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The PAT-5 Pages

PAT-5 Preamp

About the PAT-5

The following link is to a scan of a nice, clean copy of the original (not-bifet) PAT-5 assembly and user manual. The files are both kind of big because the scans are high res. You can zoom in tight to see what-ever you need, since they were scanned at 300 dpi from a manual in my files.

PAT-5 Assembly Manual, original version

PAT-5 Assembly Manual Assembly Pull-out Drawing, original version. Once again, there's enough resolution that you can zoom and pan around and pretty much see anything on the drawing.

The next link was found at www.tubes4hifi.com, where you may find the original scan.

PAT-5 Assembly Manual, bi-fet version

The PAT-5 was Dynaco's preamp that followed the PAT-4. It had more flexibility and switching capability, and featured the then new LM301 opamp in the tone-control/high level stage. The Bifet version changed from the LM-301 to the LF357 Opamp.

PAT-5 Preamp Circuits are Always Powered

In the most common wiring of the PAT-5, the preamp circuits are always powered. Here's why. In the original wiring of the PAT-5, the power switch turned the power supply to the preamp circuits on and off. However, it was noticed during an early review (I think it may have been in Stereo Review, but I couldn't swear to it.) that turning the PAT-5 on and off produced a huge transient at the output. If the PAT-5 was connected to a power amp, and the power amp was powered when you turned the preamp on or off, then the power amp would throw a full power pulse at the speakers. In addition to making you jump, this also could have lead to the speaker's demise if a big amp were paired with a small speaker.

There were a number of responses Dynaco could have made.

PAT-5 Upgrades

Lower Noise Power Supply (PAT5PWR)

This new, improved power supply has dramatically lower noise and dramatically better regulation. You can order it here.

Here's the Rev B assembly manual

Here's the Rev D assembly manual

You can see the schematic here.

Here are the specs:

These specs are more than 10 times better than those for the original power supply. Better power for better sound. Download the assembly manual for more detailed data.

Replacement Opamp

The opamp used in the high level stage can be significantly improved. You can replace it with TI's LME49710, which is available in the 8-lead round metal can package as of November 2015, though there are rumors that the package will be discontinued. If you make this modification:

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