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SurfCables: Silver Teflon Audio Cables

Made in USA

PartTimeProjects Pearl Phono Preamplifier

This is a preamplifier used for record players, a design created at Pass Labs that is described in an article published on the Pass DIY web site.

Not much to say here, I used two transformers and a shielding plate to keep down the hum. It does have more hum than the Bugle Preamp that runs on batteries, though the hum can barely be perceived as I have reduced it by playing with the grounding. This has a crisp and smooth sound, which is what I was looking for.

Here are some pictures-

Click on Picture For Zoom Description
Pearl Phono/ Power On
Power is on and this is playing music. You can see the two blue LEDs indicating each channel is operational.
Pearl Phono Top/Rear View
This is the rear top view. An alligator clip is visible. This connects the tonearm ground wire to various points in the circuit, I was looking for the best possible grouding connection.
Pearl Phono Top/Front View
This is the front top view of the unit during testing. I am fooling around with the grounding.
Pearl Phono Grounding
Here is the final view with the star grounding. OK, we have enough trouble in DIY figuring out where to connect all the input/output/ circ grounds and here with a phono preamp you also have a "third" ground- a ground wire coming out of the turntable tonearm. Where is that supposed to connect to? So what I did was give myself two options, which turned out to be about the same in practice. First, I put an islolated elbow on the chassis shown in the next picture. Tonearm ground connects to the elbow which then connects via a wire to either the circuit ground (red connection) or to the chassis ground (blue connection). One of the channel boards has a ground which I used as the 'star' ground that feeds all the other grounds. This also connects to the chassis via a 25 ohm/ 3 watt resistor to isolate the circuit ground from the case, and the case is connected to the AC inlet ground prong for anti-shock protection. So I can connect the tonearm ground to either the case ground (blue connection on the elbow) or circuit ground (red connection on the elbow). In practice I could not hear the difference, hum is very low either way and I cannot tell which connection is better.
Pearl Phono Back Panel Grounding
Back panel. The elbow is insulated from the chassis with a rubber gromet. The eblow is threaded so that an allen head screw can clamp a turntable ground wire onto the elbow. Also on the elbow is a connection to EITHER star ground or chassis ground. Not much difference in practice but I would think that the connection to star ground is better. Come to think about it, this looks kind of rough, perhaps I could install a switch to make it look more professional and easier to use. I would not have to swap the wires manually but could flip the switch to select which connection to use? Hmmm....