Radial J48 more noise than Hi-Z Input?

[Hugh Robjohns]

No, nothing, except my Sennheiser HD650s.

So nothing external to provide a solid grounding.

I also tried running the Macbook Pro on the battery, but that didn't change anything.

If the problem is due to an absent ground, I wouldn't expect it to.

The noise is also only very loud when phantom power is engaged. Could this mean that the DI box is faulty or something?

It's an active DI box, so it won't work at all when phantom is switched off!

Of course it's possible your J48 is faulty, but its very unlikely. Everything you've said suggests to me that your interface -- and therefore the J48 and your guitar -- lack a solid ground reference, and that's allowing much unwanted noise to enter the system.

[Sam Spoons]

The Radial D48 is an active device and needs phantom power to function which might explain why there is no noise when phantom power is off. The problem is likely due to a lack of a low resistance earth path which running the MBP on batteries does nothing to remedy, try connecting the chassis of the MBP/Apollo/Radial to a known good earth (the metal screws of a wall socket for example*), you can use a guitar lead by touching the tip connection to a metal part of the Apollo and the the tip of the other plug to the screw.

[YusefG]

The Radial D48 is an active device and needs phantom power to function which might explain why there is no noise when phantom power is off. The problem is likely due to a lack of a low resistance earth path which running the MBP on batteries does nothing to remedy, try connecting the chassis of the MBP/Apollo/Radial to a known good earth (the metal screws of a wall socket for example*), you can use a guitar lead by touching the tip connection to a metal part of the Apollo and the the tip of the other plug to the screw.

Well, there is still noise with phantom power turned off, even more noise that with the Hi-Z input.
If there is no low resistance earth path, shouldn't the Hi-Z input have high noise as well, then? Sorry if this question is stupid, but I have no idea about that stuff haha.
I will try and connect my monitors to it.

[Sam Spoons]

The Radial D48 is an active device and needs phantom power to function which might explain why there is no noise when phantom power is off. The problem is likely due to a lack of a low resistance earth path which running the MBP on batteries does nothing to remedy, try connecting the chassis of the MBP/Apollo/Radial to a known good earth (the metal screws of a wall socket for example*), you can use a guitar lead by touching the tip connection to a metal part of the Apollo and the the tip of the other plug to the screw.

Well, there is still noise with phantom power turned off, even more noise that with the Hi-Z input.
If there is no low resistance earth path, shouldn't the Hi-Z input have high noise as well, then? Sorry if this question is stupid, but I have no idea about that stuff haha.
I will try and connect my monitors to it.

Is there any guitar signal being passed when phantom switched off?

Different devices have different susceptibility to EMI.

Have you tried providing a good earth as I suggested, it may help?

[YusefG]

The Radial D48 is an active device and needs phantom power to function which might explain why there is no noise when phantom power is off. The problem is likely due to a lack of a low resistance earth path which running the MBP on batteries does nothing to remedy, try connecting the chassis of the MBP/Apollo/Radial to a known good earth (the metal screws of a wall socket for example*), you can use a guitar lead by touching the tip connection to a metal part of the Apollo and the the tip of the other plug to the screw.

Well, there is still noise with phantom power turned off, even more noise that with the Hi-Z input.
If there is no low resistance earth path, shouldn't the Hi-Z input have high noise as well, then? Sorry if this question is stupid, but I have no idea about that stuff haha.
I will try and connect my monitors to it.

Is there any guitar signal being passed when phantom switched off?

Different devices have different susceptibility to EMI.

Have you tried providing a good earth as I suggested, it may help?

I did connect one monitor to it (Yamaha HS8), which didn't help. Then I took a guitar cable and connected the metal casing of the Apollo to the earth of an outlet (was helped by my girlfriend, who does electrician stuff for a living) and that didn't help, either. She also said that wouldn't make any sense, because if the Apollo was constructed in a way so that it needed a ground, then the power cable would be one with a ground. But it isn't.
So the cluelessness continues haha. Should I contact Radial about this and ask?

[Hugh Robjohns]

I took a guitar cable and connected the metal casing of the Apollo to the earth of an outlet (was helped by my girlfriend, who does electrician stuff for a living) and that didn't help, either.

That's disappointing...

She also said that wouldn't make any sense, because if the Apollo was constructed in a way so that it needed a ground, then the power cable would be one with a ground. But it isn't.

Not necessarily. Many interfaces are class-II and rely on being connected to grounded devices like powered monitors...

Should I contact Radial about this and ask?

I imagine they'll be as bamboozled as the rest of us... but before you do that, you didn't answer one of my previous questions which was whether you had the ground lift switch activated on the J48? That could make a lot of difference to the noise you're getting so it's definitely worth checking.

[YusefG]

Should I contact Radial about this and ask?

I imagine they'll be as bamboozled as the rest of us... but before you do that, you didn't answer one of my previous questions which was whether you had the ground lift switch activated on the J48? That could make a lot of difference to the noise you're getting so it's definitely worth checking.

