rmorris

Hi Plankton. Another greeting from Brighton (actually 🙂)

The 300 Ohm measurement is too high. So check for a good connection pressure and any corrosion etc. Remove any tarnishing etc. But also check that when using the meter the tips of the probes are making good solid contact and breaking through any surface finish or oxidisation. 

Bizarrely some cheap probes don't have a great surface to the tips themselves so check that and touch them to themselves to check how near to Zero Ohm you get.

As for the OP question. Your grounding is fine. You are NOT "earthing" the bass when you touch strings, bridge etc. The bass is already earthed through the cable screen and amp. YOU are not "earthed" until you touch the bass. Ie it is the bass that is grounding you.

When you are not grounded your body / hands act as an antennae transmitting noise that is picked up by the bass.

When you touch the bass your body is held at the same potential as the bass so no noise is transmitted.

You can illustrate this by not touching the bass but by touching some other piece of earthed conductor eg chassis of grounded equipment.

Shielding / Screening will help reduce the amount of noise picked up on this situation.

On 31/05/2023 at 11:13, basscki said:

I have a well grounded P bass that hums slightly if I don't touch a metal component/strings (suggests shielding required) but the hum also disappears if the volume is fully down (makes sense) AND also when fully up (???!).

Any electromagnetic experts out there have an explanation for the max volume hum elimination behaviour?

This is not unusual although it may be counter intuitive.

At either end of the pot' travel the source impedance "seen" by the following stage (eg amp / DI input) is at a minimum.

At mid point* of the resistance it is at the maximum.

Noise" pickup" increases with effective source impedance.

* assuming a log' type taper for volume pot' then this will not be the mid point of the physical travel,

On 25/05/2023 at 22:05, Count Bassy said:

If it was me I would. In the old days when 50Hz main was the main problem you might get away with it. These days with all sorts of high frequency electrical noise in the environment you really should make that cage as complete as possible.

Copper or aluminium shielding won't really help with 50 Hz mains interference. But can help with harmonics resulting from its rectification - 100 Hz, 200Hz etc. And that is a lot of the mains hum you hear.

On 17/05/2023 at 14:35, SumOne said:

 

Well, I'm no expert on it which is why I called up my expert witnesses! Perhaps they aren't reliable witnesses but Witness #1 is from the Epiphan website - a professional AV company, and Witness #2 from Moon Audio - a professional AV company (that sells cables). 

 

As far as I understand though: Balanced vs un-balanced and low impedence vs high impedence are different things but generally speaking a DI with XLR balanced signal changes the impedence to mic level (low impedance, or 'weaker'),  un-balanced signals from things like guitar pedals tend to be instrument level ('stronger') and are often buffered to preserve that over long cables. Mics have to have balanced signals as the low impedence 'weak' signal they provide to the mixing desk then go through a lot of pre-amp gain at the mixing desk - so any interferance they have picked up by the cable is also amplified a lot and is noticable. But that is not usually so necessary for 'stronger' instrument or line level signals - they are potentially better off being a instrument level signal and un-balanced rather than mic level and balanced, hence guitar to pedals and pedal to pedal and pedal to amp connections using un-balanced instrument level signals and adding a buffer to preserve it over long distances if needed.  If buffered un-balanced cables at instrument level go a long distance (>25 foot) to a mixing desk then it might be preferable to have it as a mic level balanced signal, but it is not usually essential (unlike with microphones).

 

 

yeah - this stuff isn't easy if it's not your thing. And the sort of "half-information" eg in the Epiphan piece (I found it on their website) really doesn't help.

There's a lot to unpack with Hi-Z / Lo-Z / Balanced / Unbalanced etc. I'm not going to do a full treatment here 🙂 But if you want technically excellent info I'd suggest looking up the work of Bill Whitlock (associated with Jensen transformers and THAT semiconductors). But a few quick points:

• Balanced audio can be any level. Obvs if going into a mic pre it needs to be fairly low level (or padded down at the input) to avoid clipping.
• Higher Impedance connections are more susceptible to external interference - so it is often worth trading level for a lower impedance (as with a DI transformer that presents a high Z to the source and a low Z to the mixing desk input etc).
• Contrary to what the article says - it is not necessary for a balanced connection to drive the two legs in anti-phase. Impedance matching on each leg is what matters wrt noise rejection (CMRR)

On 11/05/2023 at 16:32, sirmuppet said:

Exactly that. 

 

This may sound stupid but it says DC, can that still be used on an AC adaptor?

Yes. Commonly used on AC and DC outputs (it's termed a "DC Power Plug" but there's no actual electrical polarity to the plug itself).

