AT-LP120 Pre-Amp Removal Mod - Test Recordings

AT-LP120 Pre-Amp Removal Mod - Test Recordings
44/16 FLAC (ZIP)

Many owners of the Audio Technica AT-LP120 report that when they bypass the internal pre-amp for use with an external one, the sound is somewhat dark and closed in. I, too, have found this to be the case. Using the built-in preamp results in a rather brighter sound, though it often approaches 'harsh' levels and can even accentuate surface noise. To remedy this, folks have chosen to mod this turntable by completely removing the internal preamp / USB circuit board and connecting the wires from the tonearm directly to the RCA output cables.

I have performed this mod and made a few recordings to test the before and after results.

METHOD

Here is a video demonstrating how this modification is performed (I did not make this video):

I'm no expert electrical engineer (I'm not even a novice one), and I don't have a lot of experience with this kind of thing. I probably wouldn't have been able to attempt this without the help and confidence provided by the Youtube video. But it really wasn't too difficult a process. The most tedious part is reassembling the bottom half of the table with those teeny tiny little spacers that move out of position if you merely blink in their general direction.

Aside from connecting the correct wires from the tonearm to the RCA output plugs, you need to "install" your own ground wire for use with your external preamp. It's just a matter of finding some spare wire and stripping the ends -- nothing special here, and I didn't even attach one of those fancy spade connectors to the receiver/preamp end.

The tracks I've used for the comparison are:

The Beatles - "Taxman" {Revolver (1966) - Capitol ST-2576 1971 Reissue}

Emmylou Harris - "One Of These Days" {Profile (1978) - Original US Pressing (Warner Bros. Records - BSK 3258)}

Matthew Wilder - "Break My Stride" {I Don't Speak The Language (1983) - Original CDN Pressing (Epic - FZ 39112)}

For each song, I recorded four different versions (all using the Ortofon 2M Blue moving magnet cartridge):

Unmodded with Built In Preamp - This is a straight recording using the tables internal amp switched ON.

Unmodded with Cambridge Audio 551p - This is with the internal preamp switched OFF, using an external preamp.

Modded with Cambridge Audio 551p - This is with the internal preamp board REMOVED, using an external preamp.

Rega RP1 with Cambridge Audio 551p - This is a kind of 'control' group to measure the AT-LP120 against once modded.

Note: These are straight recordings that have not been click-repaired. Volume adjustments have been made to allow for comparison.

 RESULTS

First of all, the most important result is that I didn't break the turntable. My connections all appeared to work perfectly, and there's no weird unexpected noises coming from the deck. It's the same as it ever was. A promising start, but how does it sound?

Here's what the frequency analysis looks like for "Taxman" in the order listed above (click for full view):

A simple listening test can very easily distinguish between the built-in preamp and the 551p with the internal preamp bypassed (switched off). The difference is stark and I was surprised by how much 'bypassing' the preamp affected the sound. One would assume that turning it off and using a higher quality external preamp would result in a better signal, but this is not the case. In a way, you're almost better off using the internal amp because it doesn't result in a such a muddy and dead sound. The only way to fix it is to yank the whole circuit board out all together.

So I did just that, and again the difference is noticeable. With the 551p, the sound after the mod is bright and lively, but not too harsh. The high end roll off is much less steep with the 551p after the table has been modded. There's even a slight boost in the 5kHz-10kHz range. With the internal preamp left in and switched off, the frequency response starts taking a dive at round 6kHz. You don't need to have dog-like hearing to notice that.

After the AT-LP120 has been modded, the sound it produces sounds remarkably similar to the Rega RP1 using the same cartridge and preamp. It appears the RP1 has a slightly better frequency response, but only marginally so. This likely comes down to the tonearm and overall construction of the table.

 CONCLUSION

With the internal preamp circuit board left in the AT-LP120, there is effectively no way to upgrade the sound with an external preamp. With the built in preamp switched off, the sound coming out of the turntable is veiled and somewhat muddy. Using the internal preamp goes a little too far in the opposite direction, resulting in an often excessively bright sound. The only way to get the most out of this table with an external preamp is to perform a little surgery. And it's worth it.

I would recommend this mod to anyone who wishes to use the table with an external preamp. There is literally no point in using an external preamp unless you cut out the internal one. The dark sound is unavoidable otherwise (unless you opt to continue using the built in preamp).

Vinyl Rip Test Recordings - FLAC (zip)

** These music recordings are for educational purposes only. **