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X-Altra HPA-1 Class A Headphone Amplifier
X-Altra HPA-1 Class A Headphone Amplifier
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Old 12th April 2021, 02:58 PM   #81
passive420 is offline passive420  United Kingdom
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Andrew something you may know - In a post recently I read, EUVL eluded to the fact that not all ceramics are the same, if you're critical about measurements then choice matters even within the same class.

Can you advise when to use X7R or C0G, do you worry or study the specs of ceramics?

I generally choose the cheapest/best price break usually AVX or Kemet, EUVL mentioned a particular series of Murata that is now extinct, I think CJ8 that had good noise/frequency specs.
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Old 12th April 2021, 03:41 PM   #82
Bonsai is offline Bonsai  Europe
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For DC rail decoupling, X7R. I usually use Kerry, AVX or Murata, but have used Samsung, Panasonic, TDK and Wurth without problems.

For compensation, EQ networks or filtering, only COG or NP0

Never use X7R for anything but decoupling DC rails. They have a wide initial tolerance spread (-20% to +50%) but the real problem is they have a high voltage coefficient that in some cases can be as much as 50% of the stated value from 20% to 100% of the rated working voltage. So, if you pass an AC signal through them, the value is changing dynamically with the voltage.

I made the mistake of using one in one of the early EF3 amps and when driving it into a load, the caps would sing at the test frequency from the piezo electric effect.

COG/NP0 have none of these problems, but get expensive in high values.
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Last edited by Bonsai; 12th April 2021 at 03:44 PM.
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Old 12th April 2021, 03:43 PM   #83
Bonsai is offline Bonsai  Europe
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Originally Posted by passive420 View Post
Thanks for that X Your work it notably good. It's fun to see the chips snap into place under tension. I'm finishing that exact bal board today.

Andrew those are 0603 parts, I did mine by hand and lost a resistor at the end. It arrived today.
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Old 12th April 2021, 03:44 PM   #84
kasey197 is offline kasey197
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Quote:
Originally Posted by passive420 View Post
Thanks for that X Your work it notably good. It's fun to see the chips snap into place under tension. I'm finishing that exact bal board today.

Andrew those are 0603 parts, I did mine by hand and lost a resistor at the end. It arrived today.
I never thought Iíd fall prey to solder envy ....
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Old 12th April 2021, 05:46 PM   #85
xrk971 is offline xrk971  United States
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Thatís impressive - those look like 0402 components. I donít go below 0805!
As Passive said, only 0603 - easy peasy.

0402 is another matter...

Just this week, a friend asked me to replace one resistor on his board. Itís an 0201! Now that is small. I have to use my microscope for that one. I also did not have any 0201ís in my bench. They could be mistaken for dust.
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Old 12th April 2021, 06:05 PM   #86
NickKUK is offline NickKUK  United Kingdom
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I donít use lead free for DIY. Lead free has higher melting temps and kills ultra-fine pencil tip bits on my Weller.
Surely using silver-tin solder drops the temps below leaded solder?
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Old 12th April 2021, 08:48 PM   #87
xrk971 is offline xrk971  United States
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Lead free can actually be quite lower temp. It is made of mostly tin and added silver and bismuth etc. it doesn’t flow as nicely and grows dendritic whiskers over time. These can actually short.

Billions of $ have been lost on satellites that once placed in orbit have circuits that shorted out due to tin whiskers years later and caused failures. Pb solder does not have this issue. All this was because we were pushing for Pb-free PCBs so that landfills would not be polluted. Guess what, satellites won’t ever go to a landfill! At least not on earth.
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Old 13th April 2021, 11:46 AM   #88
ChrisT84 is offline ChrisT84  Netherlands
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Hi, might be a stupid question, but does this headphone amp already have DC protection, or does it still need to be added?
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Old 13th April 2021, 01:36 PM   #89
Bonsai is offline Bonsai  Europe
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Hello Chris,
No DC protection. The output devices used in the X-Altra HPA-1 are rated at 8 Amps, the supply voltages are low (+-18 V Max) vs the rated Vce (200V IIRC) and the short circuit output current is 300 mA. The devices are on a generous heatsink so there is little chance of a failure, assuming it’s well constructed and thoroughly tested.

Most opamps are incredibly reliable so IMV you should be safe.
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Last edited by Bonsai; 13th April 2021 at 01:41 PM.
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Old 13th April 2021, 01:40 PM   #90
Bonsai is offline Bonsai  Europe
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Originally Posted by xrk971 View Post
Lead free can actually be quite lower temp. It is made of mostly tin and added silver and bismuth etc. it doesn’t flow as nicely and grows dendritic whiskers over time. These can actually short.

Billions of $ have been lost on satellites that once placed in orbit have circuits that shorted out due to tin whiskers years later and caused failures. Pb solder does not have this issue. All this was because we were pushing for Pb-free PCBs so that landfills would not be polluted. Guess what, satellites won’t ever go to a landfill! At least not on earth.
Yes, pure lead or lead-tin alloys can be as high as 250C but most are around 183C. They add silver and sometimes copper to lower the melting point (weird since both have melting points well above 183 - it’s a job for a metallurgist to explain that!). I am probably a bit jaundiced on this because I bought a roll of lead free about 5 yrs ago and it was virtually unusable. I vowed never to use lead free again.

YMMV

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