FAQ List

FAQ

Q At what current level shou= ld I drive the reverb’s input coil?
AThat’s an important question. Too little current and the output will be noisy, too much current= and the core will saturate producing a muddy sound. A maximum current of 30 amp-turns is just about right (see Tech Note)

Input Impedance Code=	Number of Turns	Max current (milliamps)<= /b>
A	124	242
B	538	56
C	600	50
D	688	44
E	1100	27
F	1700	18

Q There’s a lot of hum= on the output of my unit. How can I reduce it?
A Hum is often the thorniest problem to solve when designing with spring reverbs. The reverb unit’s coils, especially the output coil, are very susceptible to picking up hum f= rom any power transformer. You can test to see if this is your problem by unscrewing the reverb unit and moving it around.= You will almost certainly note that the hum gets loudest when the reverb is clo= sest to the power transformer. This problem is very difficult to complete elimin= ate, but you can usually get it down to acceptable levels by the following:

Mount the reverb unit and power transformer as far away from each other as possible.
Mount the transformer and reverb unit on opposite sides of the chassis so the chassis can provide some shielding.
Try turning the power transformer at different angles–some should produce less noise t= han others.
Try various orientations = of the reverb unit.
Try some shielding. Mu me= tal is the best material to use, but even thick aluminum (1/16" or thicker) can help. It is often most effective to eliminate the hum at = its source. Try placing pieces of metal around the transformer. Try differ= ent size pieces at different spots and orientations both near the transfor= mer and near the reverb unit. By playing around with shielding, you should= be able to produce a substantial reduction in hum.
Use a toroidal power transformer. This type of transformer produces much less hum. You can order toroidal transformers from Plitron www.plitron.com.
Beware of ground loops. If the reverb tank is mounted on a metal part of the chassis, try isolati= ng it. Try connecting a 0.1 uF capacitor to a test lead and connect one e= nd to the metal body of the reverb tank. Touch the other end to different ground points on the chassis.

Q When = I turn up the reverb control I get feedback. How can I stop it?
A The reverb unit can act like a microphone–especially when it is mounted in the same box as the speaker. Vibrations via the air or through the panel to which the unit is mounted can cause the reverb’s springs to vibrate, thereby setting up feedback. The first thing to try is to mount the reverb resiliently with rubber grommets or the like. This tactic will help isolate= it from panel vibrations. It may also help to mount it on its own little subpa= nel to further isolate it from vibrations. If feedback via the air is the probl= em, you can purchase a special bag in which the reverb unit can be mounted. The= y are available from many of the places the sell the reverbs themselves.

Q I hav= e an existing amp that doesn't have reverb. Should I try to add reverb to it?
A= It depends. Do you have enough space for both the tank and the circuitry? If s= pace is tight, will you be forced to mount the tank too close to the power transformer, causing excess hum? Also, does your amp's power supply have the necessary voltages and current available? If you have the space and the voltages, you could give it a try.