Weak spring reverb on a vintage SS Vox Venue Lead 100

[epizootics]

Hi guys,

I usually haunt the pickup-making part of this board...I have a pretty limited knowledge of the physiology of amps & their various pathologies, but that's something I want to get a bit more into, being the only guy in my bands who takes a soldering iron on tour and is expected to fix everything from dislocated shoulders to Fender Twins smoking ominously from the back.

I recently bought what turned out to be a really nice, well-kept vintage Vox Venue Lead 100 after becoming tired with changing tubes every other month. It is a solid state amp but the crunch that comes out of it stupidly sweet. I only went to check it out in this guy's garage but ended up taking it home as it felt as solid as a tank.

Anyway, the one issue with it is the spring reverb. It is barely audible, even with the pot on 10. I do have a few reverb pedals, but being more a straight-into-the-amp type of guy with an unhealthy tendency to crank the verb all the way up, I thought I'd give a try at sorting it out. The problem is that there is very little info about this amp on the internet, and there's very little way to tell if that 'verb was designed to be very discrete or if there is any kind of malfunction at work here. The one thing I found was a guy selling one in England who said it had a cool surf-type reverb with lots of 'boing', but that hardly qualifies as reliable information.

However, I found the correct preamp schematic online:

http://www.korguk.com/voxcircuits/circuits/vlead100.jpg

Now, my knowledge of circuitry is too limited for me to read anything into the pots, resistors and caps values here. Does any of you guys see anything here that would indicate a really quiet reverb circuit? If so, do you have any idea of what could be done to increase the level of the signal coming back from the springs? This would pretty much turn this old grandma into my ideal touring amp!

[Mick Bailey]

Make sure the tray is the original and that the input/output leads have not been reversed (or even the tray reversed). Make sure the connectors are clean and making good contact. Any resistance here will reduce the signal. Then check the continuity of the connecting leads end-to-end. Disconnect the tray and measure the tray's coil resistance either end - the input will read a few tens of ohms and the output maybe around 220 ohms. If all these are good then move on to testing the signal side of things.

If you pull the tray's output plug and touch a finger on the hot pin (assuming it has RCA plugs) you should get a loud buzz with the reverb turned up a little. This will check the recovery side is working. To check the drive I use a pair of cheap headphones to listen to the drive signal while playing the guitar and gradually turning up the volume. Unplug the tray's input and use clip leads to connect up to the headphone plug.

[J M Fahey]

Itīs a weakish reverb circuit to begin with, but it still should be usable or VOX wouldnīt have offered the amp with it.

1) it requires a high impedance input tank, please measure DC resistance at both tank ends, nominal impedance is some 10X to 20X the DC resistance (transducers are highly inductive).

2) IF they are the proper value and yet reverb is VERY weak, first we must discard other problems such as poor/dirty connectors , poor recovery, etc. but absolute worst case it can be modded into a better one, think what Music Man or modern Fender use, even with old workhorse LM741 as is.
But letīs follow a logical step by step chain.

[epizootics]

Thank you very much guys! Those are really nice step-by-step instructions. I'll open it up tomorrow and see what goes on on the inside. Thankfully, those amps are supposed to be pretty straightforward to tinker with.