Oh, sorry. But yes, I basically smashed all other buttons to bits in the hope that any one of them would change ANYTHING. Without success
I just contacted Radial, explained the details of the situation and I will post what they have to say about this! At this point, I don't even care if my unit is broken, I would just get a new one. Or maybe the Apollo Hi-Z is just so stellar and quiet, that would be ok, too! But I just want to KNOW whats going on, haha!

[Wonks]

What’s going on is you are measuring noise after putting the signal through a hi-gain amp plug-in.

Measure it before the plug-in, then see what you’ve got.

[Sam Spoons]

I did connect one monitor to it (Yamaha HS8), which didn't help. Then I took a guitar cable and connected the metal casing of the Apollo to the earth of an outlet (was helped by my girlfriend, who does electrician stuff for a living) and that didn't help, either. She also said that wouldn't make any sense, because if the Apollo was constructed in a way so that it needed a ground, then the power cable would be one with a ground. But it isn't.
So the cluelessness continues haha. Should I contact Radial about this and ask?

Your GF is only partially correct in this case, she is correct that the Apollo does not need a safety earth and that, if it did, it would be provided via mains lead. But, an audio system usually needs a connection to earth to combat EMI and while that is usually provided by a Class 1 device somewhere in the system, if the system comprises only of Class 2 or battery powered devices it may benefit from a separate earth.

[ef37a]

Can I join this band of largely boggled individuals?

Not sure if the High Z input of the Apollo can be classed as "stellar" but it is very very, very good. Dynamic range 121dB A and even though Hugh has told us several times that there are different ways peeps use to present DR that is a bloody good figure by any standard. The more so for a GUITAR* input!

Has to be close to the best HZ spec on any AI?

The maximum input level of 12dBu is around 3V rms and I cannot see many guitar pickups delivering close to that? It is also the max output of a very good guitar pedal, probably had that in mind plus the fact that it is close to a 20dB headroom for -10dBV. And, FYI most guitars have a level pot.

The Radial speccs out rather worse, noise -99dBu but that is still an excellent figure and IMHO the noise problem is either 'finger trouble' or a faulty DI box. I think the latter is unlikely. Someone asked "why the DI?" and I have that question as well. DI boxes were really invented to provide a very high impedance for a guitar (the magic 'meg') and a balanced mic level for a mixer feeding a PA or studio desk. They have I think come to be used to apply some 'character' to guitar signals but I would aver that Radial is one of the most 'Hi Fi' ones?

*Guitars are seriously noisy fekkers. They pick up all the electromagnetic poo in creation. Mostly 50Hz and harmonics but with a sprinkling of all the EMG coursing though the Ether. In my experience a guitar connected to an AI will at best give a noise floor of some -70dBFS and that only with the axe in THE most inconvenient orientation!

Dave.

[Hugh Robjohns]

Can I join this band of largely boggled individuals?

Of course!

Not sure if the High Z input of the Apollo can be classed as "stellar" but it is very very, very good. Dynamic range 121dB A and even though Hugh has told us several times that there are different ways peeps use to present DR that is a bloody good figure by any standard. The more so for a GUITAR* input!

It is damned good -- amongst the best interface/converter specs around at the moment. Although, to be fair, a mains powered box will almost always have better specs than something powered over phantom.

The Radial speccs out rather worse, noise -99dBu but that is still an excellent figure...

The -99dB noise is ref 0dBu, but the max input is +10dBu, so the actual dynamic range capability is 109dB. Not as good as the Apollo's claimed 121dB, but still far better than any electric guitar might require!

Someone asked "why the DI?" and I have that question as well.

Essentially because the OP saw the J48 being used by a favoured band.

DI boxes were really invented to provide a very high impedance for a guitar (the magic 'meg') and a balanced mic level for a mixer feeding a PA or studio desk.

Not quite. The guitar amp is supposed to provide the appropriate high impedance for the guitar. The 1M Ohm 'standard' of active DI boxes came about as a way of not loading the guitar-amp connection, and thus not affecting the tone.

However, the J48 provides an input impedance of 220k....

They have I think come to be used to apply some 'character' to guitar signals but I would aver that Radial is one of the most 'Hi Fi' ones?

I think you're right on both counts.

H

[ef37a]

Not quite. The guitar amp is supposed to provide the appropriate high impedance for the guitar. The 1M Ohm 'standard' of active DI boxes came about as a way of not loading the guitar-amp connection, and thus not affecting the tone.

Not quite sure what you are saying there Hugh? I have read of people thinking that the guitar amplifier 'tone' is in some way affected by the source impedance feeding it. I have crossed qwertys with folk who think an amp MUST be fed from a 1meg source!

Are you referring to the practice (which came later with DIs) of providing a slave output to the amp in addition to the mic level XLR feed? BTW I too noticed that 220k Zin. I wonder why?

The input impedance of a DI box or indeed an amplifier is not as critical as many people think. 220k, 500k or 2-3 meg will probably make less audible difference than changing the cable from 3 to 5 mtrs or a different brand. The whole response of the pickups inductance, any onboard pots and caps and the cable capacitance has almost infinite shapes.

