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how'd they do that?

lexington125

lexington125

Sep 11, 2013
644
390
hollywood, baby......
#1
JimiNYE69_R.jpg
The attached image from the BoG soundcheck has been discussed previously. But I've still got two questions:

1. if I decided that I wanted to use 2 or 3 (or 4 or 5...) Fender heads, each driving their own cabinet, what is the best way to feed my bass guitar output to all of the heads? There has to be a better solution than hoping all the input jacks are wired in parallel and using a lot of 'jumper cables.' Does somebody make some sort of transformer based box that takes one guitar level input and provides numerous, isolated, guitar level outputs?
2. what the heck is holding all of those Fender heads from falling over? They can't just be stacked up and precariously balanced, can they? But I don't see anything else in the photo???

I know this was discussed before, but did everyone agree on what Billy had stacked up? It looks like four Showman heads over a Showman reverb head over a Twin Reverb. And are those funky Guild bass cabs? Finally, is that a beer can on top of the highest Showman head? How the heck does he reach it?
 
#3
I'll answer n.1...
You can build a relatively simple splitter box with an opamp to boost the signal before it's split into 4, and the boosted after for individual line-level control.
But then, it's not super practical as you need a power source and you might as well just use jumpers.
 
#4
CL400Peavey said:
Why would you uses anything but jumpers?
Click to expand...

While "jumpers" should work fine with 2 heads, do you eventually run into signal loss, impedance issues or other problems when you are trying to tie together 5 or 6 heads as shown in the photo? If the answer is NO, that you can just keep adding heads without problem, great. It just intuitively seemed like it would become an issue as you moved beyond a couple of heads. But I'm happy to be wrong in this case..... can you just keep adding more heads?
 
#5
BioWeapon said:
I'll answer n.1...
You can build a relatively simple splitter box with an opamp to boost the signal before it's split into 4, and the boosted after for individual line-level control.
But then, it's not super practical as you need a power source and you might as well just use jumpers.
Click to expand...

Based on other replies, there may not be any reason for this, but my original idea was for something passive, like a transformer, to keep it simple and not require juice.

And what's holding up those heads!??
 
#6
BioWeapon said:
I'll answer n.1...
You can build a relatively simple splitter box with an opamp to boost the signal before it's split into 4, and the boosted after for individual line-level control.
But then, it's not super practical as you need a power source and you might as well just use jumpers.
Click to expand...
In the cable industry, you want to keep your line levels constant before going into a split. You do not boost before the split or you run the risk of boosting noise levels. So, run an isolated split that reduces ingress and then boost the signal back up to the original level after. The same situation would work here. As has been stated, a 2 head split will be a relatively small drop in signal (3.5dB if you're using Coax :D ). 3 amps wouldn't be much more. 4 amps would be 7dB each off the original source. All of which are very minimal to boost back up.
 
#7
lexington125 said:
View attachment 489374
The attached image from the BoG soundcheck has been discussed previously. But I've still got two questions:

1. if I decided that I wanted to use 2 or 3 (or 4 or 5...) Fender heads, each driving their own cabinet, what is the best way to feed my bass guitar output to all of the heads? There has to be a better solution than hoping all the input jacks are wired in parallel and using a lot of 'jumper cables.' Does somebody make some sort of transformer based box that takes one guitar level input and provides numerous, isolated, guitar level outputs?
2. what the heck is holding all of those Fender heads from falling over? They can't just be stacked up and precariously balanced, can they? But I don't see anything else in the photo???

I know this was discussed before, but did everyone agree on what Billy had stacked up? It looks like four Showman heads over a Showman reverb head over a Twin Reverb. And are those funky Guild bass cabs? Finally, is that a beer can on top of the highest Showman head? How the heck does he reach it?
Click to expand...

Actually I have delt with this a few times for touring bands, if it's two amp vintage heads we either use the excellent
lehle split or the dual which has additional 1,2 or both switches.
For higher numbers of amps we use the awesome Sowter Transformers 1 in an 3 out high impedance transformers and wire them into project boxes, if it's 6 amp we just use two transformers and wire the primarys in series to avoid the impedance drop of parallel.
Which ain't a problem with an active bass but can suck a little HF out of a passive pickup.
With the primaries in series no drop in HF is noticeable.
hope that helps.:)
 
#10
lexington125 said:
2. what the heck is holding all of those Fender heads from falling over? They can't just be stacked up and precariously balanced, can they? But I don't see anything else in the photo???
Click to expand...

