NAD 4155 Tuner Filter Mod

THE NAD 4155 AM/FM TUNER

Mike Bugaj

I don't know why I keep doing this. I'm just a sucker for nice looking tuners.

I found this NAD tuner in the summer of 2009 sitting on top of the hood of a car at the Mansfield Drive-In flea market in Storrs, CT (home of the University of CT). For some reason, this flea market always has a good selection of interesting electronic items and I've picked up stuff cheap there before. In this case, the guy gave this tuner to me for just ten dollars. A steal, indeed! So I got it home, not knowing if it would even work. But, it did work. Of course, the selectivity was so wide you could drive a truck through it. So, I took the top cover off and looked.

I found three filters in this tuner. If you look close you will find that I have them circled with blue rectangles. I pulled the old filters, soldered in IC socket segments and installed three Murata 150khz filters. I'd like to call your attention to an orange wire running toward the top of the photo and out through a hole in the frame in the back. This lead connects to R216 and is used to tap into the RDS for use with a Conrad RDS Manager or some other such unit.

This tuner is easy to modify. The bottom cover comes off easily and you have plenty of access to the filters.

Now to the tuner. The NAD 4155 has three filters. It's more of a basic tuner with only five presets. Next to the presets is an "enter" button you press to set the preset. Next to that is the AM-FM button. If you look at the picture you'll find a power button on the extreme left side of the front with three buttons to the right of it. One is Mono/Stereo, the middle is FM mute and the right button is something called DYN SEP/DEFEAT. I have no idea what that means. I've pressed it with no noticeable effect noticed. All that I can think of is DYNAS, but that is just a guess. If you know, please email me.

2019 UPDATE: I'm writing this in 2019. A fellow named Tom Kendall gave me the answer to DYN SEP/DEFEAT in an email. He said "It means "dynamic separation." This is similar to a Schotz circuit, insofar as it "files off the rough edges" of weak or distant FM stations. It cuts down the noise in stereo mode. And it really does work. Try it on a really crappy station sometimes. With a good signal, of course, it does nothing and has no audible effect." Thank you, Tom. Nice to know that somebody does read these pages, lol.

The tuning switch on the extreme right is a rocker switch. I prefer that to up/down buttons. Holding down the switch will tune it rapidly up and down the band. Below that switch is a "Search" button. This tuner tunes in 50khz steps and I could not find any way to change that to 100khz steps even though every pot and adjustment on the board is clearly marked.

For listening, this tuner has superb sound. I think any audiophile would be pleased, even with narrow filters in it. For DXing, the three 150khz filters do the trick. You won't have many problems with adjacent channel signals. Since I don't do a whole lot of FM Dxing anymore due to IBOC on almost every local station, I just listen to it. The sound is crisp and clear.

Before I took this tuner, I had heard of NAD, but not in any detail. This tuner has quality built into it. It is not a piece of junk. I'm impressed!