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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Ideas for a bluetooth controlled preamp / headphone amp combo (PGA2311)
Ideas for a bluetooth controlled preamp / headphone amp combo (PGA2311)
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Old 23rd August 2019, 07:02 PM   #11
dsteinman is offline dsteinman  Canada
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Join Date: Aug 2019
Despite its hideous appearance my breadboard design actually works! And it sounds really good so far. I don't have golden ears, mind you, but I'm just thrilled with the sound and the performance. No obvious hiss or distortion (will do more testing once I have it soldered up and not so dangerous), and the PGA2311 puts out enough power to power my (easy to drive) V-Moda M100's. The Bluetooth control over the PGA is amazingly fast, I was worried I'd have to rate-limit the Serial data but seems like I won't have to. And with the zero crossing pin pulled high I don't hear any clicks or pops when changing volume, even very quickly.

I ended up deciding to add 6 buttons to what will be the front panel (power, mute, and 4 dedicated buttons for source/output selection), and for the back panel I'll have 2 sets of inputs and outputs - one RCA and 3.5mm headset jack in, and one RCA and 3.5mm headset jack outputs. So the 4 source buttons would be Input 1, Input 2, Output 1, and Output 2. I can do all that with just 2 DPDT Omron signal relays. But the breadboard got messy because the NRF52 bluetooth chips is at 3.3V, and nearly everything else is at 5V. So I had to level shift, and use mosfets for nearly everything. I'm going to be adding some more stuff too, like a mute relay, and then try to add that TPA6120 headphone amp as well. I just hope the power supply has enough juice to power the TPA chip well enough.

These are the key parts relating to the PGA2311 that I'm using at the moment:

Power Supply:
Inductor 22uH Bourns 78F220J-RC
Ceramic Capacitor 2.2uF Murata RDER71E104K0K1H03B
Dual Rail +/- 5V Murata NMA0505SC

PGA caps:
Aluminum Capacitor 10uH Nichicon UFW2A100MED1TD
Ceramic Capacitor 0.1uH Vishay BC A104K15X7RF5TAA
and some cheap carbon film 100 ohm series resistors on the inputs and ouputs

Sounds good so far. But I need to now to solder everything up onto permaboards, and do some listening tests and see if I can detect which caps and resistors sound best.
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Old 23rd August 2019, 07:18 PM   #12
dsteinman is offline dsteinman  Canada
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Join Date: Aug 2019
Can anyone suggest some audiophile quality 100ohm resistors to use on my inputs and outputs that won't impact the sound very much? There's over 1000 of them to choose from:

Through Hole Resistors | Resistors | DigiKey

I was thinking these Vishay Dale ones which are reasonably priced:
CMF55100R00FKEB Vishay Dale | Resistors | DigiKey
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