Here's another: Back in a previous millennium, before cassette decks were offered in "Pro" versions with balanced, +4dBu I/O, like the Tascam 112, you would have used a box like the Aphex 124 to interface a cassette deck with the studio mixing console. Cassettes where how you would give an artist, say, rough mixes, to take home and listen to between sessions.
Power conditioners in series?
- Thread starter camshash
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As JR said, plus establishing a balanced connection reduces considerably ground loop hum that happens when an unblanced unit is grounded through the chassis, as is the case with many HiFi gear.
Newmarket
Well-known member
+1 on this. It's something I was going to say on the "terminated" thread re isolated supplies for pedalboards.
"Ground Loop" may be the most over used terms in electronics - and not just in audio circles.
Sort of conjures up live sound people - "Yeah - it's a ground loop mate" and flicking "earth lift" switches on an apparently random basis.
That's why I'm always kind of skeptic regarding these miracle products.
One must not forget that the main source of hum in an electric guitar setup is the pick-ups.
+1... this is an old discussion but there is one "magic" ground problem fixing SKU that inserts some back to back diodes in series with safety ground. In principle this allows the chassis to ignore less than a couple diode drops of ground noise. In theory the diodes should conduct for actual mains faults providing human safety.
I looked into this pretty seriously back in the mid-late 80s while at Peavey. I asked our agency approval guy to query UL about it. They said sure, just spit up the couple $10k for them to test it. I declined, because this is completely unnecessary with proper input stage design.
My crude bench testing figured out that this could provide a secure ground bond if adequately sized diodes were used. Massive enough diodes to survive the initial heat surge. Heating diodes causes the silicon to melt and fail as a short circuit, perfect for a human safety application.....BUT if the diode was sized too small to absorb the transient heat surge the diode would vaporize and turn into an unsafe open circuit. I settled on modest sized diode bridges as having adequate mass to survive a mains fault long enough to take out the fuse/breaker and still provide a low resistance safety ground bond.
From inspection the commercial product was using smaller diodes than I would, and IIRC was not UL approved. I strongly advise against using that sku or any ground lift. I did send an email to that company sharing my advice about sizing the diodes properly but like often happens they ignored my advice, just like here.
JR
Years ago, I did a teardown (unpotting) of this device. Based on the size and markings on the diodes, I was told by engineers at Motorola (now On Semiconductor) that an overcurrent (overtemperature) failure could go either way, open or short. But just the fact that there's no UL recognition should keep this device out of systems where there's legal liability (i.e., studios and performance venues), because an "open" failure could quite easily electrocute someone. I've a attached a slide from one of my seminars. The fault currents and times are from a UL study of over a thousand residences whose branch circuits were tested for short-circuit current and breaker opening times. As you might guess, the outlets farthest from the breaker panel have the lowest current and longest opening times - but all the numbers are way beyond any ratings by the manufacturer for these diodes rated for 4 to 8 A continuous.
I melted and vaporized sundry diodes in my bench work... a decent sized diode bridge will generally survive long enough to take out a fuse/breaker.
That said I never paid UL to test and bless the approach.
JR
[edit- BTW after a diode melts and fails short circuit it can pass a bunch more current for the same power dissipation due the lower forward resistance. It will still vaporize from enough current. /edit]
That said I never paid UL to test and bless the approach.
JR
[edit- BTW after a diode melts and fails short circuit it can pass a bunch more current for the same power dissipation due the lower forward resistance. It will still vaporize from enough current. /edit]
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Grounding through the chassis to the rack frame with all rack frames bonded and earthed was the old method. You can probably do one or the other in many cases. YMMV, etc......
Grounding through the rack is only a collateral of rack-mounting. Proper grounding is via the 3rd pin of the mains plug. There was a time where it was done via a dedicated binding post.
Being a collateral, it turns out to be an issue with unbalanced equipment where the audio ground is also the chassis/earth.
Being class II, they can be "ground-lifted" if needed.
