X-Altra HPA-1 Class A Headphone Amplifier

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#183
Bill, you need to go UP in value for those. Try 180 to 270 Ohms.

Sorry, I have an aversion to pots! Anywhere above 17.5 volts will work but don’t go more than a 100 -200 mV over 18 V because the opamps have max ratings at +-18V

(Other option is to solder a 500 ohm to 2 k pot in place of the resistors, adjust the O/P voltage and then measure the pot and replace with fixed resistors)
 
#185
The soldering iron has more heat then my Weller, I was having trouble soldering ground planes on 2oz copper boards. The hot air gun is handy for other things as well, preheating large boards ,and heat-shrink tubing. This despiser is handy for getting the solder on the boards. When you pre heat the board then you don’t have a problem getting the solder off the tip. Dispenser is JBC tools dpm-a.

Bill
 

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#186
Bill, I assume you are using solder paste? Never tried the hot airgun method but I think it will produce the best looking SMD boards.

I'm very pleased I transitioned to SMD - seriously good way to build stuff as long as you keep it to 0805 and above, SOT23 and bigger and TSSOP with 1mm lead spacing or better.
 
#187
Try these tapered plastic “Henna” tips. The 22ga is perfect for use with that dispenser tool and because the tip is flexible, a slight push pinches off the paste to allow neat dispensing. You don’t want to dispense on a warm board as it flows all over and makes a mess before you can place the components. This tip is very precise and lets you easily make 0603 dots or even tiny 0.5mm wide pads on some of the smaller components.

Glue Henna Dispensing Needle Tips Luer Lock Blunt End Plastic Tapered Needles 22 Gauge 100 Pieces https://www.amazon.com/dp/B07GLJZWL8/ref=cm_sw_r_cp_api_glt_fabc_XZTRDY4PK2E4BX384S2P
 
#189
Thanks X ,
yep if you heat the boards up too much the solder does turn to liquid, and if there is a via on the pad it runs through it. My hot plate has temp regulation so I turned it down to 95 degrees and the solder did not liquify but came off the tip. I do have a problem with it continuing to leak out when I set the dispenser down, maybe the tips will help. All in all I feel I will be able to continue with diy and smt parts.

Bill
 
#190
I'm going to build this maybe next year in May if things are good, along with some diy "grado" clones, their impedance is rated at 32ohms, will the amp be sufficient?

Another question Andrew, I didn't see the part no. for the heatsink in the BOM, could you elaborate on what they are? Or the dimensions would do.

Last question what is the approximate cost of the components? I just want a vague idea. Thanks.
 
#191
Stefan,

the Heatsink part number is (Mouser) is 532-529902B25G - you are correct it is not on the BOM although the pt# is screened onto the PCB overlay.

Here's the link https://www.mouser.co.uk/ProductDetail/Aavid/529902B02500G?qs=Jph8NoUxIfW2IkUxIcAaKQ==

You will need 2 of them. I will update the BOM on my website in the next few minutes

The HPA-1 is designed to drive 32 Ohm headphones in class A - so it will not be a problem with your phones.

Approx cost incl. PCB will be about $50.

🙂
 
#196
I finished pcb layout of the TI OPA1656 Baxandall Tone Control circuit from their datasheet. It's now in fab in China and I expect the boards in a week. A great project to complete over the holidays that will include the headphone amp all in one box. (This goes with the assumption that everything goes right...haha)
 
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