Most electronics these days use electrolytic capacitors (caps) to couple audio signals to different parts of the circuit. This is a poor use of these devices since they were designed more for power supply filtering (below 1 KHz). But they are cheap and compact, which is why they are used.
The first job is to add 0.01 uF “Film” type caps (the value is not critical, anything near that is fine) across all of the electrolytics that are in the audio section. Any type of film; mylar, polypropylene, polystyrene, etc will do. If power supply caps are not bypassed, you should add either film or ceramic caps there too. At the lower left hand of the picture below, I added a ceramic cap to a power supply electrolytic.
Here is a close-up view. This shows the leads of the film caps are cut and bent over the solder pad and leads of the electrolytic caps. I like to add solder to the lead of the film cap and the hold the film cap in place while placing the solder iron (with some solder on it) on the joint until it all flows together. The solder should support the weight of the film cap with no problem. If you can wiggle the film cap and break the connection, try again.
The VP29 requires a 220 pF capacitor across the input to keep a flat, balanced response using normal inexpensive cables. The picture below shows ceramic surface mount cap across each input. The ground connector relies on making good connection through the case and a standoff to the circuit board. It wasn’t working real well, so I added a wire directly between the connector and board…. No noise at all now.
Some of you may wonder why I add a film cap across an electrolytic, rather than change the electrolytic out. First, I’m cheap. Second, it really isn’t necessary. Bypassing works because the loss of electrolytic capacitors is significantly higher at high frequencies than film caps. The film cap ends up “shorting out” the electrolytic in this range, so the electrolytic contributes very little to the sound. This next picture shows regular leaded ceramic caps instead of the surface mount version. Either way, it works the same.
Parts List: Quantity:
0.01 uF Film type capacitor, 15 Volt or more 6 (7 if you add one to C2, top pic)
220 pF ceramic capacitor, 15 Volt or more 2
and a couple of inches of any kind of hook-up wire.
A cheap place to buy is Jameco.com; here are their part numbers:
920464, .01uF 100V PLYE capacitor; $0.15 each
15413, 220 pF 50V ceramic capacitor; (10 minimum) $0.09 each
You can’t go wrong with a modified VP29. To get anything better, you would have to spend a few hundred or more. I use this with a tube amp and ribbon speakers, and I’m pretty happy with it!