A in depth look at David Hafler's DH-101 Preamplifier. This was The David Hafler Co. first product. Several months later, the introduced the DH-200 Power Amplifier to go along with it. Sold either as a kit or preassembled. Part 2 will come soon with a look at a LATER DH-101 model. Same circuitry, but with some component changes.

My engineering teacher bought the DH-200 and DH-101 at a yard sale for $15, and used them for his class room to show movies and stuff. He retired in 2011, and gave me the DH-200 and DH-101.

Both were in need of a MAJOR overhaul. DC offset was 1V in one channel, and it was goofed. The preamp was major DC offset issues too. The DH-101 also has messed up traces, and a few cooked resistors. I decided to keep the DH-101 as a parts unit. It was in excellent cosmetic shape. So I bought a DH-101 off ebay (well I bought two) In this video is the first one, and once I replace the tatalum caps, it is finished, and will join the overhauled DH-200.

I bought a second that needs repair, but doesn't have any issues with the boards. Just dirty controls, and a broken patch jack on the back. This also has some circuit changes I will show in the upcoming video. The reason I have two DH-101s is because I bought a Hafler XL-280, and am in the process of installing Musical Concepts PA-4SE boards into it. I will make a video on that sometime in the future. :)

Back to the actual preamplifier. The reason I prefer this preamp over Hafler's never models (e.g. DH-100, DH-110) is this pre was built with discrete components. NO opamps. ENTIRELY transistor based. The DH-110 and DH-100 were nice units, but they used ICs, and I rather have a discrete design.

I'm not implying opamps are bad, and that I hate ICs. But back in the day, opamps and ICs were new, and weren't as good as a discrete design. Using opamps also saved money, as less components were needed. Today, opamps and such have progressed, and are way better, but so have transistors. Some folks (like me) still prefer a discrete design.