered and your pcb on the way,as well.It will take a bit of time to finish it,due to my work schedule.Eager to compare it with a Lehmann clone I already have for some time,quite good with Beyerdynamic DT 880 Premium - 600ohm(Burson OpAmp V5).
Click to expand...

Pass HA is better that Lehmann. ;)

I recommend use 2SK2013/2SJ313 and OPA627BP too.
 
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Hikari1

Member
Joined 2012
xrk971 said:
I'm late to this thread and somehow missed why this amp uses an opamp to drive the class A MOSFETs? Given that the title says PassDIY HA, I am surprised there is an IC opamp in the audio signal path.

I have built a variant of the F5 HA (Prasi mod) and I have to say that the F5 inspired 2SK170 and 2SJ74 inputs are all you need to drive the MOSFETs. I have actually made a version with 2SK2013 and 2SJ313's and it sounds great. Absolutely silent amp with very fast clean sound. Also, it is a DC coupled design all the way through.

Here it is in stereo with a cap multiplier downstream of two 19v laptop SMPS bricks in series as easy to use external PSU's.

580132d1479202840-f5-headamp-small-f5ha-2sk2013-2sj33-cap-multiplier.jpg


So just trying to understand why opamps were used here.
Click to expand...

Because they are easy and you can roll op amps and they are cheap and available. This amp is meant to be a easily built and parts sourced amp.

Unlike amps using the Toshiba Jfets.

Pass HPA-1 uses Toshiba Jfets. I am unsure of the output stage...whether it's push pull or single ended. But I see a servo IC in there (look at the stereophile review) which would suggest single ended but maybe not.
 
xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
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Russellc

Member
Joined 2003
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wayne said:
I have been looking at and measuring the one built by 6L6 and will be done soon. Sorry for the delay but things have been busy around here lately with XA25's and new designs.
Click to expand...

Yes, thanks for the update....one good thing about the delay, my targeted headphones, Audioquest Nighthawks, have a new model and the old one is reduced now from 699 to 350.....:cool:

Russellc
 
A

aradan

Member
Joined 2015
Hi all,

A quick question, is there full schematic available or a formula to calculate the amplifier gain for this circuit. I was able to find only part of the schematic in this thread.

I am thinking to use it to drive Audeze EL8 or LCD 2

LCD 2

Specifications
Style Open circumaural
Transducer type Planar magnetic
Magnetic structure Proprietary push-pull design
Magnet type Neodymium
Transducer size 106 mm
Maximum power handling 15W (for 200ms)
Sound pressure level >130dB with 15W
Frequency response 5Hz – 20kHz extended out to 50kHz
Total harmonic distortion <1% through entire frequency range
Impedance7 70 ohms
Efficiency 101dB / 1mW
Optimal power requirement 1 – 4W
Click to expand...

EL 8


Specifications
Style Open circumaural
Transducer type Planar magnetic
Magnetic structure Fluxor magnets
Magnet type Neodymium
Driver Size 100 mm
Maximum power handling 15W (for 200ms)
Maximum SPL >130dB
Frequency response 10Hz – 50kHz
Total harmonic distortion <0.1% (1kHz, 1mW)
Impedance 30 ohms
Efficiency 102dB / 1mW
Optimal power requirement 200mW – 4W
Weight 460g
Click to expand...


Trying to figure out the values of the R16/R22/R29/R32 resistors in the following configuration



Op amp OPA 627

Q1/3 Q2/4 2SK2013 and 2SJ313
Click to expand...

Thanks,
Oleg
 
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