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Pass Labs - WHAMMY diy headphone amplifier

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amirm

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That's a very nice, informative and frank talk! It gets technical but if you get past that, there is good bit of wisdom expressed in there.

The only thing I found a bit odd was series resistors everywhere including power pins for the Opamps. I get the usage of them during design to measure current but in a working system I would just leave them out.
 

Ken Newton

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...The only thing I found a bit odd was series resistors everywhere including power pins for the Opamps. I get the usage of them during design to measure current but in a working system I would just leave them out.
Wayne mentions that power supply decoupling is their other purpose. Such RC decoupling networks are commonly utilized for wideband isolatation of multi-stage tube preamp circuitry. If the bypass caps. are sufficiently sized, relative to the current swing amplitude and lowest signal frequency to be handled, the 47R series resistors likely don't induce significant modulation of the op-amp's supply pin voltages.
 
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Ken Newton

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They might be there to avoid turning the amp into an overengineered oscillator ( at least R17 / R27).
Yes, R17 and R27 appear intended to isolate the op-amp stage's output from being tasked with directly driving the power amp's input capacitance. However, I would expect to also see the feedback network's compensation cap. to then be connected in a short loop path from the op-amp output pin directly to it's inverting input pin, bypassing the power amp entirely. Wayne certainly knows what he's doing, so.
 
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Apart from some passive filters for loudspeakers over 20 years ago I've never done any soldering. Would this be within reach of a total newby? What would be a good but not too expensive soldering iron for a project like this?
Also, would it be a better match with my Focal Elear than the Topping A30 I currently use?
 

amirm

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Apart from some passive filters for loudspeakers over 20 years ago I've never done any soldering. Would this be within reach of a total newby? What would be a good but not too expensive soldering iron for a project like this?
Answering the latter part, yes, there is an excellent soldering Iron from Japan no less that doesn't cost much: the Hakko FX-888D. See https://smile.amazon.com/dp/B00ANZR...e-us000-pcomp-feature-scomp-wm-5&ref=aa_scomp

On the rest, I looked a their instructions just now. As such, I don't recommend that you tackle it for two reasons:

1. It has an internal mains power supply. This means there are high voltages inside and screwing up the wiring there could result in amplifier that actually works but may be dangerous.

2. There are a lot of parts that can be soldered backward. While in their part 2 they show these, in the power supply section I did not see them show orientation of such parts as the regulators.

For an electronics hobbyist, it is a rather simple project to build. But if you don't know what those parts are, what is dangerous and what is not, it can be quite a challenge.

If you were in US, I was going to make an offer of you buying it and me building and measuring it for you. But you are in Europe so shipping back and forth would add fair bit to the cost.
 
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