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Effects Loop Issues

Jeff,
I have a Soldano Hot Rod 50+ and on the drive channel, while running effects in the loop, it cuts the drive channel volume a great deal and the clean channel a bit less. But if I turn the effects off, then it’s just fine. If I run the effects in line with the guitar, it’s fine. Why would my effect loop have such a negative effect on my overall tone? Is there a mod or update I can do to the loop? This is the only amp I have that my delay sounds worse in the effect loop. Please help!
Thanks,
Josh


Hi Josh,
Thanks for your question. Since you say your effects work just fine with a guitar signal, I have to assume that they’re guitar level effects and they’re probably functioning just fine—which is your problem. Your effects are guitar level effects. The signal in the effects loop of your amp is more than likely much greater than a guitar level signal, and the effects are not able to process such a highlevel signal. Most effects pedals are powered by 9V DC. Those 9 volts are then generally split into the plus and minus supplies, which are necessary to power the ICs that are the basis for most effects. The voltage levels of those supplies govern the amount of signal that the effect is capable of processing. Once that level is reached, the effect can no longer produce a higher signal level.

To sum it up, if the signal in the loop is higher than the effect is capable of reproducing, the resulting output of the effect will be substantially lower than the input, leading to a reduction in volume. There are some effects that are now powered by 18V DC (two 9-volt batteries or an 18-volt supply), which would theoretically double the amount of signal the effect is capable of reproducing. You may want to search these out and see if any company (mostly boutique builders) offers the effect you require.

Another possible solution, since the effects loop in your amp is pre-Master Volume, would be to see if you could have the effects loop moved to a different location in the circuit. Since this is a circuit board amp, it may require some trace cutting, but if you find a technician who is experienced enough, you could have him locate the effects loop just prior to the phase inverter. This would place the loop post-Master Volume, and the signal level would be much lower with moderate Master Volume settings. Of course, the signal level would be dependent on the Master Volume settings, so if you run the Master Volume at very high settings, this may still pose a problem for the effect—but it may be worth a try.

Now you know how the loop affects your effects.

Jeff,
My issue: why is it that when I turn up the FX mix volume on my Mesa Boogie F-50 to anywhere near 12 o’clock I get feedback like crazy? My effects loop consists of: FX Send >Cry Baby pedal >OC3 Octave pedal >MT2 Metal Zone pedal >Return

With only the MT2 Metal Zone pedal on, with the volume set at 11 o’clock on the pedal, little to no distortion is heard. But if you run the pedals straight through the amp, and not through the effects loop, they sound perfect. What’s the deal?
Thanks,
Juan


Hi Juan,
I have a theory regarding your effects loop problem, which I ran past Dave Barber of Barber Electronics. Since he actually manufactures effects pedals, I wanted to get his take on this, and he seems to concur. I will attempt to explain it as clearly as possible; I hope it doesn’t become too convoluted.

The effects loop in your amp is a form of passive parallel loop. The “mix” control is actually blending in the wet (effected) signal into the main (dry) signal path. The problem is that the dry signal is always present at the mix point, and since there is no isolation between the dry and wet signal at that point, the dry signal can wind up appearing back at the output of the effects. What is also happening is that the wet signal can appear back at the input of the effects. While this may not be as much of an issue with timebased effects (reverb, delay, etc.), gain-based effects may react very differently.

When a dry signal appears back at the output of an effect, the signals can, depending on the effect, possibly be out of phase. This could cause a substantial reduction in amplitude, which may be why your MT-2 Metal Zone pedal has little to no level when used in the loop. Also, when the wet signal appears back at the input of an effect, it may possibly start to oscillate, giving you the feedback symptom that you are experiencing.

There are two possible fixes for your problem. The first is to run the non-time-based effects in the traditional manner, which is through the guitar input of your amp. The second would be to find a competent tech to modify the effects loop, so that it’s a standard series loop, as opposed to its current parallel status. That would completely isolate the send from the return, and it should clear up the issues you’re having.

So much for the ins and outs of your send and return.


Jeff Bober
Co-Founder and Senior Design Engineer Budda Amplification
jeffb@budda.com or www.budda.com