Valve amp speaker cables causing problems?

[SkinnyMike]

Something very strange happened to me on stage last week and I wonder if anyone can shed any light on this..

For a bit of background, I have an Orange AD200B paired up with a 4x10 and 1x15 cab.
To DI this, I use a Radial JDI placed in-between my amp and 4x10 speaker.
The amp was also serviced with new output valves by Orange back in July this year.

Using the same cables and configuration I have done since I purchased the amp, I fired the rig up and played for 10 minutes or so during sound check. Everything was fine. As I took to the stage for my set however, it didn't sound 'right'. Second song the amp started farting like nothing I had ever heard before, and eventually completely cutting out. The DI signal also completely cut out, meaning It had to have been a complete amp failure.
Post gig I bought a cable tester as I thought maybe it could be something to do with the cables as they were the oldest thing in my rig. Having tested all of them, I discovered that one of my jack/speakon cable was wired the wrong way round. I.E Positive to negative and vice versa.

Could this have caused a problem with the amp confusing it perhaps?

Best,

Mike.

[tauzero]

No, all that the positive/negative thing does is ensure that with multiple speaker cabs, they're all in phase.

From your description, I'd be looking at the power supply first.

[dmccombe7]

If your DI box is between the amp and 4x12 cab then the polarity might have some kind of effect but without knowing whats in the DI box its difficult to say. Has polarity change cured the problem ?

Dave

[Phil Starr]

Wiring live to earth isn't a great idea and you need to get it rewired. It may even have been shorting out internally and confusing the cable tester. I'd also suspect the Di box if it wont clear.

If it was all working perfectly up to then it does ask a few more questions and it is difficult to diagnose without the stuff in front of you. However, if one lead was reverse polarity and you had this on one speaker and the other spoeaker is wired normally then they are out of phase. One speaker moves forward at the same time the other moves back meaning at bass frequencies they move no air. One is sucking the other blowing. This does sound weird, completely lacks bass and that may be what you were hearing.

[obbm]

According to the User Manual you must not put the box between an amp and a speaker cab.
[font=sans-serif][size=2]
[i]Connect your amp as usual, then connect a ¼” to ¼” cable from the second (parallel) speaker cabinet jack to the JDI.[/i][/size][/font][font=sans-serif][size=2]
[i]Because of the high impedance and low draw from the JDI, the amp will only see the speaker cabinet so you do not have[/i][/size][/font][font=sans-serif][size=2]
[i]to change the amplifier’s impedance setting.[/i][/size][/font]
[font=sans-serif][size=2]
[size=4]Try hanging on the speaker out socket of the 4x10.[/size][/size][/font]

[Dad3353]

Good afternoon, Mike...

As echo for the reply from OBBM above, the JDI FAQ answers the question directly...
[quote]
[b] Can I connect the JDI between the head and cabinet instead of using the speaker parallel jack?[/b]

No. This is not advised as the signal traces in the JDI are not suitable for high levels. You can however use the parallel speaker output from the amp so long as a speaker is connected.[/quote]

Running speaker-level signals through (not 'into', but 'through'...) the JDI could well burn up the circuitry inside. This, in turn, will greatly affect the speaker load 'seen' by the amp, and could cause total failure.
I'd get the JDI checked for damage, and, whatever the outcome, change the cabling in future so as to not hang a speaker from the JDI. As mentioned above, 'daisy chain' the cabs, and hang the JDI alone from the second speaker jack on the amp.
Hope this helps

[BigRedX]

The Radial JDI is a passive transformer-based DI box designed to be driven from a speaker output so it shouldn't have suffered any damage (although I'd get it checked out just to be safe).

Although I use EMO passive DI boxes which have a speaker level input, I doubt I'd ever use it like that since what was considered to be suitable output levels 20 or 30 years ago when most of these devices were designed is a fraction of what todays amps can produce - especially when looking at bass amps.

I'd look initially at taking a line-level output from amp, and seeing how you like the sound, and if you find that you really need to sound of those power amp valves working then buy a decent mic for your cab instead.

Edit: You are using proper speaker cables for connecting up your cabs and not guitar signal leads?

Edited December 27, 2013 by BigRedX

[Dad3353]

[quote name='BigRedX' timestamp='1388148888' post='2318859']
The Radial JDI is a passive transformer-based DI box designed to be driven from a speaker output so it shouldn't have suffered any damage (although I'd get it checked out just to be safe)...[/quote]

This is true if the signal is going no further than the JDI. However, there should NOT be a speaker box plugged into the JDI; it won't like such power going [i]through[/i] it. (at least, not according to the manufacturer...).
It's fine (in fact, bloody excellent...) as a passive DI, but not designed for the passing through of speaker-level current.

[obbm]

[quote name='Dad3353' timestamp='1388149270' post='2318866']
This is true if the signal is going no further than the JDI. However, there should NOT be a speaker box plugged into the JDI; it won't like such power going [i]through[/i] it. (at least, not according to the manufacturer...).
It's fine (in fact, bloody excellent...) as a passive DI, but not designed for the passing through of speaker-level current.
[/quote]

Agree entirely. I would presume that the connectors are all pcb (circuit board) mounted and that the copper tracks between the jacks will just burn if you try to put any appreciable current through them.

