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Old 30th November 2016, 08:55 PM   #1
Hikari1 is offline Hikari1  United States
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Default Pass HPA-1, what do we know?

Pass' new HPA-1 is certainly getting good press.

Pass Labs HPA-1 headphone amplifier | Stereophile.com

Do we know anything about the design? Push-Pull or single-ended? Based on any currently known topology (Aleph, etc.)?

Just trying to figure out what Pass considers the best approach for headphone amplification.
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Old 30th November 2016, 09:32 PM   #2
xrk971 is offline xrk971  United States
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A picture is worth a thousand words...

Click the image to open in full size.

Zooming in on the left channel, I see 12 active devices in a very symmetric layout. It looks like 10 actives prior to the two big output MOSFETs with large 3w source resistors. I see one DC offset trimpot, 1 bias trimpot. There is a TO92 programmable voltage source (TLM431?) providing bias current adjustment, it's not in the audio path. The opamp is in between the two channels and I don't think it is in the audio path either.

Click the image to open in full size.

I suspect it might be a push-pull output stage with something resembling one of Juma's creations.
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Last edited by xrk971; 30th November 2016 at 09:35 PM.
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Old 1st December 2016, 02:37 AM   #3
Hikari1 is offline Hikari1  United States
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The op amp is likely a servo. Some of the to-92 active devices may be regulators or voltage references. Probably push pull I would imagine. Still would like to know more...

The big film caps are curious if they are not rail decoupling.
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Old 1st December 2016, 05:34 AM   #4
seanny is offline seanny  United States
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On the CES video someone said the only IC on the board is for servos.
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Old 1st December 2016, 05:41 AM   #5
seanny is offline seanny  United States
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5 pairs = 4 beasts and a cascode?
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Old 1st December 2016, 11:12 AM   #6
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I like 6moons better as they show lot more of the devices inside.
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Old 1st December 2016, 12:57 PM   #7
Kovax is offline Kovax  Croatia
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Current feedback design by the looks of it.
Something like one of our great minds here has already offered on the topc of another Pass designs, just this one is sized for headphones. Here is the link.

Pass XA25?
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Old 1st December 2016, 01:09 PM   #8
EUVL is offline EUVL  Europe
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> Do we know anything about the design?

More than you need to reverse engineer it, even down to component level.
Read the 6moon review in detail, not only the pictures.

> Push-Pull or single-ended?

Single-ended (as opposed to balanced) push-pull.

> Based on any currently known topology (Aleph, etc.)?

No.

> 5 pairs = 4 beasts and a cascode?

6moon :
"...... I tried different devices including bipolars and in the final analysis we chose Toshiba Jfets for the input stage,
Fairchild Mosfets for the outputs and bipolars in the current mirrors
so we ended up using all three device types.....
the voltage gain occurs in the Jfet/mirror stage and the Mosfets provide the current drive....."


Patrick
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Last edited by EUVL; 1st December 2016 at 01:11 PM.
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Old 2nd December 2016, 12:27 AM   #9
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Quote:
Originally Posted by EUVL View Post
> Do we know anything about the design?

More than you need to reverse engineer it, even down to component level.
Read the 6moon review in detail, not only the pictures.

> Push-Pull or single-ended?

Single-ended (as opposed to balanced) push-pull.

> Based on any currently known topology (Aleph, etc.)?

No.

> 5 pairs = 4 beasts and a cascode?

6moon :
"...... I tried different devices including bipolars and in the final analysis we chose Toshiba Jfets for the input stage,
Fairchild Mosfets for the outputs and bipolars in the current mirrors
so we ended up using all three device types.....
the voltage gain occurs in the Jfet/mirror stage and the Mosfets provide the current drive....."


Patrick
Sound like this one: http://gilmore.chem.northwestern.edu/lc.pdf
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Old 2nd December 2016, 09:33 AM   #10
juma is offline juma  Germany
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Something like this roughly fits the bill and sounds nice ....
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