On 11/05/2023 at 12:40, SumOne said:

 

 

• I call forward expert witness #1  
  • "when the cord length is under 10 feet, unbalanced cables actually have a stronger signal than balanced cables.
  • This is because at this length, any distortion is unlikely, and the simplicity of unbalanced cables can work wonders when there’s no detriment coming from potential distortion. For instance, mastering studios typically use unbalanced cables ranging between three and ten feet in length.".........."If you’re using a longer unbalanced cable on a loud device like a guitar, there won’t be a difference at all (vs balanced)"
  • Witness #2  " most people have the impression that a balanced connection is superior because it is more resistant to external signal noise sources. While this is true, it does not necessarily mean that the balanced line is "better" than a single-ended cable"......"Under 10 feet unbalanced cables actually have a stronger signal than balanced cables. Great for low-level/gain signals like instruments"....(unbalanced is)  effective at cable lengths up to 20-25 feet"
• b) Using XLR has a potential risk from phantom power 
  • Expert witness #3 'Wikipedia' "Phantom powering can cause equipment malfunction or even damage"
  • Expert witness #4. Line 6 LT/Floor Manual  "IMPORTANT! Never connect the Helix device's XLR outputs to a device whose XLR inputs have 48V phantom power enabled!

 

 

• • c) There is no harm in using the DI XLR for pedalboard to belt pack for IEMs or home use but it isn't necessary or preferable for those short distances, a higher volume output (instrument or line level) via un-balanced would potentially be better. 
  • d) Expert witness #5 "The  FOH guy" prefers to use their own DI box, this is usually the case. 

 

Some nonsense here tbh.

"when the cord length is under 10 feet, unbalanced cables actually have a stronger signal than balanced cables."

What does that even mean ? What does "stronger" mean here ? level ? lower impedance (So lower susceptibility to interference)

• This is because at this length, any distortion is unlikely, and the simplicity of unbalanced cables can work wonders when there’s no detriment coming from potential distortion. For instance, mastering studios typically use unbalanced cables ranging between three and ten feet in length.".........."If you’re using a longer unbalanced cable on a loud device like a guitar, there won’t be a difference at all (vs balanced)"
• Witness #2  " most people have the impression that a balanced connection is superior because it is more resistant to external signal noise sources. While this is true, it does not necessarily mean that the balanced line is "better" than a single-ended cable"......"Under 10 feet unbalanced cables actually have a stronger signal than balanced cables. Great for low-level/gain signals like instruments"....(unbalanced is)  effective at cable lengths up to 20-25 feet"

By "distortion" I guess really talking about interference ? The mastering studio point is a mixed bag. I know some do but others do not. And if they do they have a very careful and thought out "Ground" scheme applied to a relatively simple audio setup.. Unlike what you get at any live gig type event.

Level does not depend on cable type. 

"Under 10 feet unbalanced cables actually have a stronger signal than balanced cables."

Errr...no in any sense 🙄

On 15/05/2023 at 18:16, ikay said:

Yes you're right, shielding the cavities is the important bit. And, as franzbassist says, making sure you get good contact around the lip to create a continuous cage surrounding all the wiring and electronics. Shielding the upper part of the pickguard beyond the cavities has no shielding effect so it doesn't matter whether you do or don't.

Yes. But I can see that it might be preferred to have a uniform thickness under the scratchplate for mechanical reasons so that it can sit true to the body. Whether significant depends on the thickness of the aluminium (in the Fender case illustrated).

55 minutes ago, lidl e said:

This is the shielding job i did last night. Im happy with it for sure!

 

Just windering if i need to fill in around the controls on the pickguard. I suppose not.

 

 

It would be better to have the 'inside' of the area around the controls filled with the copper tape. Since otherwise it's a bit "open top". But the screening iun place should help a lot and you may think it's not a problem. But may as well fill it imo. Better is better.

On 29/04/2023 at 11:59, How1 said:

I’ve been getting a lot of noise from my Precision, so this morning I decided to shield it. I’ve covered the cavity in copper tape and attached a strip from the cavity to under the pickguard which is also shielded. It’s all one cavity, no separate PU cavity. I’ve also checked the bridge wire and added a bit of tape. It doesn’t seems to have made much difference. Do I need a wire going from the ground on the jack socket to the cavity? Or the bridge to the cavity? I’ve done all this once on a different bass and can’t remember exactly what I did.

Yes. The copper shielding needs continuity to the Screen (Ground) connection on the output jack.

The bridge should already be connected to the jack socket screen connection (check it anyway with a continuity tester / DMM).

So cavity to jack socket or to bridge will have same effect in practice.

Without a connection the copper screen is just 'floating' electrically and effects are unpredictable.

4 hours ago, Smanth said:

 

I wonder if a short length of paracord (with a Monkey fist knot to act as the bit that you grab) superglued to the current zip slider would work 🤔

 

I'd suggest that a good epoxy resin type adhesive / filler might be a better bet.

"JB Weld" works well on metals.

https://www.jbweld.co.uk/

On 11/04/2023 at 16:31, fleabag said:

Good points.  Trouble with tape in/out is the phonos. 

 

 

phonos to 3.5mm jack cables are common.

1 hour ago, fleabag said:

More good points.  I would hazard a guess and say ' Latching ' would be the right pedal, because AFAIK, momentary  pedals means one has to keep one's hoof on the pedal.

 

Not necessarily. The kit may be designed to switch on/ off etc on successive momentary switch events. Eg most fx pedals use a momentary switch which toggles the fx on/off via a bit of hardware logic. See a schematic of eg a boss fx pedal.

