Every once in a while you come across something that really, as they used to say in the Pepsi radio jingles, hits the spot.
Such are the Mark Moyer mods for the Custom Vibrolux Reverb.
With that said, a Fender Custom Vibrolux Reverb arived here with a really high level of background noise. Incidentally it had a scorched tube socket and failing electrolytics which didn't help anything.
In " The Soul of Tone" Tom Wheeler describes this as a production of Fender's Custom Amp Shop which was designed by Bruce Zinky. As a commercial item it was more or less a flop, because most people didn't like the noise level-you don't see them around much, and when you do, they aren't that expensive to acquire.
Back a decade or so ago, a fellow named Mark Moyer decided to tackle the hiss and noise problem with this amp and he developed a plateful of mods that move the CVR from an also ran to a great piece of gear.
The mods consist of delinking the reverb from the normal channel, installing a negative feedback loop, adding a shunting capacitor to the phase inverter, removing the surge protection diodes, and replacing the ground reference resistors. In addition and highly recommended is installing an adjustable bias control and replacing the 12AT7 reverb recovery tube with a 12AX7.
Don't forget to check the electrolytics for ESR-the power supply capacitors were failing on this amp.
The modifications will take you about an hour of work, after you've opened up the chassis, marked and removed the connecting wires from the board that have spade connectors, and removing the daughter boards from the front of the amp. If you're not handy with a soldering iron leave this to a professional.
You can find the rundown on these mods here.
If you're like me you'll find the transformation outstanding.
Living in Cedar Falls.. will probably purchase a Custom Vibrolux and later will want to do the Moyer mods. If i didn't want to do them myself, can you recommend a tech that would do them near me? Thanks.
ReplyDeleteI don't know anyone in the immediate area who does that kind of work. If you tackle it yourself be careful-the traces are very fragile and easily damaged.
ReplyDeleteI installed (November 2013) the Mark Moyer modifications using a pre-assembled kit that I purchased from Fromel Electronics. I bought the supreme kit which has new replacement F&T capacitors plus all of the needed resistors, along with good (pictured) clear instructions. His kit also provides Sprague “orange drop” 716P capacitors to improve the tone stack (C2, C3, C4, C7, C8 & C9). Fromel's kit will also have you braiding several internal (transformer & heater) wires to help control noise.
ReplyDeleteThe hiss is gone and the reverb now sounds much fuller and lush. As everyone probably knows this modification actually changes the circuitry back to its original platform…the 63’ Vibroverb reissue (6GI6). I also swapped out the original 25 watt Jensen P10R speakers with 30 watt Celestion G10 Greenbacks. This opened up the sound and greatly improved the bass and mid-range.
As noted in an earlier post; the PCB traces are fragile. Great care needs to be applied especially when de-soldering the old components. After each soldering you should verify continuity. Please use a good quality solder, de-solder braid and a variable soldering iron.
It's well worthe the effort. I've done two or three for people and they all were thrilled with the improvements.
ReplyDeleteI'm not normally a "mod" guy, but I had these mods done to my CVR I bought new in 2001 and as a result its a much better amp. I had a NFB pot installed (in the hole for the extension speaker jack); highly recommend that as well.
ReplyDeleteRobert, good to see your post here (you're my #1 tech and always will be!).
ReplyDeleteI have this amp but going to leave it stock for now... I have the classic Fender tones in other amps, that is why I bought this amp for something different. I might change my mind but like the characters this amp brings to the mix. I call it raw sounding, just wanting to possibly explode any minute.