need help w/ kern ip-777 and alembic sf-2

hgregs · #1 12-17-2011, 02:46 PM

i get a high-pitched buzz out of my rig running my sf-2 through the f/x loop of my kern preamp. swapping out the sf-2 for a true-bypass tuner (in the same f/x loop) removes the buzz. testing the sf-2 solo (direct to the power amp) is dead quiet. any ideas on how to eliminate the buzz or where it's coming from?

separately, i was getting really bad buzzing from the kern direct to the power amp WITH THE PREAMP ON STANDBY. i narrowed it down to a bad instrument cable, but why would the problem flow through the standby switch?

bongomania · #2 12-17-2011, 02:57 PM

Guessing here, but: The signal is most probably not flowing through the standby switch; the switch is probably opening or closing a ground path; and this is causing the ground fault that you're hearing (for that last problem).

For the first one, try running the preamps in series, rather than using the effect loop.

tlvernon · #3 12-17-2011, 09:57 PM

+1 running in series.

Does the kern buzz when standby is off and goes direct to power amp?

I would recommend selling both to me

great choice in gear

hgregs · #4 12-18-2011, 06:51 AM

running in series is easy enough. but i kinda liked using the f/x loop as on the kern it's a tube f/x loop.

the kern alone has a slight buzz (not noticeable while playing), but only a fraction of what i get using the f/x loop.

hgregs · #5 12-19-2011, 09:40 AM

so testing what i thought was a bad cable through a headphone mixer (HA-1A), it's dead quiet. why would a cable test bad on one preamp, but not another?

anyone know how to find someone to go through the kern to see that everything is copacetic?

bongomania · #6 12-19-2011, 12:46 PM

Quote:

Originally Posted by hgregs

so testing what i thought was a bad cable through a headphone mixer (HA-1A), it's dead quiet. why would a cable test bad on one preamp, but not another?

Some instrument cables have the ground lifted (cut) at one end, ostensibly as noise prevention. This makes the cable "directional", in that you're meant to have the ungrounded end plugged into the amp/preamp. I've often found that "mystery hum" and "mystery cable problems" can be traced to one of those cables.

hgregs · #7 12-19-2011, 02:15 PM

after a few hours of testing, i have determined that the kern and sf2 are working fine. the issue is with my power amp (lab.gruppen fp3400) - it wants to see a balanced input signal, and if it doesn't, i get interference. what bugs me is that even after using a balanced line (kern>1/4>xlr>LG) i still get interference. the only thing that alleviates the interference is using the Direct Output XLR from the Kern to the LG (xlr-xlr connection). removing the power amp from the signal chain, everything is dead-quiet. adding it to the chain causes interference unless using a balanced xlr/xlr line.

any thoughts on how to work around this? i'd like to be able to use my DI for it's intended purpose. might there be another thread dealing w/ this issue? i'm going to search now.

bongomania · #8 12-19-2011, 02:45 PM

The 1/4" output is most probably not balanced, and using a cable that's got an XLR at one end won't make it balanced.

There are small line-balancing adapter gadgets you can get at pro audio shops; also a unity gain (not passive) DI box will do the trick.

hgregs · #9 12-19-2011, 02:48 PM

thanks... would a shielded 1/4-xlr make a difference? i've been reading that there's a way to make a cable work, but it's stretching the abilities of my mind at the moment. any cable-only solution?

hgregs · #10 12-19-2011, 02:57 PM

something like this should do it Dual Impedance Line Matching Transformer - XLR Male to 1/4" Male - ComputerCableStore.com i'm guessing

bongomania · #11 12-19-2011, 03:24 PM

Shielding and impedance-matching are not balancing.

chadds · #12 12-20-2011, 05:41 AM

If in doubt do like the meek of us do, just use the Kern.

coyoteboy · #13 12-20-2011, 09:55 AM

If a buzzy fx loop, try cleaning the contacts first.

hgregs · #14 12-20-2011, 10:40 AM

i'm at a loss here, and fear writing more as my results seem to keep changing. sitting at my desk and using a mixer and headphone to try to diagnose the problem:
1) the kern is clean using any cable
2) the sf2 (through the effects loop) is clean
3) introducing the power amp causes an increase in noise. this is balanced or unbalanced (but unbalanced is worse). the noise sounds like radio static (but i don't think it's radio). unbalanced also introduces a low-level hum (i assume this is due to the mismatch). this is all with the power amp actually OFF (i have a link-through that doesn't require power). what's really weird is that the static i get from the power amp to the mixer (using an xlr line) is there even with that channel fader at 0. everything can be turn off but the mixer, and that one xlr line will feed static through to the master fader. another odd observation is that it's the same static i can hear on any of the inputs if i turn it up high enough. i have no idea what to make of this, or how it relates to my problem experienced at the gig. i'm afraid to go to an amp tech, as i don't even know what to tell him.

meanwhile, can someone suggest the appropriate transformer to go from unbalanced to balanced? i seem to be finding mostly unidirectional transformers that are designed for plugging a mic into a guitar amp (i want to go the opposite direction).

bongomania · #15 12-20-2011, 11:34 AM

I think this could be the perfect box for your situation: Ebtech LLS2 2-Channel Line Level Shifter, 1/4" Connectors | Full Compass

Passinwind · #16 12-20-2011, 11:47 AM

Quote:

Originally Posted by hgregs

meanwhile, can someone suggest the appropriate transformer to go from unbalanced to balanced? i seem to be finding mostly unidirectional transformers that are designed for plugging a mic into a guitar amp (i want to go the opposite direction).

Some of those will work fine going either direction, as long as they're 1:1 isolators and not meant for impedance matching. Try one of the Jensen PI-XX models if you want a really high quality solution. They only picture the stereo one, but there is a mono model and you can spec whatever connectors you need. If you're handy you can save a few bucks by rolling your own, which is what I did. You might even be able to build one into the Kern if you're brave.