1 hour ago, fleabag said:

That looks like it would use a regular TRS cable, so its a probability that his cable might be faulty,

or even the footswitch might have a fault

Yes. But from a quick look it seems designed to work with other bits of Digitech kit. And there seem to be options on how you set those up to operate with the footswitch.

...And I see BigRedx and fleabag have commented alongg similar lines while I had to go do something else.

From not my work - seems uses diode logic to signal 3 x switch states

https://www.pinterest.co.uk/pin/353884483200361260/

32 minutes ago, uk_lefty said:

Yes. And it was plugged in to an isolated power supply. It's all irrelevant now anyway. Even without the noise I didn't like the sound.

Understood. But it seems the unit was faulty. In bypass it shouldn't have a "sound". It's simply a high impedance op amp buffer direct to a balanced output circuit in parallel with an unbalanced output.Assuming output taken from XLR then there shouldn't be a problem unless it is connected to an unbalanced input (due to the topology of the output stage where one leg gets tied to 0V albeit via a build out resistor). Alternatively the internal jfet switching might have been faulty.

2 hours ago, uk_lefty said:

I've returned it and got a refund. For me, it sounded awful and introduced noise to my signal chain. Appreciate for others it's a great pedal, but I also can't stand Orange bass amps etc. Whereas other people can get phenomenal sounds from them... Each to their own. 

 

I've got an MXR M80 on the way so will see if that gives me what I'm looking for.

Was the sound / noise a problem with the BDI21 in bypass ? What was it plugged into ?

On 07/04/2023 at 13:38, Tech21NYC said:

The VT Bass has a buffered output and was designed to be connected directly to a mixer/recording interface. Its buffered output will not be degraded even when using long cable runs. If you need to use an XLR connection any decent DI box can be used. 

Old thread - but since you've chipped in now - what is the output stage detail.

Buffered - so presumably low impedance - but is it impedance balanced. This is so simple to implement that it should be standard in a high quality product. It offers real advantages wrt CMRR.

Okay. I missed the date of the original post. Doh 🙄

Have to say that this topic seems to have become a tad overcomplicated.

The OP has the "sound" required so just needs to translate it to a "balanced" (there are several 'flavours' of this) and possible attenuated low impedance output to feed a mixing desk or interface.

The most accurate and likely least expensive way to do this is with an active DI solution. Many available.

It's basically just a flat response circuit with some form of balanced output.

Passive transformer solutions are also suitable but might get expensive if going for highest fidelity. But the inexpensive solutions will likely be fine if they have enough low frequency response. They will 'colour' the sound further but you may like that or not. They may also offer better CMRR but that is unlikely to be an issue unless you are running long signals in high noise environments eg OB truck etc.

You could likely implement an effective impedance balanced output inside a (larger eg Neutrik)  jack socket body by wiring in a resistor and optionally a capacitor). But if not into DIY then a commercial solution is a good option.

For bass guitar top end isn't a thing. You don't really need to go to the expense of a Sowter / Jensen / Lundahl transformer based solution.

Also look at the (UK based) Orchid Electronics DI options. I don't have personal experience but hear from reliable sources that they are very helpful.

On 20/03/2010 at 17:51, JackLondon said:

My experience of using passive DI comes from the studio when I was recording last year, the bloke had an active box with which we recorded one track and when I listened back it wasn't a good sound, we plugged a passive box and it made it sound more natural to me, with active box there's was that little amount of boost which was even visible on the recording software, it couldn't have been playing dynamics as it was using an 8 second loop that was recorded on my effect! I'm sure Max that with proper design a quality components you use your boxes are clean, many manufacturers however tend to cut corners here and there which means that what it says on the tin isn't what it actually does!

Cheers
Jack

What DI was the problematic active one ?

was it set to flat / bypass ?

A flat response clean active DI is one of the easiest circuits to implement tbh so seems something wrong there.

Was it feeding a balanced mic or line input ?

Are you asking about cable from the power block to individual effects ?

1A is a lot of current for a single device ime.

There are mods to switch in/out both the mids cut and the "cab sim" elements of the BDI21. But what I'm suggesting is that the OP can simply use it in bypass. Used like this it's simply a clean DI. That seems comparable with the passive DI option being considered.

15 hours ago, uk_lefty said:

Some people swear by it.. I was a bit wary because I don't really like the Sansamp sound anyway.... But I'll get this returned. I managed to sell off some stuff and make enough to buy an MXR preamp that has a distortion and noise gate as well as XLR out so will see if that does anything for me... Failing that I'll go for the £11 passive DI!

Not seeing the problem with the BDI21.

Simply use it bypassed and you have an effective clean DI. As you would with a passive transformer DI. Except the input impedance will be more like your amp or pedal input.

If you find it noisy like that then probably a fault or noisy power or gain staging problem. I have both the BDI21 and the Sansamp BDDI (older model). Apart from the less robust build, odd foot switch and lack of ability to run off P48 there's not much in it.

On 10/03/2023 at 12:58, bassman7755 said:

Am I right in assuming that pretty much any single pole RC HPF gives (at least theoretically) infinite attenuation at DC ?.

Yes.