As a DIYer and engineer i’m frequently looking for projects that 1. Match up with my interests 2. Save me some money. This project definitely matches up with my interests, I’ve been an audio nut for years, built several sets of speakers and more recently a headphone amplifier (which sounds fantastic). Its no secret to audio junkies that many high end audio products come with high price tags…a lot of that is marketing budgets, fancy aesthetics etc. So I decided to use my DIY skills for a phono preamplifier upgrade.
A while back after reading some reviews I purchased my first phono preamplifier, an Audio Technica AT-PEQ3. I’ve been pretty happy with it and its sounded good for as long as i’ve had it. After upgrading everything else in my setup It had become what I perceive as the weak point in the system so i decided to pop it open (slide it out actually) and see what it looks like on the inside. If you remove all of the screws on the outside of the enclosure it will slide right out.
Immediately after opening this a few things caught my eye. One the Op amp used is an NE5532P dual op amp. A decent op amp used in quite a few commercial phono preamps and headphone amplifiers. You can check out the data sheet here. And Two there are several cheaper electrolytic caps on the signal side of this circuit. My first thoughts were to upgrade the operational amplifier and upgrade the capacitors, two cheap phono preamplifier upgrades that should yield noticeable improvement.
After a little research I found that all of the leg-work had already been done for me. The great folks over at Audiokarma.org forums had already upgraded this in the same manner at this thread .
The Chosen op amp for the upgrade is the LME49990 which has incredibly low distortion .00001% wow is that good. The datasheet for it is available here.
I decided after reading the great results from audio karma that I’d do the same and use
- Two LME49990 op amps
- Panasonic Film Capacitors
**Another good option for an upgrade is the OPA2134 which is already a dual op amp and comes in 8 pin dip configuration so its a direct replacement. This doesn’t have quite the same stats as the LME49990 but its pretty damn good. Many people build headphone amplifiers with the OPA2134 for good reason, after all it has .00008% THD+n which is pretty damn good
The first step is to remove the old capacitors. I have labeled which ones I will be replacing the following image.
Through-hole parts are usually pretty easy to remove. I suggest using solder-wick and a nice hot soldering iron. The wick should pull off all of the excess solder and the parts should come right out.
Here you can see the points you’ll need to solder wick off….Do double check them though in case i’ve messed up the alignment in my image. Also there may be other versions of this phono preamplifier.
Once all of the components have been removed we can start working on replacing them.
The Capacitors are going to take up more room than the others, particularly the 4.7uf caps which are substantially bigger. Also the spacing of the leads is much wider so you’ll have to bend them in before placing them on the board.
Use needle nose pliers to bend the leads like so.
With your new capacitors in place the board should look like this
Next we get to the Op-amp. The amp we are removing is an 8 pin dip configuration. Unfortunately the LME49990 only comes in an 8soic surface mount configuration. Because of this you will need two LME49990 chips and a dual soic to 8 pin dip adapter. I purchased my adapter on ebay and got 10 of them so i’ll probably list the rest in the DIYourfaceoff.com store for a buck or two if anyone is interested.
Update: I had a hard time finding individual dual 8soic to DIP-8 Adapters so I bought a bunch and listed them on Tindie here
for $2.99 each.
I accidentally didn’t notice that the LME49990 isn’t a dual op amp and installed a single 8soic to dip adapter with one chip…which doesn’t work, but I have parts on the way to correct this. Here’s what my phono preamplifier upgrade looks like (note make sure to get a dual 8soic to 8pin dip adapter and don’t get a single like i have pictured)
Once my dual 8soic to 8dip adapter comes in i’ll post my conclusions and listening thoughts on this upgrade.