Tuesday, August 19, 2008

The Sherwood 7310 Receiver

I have long regarded Sherwood gear as sleepers. In my young adulthood it was a brand that I could afford (via Illinois Audio: ahh, the days of discount mail order) and their receivers sounded good to my young ears. The 7310 is the middle of the line from about 1975 and boasts 38 real world, rms watts. Original list price was $380. I purchased a new 7210 in 1975, and remember it fondly.

Sherwood build quality is not as impressive as Marantz, but manages a significant sonic mojo. The receivers sound bigger than their advertised wattage and the tuners are solid all 'round performers. Cosmetically, Sherwood lags a bit behind Marantz, but a clean example represents '70s hifi style very well.
The 7310 offers the David Hafler's Dynaquad circuitry, an island of sanity in this era of quad madness:This 7310 worked well on arrival. Even the lamps worked. So, on with the restoration! The board layout is straight forward with only the treble/bass board presenting a significant challenge. Here is the bird's eye view from the top:
The power supply board is at the lower right, below the transformer. The output boards are in the upper middle and are accessible from below. The tuning capacitor is at the upper left, shielded. Immediately below it are the AM and FM boards that required removal of 4 screws and some tugging to restore. But whither phono?The phono board is located underneath the unit, at the upper left in this photo. Note the two power supply filter caps in the upper right corner. These slightly obscure the treble/bass board that hides just behind the face of the unit. Changing the caps on this board requires peeling the face and unclamping the filter caps. As luck would have it, my back order of Elna Silmic II caps had just arrived so the 8 4.7 mfd caps on this small board were replaced with silk. The tone control circuit is not defeatable, so it better sound sweet when driven by the cd player not yet imagined in 1975.

All other caps were replaced with Panasonic FCs with extra margin on the voltages. A total of 50 caps were replaced, the 6.8k main filters were left as is. Pots and switches were cleaned with Blue Foam and Deoxit Gold. The tuning capacitor was spritzed with Deoxit Gold.

The end result of my labors was a very sweet sounding unit that should last for another 20-30 years. The overall sound is lush for a string quartet with enough punch to do justice to Metallica. And it looks good. One more look with a bit of drama:

Saturday, August 2, 2008

Last of the Family: the NAD 1020 Preamp

The 1020 preamplifier is the last of the NAD family fest I celebrated last month. The exterior is very similar to the 3020a that I restored with the distinctive horizontal rear deck for connections. Acres of space are available under the hood and cap replacement is a breeze. It is much easier to work on than the Kenwood C2, no origami skills needed. Here it is with top popped:

Hmm. Looking at that board, you would think they took the 3020 and threw out the amplifer and called it a preamp. Hmm. And you would be correct, sir. The transformer is much smaller and two fuses at the left are skipped, but that is the very same board. The same tone control circuitry with the hard to find .68 mfd bass control caps is strung out along the front. The unshielded phono section is in the back right for the typically short signal path.

Restoration required 32 new Panasonic FC caps and the usual cleaning of controls. Not surprisingly this is a very nice sounding preamp, very neutral in presentation with a nice phono section. I think it would mate nicely with an amplifier with a bit of zip to it.

I love the rear deck feature which I first encountered in the Amber Model 17 preamp long ago. (Hmm again, the Amber family could use a write up.) And I love how pleasant it is to work on. Here it is in my feeble attempt at an artsy photo: