W4S STP-SE DIY mods

Well, technically, it is best for each single channel op amp to have its own capacitor. However, that is just not practical (AD797 adaptor has the second opamp underneath, and Sparkos have 2 levels of boards). I just put a 47uf + 0.1uf MKP on each DIP8 module. Here’s a pic of how I do it:

http://i824.photobucket.com/albums/zz170/ainami/electronics/AD797_Sparkos.jpg

I use a Vishay MKP416-420 for the 0.1uf on these caps (digikey # BC2054-ND). It’s metallized Polypropylene and the best I could find in this size.

You can see I have the 47pf ceramic caps between pins 6 and 8 on each AD797 for the high frequency compensation. I use AVX Skycap for this (digikey # 478-4850-ND). For SMD work, here’s a really excellent video:

https://www.youtube.com/watch?v=z7Tu8NXu5UA

When putting on the 47pf, it’s absolutely required to use flux. I use MG Chemicals 8341-10ML syringe for this (digikey # 473-1117-ND). I just put a blob of flux on the pins and melt it with soldering iron. Then I use a spring loaded tweezer to hold the 47pf ceramic down on the pins. I put a bit of solder on the tip of the iron and place it down on the pins of the ceramic. The flux allows the solder to flow down between the pins and make a good connection. Without flux, the solder tends to blob on top and you won’t get good connection.

Since the 47pf stick out, other components might get in the way and you may need to put in a riser DIP8 socket, such as Mil Max 116 (digikey # 11693-30841007000-ND). In fact, I recommend putting in a DIP8 socket for each op amp anyway, because you will probably want to swap around op amps for experimentation. Be ware that gold-plated sockets and leads on these will introduce the warm gold-plated type sound. The tin plated are actually more neutral, if you care.

Before you mount the 47uf, check around the op amp on the board to see if there is room before you make a decision on which way to diagonally bend the capacitor leads. This 47uf will provide a very fast power reserve close to the op amp circuit. It will increase attack and clarity in the mids and highs. It will also give just a bit more punch in the midbass. The 0.1uf MKP is critical because it stabilizes voltage fed from the 47uf. Without it, the high frequencies will have a blare/mess quality.

The Vishay 0.1uf can be used in all other places on the preamp as well. If the Vishay is too thick for a position, I use Kemet SMR (digikey # 399-13042-ND), which is polyphenelyne (better than polyester caps).

For op amp negative feedback loops, I upgrade the caps to Kemet PFR series (film-on-foil), or silver mica if the value is small enough and there is enough space for the cap (the silver mica can get physically too large).

Another thing I would mention here is that I am making a big assumption that those green Nichicon Muse bipolar are being used for DC blocking signal caps (why else would you use a bipolar?). If he is actually using these for power supply filters, then Elna Silmic is not the best choice. The best I found is the normal Nichicon Muse (UKZ) series. If you do this, better make damn sure you put them in the correct polarity (put in an electrolytic reverse polarity will probably blow the cap pretty quickly). Might have to use a multimeter to determine which pins are positive/negative.

Also, I don’t know if you have looked at this, but you can also upgrade the voltage regulators (unless they are already upgraded). I have used the Sparkos discrete regulators in several applications and they are just excellent. Much faster and smoother than monolithic 78xx/79xx regulators and they also shield noise from main power supply better. I have not tested the Dexa regulators, but the Dexa are much taller and I never had the space to place them. The Sparkos are same physical size as the monolithic 78xx/79xx, but a bit thicker. The Dexa uses a NE5534 op amp for error correction. The Sparkos uses a discrete Class A circuit based on their own discrete op amps.