Dave.

[BWC]

The input impedance of a DI box or indeed an amplifier is not as critical as many people think. 220k, 500k or 2-3 meg will probably make less audible difference than changing the cable from 3 to 5 mtrs or a different brand. The whole response of the pickups inductance, any onboard pots and caps and the cable capacitance has almost infinite shapes.

My IK AXE IO has variable input impedance. I can definitely tell the difference as I spin the knob, but would agree that it's very subtle, and certainly not as critical as often suggested.

[ef37a]

The input impedance of a DI box or indeed an amplifier is not as critical as many people think. 220k, 500k or 2-3 meg will probably make less audible difference than changing the cable from 3 to 5 mtrs or a different brand. The whole response of the pickups inductance, any onboard pots and caps and the cable capacitance has almost infinite shapes.

My IK AXE IO has variable input impedance. I can definitely tell the difference as I spin the knob, but would agree that it's very subtle, and certainly not as critical as often suggested.

Indeed and that is being able to instantly switch the load impedance plus I doubt the IK AXE compensates for the slight level change?

Dave.

[Hugh Robjohns]

Not quite. The guitar amp is supposed to provide the appropriate high impedance for the guitar. The 1M Ohm 'standard' of active DI boxes came about as a way of not loading the guitar-amp connection, and thus not affecting the tone.

Not quite sure what you are saying there Hugh?

As you know, the amplifier input impedance forms a resonant circuit with the guitar pickups, controls and the cable which strongly affects the overall tone.

The idea of a 'stage' DI box is to take a 'sniff' of the signal passing between guitar and amp -- hence the input and Link sockets being wired in parallel. In days of old, with passive DI boxes, the relatively low impedance of the transformer significantly lowered the load impedance seen by the guitar and thus changed the tone slightly, often to the grievance of the guitarist.

The benefit of the active DI box was that it could be engineered with an extraordinarily high input impedance -- borrowing a concept from audio measurement equipment -- so that its presence across the signal connection has no material effect on the overall load impedance seen by the guitar at all. 1 MegOhm was a good achievable value, and it has since become almost a ubiquitous standard.

However, in situations where an amp is not connected to the Link socket -- such as is often the case in the studio (or in DI boxes where a link socket is not even present), a 1M Ohm input impedance is considered, by some at least, to be too high. The claimed reason is that it does not load the guitar in the same way as a typical guitar amp which often has an input impedance closer to 250k Ohms... Hence the lower impedance offering of the J48.

I have read of people thinking that the guitar amplifier 'tone' is in some way affected by the source impedance feeding it. I have crossed qwertys with folk who think an amp MUST be fed from a 1meg source!

That would be daft... but the impedance of the guitar pickups, tone/vol/switching circuitry, cable and amp input all work together to construct a resonant circuit which certainly does affect (to some degree) the overall tone. Change any one element and the sound changes with it, slightly of radically depending on the change...

The input impedance of a DI box or indeed an amplifier is not as critical as many people think. 220k, 500k or 2-3 meg will probably make less audible difference than changing the cable from 3 to 5 mtrs or a different brand.

Quite possibly!

[ef37a]

Hugh, I don't know where you got the figure of 250k as the 'common' or preferred input impedance of guitar amplifiers but I task you to find many and there are sheds of schematics on line.

The general story is that because the first guitar amps were essentially the back end of a radio set the first valve had a 1M grid leak so as not to load the detector. In fact to save a penny the resistor was often the volume control. Always 1M and I have changed a very great number of those! (more often for the attached mains switch failure than a noisy pot)

The early guitar amps simple developed from that in terms of more valves and greater power output but that front end essentially stayed the same (but the pot was moved to the next stage). The usual arrangement was a grid leak of 1M then a grid stopper of 10-68k. A vital component as, in conjunction with the valve's input capacitance of around 120pf formed an effective RFI filter.

Had the designers of the DI wanted to keep the load on the guitar at ~1M wherer or not the slave jack was plugged in they could have cone so easily. Just make both resistors 2M2 and switch one out when the second jack is inserted. That no one seems to have bothered tells me the difference to the tone was minimal?

Pickups were therefore wound to deliver maximum mV into that load. We would have had much quieter guitars had they been designed after low Z microphones! (EMG did of course)

Dave.

[Hugh Robjohns]

What you say makes sense to me Dave... I was quoting a conversation I had a long while back with a man from Radial... Perhaps I misunderstood. I'll try to remember to do some digging after Christmas.

[ef37a]

What you say makes sense to me Dave... I was quoting a conversation I had a long while back with a man from Radial... Perhaps I misunderstood. I'll try to remember to do some digging after Christmas.

Fair enough Hugh. IF you want to waste yer loif! You ask 2 guys a question about guitar and amp interfacing and you will get at least 3 different answers!

I suspect only the beardy tweaks in the 'subject' hi fi world are more full of 'it than gitamp people. Myths painted as engineering facts abound.

I reckon it is all to keep the adpuff departments in Beamers!

Dave.