• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Troubleshooting something totally bizarre

#63
Growly Lytes said:
Cant see how it could happen with those cabs & not others ?
Click to expand...

Similar DC resistance does not equal similar impedance across the spectrum.

My guess is that somewhere in the low frequency range there is a large impedance dip with one of the cabs, and it drops below an impedance the head can drive.

It doesn't happen with the other cabs because their impedance never drops that low (or does it in an easy to reproduce part of the spectrum).
 
#64
I suspect that some really wacky impedance curves with quick deep/tall transitions in the biggest part of the power band might even upset some amps. Alex Claber indicated awhile back that one particular driver-in-cab (cabs actually change the driver's impedance sweep) wasn't so great for tube amps, ferinstance.
 
#65
aborgman said:
Similar DC resistance does not equal similar impedance across the spectrum.

My guess is that somewhere in the low frequency range there is a large impedance dip with one of the cabs, and it drops below an impedance the head can drive.

It doesn't happen with the other cabs because their impedance never drops that low (or does it in an easy to reproduce part of the spectrum).
Click to expand...
if only my wife and grandson weren't sleeping i could try measuring it while playing, i guess. but still, people match this head and two of these cabs all the time.
 
#66
Well, it's probably the head, maybe a bum low value PS filter cap, given that the problem is on the low end of the spectrum. I'd get really worried if a new head had the same problem though, then it'd be time to sweep the cabs as greenboy suggested. Maybe one of them got the wrong driver(s).
 
#68
JimmyM said:
if only my wife and grandson weren't sleeping i could try measuring it while playing, i guess. but still, people match this head and two of these cabs all the time.
Click to expand...

I suspect it's a problem with the head itself, that exhibits on the impedance dip.

Messed up head + cab without the impedance dip? Head works fine.

A perfectly working head + cab with the impedance dip? Head works fine.

Messed up head + cab with the impedance dip? Head can't handle it.
 
#70
sounds logical, aborgman. you're probably not far off from what they tell me. of course, that's all from a "don't know my ass from a hole in the ground" perspective, but i think it counts for something ;)

greenie, as always, you are right, and i probably should have just done that from the start. but like i said, i was dying to try to find out what it was.
 
#71
playerunk said:
maybe it's a combination of a 'half-bad' head and 'half bad' cab.. one cab has a bad driver that causes a impedance problem at lower frequencies and the head can't handle it and..there you go :hiding:
Click to expand...
if only it were that simple. the cabs check out for impedance, and they sound fine under any other circumstances.
 
#74
I'm guessing you'd have to play tones and measure current at the same time. And do maths. Have fun with that.

Or take it to a tech with a whizzbang gizmo that you can't buy at RadioShack, even if you wanted to outlay a weeks pay.

Over to some smart guy to tell you how to futz about sweeping it manually with your meter and a PC tone generator.......
 
#75
greenboy said:
I suspect that some really wacky impedance curves with quick deep/tall transitions in the biggest part of the power band might even upset some amps. Alex Claber indicated awhile back that one particular driver-in-cab (cabs actually change the driver's impedance sweep) wasn't so great for tube amps, ferinstance.
Click to expand...
That actually applies to any VB with very low Qts drivers, as in Kappa Pro 10, for instance. This chart compares a Kappa Pro Ten vented (red) and an Alpha 10 driver sealed (green). Both are nominal 8 ohm cabs, and obviously that nominal figure is the only characteristic that they share. Tubes like the Alpha 10, hate the KPro.


sealedventedimp.jpg


Something similar is likely happening to Jimmy, where the cabs and amp in question just don't get along.
 
#77
Kind of unrelated, but BFM's impedance comparison made me think, what shape do horn loaded cabs come out on an impedance graph like that? I'm thinking the original big lows dub rigs were valve powered, and that is what my valve slave was probably made for, is it going to be more or less suited to ported type cabs/drivers than something made for sealed cabs?
 
#78
Mr. Foxen said:
Kind of unrelated, but BFM's impedance comparison made me think, what shape do horn loaded cabs come out on an impedance graph like that? I'm thinking the original big lows dub rigs were valve powered, and that is what my valve slave was probably made for, is it going to be more or less suited to ported type cabs/drivers than something made for sealed cabs?
Click to expand...
Horns have multiple peaks like vented boxes but the peaks don't go anywhere near the values of the Kappa Pro. Part of the KPro problem is that the low Qts that creates very high impedance peaks also chokes off bass response, making them very power hungry in the low end, compounding the problem with the low power capability of tubes. Horns don't have that problem; remember that horns were invented to give high output with very low powered tube amps.
 
#80
well everyone else seems to do fine with a micro vr and two 210av's, so i'm still going by ampeg's theory that there's something going on with my head that causes it ;) i have quite enjoyed the education i'm getting, but i'm still keeping a positive outlook.

51T7q0D%2BLZL.jpg
 

Latest posts

Top Bottom
Back