Newmarket
Well-known member
Always good to be aware of nonsense solutions that solve (or don't) problems at a needlessly high cost.
But galvanically isolated supplies do offer real world benefits in the world of high impedance unbalanced connections etc.
Lots of the problems could be avoided or reduced by one to one cabling rather than the "dreaded" daisy chain. ie reduce common impedance in the return path. And yes - I did once make the error of putting a digital fx (fwiw Korg G5 bass fx) on a daisy chain with a high gain pedal. Soon learnt my lesson.
But properly isolated supplies taker much of the "danger" away and are not excessively more expensive than supplies with common 0V.
One of the associated problems is determining which supplies are really isolated as many are advertised as isolated but this refers only to the ability for individual regulation/protection such that a short on one output won't take the other outputs down with it.
Additionally the offer the ability to stack voltages to power eg "18V pedals" from two 9V outputs.
Hi-Z pickups are, indeed, inherently 'noisy'. Additionally proper shielding of pickup and control cavities can make a huge difference.
It's surprising how many guitars / basses that are "not inexpensive" have control cavity shielding that consists of poorly applied conductive paint.
Newmarket
Well-known member
What is the SKU in question ?
The back to back diode thing is interesting. Working on scientific instrumentation kit - backplane / rack system type stuff - older stuff used this technique from cards to backplane. But somewhere along the line this had been determined not to be acceptable and was changed for new designs.
Hum-W by ebtech; it's in Bill's attachment.
This is not safe for ground bonding unless substantial sized diodes are employed. AFAIK safety agencies have not approved these.
I suspect they really fell out fashion after "pin 1" problem became widely discussed and solutions implemented.
JR
Anyway, in many cases it was not adequate for suppressing hum. since it was not doing anything below 600mV peak. 400mV rms is a lot of hum.
Newmarket
Well-known member
Thanks. I missed that.
using a diode bridge I got roughly 1.2V of isolation, but there are better ways to skin that cat.
JR .
PermO
Well-known member
I've got one of those commercial available isolated PSU's and I must say, it's a godsend for my setup.
Lot's of modern pedals won't run from a 9V battery and come with a wallwart, some -9V some 12V some 18V.
Now I have 10 pedals daisy chained audio, one single PSU, no hum and no noise, I use it for guitar, synth and mostly an aux feed from my mixer using a passive reamp box (transformer / resistor).
Got the coppertape also...
Coincidentally I am having a ground loop/hum/noise problem and it seems this thread is a good place to put it,
I cant find much info on here about floating/telescoping grounds. My setup consists of all my outboard gear and converters on one power conditioner, and my monitors and amps on separate rack and power conditioner (Both conditioners are plugged into same outlet, I know it would be ideal to fit it all on one power conditioner, but due to my setup that is not possible) . I notice when open pin 1 (ground) on the balanced connections coming into my passive monitor controller, the noise competely subsides.
Is creating a floating ground a good solution to the noise issue I am having, or I am better to find exactly where in my signal chain the noise is coming from? How common are floating grounds?
I cant find much info on here about floating/telescoping grounds. My setup consists of all my outboard gear and converters on one power conditioner, and my monitors and amps on separate rack and power conditioner (Both conditioners are plugged into same outlet, I know it would be ideal to fit it all on one power conditioner, but due to my setup that is not possible) . I notice when open pin 1 (ground) on the balanced connections coming into my passive monitor controller, the noise competely subsides.
Is creating a floating ground a good solution to the noise issue I am having, or I am better to find exactly where in my signal chain the noise is coming from? How common are floating grounds?
Coming from?
I assume it's balanced and feeds balanced monitors...?
If ths signal that feeds the controller is balanced, and the monitors are balanced, as well as the controller, there should be no issue. Are you sure none of these connections are grounded?
1) signal is balanced coming from uad apollo
2) feeds into passive monitor controller, which then feeds pair of active monitors with balanced connectors (XLR), and also feeds Hafler amp with unbalanced connection (RCA).
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