Unless the OP is very lucky the damage may already have been done.

[BigRedX]

That's interesting… So why does it have a through socket if you're not supposed to connect it in-between the amp and speaker cab?

The EMO boxes I use have a through socket on the speaker level input and [url=http://www.emosystems.co.uk/Products/PDFs/DIBoxes.pdf]according to the manual[/url] this is good for high level input signals up to 100V (what's that in terms of Watts?) and shows connecting the DI between the amp and speaker as the most normal method, although other options are also shown. TBH as I said in my pervious post I would't ever consider using the speaker level connections, and in most cases there is no need.

[obbm]

Watts = Volts x Amps(Current) so just saying good for up to 100-volts is meaningless without also quoting watts or amps. It's excessive current that will burn up a circuit board tracks. Because your EMO has separate speaker connections it's probably wired with adequate size cable and not through the pcb.

The Radial specifically says NOT to put it between amp and speaker probably because it is all on a pcb.

Edited December 27, 2013 by obbm

[Billy Apple]

You know, I read stuff like this and wonder why we are getting 'whats wrong with Basschat threads. Excellent stuff.

My advice would be to check the spindley-doofer running off the foo-foo valve

[obbm]

[quote name='Billy Apple' timestamp='1388162561' post='2319017']
You know, I read stuff like this and wonder why we are getting 'whats wrong with Basschat threads. Excellent stuff.

My advice would be to check the spindley-doofer running off the foo-foo valve
[/quote]

[SkinnyMike]

Hi all and thanks for your replies!

I have inspected every cable, (they are speaker cables btw) making sure they're perfectly fine and fired up the amp WITHOUT the JDI in the output chain at all. Firstly I can say it works and i'm getting clean sound and secondly, Switching the polarity back in phase has made a massive difference to the sound. It sounds much, much fuller.
After 45 mins - 1 hour of playing it's singing just like it should.
I'm glad it's working great but what's irritating me is I can't understand and would love to know why it cut out in the first place. Sure that's great news that it works and sounds great but I really don't want it to cut out on me again, ESPECIALLY while i'm on stage.

So most of you think it's to do with the JDI and it would make sense considering even the JDI website says you shouldn't connect it the way iv'e been doing it for the past year..
The only reason I got the JDI in the first place was because I researched here on basschat and TB about a DI box that could be used to DI the tone of the power valves. After researching countless topics, I was under the impression it was fine to use the JDI in this configuration.. Quite a lot of people do this as well - We can't ALL be in the wrong can we??

Could it be the amp not understanding the load properly when its connected to the JDI first before any cabs? This makes sense to me but for it to cut out after a year of heavy use like this makes me think not.


(Oh, the JDI is also fine, I tested it earlier to make sure that it hadn't been fried from the other week)

[Dad3353]

This is all good news (except for the nagging doubt which always follows any intermittent fault...). It's your equipment, and if it's worked that way for you up to now, it can't be that bad to continue. I still don't see why it has to be connected up that way. Why do you not want to daisy-chain the cabs, and hang the JDI off the second amp o/p..? Another way of getting the same result would be to connect each cab to an amp outlet, and hang the JDI daisy-chained from either cab. Why must the very hot speaker current have to go through the JDI..?
Incidently, for the previous poster, W is not only V x A, it is also V²/R and I² x R. For 100v into 8ohms, I'd expect a current of 12.5 A, for a wattage of 1250w. That's a lot of current for a pcb. Just sayin', no malice intended.

[SkinnyMike]

There's actually no reason why I couldn't place the JDI at the end of the speaker chain, I actually never thought of doing it like that if i'm honest.

If I rigged it up the way you're suggesting Dad, I assume the signal strength would be halved after it comes out the 4x10? I'm probably talking complete tush but even if this is the case, wouldn't I still be getting pretty hot signal into my DI box, thus not solving this potential PCB frying problem?

[obbm]

By putting at the end of the line it will only draw the tiny amount of current that it needs. You signature says you are a Sound Engineer so think of it as putting a high impedance monitor or a PPM meter across a line. It takes a sniff of what is there, but doesn't interrupt or load the signal path.

By putting the Radial between the amp and the speaker you are forcing the whole current through the box. The manual clearly says don't do it.

Edited December 27, 2013 by obbm

[SkinnyMike]

Yeah I understand you obbm.

Now i'm thinking about it, putting the JDI at the start of the chain was an awful idea really. I'm surprised it's managed to last a year without any faults until now.

[Dad3353]

[quote name='SkinnyMike' timestamp='1388182757' post='2319321']...I'm probably talking complete tush...[/quote]

In this particular post, I agree. It's 'tush'.

No, the signal at amp o/p, or first cab second jack, or daisy-chained second cab will be identical (that's all in parallel...). Nice try...