zero loss fx loop noise/hum

[norburybrook]

I've revisited my FX loop issues today in my JTM 45. basically when switched in it's very noisy and when I activate my TC x4 there's a loud earth hum.

B+ voltage is showing around 285vDC, earths are good , I've had the board out whilst connected to see if moving it around made any difference...it didn't ...chopsticked everything and nothing helps.


I have a voodoo labs power supply for my loop pedals (eventide H9, TC HOF and TC alter ego x4)
they all work fine in my 2 Dumble(Klone)amps ,what going on here?

Any one?


Marcus

[norburybrook]

I've removed it now as I couldn't get it to work properly. I've left a straight passive FX loop in there and with modern digital pedals like the Eventide and TC it works fine. I can always use my Dumbleator as well this way.


Marcus

[JeffG]

I have purchased and installed the Metro FX loop kit in a tweed Bassman circuit amp of mine. I reasoned that as the Bassman is essentially the same as a JTM45, I shouldn't experience incompatibility. My insertion point is the same, between the treble pot wiper and the cap into the PI grid. The install went fine. Voltage at the resistor test point was 284V, and I set up the level for unity gain using a sig gen and a scope (did not require much adjustment). Loop operation is unsatisfactory however. Inserting a Belle Epoch delay results in VERY noisy operation. Taking the same delay and cables and inserting it in the loop in my Friedman Smallbox results in flawless operation, very quiet. Inserting a short patch cable between the send and return jacks on the amp with the Metro loop in it, I can hear the noise floor come up when I switch the loop in. It is not as bad as when the delay is inserted, but it is there never the less. I am puzzled; is it possible that I received a bad board?
thanks,
Jeff

[SDM]

Old post I know, but to JeffG:

The loop is set up for a well cranked Marshall style amp as typically that is how hey are played. When cranked, signal to noise ratios are optimal, you shouldn't hear loop or pedal noise over the amps own natural noise floor. Some pedals may be extremely noisy by their design, I cannot control that of course, but most often their noise will disappear one signal to noise ratios are in the proper range. So, if you do usually crank the amp up when playing normally, just give that a go, problem should be solved.

I'm guessing you are playing cleaner here, lower volume for testing though. If so, signal to noise ratios are simply way off from optimal. If this is how you typically play the amp, a line level loop would do much better as signal to noise ratios would be closer to ideal at low volumes in an amp like this, even with a pedal level effect in the loop. This is basically what is done in the Friedman amp I believe.

Any way, can PM me if you still need help on this. Sorry for the very late reply.