At the bottom of the stack you can see that they're on a tilt-back stand of some sort. The 'beer can' is probably the top of the stand.
 
#12
If they are in fact all being used, the likely method is by slaving the other amps from one master amp. By using the pre out of an amp, you can go to the power amp input of the others.

Another modern solution is the radial JD7. I've seen a few pros use it on rig rundown videos.
 
#13
Azure Skies said:
If they are in fact all being used, the likely method is by slaving the other amps from one master amp. By using the pre out of an amp, you can go to the power amp input of the others.

Another modern solution is the radial JD7. I've seen a few pros use it on rig rundown videos.
Click to expand...
You can only do that when you have pre amp out or Fx send, you ain't going to find one on an old fender amp.
The plexi marshall stack hasn't got those sockets either.
Is the radial box, an isolation transformer based product, what's it sound like?.
The other one that's gooo is the little labs distro.:-)
 
#14
Bassmec said:
You can only do that when you have pre amp out or Fx send, you ain't going to find one on an old fender amp.
The plexi marshall stack hasn't got those sockets either.
Is the radial box, an isolation transformer based product, what's it sound like?.
The other one that's gooo is the little labs distro.:)
Click to expand...

I checked the old fender showman schematic and you're right...no pre amp out. They were really bare bones back then, huh?

The radial box seems to have some active components and transformer isolation for each channel, according to the description. Using the Jensen name, I would imagine radial strives for transparency in the product.
 
#15
There are a few common ways that it was/is done. In part, it depends on the number of splits, but it also depends on the grounding scheme that the particular amp model used. Why would the grounding scheme matter you might ask? Because of the possibility of creating ground loops with circulating currents at the input area of the amplification which can exaggerate hum and buzz.

1. Passive hard wire split: if you have an active pickup (not many of those back then) you can split to multiple amp inputs as loading of the pickup is not an issue BUT a passive hardwire split (or jumpering the inputs if the amp is so equipped) means that the grounds will all be tied together at the input jack and also at the power ground side of things (though an ungrounded power cord might make this less of a problem but the polarity reference caps could make it a much bigger problem). This method is simple, cheap, and did I mention cheap?

2. (Passive) Transformer isolated splits: Using a splitting transformer is one way to get around the ground loop issue, by re-deriving the ground idolated from every other ground but does not get rid of the impedance loading (actually it's a bit worse). The impedance the pickup sees if the total load impedance reflected back through the transformer, plus transformer losses. This is a more expensive solution that works quite well with active pickups but not so great with passive pickups (especially with more than 2 or 3 outputs)

3. (Active) Transformer isolated split: An active buffer amplifier is placed before the transformer(s) to provide a low impedance driver. This is pretty much the gold standard for pro level applications where splitting is necessary. There is no excess loading of the pickup, and there is no ground inter-connections to cause ground loops. The buffer can be an op-amp or it can be a simple FET based circuit with adequate output current. One big advantage it that it's easier to get the more solid low end with lower distortion. A single buffer can drive multiple buffers for extreme isolation and level control between the split channels.

4. Active non-isolated splitter: An active buffer drives multiple buffers that direct drive the outputs. This generally sounds best (a relative term, of course), but ground loop noise can be a problem. There are ways (circiuit tricks) to dealing with this, but it's not all that straight forward.

5. If the amp has a slave function (ie. preamp out/power amp in), a slave out, using a suitable cable(s) can drive multiple amps without risking loading by using only one amp as a preamp only. Most of the GB and Mesa amps are designed this way, but this is true of many other more modern amps.

I have custom built some splitters for touring level use, money is rarely the object, and generally I use the active transformer isolated split method. These devices just have to work day after day, after day in grueling conditions.
 
#16
One of the problems with using a jumper cable on a Fender is the grid resistors are connected between the 2 jacks. Marshall's had the grid resistors on the circuit board so running into one jack and out the other was electrically the same, but on a Fender you'll have a 68k resistor between the 2 jacks.

So depending on the amp, you might be better off using an active buffer amp with 0 gain so there's no signal loss.
 

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